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GEOMEMBRANE CHARACTERISTICS
General Notes:
The following descriptions are relatively brief but intended to be accurate unbiased product overviews of the most popular geomembranes currently available. All technical information and statements made in this section are to C. W. Neal Corporation’s best knowledge to be true and accurate and are based on our own research and the research of others. This section is not intended to constitute a recommendation of suitability for use for any specific application since conditions of use are beyond C. W. Neal Corporation’s control. Furthermore, C. W. Neal Corporation assumes no liability in connection with any use of this information. There are going to be exceptions to materials discussed here, however, the following represents the common environmental grade of lining products encountered. There are many more geomembranes available that aren’t mentioned here due to relative scarcity. Most of the lining materials covered here are warrantable for up to 20 years.
A Special Note on Mil Thickness: One of the most common misconceptions about geomembranes is that they must be considerably thick to perform well and offer good puncture resistance. Often times products will be specified with mil thicknesses that either aren’t available or are overkill for a given application, costing owners and/or taxpayers premiums. Mil thickness and relative performance value often vary wildly with different materials. For example, .020" PVC offers as much puncture resistance as .060" HDPE according to an EPA report of March, 1988 titled, "Loading Point Puncturability Analysis of Geosynthetic Liner Materials". The presence of a geotextile can greatly affect puncture resistance as well. Some materials are not viable lining products below a relatively thick mill thickness.
R-PP Reinforced Polypropylene is one the newest but also one of the very best all around lining materials available. It is typically manufactured by either the calander (rolling of resin with rollers in series) or extrusion process into plies that are usually combined over a reinforcing polyester scrim fabric during the manufacturing process. Scrims are fully contained within two layers of polypropylene to eliminate wicking (fluid conduction into the liner that could de laminate plies). Polypropylene is commonly used in floating covers, baffles and primary containment applications.
Advantages: Polypropylene geomembranes are available in potable grades and typically offer high resistance in the following areas: weathering/UV, chemical, puncture, tear, abrasion and cold weather. Polypropylene liners are very flexible, have excellent dimensional stability. Polypropylenes are wedge and extrusion weldable and can be patched using a heat gun. Polypropylene geomembranes have low crystallinity and are not affected by environmental stress cracking (ESCR), per ASTM D1693). Polypropylene is a chemically inert polymer that imparts nothing into its environment due to leaching.
Disadvantages: Polypropylene geomembrane liners are not solvent adhesive weldable.
Typical Mil Thicknesses Encountered for Reinforced Products:
30 mil/.030" (.762mm)
36 mil/.036" (.9mm)*
45 mil/.045" (1.14mm)
60 mil/.060" (1.5mm)
Typical Mil Thicknesses Encountered for Non-Reinforced Products:
20 mil/.020" (.762mm)
30 mil/.036" (.9mm)*
40 mil/.040" (1.016mm)
60 mil/.060" (1.524mm) Normally used for vacuum formed accessory items
* 20 Year pro rated manufacturer warranties for polypropylene liners used in exposed applications are typically available for mil thickness of 36 or more.
CSPE Hypalon® has been used for over 30 years in the geomembrane lining industry. It is a synthetic rubber product manufactured by the calander process into plies that are combined over a reinforcing polyester scrim fabric during the manufacturing process. Scrims are fully contained within two layers of Hypalon® to eliminate wicking. Hypalon® is often used in floating covers, baffles and primary containment applications.
Advantages: Proven long-term track record in exposed applications. Hypalon® is both thermally and solvent weldable. It is available in potable water grades. Hypalon® is dimensionally stable and offers excellent weathering and UV resistance. Hypalon® can be pre-fabricated into large panels greatly minimizing field seaming requirements. Hypalon® is not subject to environmental stress cracking. Pro-rated manufacturer warrantees are often available up to 20 years and longer.
Disadvantages: Hypalon® doesn’t have good overall chemical resistance especially to hydrocarbons which readily swell and weaken it. Hypalon® continues to cure or vulcanize over time. It’s tensile strength continues to go up but it’s ability to accept repairs decreases with age. Special preparation and bonding agents are often required on older Hypalon® installations. Hypalon® is expensive as compared to polypropylene and typically exhibits somewhat lower physical property characteristics. It’s unit weight/square foot is high adding higher freight costs. Hypalon® doesn’t have good overall chemical resistance especially to hydrocarbons which readily swell and weaken it. Hypalon® continues to cure or vulcanize over time. It’s tensile strength continues to go up but it’s ability to accept repairs decreases with age. Special preparation and bonding agents are often required on older Hypalon® installations. Hypalon® is expensive as compared to polypropylene and typically exhibits somewhat lower physical property characteristics. It’s unit weight/square foot is high adding higher freight costs.
Typical Mil Thicknesses Encountered:
36 mil/.036" (.9mm)
45 mil/.045" (1.14mm)
60 mil/.060" (1.5mm)
90 mil/.090" (2.254mm)
PVC Polyvinyl Chloride is the oldest and one of the most proven geomembrane lining material around. PVC offers excellent performance in appropriate applications where it’s service life can exceed 20 years. PVC is manufactured by either the calander or extrusion process. Since PVC is a relatively high puncture resistant membrane by itself, it is rarely encountered in an reinforced form.
Advantages: PVC liners are typically very flexible and readily conform to subgrade contours. Due to this flexibility, PVC geomembranes offer excellent interface friction without being textured. Other geomembranes especially HDPE offer very little surface friction unless they are finished heavily textured. PVC liners are solvent adhesive weldable and wedge weldable. Excellent seams can be achieved with either method. PVC is typically prefabricated in a fabrication facility where high level quality control is easily achieved as opposed to expensive field inspection. PVC offers excellent puncture resistance compared to HDPE. 20 mil PVC offers as much puncture resistance as 60 mils of HDPE. PVC has excellent dimensional stability properties. Single PVC panels can be fabricated in sizes approaching one acre, minimizing field seaming requirements.
