- What are the advantages of LLDPE over PVC geomembrane?
The advantages are as follows:
- LLDPE has resistance to a wider range of chemicals as compared to PVC.
- LLDPE is immune from biological attack by microorganisms. Microorganisms could attack PVC and use the plasticizer as a source of food.
- LLDPE is resistant to burrowing animals, PVC is not.
- LLDPE has a lower permeability to methane than PVC.
- LLDPE has a lower moisture vapor transmission rate than PVC.
- LLDPE retains its physical properties due to long-term soil burial. PVC's physical properties diminish in time due to loss of plasticizer.
- LLDPE is resistant to ultra-violet light, PVC is not.
- LLDPE remains flexible at temperatures well below freezing at -25°C. PVC loses its flexibility and becomes brittle at -25°C
- In what type of projects are Poly-Flex liners used?
Poly-Flex geomembranes are used in a variety of applications. Most commonly, in municipal solid waste and hazardous waste landfills, landfill closures, raw water reservoirs, wastewater lagoons, industrial ponds, mining leach pads and ponds, canals, aquaculture ponds, secondary containment, etc
- Are there any limits on the project size?
No. The project size could vary from a few hundred square feet to millions of square feet of geomembrane.
- Which liner should be used for secondary containment, Poly-Flex HDPE or LLDPE? Why?
Poly-Flex HDPE liners are preferred because most secondary containment projects are for emergency containment of chemicals at high concentrations, such as fuels and acids. The Poly-Flex HDPE liners provide a higher degree of chemical resistance as compared to LLDPE liners.
- Can Poly-Flex liners be used for potable water applications?
Yes. Poly-Flex liners do not contain any plasticizers or fillers, and are therefore safe for potable water applications.
- What is the elongation or deformation limits of Poly-Flex HDPE and LLDPE geomembranes before they rupture?
In the multi-axial tension test, ASTM D 5617, the HDPE liners rupture at 15% elongation and the LLDPE liners rupture at 30% elongation.
- Does thickness affect the elongation or deformation limits?
Generally, the elongation property of Poly-Flex liners are independent of the material thickness. Although thinner liners deform with less pressure, the ultimate elongation at rupture is nearly the same for all gauges.
- Does material thickness influence puncture resistance?
Yes. Thicker liners have higher puncture resistance than the thinner ones.
- How is the thickness of a liner determined for a specific application?
In the case of landfills, U.S.E.P.A. mandates that all landfill liners must be 60 mil or thicker. Poly-Flex 40 mil geomembranes are preferred for landfill closures. The liner thickness is determined by the project engineer based on the project site specific conditions.
- How are Poly-Flex liners held in place on side slopes?
The most common method of securing the liners on side slopes is by means of an anchor trench around the perimeter. The batten strip or the PEC embed channel systems are used to attach the liner to structures. Please refer to the Poly-Flex Design Details located in Technical Information
- How steep can side slopes be designed for Poly-Flex lining applications?
The side slopes can be designed as steep as 90° or a vertical wall.
- Should Poly-Flex liners be used as reinforcement (structural) membranes?
No. Poly-Flex geomembranes are not reinforced materials and should not be used as structural membranes to carry loads.
- What are interface friction angles?
Interface friction angles express properties relating to sliding shear resistance between two materials facing each other. This property is used in stability calculations to design a stable liner system.
- How are interface friction angles determined?
The industry standard test method is the ASTM D 5321 "Determining the coefficient of soil and geosynthetic or geosynthetic and geosynthetic friction by the direct shear method".
- What are the advantages of Poly-Flex textured liners?
Our blown-film textured liners have smooth edges and are covered by U.S. Patent Nos. 5,763,047 and 5,804,112. The blown-film texturing provides increased friction angles for higher stability on steep slope applications. Additionally, the smooth edges result in easier, more cost-effective, more consistent, and better welding.
- What is the minimum degree of roughness (texturing) a textured liner should have?
The minimum industry standard specification GRI GM13 and GRI GM17, require a minimum Asperity Height of 10 mils for textured HDPE and textured LLDPE geomembranes.
- What are the temperatures for material that can be contained by Poly-Flex liners?
Poly-Flex geomembranes are thermoplastic materials, hence their physical properties are temperature dependent. The material becomes softer and more flexible at higher temperatures and stiffer and stronger at lower temperatures. We specify maximum use temperatures of 160° F for HDPE and 140° F for LLDPE liners.
