EPA/600/2-91/033
July 1991
THE SWELLING PROPERTIES OF SOIL ORGANIC MATTER AND THEIR
RELATION TO SORPTION OF NON-IONIC ORGANIC COMPOUNDS
by
WILLIAM G. LYON
and
DAVID E. RHODES
ManTech Environmental Technology, Inc.
Ada, Oklahoma 74820
EPA CONTRACT NO. 68-C8-0025
Project Officer
Roger Cosby
PROCESSES AND SYSTEMS RESEARCH DIVISION
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
ADA, OKLAHOMA 74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before complef
1. REPORT NO.
EPA/600/2-91/033
2.
PB91t217406
4. TITLE AND SUBTITLE
5. REPORT DATE
THE SWELLING PROPERTIES OF SOIL ORGANIC MATTER AND THEIR
RELATION TO SORPTION OF NON-IONIC' ORGANIC COMPOUNDS
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
William G. Lyon and David E. Rhodes
|a. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
ManTech Environmental Technology, Inc.
P.O. Box 1198
Ada, OK 74820
10. PROGRAM ELEMENT NO.
ABPC1A
11. CONTRACT/GRANT NO.
68-C8-0025
12. SPONSORING AGENCY NAME AND ADDRESS
R.S. Kerr Environmental Research Laboratory
U.S. ENvironmental Protection Agency
P.O. Box 1198
Ada, OK 74820
13. TYPE OF REPORT AND PERIOD COVERED
Final Report 8/1/88-9/30/90 -
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
Project Officer: Roger L. Cosby FTS: 743-2320
16. ABSTRACT
A method has been developed to measure the swelling properties of concentrated
natural organic materials in various organic liquids, and has been applied to various
peat, pollen, chitin and cellulose samples. The swelling of these macromolecular
materials is the volumetric manifestation of bulk sorption, i.£., sorption by dissolution
(or partitioning) of the sorbed liquids into the macromolecular solid phase. Direct
evidence for the existence of this category of sorbed materials has been obtained for
soil organic materials by the present research; swelling in liquids has long been known
in coals and polymers.
Bulk sorbed molecules are thought to be inaccessible to direct biological attack,
and may represent a continuing source of low-level rebound contamination of groundwater
at a polluted site. Equilibration of bulk-sorbed molecules with liquid phases surround-
ing the particles is kinetically slow (diffusion limited) relative to sorption and
fluid movement, and this sluggishness is probably responsible for some nonequilibrium
sorption phenomena seen in soil column flow experiments.
Molecules with molar volumes greater than about 93 cnH mol~l appear to be strongly
excluded from sorption inside the soil organic materials studied in this work. In
contrast, cellulose excluded molecules with molar volumes greater than about 88 cm^
mo-1-1';
Extensive bibliographies included.-
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
(.IDENTIFIERS/OPEN ENDED TERMS
L. COSATi Field, Group
SWELLING
SOIL ORGANIC MATTER
SORPTION
PARTITIONING
HUMIC MATERIALS
CELLULOSE
CHITIN
POLLEN
ORGANIC SOLVENTS
NAPL
18. DISTRIBUTION STATEMEN1
RELEASE TO PUBLIC
EPA Form 2220-1 (R«v. 4-77) PREVIOUS EDI T.ON is OBSOLE TE
19. SECURITY CLASS (This Report)
UNCLASSIFIED
n NO. OF PAGE;
138
20. SECURITY CLASS t Tins pate •
UNCLASSIFIED
22. PRICE
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DISCLAIMER
The information in this document has been funded wholly
or in part by the United States Environmental Protection
Agency under Contract Number 68-C8-0025 to NSI Technology
Services Corporation. It has been subject to the Agency's
peer and administrative review, and it has been approved for
publication as an EPA document.
Although mention of trade names, commercial products and
companies is made throughout this report for the sake of
completeness, such mention does not constitute endorsement or
recommendation for use.
11
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FOREWORD
The Environmental Protection Agency was established to
coordinate administration of the major Federal programs designed to
protect the quality of our environment.
An important part of the Agency's effort involves the search
for information about environmental problems, management techniques
and new technologies through which optimum use of the Nation's land
and water resources can be assured, and the threat pollution poses
to the welfare of the American people can be minimized.
EPA's Office of Research and Development conducts this search
through a network of research facilities.
As one of the facilities, the Robert S. Kerr Environmental
Research Laboratory is the Agency's center of expertise for
investigation of the soil and subsurface environment. Personnel at
the laboratory are responsible for management of research programs
to (a) determine the fate, transport and transformation rates of
pollutants in the soil, the unsaturated zone and the saturated
zones of the subsurface environment; (b) define the processes to be
used in characterizing the soil and subsurface environment as a
receptor of pollutants; (c) develop techniques for predicting the
effect of pollutants on ground water, soil and indigenous
organisms; and (d) define and demonstrate the applicability and
limitations of using natural processes, indigenous to the soil and
subsurface environment, for the protection of this resource.
This report contributes to knowledge of the environmental
compartments, previously lumped together as "sorbed phases,"
through which many pollutants pass during their transport in the
subsurface. This information should assist the construction of
more realistic computer models involving sorption of pollutants in
the subsurface by organic materials.
Clinton W. Hall, Director
Robert S. Kerr Environmental
Research Laboratory
111
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ABSTRACT
A method has been developed to measure the swelling properties
of concentrated natural organic materials in various organic
liquids, and has been applied to various peat, pollen, chitin and
cellulose samples. The swelling of these macromolecular materials
is the volumetric manifestation of bulk sorption, i.e., sorption by
dissolution (or partitioning) of the sorbed liquids into the
macromolecular solid phase. Direct evidence for the existence of
this category of sorbed materials has been obtained for soil
organic materials by the present research; swelling in liquids has
long been known in coals and polymers.
Bulk sorbed molecules are thought to be inaccessible to direct
biological attack, and may represent a continuing source of low-
level, "rebound" contamination of groundwater at a polluted site
following attempted pump-and-treat remediation. Equilibration of
bulk-sorbed molecules with liquid phases surrounding the particles
is kinetically slow (diffusion limited) relative to sorption and
fluid movement, and this sluggishness is probably responsible for
some nonequilibrium sorption phenomena seen in soil column flow
experiments.
Molecules with molar volumes greater than about 93 cm3 mol"1
appear to be strongly excluded from sorption inside the soil
organic materials studied in this work. In contrast, cellulose
excluded molecules with molar volumes greater than 88 cm3 mol"1.
Besides the size exclusion factor, the degree of swelling of
soil organic materials in different liquids is controlled mainly by
site-specific, generalized acid-base interactions between the
sorbed molecules and the various acidic sites within soil organic
materials. The swelling spectra observed for soil materials are
complex, and completely unlike the simple Gaussian swelling spectra
observed for polymers like rubber (cross-linked polyisoprene) and
for some coals. In these latter materials the intermolecular
forces are dominated by non-specific dispersion forces (van der
Waals interactions), and can be adequately treated by simple
equations (Flory-Huggins-Rehner theory) involving the solubility
parameters of the liquid and the swelling substrate.
Swelling in morpholine appears to be a characteristic of soil
organic materials containing free cellulose. Unfortunately, the
cellulose within natural ligno-cellulosic plant debris apparently
behaves differently from free cellulose, so that swelling alone
does not provide a simple measure of humification in soils or
peats. We speculate that the intimate association of lignin with
the cellulose at the molecular level blocks access to the specific
sites (alcoholic-OH groups) on the cellulose with which morpholine
interacts most strongly. Free cellulose does, however, appear to
be present in pollen intine membranes.
IV
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TABLE OF CONTENTS
FOREWORD iii
ABSTRACT iv
ACKNOWLEDGEMENTS viii
INTRODUCTION 1
Tools available for studying insoluble organic matter... 2
The swelling phenomenon 5
The connection between sorption and swelling 5
Operational definition of volumetric swelling 8
Theory of swelling for macromolecular materials 9
EXPERIMENTAL 12
Standard operating procedures developed for this project 12
Quality assurance considerations 12
Details and purpose of preparative steps 13
Provenance and processing of organic materials used in
the swelling experiments 15
Characterization data for organic materials used in the
swelling experiments 17
Solvents used for swelling experiments 19
Swelling measurements 23
INTERPRETATIONS AND CONCLUSIONS 50
General observations 50
Peat-Like Materials 50
Pine and Oak Pollen 51
Cellulose 51
Chitin 52
Molecular Size-Exclusion Effects 52
Sample Similarity Based on Swelling 56
Consequences for Environmental Studies 61
Suggestions for Future Work 61
REFERENCES 64
SUPPLEMENTARY DOCUMENTS
1. Derivation of a Simplified Thermodynamic Equation of State for
Swelling Materials
2. Review: Properties of Peats/ and Methods of Preparation and
Characterization prior to Sorption and Swelling Studies
3. Review: Thermodynamics of Polymer Swelling as an Analogy for
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Soil Organic Matter
4. Review: The swelling of coal and Kerogen, and its Relation to
the Swelling and Sorption Characteristics of Soil organic
Matter
5. Review: The Swelling of Cellulose and its Relation to the
Swelling and Sorption Characteristics of Soil Organic Matter
6. References on Drago's E and C Formulation of Generalized Acid-
Base Interactions and its Application to Sorption of Organic
Molecules on Soils, Coals, Polymers and Minerals
7. RSKSOP-104, Swelling Spectrum of Organic Matter
DIAGRAMS
I. Soil Constituents
II. Sorption Categories in Natural Soil Materials
TABLES
I. Basic Analytical Data for Organic Materials used in
Swelling Studies
II. Classification of Solvents for Swelling Experiments by
Major Functional Groups
III. Properties of Solvents for Swelling Experiments
IV. Correlation Coefficients (r-Values) between "Best"
Spectra
V. Statistics of Differences between Duplicate Spectra
VI. Maximum Observed Swelling for each Sample and the Solvent
for which this Occurred
VII. Swelling of Peat-Like Materials
A. Results Uncorrected for Ash
B. Results Corrected for Ash
VIII. Swelling of Pine and Oak Pollen
A. Results Uncorrected for Ash
B. Results Corrected for Ash
IX. Swelling of Chitin and Cellulose
VI
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FIGURES
I. Example of Duplicate Swelling Spectra for Pine Pollen
II. Absolute Deviation vs. Average Swelling for Pine Pollen
IIIA. Raw Swelling vs. <50/ Peat-Like Materials
IIIB. Ash-Corrected Swelling vs. £„, Peat-Like Materials
IV. Swelling vs. SQr Acid and Ca-Exchanged Canadian Peat
V. Swelling vs. 6Q, Pine and Oak Pollen
VI. Swelling vs.
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ACKNOWLEDGEMENTS
Many thanks are due Stan Shannon, Joyce Bergin and all the
library staff at Kerr Lab for their considerable assistance in
literature searching and in obtaining copies of the references
cited and discussed herein.
Vlll
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INTRODUCTION
Organic matter encountered in soils and sedimentary rocks is
typically a complex mixture of materials of diverse origins.
Characteristics of these mixtures that influence the sorption of
various organic pollutants species from mobile fluid phases are of
great importance in computer models of pollutant movement in the
subsurface, because the organic materials in rocks and soils
usually far surpass the mineral constituents in their ability to
sorb non-ionic substances. An understanding of the sorption
phenomena associated with natural organic materials will have
application to environmental problems in a variety of settings
including the sorption of pollutants from contaminated ground
water, and the sorption of gasoline or synfuel constituents near
leaking underground storage tanks.
Much work has been devoted to characterization of the soluble
fractions of natural organic materials. Relatively little work has
emphasized the sorption characteristics of the insoluble humin
fraction of soils, or the kerogens and coals of sedimentary rocks.
Most papers dealing with sorption onto soil organic matter propose
that sorption for many water-insoluble, non-ionizing compounds is
controlled by an hydrophobic mechanism, i.e., these compounds are
not so much attracted to soil organic matter as they are ejected
from the aqueous phase by the strong mutual attractive forces
between water molecules. For such a mechanism, the detailed nature
of the solid organic sorbents should not matter very much, and
this, perhaps, explains the general lack of concern about the
properties of solid organic soil materials.
A few papers have suggested that much of the sorption onto
soil organic matter should be treated as a partitioning process
rather than true surface adsorption (see especially the papers by
Chiou et al. . 1990, Mingelgrin and Gerstl, 1983, Chiou et al. .
1983, and Freeman and Cheung, 1981). Many aspects of these
treatments remain obscure and somewhat speculative, however. To
date very little has been done to investigate directly the
macromolecular properties of solid soil organic materials, although
analogous work on coals, kerogens, and other natural macromolecular
systems suggests that much information pertinent to environmental
problems can be obtained from studies of this type, especially
studies of swelling phenomena.1 We believe the present work fills
this gap and sheds light on the nature and limits of this
partitioning form of sorption.
Subsurface organic matter other than soil organic matter is
also of potential environmental interest concerning swelling and
sorption characteristics. Although many aquifers consist of rather
1These swelling phenomena of soil organic matter are
completely distinct from the various swelling-related phenomena
associated with clay minerals in aqueous systems (e.g. shrinkage of
clay liners exposed to organic solvents).
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organic-poor sediments, it should be noted that within the heavily
industrialized coastal plains of the United States, near-surface
lignite deposits are very commonly found in close association with,
or as a part of the aquifers. For example, the lignite deposits of
the Eocene Wilcox formation in East Texas and Louisiana are
saturated with ground water and are a significant part of the
aquifers in the region. Indeed, coal exploration in this region is
frequently assisted by an examination of water well drilling
records, because near surface lignite is so commonly encountered.
(See Kaiser, 1974, and Snider and Covay, 1987 for further details).
TOOLS AVAILABLE FOR STUDYING INSOLUBLE ORGANIC MATTER
The mixture of insoluble macromolecular substances that
compose the major portion of soil organic matter presents
significant difficulties in its chemical analysis. Furthermore,
these substances usually occur as a minor part of a very complex
mixture containing mineral matter, moisture and partially soluble
organic materials that produce interferences and complications in
the interpretation of data taken on the whole mixture. These
substances are difficult to remove in a sufficiently gentle manner
to study the macromolecular fraction by itself .(see Diagram I).
For this reason, the present work is necessarily devoted to the
study of model materials, available in concentrated form, which are
believed to provide reasonably faithful analogs of macromolecular
organic materials that actually occur in soils and sedimentary
rocks.
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DIAGRAM I
SOIL CONSTITUENTS
Soil on the microscopic scale is a heterogeneous mixture of
solid and fluid materials:
Crystalline (quartz, feldspar, etc.)
Mineral Matter
\
Amorphous (rusts, phytoliths, cutans, etc.)
Sorbed
Moisture — Capillary
\
\
Water of Hydration (e.g., gypsum, opal)
Water Soluble (sugars, tannins,
/ some fulvic acid, etc.)
Organic Matter --- Soluble in Organic Solvents (Bitumen8)
\
\ Humic and Fulvic Acids
\ / (NaOH extractables)
\ /
Insoluble — Macromolecules:
\ Cellulose15
\ Chitinc
\
Cross-Linked Macromolecules
Humin/Kerogend (lignin)
Sporopollenin6 (carotene)
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Notes to Diagram I
aThiscategory includes waxes, resins, lipids, and
miscellaneous other soluble products, including some humic and
fulvic acids in their acid forms. The split obviously depends on
the solvents used. Some of these materials (e.g., resin bodies and
waxy, leaf cuticles) can be inherited as discrete, separate phase
particles and coatings from the parent, structured botanical
material.
bCellulose is a biopolymer composed of glucose repeat units,
which can be hydrolyzed by strongly acidic solutions. The three
slightly acidic hydrogens (alcoholic) per repeat unit are the major
sites of interaction with organic bases. See Kremer and Tabb,
1990.
cAlthough chitin is usually thought of in association with
arthropod exoskeletons, it is also found in the walls of fungal
cells. It is a polymer of amino-sugar units, and like cellulose,
it can be hydrolyzed by strong acids. See Muzzarelli, 1977.
dHumin is commonly defined operationally as that soil organic
matter fraction that is insoluble in dilute NaOH solutions.
Unfortunately, this definition is not a very discriminating one,
and humin so defined may represent both unaltered and degraded
lignin-derived material, and even cellulose. (In our experience,
there is no clear-cut endpoint in extractions with NaOH; more
extraction simply seems to produce more extract.)
Kerogen and coal include humin-like materials within their
broad definitions, but also can include materials of much higher
H/C ratio (e.g., resinite, sporinite, alginite) than found in
typical soils. Generally, the terms kerogen and coal are reserved
for materials of "higher rank" (i.e., more thermally mature organic
materials) than soil organic matter. Also, the mineral matter
associated with coals and kerogens is dramatically altered by the
more extensive thermal and geochemical history of these materials;
pyrite, formed by sulfate-reducing bacteria under anaerobic
conditions, is very commonly associated with both kerogen and coal.
eSporopollenin is found in the exine wall of spores and pollen
and is thought to be a condensation product formed from carotenoid
pigments and their esters. In acidic and anaerobic soils and
sediments, it is quite resistant to degradation; however, alkaline
conditions cause etching of the exine. Presumably washing with
NaOH or sodium pyrophosphate solutions to remove humic acids can
destroy some of the sporopollenin. See Brooks and Shaw, 1968 and
1972.
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Since the macromolecules are largely involatile and insoluble,
the major tools available for their study are various spectroscopic
techniques (NMR, FTIR, etc.)/ various kinds of pyrolysis (PY-GC,
PY-MS, PY-GC/MS, etc.)/ flow microcalorimetry and certain
techniques developed to characterize polymers, such as solvent
swelling spectroscopy (chemo-elastic effects) and reversed-phase
gas and liquid chromatography- These all have their place in a
comprehensive investigation of subsurface organic matter. The
technique that is the particular focus of this report is the method
of solvent swelling spectroscopy which probes the chemo-elastic
properties.
THE SWELLING PHENOMENON
Macromolecular substances swell when placed in contact with
various fluids1; the amount of swelling depends both on the nature
of the fluid, and of the macromolecular material. Strongly cross-
linked materials swell less than weakly cross-linked materials.
Such swelling is a property of the insoluble macromolecular network
itself, and it occurs even when all associated soluble materials
have been removed by exhaustive solvent extraction.
Swelling is the dissolution of small molecules of more mobile
substances into the solid. The macromolecules act as a solvent for
these smaller molecules, and the swollen phase represents an
unusual kind of solution. An alternate point of view is that
swelling represents the solvation of internal macromolecular
"surfaces" by the smaller fluid molecules.
THE CONNECTION BETWEEN SORPTION AND SWELLING
Swelling represents a volumetric manifestation of certain
kinds of sorption involving bulk sorption (partitioning) into soil
organic matter. The various categories of sorption in soil organic
matter are detailed in Diagram II.
1Here we restrict the discussion to fluids with a single
molecular constituent. When two constituents are present, a
richer, more complex set of phenomena can occur, such as gel-
collapse, phase transitions, where a swollen gel can suddenly
decrease in volume when exposed to a fluid of different
composition.
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DIAGRAM II
8ORPTION CATEGORIES IN NATURAL SOIL ORGANIC MATTER
Insoluble Solid Phases8
/ (Humin, Cellulose, Chitin)
Swelling & /
Bulk Sorption<
/ (partitioning)\
/ \ Extractable Phases
/ (Waxes, Resins, Lipids, etc)
Organic Matter<
i \ Polarc & Hydrogen Bonding
\ / d
\ Surface Sorption <- Cation Exchange0
(adsorption) \
\ Non-Polar (hydrophobic)
Capillary Condensation6
(micropores)
Notes to Diagram II
Dissolutionin these materials is accompanied by size
exclusion. Also, within the solid macromolecular structures,
different types of organic molecules will preferentially solvate
various sites: polar, non-polar, hydrogen bonding, cation
exchange, etc. See Tegelaar et al., 1989 for a concise summary of
known biomacromolecules and their potential for preservation in
soils and sediments.
Dissolution of various sorbed molecules occurs without
significant size exclusion. Naturally, too many "sorbed" molecules
in the form of excess solvent will extract and mobilize these
materials. Here we emphasize the role of native waxes, resins,
etc., rather than that of anthropogenic residual separate-phase
liquid contaminants which can act similarly.
cPolar is used here only to denote a class of molecules.
Various authors (for example, Fowkes, 1980) have shown that dipole-
dipole interactions between polar molecules in a liquid (in
contrast to the vapor phase) represent only a very tiny portion of
the intermolecular interactions compared to donor-acceptor
interactions.
dCation exchange sorption phenomena would include replacement
of ionizable, acidic hydrogens by cationic organic species, but
also polarization of some ligands by multiply charged, exchanged
cations.
eSome size exclusion effects probably operate here also.
6
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BULK SORPTION AND SWELLING
Swelling experiments measure the maximum capacity for bulk
sorption of certain solvents that solid organic materials can hold
while in contact with the pure solvent. This limiting capacity can
be expressed in a variety of units, such as cm3 sorbed solvent per
cm3 sorbent. Sorbed material in this form represents a potential
source of residual contamination that is difficult to remove
completely by any known process (e.g., solvent extraction, vacuum
extraction, biodegradation, etc.). This residual contamination is
considered to be of greatest importance for the smaller, more polar
solvent molecules such as methanol (See later section for
experimental evidence on size exclusion supplied by the present
work, especially Figure VII). Some solid macromolecular soil
organic materials (e.g., cellulose and chitin) can themselves be
biodegraded, and would presumably release materials sorbed in bulk
as the macromolecular matrix is destroyed.
The extractable organic soil phases are also capable of bulk
sorption (dissolution) of various hydrophobic chemicals. Unlike the
insoluble solid phases, however, these materials are potentially
capable of mobilization by the right mixtures of nonaqueous
solvents. The sorbed species are probably also somewhat more
accessible to remediation measures, especially if they are sorbed
into biodegradable lipid or wax fractions.
SURFACE SORPTION
True surface sorption can be defined meaningfully for
insoluble soil organic matter for sufficiently large organic
molecules that are effectively excluded from the macromolecular
framework of humin and other macromolecules. This restriction to
surface interaction is probably very important for many
agrochemicals such as insecticides, fungicides and herbicides,
which tend to be rather large molecules2. Note, however, that the
lower molecular weight, microbial metabolites of these chemicals
may distribute themselves over the available sorption categories in
a completely different way than the parent chemical.
SORPTION IN MICROPORES
The final category of sorbed material is that which resides in
the micropores of the various solid organic materials without
causing any volumetric increase. No doubt, some size exclusion
effects operate in this situation as well, but probably not as
stringently as in the bulk sorption into macromolecular organic
matter. The difference between certain gravimetric determinations
of sorption and volumetric determinations of sorption (via
2Large in this context means somewhat larger than the aromatic
ring of benzene.
7
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swelling, see below) can indicate the magnitude of the sorption
capacity in this form. In many ways, this is the least understood
of the categories in Diagram II. Diffusion in and out of
micropores also could produce some of the non-equilibrium effects
seen in column studies (see Brusseau and Rao, 1989).
OPERATIONAL DEFINITION OF VOLUMETRIC SWELLING
The volumetric swelling3, Qv, is defined as the ratio of the
swollen volume to the unswollen volume of the sorbent; a value of
unity4 indicates no swelling. The reciprocal of the volumetric
swelling is equal to the volume fraction of macromolecular material
in the swollen, solution phase. Thus, the volumetric swelling at
equilibrium is related to the saturated solubility of the sorbed
fluid in the swollen phase. Knowledge of appropriate densities,
allows this volume-fraction solubility to be converted to the more
usual gravimetric concentration units.
The volumetric swelling5 is the quantity determined
experimentally in the present work. A swelling spectrum is
obtained when the volumetric swelling for various solvents is
plotted versus some pertinent solvent property, such as the
conventionally chosen solubility parameter.
3The volumetric swelling, Qv, should not be confused with the
volume change, AVsweUing, associated with the swelling process:
solvent + solid sorbent -»• swollen sorbent.
