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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 usually between 3.5 and 7.5 million amu.[1] 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.[2]
UHMWPE is odorless, tasteless, and nontoxic.[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.[4] It is highly resistant to corrosive chemicals except oxidizing acids; has extremely low moisture absorption and a very low coefficient of friction; is self-lubricating (see boundary lubrication); 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.[5][6]
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Polymerization of UHMWPE was commercialized in the s by Ruhrchemie AG,[1][7] 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 Ticona, 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 s, UHMWPE has also been the material of choice for total joint arthroplasty in orthopedic and spine implants.[1]
UHMWPE fibers branded as Dyneema, commercialized in the late s 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, sailing, hiking equipment, climbing, and many other industries.
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Structure of UHMWPE, with n greater than 100,000UHMWPE is a type of polyolefin. 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. Each chain is attracted to the others with so many van der Waals forces that the whole of the inter-molecular strength is high. In this way, large tensile loads are not limited as much by the comparative weakness of each localized van der Waals force.
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, Kevlar derives its strength from strong bonding between relatively short molecules.
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. Its melting point is around 130 to 136 °C (266 to 277 °F),[8] and, according to DSM, it is not advisable to use UHMWPE fibres at temperatures exceeding 80 to 100 °C (176 to 212 °F) for long periods of time. It becomes brittle at temperatures below &#;150 °C (&#;240 °F).[9]
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.
When UHMWPE is annealed, the material is heated to between 135 °C (275 °F) and 138 °C (280 °F) in an oven or a liquid bath of silicone oil or glycerine. The material is then cooled down at a rate of 5 °C/h (2.5 °F/ks) to 65 °C (149 °F) or less. Finally, the material is wrapped in an insulating blanket for 24 hours to bring to room temperature.[10]
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Ultra-high-molecular-weight polyethylene (UHMWPE) is synthesized from its monomer ethylene, which is bonded together to form the base polyethylene product. These molecules are several orders of magnitude longer than those of familiar high-density polyethylene (HDPE) due to a synthesis process based on metallocene catalysts, resulting in UHMWPE molecules typically having 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 s. Gel-spinning arrived much later and was intended for different applications.
In gel spinning a precisely heated gel (of a low concentration of UHMWPE in an oil) is extruded through a spinneret. The extrudate is drawn through the air, the oil extracted with a solvent which does not affect the UHMWPE, and then dried removing the solvent. 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.[11]
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LIROS Dyneema hollowDyneema and Spectra are brands of lightweight high-strength oriented-strand gels spun through a spinneret. They have yield strengths as high as 2.4 GPa (350,000 psi) and density as low as 0.97 g/cm (0.087 oz/in) (for Dyneema SK75).[12] High-strength steels have comparable yield strengths, and low-carbon steels have yield strengths much lower (around 0.5 GPa (73,000 psi)). Since steel has a specific gravity of roughly 7.8, these materials have a strength-to-weight ratios eight times that 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 , but commercially viable products were made available by DSM in and Southern Ropes soon after.[13]
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 hosiery, 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 kites 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.[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.[16] A multitude of UHMWPE woven fabrics are available in the market and are used as shoe liners, pantyhose,[17] fencing clothing, stab-resistant vests, and composite liners for vehicles.[18]
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 11 mm (0.43 in) UHMWPE rope of 30 m (98 ft) can weigh around 2 kg (4.4 lb), the equivalent steel wire rope would weigh around 13 kg (29 lb). 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.[19][20]
Ships' hawsers and cables made from the fiber (0.97 specific gravity) float on sea water. "Spectra wires" as they are called in the towing boat community are commonly used for face wires [21] as a lighter alternative to steel wires.
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.[clarification needed]
It is also used in lifting applications, for manufacturing low weight, and heavy duty lifting slings. Due to its extreme abrasion resistance it is also used as an excellent corner protection for synthetic lifting slings.
High-performance lines (such as backstays) for sailing and parasailing are made of UHMWPE, due to their low stretch, high strength, and low weight.[22] Similarly, UHMWPE is often used for winch-launching gliders from the ground, as, in comparison with steel cable, its superior abrasion resistance results in less wear when running along the ground and into the winch, increasing the time between failures. The lower weight on the mile-long cables used also results in higher winch launches.