- What is the cold temperature resistance of Poly-Flex liners?
Poly-Flex liners pass the low temperature brittleness test at -70° C (-94° F) according to the ASTM D 746.
- Why do Poly-Flex liners have wrinkles?
Polyethylene liners expand and contract as the sheet temperature changes. This thermal expansion/contraction will cause the liner to grow or shrink with variance in temperature.
- Are Poly-Flex liners available in any other colors than black?
Yes. Poly-Flex liners are available in white/black. A white, or reflective liner reduces heat buildup and minimizes wrinkling. For other colors contact Poly Flex, Inc.
- Are Poly-Flex liners immune to root penetration?
Poly-Flex liners resist root penetration. However, some vegetation, such as nut grass, could penetrate the liners. We recommend that the subgrade soils be prepared to be free of roots and organic material.
- Are Poly-Flex liners immune to attack by rodents?
Poly-Flex liners are generally immune to rodent and insect attack because they contain no plasticizers or scrim source proteins, which are sometimes present in other synthetic liners.
- What method is used for joining Poly-Flex liner panels together?
Poly-Flex liner panels are joined by two methods. The primary method of welding geomembrane panels together is fusion welding. In fusion welding, heat is applied directly to the geomembrane panels by a motorized hot wedge welder. The panels are then routed through a series of rollers that fuse the material together. The second method of joining Poly-Flex Liner panels is extrusion welding. This method is used primarily for performing repairs on the liner material. This method utilizes the application of molten polyethylene welding rod to the surface of the two geomembrane sheets to be joined. The molten extrudate creates a bond that seals the two pieces of geomembrane together.
- Can Poly-Flex liners of different thickness or textures be welded to each other?
Yes. Poly-Flex liners with thickness or texture differences of 20 mils or less can be fusion welded together. Liners with thickness or texture differences of greater than 20 mils should be extrusion welded together.
- Can Poly-Flex liners of different densities be welded to each other?
Yes. Welding temperature adjustments must be made to achieve a successful weld. When extrusion welding, the lower density welding rod should be used.
- Can Poly-Flex seams be tested for leaks? How?
Yes. Poly-Flex seams are non-destructively tested over 100% of the seam length for leaks. The most common method is the air pressure test for dual wedge seams. The vacuum box test is used for extrusion welds.
- Can Poly-Flex liners be installed directly on top of concrete slabs or asphalt pavement?
Yes. Concrete and asphalt slabs must be smooth and have no sharp edges.
- Can Poly-Flex liners be attached to fixed structures such as concrete, steel, pipes, etc? How?
Yes. Poly-Flex liners can be attached to fixed structures through a number of methods. With concrete structures, two methods are preferred. The first, to be used in new structures, is the Poly-Flex polyethylene embed channel (PEC). This channel can be inserted into a new concrete structure, providing for a three inch HDPE surface to which Poly-Flex liners may be welded creating a watertight seal. Secondly, Poly-Flex liners may be attached to new and existing concrete structures through the use of stainless steel or aluminum batten strips. These strips are attached to the concrete by inserting stainless steel anchor bolts into the concrete, placing the geomembrane liner over the anchor bolts, placing a strip of neoprene gasket between the liner and batten strip, and securing the batten strip with washers and nuts. Poly-Flex liners may also be secured to penetrations through the liner by the fabrication and welding of a polyethylene "boot" around the structure. Please refer to the Design Details Section of Technical Information.
- Should wind uplift forces be considered for Poly-Flex liners installed in exposed applications?
Yes. The wind suction forces can lift exposed liners off the ground and potentially damage them. A ballast system, such as dead weights, sand bags or tubes, anchor trenches, etc. should be considered for all geomembranes installed in exposed applications. For buried applications, the installed liner should be temporarily secured by means of sand bags until covered with soil.
- How much ballast is needed over exposed liners?
The ballast system should be designed to secure the liner in place under the maximum anticipated wind suction pressures for the specific project site. Wind uplift pressures can be as high as 30 psf depending on the project site geometry and wind velocity. Please call your Poly-Flex sales representative for more information.
- Can construction equipment be operated directly on the liner?
Equipment that applies less than 2 psi ground pressure can be operated directly on the liner when operated with caution, including no sudden starts, stops or turns.
- What maintenance is required for Poly-Flex liners after installation?
None, Poly-Flex liners are maintenance free.
