polyethylene terephthalate (polyethylene terephthalate) chemical formula is COC6H4COOCH2CH2O English name: Climatic Tests, PET for short. PET is a milky white or light yellow, highly crystalline polymer with a smooth glossy surface. It has excellent physical and mechanical properties in a wide temperature range, the long-term use temperature can reach 120℃, excellent electrical insulation, even at high temperature and high frequency, its electrical properties are still good, but the corona resistance is poor, creep resistance, fatigue resistance, friction resistance, dimensional stability are good.

As a packaging material PET advantages: ① good mechanical properties, impact strength is 3~5 times that of other films, good flexability. Oil resistance, fat resistance, acid resistance, alkali resistance, most solvents. (3) It has excellent high and low temperature resistance, can be used in the 120℃ temperature range for a long time, short-term use can be resistant to 150℃ high temperature, can be resistant to -70℃ low temperature, and high and low temperature has little effect on its mechanical properties. (4) Low permeability of gas and water vapor, both excellent resistance to gas, water, oil and odor performance. ⑤ High transparency, can block ultraviolet light, good luster. ⑥ Non-toxic, tasteless, can be directly used in food packaging.

Polyethylene in English is known as: Polythylene or polythene, referred to as PE (hereinafter referred to as PE). PE is a milky white translucent to opaque thermoplastic resin. According to the density, LDPE is divided into: low-degree polyethylene (LDPE), the density is 0.910~0.925g/cm2, because it is the polyethylene obtained by high pressure method (ICI) polymerization, also known as high pressure polyethylene; High density polyethylene (HDPE), the density of 0.941~0.965g/cm2; Because of its low pressure polymerization (Ziegler method) of polyethylene, also known as low pressure polyethylene, can also be used in the medium pressure method (Philip method), the density of 0.965g/cm2 above; Medium density polyethylene (MDPE), the density of 0.916-0.940 g/cm2; In addition, there are linear low polyethylene (LLDPE), high molecular weight polyethylene (HMW-HDPE), very low polyethylene (VLDPE) and so on.

At PRESENT, THE world's POLYOLEFIN polymer production is 350 million tons, of which polyethylene accounts for 65 percent, and the total plastic production of more than 30 percent. One of the largest universal plastic products. The properties of polyethylene are closely related to its density, molecular weight distribution and melting index. Generally speaking, it has excellent physical and mechanical properties, and can be used in a variety of processing methods and molding equipment to produce parts for different purposes. But the application field of different polyethylene varieties is also different.