United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/017 Mar.1988
Project Summary
Factors in Assessing the
Compatibility of FMLs and
Waste Liquids
Henry E. Haxo, Jr., Thomas P. Lahey, and Mark L. Rosenberg
This experimental research project
studied various factors in the
compatibility of flexible membrane
liners (FMLs) with waste liquids and
other hazardous substances that
may be encountered in waste
storage and disposal facilities. This
work was conducted in three basic
areas:
1. Swelling of FMLs and other
FML-related compositions in
organics, and calculation of the
solubility parameters of these
compositions.
2. Distribution of organics between
aqueous solutions, such as
leachates, and FMLs.
3. Variables in EPA Method 9090
compatibility testing of FMLs and
waste liquids.
Equilibrium swelling of 28 FML-
related polymeric compositions was
determined in 30 organics and
deionized water. These 28 polymeric
materials included thermoplastic
crosslinked and semicrystalline
compositions, of which 22 were
commercial FMLs or sheetings and
six were known compositions
prepared in the laboratory for this
study. Basic polymer and compound
variations (e.g., differences in
polymer type, level of crystallinity,
crosslink density, filler level, and
amount and type of plasticizer) were
assessed.
Crystallinity of the base polymer
appears to be the dominant factor in
reducing the swelling of an FML or
an FML-related composition in all of
the organics and to override both the
solubility parameters and cross-
linking. Among compositions based
on amorphous polymers, the
proximity of the component solubility
parameters to those of the organics
could be used in most cases to
indicate the swelling and the
probability of changes in properties.
Nevertheless, empirically derived
data are still necessary for untested
combinations of organics and FMLs.
This Project Summary was
developed by EPA's Hazardous Waste
Engineering Research Laboratory,
Cincinnati, OH, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The compatibility of a proposed
polymeric membrane liner with the waste
to be contained is a principal requirement
of the Resource Conservation and
Recovery Act permitting process for the
construction of a waste storage and
disposal facility. The other principal
requirements are low permeability and
durability. Thus, a liner material must
have low permeability to all the
constituents of a waste liquid and must
maintain its physical integrity, including
seams, to contain the particular waste
effectively for the required length of time.
In assessing the suitability of a
polymeric product designed to be in
contact with liquids and chemicals, it is
common practice in the rubber and
plastics industries to use solubility
parameters to select the polymer
compound and ultimately to expose the
composition to the liquid with which it is
-------
to be in contact. The effects of the
exposure upon the physical properties of
the compositions are measured as a
function of time. The swelling and
dimensional changes that take place and
the changes in mechanical properties,
such as tensile strength, elongation at
break, tear strength and modulus are
normally measured. For many
applications service life is estimated as
the time of a percentage change in
property relevant to its performance or
one that has been correlated with
performance. In the case of FMLs used
in lining waste storage and disposal
facilities, specific criteria for an allowable
magnitude of change in specific
properties beyond which an FML "fails"
have not been developed.
The technology involving the use of
polymeric membranes for lining storage
and disposal facilities is relatively new. At
present, information in the open literature
regarding the compatibility of FMLs and
waste liquids based on actual experience
continues to be limited. On the other
hand, considerable information regarding
the compatibility of specific polymeric
materials with specific organics and
liquids is available which the engineer
and designer can use to assess potential
compatibility of given materials with
given waste liquids. Because waste
liquids can be complex mixtures with the
possibility of detrimental effects due to
the combination of components, the
compatibility of a lining material with a
specific waste liquid needs to be
determined. Reliable test protocols are
needed so that correct assessment of the
liner-waste compatibility can be made
by the permit writer when reviewing a
permit application.
Among properties that appear to be
related to FML performance, the swelling
or loss in weight in service is one of the
most useful tools in assessing its
compatibility with wastes. Associated
with these changes in weight are
changes in most of the physical
properties, such as tensile strength, tear
strength, modulus, hardness, permea-
bility, puncture resistance, and fatigue
resistance.
Matching the solubility parameter
values of an FML with those of a specific
waste liquid and its constituents has
been suggested as a means of predicting
the swelling that might take place in an
FML on exposure. Determination of the
applicability of the solubility parameter
values to estimate the compatibility of
FMLs and specific wastes and to
estimate the service lives of FMLs was
one of the principal objectives of this
project.
In addition to the possible use of
solubility parameters for predicting
compatibility and service lives of FMLs
as liners in specific waste storage and
disposal facilities, there are several other
factors which can affect the magnitude of
swelling and possibly the ultimate
service life. The compositional factors
include:
Degrees of crystallinity of the
polymer.
