Ultra high molecular weigh polyethylene (UHMPE) and High density polyethylene (HDPE)

Ultra high molecular weight polyetyhlene (UHMWPE) is polyethylene with a molecular weight numbering in millions, usually between 3.1 and 5.67 million. The high molecular results in less efficient packing of the chains into the crystal structure as evidenced by densities of less than high density polyethylene (for example, 0.930-0.935 g/cm3). The high molecular weigh results in a very tough material. Ultra high molecular weight polyethylene (UHMWPE) can be made through any catalyst technology, although Ziegler catalyst are most common. Because of its outstanding toughness and its cut, wear and excellent chemical resistance, Ultra high molecular weight polyethylene (UHMWPE) is used in a wide diversity of applications. These include can and bottle handling maschine parts, moving parts on weaving maschines, bearings, gears, artificial joints, edge protection on ice rinks and butcher's chopping boards. It competes with Aramid in bulletproof vests, under tradenames Spectra and Dyneema, and is commonly used for the construction or articular portions of implants used for hip and knee replacements.

High density polyrthylene (HDPE) is defined by a density of greater or equal to 0.941 g/cm3. High density polyethylene has a low degree of branching and thus stronger intermolecular forces and tensile strength. High density polyethylene (HDPE) can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. High density polyethylene (HDPE) is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes.