HDPE
SELECTION OF MATERIAL
The importance of the selection of the material in regards
of the incubating leachate cannot be overemphasized. If a
worst-case leachate is selected, for example, one containing
organic solvents and similarly aggressive chemicals, the geomembrane
chosen will probably be some form of Polyethylene. The more
concentrated and aggressive the leachate is , the higher is
the required density of the polyethylene. This worst-case
leachate selection has indeed been the trend in the past and
resulted to the common use of HDPE in solid waste landfill
liners.
While the chemical resistance of HDPE is of course, a desirable
and necessary feature of the geomembrane it might not aways
appear as the judicious choice.
VARIETY
Polyethylene comes in very-low-density, low-density, linear
low-density, medium-density and high-density varieties. The
range for all geomembrane polymers falls within the general
limits of 0.85 to 1.5mg/l. HDPE resin requires a density =
0.941 mg/l. However, all commercially available HDPE geomembranes
use polyetylene resin from 0.934 to 0.938 mg/l; the resin,
itself, is actually in the medium-density range (MDPE). Only
by adding carbon black and additives to the formulation and
its gross density raised to 0.941 mb/l or slightly higher.
Thus what is called HDPE by the geomembrane industry is actually
MDPE resin to the polymer producer.
High Density Polyethylene is the most chemically resistant
member of the polyethylene family on account of its dense
configuration (>0.94 g/cm3). It is commonly used for most
containment applications. Even if less flexible than LLDPE,
it still offers great elongation properties allowing up to
12% deformation at its yield point. HDPE has little branching,
giving it stronger intermolecular forces and tensile strength
than LLDPE. It is also harder and more opaque and can withstand
higher temperatures (120° Celsius for short periods, 110°
Celsius continuously).
HDPE is resistant to many different solvents and is applied
to a wide variety of applications. For example, in sanitary
landfills, large sheets of HDPE are either extrusion or wedge
welded to form an homogeneous chemical-resistant barrier,
preventing the pollution of groundwater and soil.
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Mission 
