Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene. Also known as high-modulus polyethylene (HMPE), it has extremely long chains, with a molecular mass typically between 2 and 6 million daltons. 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 made.
UHMWPE is odorless, tasteless, and nontoxic. It embodies all the characteristics of high-density polyethylene (HDPE), i.e., being resistant to acids, alkalis, and many corrosive chemicals except some oxidizing acids. It has extremely low moisture absorption and a very low coefficient of friction; is self-lubricating (see boundary lubrication); and is highly resistant to abrasion. 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.
Development Polymerization of UHMWPE was commercialized in the 1950s by Ruhrchemie AG, which has changed names over the years. Today UHMWPE powder materials, which may be directly molded into a product's final shape, are produced by Braskem, Teijin (Endumax), Celanese, and Mitsui. Processed UHMWPE is available commercially either as fibers or in consolidated form, such as sheets or rods. Because of its resistance to wear and impact, UHMWPE continues to find increasing industrial applications, including the automotive and bottling sectors. Since the 1960s, UHMWPE has also been the material of choice for total joint arthroplasty in orthopedic and spine implants.
UHMWPE fibers branded as Dyneema, commercialized in the late 1970s by the Dutch chemical company DSM, and as Spectra, commercialized by Honeywell (then AlliedSignal), are widely used in ballistic protection, defense applications, and increasingly in medical devices, protective motorcycling gear, sailing, hiking equipment, climbing, and many other industries.
Structure and properties
UHMWPE is a type of polyethylene. It is made up of extremely long chains of polyethylene, which all align in the same direction. It derives its strength largely from the length of each individual molecule (chain). Van der Waals forces between the molecules are relatively weak for each atom of overlap between the molecules, but because the molecules are very long, large overlaps can exist, adding up to the ability to carry larger shear forces from molecule to molecule.
When formed into fibers, the polymer chains can attain a parallel orientation greater than 95% and a level of crystallinity from 39% to 75%. In contrast, aramid derives its strength from strong bonding between relatively short molecules.
Its heat resistance is poorer than other high-strength fibers. Its melting point onset is , and, according to DSM, it is not advisable to use UHMWPE fibres at temperatures exceeding for long periods of time. It becomes brittle at temperatures below .
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 does it 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.
When UHMWPE is annealed, the material is heated to between in an oven or a liquid bath of silicone oil or glycerine. The material is then cooled down to at a rate of or less. Finally, the material is wrapped in an insulating blanket for 24 hours to bring to room temperature.
UHMWPE is considered a relatively low-modulus material, with tensile strength and hardness values lower than those of many other high-performance polymers. Typical tensile yield strength values range from . The Shore D hardness is approximately 60 to 65, which is slightly lower than that of high-density polyethylene (HDPE). Despite its lower modulus, the extremely long polymer chains and high molecular weight give UHMWPE exceptional toughness and impact resistance.
UHMWPE exhibits the highest impact strength of any thermoplastic, and in standard notched Izod tests specimens often do not break (values > ). Its elongation at break can reach , and its lower chain-packing efficiency gives a density of about , a little lower than that of HDPE.
Production UHMWPE is produced by polymerization of ethylene. Many kinds of polyethylene can be prepared but the UHMW variety requires very active catalysts and high pressures of ethylene. Catalysis is effected by coordination polymerization, which involves metallocene (Kaminsky catalysts) or Ziegler-Natta catalysts.
The resulting UHMWPE molecules typically have 100,000 to 250,000 monomer units per molecule each compared to HDPE's 700 to 1,800 monomers.
UHMWPE is processed variously by compression moulding, ram extrusion, gel spinning, and sintering. Several European companies began compression molding UHMWPE in the early 1960s. Gel-spinning arrived much later and was intended for different applications. The two major producers of UHMWPE yarns via gel spinning are Honeywell and DSM. There are also several Chinese based manufacturers for UHMWPE yarn.
There are two major routes for gel spinning UHMWPE. In both routes, a precisely heated gel is created. In one route the gel is made from a mixture of UHMWPE powder and oil. In the other route, the powder is mixed with decalin. Both routes use very low concentrations of UHMWPE in the suspension (~5%).
The suspension is extruded through a spinneret. The extrudate is drawn through the air.
