High density polyethylene
HDPE has SPI
resin ID code 2
High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE.
HDPE has little branching, giving it stronger intermolecular forces and tensile strength than lower density polyethylene. It is also harder and more opaque and can withstand somewhat higher temperatures (120° Celsius for short periods, 110° Celsius continuously). The lack of branching is ensured by an appropriate choice of catalyst (e.g. Ziegler-Natta catalysts) and reaction conditions.
HDPE is resistant to many different solvents and has a wide variety of applications, including:
Laundry detergent bottles
Fuel tanks for cars
Containment of certain chemicals
Chemical-resistant piping systems
Geothermal heat transfer piping systems
Natural gas distribution pipe systems
Water distribution pipe systems
Coax cable inner insulators (dielectric insulating spacer)
Corrosion Protection for Steel Pipelines. See HDPE Liner
HDPE is also used for cell liners in subtitle D sanitary landfills, wherein large sheets of HDPE are either extrusion or wedge welded to form a homogeneous chemical-resistant barrier, preventing the pollution of soil and groundwater by the liquid constituents of solid waste.
One of the largest uses for HDPE is wood plastic composites, with recycled polymers leading the way.