High Density Polyethylene Geomembrane Liner (H.D.P.E.)
Background and characteristics:
- became commercially available in the mid 1970's as a chemical derivative of early polyethylene materials
- contains approximately 97.5% polyolefin polymer, 2% carbon black and .5% anti-oxidants and heat stabilizers
- made by polymerizing ethylene gas at low temperatures to produce long linear molecular chains of carbon and hydrogen with relatively few side branches which allows the molecules to be more tightly compressed to yield a highly dense material (in contrast to low density polyethylene)
- Higher density provides greater tensilee strength, improved heat capability, higher tear resistance, increased hardness, better chemical resistance and lower water adsorption than low density polyethylene
- very stable under buried soil conditions without any noticeable degradation over periods analyzed
- half life is estimated to be 350 years in a buried state
- most important characteristic is that H.D.P.E. can be easily seamed on site utilizing fusion and extrusion methods
The bottom line is the H.D.P.E. is one of the most cost effective lining materials available today.
Resistivity:
- high resistance to chemical attack including salts, bases, organic acids, detergents, ketones, fats, alcohols, animal oils, and others (available upon request)
- high resistance to ultra-violet degradation
- does not deteriorate in buried applications
- seaming process bonds parent materials so that the integrity and continuity of the seams is not compromised making the seams highly resistive to failure and as strong as the parent material
Test Methods:
Seams can be tested during installation of liner to ensure integrity. Typical tests performed are listed below:
- High pressure air test
- Qualification and production weld testing utilizing tensiometer peel and tensiles test, visual inspection and the vice grip peel test
- Vacuum box soap test for extrusion welds
- Spark testing
Seaming Process:
Fusion: Use of hot wedge welder which heats the parent materials to a molten state and then compresses the materials so that they adhere to each other and form a unified parental bond. Double seams about one inch apart are formed with an intermediary air space. This air space can then be filled with air to test the integrity of the seam. The wedge welder is portable and is used on site for all production runs.
Extrusion: Welding rod comprised of the parent material is fed into a hand held gun and heated to its melting point. The molten bead is laid on to an overlapped seam area that has been pre-tacked, ground to remove oxidized surface material, and preheated by a hot air nozzle attached to the extrusion gun. The resulting butt seam at a “T” intersection ensures integrity of the seam at an area where the wedge welder is not able to produce a uniform seam. Extrusion welding is also used around any appurtenances that may penetrate the liner.
