United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati. OH 45268
Research and Development
EPA/600/SR-92/069 July 1992^
«rEPA Project Summary
Evaluation of the Chemical
Resistance of Geotextiles,
Geonets, and Pipe
Patrick E. Cassidy, Matthew W. Adams, and David F. White
A technological base was sought for
determining the chemical resistance
and long-term durability of geotextiles,
geonets, and pipe exposed to liquids
representative of those in a waste con-
tainment facility. A desired end prod-
uct was to develop and validate gener-
alized test methods assessing the
chemical resistance of these products
in a laboratory setting. Although the
methods have produced valuable Infor-
mation when a high level of expertise
has been applied, the fingerprinting
techniques do not offer clear-cut means
to discriminate subtle differences in
polymer structure.
This Project Summary was developed
by EPA's Risk Reduction Engineering
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 increasing amounts of solid waste
being generated as the result of the United
States being an industrialized nation are
dealt with in many ways—from illegal
dumping to incineration. The intermediate
practice of landfill disposal has become
the method of choice among manufactur-
ers, governments, and the private sector.
Unfortunately, the advances in landfill tech-
nology have not been able to keep up
with the increasing amounts and variety
of wastes the landfills are required to iso-
late. The most significant breakthrough,
however, occurred about 10 years ago
when synthetic materials (termed
geosynthetics) began to compliment natu-
ral materials in the construction of dis
posal sites.
Research on these materials has, thus
far, been limited to generating data appli
cable to the materials' engineering abili
ties. Data such as ultimate strength, tea
resistance, and sheer strength have long
been determined for the use of designer;
and engineers planning the landfill. A!
though these data are satisfactory for ap
plications such as drainage ditches, rein
forced embankments, and paved surfaces
they are not sufficient for hazardous waste
containment designs. The importance of
physical data is not diminished in sue!
cases, but the importance of chemical re
sistance becomes crucial.
Project Objectives
The experimental program was intended
to provide a means to verify that the pro
posed generalized test program can, in
fact, identify plastic that is unacceptable
for the waste chemical to be contained.
Specific objectives were as follows:
• Recommend tests for geosynthetics
Physical testing procedures were
chosen from those currently being
employed by chemical resistance
testing laboratories. Further, analyti-
cal testing procedures were chosen
from those commonly used in ana-
lytical chemical laboratories. The
sensitivity of selected test methods
to degradation induced by chemical
exposure was evaluated,
• Correlate analytical and mechanical
test data
Analytical and microstructural data
were compared with mechanical in-
Printed on Recycled Paper
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dex property data to evaluate pro-
posed fingerprinting or equivalency
testing procedures. Relationships
between physical property and ana-
lytical data are required to relate
molecular changes to bulk physical
property losses. This relationship is
essential if such practices are to
play a significant role in chemical
resistance evaluations.
Establish guidelines for evaluation
and failure criteria
Evaluation of chemical resistance
data requires clear understanding
of the test methods used and sound
judgment to properly distinguish ran-
dom variability from degradation
caused by chemical attack.
Experimental Procedures
The materials to be tested were se-
lected according to current trends in de-
sign and use. The exposure matrix was
based on findings of earlier work in these
laboratories with an emphasis on inducing
failure. These failures are not to occur for
the purpose of invalidating the use of
geosynthetics, but rather to assess the
ability of the proposed immersion proce-
dures and test methods to identify resis-
tance of materials to immersion media.
Additionally, analytical tests common to
the chemical sciences were employed to
monitor changes on a molecular level.
The experiments followed the general
guidelines outlined in the EPA's prelimi-
nary guidance so that the program would
assess the extent to which those proce-
dures would accomplish the intended pur-
pose. This involved a 120-day exposure
period; two exposure temperatures (23 and
50 °C); and 30-day property monitoring
intervals, in accordance with EPA Method
9090 for geomembranes. It was believed
that the chemical resistance program rec-
ommendations for textiles, net, and pipe
should parallel those already employed
for geomembranes. Products representa-
tive of the most commonly specified
geotextiles, geonet, and pipe were needed
to provide an experiment that evaluated
materials representative of current indus-
try design practice for waste facility de-
sign (Table 1).
Two geotextile products represented the
principal classes of nonwoven geotextiles
currently available: polyethylene tereph-
thalate (PET) and polypropylene (PP). One
product representing each material was
tested. Nominal fabric weights were 112 g/
m2 (3.3 oz/yd2) for PET and 214 g/m2 (6.3
oz/yd2) for PP.
Because a survey of the geosynthetics
industry indicated that high-density poly-
ethylene (HOPE) is predominantly used in
the manufacture of drainage net, one rep-
resentative HOPE net product was tested.
One smooth interior/profiled exterior
HOPE pipe product was tested. Although
many diverse kinds of plastic pipe are
available in the marketplace and many of
these have found application in waste con-
tainment facility design, this program did
not permit evaluation of multiple products.
It was believed that the project objectives
could be met by selecting one representa-
tive pipe material. Polyethylene pipe was
selected because it has been widely used
in constructing leachate collection systems.
Test Selection
We sought index physical property tests
consistent with the EPA's interim guid-
ance and representing common, well-ac-
cepted standard methods that could be
easily reproduced. At the same time, at-
tention was given to evaluating alternative
tests, e.g., single-fiber tests for geotextiles
and arc bend tests for pipe sections. The
requirement of exposing samples in labo-
ratory baths for extended periods of time
ruled out tests requiring unusually large or
bulky specimens.