The values for Qy are positive values > 1.0 except in the extremely
unlikely situation where the AVSHell. is negative and exceeds the
imbibed volume of solvent. Many values of AVSHell- are potentially
negative, and they are usually not known because of the difficulty
of determination (see, however, RSKSOP-105, a standard operating
procedure listed later in the experimental section, for one method
of determination) . Usually AVSHell. values are some small
percentage of the volume of imbibed liquid.
4Apparent swelling values less than unity could occur if some
material is extracted into solution by the applied solvent.
We note that swelling can also be determined gravimetrically.
In these cases, the amount of sorbed material is determined
gravimetrically, and converted to a volume basis using densities.
Usually the gravimetrically determined swelling is larger than the
volumetric quantity because it includes the filling of micropores
without any associated swelling.
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THE THEORY OF SWELLING OF MACROMOLECDLAR MATERIALS
SWELLING OF CROSS-LINKED, MACROMOLECULAR SOIL MATERIALS
There are two kinds of swelling corresponding to the cases
when the macromolecular material is cross-linked or not cross-
linked. Substances such as humin and sporopollenin are believed to
be cross-linked materials; thus no "molecules" of humin or
sporopollenin exist to go into solution in any fluid applied to
these material. In such cases there is a clear boundary between
phases containing macromolecules and the supernatant fluid, and the
maximum amount of swelling is ultimately limited by the elasticity
of the macromolecular network.
THE EFFECTS OF IONIZABLE NETWORKS
Additionally, humins have cation-exchange characteristics
because of the presence of carboxylic acid (-COOH) groups and
phenolic (-OH) groups. The protons on these acid groups are
frequently replaced ("exchanged") by alkali or alkaline earth
cations in natural materials. Exchanged or not, these groups
represent ionizable groups whose degree of dissociation will depend
on the dielectric properties of the swelling fluid. The varying
degree of dissociation will cause the apparent elastic properties
(e.g., bulk modulus) of the matrix material to be somewhat
different for each solvent applied6. The hydrogen cations inside
the macromolecular network are thought by various authors (Flory,
1953, Tanaka et al. , 1980) to behave somewhat as an ideal gas,
contributing a linearly temperature-dependent term to the swelling
pressure.
SWELLING OF NON-CROSSLINKED MACROMOLECULES AND BIOPOLYMERS
Other soil materials such as humic acid, cellulose, and chitin
are not covalently cross-linked, but consist of mixtures of large
individual molecules with a spectrum of molecular weights. Between
the large, covalently-linked molecular blocks, there may, however,
exist weaker cross-links via hydrogen bonds, molecular
entanglements, etc.
True biopolymers such as cellulose and chitin are, in addition
to being composed of regular, repeating units, are also usually
partially crystalline. The swelling of these materials is somewhat
like melting because of the loss of crystallinity; the supernatant
fluid phase may contain some smaller polymer molecules in true
solution.
that this kind of coupling between elastic and chemical
interactions limits the accuracy of the usual separate
consideration given below.
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PHYSICAL CHEMISTRY OF SWELLING IN CROSS-LINKED. MACROMOLECULAR
MATERIALS
The equilibrium between a liquid and a cross-linked
macromolecular soil material depends on a free energy balance
involving roughly the following terms:
1. Strain Energy (isotropic stretching of cross-linked
matrix)
Parameters must be introduced here that adequately
describe the elastic properties of the macromolecular matrix
(e.g., the bulk modulus).
2. Chemical Interaction Energy (between solvent and matrix)
The interaction terms must include a. non-specific,
dispersive (van der Waals) interactions between solvent
molecules and matrix, b. site-specific interactions (acid-
base, etc.) between solvent molecules and certain functional
groups in the macromolecular structure, and c. electrostatic
interactions involving attraction between the ionized groups
of the matrix as moderated by the dielectric properties of the
solvent molecules. The dispersive interactions are usually
described using the so-called solubility parameters for the
fluid and matrix. The other interactions have been variously
described; no clear consensus on the best methods for their
formulation exists8.
3. Entropy of Mixing (entropy increase due to mixing of
solvent molecules with macromolecular matrix)
This term is commonly handled with the Flory-Huggins
7When the process is conducted under conditions of constant
volume and temperature, the Helmholtz free energy, A = E - TS, is
the appropriate function to use. For the more usual constant
temperature and pressure conditions, a volume change for the
process must be accounted for, and the Gibbs free energy function,
G = E + PV - TS , is the appropriate function to use. We have
assumed separability, e.g., G « Gelastic + Gchem1cal.
°We note that the Drago C and E parameters used to describe
generalized acid-base interactions between molecules seem to have
some merit for introducing site-specific interaction energies into
the equations. These parameters allow semi-quantitative
calculations of enthalpies of interaction which agree with
calorimetric results. Other treatments such as various donor-
acceptor numbers, or extended solubility parameter schemes do not
seem to be as well grounded in real data, and many times do not
predict even the correct sign for the enthalpy of interaction.
10
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approximation, which simply relates the entropy of mixing to
the volume fractions of fluid and sorbent. There is also an
entropy contribution from the dissociation of ionic groups in
the imbibed organic liquids.
4. Strain Entropy (entropy decrease due to stretching of
matrix)
This is a complex and important term that depends very
much on the details of macromolecular structure. In the
Flory-Rehner-Huggins theory for simple polymers, additional
parameters are introduced that describe the concentration of
cross-links in the matrix and the coordination number around
certain bonds that rotate during elastic deformation.
Isotropic expansion of the matrix decreases the degrees of
freedom of the molecular network in the neighborhood of its
cross-links.
Semi-crystalline biopolymers like cellulose require an
additional entropy (increase) term to account for the loss of
crystallinity in the swelling process.
THERMODYNAMIC MODELS OF SWELLING EQUILIBRIA; CURRENT STATUS
In modeling swelling equilibria, the various terms described
above are combined into a free energy function. This is best
expressed as a function of swelling, Q (or, equivalently, of the
volume fraction of sorbent matrix in the swollen material), and
the value of Q that minimizes this function is sought. Various
models of swelling have been developed for simple polymers, and
some of these have been applied rather naively to coals; these
models have been reviewed separately in supplementary documents on
polymers and coal, and will not be discussed in detail here. At
present, there is no adequate model available to describe swelling
in materials as complex as humin9.
The reason for the current lack of a model is twofold: 1.
soil organic matter being a mixture, requires a different model for
each component of the mixture, and 2. even a single component of
the mixture, such as humin, requires features for which the
treatment is inadequate. For any component it is easy to see that
the model will a priori contain many parameters describing both
'Recently, Chin and Weber, 1989, and Chin et al. , 1990 have
adapted an extended Flory-Huggins model to sorption of hydrophobic
organic compounds to dispersed aqueous humic acids with a view to
explaining some features of enhanced transport via natural
colloidal materials. In this treatment, molecular interactions are
handled with an extended version of solubility parameters which
allows separate parameters to account for dispersive, polar and
inductive interactions.
11
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solvent and solid sorbent that will need to be specified to
calculate the equilibrium swelling. Probably only a few of these
parameters can be obtained, even in principle, by curve-fitting the
model to experimental swelling data on real samples; the remainder
must be obtained from other experiments.
This lack of an adequate model makes interpretation of
swelling spectra very difficult, and, moreover, makes prediction of
swelling in any given solvent extremely uncertain. Therefore, in
the remainder of this report, when swelling data are plotted as a
spectrum against some solvent attribute, such as the solubility
parameter, no simple functional relationship is implied.
EXPERIMENTAL
STANDARD OPERATING PROCEDURES DEVELOPED FOR THIS PROJECT10
RSKSOP-101, OPERATION OF THE LECO WR-112 CARBON ANALYZER FOR
THE DETERMINATION OF CARBON IN PEATS AND OTHER HIGH CARBON
MATERIALS, W.G. Lyon, D.E. Rhodes, R. Powell, L. Pennington
RSKSOP-103, MOISTURE DETERMINATION OF PEATS AND SOIL ORGANIC
MATTER CONCENTRATES, W.G. Lyon, D.E. Rhodes.
RSKSOP-104, SWELLING SPECTRUM OF ORGANIC MATTER, W.G. Lyon,
D.E. Rhodes (See Supplementary Document 7)
RSKSOP-105, PRECISE DENSITY DETERMINATION OF SOIL ORGANIC
MATTER AND OTHER ORGANIC-RICH MATERIALS, W.G. Lyon
RSKSOP-106, COMBINED MOISTURE AND ASH DETERMINATIONS FOR PEATS
AND SOIL ORGANIC MATTER CONCENTRATES, W.G. Lyon, D.E. Rhodes
QUALITY ASSURANCE CONSIDERATIONS
All research projects making conclusions or recommendations
based on environmentally related measurements and funded by the
10Standard operating procedures developed for Robert S. Kerr
Environmental Research Laboratory are kept in a file maintained by
the laboratory. These supplementary documents can be obtained upon
request from the EPA Quality Assurance Officer at the Laboratory:
Jimmie L. Kingery
Quality Assurance Officer
Robert S. Kerr Environmental Research
Laboratory
P.O. Box 1198
Ada, OK 74821-1198
12
-------
Environmental Protection Agency are required to participate in the
Agency Quality Assurance Program. This project was conducted under
an approved Quality Assurance Project Plan. The procedures
specified in this plan were followed with a few exceptions.
The list of standard operating procedures given above indicate
those actually developed for the project. Certain other procedures
which were to have been developed were dropped because of time
constraints on the research program. Two methods that could not be
developed were a complementary gravimetric method for swelling
determination and application of certain statistical procedures for
un-mixing the spectral data into natural end-members. RSKSOP-101
for total carbon, RSKSOP-103 for moisture, and RSKSOP-106 were used
mainly as quality control checks on samples sent for total
elemental analysis plus ash and moisture determinations to an
independent commercial laboratory. A standard operating procedure
for density separation of soil organic matter was not specifically
developed for this research although the basic method was used in
processing the Atoka sample of pine duff as described earlier.
Further information on this method and its limitations is available
in RSKSOP-107 (Density Separation of Solid Organic Matter from
Aquifer Sediments) that was developed for a separate research
project involving sandy aquifer sediments. Many more solvents were
actually used in the swelling determinations than were originally
thought necessary in the research plan. Information on the quality
assurance activities and results is available from the principal
investigator.
DETAILS AND PURPOSE OF PREPARATIVE STEPS
Air-Drying, Diminution of Particles and Sieving
The swelling experiment requires samples of finely powdered
organic materials, relatively concentrated in their swelling
components. Fibrous materials such as the Canadian peat cannot be
readily "ground" to a fine powder, but can be chopped to a
sufficiently small size with the blades in a blender so that a
reasonable harvest of -100 mesh (i.e. less than 100 mesh) material
can be obtained by sieving.
Soxhlet Extractions
Soxhlet extractions were conducted using a three-stage
sequence of solvents consisting of 1-propanol, 1-propanol-toluene
(28% propanol) mixture, and toluene. The mixed propanol-toluene
solvent was one of those tabulated by Fuchsman, 1980 (citing older
work by Reilly) giving the greatest yield of peat bitumens (see
table on p. 29 of Fuchsman, 1980) . However, it should be noted
that this composition is apparently not the binary azeotrope at 1
atmosphere pressure; the azeotrope is closer to a mixture with ca.
50% propanol, according to Horsley, 1973. Composition shifts,
therefore, must have occurred during the course of this stage in
our soxhlet extraction procedure.
13
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The purpose of this pre-swelling extraction procedure was two-
fold:
1. to remove as much of the extractable fraction as possible
so that the various swelling solvents applied to these organic
materials would not dissolve any further materials from the
samples, and
2. to remove hydrophobic, low-melting waxes from the particle
surfaces so that the samples could be dried at 105°C without
blocking access to the particle interiors for some of the more
hydrophilic swelling solvents.
Unfortunately, some highly swelling solvents such as DMSO and
the various amides dissolved considerable amounts of humic
materials from some samples during the swelling determinations. In
several instances these solvents gave supernatant solutions over
the swollen solid material that were as dark as coffee. The
extraction of humic substances by non-aqueous solvents of various
types is discussed in detail by Hayes, 1985. A pre-extraction step
including DMSO would eliminate the humic acid dissolution problem;
however, it is very doubtful whether the relatively non-volatile
DMSO could be entirely removed from the remaining solids by any
simple procedure.
Additionally, it must be noted that a single vacuum drying
step at 105°C for 24 hours was not sufficient to remove all traces
of extraction solvents: the 1-propanol component was still clearly
visible in pre-extracted, vacuum-dried peat samples subjected to
pyrolysis-GC/MS.
Acid Washing and Cation Exchange
Acid washing with 0.1 M HC1 solutions was performed when it
was desired to have the acid form of the organic materials for
study. Washing with 0.5 M CaCl2 solution was performed when the
calcium-exchanged version of the organic materials was needed; this
was followed by water washing to a chloride-free condition as
determined by tests with aqueous AgNO3 solution.
Vacuum Oven Drying
Peats which have not been pre-extracted cannot be oven dried
without risking major alteration of their wetting (and swelling)
characteristics. Peat wax and resin components melt in the range
60-70°C (see Fuchsman, 1980) and spread on the particle surfaces
rendering them hydrophobic. De-waxed peats are, however, more
susceptible to oxidation; for the Michigan peat, heating in air at
105°C caused samples of extracted peat to ignite and burn. The
upper limit of useful drying temperature is bounded by the onset of
pyrolysis during heating under inert gas or vacuum.
14
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The above observations from the literature and from experience
led us to the provisional drying treatment for all organic
materials of vacuum oven drying at 105 °C for 24 hours at a few Torr
pressure: once just before loading the powders in the swelling
tubes, and a second time after loading in the tubes. After the
second drying, the filled tubes were quickly capped with teflon
caps to prevent uptake of moisture from the air.
PROVENANCE AND PROCESSING OF ORGANIC MATERIALS USED IN SWELLING
EXPERIMENTS
Michigan Peat
The original sample of Michigan peat consisted of a 25 pound
bag of commercial horticultural peat from the Alpar Peat Company of
Ovid, Michigan (Clinton County). The dark, muck peat is a
predominately reed-sedge peat with some contributions from tamarack
trees. The mined deposit is a layer approximately 8 to 10 feet in
thickness in a region once used for farming.
Further preparation of the as-received sample included coarse-
sieving to remove large sticks, air-drying, sieving to -100 mesh,
soxhlet extraction with 1-propanol, 1-propanol-toluene mixture, and
toluene, vacuum oven drying at 105°C for 24 hours, acid washing
with 0.1 M HC1 solution, and final drying at 105°C for 24 hours.
A density value of 1.53 g cm'3 was determined for this material
by RSKSOP-105 using methylcyclohexane.
Canadian Peat
The original sample of Canadian peat consisted of a bale of
commercial horticultural peat with a light brown color and a
distinctly fibric texture. Information on the origin of this
material was unavailable.
Further preparation of the as-received sample included coarse
sieving to remove sticks, air-drying, dry chopping in a blender,
sieving to -100 mesh, soxhlet extraction with 1-propanol, 1-
propanol-toluene mixture, and toluene, vacuum oven drying at 105°C
for 24 hours, acid washing with 0.1 M HC1 solution, and final
drying at 105°C for 24 hours.
Besides the acid-washed sample, described above, a calcium-
exchanged version of this sample was also prepared by washing a
portion of solvent-extracted peat with 0.5 M CaCl2 solution.
Atoka Pine Duff
The Atoka material consisted of composted pine needles (Pinus
echinata) that had collected in small pockets on a rocky slope
located in Atoka County, Oklahoma (S20, T1S, R13E). The
15
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predominate pine needle contribution to the compost was readily
identified from the intact needles in the top layer. The mineral
constituents were in the form of fine, windblown, clay-sized dust.
Preparative steps for this material included coarse sieving
(10 mesh) to remove large sticks and stones, water washing on a
sieve (200 mesh) to remove fine dust, density separation using
carbon tetrachloride-bromoform mixtures (density 2.0 g cm"3),
chopping in a blender, sieving to -100 mesh, soxhlet extraction
with 1-propanol, 1-propanol-toluene mixture, and toluene, vacuum
oven drying at 105°C for 24 hours, acid washing with 0.1 M HC1
solution, and final drying at 105°C for 24 hours.
Pine Pollen (Pinus echinata) & Oak Pollen (Quercus stellata)
The samples of pine pollen and oak pollen were obtained from
a commercial laboratory that supplies various species of pollen and
mold spores to allergists11.
Further preparation of the as-received pollen samples included
soxhlet extraction with 1-propanol, 1-propanol-toluene mixture, and
toluene, and vacuum oven drying at 105°C for 24 hours.
Cellulose
The sample of cellulose was obtained from Aldrich Chemical
Company, Inc. (Cat. 31069-7, Lot #07809TV) and consisted of 1 kg of
powdered cellulose, nominally 20/i average diameter. Data from the
supplier showed an average assay of about 90% a-cellulose based on
acid hydrolysis and an average residue on ignition ("ash") of about
0.05%. Cellulose has the stoichiometry (C6H10O5)n (see Kremer and
Tabb, 1990) leading to theoretical values of 44.45% C, 6.22% H, and
49.34% 0.
A density value of 1.57 g cm"3 was determined by RSKSOP-105
using methylcyclohexane. The production of static during drying
was a major problem for this density determination.
The sample was examined by optical microscopy at lOOOx and was
found to consist primarily of cylindrical particles with lengths
usually several particle diameters.
The sample was used for the swelling experiments after final
vacuum oven drying at 105"C for 24 hours.
11Greer Laboratories Inc.
P.O. Box 800
Lenoir, N.C. 28645
16
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Chitin fCrab Shell Chitin)
The sample of crab shell chitin was obtained from Sigma
Chemical Company (Catalog C3641, Lot #107f-7115), and had been de-
mineralized and purified by the method of Skujins et al. , 1965.
The sample was used as-is following vacuum oven drying at 105°C for
24 hours. Our swelling studies were limited to 25 solvents for
this material because of the small supply of chitin available.
Chitin has the stoichiometry (C8H13N05)n, with a monomer unit of 2-
acetamido-2-deoxy-B-D-glucose (See Muzzarelli, 1977).
CHARACTERIZATION DATA FOR ORGANIC MATERIALS USED IN SWELLING
EXPERIMENTS
Elemental Analyses. Moisture and Ash
Samples of all organic materials were submitted to a
commercial analytical laboratory12 for determination of moisture,
ash, and the elements C, H, O, N, S, and P. These data are
presented in Table I. The direct determination of oxygen permits
a test for closure by comparison of the sum
(%C+%H+%O+%N+%S+%P+%ASH) with 100%. These values are given as
follows:
Michigan Peat, Acid 99.99 ± 0.28
Canadian Peat, Acid 100.24 ±0.18
Canadian Peat, Ca-Exchanged 99.66 ± 0.23
Atoka Pine Duff 99.01 ± 1.28
Pine Pollen 100.40 ±0.32
Oak Pollen 100.06 ± 0.22
Cellulose 99.17 ± 0.07
Chitin 99.03 ± 0.50
The overall standard deviations were estimated as the square-root
of the sum of the squares of the individually estimated standard
deviations of the analyses. These values seem good considering the
assumed equivalence between "ash" and mineral matter. The direct
determination of organic oxygen is generally less reliable, the
larger the ash content of the sample becomes.
12Huffman Laboratories, Inc.
4630 Indiana Street
Golden, Colorado 80403
17
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TABLE I
BASIC ANALYTICAL DATA FOR ORGANIC MATERIALS
USED IN SWELLING STUDIES
SAMPLE
MP
CP
CPCa
AT
PP
OP
C
CH
C
48.20
0.08
48.96
0.01
49.40
0.10
37.26
0.08
55.21
0.10
56.76
0.15
44.48
0.03
46.82
0.02
H
4.25
0.05
5.26
0.05
5.39
0.06
3.61
0.01
7.51
0.04
7.56
0.06
6.48
0.05
6.59
0.01
0
26.52
0.10
39.50
0.05
38.33
0.19
22.51
0.37
32.59
0.29
24.78
0.06
48.17
0.04
38.60
0.49
N
3.34
0.01
1.01
0.04
0.96
0.02
1.18
0.05
2.17
0.02
6.22
0.08
<0.01
0.01
6.87
0.01
s
0.74
0.05
0.14
0.01
0.12
0.01
0.09
0.01
0.24
0.01
0.40
0.01
0.01
0.01
0.02
0.01
p
0.17
0.07
0.08
0.05
0.07
0.02
0.32
0.01
0.27
0.07
0.68
0.07
0.01
0.01
0.03
0.03
ASH
16.77
0.23
5.29
0.15
5.39
0.03
34.04
1.22
2.40
0.05
3.66
0.09
<0.01
0.01
0.10
0.10
MOIST
13.45
0.22
12.50
0.01
13.33
0.10
5.80
0.09
7.60
0.01
4.00
0.03
5.06
0.03
12.30
0.04
Key: MP=Michigan Peat, Acid; CP=Canadian Peat, Acid; CPCa=Canadian
Peat, Calcium Exchanged, AT=Atoka Pine Duff; PP=Pine Pollen, OP=Oak
Pollen, C=Cellulose; CH=Chitin.
The tabulated elemental and ash compositions are presented on
a dry sample basis (24 hours at 105°C in vacuum). The moisture
contents are presented as a percentage of the original, air-dried
sample mass. All values given in bold represent the average of
duplicate elemental determinations. Uncertainties are given
immediately beneath the percentages as one half the difference in
duplicate determinations, or a minimum of 0.01.
The values reported were adjusted from raw values by a factor
obtained from ratioing the standard theoretical values to the value
obtained. These standards were interspersed with the sample runs
during analyses: stearic acid, triphenylmethane, and anthracene (C
& H) ; acetanilide (N); benzoic acid (O); triphenylphosphine (P) ; 4
certified coal and oil standards ranging from 0.18 to 3.93% S.
18
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Pvrolysis-GC/MS Analyses. FTIR Spectra and CEC Data
All organic materials from these swelling studies were
submitted for pyrolysis-GC/MS analysis as part of other projects
involved with characterization of subsurface organic matter. These
data will not be discussed further here, but are available as part
of the growing analytical information being gradually accumulated
on these known materials. FTIR spectra in a variety of modes (KBr-
Pellet, DRIFT, ATR, and PAS) will also be obtained on these
materials.
Accurate and informative evaluation of the cation exchange
capacity (CEC) of concentrated organic materials is not easily
accomplished. The best methods for CEC (discriminating carboxylic
acid and phenolic hydrogens) apparently involve a combination of
chemical and infrared analyses. There are also serious questions
whether aqueous cations really have access to all (or the greatest
number) of cation exchange sites in swelling macromolecular media.
Values of 158 and 124 meq/100 g (air-dried basis) have been
obtained for unextracted samples of Michigan and Canadian peat,
respectively, by a barium acetate saturation procedure (see the
Peat Testing Manual. Day et al., 1979).
SOLVENTS USED FOR SWELLING EXPERIMENTS
Classification of Solvents
The liquids selected for the swelling studies had to fulfill
two basic requirements: a wide range of solvent properties, and a
lack of chemical reaction with the organic matrix. Selection even
within these constraints was not random; availability, purity,
price, and safety in handling also had to be considered. Within
these limitations, we believe that we have used representative
liquids, some of which swell the organic materials to the maximum
limits set by their elastic properties and compositions. The
liquids used for the swelling experiments are classified in Table
II, and certain of their properties are given in Table III. They
were obtained in the highest available purity, and were used
without further purification.