Level of crosslinking of the polymer.
Amount of filler in the compound
formulation.
Amount of plasticizer in the
compound.
Amount of waste soluble constituents
in the compound.
The environmental factors include:
Concentration of the organics and the
partitioning of an organic dissolved in
the waste liquid with a polymeric liner.
The effect of strain or stress on a liner
in service.
This project was undertaken to
investigate and quantify the various
factors that contribute to the performance
of FMLs and their compatibility with
waste liquids in waste storage and
disposal facilities and to investigate
factors involved in predicting long-term
compatibility and service life.
Objectives
The four principal objectives of this
project were:
To develop a methodology that can
be used to predict the compatibility of
FMLs with specific waste liquids and
to estimate their service lives for lining
waste storage and disposal facilities.
To determine the solubility
parameters of polymeric FMLs and to
explore their use for determining the
compatibility of FMLs with waste
liquids of different types.
To assess the different factors that
affect the magnitude of swelling of an
FML in contact with waste liquids.
To determine the effects of swelling
on mechanical and permeability
characteristics of FMLs in service.
In addition to the above, this project
had the following secondary objectives:
To assess the effects on polymeric
FMLs of organics in dilute solutions
and determine whether threshold
levels for organic species in waste
liquids can be set.
To assess the effects on polymeric
FMLs of exposure to waste liquids,
such as in the testing of environment!
stress-cracking resistance.
To determine the importance c
crosslink type and crosslink densit
upon FML behavior in wast
impoundment environments.
To determine the applicability c
higher exposure temperatures i
performing compatibility tests and i
estimating the service life of an FM
as a liner in a waste storage an
disposal facility.
Summary and Conclusions
The work conducted on this projec
was in three major areas relating to th
chemical compatibility of FMLs wit
waste liquids and leachates:
Swelling of FMLs in organics an
calculations of the solubilit
parameters of the FMLs and relate
compositions.
Distribution of organics in aqueou
solutions between water and FMLs.
Study of variables in FML/waste liqui
compatibility testing.
Swelling of FMLs in Organics
and Calculations of the
Solubility Parameters of the
FMLs and Related Composition
Equilibrium swelling of 28 FML
related polymeric compositions wa
determined in 30 organics and deionize
(Dl) water. These 28 polymeric material
included thermoplastic, crosslinked, an
semicrystalline compositions, of which 2
were commercial FMLs or sheetings an
six were laboratory-prepared com
positions. Within these 28 composition:
basic polymer and compound variation
were included, such as polymer type;
level of crystallinity, crosslink density
filler level, and amount and type c
plasticizer.
The organics covered a wide range c
Hildebrand solubility parameters as we
as the component solubility parameter:
i.e., the dispersive ( d), polarity ( p), an
hydrogen-bonding ( h) components. Th
organics were selected by a compute
program from a list of 131 organics o
which the solubility parameter data wer
available and which covered the range
of component solubility parameter value:
as well as the Hildebrand parameter.
Equilibrium swelling was measured b
weighing specimens of polymeri
compositions that had been immersed i
the individual neat organics until ther
was essentially no change in weigh
Each of the solubility parameter:
including the Hildebrand and componer
parameters, were then calculated fror
-------
he swelling data for each of the
olymeric compositions through a
computer program which generated the
curve that best fit the data for that
parameter.
The most significant results of this
swelling study were:
The crystallinity of the polymer
appeared to be the dominant factor in
reducing the swelling of the polymeric
composition in all of the organics and
appeared to override both the
crosslinking and the solubility
parameters.
The crosslinking of an amorphous
polymer reduced swelling in all of the
organics compared with the
uncrosslinked polymer. Increasing the
crosslinking density reduced the
swelling.
Note: The crystallinity and crosslinking
factors are not additive. The
introduction of crosslinking in
semicrystalline polymeric
compositions tends to reduce
the amount of crystallinity.
Though the magnitude of swelling of
amorphous polymers could, in many
instances, be estimated from the
proximity of the values of the
component solubility parameters of
the polymer and those of the organic,
the swelling of the FML in many
combinations could only be roughly
estimated based upon the type of
organic. The matching of the
Hildebrand solubility parameter values
remains a necessary but not sufficient
condition for swelling. The swelling
tests should be performed to ensure
that an amorphous FML will not swell
in a particular organic. Thus,
empirically derived data are still
needed for untested combinations of
organics and FMLs.
