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Polypropylene (PP) is a thermoplastic polymer of propylene (propane).

Production

Polypropylene is produced in the form of white powder or granules with a bulk density of 0.4-0.5 g/cm3. Polypropylene is available in stabilised, coloured and undyed versions.

Physical and mechanical properties

Unlike polyethylene, polypropylene is less dense (density 0.91 g/cm3, which is the lowest value for all plastics), harder (resistant to abrasion), more heat-resistant (begins to soften at 140 °C, melting point 175 °C), and almost not subject to corrosion cracking. It has a high sensitivity to light and oxygen (sensitivity decreases with the introduction of stabilisers).

Thermal and physical properties

Polypropylene has a higher melting point than polyethylene and, accordingly, a higher decomposition temperature. Pure isotactic polypropylene melts at 176 °C. The maximum operating temperature for polypropylene is 120-140°C. All polypropylene products can withstand boiling and can be sterilised by steam without any change in their shape or mechanical properties.

Surpassing polyethylene in heat resistance, polypropylene is inferior to it in frost resistance. Its brittleness temperature (frost resistance) ranges from -5 to -15°C. Frost resistance can be increased by introducing ethylene links into the macromolecule of isotactic polypropylene (for example, by copolymerising propylene with ethylene).

Processing

The main processing methods are extrusion moulding, vacuum and pneumatic moulding, extrusion-blow moulding, injection-blow moulding, injection moulding, compression moulding, injection moulding.

Applications

A material for the production of films (especially packaging films), bags, containers, pipes, technical equipment parts, plastic cups, household items, nonwovens, electrical insulation material, in construction for vibration and noise insulation of interfloor floors in floating floor systems. When propylene is copolymerised with ethylene, non-crystallising copolymers are obtained that exhibit rubber properties, characterised by increased chemical resistance and resistance to ageing. Polypropylene foam (PPP) is also widely used for vibration and thermal insulation. It has similar characteristics to polyethylene foam. There are also decorative extrusion profiles made of PPP that replace polystyrene foam. Attack polypropylene is used to make construction adhesives, mastics, sealing mastics, road surfaces and adhesive films.

Polypropylene market

Polypropylene currently ranks 2nd in the world among polymers in terms of consumption, with a 26% share, second only to polyethylene. The share of polyvinyl chloride (18%), which is ranked 3rd, is declining in favour of polypropylene. Homopolypropylene accounts for 76% of global polypropylene consumption, while copolymers account for the rest.