PP
A lightweight polymer that can be moulded into rigid storage containers.
- Also known as
- polypropylene, polypropene, poly(propene), PP
In everyday products
- Storage box — Box body
- Flip-top bottle cap — Cap body and living hinge
- Garden chair — PP matrix of the chair body
- Woven rug — Woven surface yarn
- Clothes hanger — Moulded hanger body
- Laundry basket — Basket body and handles
- Plastic plant pot — Pot body
- Dustpan — Moulded scoop and handle
- PP food tray — Polypropylene tray body
- Reusable PP foam packaging — Expanded polypropylene cushion
Structure and behaviour
[–CH₂–CH(CH₃)–]ₙ
Each repeat unit has a methyl side group. Its stereochemical arrangement along the chain, called tacticity, affects how regularly chains can pack; the flat repeat formula does not specify that arrangement.
- Low density makes solid mouldings relatively light, while ribs allow thin walls to carry practical loads.
- A suitable grade and a carefully formed thin section allow repeated bending in a living hinge.
- Melt spinning and drawing produce oriented yarn; injection moulding instead fixes a three-dimensional product shape.
- Glass fibres can stiffen a chair compound, but the reinforcement is a separate ingredient, not part of the propene repeat unit.
- Foaming PP beads gives EPP cushions: the gas cells and bead connections contribute properties absent from solid resin.
Preparation routes
Propene route
Catalytic addition polymerisation. Propene molecules join into chains. A suitable catalyst controls chain growth and the arrangement of the methyl side groups. Catalyst-controlled arrangement of methyl groups can favour regular packing. The monomer formula alone does not describe this tacticity.
A coordination catalyst system is used; it is not counted as a monomer. A thermoplastic moulding or foam uses already-made PP, not propene reacting inside the final product.
- Poly(propene): manufacture and usesChemical Industry Education Centre, University of York
Material limits
Unfilled, glass-filled, foamed and copolymer PP have different specifications. Fillers, pigments and thermal history affect reprocessed material.
Sources
- Poly(propene): manufacture and usesChemical Industry Education Centre, University of York
- Moplen HP501H: PP homopolymer for caps and hingesLyondellBasell
- Bit chair: glass-fibre-reinforced polypropyleneNardi
- MORUM flatwoven rug: polypropylene surfaceIKEA
- Polymer structure, crystallinity and physical propertiesOpenStax, Rice University
- Neopolen expanded polypropylene: bead structure and packagingKnauf Industries
- Sustainable plastics: the role of chemistryRoyal Society of Chemistry