Polyethylene - U.H.M.W. - UHMW PE
See also General Information under Polyethylene - Low Density General Description : A semi-crystalline, whitish and effectively opaque engineering thermoplastic which, chemically, is a very high molecular weight (3-6 million) HDPE. As a result it has an extremely high melt viscosity and normally can only be processed by powder sintering methods. It also has outstanding toughness and cut and wear resistance and very good chemical resistance, somewhat better than that of HDPE. Applications include many "wear parts" (eg bottle handling machine components), gears, bearings, artificial joints and marine quay headings. Fibres of very high molecular orientation can also be made from polyethylene of very high molecular weight by gel spinning and subsequent drawing to give fibres which are reported to be up to 85% crystalline and with 95% parallel orientation. They are known as Ultra High Modulus or High Performance Polyethylene fibre (UHMPE or HPPE). A modest range of fibre, braided cord and fabrics are available from Goodfellow. Like Kevlar, these fibres have very high tensile properties and (small) negative CTE's. On a volume basis, their tensile properties are broadly similar to Kevlar's but, on a weight basis, they are superior thanks to an almost 50% density advantage - but they are not up to the properties of carbon fibre on either basis. Their energy absorption and acoustic velocity characteristics are superior to Kevlar's both as fabric and composite. Applications are being developed particularly in the areas of ballistic protection and ropes (in the widest sense).