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81-442: UHMWPE is odorless, tasteless, and nontoxic. 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. 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

162-476: A carbonyl group C=O, which is a divalent group at C atom, which gives rise to 120° C–C–O and O–C–O angles. Unlike amides , carboxylic acid esters are structurally flexible functional groups because rotation about the C–O–C bonds has a low barrier. Their flexibility and low polarity is manifested in their physical properties; they tend to be less rigid (lower melting point) and more volatile (lower boiling point) than

243-425: A carboxylic acid ( R−C(=O)−OH ) and an alcohol ( R'−OH ), forming an ester ( R−C(=O)−O−R' ), where R stands for any group (typically hydrogen or organyl) and R ′ stands for organyl group. Organyl esters of carboxylic acids typically have a pleasant smell; those of low molecular weight are commonly used as fragrances and are found in essential oils and pheromones . They perform as high-grade solvents for

324-444: A dehydrating agent: The equilibrium constant for such reactions is about 5 for typical esters, e.g., ethyl acetate. The reaction is slow in the absence of a catalyst. Sulfuric acid is a typical catalyst for this reaction. Many other acids are also used such as polymeric sulfonic acids . Since esterification is highly reversible, the yield of the ester can be improved using Le Chatelier's principle : Reagents are known that drive

405-619: A broad array of plastics , plasticizers , resins , and lacquers , and are one of the largest classes of synthetic lubricants on the commercial market. Polyesters are important plastics, with monomers linked by ester moieties . Esters of phosphoric acid form the backbone of DNA molecules. Esters of nitric acid , such as nitroglycerin , are known for their explosive properties. There are compounds in which an acidic hydrogen of acids mentioned in this article are not replaced by an organyl, but by some other group. According to some authors, those compounds are esters as well, especially when

486-955: A combination of hyperconjugation and dipole minimization effects. The preference for the Z conformation is influenced by the nature of the substituents and solvent, if present. Lactones with small rings are restricted to the s -trans (i.e. E ) conformation due to their cyclic structure. Esters derived from carboxylic acids and alcohols are more polar than ethers but less polar than alcohols. They participate in hydrogen bonds as hydrogen-bond acceptors, but cannot act as hydrogen-bond donors, unlike their parent alcohols. This ability to participate in hydrogen bonding confers some water-solubility. Because of their lack of hydrogen-bond-donating ability, esters do not self-associate. Consequently, esters are more volatile than carboxylic acids of similar molecular weight. Esters are generally identified by gas chromatography, taking advantage of their volatility. IR spectra for esters feature an intense sharp band in

567-529: A good abrasion resistance but is better suited to soft mating surfaces. 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. UHMWPE

648-453: 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), and, according to DSM, it

729-430: A malfunction instead of shattering and becoming shrapnel like the other materials. Milk bottles, jugs, and other hollow goods manufactured through blow molding are the most important application area for HDPE, accounting for one-third of worldwide production, or more than 8 million tonnes. Above all, China, where beverage bottles made from HDPE were first imported in 2005, is a growing market for rigid HDPE packaging as

810-565: A part of metal and metalloid alkoxides , of which many hundreds are known, could be classified as esters of the corresponding acids (e.g. aluminium triethoxide ( Al(OCH 2 CH 3 ) 3 ) could be classified as an ester of aluminic acid which is aluminium hydroxide , tetraethyl orthosilicate ( Si(OCH 2 CH 3 ) 4 ) could be classified as an ester of orthosilicic acid , and titanium ethoxide ( Ti(OCH 2 CH 3 ) 4 ) could be classified as an ester of orthotitanic acid ). Esters derived from carboxylic acids and alcohols contain

891-464: 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. 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

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972-518: A result of its improving standard of living . In India and other highly populated, emerging nations, infrastructure expansion includes the deployment of pipes and cable insulation made from HDPE. The material has benefited from discussions about possible health and environmental problems caused by PVC and polycarbonate associated bisphenol A (BPA), as well as its advantages over glass, metal, and cardboard. Industrial production of HDPE from ethylene happens through either Ziegler-Natta polymerization or

1053-893: 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 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 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,

1134-469: 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 1960s. Gel-spinning arrived much later and