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, .[23]
Dyneema Composite Fabric (DCF) is a laminated material consisting of a grid of Dyneema threads sandwiched between two thin transparent polyester membranes. This material is very strong for its weight, and was originally developed for use in racing yacht sails under the name 'Cuben Fiber'. More recently it has found new applications, most notably in the manufacture of lightweight and ultralight camping and backpacking equipment such as tents, backpacks, and bear-proof food bags.
In archery, UHMWPE is widely used as a material for bowstrings because of its low creep and stretch compared to, for example, Dacron (PET).[citation needed] Besides pure UHMWPE fibers, most manufacturers use blends to further reduce the creep and stretch of the material. In these blends, the UHMWPE fibers are blended with, for example, Vectran.
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. It is also almost completely inelastic, which can exacerbate the opening shock. 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. UHMWPE are also used for reserve parachute closing loops when used with automatic activation devices, where their extremely low coefficient of friction is critical for proper operation in the event of cutter activation.
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UHMWPE has a clinical history as a biomaterial for use in hip, knee, and (since the s), for spine implants.[1] An online repository of information and review articles related to medical grade UHMWPE, known as the UHMWPE Lexicon, was started online in .[24]
Joint replacement components have historically been made from "GUR" resins. 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 by Sir John Charnley and emerged as the dominant bearing material for total hip and knee replacements in the s.[24] Throughout its history, there were unsuccessful attempts to modify UHMWPE to improve its clinical performance until the development of highly cross-linked UHMWPE in the late s.[1]
One unsuccessful attempt to modify UHMWPE was by blending the powder with carbon fibers. This reinforced UHMWPE was released clinically as "Poly Two" by Zimmer in the s.[1] The carbon fibers had poor compatibility with the UHMWPE matrix and its clinical performance was inferior to virgin UHMWPE.[1]
A second attempt to modify UHMWPE was by high-pressure recrystallization. This recrystallized UHMWPE was released clinically as "Hylamer" by DePuy in the late s.[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).[24] Hylamer fell out of favor in the United States in the late s with the development of highly cross-linked UHMWPE materials, however negative clinical reports from Europe about Hylamer continue to surface in the literature.
Highly cross-linked UHMWPE materials were clinically introduced in 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).[24] Clinical studies are still underway to investigate the performance of highly cross-linked UHMWPE for knee replacement.[24]
In , manufacturers started incorporating anti-oxidants into UHMWPE for hip and knee arthroplasty bearing surfaces.[1] Vitamin E (a-tocopherol) is the most common anti-oxidant used in radiation-cross-linked UHMWPE for medical applications. 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.[26] Several companies have been selling antioxidant-stabilized joint replacement technologies since , using both synthetic vitamin E as well as hindered phenol-based antioxidants.[27]
Another important medical advancement for UHMWPE in the past decade has been the increase in use of fibers for sutures. Medical-grade fibers for surgical applications are produced by DSM under the "Dyneema Purity" trade name.[28]
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UHMWPE is used in the manufacture of PVC (vinyl) windows and doors, as it can endure the heat required to soften the PVC-based materials and is used as a form/chamber filler for the various PVC shape profiles in order for those materials to be 'bent' or shaped around a template.
UHMWPE is also used in the manufacture of hydraulic seals and bearings. It is best suited for medium mechanical duties in water, oil hydraulics, pneumatics, and unlubricated applications. It has a good abrasion resistance but is better suited to soft mating surfaces.
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Fluoropolymer / HMWPE insulation cathodic protection cable is typically made with dual insulation. It features a primary layer of a fluoropolymer such as ECTFE which is chemically resistant to chlorine, sulfuric acid, and hydrochloric acid. Following the primary layer is an HMWPE insulation layer, which provides pliable strength and allows considerable abuse during installation. The HMWPE jacketing provides mechanical protection as well.[29]
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UHMWPE is used in marine structures for the mooring of ships and floating structures in general. The UHMWPE forms the contact surface between the floating structure and the fixed one. Timber was and is used for this application also. UHMWPE is chosen as facing of fender systems for berthing structures because of the following characteristics:[30]
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There are many possibilities available when selecting the appropriate polymers for your special projects, which can make it challenging to make a decision. UHMW plastic could be the best option for you if you&#;re looking for a robust, lightweight, and long-lasting plastic. This plastic, often referred to as Ultra High Molecular Weight Polyethylene frequently goes under the radar and is not widely used by manufacturers and enterprises.
