Polypropylene, like polyethylene, is an olefin plastic. Its properties are similar to those of polyethylene, but PP is stiffer and has better mechanical strength. The plastic is available as both homo- and copolymer.
The co-polymer PP-PE copes with low temperatures better than the homopolymer. The natural colour of polypropylene is white, colourless. The options for colouring are unlimited. There are self-extinguishing grades.
PP has low density and very good chemical resistance, particularly to fats and organic solvents. The heat deflection temperature is high at small loads. Propylene has high tensile strength and excellent electrical properties which are also retained in water.
Aggressive substances for PP are aromatics, halogenised hydrocarbons and strongly oxidising acids. UV radiation breaks down polypropylene unless it is stabilised; in addition unmodified PP has poor tolerance of low temperatures. The plastic is difficult to bond.
One of the principal uses of PP is in packaging, such as bottles, containers and packaging for medicines and cosmetics. Examples of other uses are in electrical insulators, textiles, kitchen appliances, cords, chassis, fans, car grilles, backing for instrument panels, stamping and filter sheets and for parts used in the chemical engineering industry.
Polypropylene floats on water. Burns even after it has been removed from the flame, with a bright, non-sooting flame, blue at the core and yellow at the tip. Drips and has an oil or paraffin odour.