1215-684: Is γ-valerolactone . An uncommon class of esters are the orthoesters . One of them are the esters of orthocarboxylic acids. Those esters have the formula RC(OR′) 3 , where R stands for any group (organic or inorganic) and R ′ stands for organyl group. For example, triethyl orthoformate ( HC(OCH 2 CH 3 ) 3 ) is derived, in terms of its name (but not its synthesis) from esterification of orthoformic acid ( HC(OH) 3 ) with ethanol . Esters can also be derived from inorganic acids. Inorganic acids that exist as tautomers form two or more types of esters. Some inorganic acids that are unstable or elusive form stable esters. In principle,

1296-529: Is a dibutylstannylene ester of lauric acid , and the Phillips catalyst CrO 2 (OSi(OCH 3 ) 3 ) 2 is a trimethoxysilyl ester of chromic acid ( H 2 CrO 4 ). The word ester was coined in 1848 by a German chemist Leopold Gmelin , probably as a contraction of the German Essigäther , " acetic ether ". The names of esters that are formed from an alcohol and an acid, are derived from

1377-403: Is a thermoplastic polymer produced from the monomer ethylene . It is sometimes called "alkathene" or " polythene " when used for HDPE pipes . With a high strength-to-density ratio, HDPE is used in the production of plastic bottles , corrosion-resistant piping, geomembranes and plastic lumber . HDPE is commonly recycled, and has the number "2" as its resin identification code . In 2008,

1458-399: 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

1539-677: 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

1620-458: Is also an equilibrium process – essentially the reverse of the Fischer esterification reaction. Because an alcohol (which acts as the leaving group) and water (which acts as the nucleophile) have similar p K a values, the forward and reverse reactions compete with each other. As in transesterification, using a large excess of reactant (water) or removing one of the products (the alcohol) can promote

1701-648: Is considered too hazardous and expensive for large-scale applications. Carboxylic acids are esterified by treatment with epoxides , giving β-hydroxyesters: This reaction is employed in the production of vinyl ester resin from acrylic acid . Alcohols react with acyl chlorides and acid anhydrides to give esters: The reactions are irreversible simplifying work-up . Since acyl chlorides and acid anhydrides also react with water, anhydrous conditions are preferred. The analogous acylations of amines to give amides are less sensitive because amines are stronger nucleophiles and react more rapidly than does water. This method

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1782-687: Is critical for proper operation in the event of cutter activation. UHMWPE has a clinical history as a biomaterial for use in hip, knee, and (since the 1980s), for spine implants. An online repository of information and review articles related to medical grade UHMWPE, known as the UHMWPE Lexicon, was started online in 2000. 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, and then machined into implant components and sterilized by device manufacturers. UHMWPE

1863-605: Is employed only for laboratory-scale procedures, as it is expensive. Trimethyloxonium tetrafluoroborate can be used for esterification of carboxylic acids under conditions where acid-catalyzed reactions are infeasible: Although rarely employed for esterifications, carboxylate salts (often generated in situ ) react with electrophilic alkylating agents , such as alkyl halides , to give esters. Anion availability can inhibit this reaction, which correspondingly benefits from phase transfer catalysts or such highly polar aprotic solvents as DMF . An additional iodide salt may, via

1944-481: 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 . 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 as a lighter alternative to steel wires. It is used in skis and snowboards, often in combination with carbon fiber , reinforcing

2025-428: 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. Polymerization of UHMWPE was commercialized in the 1950s by Ruhrchemie AG, which has changed names over

2106-554: 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). 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

2187-429: 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

2268-603: Is one illustrative example. The carbonylation of methanol yields methyl formate , which is the main commercial source of formic acid . The reaction is catalyzed by sodium methoxide : In hydroesterification , alkenes and alkynes insert into the O−H bond of carboxylic acids. Vinyl acetate is produced industrially by the addition of acetic acid to acetylene in the presence of zinc acetate catalysts: Vinyl acetate can also be produced by palladium -catalyzed reaction of ethylene, acetic acid , and oxygen : Silicotungstic acid

2349-442: Is resistant to many different solvents , and is exceptionally challenging to glue; joints are typically made by welding. The physical properties of HDPE can vary depending on the molding process that is used to manufacture a specific sample; to some degree, a determining factor is the international standardized testing methods employed to identify these properties for a specific process. For example, in rotational molding, to identify

