Ultra-high-molecular-weight polyethylene 1

Ultra-high-molecular-weight polyethyleneUltra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene.Also known as high-modulus polyethylene, (HMPE), or high-performance polyethylene (HPPE), it hasextremely long chains, with a molecular weight usually between 2 and 6 million. The longer chain serves to transferload more effectively to the polymer backbone by strengthening intermolecular interactions. This results in a verytough material, with the highest impact strength of any thermoplastic presently made.[1]

UHMWPE is odorless, tasteless, and nontoxic.[2] 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; and is highlyresistant to abrasion, in some forms being 15 times more resistant to abrasion than carbon steel. Its coefficient offriction 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.[3][4]

DevelopmentPolymerisation of UHMWPE was commercialised in the 1950s by Ruhrchemie AG, which changed names over theyears. Today UHMWPE powder materials, which may be directly molded into a product's final shape, are producedby Ticona, Braskem, and Mitsui. Processed UHMWPE is available commercially either as fibers or in consolidatedform, such as sheets or rods. Because of its resistance to wear and impact, UHMWPE continues to find increasingindustrial applications, including the automotive and bottling sectors. Since the 1960s, UHMWPE has also been thematerial of choice for total joint arthroplasty in orthopedic and spine implants.[5]

UHMWPE fibers, commercialized in the late 1970s by the Dutch chemical company DSM, are widely used inballistic protection, defense applications, and increasingly in medical devices.

Structure and properties

Structure of UHMWPE, with ngreater than 100,000

UHMWPE is a type of polyolefin. It is made up of extremely long chains ofpolyethylene, which all align in the same direction. It derives its strength largelyfrom the length of each individual molecule (chain). Van der Waals bonds betweenthe 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 theability to carry larger shear forces from molecule to molecule. Each chain isbonded to the others with so many Van der Waals bonds that the whole of theinter-molecule strength is high. In this way, large tensile loads are not limited asmuch by the comparative weakness of each Van der Waals bond.

When formed to fibers, the polymer chains can attain a parallel orientation greaterthan 95% and a level of crystallinity from 39% to 75%. In contrast, Kevlar derives its strength from strong bondingbetween relatively short molecules.

The weak bonding between olefin molecules allows local thermal excitations to disrupt the crystalline order of agiven chain piece-by-piece, giving it much poorer heat resistance than other high-strength fibers. Its melting point isaround 130 to 136 °C (266 to 277 °F),[6] and, according to DSM, it is not advisable to use UHMWPE fibers attemperatures exceeding 80 to 100 °C (176 to 212 °F) for long periods of time. It becomes brittle at temperaturesbelow −150 °C (−240 °F).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

Ultra-high-molecular-weight polyethylene 2

polymers difficult. For the same reasons, skin does not interact with it strongly, making the UHMWPE fiber surfacefeel slippery. In a similar manner, aromatic polymers are often susceptible to aromatic solvents due to aromaticstacking interactions, an effect aliphatic polymers like UHMWPE are immune to. Since UHMWPE does not containchemical 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 135 °C to 138 °C in an oven or a liquid bath of silicone oil orglycerine. The material is then cooled down at a rate of 5 °C/h to 65 °C or less. Finally, the material is wrapped in aninsulating blanket for 24 hours to bring to room temperature.[7]

ProductionUHMWPE is synthesized from monomer of ethylene, which are bonded together to form the base polyethyleneproduct. These ultra-high-molecular-weight polyethylene molecules are several orders of magnitude longer thanthose 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 comparedto HDPE's 700 to 1,800monomers.UHMWPE is processed varously by compression molding, ram extrusion, gel spinning, and sintering. SeveralEuropean companies began compression molding UHMW in the early 1960s. Gel-spinning arrived much later andwas intended for different applications.In gel spinning a precisely heated gel of UHMWPE is extruded through a spinneret. The extrudate is drawn throughthe air and then cooled in a water bath. The end-result is a fiber with a high degree of molecular orientation, andtherefore exceptional tensile strength. Gel spinning depends on isolating individual chain molecules in the solvent sothat intermolecular entanglements are minimal. Entanglements make chain orientation more difficult, and lower thestrength of the final product.[8]

