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Product overview
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high pressure-low density polyethylene (HP-LDPE, abbreviated as LDPE) has been industrialized for more than 70 years, although with the discovery and development of olefin polymerization catalysts, the varieties and yields of polyethylene have made great progress. However, high-pressure polyethylene still plays an important role. Ethylene is polymerized into high molecular weight polyethylene by free radical mechanism under high temperature and high pressure, which has the following characteristics:
(1) The process of ethylene polymerization is a strong exothermic process. The polymerization heat of ethylene is about 93.5kJ/mol (or 3.3kJ/g), and the specific heat capacity of ethylene at 235MPa and 150-300 ℃ is 2.51~2.85J/(g·℃). If the reaction heat cannot be removed in time, the temperature will rise by 12~13℃ for every 1% of ethylene polymerization. If the temperature is too high, it will also cause ethylene to decompose.
(2) Under high pressure, ethylene has been compressed to a density of 0.5g/mL, similar to a liquid that can no longer be compressed, at this time the distance between ethylene molecules is significantly shortened, thereby increasing the probability of collision between free groups and ethylene molecules, so it is easy to polymerization.
(3) At high temperature, the free radical activity of the growth chain is large, and chain transfer reaction is easy to occur, and the obtained polymer has a linear structure with more branch chains. Usually every 1000 carbon chain atoms contain 20 to 30 branch chains, crystallinity is 45% to 65%, density is 0.910 to 0.925g/mL, light weight, flexible, low temperature resistance, impact resistance is good.
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Application field
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Application range of low density polyethylene: suitable for seasoning, pastry, sugar, preserves, biscuits, milk powder, tea, fish floss and other food packaging. Tablets, powders and other medicine packaging, shirts, clothing, knitted cotton products and chemical fiber products packaging. Washing powder, detergent, cosmetics and other daily chemical products packaging. Due to the poor mechanical properties of single-layer PE film, it is usually used as the inner layer of composite packaging bags, that is, multi-layer composite film heat sealing substrate. [3]
