PVC Geomembranes - Good, Better, Best
Are different grades of PVC Geomembranes available or are they all the same?
There has been a common misperception in our industry that all polyvinyl chloride (PVC) membranes are the same. The fact is that this is far from the truth and as we explain in this blog there are several different grades, and each has its own specific properties with respect to geomembrane applications. Without providing a “Wikipedia” on polyvinyl chloride, it is one of the most commonly specified lining materials in the industry with over 60 years of use, very flexible, available as reinforced substrates or non-reinforced membranes, or sheets, ideal for both buried and exposed applications, and highly effective as primary or secondary containment.
Because of its high flexibility, PVC liners readily conform to sub grade contours and offer excellent interface friction without being textured. One of the more common uses of a PVC liner is to prevent contaminants from entering groundwater sources or streams. In addition, it conserves potable water resources by preventing seepage loss.
Primary typical features/benefits of PVC geomembranes include:
Availability of 20-year warranty
10 to 120 mils
Very flexible - readily conforms to ground contours
Seaming options include Hot Air, Wedge and RF
Available in various grade to meet your application needs
Plasticizer selection is an extremely important aspect of a PVC liner material since the loss of plasticizer will result in a reduction of physical properties such as low temperature resistance and elongation. There is a wide choice of liquid plasticizers that can be used in PVC sheeting, depending upon the application and service conditions under which the PVC compound will be used. There are three basic mechanisms for liquid plasticizer loss: volatilization, extraction and microbiologic attack. The use of the proper liquid plasticizers and an effective biocide can virtually eliminate microbiological attack and minimize volatility and extraction. The PVC polymer itself is not affected by these conditions.
The finalists – and where they stand
Let’s start with the Bronze Medalist, IG Industrial Grade (IG), designed for low risk liquid containment and short life expectancy.
The Silver Medalist is 7176 Grade designed to meet the requirements of ASTM-7176 and FGI-1115 Requirements, intended for long life buried applications and low risk liquid containment.
The Gold Medalist is UV Grade 7176 for 20-year exposed applications and low risk liquid containment. EPT’s product offering in exposed geomembrane liners is our XTRM Ply PVC. For many years it was believed that PVC could not be used for 20-year exposed applications because the products available at the time did not have enhanced UV protection. Interestingly, PVC roofing with enhanced UV has been in use for over 30 years with great success. Today most geomembrane polymers are available with enhanced UV protection, as well as without.
Two nominees that should not be ignored:
Fish Grade PVC for lining applications like aquaculture, fish farms and decorative ponds that will be used to cultivate or contain fish. Standard PVC geomembranes should not be used for this application; always request fish grade.
Our last nominee is a very important product offering for geomembrane applications and although it is a member of the PVC family, it is usually recognized by its alias EIA or ethylene interpolymer alloy. The name sounds very technical, but actually it is simply created by the substitution of a liquid plasticizer for a solid one. The solid plasticizer is KEE (ketone ethylene ester), which is more commonly known as DuPont Elvaloy®. The use of Elvaloy in PVC enhances the geomembranes performance and resistance to petrochemicals and hydrocarbon. This results in the DuPont Elvaloy®/KEE alloy providing enhanced resistance to volatilization, extraction and microbiologic attack. When first introduced, the use of PVC with Elvaloy in the geomembrane market was a significant game changer. Finally, the industry had a true high-performance product that could be applied to a wide range of applications ranging from Bio Digesters, reservoirs (EIA is also available in a Potable Water Grade with NSF approval), primary and secondary volatile chemical container, hydrocarbons, and floating covers -- all of which are exposed applications, which is why most EPT XTRM PLY EIA products contain enhanced UV protection for 20+ year life. EPT has many years of experience with EIA. Our XTRM Ply HP with high chemical, microbial and UV resistance, available up to 10’ width for reduced fabrication costs, is the ideal product for these types of application.
The use of EIA in geomembranes has an interesting history. We need to go back to the roofing industry and specifically roofing composed of EIA products for over 30 years, for the answer. In that industry, EIA provided the perfect solution to constant UV exposure. In fact, over many decades, EPT has gained extensive experience manufacturing these products by supplying its sister company Flex Membranes with over 500,000,000 million s/f of combined PVC UV and EIA UV single-ply commercial roofing membranes.
PVC has always been one of the most versatile plastics available with formulations that can provide oil resistance, UV stability, low temperature resistance, and other specific properties. PVC liner materials are produced in roll form from the factory. It is also the easiest material to repair with kits available from most fabricators or installers. PVC can be formulated for longevity and/ low cost. In short, your application and its expected service life will determine which version of PVC is best for you.
Below is a list of some typical PVC Geomembrane applications:
Decorative Ponds & Water Features
Golf Course Ponds
Oil Drilling and Fracking Reserve Pits
Lakes & Streams
Canals and Channels
Waste Water Treatment Facilities