Polypropylene, abbreviated as PP, is a polymer formed by the addition of propylene. Product appearance is transparent and light. The density is 0.91-0.94g/cm3, inflammable, melting point is 165 ℃， soften at about 155 ℃， and use temperature range is - 30-120 ℃ [2]. Under 80 ℃， it can resist the corrosion of acid, alkali, salt solution and various organic solvents, and decompose under high temperature and oxidation. Polypropylene is widely used in the production of medical devices, chemical industry, mechanical parts, automobile parts, transportation pipelines, chemical containers, etc., as well as food and drug packaging.
　　
　　Polypropylene PP is a colorless, odorless, nontoxic and translucent solid substance with certain strength and toughness, which can withstand strong acid, strong alkali and a variety of organic solvents; polypropylene has poor impact resistance, poor weather resistance, poor aging resistance and poor surface decoration at low temperature.
　　
　　Polyethylene （PE, for short） is a thermoplastic resin prepared by polymerization of ethylene. In industry, it also includes copolymers of ethylene and a small amount of α - olefins. Polyethylene is odorless, nontoxic, wax like, with excellent low-temperature resistance （the minimum operating temperature can reach - 100 ~ - 70 ° C）， good chemical stability, resistance to most acid and alkali corrosion （not resistant to acids with oxidation properties）， insoluble in general solvents at room temperature, small water absorption, excellent electrical insulation.
　　
　　The mechanical properties of polyethylene PE are general, tensile strength is low, creep resistance is not good, impact resistance is excellent; heat resistance is not high, with the improvement of relative molecular weight and crystallinity, low temperature resistance is good, brittleness temperature is generally below - 50 ℃， and with the increase of relative molecular weight, the minimum is - 140 ℃。