2430-499: Is used as an acyl-transfer catalyst . Another method for the dehydration of mixtures of alcohols and carboxylic acids is the Mitsunobu reaction : Carboxylic acids can be esterified using diazomethane : Using this diazomethane, mixtures of carboxylic acids can be converted to their methyl esters in near quantitative yields, e.g., for analysis by gas chromatography . The method is useful in specialized organic synthetic operations but

2511-452: 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: High-density polyethylene High-density polyethylene ( HDPE ) or polyethylene high-density ( PEHD )

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2592-495: Is used in the production of ethyl acetate from acetaldehyde . Esters are less reactive than acid halides and anhydrides. As with more reactive acyl derivatives, they can react with ammonia and primary and secondary amines to give amides, although this type of reaction is not often used, since acid halides give better yields. Esters can be converted to other esters in a process known as transesterification . Transesterification can be either acid- or base-catalyzed, and involves

2673-411: Is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene: The Tishchenko reaction involves disproportionation of an aldehyde in the presence of an anhydrous base to give an ester. Catalysts are aluminium alkoxides or sodium alkoxides. Benzaldehyde reacts with sodium benzyloxide (generated from sodium and benzyl alcohol ) to generate benzyl benzoate . The method

2754-561: Is usually economic: HDPE is also used for cell liners in United States subtitle D sanitary landfills , wherein large sheets of HDPE are either extrusion welded or wedge welded to form a homogeneous chemical-resistant barrier, with the intention of preventing the pollution of soil and groundwater by the liquid constituents of solid waste . HDPE is preferred by the pyrotechnics trade for mortars over steel or PVC tubes, being more durable and safer: HDPE tends to rip or tear in

2835-419: 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

2916-500: The Finkelstein reaction , catalyze the reaction of a recalcitrant alkyl halide. Alternatively, salts of a coordinating metal, such as silver, may improve the reaction rate by easing halide elimination. Transesterification , which involves changing one ester into another one, is widely practiced: Like the hydrolysation, transesterification is catalysed by acids and bases. The reaction is widely used for degrading triglycerides , e.g. in

2997-608: The fiberglass composite material, 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 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. Similarly, UHMWPE

3078-573: The organyl parts of the carboxylic acid and the alcohol, respectively, and R can be a hydrogen in the case of esters of formic acid . For example, butyl acetate (systematically butyl ethanoate), derived from butanol and acetic acid (systematically ethanoic acid) would be written CH 3 CO 2 (CH 2 ) 3 CH 3 . Alternative presentations are common including BuOAc and CH 3 COO(CH 2 ) 3 CH 3 . Cyclic esters are called lactones , regardless of whether they are derived from an organic or inorganic acid. One example of an organic lactone

3159-400: The reaction product . Esters are common in organic chemistry and biological materials, and often have a pleasant characteristic, fruity odor. This leads to their extensive use in the fragrance and flavor industry. Ester bonds are also found in many polymers . The classic synthesis is the Fischer esterification , which involves treating a carboxylic acid with an alcohol in the presence of

3240-565: The "Dyneema Purity" trade name. 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

3321-491: The ESA/Russian Young Engineers' Satellite 2 of September, 2007. 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

Ultra-high-molecular-weight polyethylene - Misplaced Pages Continue

3402-531: The HDPE has been synthesized, it is ready to be used in commercial products. Industrial production methods for HDPE products include injection molding for complex shapes such as toys. Extrusion molding is used for constant-profile products such as pipes and films. Blow molding is intended for hollow products, specifically bottles and plastic bags. Rotational molding is used for large, seamless parts such as chemical drums and kayaks. The method used during processing depends on

3483-458: The Phillips slurry process. The Ziegler-Natta method uses a combination of catalysts, including titanium tetrachloride, in contact with gaseous ethylene to precipitate high-density polyethylene. In a similar way, the Phillips slurry process uses silica-based catalysts in contact with a fast-moving hydrocarbon and polyethylene slurry to precipitate high density polyethylene. Processing will determine

3564-530: 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. 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

3645-429: The UHMWPE without the need for thermal treatment. Several companies have been selling antioxidant-stabilized joint replacement technologies since 2007, using both synthetic vitamin E as well as hindered phenol-based antioxidants. 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

3726-422: 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

3807-417: The aroma of fruits, butter, cheese, vegetables like celery and other foods. Esters can be formed from oxoacids (e.g. esters of acetic acid , carbonic acid , sulfuric acid , phosphoric acid , nitric acid , xanthic acid ), but also from acids that do not contain oxygen (e.g. esters of thiocyanic acid and trithiocarbonic acid ). An example of an ester formation is the substitution reaction between

