Geosynthetics June/July 2019 - 8

UPDATE

Clarifying the nomenclature of
Elvaloy-based geomembranes:
EIA, EIP or KEE
By E. Silva and T. D. Stark

E. Silva is vice president of Engineered
Polymer Technologies.
T. D. Stark is professor of civil
engineering at the University of
Illinois at Urbana-Champaign.
8

Geosynthetics | June July 2019

ince the first flexible membrane liner (FML) was used as part of an environmental
liner system, the geomembrane industry has always looked for innovative solutions
for chemical containment applications. Although there have been many innovations
over the last 50 years, one of the most significant is the introduction of ketone ethylene
ester (KEE), which is a solid plasticizer. KEE is available under the Elvaloy trade or
product name and is used to plasticize polyvinyl chloride (PVC) geomembranes, as
discussed in detail in this article.
KEE was invented by DuPont, and the original 1973 patent has expired. DuPont
developed KEE to provide a solid plasticizer or polymer to replace liquid plasticizers
that would make PVC and other polymers flexible without concerns of plasticizer
migration and loss. Plasticizer migration and loss usually results in the material becoming stronger but more brittle and susceptible to cracking.
Unfortunately, Elvaloy has been known by several acronyms, e.g., KEE, ethylene
interpolymer alloy (EIA) and ethylene interpolymer (EIP), which has caused confusion in the industry. As a result, the purpose of this article is to clarify the meaning of
KEE, EIA and EIP for geomembrane-related applications. Some people in the trade
are not aware that a KEE-based geomembrane is a flexible PVC geomembrane with
a new plasticizer.
Compared to conventional polymeric and monomeric liquid plasticizers, KEE
exhibits a significantly higher molecular weight, which greatly reduces plasticizer
migration (Stark et al. 2005) in PVC geomembranes. Stark et al. (2005) shows that
increasing plasticizer molecular weight decreases plasticizer migration because the
higher molecular weight yields a larger molecule that has greater difficulty migrating to the top surface of the geomembrane and out of the geomembrane. As a result,
plasticizer migration and loss decreases with increasing molecular weight. In 2004
the Fabricated Geomembrane Institute (FGI) set the minimum plasticizer molecular weight at 400 grams/mole to ensure suitable long-term performance of PVC
geomembranes in containment applications. This is the FGI Material Specification
dated Jan. 1, 2017, and termed FGI 1117. A minimum plasticizer molecular weight of
400 grams/mole has worked well and created more consistency in the marketplace.
However, recent applications, e.g., exposed and elevated temperature applications,
have created a demand for even higher-performance PVC geomembranes and thus
higher-performance plasticizers.
As a result, considerable interest has developed for use of higher molecular weight
plasticizers, such as KEE. In addition to having a higher molecular weight, KEE is a
solid plasticizer/polymer that does not break down, which prevents migration and
loss from the geomembrane because it retains its large structure and remains a solid.

Geosynthetics June/July 2019

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