Chemical and Physical Properties :

Most commercial polypropylene is isotactic and has a medium level of crystallinity between that of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Polypropylene when copolymerized with ethylene return into tough and flexible . This lets polypropylene to be use as an engineering plastic, competing with materials such as ABS. Polypropylene is very economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic, or certain other plastics. It is often opaque or colored using pigments. Polypropylene has good resistance to fatigue.

The melting point of polypropylene happens in different range, so a melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. Perfectly isotactic PP has a melting point of 171 °C (340 °F). melting point of Commercial isotactic PP has a melting point with the range from 160 to 166 °C (320 to 331 °F), depending on atactic material and crystallinity. Syndiotactic PP with a crystallinity of 30% has a melting point of 130 °C (266 °F).

The melt flow rate (MFR) or melt flow index (MFI) is a measure of molecular weight of polypropylene. The measure assists to determine how easily the melt raw material will flow during processing. Polypropylene with higher MFR will fill the plastic mold more simply during the injection or blow-molding production. As the melt flow increases, however, some physical properties, like impact strength, will decrease.

There are three kind of polypropylene:1. Homopolymer,2. Random Copolymer, 3. Block copolymer. The comonomer is usually use along ethylene. Ethylene-propylene rubber or EPDM added to polypropylene homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to polypropylene homopolymer declines the polymer crystallinity and result will be more transparent.