Applications

FiberDyneema and Spectra are lightweight high-strength oriented-strand gel spun through a spinneret. They have yieldstrengths as high as 2.4 GPa (350,000 psi) and specific gravity as low as 0.97 (for Dyneema SK75).[9] High-strengthsteels have comparable yield strengths, and low-carbon steels have yield strengths much lower (around 0.5 GPa).Since steel has a specific gravity of roughly 7.8, this gives strength-to-weight ratios for these materials in a rangefrom 8 to 15 times higher than steel. Strength-to-weight ratios for Dyneema are about 40% higher than for aramid.UHMWPE fibers are used in armor, in particular, personal armor and on occasion as vehicle armor, cut-resistantgloves, bow strings, climbing equipment, fishing line, spear lines for spearguns, high-performance sails, suspensionlines on sport parachutes and paragliders, rigging in yachting, kites, and kites lines for kites sports. Spectra is alsoused as a high-end wakeboard line.For personal armor, the fibers are, in general, aligned and bonded into sheets, which are then layered at variousangles to give the resulting composite material strength in all directions.[10][11] Recently developed additions to theUS Military's Interceptor body armor, designed to offer arm and leg protection, are said to utilize a form of Spectraor Dyneema fabric.[12] Dyneema provides puncture resistance to protective clothing in the sport of fencing.Spun UHMWPE fibers excel as fishing line, as they have less stretch, are more abrasion-resistant, and are thinnerthan traditional monofilament line.In climbing, cord and webbing made of combinations of UHMWPE and nylon yarn have gained popularity for their low weight and bulk, though, unlike their nylon counterparts, they exhibit very low elasticity, making them

Ultra-high-molecular-weight polyethylene 3

unsuitable for limiting forces in a fall. Also, low elasticity translates to low toughness. The fiber's very high lubricityleads to poor knot-holding ability, and has led to the recommendation to use the triple fisherman's knot rather thanthe traditional double fisherman's knot in 6mm UHMWPE core cord to avoid a particular failure mechanism of thedouble fisherman's, where first the sheath fails at the knot, then the core slips through.[13][14]

Owing to its low density, ships' hawsers and cables can be made from the fibre, and float on sea water. "SpectraWires" as they are called in the towboat community are commonly used for face wires as a lighter alternative to steelwires.It is used in skis and snowboards, often in combination with carbon fiber, reinforcing the fiberglass compositematerial, adding stiffness and improving its flex characteristics. The UHMWPE is often used as the base layer,which contacts the snow, and includes abrasives to absorb and retain wax.It is also used in lifting applications for manufacturing low weight, and heavy duty lifting slings . Due to its extremeabrasion 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 lowstretch, high strength, and low weight.[15]

Dyneema was used for the 30-kilometre space tether in the ESA/Russian Young Engineers' Satellite 2 of September,2007.

MedicalUHMWPE has over 40 years of clinical history as a successful biomaterial for use in hip, knee, and (since the1980s), for spine implants.[5] An online repository of information and review articles related to medical gradeUHMWPE, known as the UHMWPE Lexicon, was started online in 2000.[16]

Joint replacement components have historically been made from "GUR" resins. These powder materials areproduced by Ticona, typically converted into semi-forms by companies such as Quadrant and Orthoplastics,[5] andthen machined into implant components and sterilised by device manufacturers.[17]

UHMWPE was first used clinically in 1962 by Sir John Charnley and emerged as the dominant bearing material fortotal hip and knee replacements in the 1970s. Details about the "discovery" of UHMWPE for orthopedic applicationsby Charnley and his engineering associate Harry Craven are available[16] Throughout its history, there wereunsuccessful attempts to modify UHMWPE to improve its clinical performance until the development of highlycrosslinked UHMWPE in the late 1990s.[5]

One unsuccessful attempt to modify UHMWPE was by blending the powder with carbon fibers. This reinforcedUHMWPE was released clinically as "Poly Two" by Zimmer in the 1970s.[5] The carbon fibers had poorcompatibility with the UHMWPE matrix and its clinical performance was inferior to virgin UHMWPE.[5]

A second attempt to modify UHMWPE was by high-pressure recrystallisation. This recrystallised UHMWPE wasreleased clinically as "Hylamer" by DePuy in the late 1980s.[5] When gamma irradiated in air, this material exhibitedsusceptibility to oxidation, resulting in inferior clinical performance related to virgin UHMWPE. Today, the poorclinical history of Hylamer is largely attributed to its sterilisation method, and there has been a resurgence of interestin studying this material (at least among certain research circles).[16] Hylamer fell out of favor in the United States inthe late 1990s with the development of highly crosslinked UHMWPE materials, however negative clinical reportsfrom Europe about Hylamer continue to surface in the literature.Highly crosslinked UHMWPE materials were clinically introduced starting in 1998 and have rapidly become thestandard of care for total hip replacements, at least in the United States.[5] These new materials are crosslinked withgamma or electron beam radiation (50–105 kGy) and then thermally processed to improve their oxidationresistance.[5] Five-year clinical data, from several centers, are now available demonstrating their superiority relativeto conventional UHMWPE for total hip replacement (see Arthroplasty).[16] Clinical studies are still underway toinvestigate the performance of highly crosslinked UHMWPE for knee replacement.[16]