19
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TABLE II
SOLVENTS FOR SWELLING EXPERIMENTS: CLASSIFICATION
BY MAJOR FUNCTIONAL GROUPS
Alkanes:
Pentane
Heptane
Cycloalkanes:
Cyclohexane
Methylcyclohexane
Carbonyl Groups: >C=O
Acetone
Acetylacetone
Ethyl Acetate
Propylene Carbonate
Nitrile: R-CSN
Acetonitrile
Nitro-group:
N itromethane
Nitroethane
Nitrobenzene
R-N02
Chloro-group: R-C1
Chlorobenzene
Dichloromethane
Aromatic Rings:
Benzene
Toluene
p-Xylene
Tetralin
Ether-group: R-o-R1
1,4-Dioxane
[Morpholine]
Amines:
Pyridine
Morpholine
Sulfoxide: >s=O
Dimethylsulfoxide
sulfide: S=C=S
Carbon Disulfide
Alcoho1s: R-OH
(Water)
Methanol
Ethanol
1-Propanol
2-Propanol
1-Butanol
1-Pentanol
3-Methyl-l-Butanol
1-Octanol
1,2-Ethanediol
1,2-Propanediol
Amides: -C=O
\
NH2
Formamide
N-Methy1formamide
N,N-Dimethy1formamide
N,N-Dimethylacetamide
20
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TABLE III
SOLVENTS FOR SWELLING EXPERIMENTS: PROPERTIES
Solvent
n-Pentane
n-Heptane
Methylcyclohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone c
Chlorobenzene
Dichloromethane
Acetone
Carbon Disulfide
1,4-Dioxane
Nitrobenzene
3-Methyl-l-butanol
1-Octanol
Pyridine
Morpholine
N,N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dimethylsulfoxide
N,N-Dimethylformamide
Nitromethane
Ethanol (99.9%)
Propylene Carbonated
Methanol
1,2-Ethanediol
1,2-Propanediol
N-Methy1formamide
Formamide
Water
6Q (MPaV
14.3
15.1
16.0
16.8
18.0
18.2
18.6
18.8
19.4
19.5
19.6
19.8
20.2
20.4
20
20
20
21
21.9
22.1
22.1
22.3
22.7
23.3
23.5
24
5
5
,5
1
1
24.3
24.5
24.8
26.0
26.0
27.2
29.6
29.9
30.7
32.9
39.3
47.9
Molar Volume (cmymol)1
116.3
147.6
127.6
108.1
123.3
106.8
98.5
89.4
137.1
103.4
102.6
64.5
74.0
60.6
85.7
103.4
108.9
158.4
80.9
87.5
93.0
108.8
71.9
91.9
77.0
53.0
75.2
70.9
77.0
53.7
58.7
85.9
40.7
55.9
73.7
58.4
39.7
18.1
21
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NOTES TO TABLE III
"The delta values tabulated here are mostly the simple solubility
parameters of the liquids at 25°C tabulated by Barton, 1983; in a
few instances where these were missing, the total solubility
parameter, «5t, from the same reference was used instead.
bThe values for the molar volume (cm3/mol) were in most cases
computed from molecular weights (g/mol) and density (g/cm3) values
for the liquids at 25°C tabulated by Barton, 1983. A few missing
values were computed from similar data tabulated in standard
handbooks elsewhere (e.g., Weast, 1984)
C2,4-Pentanedione
dl,2-Propanediol cyclic carbonate
CH2-0
\
C=0
CH2-0
CH3
22
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SWELLING MEASUREMENTS
PROCEDURES
The detailed procedures for the swelling measurements are
documented in RSKSOP-104 (see Supplementary Document 7) . For each
sample of organic material at least a pair of spectra were obtained
at 30°C, representing successive measurements taken over several
weeks. From these data over time, a "best" spectrum was taken, and
duplicate best spectra were averaged for each sample. Figure I
gives an example of paired swelling spectra for the pine pollen in
which volumetric swelling data are plotted versus solvent
solubility parameter. The multiple points vertically in each plot
represent measurements made at successive times.
23
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Legend for Figure I. Pine Pollen Swelling Spectra
These paired spectra represent the results for swelling
measurements at 30°C on duplicate samples of pine pollen (pinus
echinata) plotted versus solvent solubility parameter. The
sequence of points labeled H2ONH1, H3ONH1 etc. denote swelling
ratios based on heights (H2/H1 etc.) taken at successively later
times after application of the solvent; HI denotes the initial
height of the column of unswollen powder.
24
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SPECTRUM J2, PRE-EXTRACTED, 30 de9 C
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-
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24 34
BELTA, SOUEKT SOLUBILITY IW«ETIR
44
54
25
-------
The reason for the choice of 30°C as the standard temperature
was the avoidance of kinetically sluggish swelling observed in
cellulosic materials by Chitumbo et al.. 1974, and interpreted by
them as phase transitions. (See discussion of cellulose in
Supplementary Document 5 for further details.) Temperature control
was achieved by immersing the teflon-capped sample tubes in a
precision (± 0.1"C) water bath (Neslab Models RTE-220 and EX-210).
Absolute temperatures were checked periodically against a
calibrated mercury in glass standard thermometer (Brooklyn
Thermometer Co., model 21256, 0.1'C div-)
ELECTROSTATIC EFFECTS
Large electrostatic charges could be produced in the samples
by vacuum drying. When such samples were immersed in non-
conductive liquids like pentane or heptane the charges were very
slow to dissipate; the approach of a finger in a rubber glove would
polarize the particles and move them around much like iron-filings
attracted by a magnet. We believe the presence of a static charge
on a sample at times influenced the uptake of certain organic
liquids. However, having no way to quantify the amount of the
charge, we could not establish this effect with any confidence. It
proved possible to lessen the build-up of static charge during the
drying procedure and to improve greatly the handling
characteristics of the dry organic powders by mounting ionizing
radioactive strips (Staticmaster Ionizing Units, Model 2U500)
inside the heated vacuum desiccator during the drying step.
CALCULATIONS
For most samples, the averaged raw volumetric swelling results
are reported as they were obtained. For cellulose, the raw
swelling results contained so many values less than unity, that a
renormalization factor was applied to the best averaged swelling
spectrum so that the averaged, background value for no-swelling was
then unity. It is believed that the low apparent swelling values
represented the effect of lubrication of solvents in producing a
slightly denser state of compaction than could be obtained in the
dried powder cellulose by standard centrifugation alone. The
cylindrical shape of the cellulose particles may have contributed
in some way to the apparently lower density of packing in the dry
state.
For the samples of peat-like materials, a fair comparison of
swelling requires corrections for ash. From the analytical data
given in Table I, approximate ash corrections were calculated as
follows:
Atoka Pine Duff C- r a 1.299*C- - 0.299
corn raw
Michigan Peat Qcorr * 1.116*Qrau - 0.116
26
-------
Canadian Peat, Acid <)r « 1.033*QrBU - 0.033
raw
r
corr
Canadian Peat, Ca Qcorr « 1.034*Qraw - 0.034
These corrections were based upon the correction formula for inert,
non-swelling diluents derived in Appendix II of RSKSOP-104 (See
Supplementary Document 7). The conversion from mass fraction to
volume fraction was accomplished by the formula:
CO.
Volume Fraction OM, q>* =
1 - «2 1 -
using approximate densities. In this expression, the subscript 1
denotes the organic matter, and 2 denotes inert diluent; the
symbols 0, u, and p denote, respectively, volume fraction, mass
fraction, and density. Corrected swellings are given in Table VI,
and are used in Figure IIIB.
DUPLICATE SWELLING SPECTRA AND EVALUATION OF EXPERIMENTAL ERRORS
The evaluation of experimental errors was based on the
reproducibility of swelling values between duplicate swelling
spectra. This reproducibility was assessed in two ways. First,
the correlation coefficient was computed between each pair of
duplicate spectra. These values are given as the principal
diagonal elements in Table IV, and range from 0.95 to 0.99. Note
that the correlation coefficient should detect similarities between
spectra independently of scaling by a constant, such as might occur
for a sample with more of an inert diluent than some other sample.
Since all points were used for these calculations, the correlations
are diluted by the inclusion of a great many points with a low
signal-to-noise ratio (low-swelling solvents). Later in the
discussion we give a graphical means of comparing samples (star
plots) that emphasizes only selected high-swelling solvent values.
Secondly, the absolute values of the differences between
duplicate spectra for each solvent were plotted against the average
swelling given by the two spectra. An example is given in Figure
II for the pine pollen sample. This type of plot detected
departures (probably sample handling difficulties, such as static
problems) from random distribution of errors in two instances
(Michigan peat and cellulose); fortunately, the largest differences
involved only a few low-swelling solvents. In Table V the
statistics associated with these differences between duplicate
spectra are summarized for the eight samples. The absolute
differences between spectra were in all cases not normally
distributed; the histograms for the differences are highly skewed
to the left because of the effect of the absolute value function in
27
-------
folding the distribution over on itself about zero.13
The raw swelling measurements are computed as a ratio of
lengths measured to the nearest tenth of a millimeter using a
calibrated measuring reticle and magnifier. These ratios have a
propagated measurement error in the second decimal digit on the
order of one or two units. The average deviations given in Table
V are typically larger than this by a factor of 3 or 4. Several
factors probably account for these larger errors: occasional
fuzziness of the liquid/powder boundary, extraction of humic
materials by some solvents, electrostatic effects, irregularities
in the calibration marks on the glass tubes, and incomplete wetting
of the powder by the solvent. Nevertheless, the large-scale
features of the swelling spectra are clearly visible even with this
higher than expected level of noise.
Despite the non-normality of this distribution, it seemed
more appropriate to treat the differences on an absolute value
basis because treatment of a swelling value for a given solvent as
if it "belonged" to one spectrum or the other is really an
arbitrary decision. Each swelling measurement with a given solvent
is really an independent experiment.
28
-------
TABLE IV
CORRELATION COEFFICIENTS (r-VALUES) BETWEEN "BEST" SPECTRA
1234 56 78
1
2
3
4
5
6
7
8
0.95
0.92
0.97
0.92
0.89
0.84
0.67
0.90
***
0.97
0.93
0.91
0.83
0.85
0.57
0.92
***
***
0.97
0.89
0.88
0.86
0.71
0.95
***
***
***
0.98
0.86
0.74
0.47
0.75
***
***
***
***
0.99
0.77
0.71
0.81
***
***
***
***
***
0.97
0.78
0.91
***
***
***
***
***
***
0.95
0.77
***
***
***
***
***
***
***
0.98
1. Michigan Peat, Acid Washed
2. Canadian Peat, Acid Washed
3. Canadian Peat, Ca-Exchanged
4. Atoka Pine Duff, Acid Washed
5. Pine Pollen
6. Oak Pollen
7. Cellulose
8 Chitin (only 25 points)
In the above table, the correlations are computed between the
averaged spectra when the spectra are from different materials, but
are computed between the individual, duplicate spectra when the
spectra are from the same material. This is the reason that the
correlations along the main diagonal are not identically unity.
Note that these overall correlations give equal weight even to
noisy parts of the spectra where the swelling is barely above
background. Alternatives are presented later for comparing samples
based on swelling behavior with the most highly swelling solvents
only-
29
-------
TABLE V
STATISTICS OF DIFFERENCES BETWEEN DUPLICATE SPECTRA
SAMPLE
Michigan Peat
Canadian Peat,
Acid
Canadian Peat,
Ca-Exchanged
Atoka Pine
Duff
Pine Pollen
Oak Pollen
Cellulose
Chitin
NUMBER OF
POINTS
38
38
38
38
38
38
38
25
MEAN ABSOLUTE
DEVIATION*
0.082
0.044
0.046
0.039
0.045
0.037
0.055
0.064
STANDARD
DEVIATION**
0.097
0.040
0.040
0.035
0.037
0.033
0.063
0.063
The mean absolute deviation refers to the mean of the absolute
values of the differences between duplicate swelling spectra.
**The standard deviation refers to the standard deviation computed
for the mean of the absolute differences.
30
-------
Legend for Figure II. Absolute Deviation vs. Average Swelling for
Pine Pollen
Here the absolute value of the difference between duplicate
spectra is plotted versus the average value of the duplicate
swelling determinations. This example shows little sign of
systematic trends in the distribution of errors.
31
-------
ABSOLUTE DEVIATION vs~ AVERAGE SWELLING
PINE POLLEN SPECTRA 1 AND 2
6.15
UJ
0
z
LLl
DC
UJ
U. al,
lL U2
N
._
Z
H
JO on
D.D7
J
UJ
Z
(0
U.
Q (U
Oi TO
UJ
D
J
-------
AVERAGED SWELLING DATA SUMMARIZED IN VARIOUS WAYS
One simple property of the samples which can be derived from
the full data set is the maximum swelling that occurred for any of
the solvents used. These values are given in Table VI. These
values probably reflect the intrinsic elasticity of the
macromolecular matrix as well as certain other chemical properties
of the samples.
The complete swelling data for all solvents are split into
Tables VII (A & B) , VIII (A & B) , and IX, which correspond to peat-
like materials, pollens, and polysaccharides respectively; swelling
spectra are similarly subdivided in Figures III (A & B) , IV, and V.
In all instances the best averaged swelling values at 30°C are
plotted against the solvent solubility parameter at 25°C.
33
-------
TABLE VI
MAXIMUM OBSERVED SWELLING FOR EACH SAMPLE AND THE SOLVENT FOR
WHICH THIS OCCURRED
SAMPLE
Pine Pollen
Michigan Peat
Chitin
Aldrich Cellulose
Oak Pollen
Canadian Peat, Ca
Atoka Pine Duff
Canadian Peat, Acid
RAW
MAXIMUM
SWELLING
2.86
2.46
2.35
1.93
1.89
1.85
1.79
1.78
SOLVENT
FOR
MAXIMUM
SWELLING
DMSO
DMSO
DMSO
DMSO
Formamide
DMSO
DMSO
DMF
ASH-
CORRECTED
SWELLING*
2.89
2.63
2.35
1.93
1.91
1.88
2.03
1.88
SOLVENT KEY: DMSO = Dimethylsulfoxide, DMF =
N,N-Dimethylformamide.
*Ash corrections were based on the analytical data given in Table
I, using the formula given in RSKSOP-104 (Appendix II), and an
"ash" density of 2.65 g cm"3. Values given in bold denote large
changes after ash correction.
34
-------
TABLE VIIA
SWELLING OF PEAT-LIKE MATERIALS
(No Ash Correction Applied)
HP
CP
CPCa
AT
n-Pentane
n-Heptane
Methylcyclohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone
Chlorobenzene
Dichloromethane
Acetone
Carbon Disulfide
1, 4-Dioxane
Nitrobenzene
3-Methyl-l-butanol
1-Octanol
Pyridine
Morpholine
N , N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dimethy Isul f oxide
N , N-Dimethyl f ormamide
Nitromethane
Ethanol (99.9%)
Propylene Carbonate
Methanol
1,2-Ethanediol
1, 2-Propanediol
N-Methy 1 f ormamide
Formamide
Water
0.98
0.95
1.09
1.06
1.03
1.01
1.11
1.08
1.01
1.18
1.03
1.13
1.24
1.04
1.13
1.02
1.04
1.04
1.65
1.17
1.82
1.09
1.04
1.19
1.25
1.38
1.33
2.46
2.18
1.11
1.47
1.03
1.49
1.76
1.49
2.38
2.29
1.53
0.96
1.07
1.14
1.08
1.11
1.07
1.08
1.08
1.06
1.18
1.11
1.17
1.17
1.11
1.16
1.17
1.13
1.22
1.61
1.19
1.71
1.16
1.18
1.22
1.38
1.21
1.33
1.76
1.78
1.25
1.51
1.14
1.51
1.71
1.63
1.71
1.74
1.57
1.05
1.09
1.10
1.10
1.03
1.05
1.10
1.07
1.09
1.23
1.05
1.05
1.29
1.04
1.08
1.08
1.13
1.12
1.45
1.20
1.51
1.06
1.07
1.07
1.16
1.20
1.17
1.85
1.75
1.11
1.40
1.01
1.43
1.65
1.34
1.78
1.75
1.52
1.08
1.09
1.12
1.16
1.09
1.12
1.23
1.15
1.09
1.32
1.15
1.28
1.33
1.18
1.27
1.19
1.12
1.13
1.69
1.35
1.79
1.18
1.23
1.27
1.34
1.32
1.38
1.80
1.80
1.26
1.38
1.20
1.43
1.52
1.47
1.72
1.65
1.24
Key: MP=Michigan Peat, CP=Canadian Peat, CPCa=Canadian Peat, Ca-
Exchanged, AT=Atoka Pine Duff
35
-------
TABLE VIIB
SWELLING OF PEAT-LIKE MATERIALS
(Ash-Corrected Values)
HP
CP
CPCa
AT
n-Pentane
n-Heptane
Methyl eye 1 ohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone
Chlorobenzene
Dichloromethane
Acetone
Carbon Disulfide
1,4-Dioxane
3-Methyl-l-butanol
Nitrobenzene
1-Octanol
Pyridine
Morpholine
N , N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dime thy Isulf oxide
N , N-Dimethylf ormamide
Nitromethane
Ethanol(99.9%)
Propylene Carbonate
Methanol
1,2-Ethanediol
1 , 2-Propanediol
N-Methy 1 f ormamide
Formamide
Water
0.98
0.94
1.10
1.07
1.04
1.01
1.12
1.08
1.01
1.20
1.03
1.14
1.27
1.05
1.15
1.05
1.02
1.04
1.72
1.19
1.91
1.10
1.04
1.21
1.28
1.42
1.36
2.63
2.31
1.12
1.52
1.03
1.55
1.85
1.54
2.54
2.44
1.59
0.96
1.08
1.15
1.09
1.11
1.07
1.09
1.08
1.06
1.19
1.12
1.18
1.17
1.12
1.16
1.13
1.17
1.22
1.63
1.20
1.74
1.17
1.18
1.23
1.39
1.21
1.34
1.78
1.80
1.26
1.52
1.15
1.53
1.73
1.65
1.74
1.76
1.58
1.05
1.09
1.10
1.10
1.03
1.05
1.10
1.07
1.09
1.23
1.05
1.05
1.29
1.04
1.08
1.13
1.08
1.12
1.46
1.21
1.53
1.06
1.07
1.07
1.17
1.21
1.18
1.87
1.77
1.11
1.41
1.01
1.44
1.67
1.35
1.81
1.77
1.54
1.10
1.11
1.15
1.20
1.11
1.16
1.29
1.19
1.11
1.42
1.19
1.36
1.42
1.23
1.34
1.15
1.24
1.16
1.90
1.45
2.02
1.23
1.29
1.34
1.44
1.42
1.49
2.03
2.03
1.34
1.49
1.25
1.56
1.68
1.60
1.94
1.84
1.31
Key: MP=Michigan Peat, CP=Canadian Peat, CPCa=Canadian Peat, Ca-
Exchanged, AT=Atoka Pine Duff. Ash corrections were computed as
follows: QMP(ASH FREE) = 1.116*QMP - 0.116
QCP(ASH FREE) = 1.033*QCP - 0.033
QCPCa(ASH FREE) = 1.034*QCPCa - 0.034
QAT (ASH FREE) = 1.299*QAT - 0.299
36
-------
TABLE VIIIA
SWELLING OF PINE AND OAK POLLEN
(No Ash Correction Applied)
PP
OP
n-Pentane
n-Heptane
Methylcyclohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone
Chlorobenzene
Dichloromethane
Acetone
Carbon Bisulfide
1, 4-Dioxane
Nitrobenzene
3-Methyl-l-butanol
1-Octanol
Pyridine
Morpholine
N , N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dimethylsulf oxide
N , N-Dimethyl f ormamide
Nitromethane
Ethanol (99.9%)
Propylene Carbonate
Methanol
1 , 2-Ethanediol
1 , 2-Propanediol
N-Methy 1 f ormamide
Formamide
Water
1.04
1.03
1.02
1.00
0.99
1.05
1.03
1.06
1.03
1.21
1.06
1.19
1.16
0.93
1.22
1.13
1.09
1.09
1.57
1.82
1.93
1.21
1.08
1.23
1.26
1.06
1.29
2.86
1.88
1.02
1.29
1.01
1.49
1.74
1.41
1.99
1.79
1.55
1.00
1.00
0.99
1.02
1.06
1.05
1.06
1.02
1.04
1.21
1.09
1.06
1.12
1.10
1.14
1.17
1.14
1.11
1.27
1.31
1.28
1.13
1.13
1.14
1.19
1.15
1.17
1.61
1.29
1.14
1.27
1.25
1.42
1.66
1.44
1.63
1.89
1.51
KEY: PP=Pine Pollen,
stellata
Pinus echinata, OP=Oak Pollen, Quercus
37
-------
TABLE VIIIB
SWELLING OF PINE AND OAK POLLEN
(Ash-Corrected Values)
PP
OP
n-Pentane
n-Heptane
Methylcyclohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone
Chlorobenzene
Dichloromethane
Acetone
Carbon Bisulfide
1,4-Dioxane
3-Methyl-l-butanol
Nitrobenzene
1-Octanol
Pyridine
Morpholine
N , N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dimethylsulf oxide
N , N-Dimethy 1 f onnamide
Nitromethane
Ethanol(99.9%)
Propylene Carbonate
Methanol
1,2-Ethanediol
1 , 2-Propanediol
N-Methy 1 f ormamide
Formamide
Water
1.04
1.03
1.02
1.00
0.99
1.05
1.03
1.06
1.03
1.21
1.06
1.19
1.16
0.92
1.22
1.09
1.13
1.09
1.57
1.83
1.94
1.21
1.08
1.23
1.27
1.06
1.30
2.89
1.89
1.02
1.30
1.01
1.50
1.75
1.41
2.00
1.80
1.55
1.00
1.00
0.99
1.02
1.06
1.05
1.06
1.02
1.04
1.21
1.09
1.06
1.12
1.10
1.14
1.14
1.17
1.11
1.28
1.32
1.29
1.13
1.13
1.14
1.19
1.15
1.17
1.62
1.30
1.14
1.28
1.26
1.43
1.67
1.45
1.64
1.91
1.52
KEY: PP=Pine Pollen, Pinus echinata, OP=Oak Pollen, Quercus
stellata. Ash corrections were computed as follows:
QPP(ASH FREE) = 1.014*QPP - 0.014
QOP(ASH FREE) = 1.022*QOP - 0.022
38
-------
TABLE IX
SWELLING OF CHITIN AND CELLULOSE
CHITIN
CELLULOSE
n-Pentane
n-Heptane
Methylcyclohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone
Chlorobenzene
Dichloromethane
Acetone
Carbon Bisulfide
1,4-Dioxane
Nitrobenzene
3-Methyl-l-butanol
1-Octanol
Pyridine
Morpholine
N,N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dimethyl sulf oxide
N , N-Dimethy 1 f ormamide
Nitromethane
Ethanol (99.9%)
Propylene Carbonate
Methanol
1,2-Ethanediol
1 , 2-Propanediol
N-Methy 1 f ormamide
Formamide
Water
**
**
**
**
**
**
1.03
0.99
**
**
**
1.05
1.19
1.00
0.92
**
**
**
1.33
1.28
1.59
**
1.00
1.13
1.27
1.23
1.31
2.35
1.92
1.15
1.71
1.01
1.66
2.11
1.88
2.11
2.24
1.99
1.03
1.06
1.17
0.96
1.01
1.00
1.07
0.99
1.16
1.05
1.00
1.03
1.03
1.03
1.04
0.78
1.01
0.92
0.93
1.61
0.82
0.91
1.00
0.94
1.01
1.08
1.01
1.93
1.03
1.06
1.22
0.89
1.29
1.58
1.24
1.70
1.70
1.56
Value not measured.
39
-------
Legend for Figure IIIA. Raw Swelling vs. £_, Peat-Like Materials
The swelling spectra for Michigan and Canadian peat and for
the Atoka pine duff are compared in this figure before ash
corrections. All materials were in their acid forms for these
measurements.
40
-------
SUELLIN6 vs SOLVENT SQLUE1 TTV
iLi i i i mnnuiu'i
2.5 —
o
z
M
J
J
LU
Z
(0
DC
h
UJ
z
D
J
O
1.3
PEAT-LIKE MATERIALS WITH ASH
i I I i ! I I I I 1 I I I r i
8.9
I I I I I I I I I I I 1 | | I L J I !
14
24
34
44
54
DELTA, SOLVENT SOLUBILITY PARAMETER
-------
Legend for Figure IIIB. Ash-Corrected Swelling vs. SQ, Peat-Like
Materials
The swelling spectra for Michigan and Canadian peat and for
the Atoka pine duff are compared in this figure after ash
corrections.