3888-427: The aroma of many fruits, including apples , durians , pears , bananas , pineapples , and strawberries . Several billion kilograms of polyesters are produced industrially annually, important products being polyethylene terephthalate , acrylate esters , and cellulose acetate . Esterification is the general name for a chemical reaction in which two reactants (typically an alcohol and an acid) form an ester as

3969-558: 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, sailing, hiking equipment, climbing, and many other industries. UHMWPE

4050-420: The corresponding amides . The p K a of the alpha-hydrogens on esters of carboxylic acids is around 25 (alpha-hydrogen is a hydrogen bound to the carbon adjacent to the carbonyl group (C=O) of carboxylate esters). Many carboxylic acid esters have the potential for conformational isomerism , but they tend to adopt an S - cis (or Z ) conformation rather than the S - trans (or E ) alternative, due to

4131-460: The dehydration of mixtures of alcohols and carboxylic acids. One example is the Steglich esterification , which is a method of forming esters under mild conditions. The method is popular in peptide synthesis , where the substrates are sensitive to harsh conditions like high heat. DCC ( dicyclohexylcarbodiimide ) is used to activate the carboxylic acid to further reaction. 4-Dimethylaminopyridine (DMAP)

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4212-449: The difference in density, giving HDPE a higher specific strength . It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/248 °F for short periods). High-density polyethylene, unlike polypropylene , cannot withstand normally required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst (e.g., Ziegler–Natta catalysts ) and reaction conditions. HDPE

4293-403: The environmental stress crack resistance of a sample, the notched constant tensile load test (NCTL) is put to use. Owing to these desirable properties, pipes constructed out of HDPE are ideally applicable for drinking water and waste water (storm and sewage). HDPE has a wide variety of applications; for applications that fall within the properties of other polymers, the choice to use HDPE

4374-455: 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

4455-423: 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

4536-555: The ester category as well. According to some authors, organyl derivatives of acidic hydrogen of other acids are esters as well (e.g. amides ), but not according to the IUPAC . Glycerides are fatty acid esters of glycerol ; they are important in biology, being one of the main classes of lipids and comprising the bulk of animal fats and vegetable oils . Lactones are cyclic carboxylic esters; naturally occurring lactones are mainly 5- and 6-membered ring lactones. Lactones contribute to

4617-649: 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

4698-408: The first carbon atom of the organyl group replacing acidic hydrogen, is replaced by another atom from the group 14 elements ( Si , Ge , Sn , Pb ); for example, according to them, trimethylstannyl acetate (or trimethyltin acetate) CH 3 COOSn(CH 3 ) 3 is a trimethylstannyl ester of acetic acid , and dibutyltin dilaurate (CH 3 (CH 2 ) 10 COO) 2 Sn((CH 2 ) 3 CH 3 ) 2

4779-495: The forward reaction. Basic hydrolysis of esters, known as saponification , is not an equilibrium process; a full equivalent of base is consumed in the reaction, which produces one equivalent of alcohol and one equivalent of a carboxylate salt. The saponification of esters of fatty acids is an industrially important process, used in the production of soap. Esterification is a reversible reaction. Esters undergo hydrolysis under acidic and basic conditions. Under acidic conditions,

4860-444: The global HDPE market reached a volume of more than 30 million tons. HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 to 970 kg/m . Although the density of HDPE is only marginally higher than that of low-density polyethylene , HDPE has little branching , giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. The difference in strength exceeds

4941-579: The literature. 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. These new materials are cross-linked with gamma or electron beam radiation (50–105 kGy) and then thermally processed to improve their oxidation resistance. Five-year clinical data, from several centers, are now available demonstrating their superiority relative to conventional UHMWPE for total hip replacement (see arthroplasty ). Clinical studies are still underway to investigate

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5022-409: 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). Besides pure UHMWPE fibers, most manufacturers use blends to further reduce the creep and stretch of the material. In these blends,

5103-412: 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

5184-448: The other hand, more frequently named using the systematic IUPAC name, based on the name for the acid followed by the suffix -oate . For example, the ester hexyl octanoate, also known under the trivial name hexyl caprylate , has the formula CH 3 (CH 2 ) 6 CO 2 (CH 2 ) 5 CH 3 . The chemical formulas of organic esters formed from carboxylic acids and alcohols usually take the form RCO 2 R' or RCOOR', where R and R' are

