Polypropylene, as one of the least dense plastics, has high compressive strength, yield force and hardness, and good rigidity and temperature resistance.

Molecular formula of polypropylene :(C3H6)n. CAS accession number: 9003-07-0, it is a thermoplastic resin prepared by polymerization of propylene. According to the position of methyl groups are divided into isotactic polypropylene, atactic polypropylene and intertactic polypropylene.

The water absorption rate of polypropylene is very low, soaking in water for 1 day, the water absorption rate is only 0.01% ~ 0.03%, so there is no need to dry the granules before forming processing. The melt of PP is close to that of non-Newtonian fluid, and the viscosity is sensitive to both shear rate and temperature. Increasing pressure or temperature can improve the fluidity of PP, especially the fluidity of PP. Because PP is a crystalline polymer, so the molding shrinkage is relatively large, generally in the range of 1% ~ 2.5%, and has obvious post-shrinkage. PP is easy to oxidative degradation when heated, and is particularly sensitive to oxygen at high temperature. In order to prevent thermal degradation in processing, antioxidants are generally added when resin synthesis. In addition, exposure to heat should be minimized and contact with oxygen should be avoided.