Bulletproof polythene is 40% stronger than Kevlar
10:00 02 June 2007
NewScientist.com news service
It's the mundane stuff of plastic bags and sandwich boxes, but polyethylene has a more streetwise talent: in the form of dense, high-molecular-weight fibres it can stop a bullet in its tracks. But no one has ever succeeded in making an ultra-thin, concealable, easy-to-move-in bulletproof vest from it.
Until now, that is. Polymer maker DSM of Heerlen, the Netherlands, is selling Dyneema SB61, a still tougher - and secret - formulation of polyethylene fibre. Weight for weight, it is 15 times stronger than steel and 40 per cent stronger than that other staple of the bulletproof vest, Kevlar. American Body Armor of Los Angeles is using the new fibre to make flexible, concealable vests just 5 millimetres thick for US police forces.
The vests are likely to find a ready market: a year ago, the US Department of Justice banned police officers from using ultra-lightweight vests based on a polymer called Zylon. Over time, water damage can cause the Zylon polymer backbone to degrade, and some officers were severely injured when they were shot. Their vests were not pierced, but they were injured by the dent in the jacket protruding into their body.
These "backface" injuries are an increasing risk as vests get thinner, says ballistics engineer Cindy Bir of Wayne State University in Detroit. In tests in which nine human cadavers dressed in different makes of body armour were shot, eight experienced backface injuries. In living patients, doctors often misinterpret such wounds as entrance wounds and perform unnecessary exploratory surgery, Bir says.
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