In the case where decalin is used, the decalin is left to evaporate from the yarn. When producing at industrial levels, this decalin can be recovered and recycled.
When oil is used to suspend UHMWPE, the oil extracted with a solvent (typically hexane or dichloromethane which does not affect the UHMWPE, and then dried removing the solvent. Again at large scales these hazardous solvents can be captured.
It has been reported that for every kilogram of UHMWPE yarn that is manufactured, of oil is required. Furthermore, the removal of this oil requires between of hexane.
Following the decalin or oil removal process, the partially orientated yarn is transported through heated ovens to draw the yarn. At industrial scale, these ovens can be over long. This aligns the crystal structure of the UHMWPE and enables the yarn to reach very high tensile strengths.
The end-result is a fiber with a high degree of molecular orientation, and therefore exceptional tensile strength. Gel spinning depends on isolating individual chain molecules in the solvent so that intermolecular entanglements are minimal. Entanglements make chain orientation more difficult, and lower the strength of the final product.
Recently, an alternative route for manufacturing UHMWPE yarn has been developed utilising supercritical carbon dioxide. This new route has been shown to be much more environmentally friendly than the conventional route. Specifically, the use of carbon dioxide as a solvent has been reported to reduce the carbon footprint of the manufacturing route by more than 50%. The use of supercritical carbon dioxide as a solvent enables the mineral oil to be recovered from the partially oriented yarn and recycled. Additionally, it eliminates the need for any hexane, dichloromethane or decalin use within the manufacturing process.
The company behind this new development (FET) recently won a TechTextil 2026 Innovation Award for new technology.
Applications
Fiber
Dyneema, Spectra, and Cortex are brands of lightweight high-strength oriented-strand gels spun through a spinneret. They have yield strengths as high as and density as low as (for Dyneema SK75). High-strength steels have comparable yield strengths, and low-carbon steels have yield strengths much lower (around ). Since steel has a specific gravity of roughly 7.8, these materials have strength-to-weight ratios eight times those of high-strength steels. Strength-to-weight ratios for UHMWPE are about 40% higher than for aramid. 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.
Derivatives of UHMWPE yarn are used in composite plates in armor, in particular, personal armor and on occasion as vehicle armor. Civil applications containing UHMWPE fibers are cut-resistant gloves, tear-resistant pantyhose, bow strings, climbing equipment, automotive winching, fishing line, spear lines for spearguns, high-performance sails, suspension lines on sport parachutes and paragliders, rigging in yachting, kites, and kite lines for kite sports.
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. 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. A multitude of UHMWPE woven fabrics are available in the market and are used as shoe liners, pantyhose, fencing clothing, stab-resistant vests, and composite liners for vehicles.
The use of UHMWPE rope for automotive winching offers several advantages over the more common steel wire rope. The key reason for changing to UHMWPE rope is improved safety. The lower mass of UHMWPE rope, coupled with significantly lower elongation at breaking, carries far less energy than steel or nylon, which leads to almost no snap-back. UHMWPE rope does not develop kinks that can cause weak spots, and any frayed areas that may develop along the surface of the rope cannot pierce the skin like broken steel wire strands can. UHMWPE rope is less dense than water, making water recoveries easier as the recovery cable is easier to locate than wire rope. The bright colours available also aid with visibility should the rope become submerged or dirty. Another advantage in automotive applications is the reduced weight of UHMWPE rope over steel cables. A typical UHMWPE rope of can weigh around , the equivalent steel wire rope would weigh around . 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. It is also vulnerable to heat damage from contact with hot components.
Spun UHMWPE fibers excel as fishing line, as they have less stretch, are more abrasion-resistant, and are thinner than the equivalent monofilament line.
In climbing, cord and webbing made of combinations of UHMWPE and nylon yarn have gained popularity for their low weight and bulk. They exhibit very low elasticity compared to their nylon counterparts, which translates to low toughness. The fiber's very high lubricity causes poor knot-holding ability, and it is mostly used in pre-sewn 'slings' (loops of webbing)—relying on knots to join sections of UHMWPE is generally not recommended, and if necessary it is recommended to use the triple fisherman's knot rather than the traditional double fisherman's knot.