The chemical formula of polyethylene terephthalate is COC6H4COOCH2CH2O. Its English name is polyethylene terephthalate, abbreviated as PET. PET is a milky white or light yellow, highly crystalline polymer with a smooth and glossy surface. It has excellent physical and mechanical properties over a wide temperature range, with a long-term use temperature of up to 120 ℃. It has excellent electrical insulation properties, and even at high temperatures and frequencies, its electrical performance is still good, but its corona resistance is poor, creep resistance, fatigue resistance, friction resistance, and dimensional stability are all good. As a packaging material, PET has the following advantages: ① It has good mechanical properties, with an impact strength 3-5 times that of other films, and good folding resistance. ② Resistant to oil, fat, dilute acid, dilute alkali, and most solvents Has good resistance to high and low temperatures, can be used for a long time within the temperature range of 120 ℃, can withstand high temperatures of 150 ℃ for short-term use, and can withstand low temperatures of -70 ℃, with little impact on its mechanical properties at high and low temperatures Low gas and water vapor permeability, with good gas barrier, water, oil and odor resistance properties High transparency, can block ultraviolet rays, and has good luster Non toxic, odorless, with good hygiene and safety, it can be directly used for food packaging. Polyethylene, also known as polyethylene or polythene in English, is abbreviated as PE (hereinafter referred to as PE). PE is a milky white semi transparent to opaque thermoplastic resin. Divided by density: Low density polyethylene (LDPE), with a density of 0.910-0.925g/cm2, also known as high-pressure polyethylene due to its high pressure polymerization (ICI) method; High density polyethylene (HDPE) with a density of 0.941-0.965g/cm2; Because it is polyethylene obtained by low-pressure polymerization (Ziegler process), also known as low-pressure polyethylene, it can also be produced by medium pressure method (Phillips process), with a density of 0.965g/cm2 or above; Medium density polyethylene (MDPE) with a density of 0.916~0.940g/cm2; In addition, there are also linear low-density polyethylene (LLDPE), ultra-high molecular weight polyethylene (HMW-HDPE), and very low-density polyethylene (VLDPE). Currently, the world's production of polyolefin polymers is 350 million tons, of which polyethylene accounts for 65% and more than 30% of the total plastic production. One of the larger general plastic products. The various properties of polyethylene are closely related to its density, molecular weight distribution, and melt index. Generally speaking, it has good physical and mechanical properties and can be used to produce parts for different purposes using various processing methods and forming equipment. But the application fields of different polyethylene varieties are also different.