With waste liquids that contained
dissolved organics, the organics were
absorbed by the FML; the amounts
absorbed depended on: (1) the
relationship of the solubility
parameters of the organic and the
FML, and (2) the solubility of the
organic in water.
Distribution of Organics in
Aqueous Solutions Between
Water and FMLs
A series of experiments was
performed to study the distribution of
organics from dilute aqueous solutions to
FMLs and the permeation of these
organics through the FMLs. Three
jreliminary experiments were performed
to explore the movement of organics with
respect to water and FMLs and to assess
gas chromatography as a means of
measuring the concentrations of organics
so that their movement from one solution
into another could be followed. These
experiments were as follows:
Measurement of the distribution of
seven organics in mixtures at different
ratios with water between the organic
phase and water. The mixtures
included organics having a wide range
of solubilities in water from miscibility
to almost complete insolubility.
Measurement of the distribution of
organics between water and a
paraffinic oil which was selected to
simulate polyethylene because of their
chemical similarity.
Measurement of the distribution of
organics in a dilute aqueous solution
of organics and a high-density
polyethylene FML which was
immersed in the solution.
A series of six additional and more
extensive experiments was conducted to
assess the distribution of organics
between water and FMLs:
To determine the distribution of
organics between saturated aqueous
solutions of individual organics and a
polyethylene FML
To determine the distribution of
organics between organic-saturated
FML specimens and deionized water.
To determine, in a two-compartment
test apparatus, the distribution and
transmission of nine organics in a
dilute aqueous solution through a
linear low-density polyethylene FML.
To determine, in the two-
compartment test apparatus, the
distribution of trichloroethylene (TCE)
in a dilute aqueous solution among
the air-spaces, the water layer, and
the FML separating the two
compartments.
To determine, in a vapor-tight
three-compartment test apparatus,
the distribution of the trichloroethylene
and toluene from a dilute solution to
the vapor, water, and FML layers.
To determine the distribution, in the
three-compartment test apparatus
separated by polyethylene FMLs, of
six volatile organics initially in a dilute
aqueous solution. These organics
covered the range of solubility
parameters from an alkane to an
organic acid.
The results of these experiments
demonstrated that the organics, based
upon their solubility parameters, will
transfer from a dilute aqueous solution to
the FML with which the solution is in
contact and, if volatile, permeate into the
airspace on the opposite side of the FML
as a vapor. The ultimate ratio, at
equilibrium, of the concentration of the
organics in the FML to that in the water
can vary over hundreds of orders of
magnitude, depending on the solubility
parameters of the organics.
A multi-compartment test apparatus
with FML specimens between the
compartments to simulate the condition
of a waste liquid in service appears to be
an appropriate means of measuring the
movement of organics from dilute
solutions and transmission through FMLs.
The concentration of the organics in the
various zones of the test apparatus can
be followed by gas chromatographic
analysis of the vapors and liquids and
headspace gas chromatographic analysis
of the FML.
The solubility of an organic in water
appears to have been a significant factor
in its movement through the apparatus.
For example, n-octane, when added to
water in the three-compartment test
apparatus, tended to volatilize and be
transported into the airspace above the
top FML rather than into the lower FML
and the airspace below the dilute
aqueous solution of organics. TCE, which
is highly volatile and yet has a relatively
high solubility in water, was transmitted
relatively fast throughout the three
compartments of the test apparatus, thus
showing its high mobility.
Considerable time was required for the
organics originally in the dilute solution in
the apparatus to reach equilibrium in the
vapor, the water, and the FMLs layers.
This indicates the need for relatively long
exposure periods, e.g., four months, for
conducting compatibility tests of FMLs in
dilute solutions and waste liquids.
Because of the long exposure period,
vapor-tight exposure tanks should be
used.
-------
Henry E. Haxo, Jr., Thomas P. Lahey, and Mark L. Rosenberg are with
Matrecon, Inc., Alameda, CA 94501.
Robert E. Landreth is the EPA Project Officer (see below).
The complete report, entitled "Factors in Assessing the Compatibility of FMLs
and Waste Liquids," (Order No. PB 88-173 3721 AS; Cost: $19.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
\ PERMif Nb3.^-350 .2 5
V /-,. . . r\ S i- :! METERi
Official Business
Penalty for Private Use $300
EPA/600/S2-88/017
0000329 PS
60404
ifrU.S. GOVERNMENT PRINTING OFFICE: 1988548-013/8'
------- |