Disadvantages: PVC liners are typically not suitable for prolonged exposure to sunlight (UV). If specified for an exposed application the expected life span will be for two to three years (could be less or more) pending climatic and chemical environment. PVC needs to be buried by 1’ of topsoil for UV protection. Most PVC manufacturers require this before warranting their installed products. Some manufactures offer exposable PVC liners but the price is typically premium. PVC liners are typically not suitable for prolonged exposure to sunlight (UV). If specified for an exposed application the expected life span will be for two to three years (could be less or more) pending climatic and chemical environment. PVC needs to be buried by 1’ of topsoil for UV protection. Most PVC manufacturers require this before warranting their installed products. Some manufactures offer exposable PVC liners but the price is typically premium.
PVC liners are formulated with plasticizers and biocides. Plasticizers are what make an otherwise rigid PVC film flexible. Plasticizers continuously migrate from PVC causing it to stiffen and eventually become brittle. This typically doesn’t present a problem in installations unless the PVC liner is in direct contact with another substance that has an affinity for the plasticizers and "robs" them at an accelerated rate. This has been noted to happen with concrete for example. Biocides protect PVC plasticizers (which are most commonly pthalate based) from microbial attack. Without biocides, plasticizers will be consumed by soil borne microbes leaving the geomembrane brittle. Biocides found in PVC can be toxic to fish. Fish grade PVC usually does not include a biocide, therefore this grade typically doesn’t survive more than a few years.
Typical Mil Thicknesses Encountered*:
20 mil/.020" (.508mm)
30 mil/.030" (.762mm)
40 mil/.040" (1.016mm)
*10 and 50 mil PVC geomembranes are often available but are rarely specified.
HDPE High Density Polyethylene is typically manufactured as a blown film product. HDPE is an enormously popular product due to it’s UV resistance, low cost and very good overall chemical resistance. is typically manufactured as a blown film product. HDPE is an enormously popular product due to it’s UV resistance, low cost and very good overall chemical resistance.
Advantages: Relatively inexpensive material cost, good overall chemical resistance and is typically suitable for potable water applications.
Disadvantages: HDPE is almost impossible to repair without the use of an expensive extrusion gun. All welds on environmental grade HDPE liners are field welds which greatly increased installation and third party field quality control costs. HDPE is almost never pre-fabricated in a controlled factory setting. HDPE is a very stiff "flexible" liner with a high coefficient of thermal expansion often requiring special design considerations. HDPE is prone to environmental stress cracking (ESCR) due to a crystal lattice structure. Environmental stress cracking is similar to taking a dark colored credit card and bending it until a fracture plane appears as a white crease. HDPE has virtually no surface friction unless heavily textured. Puncture resistance properties require that a minimum of 60 mils of thickness be specified for most exposed applications. Due to tremendous marketing push, HDPE has often been notoriously over specified in applications where other materials are better suited.
Typical Mil Thicknesses Encountered:
40 mil/.040" (1.016mm)
60 mil/.060" (1.524mm)
80 mil/.080" (2.032mm)
100 mil/.100" (2.54mm)
LLDPE Linear low Density Polyethylene is relatively new to the geomembrane lining industry that’s typically produced as a blown film. LLDPE is a close cousin to HDPE. Compared to HDPE, LLDPE is much more flexible, offers better multiaxial stress resistance, higher puncture resistance and far superior stress crack resistance.
Advantages: LLDPE is available in potable water grades and is relatively inexpensive.
Disadvantages: Has very poor weathering/UV resistance qualities and therefore, must be buried. LLDPE has fair chemical resistance and poor dimensional stability. Surface friction properties are poor unless the geomembrane is heavily textured.
Typical Mil Thicknesses Encountered:
40 mil/.040" (1.016mm)
60 mil/.060" (1.524mm)
80 mil/.080" (2.032mm)
100 mil/.100" (2.54mm)
Coolguard™ HR geomembrane liner is a scrim reinforced tripolymer alloy that includes DuPont Elvaloy® . Coolguard Coolguard™ HR geomembrane liner is a scrim reinforced tripolymer alloy that includes DuPont Elvaloy® . Coolguard™ is very similar to Seaman corporation’s XR-5™ products and is intended to perform in the same type of environments. Coolguard™ HR is a product specially formulated for a wide spectrum of chemical resistance’s including hydrocarbons. Coolguard™ HR is for use in primary and secondary containment of liquids and materials that may be chemically aggressive such as crude oil, fuel oils, aviation fuels, diesel, kerosene, refinery wastes, alcohols, glycols, and many other substances. Coolguard™ can be thermally or dielectrically seam welded.
Advantages: Coolguard™ HR is flexible and can be pre-fabricated into large scale panels minimizing required field seams. In many instances Coolguard™ may perform where no other membranes can survive except much more costly materials such as Hytrel®. Coolguard™ can typically be used in the same applications that XR-5™ can but with greater economy and less factory seams because of a much wider finished sheet width. Coolguard™ HR is relatively easily repaired with a hand held seam heat gun, seam roller.
Disadvantages: Coolguard™ is expensive but can prove to be the least expensive alternative to many containment applications. Manufacturer warranties are usually no longer than 10 years.
Typical Mil Thicknesses Encountered:
36 mil/.036" (.9mm)
45 mil/.045" (1.14mm)
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