Ultra-high-molecular-weight polyethylene 4

Another important medical advancement for UHMWPE in the past decade has been the increase in use of fibers forsutures. Medical-grade fibers for surgical applications are produced by DSM under the "Dyneema Purity" tradename.

ManufacturingUHMWPE is used in the manufacture of PVC (vinyl) windows and doors, as it can stand up to the heat required tosoften the PVC-based materials and is used as a form/chamber filler for the various PVC shape profiles in order forthose 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 mechanicalduties in water, Oil Hydraulics, pneumatics, and unlubricated applications. It has a good abrasion resistance but isbetter suited to soft mating surfaces.

Wire/CableHALAR cathodic protection cable is made of a fluoropolymer insulation that exhibits superior chemical resistance.Made with dual insulation, HALAR wire can be used in any situation where chlorine and hydrogen gases arepresent. HALAR cable is made with a primary layer, which is most resistant to chlorine, sulfuric acid andhydrochloric acid. Following the primary layer is a high molecular weight polyethylene (HMWPE) insulation, whichprovides pliable strength and allows considerable abuse during installation. The HMWPE jacketing providesmechanical protection as well.[18]

References[1] Stein, H. L. (1998). Ultrahigh molecular weight polyethylenes (uhmwpe). Engineered Materials Handbook, 2, 167–171.[2] D.W.S. Wong, W.M. Camirand, A.E. Pavlath J.M. Krochta, E.A. Baldwin, M.O. Nisperos-Carriedo (Eds.), Development of edible coatings

for minimally processed fruits and vegetables. Edible coatings and films to improve food quality, Technomic Publishing Company, Lancaster,PA (1994), pp. 65–88

[3] Tong, Jin; Ma, Yunhai; Arnell, R.D.; Ren, Luquan (2006). "Free abrasive wear behavior of UHMWPE composites filled with wollastonitefibers". Composites Part A: Applied Science and Manufacturing 37: 38. doi:10.1016/j.compositesa.2005.05.023.

[4] Budinski, Kenneth G. (1997). "Resistance to particle abrasion of selected plastics". Wear 203–204: 302.doi:10.1016/S0043-1648(96)07346-2.

[5] Steven M. Kurtz (2004). The UHMWPE handbook: ultra-high molecular weight polyethylene in total joint replacement (http:/ / books.google. com/ books?id=bkuFjppEdMcC). Academic Press. ISBN 978-0-12-429851-4. . Retrieved 19 September 2011.

[6] http:/ / chemyq. com/ En/ xz/ xz4/ 39468nvyng. htm[7][7] Hoechst: Annealing (Stress Relief) of Hostalen GUR[8] A.J. Pennings, R.J. van der Hooft, A.R. Postema, W. Hoogsteen, and G. ten Brinke (1986). "High-speed gel-spinning of ultra-high molecular

weight polyethylene" (http:/ / msc. eldoc. ub. rug. nl/ FILES/ root/ BrinkeGten/ 1986/ PolymBullPennings/ 1986PolymBullPennings. pdf).Polymer Bulletin 16 (2–3): 167–174. doi:10.1007/BF00955487. .

[9] Tensile and creep properties of UHMWPE fibres (http:/ / web. archive. org/ web/ 20060927232646/ http:/ / www-lgm2b. iut. u-bordeaux1. fr/publi/ PE+ fibre. pdf). Retrieved on 2012-06-30.