42
-------
2.7 —
(D
I
M
J
J
LU
2
0)
O
h
U
E
D
J
O
fi
LLJ
h
O
UJ
K
ir
o
o
i
i
to
2.4 —:
2.1
1.8
1.5
1.2
SWELLING vs SOLVENT SOLUBILITY PARAMETER
PEAT-LIKE MATERIALS, ASH-CORRECTED
1 1 1 1 1 : 1 r
MICHIGAN PEAT
0.9
i i
' i i i
i i
14
24
34
44
J 1 L
DELTA, SOLVENT SOLUBILITY PflRflflETER
54
-------
Legend for Figure IV. Swelling vs. S0/ Acid and Ca-Exchanged
Canadian Peat
The swelling spectra of Canadian peat in its acid and Ca-
exchanged forms are compared in this plot. No ash corrections were
applied to these data.
44
-------
0
z
M
J
J
LU
3
0)
o
M
OC
h
UJ
E
D
J
O
2 —
1.9
1.8 -
1.7
1.6
1.5
1.4
1.3
1.2
1.1
SWELLING vs SOLVENT SOLUBILITY PARAfCTER
CANADIAN PEAT, ACID AND CarEXCHANGED
*$i £ >;"
....! 1
4 n
8.9
I I I I I I I I I I I I I I I 1 I I I
14
24
34
44
54
DELTA, SOLVENT SOLUBILITY PARAMETER
-------
Legend for Figure V- Swelling vs. 6Q, Pine and Oak Pollen
The swelling spectra of Pine Pollen and Oak Pollen are
compared in this plot. No ash corrections were applied to these
data.
46
-------
2.9
2.5 -
0
I
H
J
J
Ui
3
0)
0
H
IL
h
LU
E
D
J
0
2.1
1.7
1.3
8.9
14
SWELLING vs SOLVENT SOLUBILITY PARAMETER
PINUS ECHINATA AND QUERCUS STELLATA
_iiiii
i t i
i i i i i _ 1111
24
34
44
DELTA, SOLVENT SOLUBILITY PARAMETER
54
-------
Legend for Figure VI. Swelling vs. SQ, Cellulose and Chitin
This figure compares the swelling spectra for cellulose and
chitin. The raw spectrum for cellulose was scaled by a constant
factor so that the average background value of the swelling was
shifted upwards to 1.0. No corrections for ash were applied to
either spectrum.
48
-------
2.5 —
SWELLING vs SOLVENT SOLUBILITY PARAMETER
CELLULOSE AND CHITIN
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DELTA, SOLVENT SOLUBILITY PARAMETER
54
-------
INTERPRETATIONS AND CONCLUSIONS
GENERAL OBSERVATIONS
The choice of solvent solubility parameter as the abscissa is
traditional in plots of swelling, but solubility parameter, by
itself, has no special predictive power for the swelling in these
materials. What is seen instead, are spectra with large jumps in
swelling for very small changes in solvent solubility parameter.
These jumps in swelling are largely attributable to site-specific
chemical interactions of the donor-acceptor type that lower the net
free energy of the swollen state for some swelling agents.
Additionally, there is a molecular size-exclusion effect (discussed
later) that excludes some larger molecules from swelling these
materials even if the donor-acceptor characteristics were correct
for larger swelling.
The importance of site-specific interactions in no way
diminishes the role of dispersive interactions in the complete free
energy balance. A significant issue is the calculation of a
properly corrected solvent solubility parameter that might be used
to include them. Fowkes, 1990 has discussed calculations of 5d, a
modified solubility parameter describing dispersive interactions
only; note that this is completely unrelated to the "<5d" notation
commonly used for one of the empirical three dimensional solubility
parameters developed by Hansen (see Barton, 1983).
PEAT-LIKE MATERIALS
The swelling spectra (Figures III A, III B and IV) for the
various pre-extracted peat-like materials studied here seem
interpretable in terms of a mixture of "humic materials," including
both humic acids and humin, and of relatively undegraded ligno-
cellulosic materials. The cellulose present in these peats does
not appear to behave like free cellulose when exposed to the
solvent morpholine. The possible explanation for this difference
is that the intimate association of lignin with cellulose in the
undegraded plant debris may be sufficient to block the alcoholic-OH
sites on the cellulose chains.
The results for Canadian Peat in its acid and calcium-
exchanged form (Figure IV) are puzzling. If, as supposed, organic
bases such as DMSO interact strongly with phenolic hydrogens and
with the hydrogens associated with carboxylic acid groups, why
aren't there major differences in swelling when these acidic
hydrogens are replaced with calcium? We can only guess at this
point that the small differences observed might be due to a
compensating strong coordination of DMSO with the calcium cations
in this slightly humified peat. Supporting evidence for this
explanation could possibly be obtained from a functional group
analysis for this peat, and a better understanding of its cation
exchange capacity. We note that the very slight increase in ash
50
-------
for the Ca-exchanged sample compared to the acid washed peat does
not seem consistent with complete cation exchange to the calcium
form, assuming reasonable values for the cation exchange capacity
(i.e., CEC = ca. 124 meq/100 g).
PINE AND OAK POLLEN
The swelling spectra for pine and oak pollen (Figure V) can be
interpreted in terms of the basic structure and chemistry of pollen
grains. The cell wall has an exine layer composed of
sporopollenin, and an intine layer, composed of cellulose. In the
present experiments, solvent-soluble cell material was removed by
soxhlet extraction before swelling determination.
According to Brooks and Shaw, 1972 (see especially their Table
I) , the proportion of the pollen grain due to the cell wall is
unusually high in the pine pollens they examined, ranging from 26
to 31% of the cell mass. Of this wall fraction of the cell, the
sporopollenin represents the larger portion, and cellulose the
smaller, in a ratio of about 3.8 to 1. From the very large
swelling observed in DMSO (2.86), we infer that the sporopollenin
probably has a very large swelling in this solvent because even
pure free cellulose (1.93) can't account for the magnitude of the
net swelling observed in this solvent. There is, however, some
uncertainty concerning the swelling properties of other materials
still present in the cell interiors of solvent-extracted pollen
grains.
The swelling observed in DMSO for oak pollen (1.61) was
significantly less than that for pine pollen (2.86). This is in
accordance with the substantially lower wall fraction (7.1%) found
in the single oak pollen (Quercus robur) included in the tabulation
of Brooks and Shaw, 1972. The measured proportion of sporopollenin
in the wall was larger than that for cellulose by a ratio of 4.5 to
1.
The swelling in morpholine, characteristic of free cellulose,
is present in both pollens examined. The net swelling of oak
pollen (1.31) and pine pollen (1.82) in morpholine are both
significant, and in the order expected; however, the swelling of
pine pollen in this solvent exceeds the swelling of pure cellulose
(1.61) in this solvent, so that at least some pollen swelling in
morpholine must be attributed to sporopollenin itself or to some
other non-extractable cell material.
CELLULOSE
The swelling of cellulose in various solvents has been
investigated previously by various authors; much of this voluminous
literature from the paper industry is reviewed in Supplementary
Document 5. It is difficult to compare previously obtained results
with the present work since many of the solvents and methods used
51
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were quite different from those of the present study. As mentioned
in an earlier section, the choice of 30°C for the swelling studies
was prompted by the unusual behavior of cellulose-solvent systems
reported by Chitumbo et al., 1974. These sensitive temperature
dependent effects and the effect of different samples (different
degrees of crystallinity, etc.) probably account for many seeming
discrepancies in the literature.
The present results for cellulose (Figure VI) do not suggest
any global maximum in the swelling when it is plotted as a function
of solvent solubility parameter. Instead, the results are
indicative of site-specific interactions apparently involving the
alcoholic-OH groups on the glucosidic rings.
There are three hydroxyl groups per glucose subunit, one of
which (C6) is a primary hydroxyl, and two of which (C2 & C3) are
secondary hydroxyls. According to Kremer and Tabb, 1990, the
acidity of the hydroxyls varies in the order C2 > C3 > C6. Since
DMSO (an organic base) readily interacts with slightly acidic
groups like alcoholic hydroxyls, it probably interacts with these
hydroxyls. Our swelling results indicate an uptake of 0.93 cm3 of
DMSO per cm3 of cellulose. Using the molar volume of DMSO (70.94
cm3 mol"1) and the molar volume of cellulose per glucosidic subunit
(103.27 cm3 mol"1) allows calculation of the swelling as ca. 1.35
mol of DMSO per mol of glucosidic subunit. This implies that
mainly the C2 hydroxyl is involved in bonding to DMSO, but perhaps
some C3 is also involved. Possibly, the peculiar temperature
dependent swelling effects seen by Chitumbo et al. , 1974 for
cellulose in DMSO are related to the degree of ionization of
hydroxyls other than C2.
CHITIN
The swelling of chitin has not been previously investigated.
Austin, 1984 has considered the best estimate of the solubility
parameter characteristic of chitin itself; these estimates do not
have any apparent relationship to the swelling spectrum observed in
the present work, which does not show any clearly defined global
maximum swelling with respect to solvent solubility parameter.
Instead, we observe a pattern for chitin somewhat similar to
cellulose, but with larger swellings in most cases other than the
solvent morpholine.
MOLECULAR SIZE-EXCLUSION EFFECTS
The evidence for molecular size-exclusion is simple and
direct. Figure VII displays a graph of swelling values plotted
against solvent molar volume for all materials except cellulose.
The largest solvent still capable of significantly swelling these
materials is N,N-dimethylacetamide with a molar volume of ca. 93
cm mol" . Many solvents with molar volumes less than this can
swell these materials. For cellulose, the pattern is similar
52
-------
except that morpholine with a molar volume of ca. 87 cm3 mol"1
represents the largest swelling solvent observed.
Since volume is only a partial constraint on molecular shape,
it is to be expected that the volume boundary for swelling is a
somewhat blurry barrier; some long rod-like molecules might retain
some swelling ability, though more globular molecules with similar
donor-acceptor capabilities might not. The magnitude of molecular
exclusion has been partially delimited by the present work, but
these limits really need to be challenged with further swelling
studies using carefully chosen homologous series of compounds
(e.g., substituted pyridines or sulfoxides).
The volume exclusion effect introduces an additional term to
the (strain) energy portion of the free energy expression for
swelling; one expects the energy to rise rapidly as the molecules
exceed the size of entry-microporesu. There may be possibilities
of pressure-induced "encapsulation" phenomena by which higher
pressures could force slightly size-mismatched molecules into the
macromolecular structure of the organic matter.
uOne uses this expression only for want of a better term.
Probably, the micropores providing entry into the macromolecular
structure are micropores on a smaller size scale from those
micropores involved in capillary condensation phenomena such as
discussed in Diagram II.
53
-------
Legend for Figure VII. Swelling vs. Solvent Molar Volume
Swelling for Michigan and Canadian peats, Ca-exchanged
Canadian Peat, Atoka pine duff, pine and oak pollen and chitin are
plotted versus solvent molar volume. The data exhibit an abrupt
drop-off for solvents with volumes larger than N,N-
dimethylacetamide (ca. 93 cm3 mol"1) . Above this rather fuzzy
boundary, swellings tend to be near 1.0 plus some background
imprecision.
54
-------
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AVERAGE SWELLING vs MOLAR VOLUME
ALL MATERIALS EXCEPT CELLULOSE
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VBflR, SOLVENT MOLAR VOLUME
-------
SAMPLE SIMILARITY BASED ON SWELLING
It was previously mentioned that comparisons of spectra might
be best made with a restriction of the comparison to the highest
swelling solvents. One way of performing this comparison that has
a good visual appeal is the method of "star plots," which is
available in the STATGRAPHICS15 software package. In this method
of plotting, several variables may be simultaneously plotted for
each sample. In Figure VIII swelling values for eight highly
swelling solvents are plotted for all eight samples and for a blank
(ideal, non-swelling material). Each direction corresponds to
swelling for a particular solvent (note the key given in Figure
VIII) that is scaled onto a plotting interval from 1 to 10 in the
following manner: the swelling for the blank is plotted as 1 unit
for all solvents; the maximum swelling (over all samples) for each
solvent is plotted as 10 units. The polygonal patterns for each
sample allow a simple visual comparison of relatedness. For
example, all the peat-like samples have a characteristic "notch" in
the morpholine direction corresponding to the lower swelling of
ligno-cellulose compared to free cellulose. The two pollens have
rather homogeneous swelling in all eight dimensions, but the oak
pollen makes a much smaller polygon. Cellulose and chitin are
similar in the bottom five dimensions, but differ considerably for
the two amides and morpholine.
A full statistical treatment of sample-based similarities
would involve the methods of cluster analysis and Q-mode factor
analysis. These complex approaches are probably not justified for
a set of samples as small as the present one; two or three times
the present number of samples would be desirable.
15STSC, Inc.
2115 East Jefferson Street
Rockville, Maryland 20852
56
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Legend for Figure VIII. "Star" Plot of Swelling in Eight Solvents
This plot exhibits the ash-corrected swelling of all samples
in eight high-swelling solvents. The solvent key is given in
Figure IX. Each direction corresponds to a different solvent; the
blank indicates unit swelling (i.e., no swelling) in each
direction. The maximum swelling material for any solvent is
assigned 10 units, and intermediate values are scaled between 1 and
10.
57
-------
OAK POLLEN
CELLULOSE
CHITIN
CANADIAN PEAT, Ca
ATOKA PINE DUFF
PINE POLLEN
nrAT n
11
j n
^Al I ATI T Al I HPAT I
TLHIj
-------
Legend for Figure IX. Solvent Key to Star Plot
This plot represents the solvent key to the principal
directions used in the star plot of Figure VIII.
59
-------
N?N-Dimethylacetamide
Morpholine
Pyridine
1,2-Ethanediol
N»N-Dimet hy Homamide
DimethylsuHbxide
Water
Methanol
-------
CONSEQUENCES FOR ENVIRONMENTAL STUDIES
It would be desirable in environmental studies of the fate and
transport of organic contaminants in the subsurface to delineate
all possible categories of sorption onto soil and aquifer materials
in terms of capacity, equilibrium, energetics and kinetics. This
is far from being accomplished even for the simplest of typical
real systems.
The major application of the present work to real
environmental questions centers on the direct demonstration of an
additional category of sorbed substances that can occur in soil and
aquifer systems. Some nonequilibrium partitioning effects seen in
certain column experiments by Brusseau and Rao, 1989 may well
involve a diffusion-limited step between swollen organic particles
and the external fluid phase. We wonder, also about laboratory
biodegradation studies using small molecules such as methanol as a
carbon source. Here we would expect methanol to swell any soil
organic matter that was present, and thus, add a slow diffusion
step to the overall kinetics of the degradation process for
methanol. In dilute systems, this would be complicated by
competitive sorption phenomena involving water also.
The bulk-sorbed fraction inside macromolecular organic
materials probably can serve as a source of hard-to-remove residual
contamination in a pump and treat remediation; however, not all
organic molecules can participate in bulk sorption into the solid
organic matter. Size exclusion seems to limit the category to
fairly small, polar molecules such as some alcohols and amides. If
these species were present in a contaminating mixture, they also
might serve as co-sorbents for other small molecules with less
polar character, such as the smaller chlorinated hydrocarbons.
Most of the alkanes and aromatic species present in fuels are not
expected to undergo significant bulk sorption into macromolecular
organic materials in soils and aquifers.
The present work with its emphasis on macromolecular materials
does not, however, rule out the possible bulk sorption of
hydrophobic organic molecules into the wax-resin-lipid fraction of
soils, nor does it rule out significant sorption into micropores
(i.e., capillary condensation). These sorption categories,
extractable materials (bitumens) and microporosity, represent
potentially important separate areas for further study, and may be
responsible for much supposed "partitioning" of non-ionic organic
contaminants.
SUGGESTIONS FOR FUTURE WORK
The present method of obtaining swelling measurements is
fairly labor intensive, and, unfortunately, rather imprecise.
Recently, various instrumental methods have become available for
61
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studying the particle-size distributions of powdered materials
dispersed in liquids. It would be very worthwhile to explore the
use of these instruments for obtaining swelling data on a given
material from particle size distributions taken in different
solvents. This should be relatively simple to do for powders
consisting of a single substance like cellulose or chitin. The
swelling of a heterogeneous mixture of insoluble organic materials
might still be successfully analyzed by such methods, provided:
1. a series of solvents were used that affected the
components differently, and
2. the size distribution functions for the different
components were of relatively simple analytical types, such as
lognormal or Gaussian.
Many features of sorption on organic materials have already
been pointed out as not well understood; in particular, the
energetics of site-specific sorption are not yet incorporated into
environmental models. The level at which understanding must
eventually occur has shifted recently from a concern with average
batch sorption properties to a concern with molecular level
interactions and with the behavior of individual components of very
complex mixtures. This level of understanding is probably
essential for the modeling of typical column sorption experiments
to match the experimental data at their full precision. A
compelling demonstration of adequate understanding of break-through
curves will require a major increase in the characterization of
materials used in the preparation of columns.
It became increasingly clear during the course of this work
that the presence of ionizable groups containing oxygen is one of
the key characteristics of soil and sediment organic matter that
will affect sorption characteristics. Therefore, the various
analytical techniques for determining the disposition of oxygen in
these materials are of major interest; among these are FTIR and
pyrolysis-GC/MS methods. These spectroscopic techniques, in
combination with appropriate multivariate statistical methods, are
probably the most appropriate techniques available for the
development of rapid site-characterization tools for organic
matter. Flow microcalorimetry or titration calorimetry with
various kinds of probe molecules may provide methods of analyzing
for number and energetics of different sorption sites based on
direct measurement of the enthalpies of sorption.
Besides these newer instrumental methods, classical techniques
for the determination of cation exchange capacity (CEC) of high-
organic materials need re-examination, if only to clarify their
interpretation for environmental work. Just as the apparent
surface area of swelling materials is dependent on the nature of
the molecular probe (see Chiou et al. , 1990) , so should the
apparent cation exchange capacities of macromolecular organic
62
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materials depend on the nature of the solvent system; cations
dissolved in the maximally swelling solvent DMSO should have much
greater access to the cation exchange sites in these materials than
the usual aqueous cations (e.g., Ba+2, NH4+) employed for this
purpose. Unfortunately, highly swelling solvents such as DMSO also
have considerable dissolving power for humic acids, and would tend
to mobilize these materials; therefore, the usual cation exchange
procedures, if they were adapted to a DMSO solvent system, probably
would have to use organic matter pre-extracted with DMSO. The
competition between the cation exchange equilibrium, and the donor-
acceptor interaction involving DMSO and acidic hydrogens is not
understood, and investigations here might also lead to useful
analytical procedures.
Development of CEC measurement procedures based on a better
understanding of swelling materials may have an improved chance of
measuring a true total cation exchange capacity (at least of the
humin fraction) that bears some relation to bulk chemical
composition, especially the 0/C ratio. A statistical examination
of CEC versus O/C plots for many different kinds of organic
materials would perhaps be of some use in constructing a sorption
typology for these materials in much the same way as H/C versus O/C
plots (Van Krevelen diagrams) have provided a simple classification
of coals and kerogens corresponding to their potential for
generation of hydrocarbon gases and liquids (see, for example,
Tissot and Welte, 1984).
63
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REFERENCES
Austin, P.R., 1984, "Chitin Solvents and Solubility Parameters", in
Chitin. Chitosan. and Related Enzymes. Academic Press, Inc., NY, p.
227-237-
Barton, A.F.M., 1983, CRC Handbook of Solubility Parameters and
other Cohesion Parameters. CRC Press, Inc., Boca Raton, Florida.
Brooks, J., and Shaw, G., 1968, Chemical Structure of the Exine of
Pollen Walls and a New Function for Carotenoids in Nature, Nature
V. 219, p. 532-533.
Brooks, J., and Shaw, G., 1972, Geochemistry of Sporopollenin,
Chem. Geol. v. 10, p. 69-87.
Brusseau, M.L., and Rao, P.S.C, 1989, The Influence of Sorbate-
Organic Interactions on Sorption Nonequilibrium, Chemosphere v.
18(9/10), p. 1691-1706.
Chin, Y.-P., Weber, W.J., Jr., 1989, Estimating the Effects of
Dispersed Organic Polymers on the Sorption of Contaminants by
Natural Solids. 1. A Predictive Thermodynamic Humic-Substance-
Organic Solute Interaction Model, Environ. Sci. Technol. v. 23(8),
p. 978-984.
Chin, Y.-P., Weber, W.J., Jr., and Eadie, B.J., 1990, Estimating
the Effects of Dispersed Organic Polymers on the Sorption of
Contaminants by Natural Solids. 2. Sorption in the Presence of
Humic and other Natural Macromolecules, Environ. Sci. Technol. v.
24(6), p. 837-842.
Chiou, C.T., Lee, J.-F., and Boyd, S.A., 1990, The Surface Area of
Soil Organic Matter, Environ. Sci. Technol. v. 24, p. 1164-1166.
Chiou, C.T., Porter, P.E., and Schmedding, D.W., 1983, Partition
Equilibria of Nonionic Organic Compounds between Soil Organic
Matter and Water, Environ. Sci. Technol. v. 17(4), p. 227-231.
Chitumbo, K. , Brown, W. , and De Ruvo, A., 1974, Swelling of
Cellulosic Gels, J. Polymer Sci., Symposium No. 47, p. 261-268.
Day, J.H., Rennie, P.J., stanek, W., and Raymond, G.P., 1979, Peat
Testing Manual. National Research Council of Canada, Associate
Committee on Geotechnical Research, Technical Memorandum No. 125.
Flory, P.J., 1953, Principles of Polymer Chemistry. Cornell
University Press, Ithaca, NY.
Fowkes, F.M., 1980, "Donor-Acceptor Interactions at Interfaces",
Polymer Science and Technology, v. 12A, p. 43-52, Plenum Press, NY.
64
-------
Fowkes, F.M., 1990, Acid-Base Measurements of Solvents, Polymers
and Inorganic Surfaces, Preprint.
Freeman, D.H., and Cheung, L., 1981, A Gel Partition Model for
Organic Desorption from a Pond Sediment, Science v. 214, p. 790-
792.
Fuchsman, C.H., 1980, Peat, Academic Press, NY.
Hayes, M.H.B., 1985, "Extraction of Humic Substances from Soil",
chapter 13 in Humic Substances in Soil. Sediment, and Water. Aiken,
G.R., McKnight, D.M., Wershaw, R.L., and MacCarthy, P., editors,
John Wiley & Sons, NY.
Horsley, L.H., (ed.), 1973, Azeotropic Data III. American Chemical
Society, Washington, D.C., p. 202.
Kaiser, W.R., 1974, Texas Lignite: Near Surface and Deep-Basin
Resources, Report of Investigations No. 79, Bureau of Economic
Geology, The University of Texas at Austin, Austin, TX.
Kremer, R.D., and Tabb, D. , 1990, Paper: The Beneficially
Interactive Support Medium for Diagnostic Test Development, Amer.
Lab. v. 22(3), p. 136,138-140,142-143.
Mingelgrin, U., and Gerstl, F., 1983, Reevaluation of
Partitioning as a Mechanism of Nonionic Chemicals Adsorption in
Soils, J. Environ. Qual. v. 12(1), p. 1-11.
Muzzarelli, R.A., 1977, Chitin. Pergamon Press, NY.
Skujins, J.J., Patgieter, H.J., and Alexander, M. , 1965,
Dissolution of Fungal Cell Walls by a Streptomycete Chitinase and
6- (1-^3) Glucanase, Arch. Biochem. Biophys. v. Ill, p. 358-364.
Snider, J., and Covay, K.J., 1987, Premining Hydrology of the
Logansport Lignite Area, DeSoto Parish, Louisiana, Water Resources
Technical Report No. 41, Louisiana Department of Transportation and
Development, Baton Rouge, Louisiana.
Tanaka, T., Fillmore, D., Sun, S.-T., Nishio, I., Swislow, G., and
Shah, A., 1980, Phase Transitions in Ionic Gels, Phys. Rev. Lett.
