High-density polyethylene (HDPE) or polyethylene high-density (PEHD) 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 is commonly recycled, and has the number "2" as its recycling symbol. In 2007, the global HDPE market reached a volume of more than 30 million tons.
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 °C/ 248 °F for short periods, 110 °C /230 °F continuously). High-density polyethylene, unlike polypropylene, cannot withstand normally-required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst (e.g., Ziegler-Natta catalysts) and reaction conditions. HDPE contains the chemical elements carbon and hydrogen.
HDPE is resistant to many different solvents and has a wide variety of applications, including:
Laundry detergent bottles
Fuel tanks for vehicles
Portable basketball system bases
Geomembrane for hydraulic applications (canals, bank reinforcements...) and the containment of certain chemicals
Chemical-resistant piping systems
Heat-resistant fireworks display mortars
Geothermal heat transfer piping systems
Natural gas distribution pipe systems
Water pipes, for domestic water supply
Coax cable inner insulators (dielectric insulating spacer)
Corrosion protection for steel pipelines
Snowboard rails and boxes
Bottles, suitable for use as refillable bottles
Modern hula hoops
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, with the intention of 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 and composite wood, with recycled polymers leading the way.
HDPE is also widely used in the pyrotechnics trade. HDPE mortars are preferred to steel or PVC tubes because they are more durable and more importantly they are much safer compared to steel or PVC. If a shell or salute were to malfunction (flowerpot) in the mortar, HDPE tends to rip and tear instead of shattering into sharp pieces which can kill or maim onlookers. PVC and steel are particularly prone to this and their use is avoided where possible.
Milk bottles and other hollow goods manufactured through blow molding are the most important application area for HDPE - More than 8 million tons, or nearly one third of worldwide production, was applied here. Above all, China, where beverage bottles made from HDPE were first imported in 2005, is a growing market for rigid HDPE packaging, as a result of its improving standard of living. In India and other highly populated, emerging nations, infrastructure expansion includes the deployment of pipes and cable insulation made from HDPE. The material has benefited from discussions about possible health and environmental problems caused by PVC and Polycarbonate associated Bisphenol A, as well as, its advantages over glass, metal and cardboard.