Dyneema or Spectra is a synthetic fibre, 15 times stronger than steel, three times stronger than Kevlar. It is usually used in bulletproof vests, bow strings and sails on high-performance yachts. It was invented by DSM in 1979. Dyneema fibres have been in commercial production since 1990 at a plant in Heerlen, the Netherlands. In the Far East DSM has a cooperation agreement with Toyobo Co. for commercial production in Japan. In the USA DSM has granted a license to Allied Signal. Spectra was developed independently by AlliedSignal (now Honeywell) in the USA. Though the production details will undoubtedly be differenyt, the result is comparable to Dyneema. In this article, we will refer to both Dyneema and Spectra as Dyneema
Properties
Dyneema is a type of olefin and derives its strength from relatively weak Van der Waals bonds between the strands. It is made up of extremely long chains of polyethylene, which all align in the same direction. Each chain is bonded to the others with so many Van der Waals bonds that the whole can support great tensile loads. The fibre can attain a parallel orientation greater than 95% and a level of crystallinity of up to 85%. In contrast, Kevlar derives its strength from strong bonds, of which it has fewer.
Dyneema is not a good heat conductor, so local thermal excitations can disrupt the crystalline order of a given chain piece-by-piece, giving it a melting point of around 144 or 152 degrees Celsius (though it is not advisable, according to DSM, to use Dyneema at prolonged temperatures exceeding 80 to 100°C). It becomes brittle at temperatures below -150°C.
Dyneema has no unbonded groups on the outside which easily bond to water. Because of this, Dyneema does not absorb water readily, but it also does not wet easily, which makes bonding it to other polymers difficult. The weak bonding at the sides of the chain means that the edges break easily, making the fiber surface feel "slippery". Since Dyneema does not contain chemical groups (such as aromatic rings, 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.
Most people do not like the way Dyneema feels. Fabric made of Dyneema do not offer great dexterity, and will feel slick and quite different from cotton. It is not often used in fabric, for these reasons. Another problem, in some applications, is that Dyneema will creep, meaning it will stretch and continue to stretch when placed under tensile stress.
Production
Dyneema is synthesized from monomers of ethylene, which are bonded together to form what is called ultra high molecular weight polyetylene (or UHMWPE). These are molecules of polyethylene which are several orders of magnitude longer than familiar high-density polyethylene due to an exotic synthesis process based on metallocene catalysts. The material is also known as high modulus polyethylene (HMPE) or high performance polyethylene (HPPE). The polymers are aligned randomly when they are produced. To make Dyneema, they are dissolved and spun around, causing the polymer chains to orient in the direction of the fiber.
The production of Dyneema fibres demands relatively little energy and uses no aggressive chemicals. The product can easily be recycled so environmental pollution from product and process is minimal.
See also
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