V. 45(20), p. 1636-1639.
Tegelaar, E.W., de Leeuw, J.W., Derenne, S., and Largeau, C., 1989,
A Reappraisal of Kerogen Formation, Geochim. Cosmochim. Acta v. 53,
p. 3103-3106.
Tissot, B.P., and Welte, D.H., 1984, Petroleum Formation and
Occurrence, Springer-Verlag, NY.
Weast, R.C., 1984, CRC Handbook of Chemistry and Physics. CRC
65
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Press, Inc., Boca Raton, FL, p. F8,
66
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SUPPLEMENT 1
PAGE 1
DERIVATION OF A SIMPLIFIED THERMODYNAMIC EQUATION
OF STATE FOR SWELLING
\\\\\\-
o ft
Consider the apparatus depicted in the above diagram. The
side labeled a denotes a sample of a solid, swelling material
confined by a frictionless piston producing pressure Pa, and
separated by a strong porous barrier from a chamber containing pure
solvent. The pure solvent side of the apparatus, denoted by jS, is
maintained at a constant reference pressure, P. (usually taken as
1 atmosphere or 1 bar) . The porous barrier allows solvent, but not
solid, to pass from one side to the other. It will be assumed in
all the following derivations that no volume change accompanies
this solvent transfer from one side to another, so that dVa = -dV^.
STATE VARIABLES
The state variables to be considered for this system are the
temperature, T, the applied pressure P , and the volume occupied by
the swollen material, Vfl. At equilibrium, these are sufficient to
specify the condition of the system.
When Pa = P», the system is in a state of "free swelling", in
which solvent will be sorbed by the material on the a side of the
apparatus up to some limit set by the cross-linking and the elastic
properties of the material. This free swelling, Qv, is essentially
what is measured in the usual swelling experiment, in which the
fully swollen volume, Va*, is compared to the original volume
occupied by the dry material (including its micro-porosity) , V0;
_i.e. Qv = Vtf*/vo' Tne Pressure/ pa ~ Vft needed to prevent solvent
from swelling the dry material is known as the "swelling pressure"
(for the dry material) and can be enormously large for strongly
swelling systems; for this reason, the swelling pressure of dry
materials can seldom be measured directly -
WORK DUE TO A CHANGE IN Va
The work due to a change in Vc can be calculated as:
(l) dW = -PadVa - PpdVp = -(Pa - Pp)dVa
The swelling pressure is denoted as follows:
if]
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SUPPLEMENT 1
PAGE 2
(2) n = pa -
ENERGY FUNCTION
Consider the internal energy E = E(Va,T); the total energy
differential may be expressed as:
For reversible changes,
(4) dqiev = TdS
This allows the substitution:
Since dS is an exact differential, we may also write the equation,
"> —
This allows identification of the terms as follows
(7) ldS\
and
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SUPPLEMENT 1
PAGE 3
E
T
Taking cross-partial derivatives, we may equate:
(9)
This yields the following final equation:
Equation 10 is a thermodynamic equation of state completely
homologous to the usual thermodynamic equation of state for fluids.
CONNECTIONS TO CALORIMETRY
The thermodynamic equation of state for the swelling situation
contains the differential of the internal energy with respect to
the volume, Va. This term can be related to a set of calorimetric
experiments as follows. Assume that a series of samples of the
swelling powder are prepared with varying amounts of pre-sorbed
solvent. These samples are then immersed in excess solvent at some
constant temperature, and the heat evolved in each case is
measured. The free swelling is known for this material, so that
the internal energy changes for each sample can be normalized with
respect to the final volume of the swollen paste. A plot of the
volume-normalized internal energy changes versus the volume of the
material with pre-sorbed solvent gives a curve whose slope at any
given volume is the volumetric energy differential in question.
TOTAL ENTROPY CHANGE CONNECTED WITH SWELLING
By substitution of equation 10 into equation 8, we obtain an
expression for the differential of the total system entropy with
respect to volume changes:
1The pre-sorbed solvent is assumed to be homogeneously spread
throughout the swollen sample.
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SUPPLEMENT 1
PAGE 4
as
Isothermal integration of this expression from the original volume,
V0, to the final swollen volume, Va*, yields the entropy
increment associated with swelling:
(12) AS- dV
«
In actual modeling of swelling data, this entropy is usually
calculated from separate statistical mechanical expressions for the
entropy of mixing, strain entropy, etc. Equation 12 allows an
alternative determination of the net effect, at least in principal,
from equation of state data along an isotherm.
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SUPPLEMENT 2
PAGE 1
REVIEW;
PROPERTIES OF PEATS, AND METHODS OF PREPARATION AND
CHARACTERIZATION PRIOR TO SORPTION AND SWELLING STUDIES
William G. Lyon
NSI Technology Services Corporation
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
INTRODUCTION
Understanding the unique properties of peats and other organic
rich soils is essential to understanding fate and transport of
pollutants, and ultimately to designing remediation measures for
pollution in wetlands of various types. Additionally, there is an
increasing appreciation that the sorption characteristics of peats
make them potentially useful materials for various kinds of waste
water treatment processes.
The essential features of peats which affect their sorption
characteristics are as follows:
1. The organic constituents of Peat are a mixture of humic
materials, cellulose, spores, and various soluble fractions.
2. The acidic depositional environment and the antiseptic
nature of the water-soluble phenolic compounds tends to
preserve more and different organic materials than other
environments.
3. The wax and resin fraction of peats can be a fairly large
portion of the organic mass (up to 10 or 15% sometimes).
4. Peat waxes and resins melt in the 60 - 70°C range, and
spread on the peat surfaces, blocking access to sorption
sites. Such samples are difficult to rewet with water.
5. Peat which has been extracted of its wax and resin
fraction is much more subject to air oxidation: it can catch
fire on drying in air at 105°C.
6. Peats tend to have large cation exchange capacities from
their relatively large carboxylic acid and phenolic group
contents.
7. Peats are capable of swelling in organic solvents, and
show size exclusion behavior for molecules larger than about
93 cm3 mol"1. The cellulosic components of peats exclude
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molecules somewhat smaller than this.
It is clear from the literature surveyed that peats are, in
fact, a very diverse group of materials with considerable variation
in sorption properties depending on their detailed chemical nature
as shaped by source material, depositional environment, and
subsequent diagenetic processes. Classification schemes for peat
which were designed for fuel or agricultural purposes are clearly
inadequate for the more sophisticated uses of this resource which
are anticipated.
ANNOTATED BIBLIOGRAPHY
Aho, M.J., Tummavuori, J.L., Hamalainen, and Saastamoinen, J.L.,
1989, Determination of Heats of Pyrolysis and Thermal Reactivity of
Peats, Fuel v- 68, p. 1107-1111.
Aho, M., Kortelainen, P., Rantanen, J., and Linna, V., 1989,
Pyrolysis of Peat Studied by Thermogravimetry and Fourier Transform
Infrared Spectroscopy, J. Anal. Appl. Pyrolysis v. 15, p. 297-306.
Aho, M.J., Tummavuori, J.L., Hamalainen, and Saastamoinen, J.L. ,
1989, Determination of Heats of Pyrolysis and Thermal Reactivity of
Peats, Fuel v. 68, p. 1107-1111.
Allen, S.J., McKay, G., and Khader, K.Y., 1989, Intraparticle
Diffusion of a Basic Dye During Adsorption onto Sphagnum Peat,
Environ. Poll. v. 56, p. 39-50.
Allen, S.J., McKay, G. , and Khader, K.Y., 1988, Multi-component
Sorption Isotherms of Basic Dyes onto Peat, Environ. Poll. v. 52,
p. 39-53.
Allen, S.J., McKay, G., and Khader, K.Y., 1988, The Adsorption of
Acid Dye onto Peat from Aqueous Solution - Solid Diffusion Model..
J. Colloid Interface Sci. v. 126(2), p. 517-524.
[Concerned with the ability of peat to treat textile effluents
containing dyes, and focuses on theoretical models of
sorption. Not a sufficiently detailed characterization of the
sphagnum peat used. Would removal of the peat wax fraction
have improved the sorption characteristics? Did drying at 60°
spread the bitumens over the particle surfaces?]
Allen, S.J., 1987, Equilibrium Adsorption Isotherms for Peat, Fuel
v- 66, p. 1169-75.
[Sorption isotherms for acid dyes, basic dyes, and zinc
cations.]
Andrejko, M.J., Fiene, F., and Cohen, A.D., 1982, Comparison of
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Ashing Techniques for Determination of the Inorganic Content of
Peats, in Testing of Peats and Organic Soils. Proceedings of a
Symposium sponsored by ASTM Committee D-18 on Soil and Rock,
Toronto, Canada, 23 June 1982.
[It is the mineral matter content of peats that is really
desired, not the "ash" content. Examines the difficulties in
methods borrowed from coal analysis, and the assumptions used
in converting from ash content to mineral matter content.]
Anonymous, 1990, Simple Solutions May Soon Solve Contamination
Problems, Geotimes v. 35(7), p. 10.
[A naive publicity piece concerning the work of Cohen and
Durig at the University of South Carolina which claims that
peats can be used to clean up various kinds of waste water.]
Antworth, C.P., Yates, R.R., and Cooper, W.T., 1989, Applications
of Inverse Chromatography in Organic Geochemistry - I.
Characterization of Polar Solute-Soil Organic Matter Interactions
by High Performance Liquid Chromatography, Org. Geochem. v. 14(2),
p. 157-164.
[Valuable information on a new technique, but rather skimpy on
experimental details. The characterization of the commercial
peat used for these experiments is inadequate. No mention was
made of the possibility that the cellulose component of peat
might be sorbing polar materials.]
Arpiainen, V., and Lappi, M. , 1989, Products from the Flash
Pyrolysis of Peat and Pine Bark, J. Anal. Appl. Pyrolysis v. 16, p.
355-376.
Bailey, A., and Rosters, E.G., 1983, Silicate Minerals in Organic-
Rich Holocene Deposits in Southern Louisiana, Proc. Workshop on
Mineral Matter in Peat: Its Occurrence. Form and Distribution. R.
Raymond and M.J. Andrejko, eds, Sept. 26-30, 1983, Los Alamos
National Laboratory, Los Alamos, NM.
Bohlin, E., Hamalainen, M. , and Sunden, T. , 1989, Botanical and
Chemical Characterization of Peat Using Multivariate Methods, Soil
Sci. V. 147(4), p. 252-263.
[Use of principal components analysis to separate the 41 peat
samples into 8 groups. Ultimately one would hope for a
comprehensive typology of peats and histosols to arise from
this sort of chemometric analysis of a sufficiently large data
base.]
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Bracewell, J.M., Robertson, G.W., and Williams, B.L., 1980,
Pyrolysis-Mass Spectrometry Studies of Humification in a Peat and
a Peaty Podzol, J. Anal. Appl. Pyrolysis v. 2, p. 53-62.
Brown, A., Mathur, S.P., Kauri, T. , and Kushner, D.J., 1988,
Measurement and Significance of Cellulose in Peat Soils, Can. J.
Soil Sci. v. 68, p. 681-685
Cloutier, J.-N., Leduy, A., and Ramalho, R.W., 1985, Peat
Adsorption of Herbicide 2,4-D from Wastewaters, Can. J. Chem. Eng.
V. 63(2), p. 250-257.
Cohen, A.D., and Spackman, W., 1977, Phytogenic Organic Sediments
and Sedimentary Environments in the Everglades-Mangrove Complex
Part II. The Origin, Description, and Classification of the Peats
of Southern Florida, Palaeontographica, Part B, v. 162(4-6), p. 71-
114.
Cohen, A.D., and Spackman, W., 1972, Methods in Peat Petrology and
their Application to Reconstruction of Paleoenvironments, GSA Bull.
v. 83, p. 129-142.
Day, J.H., Rennie, P.J., Stanek, W., and Raymond, G.P., 1979, Peat
Testing Manual. NRC Canada, Associate Committee on Geotechnical
Research, Technical Memorandum No. 125, 193 pp
[An extremely useful compendium of standard methods for
testing organic rich sediments and soils, especially peat.]
Durig, D.T., Esterle, J.S., Dickson, T.J., and Durig, J.R., 1988,
An Investigation of the Chemical Variability of Woody Peat by FT-IR
Spectroscopy, Appl. Spec. v. 42(7), p. 1239-1244.
Durig, J.R., Calvert, G.D., and Esterle, J.S., 1989, Development of
a Pyrolysis-Gas Chromatographic-Fourier Transform Infrared
Spectroscopic Technique for the Study of Woody Peats, J. Anal.
Appl. Pyrolysis v. 14, p. 295-308.
Forsberg, S., and Alden, L., 1989, Dewatering of Peat, Fuel v. 68,
p. 446-455.
Fuchsman, C.H., 1980, PEAT Industrial Chemistry and Technology.-
Academic Press, NY.
[A very valuable survey of analytical results accumulated over
the years. The section (Chapter 3) on solvent extraction of
peat bitumens gives comparative yields for various solvent
systems. Table XIII gives softening points and various other
properties of peat bitumens.]
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Gafni, A., and Brooks, K.N., 1990, Hydraulic Characteristics of
Four Peatlands in Minnesota, Can. J. Soil Sci. V- 70, p. 239-253.
[Contains an excellent set of references on the hydraulic
properties of peat deposits.]
Hatcher, P.G., Breger, I.A., Maciel, G.E., and Szeverenyi, N.M.,
1985, Geochemistry of Humin, chapter 11 in Humic Substances in
Soil. Sediment and Water: Geochemistry, Isolation. and
Characterization. John Wiley & Sons, NY, pp. 275-302.
Hatcher, P.G., Lerch, H.E., III, Kotra, R.K., and Verheyen, T.V.,
1988, Pyrolysis G.C.-M.S. of a Series of Degraded Woods and
Coalified Logs that Increase in Rank from Peat to Subbituminous
Coal, Fuel v. 67, p. 1069-1075.
Holmgren, A., and Norden, 1988, Characterization of Peat Samples by
Diffuse Reflectance FT-IR Spectroscopy, Appl. Spect. v. 42(2), p.
255-262.
Joshi, H.C., and Misra, S.G., 1983, Adsorption of Three
Organophosphorus Insecticides on Different Soils, Environ. & Ecol.
v- 1, p. 75-81.
[One peat soil sample with a TOM of 20.7% was included. The
three pesticides investigated were malathion, parathion, and
phosphamidon.]
Katase, T., and Kondo, R., 1989, Vertical Profiles of trans-
and cis-4-Hydroxycinnamic Acids and Other Phenolic Acids in
Horonobe Peat Soils, Japan, Soil Sci. v- 148(4), p. 258-264.
Kornder, S.C., and Carpenter, J.R., 1984, Application of a Linear
Unmixing Algorithm to the Normal Alkane Patterns from Recent Salt
Marsh Sediments, Org. Geochem. v. 7(1), p. 61-71.
Rosters, B.C., and Bailey, A., 1953, Characteristics of Peat
Deposits in the Mississippi River Delta Plain, Trans. Gulf Coast
Assoc. Geol. Soc. v. 33, p. 311-325.
Kumari, D., 1987, Analysis of Wax and Resin Components from
Minnesota Peat Bog, Int. J. Coal Geology v. 8, p. 99-109.
Leger, S., Chornet, E., and Overend, R.P., 1987, Characterization
and Quantification of Changes Occurring in the Low-Severity
Dewatering of Peat, Int. J. Coal Geology v- 8, p. 135-146.
Loxham, M. , 1981, Pollution in Peats, Proc. 10th Int. Conf. Soil
Mech. Found. Eng. Stockholm, Sweden, June 15-19, 1981, v. 2, p.
345-348, A.A. Balkema, Publisher, Rotterdam, Neth. and Salem, NH.
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MacCarthy, P., and Djebbar, K.E., 1986, Removal of Paraquat,
Diquat, and Amitrole from Aqueous Solution by Chemically Modified
Peat, J. Eriviron. Qual. v- 15(2), p. 103-107.
McCarthy, T.S., Mclver, J.R., Caimcross, B., Ellery, W.N., and
Ellery, K., 1989, The Inorganic Chemistry of Peat from the
Maunachira Channel-Swamp System, Okavango Delta, Botswana, Geochim.
Cosmochim. Acta v. 53, p. 1077-1089.
Martin, A.M., and Manu-Tawiah, W., 1989, Study on the Acid
Hydrolysis of Peat: Composition of the Extracts from Sphagnum
Peat, J. Chem. Tech. Biotechnol. v. 45, p. 171-179.
Moers, M.E.C., Boon, J.J., de Leeuw, J.W., Baas, M., and P.A.
Schenck, 1989, Carbohydrate Speciation and Py-MS Mapping of Peat
Samples from a Subtropical Open Marsh Environment, Geochim.
Cosmochim. Acta v. 53, p. 2011-2021.
Moore, P.O., 1989, The Ecology of Peat-Forming Processes: A Review,
Int. J. Coal Geol. v. 12, p. 89-103.
Orem, W.H., and Hatcher, P.G., 1987, Early Diagenesis of Organic
Matter in a Sawgrass Peat from the Everglades, Florida, Int. J.
Coal Geology v. 8, p. 33-54.
Preston, C.M., Axelson, D.E., Levesque, M., Mathur, S.P., Dinel,
H. , and Dudley, R.L., 1989, Carbon-13 NMR and Chemical
Characterization of Particle-Size Separates of Peats Differing in
Degree of Decomposition, Org. Geochem. v. 14(4), p. 393-403.
Roy, C., Chornet, E., and Fuchsman, C.H., 1983, The Pyrolysis of
Peat, A Comprehensive Review of the Literature, J. Anal. Appl.
Pyrolysis v. 5, p. 261-332.
Ryan, N.J., Given, P.H., Boon, J.J., and de Leeuw, J.W., 1987.
Study of the Fate of Plant Polymers in Peats by Curie-Point
Pyrolysis, Int. J. Coal Geol. v. 8, p. 85-98.
M. Schnitzer, M., and Levesque, M., 1979, Electron Spin Resonance
as a Guide to the Degree of Humification of Peats, Soil Sci. v.
127(3), p. 140-145.
[A partially successful attempt to apply ESR spectroscopy of
free radicals to the estimation of degree of humification of
peats.]
Sheppard, S.C., Gibb, C.L., and Hawkins, J.L., 1989, Fate of
Contaminants during Utilization of Peat Materials, J. Environ.
Qual. v. 18, p. 503-506.
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Stevenson, F.J., and Butler, J.H.A., 1969, Chemistry of Humic Acids
and Related Pigments, Chapter 22 in Organic Geochemistry
edited by G. Eglinton and M.T.J. Murphy, Springer-Verlag, NY.
Ting, F.T.C. 1977, Microscopical Investigation of the
Transformation (Diagenesis) from Peat to Lignite, J. Microscopy v.
109(1), p. 75-83.
[Estimates approximately a 4:1 compaction of peat passing to
the lignite stage of coalification.]
van Smeerdijk, D.G., and Boon, J.J., 1987, Characterization of
Subfossil Sphagnum Leaves, Rootlets of Ericaceae and their Peat by
Pyrolysis-High Resolution Gas Chromatography-Mass Spectrometry, J.
Anal. Appl. Pyrolysis v. 11, p. 377-402.
Viraraghavan, T. , and Mathavan, G.N. , 1988, Use of Peat in the
Treatment of Oil-In-Water Emulsions, Proceedings of the 42nd
Industrial Waste Conference, Purdue University, Lafayette, Indiana,
May 12-14, 1987.
77
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REVIEW;
THERMODYNAMICS OF POLYMER SWELLING
AS AN ANALOGY FOR SOIL ORGANIC MATTER
William G. Lyon
NSI Technology Services Corporation
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
INTRODUCTION
The thermodynamics of polymers in contact with orgarfic liquids
might seem remote from the sorption properties of soil organic
matter (SOM); nevertheless, the analogy has been successfully drawn
between the sorption behavior of coal and of cross-linked polymers.
With some significant modifications, several of the theoretical
constructs for polymers are expected to apply also to soil organic
matter.
SWELLING
For historical reasons, polymeric systems were studied at an
early stage in the development of physical chemistry, because it
was known that solutions of large molecules departed from ideal
behavior at extremely small molar concentrations. Cross-linked
polymeric systems, which swell rather than dissolve, were studied
during this period, and it is these systems especially which are
analogous to certain components of soil organic matter. Swelling
is simply defined as the ratio of the swollen volume (at
equilibrium) to the unswollen volume of the polymer.
THE LIMITS OF THE POLYMER-SOM ANALOGY
The limitations of the Polymer-SOM analogy are useful to keep
in mind throughout the following discussion. Soil organic matter
is a mixture of components of different origin, some of them
soluble, and some insoluble. The cross-linked macromolecular
components are of primary concern here, so we will assume that all
soluble components have been removed when swelling in a given
liquid is being considered. In addition to being a mixture, soil
organic matter is polymeric, in the strict sense of the term, only
for certain constituents such as cellulose and chitin. Other
components such as humin or humic acid are macromolecular rather
than polymeric: there is no regularly repeating unit in these
materials. Another manner in which macromolecular soil components
differ from synthetic polymers is in their cross-linkages: these
are not regular in soil organic matter either, but consist of a
hodge-podge of covalent cross-links, hydrogen-bond cross-links,
molecular entanglements, and perhaps even pi-bonded cross-links.
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SOME RELATIONS BETWEEN SOM AND COAL
The intrinsic irregularity of soil organic matter is shared
with coal; however, soil organic matter, typically, is a much more
complex mixture of terrestrially derived macromolecular materials
than is coal. The diagenetic processes occurring in the initial
coalification of plant debris removes many sorptive materials
(e.g.. cellulose) which can be readily metabolized by
microorganisms, leaving a fairly inert, and simpler collection of
bio-resistant molecules as lignite. As coal passes from lignite to
sub-bituminous rank, surface functionalities, like -COOH groups,
responsible for cation exchange properties are lost, sometimes
abruptly, through abiotic diagenesis coming into play under the
increasing severity of surrounding conditions.
PHYSICAL CHEMISTRY OF CROSS-LINKED, POLYMER SWELLING
The equilibrium between a liquid and a cross-linked polymer
depends on a free energy balance involving roughly the following
terms:
1. Strain Energy (isotropic stretching of cross-linked
matrix)
2. Chemical Interaction Energy (between solvent and matrix)
3. Entropy of Mixing (entropy increase due to mixing of
solvent with macromolecular matrix)
4. Strain Entropy (entropy decrease due to stretching)
The above subdivision is described as a rough one, because it
is not clear experimentally whether the free energy can always be
legitimately subdivided into elastic and chemical components. The
assumption of separability of the free energy into these components
was introduced by Flory and Rehner, 1943.
It may be significant that the known apparent disagreements
with the Flory-Rehner assumption, appear to show up in systems
involving a polymer in equilibrium with a vapor. As discussed by
Vink, 1983, vapor phase equilibria with homogeneous gels seem to be
inadmissable thermodynamically, because of the formation of
heterogeneities in the gels (i.e. the assumption of a single
homogeneous gel phase used in certain thermodynamic derivations
breaks down). At present, the Flory-Rehner assumption remains
largely untested for Polymer-Liquid systems (binary or ternary).
For the moment we will not worry about this unresolved dilemma, but
merely note that it is currently an item of active debate and
research even for such well-studied polymers as rubber. (See
especially the papers by Neuburger and Eichinger, 1988, and by Gee
et al., 1965).
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CAVEATS CONCERNING APPLICATIONS TO COMPLEX SUBSTANCES
The polymer literature (especially on rubber) may be somewhat
misleading on what to expect for the relative importance of the
four free energy terms, in applications involving naturally
occurring macromolecular substances. In general, the energetic
components of the free energy balance are thought to be less
important for the swelling of rubbery polymers than the entropic
contributions; this is not necessarily the case for swelling in
other types of substances such as cellulose etc. Therefore, models
appropriate to these more complex substances should not, in
general, either ignore (elastic strain energy) or oversimplify the
energetic effects (chemical interaction energy). This caveat
applies especially to the uncritical application of unmodified
Flory-Huggins-Rehner theory to humic materials as has been reported
by Chin and Weber, 1989. The parameters derived from such
treatments may be of dubious validity.
