Dyneema
From Freepedia
Dyneema® is a synthetic fiber based on UHMWPE, 15 times stronger than steel and three times stronger than Kevlar. It is usually used in bulletproof vests, bow strings, climbing equipment and high performance sails in yachting. Dyneema® was invented by DSM in 1979. It has 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 United States, DSM has granted a license to Allied Signal. Spectra is the brandname of the chemically identical product developed independently by Allied Signal (now Honeywell) in the USA. Though the production details will undoubtedly be different, the result is comparable to Dyneema. In this article, we will refer to both Dyneema and Spectra as Dyneema. Dyneema® is a registered trademark of Royal DSM N.V. (The Netherlands).
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Chemistry and properties
For details, see the properties section of Ultra high molecular weight polyethylene.
Dyneema fibers derive their strength from the extreme length of each individual molecule. 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 bonding between relatively short molecules.
Its melting point is around 144 or 152 degrees Celsius, and according to DSM, it is not advisable to use Dyneema at temperatures exceeding 80 to 100 °C for long periods of time. It becomes brittle at temperatures below −150 °C. This contrasts strongly with other high-performance fibers, which tend to be quite heat-resistant.
The fibers feel slippery, similar to polypropylene and other hydrophobic fibers. Most people do not like the way Dyneema feels; for this reason, it is not often used in fabric. The slipperiness also makes such fibers less suitable for use in fibre reinforced plastics.
Another problem, in some applications, is that Dyneema will creep, meaning it will stretch, and continue to stretch continually, when placed under tensile stress. Like other olefins, it is very resistant to water, moisture, most chemicals, UV radiation, and micro-organisms.
Production
To make Dyneema fibers, a solution of UHMWPE is drawn into fibers as the solvent evaporates, causing the polymer chains to orient in the direction of the fiber.
Applications
For body armor, the fibers are generally aligned and bonded into sheets, which are then layered at various angles to give the resulting composite material strength in all directions.
Both Spectra and Dyneema excell as fishing line as they have less stretch, are more abrasion resistant, and are thinner than traditional monofilament line.
In recent years certain items of climbing equipment have started making use of dyneema. In particular "slings", sewn loops of material that can be wrapped around sections of rock, hitched (tied) to other pieces of equipment or even tied directly to a tensioned line using a special prussik knot, have benefited from this material. It has limited applications however as these items are not dynamic (do not stretch) and therefore a fall on them involves considerable shock loading of the other pieces of equipment and the climber's body. They are however much lighter and finer than the alternatives (nylon) and therefore very popular. Usually sold in lengths of 10 cm, 30 cm, 60 cm, 120 cm or 400 cm at either 10 mm or 12 mm widths, these slings have a breaking strain of around 22 kN.
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 Dyneema fabric.
