HDPE
Relatively stiff polyethylene used in hollow containers and solid sheet products.
- Also known as
- high density polyethylene, high-density polyethene, HDPE
In everyday products
- Detergent bottle — Bottle body
- Chopping board — Board body
- Watering can — Hollow plastic body
Structure and behaviour
[–CH₂–CH₂–]ₙ
The carbon backbone is the same as LDPE, but fewer branches allow more chain segments to pack into ordered crystalline regions. The repeat unit does not show branch frequency, chain length or the mixture of crystalline and disordered regions.
- Closer chain packing generally makes HDPE stiffer and denser than LDPE, which helps bottles and boards hold their shape.
- Its non-polar hydrocarbon chains have low water uptake; detergent compatibility still depends on the complete formulation.
- A blow-moulding grade must remain coherent as a hot hollow tube before inflation; a sheet grade serves a different forming process.
- Wall thickness and ribs can stiffen an object without changing the ethene-derived backbone.
- Melting and reshaping are physical processing steps. They do not regenerate ethene or repeat the original polymerisation.
Preparation routes
Ethene route
Catalytic addition polymerisation. A catalyst builds relatively unbranched polyethylene chains. This differs from the high-pressure radical process for LDPE even though both begin with ethene. The repeat formula alone cannot distinguish this material from LDPE: branch structure is the missing information that links catalyst choice to packing and stiffness.
Catalyst and process control determine chain structure. Some commercial grades use small amounts of comonomer; this overview follows the ethene backbone. Controlled chain length and comonomer content select a grade, rather than changing a pellet into a finished bottle.
- Poly(ethene): structure, manufacture and usesChemical Industry Education Centre, University of York
Material limits
A stiff bottle can still crack under sustained stress and exposure to some contents. Food contact, UV durability and chemical compatibility require a grade and product specification. For recycling, a clean sorted HDPE stream is more useful than a mixture of unrelated polymers; labels, closures and contamination still matter.
Sources
- Poly(ethene): structure, manufacture and usesChemical Industry Education Centre, University of York
- HDPE bottles for household chemicalsSABIC
- KPC HDPE sheet: fabrication and cutting boardsKing Plastic Corporation
- HDPE watering cansTremalin
- Polymer structure, crystallinity and physical propertiesOpenStax, Rice University
- Sustainable plastics: the role of chemistryRoyal Society of Chemistry