ELASTIC STRAIN ENERGY
The strain energy stored in a stretched spring (i.e. the iskx2
term for the potential energy) has a similar, but generalized,
formulation (see Kittel, 1966) for isotropically expanded swollen
polymers: the strain energy density, U, is equated to a quadratic
expression involving the bulk modulus, B, and the volume dilation,
d, i.e. U = ^Bd2. The volume dilation, d, is defined as the
increase in volume, divided by the original volume, V0, and can be
easily related to the swelling, Q. Departures from Hooke's law
behavior are expected to become serious when swelling greater than
about 1.3 is observed. In this region of large strain, the theory
might be adjusted either by allowing B = B(d), or by including
higher order terms in the expansion of the strain energy.
It should be noted that calorimetric determinations of heats
of immersion of a cross-linked, macromolecular material in a
swelling solvent determine a net heat effect, which is the sum of
strain energy and chemical interaction energy terms. Careful
calorimetric work on model systems with simple chemical
interactions would allow a direct determination of the importance
of a strain energy term in the swelling equilibrium.
CHEMICAL INTERACTION ENERGY AND SOLVENT PARAMETER (6)
When two components are admixed on a molecular scale, the
energy change involved represents a difference in the final state,
component 1 and 2 molecules interacting with each other, and the
initial state, component 1 and two molecules interacting with
themselves. This can be expressed in a number of ways, the
simplest being in terms of differences in solvent parameters for
the liquid and the polymeric matrix. Such a description is
sufficient only in instances for which the molecular interactions
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are very non-specific and dominated by dispersive contributions.
SOLVENT PARAMETERS FOR LIQUIDS
The solvent parameter for a liquid can be simply calculated
from its energy of vaporization and its molar volume; it represents
the square-root of a cohesive energy density, and is found useful
in approximating non-specific, van der Waals-type interactions
between molecules. Empirical generalizations of the solvent
parameter concept break the overall parameter into components which
describe, for example, the dispersive, polar, and hydrogen-bonding
interactions between molecules. These parameters have been
conveniently tabulated for many substances by Barton, 1983.
SOLVENT PARAMETERS FOR MACROMOLECULAR MATERIALS
Solvent parameters for macromolecular or polymeric substances
are defined and determined quite differently than those for simple
liquids; Huglin and Pass, 1968 have applied many of these diverse
methods of determination to the polymer, polytetrahydrofuran. One
of the simplest methods involves identifying the solvent parameter
of the solvent which gives the largest swelling, with the solvent
parameter of the macromolecular matrix. This method seems to work
fairly well for simple polymers, but is misleading, in many
instances, when applied naively to heterogeneous mixed materials
like coal or soil organic matter which also have site-specific
interactions with many polar molecules. It is almost certainly
true that no single measure of cohesive energy density is entirely
adequate for describing one of these complex materials, or even an
isolated pure component of one of these materials.
INCLUSION OF SITE-SPECIFIC INTERACTIONS
A modification of the simple Flory-Huggins-Rehner picture is
needed to handle the large chemical interaction energies associated
with site-specific, generalized acid-base interactions. The
quantitative empirical, "E-C" formulation suggested by Drago et
al. . 1971, and applied by Fowkes et al. . 1984 to polymers, has
great promise as a means of correcting the equations for swelling
of cross-linked polymers. The additional parameters added by this
treatment would be the appropriate E and C parameters describing
the liquid molecules (many of these are already known from the work
of Drago et al. , 1971) , another set of E and C parameters
describing the polymer interaction sites, and a concentration
parameter, defining how many moles of interaction sites are
available per unit mass of unswollen polymer.
VOLUME OF MIXING
It should be mentioned that systems for which there is a
significant volume of mixing, require a "P delta V" term to adjust
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for the difference between energy and enthalpy. Volume of mixing
in swelling systems can be determined for powdered materials by
careful pycnometric determinations in swelling and non-swelling
liquids.
ENTROPY OF MIXING
Admixture of substances also produces an entropy effect.
Fortunately, this can largely be calculated as a configurational
entropy of mixing term of the sort recommended independently by
Flory and Huggins for molecules of greatly dissimilar size. Their
amazingly simple reformulation of the mixing entropy in terms of
volume fractions rather than mole fractions has proved extremely
useful whenever molecules of dissimilar sizes are involved.
Modifications of the simple Flory-Huggins entropy are needed
when some of the mixing is not entirely random, as for instance,
when strong hydrogen-bonded interactions exist between some liquid
molecules and some sites on the macromolecular matrix. The usual
calculation of mixing entropy is expected to overestimate the true
mixing entropy in such cases.
ELASTIC ENTROPY
When a polymer is stretched, the molecular chains are
generally forced to occupy positions with fewer possible
configurations; hence, the entropy decreases in such a process, and
opposes the entropy increase due to mixing. The calculation of
such strain entropy requires a model of the polymer structure.
TERNARY AND MULTICOMPONENT SYSTEMS
Thus far, we have considered systems consisting of a single
liquid and an insoluble, cross-linked polymeric component. The
next level of complexity is a ternary system with two, miscible
liquids and a single cross-linked polymer. In general, such
systems are more complex, because of the possibility of the mixed
liquids changing their relative proportions as they pass from the
supernatant liquid phase to the swollen polymer phase. In other
words, various additional phenomena involving selective and
competitive sorption are possible in such systems.
The phenomenology of simple ternary systems involving mixed
solvents and polymers has been studied sporadically, since the
exemplary early experimental work of Bronsted and Volqvartz, 1940.
Until quite recently, such work has not proven popular, perhaps
because of the lack of a firm theoretical foundation for analyzing
the results. In principle, the phase behavior cap be mapped out by
examining both swelling and changes in composition in a series of
mixtures applied to a polymer specimen, as was done in the classic
work of Bronsted and Volqvartz, 1940.
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ANNOTATED BIBLIOGRAPHY
Barton, A.P.M., 1983, Handbook of Solubility Parameters and Other
Cohesion Parameters. CRC Press, Inc., Boca Raton, FL.
Bastide, J., Picot, C.,and Candau, S., 1981, Some Comments on the
Swelling of Polymeric Networks in Relation to their Structure, J-
Macromol. Sci.-Phys., v. B19(l), p. 13-34.
Brandup,J., and Immergut, E.H.,eds, 1975, Polymer Handbook, John
Wiley & Sons, NY.
Bronsted, J.N., and Volqvartz, K. , 1940, Solubility and Swelling of
High Polymers in Ternary Mixtures, Trans. Faraday Soc. v. 36, p.
619-624.
[One of the first, and simplest papers on ternary mixtures
with a swelling polymer as one constituent. The value of
triangular diagrams for concisely and completely summarizing
the isothermal experimental phase information about such
systems is shown here.]
Brown, H.R., 1978, Flory-Huggins-Rehner Theory and the Swelling of
Semicrystalline Polymers by Organic Fluids, J. Polymer Sci.,
Polymer Physics ed., v. 16, p. 1887-1889.
Campos, A., Gavara, R., Tejero, R., Gomez, C., and Celda, B., 1989,
A Flory-Huggins Thermodynamic Approach for Predicting Sorption
Equilibrium in Ternary Polymer Systems, J. Polymer Sci: Part B:
Polymer Physics, v. 27, p. 1569-1597.
Campos, A., Gavara, R., Tejero, R., Gomez, C., and Celda, B., 1989,
A Procedure for Predicting Sorption Equilibrium in Ternary Polymer
Systems from Flory-Huggins Binary Interaction Parameters and the
Inversion Point of Preferential Solvation, J. Polymer Sci: Part B:
Polymer Physics, v. 27, p. 1599-1610.
Candau, S., Bastide, J., Delsanti, M., 1982, Structural, Elastic,
and Dynamic Properties of Swollen Polymer Networks, Adv. Polymer
Sci. v. 44, p. 27-71.
Chin, Y.-P-, and Weber, W.J., Jr., 1989, Estimating the Effects of
Dispersed Organic Polymers on the Sorption of Contaminants by
Natural Solids. 1. A Predictive Thermodynamic Humic Substance -
Organic Solute Interaction Model, Environ. Sci. Technol. v. 23(8),
p. 978-984.
Cowie, J.M. G., Dey, R., and McCrindle, J.T., 1971, A Comparative
Study of Preferential Adsorption in Bromoform (1) , Benzene (2), and
Polymer (3) Systems by Light Scattering and Density Gradient
Ultracentrifugation, Polymer J. v. 2(1), p. 88-93.
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Gee, G., and Treloar, L.R.G., 1942, The Interaction between Rubber
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Gee, G., 1940, The Molecular Weights of Rubber and Related
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259.
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177.
Neuburger, N.A., and Eichinger, B.E., 1987, The Status of Flory-
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Pouchly, J., and Zivny, A., 1982, Correlation of Data on
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REVIEW;
THE SWELLING OF COAL AND OF KEROGEN. AND ITS RELATION TO
THE SWELLING AND SORPTION CHARACTERISTICS OF SOIL ORGANIC MATTER
William G. Lyon
NSI Technology Services Corporation
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
INTRODUCTION:
The swelling properties of coal provide a useful analogy,
intermediate in complexity between soil organic matter and
synthetic polymers. Many experimental techniques and theoretical
constructs applicable to coal, might have direct and obvious
applications to soil organic matter. It is often overlooked that
coal itself also has some intrinsic interest from an environmental
point of view: many shallow lignite deposits occur within the
highly industrialized, coastal plains of the Southern and Eastern
United States. In many instances these lignite deposits are in
contact with, or are part of aquifer systems; hence, their sorptive
characteristics are of interest in modeling ground water systems in
these regions (see Kaiser, 1974, and Snider and Covay, 1987).
Soil organic matter, typically, is a much more complex mixture
of terrestrially derived macromolecular materials than is coal.
The diagenetic processes occurring in the initial coalification of
plant debris remove many sorptive materials (e.g.. cellulose) that
can be readily metabolized by microorganisms, leaving a fairly
inert, and simpler collection of bio-resistant molecules as
lignite. As coal passes from lignite to sub-bituminous rank,
surface functionalities, like -COOH groups, responsible for cation
exchange properties are lost, sometimes abruptly, through abiotic
diagenesis operating under the increasing severity of surrounding
conditions.
Coal is most assuredly not a simple material; rather, it is
itself a complex mixture of cross-linked, macromolecular materials
and sorbed molecules of varying origin. Coal, like soil organic
matter, is microporous in its structure, a fact that makes sorption
and swelling phenomena much more difficult to interpret from the
experimental data than those obtained for synthetic polymeric
materials. Also, coal lacks a repeating polymeric unit like
synthetic polymers; therefore, many formulas describing extensive
polymer properties in units "... per monomer formula unit" are
not so simply applicable to coals.
Kerogen, the insoluble organic matter found in sedimentary
rocks, differs from typical coals in several aspects, the most
important being the occurrence of more hydrogen-rich components,
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usually of marine origin. The full range of kerogens does,
however, span the full range in organic matter content, from
exclusively terrestrial to exclusively marine in origin. The bound
lipid material in kerogen, especially from marine algal sources, is
known to be the optimal source material for generation of petroleum
deposits (see Durand, 1980). Relatively little has been published
on kerogens concerning their swelling or other macromolecular
properties; the sole example to date is the work of Shadle et al. .
1989, who studied the swelling of kerogens isolated from Western
and Eastern oil shales.
COAL STRUCTURE AND SWELLING IN SOLVENTS
The known facts of coal structure that are of greatest concern
in the fundamental description of processes such as swelling,
sorption, and extraction are as follows:
1. Coal contains a cross-linked, macromolecular matrix
material.
2. The cross-links are of at least two, distinct kinds,
covalent and hydrogen-bonds.
3. Some hydrogen-bonding solvents are capable of disrupting
the hydrogen-bond cross-links of coal, causing a very large
swelling of the matrix structure.
4. Coal also contains somewhat mobile, extractable molecules
of a wide range of composition, that are sorbed or
"clathrated" by the macromolecular matrix.
5. The coal matrix material is microporous, and is capable of
sorbing chemical vapors by capillary condensation as well as
by swelling-sorption.
6. The "surfaces" of the coal matrix that are accessible to
solvents contain functional groups capable of specific, non-
bonded interactions (i.e.. not covalent bonds) of various
types with appropriate solvents.
Later sections will elaborate on these various aspects of coal
structure and their impact on swelling, sorption and extraction.
Many excellent reviews of coal structure in general have been
published; several better ones are listed in the Annotated
Bibliography-
VOLUMETRIC VERSUS GRAVIMETRIC SWELLING
Experimentally, coal swelling has been determined by two major
methods: the volumetric method, and the gravimetric method. In
the former, coal is put in direct contact with a liquid, and the
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change in the volume of the coal is measured directly. The
swelling, Qv, determined by this method is simply the ratio of
swollen to unswollen volume.
The usual gravimetric method involves equilibration of coal
with saturated vapors of the chosen liquid, and successive
weighings to determine when equilibrium is achieved. The limited
rate of mass transport via the vapor phase makes this a slow and
tedious procedure, although it can be automated with continuous
weighing on a specially modified electrobalance. The masses
involved can be converted to an equivalent volumetric swelling, QH,
provided the densities of the matrix and sorbed liquid are known.
A much faster gravimetric method (apparently not yet used for
coal) would involve putting coal powder in direct contact with a
liquid for some pre-determined period, and centrifuging off the
excess liquid through a special centrifuge tube (or an extraction
thimble with a fritted bottom) under standard conditions. Here the
liquid retention mass is an indication of swelling, and can be
converted to an equivalent volumetric swelling.
The fact that, generally, the gravimetric method gives
swelling considerably in excess of the volumetric measurements for
materials like coal has been attributed to the microporous nature
of coals by Nelson et al.. 1980. That is, a major portion of the
weight gain observed in the gravimetric method, is capillary
condensation of solvent vapors into the micropores of coal. This
seems to subdivide sorbed solvent into two categories: capillary
condensed solvent, and solvent imbibed into the macromolecular
structure. Presumably, the factors governing the equilibria in the
two cases are different, and the macroscopic thermodynamic
description of the system would have to take both processes into
account to calculate the overall vapor sorption equilibrium
isotherms.
An alternate view is that the micropore system constitutes
merely a "dead" volume, VQ, which must be filled before the matrix
starts to stretch. In the case of equilibrium by direct contact
with a liquid, there would be no real distinction between the two
categories of sorbed liquid, and the thermodynamic treatment would
merely have to recognize that the dead volume can be filled with
liquid without producing any strain energy or strain entropy
effects (see discussion under Physical Chemistry of Coal Swelling)
provided the molecules of the liquid can fit into the dead volume.
Some dependence of VQ on the molecular dimensions of the swelling
liquid relative to the micropore size distribution is thus expected.
COAL, SOLVENTS, AND SWELLING: AN HISTORICAL PERSPECTIVE
During the classical period of coal chemistry, much work was
expended searching for "coal solvents" that would dissolve all the
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organic materials contained in coal (leaving the mineral matter),
and thus produce a liquid feedstock that could be more readily
handled in the refineries and chemical plants designed for liquid
materials like petroleum. This work culminated in the extensive
investigations of Dryden, and of Van Krevelen in the fifties and
early sixties which pretty much ruled out the existence of such
magic solvents, at least among the commonly known organic liquids.
There thus appeared to be definite limits to the solubility of coal
without using rather aggressive reagents capable of breaking up its
bonded structure. The phenomenon of swelling in organic solvents
was well known from the work of this period, and some rough notions
of the physical chemistry of this process were inferred by analogy
with properties of synthetic and natural, cross-linked, rubbery
polymers.
The energy crisis of the mid-seventies produced a surge in
coal research aimed especially at solving some of the many
engineering problems associated with producing liquid fuels from
coal. Studies of swelling were undertaken, because it seemed
plausible that coal in its fully expanded, swollen state would be
more susceptible to reagents capable of breaking up the coal
structure. Certainly it appeared to be true that solvents that
produced the greatest swelling of coal, also seemed to yield the
greatest amount of extract.
For a variety of reasons, such work on liquefaction has_ not
yet met with economic success, and has been largely halted since
the oil price collapse of the eighties. Despite the heavy emphasis
on engineering during this period, many interesting aspects of
coal chemistry and structure were restudied, and more firmly
established by some of the newer methods for characterization of
complex solids, such as FTIR, proton and 13C-NMR, and the various
pyrolysis based techniques (Py-GC, Py-GC/MS, etc.). The conceptual
model of coal as a macromolecular matrix plus a sorbed, mobile
phase of extactable constituents was evolved and popularized during
this post-classical period (see Given, 1986).
PHYSICAL CHEMISTRY OF COAL SWELLING
For the purposes of the following discussion, it is presumed
that the macromolecular matrix of coal, exhaustively extracted of
any small sorbed species is the subject of intrinsic interest.
When swelling studies are attempted on coal without pre-extraction,
soluble material dissolves from the coal into the test solvents for
long periods of time (months) , and shifts the final equilibrium.
In the following discussion, "matrix" or "coal matrix" will denote
an ideal, totally extracted sample.
Equilibrium volumetric swelling of coal matrix in contact with
an organic liquid represents a free energy balance involving
several contributions, more or less separable:
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1. Strain Energy (isotropic stretching of macromolecular
matrix)
2. Chemical Interaction Energy (between solvent and matrix)
3. Entropy of Mixing (entropy increase due to mixing of
solvent with macromolecular matrix)
4. Strain Entropy (entropy decrease due to stretching)
Depending on the details of the statistical mechanical
treatment of these energetic and entropic contributions, various
levels of realism can be achieved.
The simplest statistical mechanical model that has been
applied to coal is that of Flory and Rehner, 1943 that ignores term
1, treats only van der Waals interactions in term 2 (i.e.,
specific, site-dependent interactions are completely ignored), and
treats terms 3 and 4 with expressions involving a mixing entropy
computed from volume fractions, and a strain entropy calculated
from a Gaussian model of cross-linked chain structure.
For the most part, the Flory-Rehner model fails in its
application to coal, and the most obvious flaw is the lack of
inclusion of site-specific interactions. The inclusion of these
terms via the Drago, E & C formulation of general acid-base
interactions has been suggested by Fowkes, 1980, and are definitely
needed to account for the exothermic heats of wetting observed for
coals in many solvents.
It is not so obvious that the strain energy term can be
ignored in coal-solvent systems. The observed heats of wetting in
coal immersion experiments should be a net heat effect including
both chemical interaction terms, and a strain energy term; careful
calorimetric studies are needed here to determine the importance of
the strain energy term directly.
ANNOTATED BIBLIOGRAPHY
Allen, S.J., McKay, G. , and Khader, K.Y.H., 1989, Equilibrium
Adsorption Isotherms for Basic Dyes onto Lignite, J. Chem. Tech.
Biotech, v. 45, p. 291-302.
[The authors conclude that the sorption isotherms exhibit
deviations from the models, because the sorbed substances
expand the sorbing particles by swelling, and thus create "new
surface."]
Brenner, D., 1983, In Situ Microscopic Studies of the Solvent
Swelling of Polished Surfaces of Coal, Fuel v. 62, p. 1347-1350.
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Brenner, D. , 1984, Microscopic in-situ Studies of the Solvent
Induced Swelling of Thin Sections of Coal, Fuel v. 63, p. 1324-
1328.
Brenner, D. , 1985, The Macromolecular Nature of Bituminous Coal,
Fuel v. 64, p. 167-173.
Callanan, J.E., Filla, B.J., McDennott, K.M. , and Sullivan, S.A.,
1987, Enthalpies of Desorption of Water from Coal Surfaces, Amer.
Chem. Soc., Div. Fuel Chem. Preprints v- 32(1), p. 185-192.
Cody, G.D., Jr., Larsen, J.W. , and Siskin, M. , 1988, Anisotropic
Solvent Swelling of Coals, Energy & Fuels v. 2, p. 340-344.
Collins, C.J., Hagaman. E.W., Jones. R.M. , and Raaen, V.F., 1981,
Retention of Pyridine-^C and other f4C-Labelled Amines by Illinois
No. 6 Coal, Fuel v. 60, p. 359-360.
Cooke, N.E., and Gaikwad, R.P., 1984, Removal of Pyridine and
Quinoline from Coal and Coal Extracts, Fuel v. 63, p. 1468-1470.
Dryden, I.G.C., 1951, Action of Solvents on Coals at Lower
Temperatures I- A Qualitative Survey of the Effects of Liquids upon
Bright Coals of Low Rank, Fuel v. 30, p. 39-44.
Dryden, I.G.C., 1951, Action of Solvents on Coals at
Temperatures II- Mechanism of Extraction of Coals by Specific
Solvents and the Significance of Quantitative Measurements, Fuel v.
30, p. 145-158.
Dryden, I.G.C., 1951, Action of Solvents on Coals at Lower
Temperatures III- Behavior of a Typical Range of British Coals
Towards Specific Solvents, Fuel v. 30, p. 217-233.
Dryden, I.G.C., 1951, Action of Solvents on Coals at Lower
Temperatures IV- Characteristics of Extracts and Residues from the
Treatment of Coal with Amine Solvents, Fuel v. 31, p. 176-199.
Durand, B. (ed.), 1980, KEROGEN Insoluble Organic Matter from
Sedimentary Rocks. Editions Technip, Paris.
Fowkes, F.M. , 1980, Donor-Acceptor Interactions at Interfaces, in
Polymer Science and Technology vol. 12A, Plenum Press, NY, p. 43-
52.
Given, P.H. , 1984, An Essay on the Organic Geochemistry of Coal,
Coal Science, vol. 3, Academic Press, Inc., p. 63-252.
Given, P.H., 1986, The Concept of a Mobile or Molecular Phase
within the Macromolecular Network of Coals: A Debate, Fuel v. 65,
p. 155-163.
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Green, T.K., Kovac, J. , and Larsen, J.W., 1984, A Rapid and
Convenient Method for Measuring the Swelling of Coals by Solvents,
Fuel v- 63, p. 935-938.
Green, T.K., and Larsen, J.W., 1984, Coal Swelling in Binary
Solvent Mixtures: Pyridine-Chlorobenzene and N,N-Dimethylaniline-
Alcohol, Fuel V- 63, p. 1538-1543.
Green, T.K., and West, T.A., 1986, Coal Swelling in Straight-Chain
Amines: Evidence for Specific Site Binding, Fuel v.65, p. 298-299.
Green, T.K., 1987, The Macromolecular Structure of Coal, J. Coal
Quality v- 6(3), 90-93.
Grillet, Y., and Starzewski, P., 1989, Thermocheroical Studies of
Wetting Phenomena of Coals by Organic Solvents such as Methanol or
Tetralin, Fuel v. 68, p. 55-57.
Flory, P.J., and Rehner, J., Jr., 1943, Statistical Mechanics of
Cross-Linked Polymer Networks II. Swelling, J. Chem. Phys. v-
11(11), p. 521-526.
Hall, P.J., Marsh, H., and Thomas, K.M., 1988, Solvent Induced
Swelling of Coals to Study Macromolecular Structure, Fuel v. 67, p.
863-866.
Hombach, H.-P-, 1980, General Aspects of Coal Solubility, Fuel v.
59, p. 465-470.
Howell, J.M., and Peppas, N.A., 1987, Macromolecular Structure of
Coals 8. Viscoelastic Behavior of Coal Networks Determined by
Thermomechanical Analysis, Fuel v. 66, p. 810-814.
Kaiser, W.R., 1974, Texas Lignite: Near Surface and Deep-Basin
Resources, Report of Investigations No. 79, Bureau of Economic
Geology, The University of Texas at Austin, Austin, TX.
Kirov, N.Y., O'Shea, J.M., and Sergeant, G.D., 1967, The
Determination of Solubility Parameters for Coal, Fuel v. 46, p.
415-424.
Kybett, B. , Potter, J., Etter, M., and Krahe, M., 1987, The Effect
of Solvent Extraction on the Reflectance of Coal and Coal-Oil
Mixtures, Amer. Chem. Soc., Div. Fuel Chem. Preprints v. 32(1), p.
9-11.
Larsen, J.W. , and Kuemmerle, E.W., 1978, Heat of Wetting of Coal by
Tetralin: Evidence for Structural Disruption at 25°C, Fuel v. 57,
p. 59.
Larsen, J.W., Kennard, L., and Kuemmerle, E.W., 1978,
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SUPPLEMENT 4
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Thermodynamics of Adsorption of Organic Compounds on the Surface of
Bruceton Coal Measured by Gas Chromatography, Fuel v. 57, p. 309-
313.
Larsen, J.W., and Lee, D. , 1983, Effect of Solvent Swelling on
Diffusion Rates in Bituminous Coal, Fuel v. 62, p. 1351-1354.
Larsen, J.W., and Lee, D. , 1985, Steric Requirements for Coal
Swelling by Amine Bases, Fuel v. 64, p. 981-984.
Larsen, J.W., Green, T.K., and Kovac, J., 1985, The Nature of the
Macromolecular Network Structure of Bituminous Coals, J. Org. Chem.
V. 50, p. 4729-4735.
Larsen, J.W., and Wernett, P., 1988, Pore Structure of Illinois No.
6 Coal, Energy & Fuels v. 2, p. 719-720.
Lucht, L.M., and Peppas, N.A., 1984, The Molecular Weight between
Crosslinks of Selected American Coals, Preprints Amer. Chem. Soc. ,
Div. Fuel Chem. v- 29(1), p. 213-219.
Mastral, A.M., Izquierdo, M.T., and Rubio, B. , 1990, Network
Swelling of Coals, Fuel v. 69, p. 892-895.
Nelson, J.R., Mahajan, O.P., and Walker, P.L., Jr., 1980,
Measurement of Swelling of Coals in Organic Liquids: A N<^w
Approach, Fuel v. 59, p. 831-837-
Painter, P.C., Nowak, J., Sobkowiak, M., and Youtcheff, J., 1987,
Hydrogen Bonding and Coal Structure, Amer. Chem. Soc, Fuel Div.
Preprints 32(1), p. 576-582.
Painter, P.C., Sobkowiak, M., and Youtcheff, J., 1987, FT-I.R.
Study of Hydrogen Bonding in Coal, Fuel v. 66, p. 973-978.
Reucroft, P.J., and Patel, K.B., 1983, Surface Area and
Swellability of Coal, Fuel v. 62, p. 279-284.
Sanada, Y. , and Honda, H., 1966, Swelling Equilibrium of Coal by
Pyridine at 25°C, Fuel v. 45, p. 295-300.
Sanada, Y., and Honda, H., 1967, Equilibrium Swelling of Coal by
Various Solvents, Fuel v. 45, p. 451-456.
Schafer, H.N.S., 1984, Determination of Carboxyl Groups in Low-Rank
Coals, Fuel v. 63, p. 723-726.
Shadle, L.J., Khan, M.R., Zhang, G.Q., and Bajura, R.A., 1989,
Investigation of Oil Shale and Coal Structures by Swelling in
Various Solvents, Amer. Chem. Soc., Div- Petroleum Chem, Inc.
Preprints v. 34(1), p. 55-61.
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Shibaoka, M., Stephens, J.F., and Russell, N.J., 1979, Microscopic
Observations of the Swelling of a High-Volatile Bituminous Coal in
Response to Organic Solvents, Fuel v. 58, p. 515-522.
Snider, J., and Covay, K.J., 1987, Premining Hydrology of the
Logansport Lignite Area, DeSoto Parish, Louisiana, Water Resources
Technical Report No. 41, Louisiana Department of Transportation and
Development, Baton Rouge, Louisiana.
Szeliga, J., and Marzec, A., 1983, Swelling of Coal in Relation to
Solvent Electron-Donor Numbers, Fuel v. 62, p. 1229-1231.
Van Krevelen, D.W., 1965, Chemical Structure and Properties of Coal
XXVIII - Coal Constitution and Solvent Extraction, Fuel v. 44, p.
229-241.
Van Krevelen, D.W., 1981, COAL Typology-Chemistry-Physics
Constitution. Elsevier Scientific Publishing Co., N.Y.
Weinberg, V.L., and Yen, T.F., 1980, 'Solubility Parameters' in
Coal and Coal Liquifaction Products, Fuel v. 59, p. 287-289.
Wightman, J.P., Glanville, J.O., Hollenhead, J.B., Phillips, and
Tisa, K.N., 1987, Heats of Immersion of Bituminous Coals in
Liquids, Amer. Chem. Soc., Div. Fuel Chem. Preprints v. 32(1), p.
205-208.
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PAGE 1
REVIEW;
THE SWELLING OF CELLULOSE AND ITS RELATION TO
THE SWELLING AND SORPTION CHARACTERISTICS OF SOIL ORGANIC MATTER
William G. Lyon
NSI Technology Services Corporation
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
INTRODUCTION
Cellulose is a biopolymer of glucose, and an important
constituent of soil organic matter or peat which has been only
slightly humified. The polymeric chains of cellulose are cross-
linked by hydrogen-bonds, which in most instances permit only
solvent-swelling to occur when common organic liquids are applied,
rather than formation of true polymer solutions.
The sorption/swelling characteristics of cellulose are
dominated by site-specific, hydrogen-bonded interactions with the
glucose monomer units. In mixtures of organic liquids capable of
hydrogen-bonding, complex preferential sorption phenomena are
observed. These are expected also in soils containing cellulose as
a component.
CRITICAL POINT PHENOMENA
The occurrence of critical temperature phenomena in swollen
cellulosic gels seems to have been tentatively established for time
scales on the order of a day, but it has not yet been widely
recognized. These phenomena can give rise to very puzzling
sorption behavior, such as the sudden doubling of saturation
sorption when the temperature is increased by a small amount. The
fortuitous location of these transition points near ambient room
temperature for many solvent-cellulose systems makes careful
control of temperature in determination of swelling spectra or
sorption isotherms an experimental necessity.
Critical composition phenomena are known to occur in many gel
systems; these are also to be expected in cellulosic gels. This
kind of behavior should be sought in ternary systems: H-bonding
solvent (1) - Miscible Solvent (2) - Cellulose. For example, H20 -
Acetone - Cellulose, or DMSO - Acetone - Cellulose (above 24°C)
would be reasonable candidates for such a transition. In these
examples, it might be expected that as the acetone concentration of
the external solution is gradually increased, the initially large
swelling of the cellulose will abruptly decrease over a very small
range of composition.
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On time scales much longer than a day, the critical
temperature phenomena, noted earlier, apparently disappear. This
means that these phase transitions are probably kinetic artifacts
of a very slow solvation step in which a hydrogen-bonding solvent
disrupts the interchain, hydrogen-bonded cross-links.
BIBLIOGRAPHY
Calahorra, M.E., Cortazar, M., Eguiazabal, J.I., and Guzman, G.M.,
1989, Thermogravimetric Analysis of Cellulose: Effect of the
Molecular Weight on Thermal Decomposition, J. Appl. Polymer Sci. v.
37, p. 3305-3314.
[These results are the best available guide to maximum drying
temperature for cellulosic soil organic matter; the oft-cited
limit of 105°C appears reasonable (but only in vacuum or inert
gas!); however, some celluloses may not have a truly constant
dry mass without pyrolysis.]
Chitumbo, K. , Brown, W. , and De Ruvo, A., 1974, Swelling of
Cellulosic Gels, J. Polymer Sci., Symposium No. 47, p. 261-268.
[A key set of results which firmly established the existence
of phase transitions in swelling versus temperature data for
a variety of strongly hydrogen-bonding solvents, such as DMSO.
DMF etc. interacting with cellulose. Two aspects which seem
to have been left uninvestigated were the possibilities of
kinetic sluggishness and of hysteresis being associated with
these transitions; such accompanying phenomena do seem to be
present in Coal-Pyridine systems.]
Golub, N.V., Kaputskii, F.N., and Yurkshtovich, T.L., 1986,
Mechanisms of Swelling of Cellulose and Diethylaminohydroxy-
cellulose in Water-Organic Solvent Systems, Kolloid. Zhur. v. 48,
p. 1009-1014. [English Transl. Plenum Publ. Corp., 1987]
[Equilibrium isotherms are given for Methanol-Water-Cellulose
and for 2-Propanol-Water-Cellulose Systems. The data for the
preferential sorption of Methanol-Water solutions on Cellulose
agree qualitatively with our swelling data taken at Kerr Lab:
there exists an intermediate composition (crossover
composition) of aqueous methanol which is sorbed without
change in composition. The published data do not include
total sorption data, and are thus, not sufficient to construct
the complete ternary phase diagrams for the systems studied.]
Hudson, S.M., and Cuculo, J.A., 1980, The Solubility of Unmodified
Cellulose: A Critique of the Literature, J. Macromol. Sci. - Rev.
Macromol. Chem. v. C18(l), p. 1-82.
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[A very useful review of the literature. Emphasizes the lack
of true solubility in single, non-reactive organic solvents.]
Koura, A., Schleicher, H., and Philipp, B., 1972, Untersuchungen
zur Quellung und Losung von Cellulose in aminhaltigen
Flussigkeitsgemischen, 2. Mitt.: Untersuchungen zur Loslichkeit
von Cellulose in Dimethylsulfoxid/Amin-Gemischen, Faserforsch.
Textiltech. v. 23(3), p. 128-133.
[Investigation of Swelling and Solution of Cellulose in Amine-
Containing Liquid Mixtures 2. Investigation of Solubility of
Cellulose in Dimethlsulfoxide/Amine Mixtures.]
Koura, A., Schleicher, H., and Philipp, B., 1973, Untersuchungen
zur Quellung und Losung von Cellulose in aminhaltigen
Flussigkeitsgemischen, 6. Mitt.: Zur Strukturveranderung von
Cellulose durch Amine und Aminlosungen, Faserforsch. Testiltech. v.
24(5), p. 187-194.
f...6. On Structural Modification of Cellulose by Amines and
Amine Solutions.]
Kremer, R.D., and Tabb, D. , 1990, Paper: The Beneficially
Interactive Support Medium for Diagnostic Test Development, Amer.
Lab. v- 22(3), p. 136-143.
[An excellent introduction to the hydrogen-bonded structure of
cellulose, and the various hydroxyl-group binding sites.]
Larsson, A., and Johns, W.E., 1988, Acid-Base Interactions between
Cellulose/Lignocellulose and Organic Molecules, J. Adhesion v. 25,
p. 121-131.
[A chemometric approach, which attempts a canonical
correlation between swelling and tensile energy absorption
with various organic fluid descriptors. These authors
recognize the importance of the Drago C&E model of acid-base
interactions for describing the site-specific interactions
that dominate the enthalpic portion of the chemical
interactions; unfortunately, they are forced to use the less
adequate formulations of donor-acceptor parameters for their
solvent descriptors.]
Lokhande, H.T., 1978, Swelling Behavior of Cotton Fibers in
Morpholine and Piperidine, J. Appl. Polymer Sci. v. 22, p. 1243-
1253.
Moers, M.E.C., Boon, J.J., de Leeuw, J.W., Baas, M. , and P.A.
Schenck, 1989, Carbohydrate Speciation and Py-MS Mapping of Peat
Samples from a Subtropical Open Marsh Environment, Geochim.
Cosmochim. Acta v. 53, p. 2011-2021.
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Nayer, A.N., and Hossfeld, R.L., 1949, Hydrogen Bonding and the
Swelling of Wood in Various Organic Liquids, J. Amer. Chem. Soc. v.
71, p. 2852-2855.
Philipp, B., Schleicher, H. , and Wagenknecht, W. , 1973, The
Influence of Cellulose Structure on the Swelling of Cellulose in
Organic Liquids, J. Polymer Sci., Symposium No. 42, p. 1531-1543.
[One of the most striking results of this work, is the kinetic
study of DMSO sorption as a function of temperature depicted
in Fig. 2. The discontinuity between the 20° and the 40°C
result is apparently connected to the phase transition
observed by Chitumbo et al. 1974. The discontinuity in
swelling is observed on time scales up to 20 hours, but
apparently disappears on time scales of 200 hours or more.
The implication is that the apparent equilibrium swelling
achieved after one day. slowly shifts to a markedly different
value, given sufficient time.]
Philipp, B., Schleicher, H., and Wagenknecht, W., 1973, Quell- und
Loseprozesse bei Zellulose mit unterschiedlicher Struktur,
Zellstoff und Papier v- 23(11), p. 324-330.
[Swelling and Solution Processes in Celluloses with Different
Structures.]
Robertson, A.A., 1970, Interactions of Liquids with Cellulose,
Tappi v. 53(7), p. 1331-1339.
Schleicher, H., 1982, Zur Abhangigkeit der Cellulosequellung von
den Donor- und Acceptorzahlen der Quellmittel, Acta Polymerica v.
34, p. 63-64.
[The Dependence of Cellulose-Swelling on the Donor- and
Acceptor-Numbers of the Swelling Agent.
Has plot of mols swelling medium per mole glucose-unit versus
the sum of donor and acceptor numbers, squared. The data were
taken at 20°C; therefore, the swellings observed for many of
the polar molecules (including DMSO) were not at their maximum
values.]
Thode, E.F., and Guide, R.G., 1959, A Thermodynamic Interpretation
of the Swelling of Cellulose in Organic Liquids: The Relations
Among Solubility Parameter, Swelling, and Internal Surface, Tappi
v- 42(1), p. 35-39.
[This is one of the more lucid treatments of the
thermodynamics of swelling.]
lot
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REFERENCES ON DRAGO'S E AND C FORMULATION OF GENERALIZED
ACID-BASE INTERACTIONS AND ITS APPLICATIONS TO SORPTION OF
ORGANIC MOLECULES ON SOILS. COALS. POLYMERS AND MINERALS
William G. Lyon
NSI Technology Services Corporation
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
The empirical theory developed by Drago and his collaborators
attempts to reproduce quantitatively the enthalpies of mixing of
liquids, including a broad range of site-specific associations in
dilute solution. The Drago equations, although not as economical
of parameters as some other donor-acceptor formulations, seem to
reproduce the calorimetric data better than other contending
models, and to have an intimate connection with vibrational
frequency shifts observed for active functional groups by infrared
spectroscopy.
The heart of the Drago approximation is the empirical
equation:
-AH = EaEb + CaCb
where the enthalpy of mixing acid A and base B per mole of
interaction is represented as a dot product of parameter vectors
describing the generalized acid and generalized base properties of
the substances being mixed. The parameters Ea and Eb are said to
describe the electrostatic contributions, and the parameters Ca and
Cb are said to represent the covalent contributions from acid A and
base B, respectively. As recently pointed out by Fowkes, 1990, the
acid A also has a set of parameters describing its basic
characteristics, and likewise, the base B also has a set of
parameters describing its acid characteristics. While these
usually represent much smaller contributions to the total,
recognition of this "amphipathic" character for most organic
solvents other than hydrocarbons is important.
The parameters involved in the Drago approximation can be
obtained for sites on polymers and solid surfaces by means of
"probe" molecules whose properties have already been established.
These test substances must have significantly different values of
E and C so that the simultaneous equations lead to precise values
for the unknown parameters. Several different approaches to this
measurement problem have been reviewed recently by Fowkes, 1990.
Among the more useful approaches are measurements of frequency
shifts of interacting functional groups with respect to a standard
(03
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SUPPLEMENT 6
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dilute solution by fourier transform infrared spectroscopy.
The frequency shift method depends on the empirical
observation that the shift "in frequency, Av, is a linear function
of the enthalpy of interaction described above as a function of the
E and C parameters. The frequency-shift relationship for a test
substance must be calibrated against calorimetric data, but once
this has been accomplished, the frequency-shift method can be used
to derive E and C parameters for unknown substances including
polymers and solid surfaces. This method seems to have the most
potential for defining the nature and number of binding sites on
very complex sorbents such as soils.
Chamberlain, C.S., and Drago, R.S., 1979, Comparison of
Thermodynamic Parameters Obtained by Gas Chromatographic and
Spectrophotometric Methods for the Interaction of a Lewis Acid
Transition Metal Complex with a Lewis Base, J. Amer. Chem. Soc. v.
101(18), p. 5240-5245.
Doan, P.E., and Drago, R.S., 1982, An E and C Modification of the
0 - TT* Solvation Approach, J. Amer. Chem. Soc. v. 104, p. 4524-
4529.
Doan, P.E., and Drago, R.S., 1984, Requirements and Interpretation
of Linear Free Energy Relations, J. Amer. Chem. Soc. v. 106, p.
2772-2774.
Drago, R.S., O'Bryan, N., and Vogel, G.C., 1970, A Frequency Shift-
Enthalpy Correlation for a Given Donor with Various Hydrogen-
Bonding Acids, J. Am. Chem. Soc. v. 92, p. 3924-3929.
Drago, R.S., Vogel, G.C., and Needham, T.E., 1971, A Four-Parameter
Equation for Predicting Enthalpies of Adduct Formation, J. Am.
Chem. Soc. v. 93, p. 6014-6026.
Drago, R.S., Nusz, J.A., and Courtright, R.C., 1974, Solvation
Contributions to Enthalpies Measured in Methylene Chloride, J.
Amer. Chem. Soc. v. 96(7), p. 2082-2086.
Drago, R.S., 1977, Modern Acid-Base Chemistry/ Proc. Summer School
on Stability Constants, Florence, Italy, June 1974, p. 117-123.
Drago, R.S., Parr, L.B., and Chamberlain, C.S., 1977, Solvent
Effects and Their Relationship to the E and C Equation, J. Am.
Chem. Soc. v. 99, p. 3203-3209.
Drago, R.S., 1980, The Interpretation of Reactivity in Chemical and
Biological Systems with the E and C Model, Coord. Chem. Rev. v- 33,
p. 251-277.
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Fowkes, F.M., 1968, Comments on "The Calculation of Cohesive and
Adhesive Energies," by J.F- Padday and N.D. Uffindell, J. Phys.
Chem. v. 72(10), p. 3700.
Fowkes, P.M., 1973, Donor-Acceptor Interactions at Interfaces,
Recent Adv. Adhes., Proc. Amer. Chem. Soc. Symp., p. 39-44 (meeting
1971).
Fowkes, P.M., and Mostafa, M.A., 1978, Acid-Base Interactions in
Polymer Adsorption, Ind. Eng. Chem. Prod. Res. Dev- v- 17(1), p. 3-
7.
Fowkes, F.M., 1979, Donor-Acceptor Interactions at Interfaces,
Amer. Chem. Soc., Div. Org. Coatings end Plastics Chem. Preor. v.
40, p. 13-18.
Fowkes, F.M., 1980, Donor-Acceptor Interactions at Interfaces, in
Polymer Science and Technology vol. 12A, Plenum Press, NY, p. 43-
52.
Fowkes, F.M., Tischler, D.O., Wolfe, J.A., and Halliwell, M.J. ,
1981, Acid-Base Complexes of Polymers with Solvents, Amer. Chem.
Soc., Div. Org. Coatings and Plastics Chem. Prepr. v. 46, p. 1-6.
Fowkes, F.M., 1982, "Characterization of Solid Surfaces by Wet
Chemical Techniques", chapter 5 in Industrial Applications of
Surface Analysis. L.A. Casper, C.J. Powell, eds., ACS Symposium
Series 199, Amer. Chem. Soc., Wash. D.C., pp 69-88.
Fowkes, F.M., McCarthy, D.C., and Wolfe, J.A., 1983, Predicting
Enthalpies of Interfacial Bonding of Polymers to Reinforcing
Pigments, Amer. Chem. Soc. Div. Polymer Chem. Prepr. v. 24(1), p.
228-9.
Fowkes, F.M., McCarthy, D.C., and Tischler, D.O., 1983, Predicting
Enthalpies of Interfacial Bonding of Polymers to Reinforcing
Pigments, in Molecular Characterization of Composite Interfaces.
edited by H. Ishida and G. Kumar, Plenum Press, NY, pp 401-411.
Fowkes, F.M., Tischler, D.O., Wolfe, J.A., Lannigan, L.A., Ademu-
John, C.M., and Halliwell, M.J., 1984, Acid-Base Complexes of
Polymers, J. Polymer Sci., Polymer Chemistry Edition, v. 22, p.
547-566.
Fowkes, F.M., 1984, Acid-Base Contributions to Polymer-Filler
Interactions, Rubber Chem. Technol. v. 57(2), p. 328-343.
Fowkes, F.M., 1984, Spectral and Calorimetric Determination of the
Intermolecular Interactions of Solvents, Amer. Chem. Soc. Div.
Polymeric Mater. Prepr. v- 51, p. 522-7.
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Fowkes, P.M., Lloyd, T.B., Li, G. , Jones, K.L., and Wolfe, J.A. ,
1985, Final Report, untitled, [Techniques for the study of the
surface sites of coal powders], DOE/PC/50809-T11 under DOE Grant
No. DE-FG22-82PC50809, 27 pp.
Fowkes, F.M., Jones, K.L., Li, G., and Lloyd, T.B., 1989, Surface
Chemistry of Coal by Flow Microcalorimetry, Energy & Fuels v- 3, p.
97-105.
Fowkes, F.M., Riddle, F.L., Jr., and Cole, D.A., 1989, Chemical
Characterization of the Surface Sites of Coal, Report DOE/PC/79925-
4 under Contract No. DE-FG22-87PC79925.
Fowkes, P.M., 1990, Acid-Base Measurements of Solvents, Polymers,
and Inorganic Surfaces, Preprint, 36 pp.
Guidry, R.M., and Drago, R.S., 1973, An Extension of the E and C
Equation to Evaluate Constant Contributions to a Series of Observed
"Enthalpies of Adduct Formation", J. Amer. Chem. Soc. v. 95(3), p.
759-763.
Joslin, S.T., 1984, Characterization of the Acidic Surface Sites on
Alpha-Ferric Oxide Using Flow Microcalorimetry, Ph.D. Thesis,
Lehigh University, 210 pp.
Karger, B.L., Snyder, L.R., and Eon, C. , An Expanded Solubility
Parameter Treatment for Classification and Use of Chromatographic
Solvents and Adsorbents, J. Chromatog. v. 125, p. 71-88.
Rolling, O.W., 1978, Comparisons between Hydrogen Bond Donor-
Acceptor Parameters and Solvatochromic Red Shifts, Anal. Chem. v.
50(2), p. 212-215.
Kroeger, M.K., and Drago, R.S., 1981, Quantitative Prediction and
Analysis of Enthalpies for the Interaction of Gas-Phase Ion-Ion,
Gas-Phase Ion-Molecule, and Molecule-Molecule Lewis Acid-Base
Systems, J. Amer. Chem. Soc. v. 103, p. 3250-3262.
Lim, Y.Y., Drago, R.S., Babich, M.W., Wong, N. , and Doan, P.E. ,
1987, Thermodynamic Studies of Donor Binding to Heterogeneous
Catalysts, J. Amer. Chem. Soc. v. 109, p. 169-174.
Marmo, M.J., Mostafa, M.A., Jinnal, J., Fowkes, F.M., and Manson,
J.A., 1976, Acid-Base Interaction in Filler-Matrix Systems, Ind.
Eng. Chem., Prod. Res. Dev. v. 15(3), p. 206-210.
Nozari, M.S., and Drago, R.S., 1970, Spectral and Calorimetric
Studies of Hydrogen Bonding with Pyrrole, J. Amer. Chem. Soc. v.
92(24), p. 7086-7090.
Nozari, M.W., and Drago, R.S., 1972, Elimination of Solvation
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Contributions to the Enthalpies of Adduct Formation in Weakly Polar
Solvents. II. Adducts of Bis(hexafluoroacetylacetonato)
copper(I), Inorg. Chem. v. 11(2), p. 280-283.
Nozari, M.S., Jensen, C.D., and Drago, R.S., 1973, Eliminating
Solvation Contributions to the Enthalpy of Adduct Formation in
Weakly Polar, Acidic Solvents, J. Amer. Chem. Soc. v. 95(10), p.
3162-3165.
Pugh, R.J., and Fowkes, F.M., 1984, The Dispersibility and
Stability of Carbon Black in Media of Low Dielectric Constant. 2.
