High-density polyethylene

High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code.
In 2007, the global HDPE market reached a volume of more than 30 million tons.
Properties
HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 to 970 kg/m3. The standard method to test plastic density is ISO 1183 part 2 (gradient columns), alternatively ISO 1183 part 1 (MVS2PRO density analyzer). Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/248 °F for short periods). 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 is resistant to many different solvents, and is exceptionally challenging to glue; joints are typically made by welding.
The physical properties of HDPE can vary depending on the molding process that is used to manufacture a specific sample; to some degree, a determining factor is the international standardized testing methods employed to identify these properties for a specific process. For example, in rotational molding, to identify the environmental stress crack resistance of a sample, the notched constant tensile load test (NCTL) is put to use.
Owing to these desirable properties, pipes constructed out of HDPE are ideally applicable for drinking water and waste water (storm and sewage).
Applications
HDPE has a wide variety of applications; for applications that fall within the properties of other polymers, the choice to use HDPE is usually economic:
3D printer filament
Arena board (puck board)
Backpacking frames
Ballistic plates
Banners
Bottle caps
Boats
Chemical containers
Chemical-resistant piping
Coax cable inner insulator
Conduit protector for electrical or communications cables
Corrosion protection for steel pipelines
Electrical and plumbing boxes
Far-IR lenses
Fireworks
Folding chairs and tables
Food storage containers
Fuel tanks for vehicles
Geomembrane for hydraulic applications (such as canals and bank reinforcements)
Geothermal heat transfer piping systems
Heat-resistant firework mortars
Housewrap (Tyvek)
Hovercraft: The material is too heavy and dense for such craft but is still used occasionally
Ionizing radiation shield
Laundry detergent jugs
Lasts for shoes
Microwave telescope windows
Milk jugs
Natural gas distribution pipe systems
Piping for fluid, slurry and gas purposes
Plastic bags
Plastic bottles suitable both for recycling or re-use
Plastic surgery (skeletal and facial reconstruction)
Potable water mains
Root barrier
Shampoo bottles
Sewage mains
Snowboard rails and boxes
Stone paper
Storage sheds
Swimming pool installation
Trackout control mats
Telecom ducts
Water pipes for domestic water supply and agricultural processes
Wood plastic composites (utilizing recycled polymers)
HDPE is also used for cell liners in United States subtitle D sanitary landfills, wherein large sheets of HDPE are either extrusion welded 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.
HDPE is preferred by the pyrotechnics trade for mortars over steel or PVC tubes, being more durable and safer: HDPE tends to rip or tear in a malfunction instead of shattering and becoming shrapnel like the other materials.
Milk bottles, jugs, and other hollow goods manufactured through blow molding are the most important application area for HDPE, accounting for one-third of worldwide production, or more than 8 million tonnes.
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 (BPA), as well as its advantages over glass, metal, and cardboard.
See also
Cross-linked polyethylene (PEX)
HDPE pipe (HDPE)
Low-density polyethylene (LDPE)
Linear low-density polyethylene (LLDPE)
Medium-density polyethylene (MDPE)
Phillips Disaster
Plastic recycling
Polyethylene (PE)
Resin identification code
Stretch wrap
Ultra-high-molecular-weight polyethylene (UHMWPE)
References
Plastics
Polyolefins
de:Polyethylen