Ultra-high-molecular-weight polyethylene

[3] It embodies all the characteristics of high-density polyethylene (HDPE) with the added traits of being resistant to concentrated acids and alkalis, as well as numerous organic solvents.

Today UHMWPE powder materials, which may be directly molded into a product's final shape, are produced by Ticona, Braskem, Teijin (Endumax), Celanese, and Mitsui.

Because of its resistance to wear and impact, UHMWPE continues to find increasing industrial applications, including the automotive and bottling sectors.

The weak bonding between olefin molecules allows local thermal excitations to disrupt the crystalline order of a given chain piece-by-piece, giving it much poorer heat resistance than other high-strength fibers.

Because olefins have no such groups, UHMWPE does not absorb water readily, nor wet easily, which makes bonding it to other polymers difficult.

The high qualities of UHMWPE filament were discovered by Albert Pennings in 1968, but commercially viable products were made available by DSM in 1990 and Southern Ropes soon after.

For personal armor, the fibers are, in general, aligned and bonded into sheets, which are then layered at various angles to give the resulting composite material strength in all directions.

[14][15] Recently developed additions to the US Military's Interceptor body armor, designed to offer arm and leg protection, are said to utilize a form of UHMWPE fabric.

One notable drawback of UHMWPE rope is its susceptibility to UV damage, so many users will fit winch covers in order to protect the cable when not in use.

In climbing, cord and webbing made of combinations of UHMWPE and nylon yarn have gained popularity for their low weight and bulk.

It is used in skis and snowboards, often in combination with carbon fiber, reinforcing the fiberglass composite material, adding stiffness and improving its flex characteristics.

[clarification needed] The UHMWPE is often used as the base layer, which contacts the snow, and includes abrasives to absorb and retain wax.

UHMWPE was used for the 30 km (19 mi) long, 0.6 mm (0.024 in) thick space tether in the ESA/Russian Young Engineers' Satellite 2 of September, 2007.

In skydiving, UHMWPE is one of the most common materials used for suspension lines, largely supplanting the earlier-used Dacron, being lighter and less bulky.

[citation needed] UHMWPE has excellent strength and wear-resistance, but is not dimensionally stable (i.e. shrinks) when exposed to heat, which leads to gradual and uneven shrinkage of different lines as they are subject to differing amounts of friction during canopy deployment, necessitating periodic line replacement.

For that reason, Dacron lines continue to be used in student and some tandem systems, where the added bulk is less of a concern than the potential for an injurious opening.

In turn, in high-performance parachutes used for swooping, UHMWPE is replaced with Vectran and HMA (high-modulus aramid), which are even thinner and dimensionally stable, but exhibit greater wear and require much more frequent maintenance to prevent catastrophic failure.

These powder materials are produced by Ticona, typically converted into semi-forms by companies such as Quadrant and Orthoplastics,[1] and then machined into implant components and sterilized by device manufacturers.

[25] UHMWPE was first used clinically in 1962 by Sir John Charnley and emerged as the dominant bearing material for total hip and knee replacements in the 1970s.

[1] When gamma irradiated in air, this material exhibited susceptibility to oxidation, resulting in inferior clinical performance relative to virgin UHMWPE.

Today, the poor clinical history of Hylamer is largely attributed to its sterilization method, and there has been a resurgence of interest in studying this material (at least among certain research circles).

Highly cross-linked UHMWPE materials were clinically introduced in 1998 and have rapidly become the standard of care for total hip replacements, at least in the United States.

[1] These new materials are cross-linked with gamma or electron beam radiation (50–105 kGy) and then thermally processed to improve their oxidation resistance.

[1] Five-year clinical data, from several centers, are now available demonstrating their superiority relative to conventional UHMWPE for total hip replacement (see arthroplasty).

The anti-oxidant helps quench free radicals that are introduced during the irradiation process, imparting improved oxidation resistance to the UHMWPE without the need for thermal treatment.