Engineering Rubber and Plastics in Use

  Aramid yarns known by the brand name Kevlar yarn from Dupont is a high-performance yarn which can sustain temperatures in the range of 250 degree Celsius, as it was initially developed by Dupont their brand name became pretty popular in the name Kevlar although its chemical name is Poly-para-phenylene terephthalamide. Para-Aramid fibres are produced by a two-step process - polymer production followed by spinning. The first step is the low-temperature-solution polymerization of diacid chlorides (e.g. terephthaloyl chloride) and diamines (e.g. para-phenylenediamine) in amide solvents. Polar solvents such as N-methyl pyrrolidone and dimethylacetamide are used as polymerization solvents; formerly, hexamethyl phosphoramide was used. The para-aramid polymer is neutralized and then isolated from the polymerization solution. Next, a 'spinning solution' is created by redissolving the polymer in concentrated sulfuric acid. This liquid crystalline solution is extruded through a spinnere...