Sedimentation Volume of Concentrated Dispersions, Adsorption and
Surface Calorimetry Studies, Coll. Surf, v- 9, p. 33-46.
Riddle, F.L., and Fowkes, F.M., 1988, Spectral Shifts in the Acid-
Base Chemistry of Polymers. I., Amer. Chem. Soc. Div. Polymer
Chem. Prepr. v. 29(1), p. 188-189.
Rider, P.E., 1980, A Two-Parameter Model for Estimating Hydrogen
Bond Enthalpies of Reaction, J. Appl. Polymer Sci. v. 25, p. 2975-
2984.
107
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SUPPLEMENT 7
RSKSOP-104
Revision No. 1
Date: March 25, 1991
Page l of 22
William G. Lyon
David E. Rhodes
STANDARD OPERATING PROCEDURE
SWELLING SPECTRUM OF ORGANIC MATTER
Disclaimer;
This Standard Operating Procedure has been prepared for the
use of the Robert S. Kerr Environmental Research Laboratory of
The U.S. Environmental Protection Agency and may not be
specifically applicable to the activities of other
organizations.
1. Purpose; (Scope and Application)
To determine the swelling spectrum of an organic-rich material
(concentrated soil organic matter, peat, pollen, spores, etc.) in
a wide range of organic solvents and water.
2. Background;
The swelling spectrum of an insoluble organic material gives
quantitative information on the interaction between the material
and organic solvents. Swelling is the volumetric manifestation of
bulk sorption; that is, swelling is concerned with those
sufficiently small molecules that can partition into the solid
organic material. The swelling spectrum can be used qualitatively
for "finger printing" a complex mixture of solid organic materials
for comparison with standards, and also to determine the size-
exclusion limits of a macromolecular material.
3. Summary of Method;
Powdered organic matter is placed in small glass tubes and
exposed to liquid organic solvents. Length measurements are made
before and after wetting with each solvent. The basic method has
been described by Green et al., 1984 for coal samples.
4. Equipment Needed;
A. A 7 or 8 cm3 sample of organic matter sieved to pass 100
mesh standard sieve. (Sample may be dry or partly moist
depending on the purpose of the determination). The procedure
works best on materials from which all soluble materials have
been removed by extraction.
B. Disposable Wintrobe Tubes, 3 mm ID, mm etched scale.
(Scientific Products, Cat. No. B4449). These represent about
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the smallest tubes for which this technique is practical.
C. Centrifuge Adaptor so Wintrobe tubes can be spun in a
standard centrifuge.
D. Centrifuge capable of 2000 rpm. (Most bench top models)
swivel head.
E. Magnifier with measuring reticle capable of reading to 0.1
mm. (Bausch & Lomb, Cat. No. 81-34-35, 81-34-38) . Note that
we use the measuring reticle to interpolate precisely between
the graduations etched on the Wintrobe tubes.
F. 2 ml luer-lok syringes and 8" pipetting needles (18 gauge)
for dispensing solvents.
G. Wide selection of solvents (see Appendix I) spanning
solvent parameter values from 14 to 48 MPa*.
H. Teflon caps, drilled from short lengths of 5/16" Teflon
rods, are very much better than Teflon tape for sealing the
Wintrobe tubes. The holes drilled in the caps need to taper
so that the caps will fit despite the slightly varying OD of
the Wintrobe tubes.
I. Fume Hood and protective equipment for handling solvents.
(See MSD sheets for information on proper protective
measures.)
J. Coded sample rack with holes for Wintrobe tubes.
K. Constant temperature bath or incubator for equilibration of
loaded tubes.
L. Radioactive strips to discharge static build-up (e.g.,
Staticmaster Ionizing Units, Model 2U500).
M. Heated vacuum desiccator, capable of reaching 105°C and
pressures of a few Torr.
5. Procedure;
A. Load the necessary Wintrobe tubes (20-50) with powdered
organic matter to about the 20% level (a 2 cm column of powder
is equivalent to ca. 0.14 cm3).
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Note: If it is desired to run the powdered organic
material in the dried condition, it is usually necessary
to redry the material in the tubes by heating at 105°C
for 24 hours in a vacuum desiccator. The tubes are
capped as soon as possible after vacuum is broken through
a drierite tube. It is recommended that radioactive,
anti-static strips be placed in the desiccator during
heating to discharge the build-up of static on the
powdered samples.
B. Spin the loaded, capped tubes at 1800 rpm for five minutes
on the centrifuge to get a standard packing. (This speed is
a provisional value; further experimentation is needed to
determine if higher values give more reproducible values for
some materials. See Appendix V for discussion of this issue.)
C. Measure initial height, HI, for each tube with magnifier
and measuring reticle. Record results.
D. Apply solvent to each sample. Sample should be tapped onto
the side of the tube so that pipetting needle can be used to
introduce solvent starting at the bottom of the tube. With
many samples, the solvent can be stirred into the powder with
the syringe needle. Fill tubes with solvent to 80% mark. Cap
immediately with Teflon caps.
E. Rotate and tap tube to release small bubbles from powder.
F. Allow tube to sit undisturbed in sample rack overnight in
a nearly horizontal position with the sample spread out.
Check again for bubbles. Tubes should be placed in a constant
temperature bath or an incubator to equilibrate between
readings.
G. Before each height reading, spin tubes at 1800 rpm for five
minutes on Centrifuge.
H. Measure swollen heights H2, H3 etc. for each tube as in
step C. Record heights, date and time.
I. Final height measurement is taken when measurements agree
for successive measurements within the typical uncertainty of
the measurement. Otherwise, repeat steps G and H. Note any
changes in color of solvent above sample.
\\0
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6. Calculations;
A sequence of raw volumetric swelling values is calculated from
the height ratios H2/H1, H3/H1, etc. These swelling values are
plotted versus the solvent parameter, 6, for each solvent. (See
Appendix I) . Corrections can be made for inert diluents by the
method outlined in Appendix II. If other soil minerals such as
Kaolinite or Montmorillonite are present, the corrections become
much more complex. Various strategies for this type of correction
are discussed in Appendix III.
Besides the above elementary manipulations of the data,
several additional transformations are useful. The quantity C> lar,
which represents the number of moles of imbibed solvent per cirr of
sorbent can be calculated from the volumetric swelling, Q and the
solvent molar volume (cm3 mol"1) for each solvent (see Appendix I) :
If additionally, the density of the solid sorbent is known (see
RSKSOP-105) and some composition data are available, further useful
transformations are possible. For example, sorption on Cellulose,
a biopolymer of glucose, can be recalculated as moles of sorbed
solvent per mol of monomer unit, X lar; this transformation
emphasizes the formation of specific molecular complexes (if such
are present). Other transformations of this type might be based on
moles of carboxylic acid or phenolic groups per unit mass should
these seem to be involved in sorption. Finally, if the carbon
content of the sorbent (RSKSOP-101) has been measured, values of
the amount sorbed can be put on a per gram organic carbon basis.
Examples of various calculations on a swelling spectrum are shown
as figures in Appendix IV-
7. Quality Control:
The most important consideration in working with this many
samples in small tubes is the potential for mixing them up during
handling. Coding of loading rack and of Centrifuge tube adaptor
will assist in this bookkeeping. Labeling on the tubes is the
safest measure.
A second factor that is important in obtaining reproducible
If
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values is the total elimination of gas bubbles from the wetted
samples before measurement of length. Various tricks that can
assist this process include lowering the pressure to enlarge the
bubbles, and using ultrasonic vibrations to help fluidize the
powder and allow bubbles to float up.
A third factor that can be a source of error in the procedure
as currently described is the variability of the etch marks on the
Wintrobe tubes. Since the measuring reticle is capable of spanning
only 1 cm, our measurements are an interpolation procedure that
relies on the accuracy of the etched graduations for part of the
total height. Alternatives to the present procedure would be
calibration of the etch marks against a standard probe, or use of
a precision cathetometer (or similar instrument) for the
measurement of total heights. Either of these measures would add
significantly to the time and expense of obtaining swelling data,
and would be recommended only when the need for higher precision
justifies the added difficulties.
Finally, the proper conditions of compaction for comparison of
swollen powder heights with dry powder heights is an issue raised
by one of the reviewers of the project report. It has been found
that constant starting amounts of powder helps achieve consistent
results. Our use of a constant 1800 rpm value for both wetted and
dry powders merely followed the published procedure of Green et
al., 1984. Appendix V contains a discussion of a correction for
the variable buoyancy component to the net compacting force from
the various organic liquids. Our opinion is that this additional
correction would multiply the time and expense of the method at
least 10 fold, and would greatly undermine the usefulness of what
is, at best, a semi-quantitative survey technique.
Purified cellulose (Aldrich 31,069-7) is recommended as a
standard for checking out the procedure. It is fairly hygroscopic
when dried, and must be dried carefully under vacuum to prevent
oxidation. Prevention of the build-up of static charges during
drying by means of a radioactive source mounted inside the vacuum
drying apparatus is essential.
8. Safety Considerations;
All operations involving manipulation of solvents should be
conducted under a fume hood. Many of the suggested solvents on the
attached list (Appendix I) are flammable, toxic or corrosive; the
experimenter should be familiar with the hazards associated with
all solvents used, and wear appropriate eye and hand protection.
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See MSD sheets for details.
Nitromethane and nitroethane apparently have some potential
for detonation under adiabatic compression; thus, it is recommended
that these substances not be exposed to ultrasonic vibrations,
especially while in contact with organic matter. We have
cautiously tested these substances ultrasonically while contacted
with several types of peat, and have found no problem (so far!) in
an ordinary laboratory ultrasonic bath.
Chlorinated solvents must be disposed of in a separate waste
container from other solvents. Carbon Disulfide wastes must now be
kept separate from all other flammable solvent wastes.
9. References;
Barton, A.F.M., 1983, Handbook of Solubility Parameters and Other
Cohesion Parameters, CRC Press, Boca Raton, FL.
Green, T.K., Kovac, J. , and Larsen, J.W., 1984, A Rapid and
Convenient Method for Measuring the Swelling of Coals by Solvents,
Fuel v. 63, p. 935-938.
Greene-Kelly, R., 1955, Sorption of Aromatic Organic Compounds by
Montmorillonite, Trans. Faraday Soc. v. 51, p. 412-424.
Lyon, W.G., 1989, Precision Density Determination of Soil Organic
Matter and Other Organic - Rich Materials, RSKSOP-105.
Lyon, W.G., Rhodes, D.E., Powell, R.M., and Pennington, L., 1990,
Operation of the Leco WR-112 Carbon Analyzer for the Determination
of Carbon in Peats and Other High Carbon Materials, RSKSOP-101.
Olejnik, S., Aylmore, L.A.G., Posner, A.M., and Quirk, J.P., 1968,
Infrared Spectra of Kaolin Mineral - Dimethyl Sulfoxide Complexes,
J. Phys. Chem. v. 71(1), p. 241-249.
Olejnik, S., Posner, A.M., and Quirk, J.P-, 1968, Swelling of
Montmorillonite in Polar Organic Liquids, Clays and Clay Minerals
V. 22, p. 361-365.
Starkey, H.C., Blackmon, P.O., and Hauff, P.L., 1984, The Routine
Mineralogical Analysis of Clay-Bearing Samples, U.S. Geological
Survey Bulletin 1563, U.S. Govt. Printing Office, Washington D.C.
Thompson, J.G., and Cuff, C., 1985, Crystal Structure of Kaolinite
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- Dimethylsulfoxide Intercalate, Clays and Clay Minerals v. 33,
490-500.
Weast, R.C., 1984, CRC Handbook of Chemistry and Physics. CRC
Press, Inc., Boca Raton, FL, p. F8.
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APPENDIX I
Solvents for Obtaining Swelling Spectra
Solvent
n-Pentane
n-Heptane
Methy1eye1ohexane
Cyclohexane
p-Xylene
Toluene
Ethyl Acetate
Benzene
Tetralin
Acetylacetone c
Chlorobenzene
Dichloromethane
Acetone
Carbon Bisulfide
1,4-Dioxane
Nitrobenzene
3-Methyl-l-butanol
1-Octanol
Pyridine
Morpholine
N,N-Dimethylacetamide
1-Pentanol
Nitroethane
1-Butanol
2-Propanol
Acetonitrile
1-Propanol
Dimethylsulfoxide
N,N-Dimethy1formamide
Nitromethane
Ethanol (99.9%)
Propylene Carbonated
Methanol
1,2-Ethanediol
1,2-Propanediol
N-Methy1formamide
Formamide
Water
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NOTES TO APPENDIX I
8The delta values tabulated here are mostly the simple solubility
parameters of the liquids at 25°C tabulated by Barton, 1983; in a
few instances where these were missing, the total solubility
parameter, St, from the same reference was used instead.
values for the molar volume (cm/mol) were in most cases
computed from molecular weights (g/mol) and density (g/cm3) values
for the liquids at 25°C tabulated by Barton, 1983. A few missing
values were computed from similar data tabulated in standard
handbooks elsewhere (e.g. , Weast, 1984)
C2 , 4-Pentanedione
dl,2-Propanediol cyclic carbonate
CH2-0
c=o
! /
CH?-0
I '
I
CH,
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APPENDIX II.
Correction for the Effect of Non-Swelling Diluents
If the sample contains a small amount of a non-swelling
diluent such as sand, a simple correction can be made to obtain
the swelling for pure organic matter, Q°. This simple correction
will not be sufficient if clays such as montmorillonite or
kaolinite are present; clays such as these can form crystalline,
interlayer complexes with certain polar organic solvents.
Notation: Qnet measured swelling, impure organic matter
Q° swelling of pure organic matter
V^ volume of organic matter in sample
V^ volume of mineral matter in sample (assumed
inert)
z^ volume-fraction of organic matter in sample
z volume-fraction of mineral matter in sample
rorn
on mri
Qnet is defined as:
(Volume Swollen Sample)
(Volume Unswollen Sample)
Therefore,
(O °*V + V )
\<^ * V - -r t'm-y
+ V )
oin mm'
noting that:
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*'on
(V + V )
v vom vmn'
om
and
_
om ram'
allows the simplification:
In other words, the observed swelling is a volume-fraction,
weighted-average of the swelling of the minerals (Q^ assumed =
1.000) and of the organic matter. Hence, the correction for non-
swelling diluents is given by the formula,
zom
For a truly inert ingredient such as a small amount of quartz
or feldspar sand estimates of z^ can be based on determinations of
"ash content" of the sample ignited in air plus estimates of the
mineral grain density and organic matter density. More complex
calculations are required to correct ash content to mineral matter
content when thermally unstable minerals such as calcite, opal or
gypsum are present; in these cases, the ASTM methods and
approximations used for coal calculations seem appropriate. Powder
x-ray diffractograms of the organic matter and ash are useful
guides to the correction procedure.
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APPENDIX III.
Corrections for the Effect of Swelling Clay Mineral Diluents
If the sample is an organic-rich soil rather than a
concentrate, the corrections for swelling of mineral species
become a major problem. Both kaolinite and smectite minerals are
capable of swelling in polar organic solvents; see papers by
Greene-Kelly, 1955, Olejnik et al.. 1968, 1974, and Thompson and
Cuff, 1985. Two approaches seem feasible and need further
experimental investigation.
The first correction method requires having volume-fraction
estimates for each swelling mineral and for all inert minerals
(lumped together); these could be obtained from careful x-ray
diffraction analysis. Additionally, swelling spectra would be
needed for pure representatives of each swelling mineral.
Expanding the formula of Appendix II yields the equation,
that can be rearranged to give a formula for Q°.
A second alternative would be to use chemical treatment with
dilute acid to remove any carbonate minerals (non-swelling)
followed by hydrogen peroxide to remove the organic matter. A
separate swelling spectrum could then be obtained directly from
the residual material that might be representative of the
lumped-together swelling clays and inert minerals present in the
sample.
Several difficulties should be mentioned concerning both these
methods. Quantitative x-ray diffraction analysis is highly
dependent on the standards used for the pure clay minerals; clay
minerals found in soils are usually not as well-ordered in their
crystals as the standards and may differ substantially from the
standards in their composition as well. Moreover, organic matter
frequently must be removed from soil samples to get a clean x-ray
diffractogram. (See Starkey et al., 1984).
The chemical removal of organic matter by oxidation presents
three problems: formation of oxalate minerals from any soluble
calcium minerals present (such as calcite or gypsum), chemical
alteration of the swelling character of the clays and removal of
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organic coatings that can limit the swelling of clay minerals in
their native, mixed state. The first of these problems can be
greatly lessened by an acid treatment to remove carbonates etc. ;
however, this acid wash procedure inevitably alters the exchange
cation composition of the clays, and that, in turn, changes their
swelling behavior in polar solvents. This effect makes some sort
of standardization of the exchangeable cations on both the
original sample (containing organic matter) and the acid-washed,
oxidized sample a practical necessity; an exchange to the sodium
form following acid washing is provisionally recommended.
Chemical oxidation of clay minerals also can occur during
peroxide destruction of organic matter. This can occur when
ferrous iron is present in a clay, for example, substitution of
Fe+3 onto some Al+3 sites of a dioctahedral smectite. Oxidation of
this ferrous iron to ferric causes a decrease in cation
exchange capacity, and thus an alteration of solvent swelling
characteristics. Fortunately, smectite minerals in the oxic zone
of surface sediments are typically completely oxidized already;
the main difficulty is expected from anoxic sediments or soils.
The removal of organic coatings from the clay minerals in a
sample activates them and produces a material more likely to swell
in organic solvents than the minerals in the original mixture.
Naturally, corrections based on the swelling of such cleaned-up
mineral matter will be too large; however, this is probably no
worse than corrections based on swelling properties of pure mineral
standards.
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APPENDIX IV.
Examples of Calculations on a Swelling spectrum for Cellulose
A. Qraw versus Delta
This figure displays the raw volumetric swelling versus
solvent solubility parameter.
B. Q versus Delta
The raw swelling data were adjusted by a factor so that the
background swelling for non-swelling solvents averaged to
unity (i.e., no swelling).
C. 0,0^ versus Delta
The scaled swelling data minus one1 were divided by the
solvent molar volume so that the units are now moles of
solvent per cm3 of solid sorbent.
D. X^ar versus Delta
The values for Q^^,. were multiplied by the molar volume of the
cellulose repeat unit (ca. 103 cm3 mol"1) so that the final
value has units of moles of solvent per mole of repeat unit.
E. (g sorbed liquid/g sorbent) versus Delta
Densities of liquids and of the solid sorbent (1.57 g cm"3)
were used to convert the scaled swelling values (Q-l) to more
typical gravimetric sorption units: g sorbed liquid per g
solid sorbent.
1Note that the quantity Q-l represents volume of sorbed liquid
per volume solid sorbent.
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1.9
RffiH VOLUMETRIC SHELL!H6 vs= DELTA
CELLULOSE? 30 dege C
T 1 I 1
1 1 T
(D
Z
M
J
J
LU
Z
0)
o
M
c
h
u
E
D
z
-------
2.2
CD
I
M
J
J
UJ
z
(0
0
M
o:
E
D
J
0
0
111
J
-------
h
I
UJ
ft
tL
0
(0
\
h
z
111
:>
j
o
0)
w
UJ
ft
M
ft
E
(0
UJ
J
o
E
e.w
e.e3
6.02
e.ei
MOLES IMBIBEB SOLVENT PER GRAM SORBEHT
vs. DELTA
T 1 T
1 1 T
o
E
O
-e.ei
14
24
44
DELTft, SOLVENT SOLUBILITY PARAMETER
54
-------
Xmohr vs. DELTA
CELLULOSE, 38 deg. C
3.5
1 I
I I i r
i i i
i i i i
Z
D
LI
0)
o
o
D
J
CD
0
E
\
h
Z
HI
:>
J
o
(0
0
E
2.5
1.5
6.5
o
E
X
-6.5 — •:••
J I
I I I I
1 I I I
I I I I
34
44
DELTA, SOLVENT SOLUBILITY PARAMETER
54
-------
4*
c
i.
0
(0
\
u
•H
•H
J
II
L
0
(0
-e.2 -
14
(g Sorbed Liquid/g Sorbent) vs. DELTA
CELLULOSE, 38 deg. C
I I . , I
24
34
44
54
DELTA, SOLVENT SOLUBILITY PARAMETER
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APPENDIX V.
Consideration of the Different Standard Compaction Conditions
needed for Dry and Wetted Powder Columns: Buoyancy Effects
In this section we consider the conditions of compaction of a
column of powder spun in a centrifuge in both dry and solvent-
wetted conditions. We specifically ignore:
1. any effects of particle-to-particle adhesion,
2. any variable effects of particle "lubrication" by the
different solvents, and
3. compaction re-bound following removal of the powder column
from the centrifuge.
These possibly important additional effects do not lend themselves
to simple analysis at present.
The reality of adhesive forces seems proved by the fact that
dry cellulose powder always is under-compacted compared to wetted
cellulose powder in non-swelling liquids, yielding apparent values
of swelling less than unity. Without some framework for including
(or even estimating) these effects, we cannot wholeheartedly
recommend the corrections for buoyancy, derived below, as an
improvement upon the raw volumetric swelling values.
The compaction of a powder column achieved at a given angular
velocity on a centrifuge when the free pore space is air-filled
should be different from the state of compaction when the free pore
space is liquid-filled. The generally smaller effective stress
causing compaction in the liquid-saturated case is due to the
substantial buoyant force on the particles exerted by the liquid.
Calculation of the Buoyant Force Contribution
For a particle of powdered material at the top of a column of
solvent-wetted powder, the net compacting force on the particle
will depend on the densities of solid and liquid, and on the
effective "gravitational" force constant, g, which will be a
function of the angular velocity of the tube, and the distance of
the particle from the axis of rotation of the centrifuge.
Noting that g = g(o>,R) = Ru2, where w = angular velocity, and
R = distance from axis of rotation, we may write for the net force:
12-7
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Rearranging this expression slightly, yields:
ro
where F = net force on a particle of mass nu and density p0 when
immersed in a liquid of density pL. Strictly speaking, samples
should be spun at different angular velocities to achieve the same
packing when the density of the liguid varies. Similarly, when the
pore space is filled with air, the angular velocity should be at
its lowest to account for the very low buoyant force from air.
Derivation when Swelling Occurs
The above derivation assumed that no swelling of the particles
in the liquid occurs. Even with the assumption of swelling, the
same formula for net force holds approximately due to cancellation
of terms involving the swelling, Q, as long as the AV of the
swelling process can be taken as approximately zero. That is, the
mass of the imbibed liquid in a swollen particle of original mass
m0 can be taken exactly as:
p
Mass of Imbibed Liguid inside Swollen Particle = mQ —- (Q - 1)
Po
Correction to Conditions of Equivalent Applied Force
Correction of swelling measurements to a standard state of
equivalent applied force should be possible with additional data on
powder compaction at different angular velocities. We have taken
some preliminary data indicating that the effective swelling of a
column of solvent wetted powder is approximately an exponential
function of the angular velocity, <•>, over the 1600 to 4000 rpm
range on our centrifuge. That is,
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ln(Qaff) = A + BCD
Here, the heights of a wetted powder column were each divided by
the height of the corresponding dry powder column compacted at the
standard angular velocity to yield effective swelling values at
different angular velocities.
Operationally, one would take column height data on the wetted
powders at increasingly higher angular velocities (starting with
the standard velocity of 1800 rpm) up to the velocity needed to
overcome the buoyant force, and then apply a correction to a final
standard state for each solvent. If the standard angular velocity
is given by o)0, then the adjusted angular velocity,
solvent on a given sorbent would be given by:
0)
for each
Adjusted Angular Velocity, GO" =
1--
Po
From these data, an adjusted value of the swelling, Qadj. could be
computed by the expression:
O)n)
where B represents a parameter describing compaction.
Unfortunately, it appears from our preliminary tests that each
solvent which swells the powder, in effect, produces a distinct
material with a different B value; hence, powders wetted with each
solvent would require a whole series of measurements at different
rpm values to estimate B from least-squares regression.
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