Kevlar - Production

Production

Kevlar is synthesized in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct. The result has liquid-crystalline behavior, and mechanical drawing orients the polymer chains in the fiber's direction. Hexamethylphosphoramide (HMPA) was the solvent initially used for the polymerization, but for safety reasons, DuPont replaced it by a solution of N-methyl-pyrrolidone and calcium chloride. As this process was patented by Akzo (see above) in the production of Twaron, a patent war ensued.

Kevlar (poly paraphenylene terephthalamide) production is expensive because of the difficulties arising from using concentrated sulfuric acid, needed to keep the water-insoluble polymer in solution during its synthesis and spinning.

Several grades of Kevlar are available:

  1. Kevlar K-29 – in industrial applications, such as cables, asbestos replacement, brake linings, and body/vehicle armor.
  2. Kevlar K49 – high modulus used in cable and rope products.
  3. Kevlar K100 – colored version of Kevlar
  4. Kevlar K119 – higher-elongation, flexible and more fatigue resistant.
  5. Kevlar K129 – higher tenacity for ballistic applications.
  6. Kevlar AP – has 15% higher tensile strength than K-29.
  7. Kevlar XP – lighter weight resin and KM2 plus fiber combination.
  8. Kevlar KM2 – enhanced ballistic resistance for armor applications

The ultraviolet component of sunlight degrades and decomposes Kevlar, a problem known as UV degradation, and so it is rarely used outdoors without protection against sunlight.

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