Polyethylene

Chemical Description

• Chemical and physical properties are markedly affected by increasing density, which is affected by the shape and spacing of the molecular chain.
• Low-density materials have highly branched and widely spaced chains, whereas high-density materials have comparatively straight and closely aligned chains.
• Low-density polyethylene (0.926–0.9409 g/cm3) is soluble in organic solvents at temperatures higher than 200 & deg;F.
• It is insoluble at room temperature. High-density polyethylene (0.041–0.965 g/cm3) is hydrophobic, permeable to gas, and has high electrical resistivity.
• Low molecular weight polyethylenes have excellent electrical resistance and resistance to water and to most chemicals.
• Medium molecular weight polymers are waxes miscible with paraffin wax, and polyethylene polymers whose molecular weights are higher than 10,000 are the familiar tough and strong resins that are flexible or stiff.
• By varying the catalyst and methods of polymerization, properties such as density, crystallinity, molecular weight, and polydispersity can be regulated over wide ranges.
• Polymers with densities ranging from approximately 0.910 to 0.925 g/cm3 are low-density polyethylenes; those with densities ranging from 0.926 to 0.940 g/cm3 are medium-density polyethylenes; and those with densities ranging from 0.941 to 0.965 g/cm3 and higher are high-density polyethylenes.
• Polyethylene is used in the development of plastics.
• Polyethylene is a flexible waxy translucent polyalkene thermoplastic made in a variety of ways producing a polymer of varying characteristics.
• In the ICIprocess, ethene containing a trace of oxygen is subjected to a pressure in excess of 1500 atmospheres and temperature of 200°C. Low-density polyethene (r.d. 0.92) has a formulaweight between 50 000 and 300 000,softening at a temperature around 110°C, while the high-density polythene(r.d. 0.945–0.96) has a formulaweight up to 3 000 000, softening around 130°C.
• The low-density polymers are less crystalline, being more atactic.Polyethene is used as an insulator; it is acid resistant and is easily molded and blown.
• Polyethylene is a water-repellent, white, tough, leathery, thermoplastic resin very similar in appearance to paraffin wax. Properties vary from a viscous liquid at low molecular weights to a hard wax like substance at high molecular weights.
• It is used as a coating for glass bottles and fiberglass fabrics (special treatments for glass are required to obtain good adhesion between polyethylene and glass) and is also used as an injection-molding material for ceramics.
• In the polymerization process, the double bond connecting the carbon atoms is broken. Under the right conditions, these bonds reform with other ethylene molecules to form long molecular chains.
• Ethylene copolymers, EVA, and EEA are made by the polymerization of ethylene units with randomly distributed comonomer groups, such as vinyl acetate (VA) and ethyl acrylate (EA).