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PP is a kind of semi-crystalline material. It is harder than PE and has a higher melting point. Copolymer PP material has lower thermal distortion temperature (100℃), low transparency, low gloss, low rigidity, but has stronger impact strength. The strength of PP increases with increasing ethylene content. There is no environmental stress cracking problem in PP. Generally, low MFR PP materials have good impact resistance but low tensile strength. For materials with the same MFR, the strength of copolymer type is higher than that of homopolymer type. Due to crystallization, the shrinkage rate of PP is quite high, and the directional uniformity of shrinkage rate is much better than that of materials such as PE-HD. Homopolymer type and copolymer type PP materials have excellent hygroscopic resistance, acid and alkali corrosion resistance, solubility resistance. However, it has no resistance to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. PP also does not have oxidation resistance at high temperature like PE.