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High-density polyethylene

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HDPE has SPI resin ID code 2

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.[1] 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.[2]

Properties

Thermophysical properties of high density polyethylene (HDPE)[3]
Density 940 kg/m3
Melting point 130.8 °C.
Temperature of crystallization 111.9 °C.
Latent heat of fusion 178.6 kJ/kg.
Thermal conductivity 0.44 W/m.°C. at °C.
Specific heat capacity 1330 to 2400 J/kg-K
Specific heat (solid) 1.9 kJ/kg. °C.
Crystallinity 60%

HDPE is known for its high strength-to-density ratio.[4] The density of HDPE ranges from 930 to 970 kg/m3.[5] The standard method to test plastic density is ISO 1183 part 2 (gradient columns), alternatively ISO 1183 part 1 (MVS2PRO density analyzer).[6] 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.[7] The difference in strength exceeds the difference in density, giving HDPE a higher specific strength.[8] 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.

High DPE is resistant to many different solvents, so it cannot be glued.[clarification needed] Pipe joints must be 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.[9]

Owing to these desirable properties, pipes constructed out of HDPE are ideally applicable for drinking water[10] and waste water (storm and sewage).[11]

Applications

  • HDPE fibers can be spun into rope
    HDPE fibers can be spun into rope
  • Disposable suits; nonwoven HDPE fabric
    Disposable suits; nonwoven HDPE fabric
  • Housewrap
    Housewrap
  • Plastic mailing envelopes
    Plastic mailing envelopes
  • Flexible HDPE pipes
    Flexible HDPE pipes
  • Corrugated HDPE pipe installation in storm drain project in Mexico
    Corrugated HDPE pipe installation in storm drain project in Mexico
  • The monobloc chair
    The monobloc chair
  • Stools for outdoor use
    Stools for outdoor use
  • Bottle crates
    Bottle crates
  • Toys and playground equipment
    Toys and playground equipment
  • Clear plastic bags (shown) are made of LDPE; blown-film shopping bags with handles are now made of HDPE
    Clear plastic bags (shown) are made of LDPE; blown-film shopping bags with handles are now made of HDPE
  • HDPE is used to make sturdy bottles that resist oils. Transparent bottles are usually made of other plastics, such as polyethylene terephthalate
    HDPE is used to make sturdy bottles that resist oils. Transparent bottles are usually made of other plastics, such as polyethylene terephthalate
  • Milk jug
    Milk jug
  • HDPE jerrycans resist softening and swelling from aromatic components of fuels
    HDPE jerrycans resist softening and swelling from aromatic components of fuels
  • Roller on HDPE construction entrance mat
    Roller on HDPE construction entrance mat

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:

HDPE sheet which has been extrusion welded

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.[2] 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

References

  1. ^ Pipe materials. level.org.nz
  2. ^ a b "Market Study: Polyethylene HDPE". Ceresana Research.
  3. ^ Araújo, J. R.; Waldman, W. R.; De Paoli, M. A. (2008-10-01). "Thermal properties of high density polyethylene composites with natural fibres: Coupling agent effect". Polymer Degradation and Stability. 93 (10): 1770–1775. doi:10.1016/j.polymdegradstab.2008.07.021. ISSN 0141-3910.
  4. ^ Thermoforming HDPE Archived 2012-02-05 at the Wayback Machine. Dermnet.org.nz
  5. ^ Typical Properties of Polyethylene (PE). Ides.com. Retrieved on 2011-12-30.
  6. ^ "PLASTIC DENSITY IN 2 MINUTES". www.plastic-density.com. Retrieved 2021-06-18.{{cite web}}: CS1 maint: url-status (link)
  7. ^ Askeland, Donald R. (2016). The science and engineering of materials. Wendelin J. Wright (7 ed.). Boston, MA. p. 594. ISBN 978-1-305-07676-1. OCLC 903959750.{{cite book}}: CS1 maint: location missing publisher (link)
  8. ^ Compare Materials: HDPE and LDPE. Makeitfrom.com. Retrieved on 2011-12-30.
  9. ^ www.rotomolding.org. Retrieved 2016-4-20.
  10. ^ a b c "Acu-Water | HDPE Blueline Water Pipe". Acu-Tech Piping Systems.
  11. ^ a b "Acu-Sewer Pressure Pipe for Sewer Mains". Acu-Tech Piping Systems.
  12. ^ "Puck Board (HDPE Sheets)". Professional Plastics. Retrieved 24 December 2018.
  13. ^ AstroRad. European Space Agency. 25 January 2019.
  14. ^ Gaza, Razvan (14 July 2018). "International Science Aboard Orion EM-1: The Matroshka AstroRad Radiation Experiment (MARE) Payload" (PDF). nasa.gov. Retrieved 27 August 2019.
  15. ^ "Acu-Gas Yellow High Pressure HDPE Pipe". Acu-Tech Piping Systems.
  16. ^ Dermnet.org.nz. Dermnet.org.nz (2011-07-01). Retrieved on 2011-12-30.
  17. ^ "Acu-Comms White Communications Conduit". Acu-Tech Piping Systems.
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