Fourier transform infrared spectroscopy
(FTIR) was used because it can indicate
oxidative degradation and qualitatively
characterize polymer surfaces by measur-
ing a wide range of chemical structures.
Thermal analysis was applied because of
its ability to detect changes in crystallinity
of polymeric materials.
As tools for fingerprinting and equiva-
lency testing geosynthetics, the evaluated
analytical techniques presented some
problems. First, the lack of test standard-
ization and technical documentation hin-
dered efforts to provide consistent, repeat-
able results. It was necessary to develop
individual sampling methods for each ma-
terial examined. Although the methods
employed are by no means definitive, they
helped to solve the problems encountered
when applying analytical techniques to
geosynthetics.
Second, the equipment used is not nec-
essarily representative of that available to
other laboratories and manufacturers. Be-
fore applying a technique, the limits of
each machine must be assessed and then
taken into account when interpreting data.
Each experiment must be carefully moni-
tored for sources of interference, and ex-
perience must be applied to individual
methods. Such expertise comes from a
learned researcher who is able to apply
polymer chemistry in conjunction with ana-
lytical instrumentation.
The third consideration is that of inter-
preting analytical data. The microstruc-
tural changes being investigated are very
minuscule, and therefore even sensitive
methods may provide data that are diffi-
cult to interpret (Figure 1).
Presently, the fingerprinting techniques
that were evaluated do not offer a clear-
cut, readily-applied means to discriminate
subtle differences in polymer structure.
Further, minute changes in bulk proper-
ties cannot yet be detected using analyti-
cal methods. Without significant attention
to method development, laboratory tech-
nique, and interpretation, the development
of useful results is difficult. The potential
usefulness of these methods should not
be discounted since they have already
produced valuable information when a high
level of expertise has been applied to
experimental design and evaluation crite-
ria. With respect to fingerprinting, this
project has better defined set-up, test ap-
plication, and data evaluation problems
so that future research will have a more
defined approach.
Outlook
The largest problem now facing wide
acceptance and use of fingerprinting tech-
niques is the lack of uniform, repeatable
test procedures. The level of accuracy
and repeatability remain in question as
does the proper interpretation of data. The
technology base needs to be expanded
so that analytical tests of demonstrated
value can be specified with confidence,
regardless of who performs the test or
interprets the results.
Although some methods (mechanical
and analytical) have been identified here
as useful, this should not be taken as a
complete list. Rather, it should be consid-
ered a foundation for further work. Other
tests are available to complement those
performed here. As geosynthetics experi-
ence greater applications in waste con-
tainment, such work is needed to fully
develop chemical resistance testing.
Analytical testing is believed capable of
indicating deterioration before physical
methods can, and, therefore, these more
sensitive, molecular-level indicators should
receive principal attention. For example,
the field of reflectance spectroscopy can
provide an experienced spectroscopist a
wide range of techniques from which to
choose; this technology must be further
examined. Further, thermal analysis has
been shown to indicate degradation both
quantitatively and qualitatively; thermal
analysis should be continually applied to
geosynthetic studies.
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Table 1. Exposure Matrix
Exposure Conditions
Tests
Geosynthetic
Material
Geotextile 1
(PP*)
Geotextile II
(PET")
Geonet
(HOPE"')
Pipe
(HOPE***)
Water H2SO4
(50%)
23 °C
50 °C 50 °C
50 °C
23 °C
50 °C 50 °C
23 °C
50 °C 50 °C
Ca(OH)2 Physical
(replicates)
Grab Tensile (10)
Mullen Burst (10)
Permittivity (10)
Melt Flow Index (3)
Specific Gravity (3)
23 °C Grab Tensile (10)
50 °C Mullen Burst (10)
Permittivity (10)
Specific Gravity (3)
Transmissivity (2)
Net Compression (3)
Tensile Strength (3)
Melt Flow Index (3)
Gradient Density (3)
Pipe Stiffness (3)
Gradient Density (3)
Melt Flow Index (3)
Analytical
FTIFP
TGA*
DSC*
FTIFP
TGA*
DSC"
FTIFT
TGA*
DSC*
FTIFP
TGA*
DSC*
'Polypropylene; "polyethylene terephthalate; ***high-density polyethylene; Courier transform infrared spectroscopy;
*thermogravimetric analysis; 'differential scanning calorimetry.
Exposed to Ca(OH)2 for 120 Days at50°C
102.2 —
76.6
4000
Wavelength (cm '')
Figure 1. Fourier transform infrared spectra of polyethylene terephthalate (PET) exposed to base solution (top) and unexposed
PET.
•U.S. Government Printing Office: 1992— 64S-080/60031
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Additional analytical techniques to be
evaluated include gel permeation chroma-
tography, rheology, nuclear magnetic reso-
nance (NMR) spectroscopy, etc. A broader
recommendation is to establish a continu-
ing program of evaluating existing landfill
facilities to identify field failures and to
assess the condition of installed materi-
als.
The full report was submitted in fulfill-
ment of Cooperative Agreement Number
CR815495 by Southwest Texas State Uni-
versity under the sponsorship of the U.S.
Environmental Protection Agency.
Patrick E. Cassidy and Matthew W. Adams are with Polymer Research Group of
Southwest Texas State University, San Marcos, TX, and David F. White is with
TRI Environmental, Inc., Austin, TX.
Robert E. Landreth is the EPA Project Officer (see below)
The complete report, entitled "Evaluation of the Chemical Resistance of Geotextiles,
Geonets, and Pipe," (Order No. PB92-170 562/AS; Cost: $19.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/SR-92/069
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