Today's article mainly introduces polypropylene, polyethylene (PE) is a thermoplastic resin produced by polymerization of ethylene.
Polyethylene odorless, non-toxic, feel like wax, has excellent low temperature resistance (minimum use temperature can reach -100~-70°C), good chemical stability, resistance to most acid and alkali erosion (not resistant to acid with oxidation properties). Insoluble in general solvents at room temperature, low water absorption, good electrical insulation.
Polyethylene can be processed in the same way as ordinary thermoplastics. It is widely used in the manufacture of films, packaging materials, containers, pipes, wire and cable, daily necessities, etc., and can be used as high frequency insulation materials for TV, radar, etc.
With the development of petrochemical industry, the production of polyethylene has developed rapidly, and the output accounts for about 1/4 of the total output of plastics. In 1983, the world's total polyethylene production capacity was 24.65 Mt, and the plant capacity under construction was 3.16 Mt. According to the latest statistics in 2011, the global production capacity reached 96 Mt, and the development trend of polyethylene production shows that production and consumption have gradually transferred to Asia, and China has increasingly become the most important consumer market.
The heat resistance of polyethylene is not high, and it is improved with the increase of relative molecular weight . Good low temperature resistance, brittle temperature can generally reach -50℃ below; And with the increase of relative molecular weight, the lowest can reach -140℃. The linear expansion coefficient of polyethylene is large, up to (20 ~ 24)×10-5/K. High thermal conductivity.
Because LDPE and HDPE have good fluidity, low processing temperature, moderate viscosity, low decomposition temperature, and do not decompose at a high temperature of 300 °C in the inert gas, it is a plastic with good processing performance. However, the viscosity of LLDPE is slightly higher, and the motor power needs to be increased by 20% to 30%; It is easy to break the melt, so it is necessary to increase the die gap and add processing AIDS. The processing temperature is slightly higher, up to 200 ~ 215℃. Polyethylene has low water absorption and does not need to be dried before processing.
Polyethylene products, such as polyethylene drum plugs, are easy to crystallize during cooling, so pay attention to mold temperature during processing. To control the crystallinity of the product, so that it has different properties. The molding shrinkage of polyethylene is large, which must be considered when designing molds.
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