Polypropylene - PP

Polypropylene (PP) is a semi-crystalline, white, semi-opaque commodity thermoplastic that is made in numerous different grades and modifications. It is a linear polyolefin which can be compared in many ways to high density polyethylene (HDPE) and that is produced in a very similar way.

The catalysts used regulate the polymer's stereoregularity quite well so that commercial polypropylenes (PP) are predominantly isotactic. PP homopolymer is harder and has a higher temperature resistance than HDPE but lower impact resistance and becomes brittle below ~0 °C. Hence copolymer grades are preferred for all applications exposed to cold/winter conditions.

These copolymers have improved impact strength, maintained down to lower temperatures, than homopolymer at the expense of very small cutbacks in other properties. Similar to polyethylenes, PP has good chemical but poor UV resistance (unless protectedor stabilized).

Due to thermal stability problems with materials such as PP, additives such as anti-oxidants are consistently used during processing. It should also be noted that when looking to employ heat sealable films, that this product is in fact a coextruded film, containing a PP core layer and PP/PE copolymer outer layers.

These films are also corona treated to help adhesion and may well also contain an anti-blocking additive such as silica. In case of any doubts about the suitability of any of these materials, customers can ask for confirmation before placing a purchase order.

Polymer Type

Thermoplastic

Advantages

Advantages of Polypropylene include:

  • Good chemical resistance.
  • Good fatigue resistance. 
  • Better temperature resistance than HDPE.
  • Lower density than HDPE.

Disadvantages

Oxidative degradation is accelerated by contact with certain materials, e.g. copper. 

Other disadvantages incude:

  • High mould shrinkage and thermal expansion.
  • High creep.
  • Poor UV resistance.

Applications

Buckets, bowls, general mechanical parts, bottle crates, toys, medical components, washing machine drums, pipes, battery cases bottles, bottle caps.

Rubber modified PP for impact resistant components such as bumpers. Talc-filled Polypropylene for additional stiffness at elevated temperatures. Films for packaging (e.g. cigarette packets). Fibres for carpeting and artificial sports surfaces.

Applications include (for homopolymers) housewares, packaging, appliance housings, cassette holders and fibers, monofilaments and slit-film tapes; for containers, copolymers pipes, boat hulls, seat shells and automotive parts.

PP can be used in many applications including cassette holders. Image Credit: ShutterStock/MARCHPN

PP can be used in many applications including cassette holders. Image Credit: ShutterStock/MARCHPN

Source : Abstracted from Plascams

For more information on Plascams please visit RAPRA Technology Ltd.

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