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Structure and properties
Ultra-high-molecular-weight polyethylene (UHMWPE or sometimes shortened to UHMW), also known as
highmodulus polyethylene (HMPE) or highperformance polyethylene (HPPE), is a subset of the thermoplastic
polyethylene. It has extremely long chains, with molecular weight numbering in the millions, usually between
2 and 6 million. The longer chain serves to transfer load more effectively to the polymer backbone by
strengthening intermolecular interactions. This results in a very tough material, with the highest impact strength
of any thermoplastic presently made1] It is highly resistant to corrosive chemicals with exception of oxidizing
acids; has extremely low moisture absorption and a very low coefficient of friction; is self-lubricating; and is highly resistant to abrasion, in some forms being 15 times more resistant to abrasion than
carbon steel. Its coefficient of friction is significantly lower than that of nylon and acetal, and is comparable
to that of polytetrafluoroethylene (PTFE, Teflon), but UHMWPE has better abrasion resistance than PTFE.[2][3] It is odorless, tasteless, and nontoxic.
The simple structure of the molecule also gives rise to surface and chemical properties that are rare in high-performance polymers. For example, the polar groups in most polymers easily bond to water. Because olefins
have no such groups, UHMWPE does not absorb water readily, nor wet easily, which makes bonding it to other
polymers difficult. For the same reasons, skin does not interact with it strongly, making the UHMWPE fiber
surface feel slippery. In a similar manner, aromatic polymers are often susceptible to aromatic solvents due to
aromatic stacking interactions, an effect aliphatic polymers like UHMWPE are immune to. Since UHMWPE
does not contain chemical groups (such as esters, amides or hydroxylic groups) that are susceptible to attack
from aggressive agents, it is very resistant to water, moisture, most chemicals, UV radiation, and micro-organisms.
Under tensile load, UHMWPE will deform continually as long as the stress is present—an effect called creep.
Production
UHMWPE is processed using the following methods: compression molding, ram extrusion, gel spinning, and
sintering.
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