5265-464: The parent alcohol and the parent acid, where the latter may be organic or inorganic. Esters derived from the simplest carboxylic acids are commonly named according to the more traditional, so-called " trivial names " e.g. as formate, acetate, propionate, and butyrate, as opposed to the IUPAC nomenclature methanoate, ethanoate, propanoate, and butanoate. Esters derived from more complex carboxylic acids are, on

5346-450: The performance of highly cross-linked UHMWPE for knee replacement. In 2007, manufacturers started incorporating anti-oxidants into UHMWPE for hip and knee arthroplasty bearing surfaces. 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

5427-451: The polyethylene chains, and helps determine properties such as flexibility, yield strength, and melt temperature. After the precipitate is formed, the temperature, pressure, and cooling time during processing will dictate the degree of crystallinity, with a higher degree of crystallinity resulting in greater rigidity and chemical resistance. Depending on the application, the method and processing steps can be adjusted for an ideal result. Once

5508-410: 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). Hylamer fell out of favor in the United States in the late 1990s with the development of highly cross-linked UHMWPE materials, however negative clinical reports from Europe about Hylamer continue to surface in

5589-454: The product requirements, with each having benefits for a given application. Ester In chemistry , an ester is a compound derived from an acid (organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group ( −OH ) of that acid is replaced by an organyl group (R ′ ). These compounds contain a distinctive functional group . Analogues derived from oxygen replaced by other chalcogens belong to

5670-467: The production of fatty acid esters and alcohols. Poly(ethylene terephthalate) is produced by the transesterification of dimethyl terephthalate and ethylene glycol: A subset of transesterification is the alcoholysis of diketene . This reaction affords 2-ketoesters. Alkenes undergo carboalkoxylation in the presence of metal carbonyl catalysts. Esters of propanoic acid are produced commercially by this method: A preparation of methyl propionate

5751-452: The properties of the HDPE. The method used to synthesize the HDPE is crucial because the micro structure of the HDPE will vary. The Phillips Slurry process results in HDPE with less branching and more precise molecular weights than the Ziegler process, but the Ziegler process provides greater flexibility in the type of polyethylene produced. The molecular weight of HDPE refers to the length of

5832-440: The range 1730–1750 cm assigned to ν C=O . This peak changes depending on the functional groups attached to the carbonyl. For example, a benzene ring or double bond in conjunction with the carbonyl will bring the wavenumber down about 30 cm . Esters are widespread in nature and are widely used in industry. In nature, fats are, in general, triesters derived from glycerol and fatty acids . Esters are responsible for

5913-406: The reaction is the reverse reaction of the Fischer esterification . Under basic conditions, hydroxide acts as a nucleophile, while an alkoxide is the leaving group. This reaction, saponification , is the basis of soap making. The alkoxide group may also be displaced by stronger nucleophiles such as ammonia or primary or secondary amines to give amides (ammonolysis reaction): This reaction

5994-420: The reaction of an ester with an alcohol. Unfortunately, because the leaving group is also an alcohol, the forward and reverse reactions will often occur at similar rates. Using a large excess of the reactant alcohol or removing the leaving group alcohol (e.g. via distillation ) will drive the forward reaction towards completion, in accordance with Le Chatelier's principle . Acid-catalyzed hydrolysis of esters

6075-445: 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

6156-485: 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),

6237-600: The solvent so that intermolecular entanglements are minimal. Entanglements make chain orientation more difficult, and lower the strength of the final product. Dyneema 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/mL (0.035 lb/cu in) (for Dyneema SK75). 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

6318-409: 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

6399-448: 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. 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 1990s. One unsuccessful attempt to modify UHMWPE was by blending the powder with carbon fibers. This reinforced UHMWPE

6480-488: 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

6561-513: Was released clinically as "Poly Two" by Zimmer in the 1970s. The carbon fibers had poor compatibility with the UHMWPE matrix and its clinical performance was inferior to virgin UHMWPE. A second attempt to modify UHMWPE was by high-pressure recrystallization. This recrystallized UHMWPE was released clinically as "Hylamer" by DePuy in the late 1980s. When gamma irradiated in air, this material exhibited susceptibility to oxidation, resulting in inferior clinical performance relative to virgin UHMWPE. Today,

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