United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-90/041 Sept. 1990
&EPA Project Summary
Fundamental Approach to
Service Life of Flexible
Membrane Liner's (FML's)
Arthur E. Lord, Jr., and Robert M. Koerner
Predicting the service life of
flexible membrane liners (FML's)
exposed to chemicals has usually
been done by physical or mechanical
changes after exposure. The report
summarized here presents an
alternative approach-that to water for
periods up to fifteen months were
tested by five different chemicals and
transport related measurements. The
results indicated that monitoring the
transport properties of FML's
exposed to particular chemicals over
a reasonable exposure time could be
considered as one possible method
for predicting an FML's lifetime.
7"n/s 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
Because of the extremely large
amounts of waste disposed to landfills
each year, it is essential that when FML's
are the liner of choice, they be sound.
Predicting the service life of FML's
exposed to chemicals has been
attempted by measuring physical or
mechanical property changes after
periodic exposure times (EPA 9090).
Here five different mass transport
measurements are evaluated as a
function of exposure time to simple
chemicals.
Experimental Design
Four experimental techniques were
employed:
1. Water vapor transmission (WVT)
2. Diffusion coefficient determinations
• Water absorption (WA)
• Water vapor absorption (WVA)
• Radioactive tracer measurement
(RT)
• Benzene adsorption (BA)
3. Microstructural observations
4. Differential scanning calorimetry
(DSC)
Four FML's were chosen for the
study:
1. Polyvinyl chloride (PVC)
2. Chlorinated polyethylene (CPE)
3. Ethylene propylene diene monomer
(EPDM)
4. High density polyethylene (HOPE)
Five liquids were used:
1. Water, as a control
2. 10% sulfuric acid (in water), a strong
acid solution
3. 10% sodium hydroxide (in water), a
strong base solution
4. 100% xylene, a common solvent
5. 10% phenol (in water), a common
and troublesome byproduct of many
commercial processes.
The FML's were taken from the
exposure tubs, cut to the appropriate size
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for measurement, and sealed in properly
identified plastic bags. Before actual
measurements, many samples were
taken from the plastic bags and
desiccated in a vacuum desiccator for 1
month to attempt to ensure they were
completely dry.
Water Vapor Transmission
To see if changes indicating
instability of the FML structure could be
observed, WVT tests were run according
to ASTM E-96-80. A commercial
humidity/temperature chamber was used
to maintain the required ASTM
temperature and humidity environment.
Diffusion Coefficient
Determinations
There are no standard tests for
diffusion coefficient determinations.
Following a literature survey, the methods
researchers found most satisfactory and
reliable were used.
Water Absorption
To determine the diffusion coefficient
of water in a particular FML, the FML was
immersed in water and the weight gain
was monitored as a function of time.
Water Vapor Absorption
The WVA test followed that of the
liquid WA test. Instead of suspending an
FML directly in a controlled temperature
bath, however, the FML was placed in a
separate glass cylinder with water in the
bottom; this, in turn was suspended in the
water bath. This, 100% humidity
conditions were present, and water vapor
entered the FML as a function of time.
The increase in weight was plotted
against time.
Radioactive Tracer Measure-
ments
RT measurements were employed to
determine the diffusion coefficient of a
particular molecule. Although tritiated
water would be the preferred diffusant, it
is difficult to work with. Benzene with 14C
was, therefore, used. Although benzene
is a very good swelling agent for rubber-
type materials and swelling agents have
unusually high values for apparent
diffusion coefficients, the method's value
is not lessened because it does
determine the relative changes in
diffusion properties of PVC, EPDM, and
CPE samples.
Benzene Absorption
BA was used (in Phase II) for HOPE
because HOPE has a low solubility.
Relatively large amounts of radioactivity
would have been needed to produce a
high enough count rate for the Geiger-
Mueller tube detection used here.
Microstructural Observations
To see if severe chemical attack could
be monitored on a small (microstructural)
scale with the use of SEM (Scanning
Electron Microscopy), observations were
made on as-received PVC and on PVC
exposed to methylene chloride.
Differential Scanning
Calorimetry Measurements
DSC measurements were made to see
if a chemically induced structural change
could be detected with this method.
Six-Month Exposure Results,
Phase I
The six-month exposure results for
WVT and for RT are summarized in
Table 1.
Water Vapor Transmission
For PVC, exposure to NaOH and
H2S04 had little effect on the WVT;
phenol and xylene, which leach
plasticizer from PVC, definitely lowered
the WVT. For EPDM, exposure to the
four chemicals had little effect on the
WVT, but phenol exposure significantly
increased WVT. Because xylene
destroyed CPE in a few days, no results
are given for CPE and xylene. Thus, the
WVT depended on the chemical to which
the FML was exposed.
Diffusion Coefficient
Water Absorption and Water
Vapor Transmission
Because the FML's did not in
general achieve a constant equilibrium
weight during a long immersion time and
because the diffusion coefficient cannot
be determined without this final weight,
WA and WVA presented problems. The
uptake process was more complicated
than simple diffusion and may be
complicated by surface absorption
effects. These and other problems made
WA and WVA unreliable methods with
which to determine diffusion coefficients
of water in commercial FML's.
Radioactive Tracer
For PVC, the results genera
agreed with those for WVT: exposure
acid and base do little to the diffusi
coefficient, but leaching agents (phei
and xylene) leach out the plasticizer a
the PVC becomes stiffer and the diffusi
coefficient is reduced.
For EPDM, the results agre
exactly with those for WVT with resp<
to relative change. Unfortunately, t
agreement for PVC and EPDM do r
extend to CPE. Agreement for acid a
base are good, but for phenol t
agreement is poor.
Microstructural Observations
SEM photos of samples soaked
methylene chloride for various times (o
minute to ten minutes) and magnific
100, 300, and 3000 times indicated
change. Although these observatio
were preliminary, the results showed
little promise that further work in this ar
was halted.
Differential Scanning
Calorimeter Results
That xylene removes plasticizer frc
PVC is seen vividly on the DSC trace
After one month's exposure, the mater
is noticeably stiffer and shows a ve
definite glass transition. The DSC resu
for CPE exposure to phenol are al
shown. The structure becomes evidc
as the CPE is exposed to phenol o
month, three months, and six montf
The longer the exposure, the mo
structure in the DSC traces.
Fifteen-Month Exposure Re-
sults, Phase II
The fifteen-month results from Pha
II are summarized in Table 2. Becau
Table 2 involved different lots of t
same FML (as were used in Phase I), t
two sets of data cannot be present
together on a continuous basis.
The exposure matrix for Phase
included the following:
HOPE was exposed to water, NaO
H2SO4, phenol, and xylene,
CPE was exposed to water, NaO
H2S04, and phenol; and
EPDM, PVC, CPE, and HOPE we
exposed to water.
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Table 1. Percent Change (from 0 to 6-mo. exposure) in Transport
Properties for WVT* and RT»
Table 2. Percent Change (from 0 to 15-mo. exposure) in Transport
Properties for WVT<>, and RT», and BA*
FML
PVC:
WVT
RT
%
Change
Data Trend
at 6 Mo.
%
Change
Data Trend
at 6 Mo.
FML
PVC:
WVT
RT
%
Change
Data Trend
at 15 Mo.
%
Change
Data Trend
at 15 Mo.
H2SO4
NaOH
Phenol
Xylene
+ 12% Steady +4% Steady
+ 10% Steady -11% Steady
-30% Steady -50% Steady
-25% Steady -85% Steady
H2SO4
NaOH
Phenol
Water
-28% Rising
-25% Rising
+ 56% Rising*
-25% Steady
+ 50% Decreasing
+ 42% Decreasing
+ 100% Rising11
+ 44% Rising
EPDM:
HOPE:
H2SO4
NaOH
Phenol
Xylene
CPE:
H2S04
NaOH
Phenol
Xylene
+ I38%b Rising1'
+1000% Steady
+ 70% Steady
+ 54%* Steady
+ 46% Steady
+ 260%b Rising*
+ 37% Rising
+ 20% Steady
+ 17% Steady
+15% Rising
-11% Steady
-9% Steady
* Water vapor transmission, radioactive tracer
An arbitrary, but reasonable, criteria for a degrading effect from a
particular exposure is a large, absolute increase and a continuing upward
trend at 6 mo.
c No data; xylene destroyed CPE after a few days
H2SO4
NaOH
Phenol
Xylene
Water
FML's in
Water:
EPDM
PVC
CPE
HOPE
-12.5% Rising"
+12.5% Decreasing
+12.5% Steady
-12.5% Decreasing
-12.5% Rising
0%
-5%
-29%
0
+ 23%
+ 54%
+ 23%
+ 23%
+ 23%
Steady
Steady
Steady
Steady
Steady
Rising
Decreasing
Steady
Steady
+ 35% Steady
+ 6% Steady
+ 50% Steady
+ 50% Steady
j> Water vapor transmission; radioactive tracer; benzene absortpion.
An arbitrary, but reasonable, criteria for a degrading effect from a
particular exposure is a large, absolute increase and a continuing upward
trend at 15 mo.
0 Liquid benzene absorption was used for HOPE
The major finding of Phase II was
that CPE showed a significant increase in
WVT and RT diffusion coefficient with
exposure to phenol.
Conclusions
1. WVT and RT were found to be quite
reliable test methods, whereas WA
and WVA techniques experienced
serious problems in regard to
obeying simple, one-dimensional dif-
fusion theory.
2. The BA method worked well for
HOPE.
3. The various transport coefficients
showed all the expected types of
behavior with chemical exposure:
- constancy with exposure (acids and
bases on most all FML's and all
chemicals on HOPE)
- decrease with exposure (plastic-
izers leaching from FML's)
- increase with exposure (phenol-
treated CPE).
4. The WVT and RT results were
generally complementary to one
another. The transport approach was
quite successful in predicting the
instability of CPE exposed to phenol.
This instability was further verified by
DSC measurements.
5. The work lends credence to the use
of mass transport measurements to
determine structural change in
FML's. The EPA 9090 method
includes physical and mechanical
testing of the compatibility of FML to
prospective chemicals. Mass trans-
port measurements could be added
to or be complimentary to EPA 9090
testing, because transport of waste
leachate through the FML is the
property of paramount importance
The full report was submitted in
fulfillment of Cooperative Agreement No.
CR-810977 by Drexel University under
the sponsorship of the U.S. Environ-
mental Protection Agency.
•&U. S. GOVERNMENT PRINTING OFFICE: 1990/748-012/20114
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Arthur E. Lord Jr., and Robert M. Koerner are with Drexel University, Philadelphia,
PA 19104.
Paul dePercin was the EPA Project Officer (see below).
The complete report, entitled "Fundamental Approach to Service Life of Flexible
Membrane Liners (FML's)," (Order No. PB 90-263 856/AS; Cost: $17.00, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For further information, Robert Landreth 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
n ?
\J .L
Official Business
Penalty for Private Use $300
EPA/600/S2-90/041
000085833 PS
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REGION 5 LIBRART
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