But as it turns out, this plastic is perfect for industrial and commercial uses. For a good reason, too&#;it offers a wealth of advantages over other kinds of plastic available on the market. Look at this:
What is UHMWPE Material?UHMW stands for Ultra High Molecular Weight Polyethylene, as was previously mentioned. This material is robust and adaptable, with good abrasion, impact, and wear resistance while yet being relatively light. The large molecular weight and surface of UHMW&#;between 3 and 6 million molecules&#;are the key to this material&#;s exceptional qualities. Since of this, UHMW is perfect for high-temperature locations because it won&#;t melt or transform into molten liquid.
What is Polyethylene Plastic Used For?
In general, polyethylene plastic has a number of beneficial uses. When precautions must be taken as well, it is appropriate due to its strength and longevity. Let&#;s examine UHMWPE Material and how it may benefit you, spanning a range of commercial and industrial usage.
AutomotivesUHMWPE does not meet the criterion since PTFE is often used in automotive applications in high-temperature settings. However, there are a variety of applications where the components function at room temperature, e.g., automobile doors, seats, hand levers, etc., and UHMWPE can find a lot of use here. We are aware that UHMWPE is employed in the worn strip found within automobile doors. UHMWPE wear strips are often a good, affordable substitute for PTFE wear strips.
InfrastructureAlthough legal limitations forbid the use of materials other than PTFE in POT bearings, there are several sliding bearing applications that do not comply with government regulations and are thus potential uses for UHMWPE. UHMWPE might be used to make plain sliding pads and sliding bearings successfully.
ElectronicsPTFE has historically been utilized as insulation in many electronics component parts. We have successfully tested UHMWPE for these applications in a number of instances and persuaded the customer to switch.
Food Service CabinetryMaterials used in food service must be simple to sanitize while preventing the growth of mold and germs. Additionally, materials must be durable enough to withstand potentially harsh cleansers. UHMW is robust enough to withstand all kinds of cleansers and is rust-resistant. The best part is that it is available in a variety of finishes, making it simple to match a UHMW food shelf to existing decor.
UHMW polyethylene conveyor systemUHMWPE material is ideally suited for conveyor systems because of its capacity to tolerate high temperatures, frequent stress, and chemical exposure. This material is also perfect for making star wheels for conveyor systems, which hasten and effectively move goods through assembly and sorting processes.
UHMW polyethylene dockUHMW is frequently used to make docks and dock fenders for a good cause. This material can survive moisture for a long time and is water-resistant. Additionally, it is resistant to abrasion. Thus there is almost little risk that it will sustain damage when boats crash into it when docking.
Boom Trucks and Outrigger PadsUHMW is frequently used for boom trucks and outrigger pads. UHMWPE Material performs well in these high-stress applications due to its low friction coefficient and excellent impact strength. Outrigger pads can prevent cranes and boom trucks from slipping on unsteady construction sites. Furthermore, UHMWPE Material performs well outdoors since it can withstand a broad range of temperatures.
UHMW Polyethylene Body armorIt might surprise you to hear that impact resistance makes UHMW plastic the perfect material for body armor. Additionally, it is flexible and lightweight, which makes it pleasant to wear and allows it to be twisted into the various sizes and forms required to shape armor properly.
The advantages of UHMWPE include, but are not limited to:Although this can seem like the perfect material, there are a few drawbacks you need to be aware of. UHMWPE is not appropriate for high-temperature applications since it has a lower melting point (297° to 305° F) than several popular polymers. It also has a low coefficient of friction, which may be a disadvantage depending on the application.
Under steady stress, UHMWPE Material yarns can also experience &#;creep,&#; which is a progressive elongation of the fibers. Some individuals would see the cost as a drawback, but with UHMWPE, less really is more. Given this material&#;s robustness, you wouldn&#;t need to purchase as much as you could with other materials.
Still unsure if UHMWPE is the best material for your product? For the benefit of our clients, Service Thread creates and provides engineered yarns and sewing threads to address product and processing issues. We weave proactive, individualized service throughout all we do. Get in touch with us to learn which fiber is suitable for your application.
Final ThoughtsUHMW can be the ideal choice for you if you&#;re looking for a new abrasion-resistant plastic or need one that will last for a long period. Looking at a few of the practical uses that highlight these advantages can encourage you to choose UHMWPE Material for your upcoming project. Please visit the website of Petron Thermoplast and learn more about the product online.
If you are looking for more details, kindly visit Bullet-Proof Helmet.