[10] "Dyneema" (http:/ / www. tote. com. au/ dyneema. htm). Tote Systems Australia. .[11] Lightweight ballistic composites: Military and law-enforcement applications. ed. A Bhatnagar, Honeywell International[12] Monty Phan, Lou Dolinar (February 27, 2003). "Outfitting the Army of One – Technology has given today's troops better vision, tougher

body armor, global tracking systems – and more comfortable underwear" (Nassau and Queens edition ed.). Newsday. pp. B.06.[13] Tom Moyer, Paul Tusting, Chris Harmston (2000). "Comparative Testing of High Strength Cord" (http:/ / www. xmission. com/ ~tmoyer/

testing/ High_Strength_Cord. pdf) (PDF). .[14] "Cord testing" (http:/ / www. xmission. com/ ~tmoyer/ testing/ High_Strength_Cord. pdf) (PDF). .[15] AMSTEEL (http:/ / www. samsonrope. com/ index. cfm?rope=190). samsonrope.com[16] UHMWPE Lexicon (http:/ / www. uhmwpe. org). Uhmwpe.org. Retrieved on 2012-06-30.[17] GHR® HMW-PE and VHMW-PE (http:/ / web. archive. org/ web/ 20080515221838/ http:/ / www. ticona. com/ redesign/ index/ products/

gur-uhmw-pe/ ghr. htm). ticona.com[18] Cathodic Protection Cable Spreadsheet (http:/ / www. performancewire. com/ halar_cathodicpro. htm)

Ultra-high-molecular-weight polyethylene 5

Further reading• Southern et al., The Properties of Polyethylene Crystallized Under the Orientation and Pressure Effects of a

Pressure Capillary Viscometer, Journal of Applied Polymer Science vol. 14, pp. 2305–2317 (1970).• Kanamoto, On Ultra-High Tensile by Drawing Single Crystal Mats of High Molecular Weight Polyethylene,

Polymer Journal vol. 15, No. 4, pp. 327–329 (1983).

External links• US Patent 5342567 Process for producing high tenacity and high modulus polyethylene fibers, issued 1994-08-30

(http:/ / www. patentstorm. us/ patents/ 5342567-description. html)• Polymer Gel Spinning Machine (http:/ / dspace. mit. edu/ handle/ 1721. 1/ 34092) Christine A. Odero, MIT, 1994• Patent application 20070148452 High strength polyethylene fiber, 2007-06-28 (http:/ / www. freshpatents. com/

High-strength-polyethylene-fiber-dt20070628ptan20070148452. php)

Article Sources and Contributors 6

Article Sources and ContributorsUltra-high-molecular-weight polyethylene  Source: http://en.wikipedia.org/w/index.php?oldid=534976286  Contributors: 2006sf, Abidder, Agentilini, Ali@gwc.org.uk, Amatulic,AnarchMonarch, Aszazin, AxeMan, BD2412, BenFrantzDale, Berlioz26, Bhudson, BrianSfinasSSI, BritishWatcher, Buddy431, CB216A, Cacycle, Casito, ChemGardener, Chenyaxi, Chris thespeller, CiaPan, Cmokeefe, Cmsjustin, DCGarland, Deli nk, Deus257, Dietrich1958, Disgronification, DocWatson42, Dougher, Drphilharmonic, Dubhbairn, Dwane E Anderson, Dyneemapurity,Edgar181, Egel, El0i, EnZero, Eone22, Erockrph, Evand, Fcsuper, GLaDOS, Garlandmfg, Gene Nygaard, Gracefool, GregorB, Hankwang, HappyCamper, Hermanoere, Hooperbloob, Ingolfson,IraqVet225, Iridium77, JHunterJ, Julesd, Karnesky, Knuck, Lamro, LeadSongDog, LorenzoB, Lylegordon, Magma, Marcika, Marcus Qwertyus, Markguitar333, Marshalldunn, Materialscientist,Mbvanleeuwen, Michael Hardy, Mike.lifeguard, Mjharding42, Mmeijeri, MrBell, Msjayhawk, NescioNomen, Nihiltres, Nlu, Nprayag, Od Mishehu, Ordosingularis, Ossipewsk, Ouroboros0427,Peak, Peterlewis, PlasticsData, Polyparadigm, Polyplas, Prari, Prillen, Pro crast in a tor, Ratagonia, Rettetast, Rjwilmsi, Rl, RobertStar20, Robinwillems, Ronz, Rracecarr, Rstehr, ST47,Saurabhwork, Saxifrage, Selket, Shaddack, Shadowlynk, Slu2com, Spdelta3, Steven M. Kurtz, Ph.D., Stone, Superowls, TeaDrinker, Themfromspace, Triplesdynamics, Uprightcomm,Uruiamme, Vectro, Verbify, VincentBaas, Wikiuser100, William Avery, Wizard191, Ww, Xcomradex, Ziggy Sawdust, 189 anonymous edits

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