Preparation of high‐modulus and high‐strength fibers from high molecualar weight poly(ethylene terephthalate)

High molecular weight poly(ethylene terephthalate) (PET) was obtained by solid‐state polymerization of solution‐grown crystals of PET that were prepared from commercially available PET. The intrinsic viscosities of the sample before and after the polymerization were 0.67 and 2.41 dL/g, respectively. As‐spun fibers from the high molecular weight material were prepared by a solution spinning method using two kinds of solvents: nitrobenzene (NB) and a mixture of hexafluoro‐2‐propanol and dichloromethane (HD). Both as‐spun fibers could be drawn up to a draw ratio of 12–13 by a two‐stage drawing technique. The highest tensile modulus and strength of 275 g/d (34.4 GPa) and 15 g/d (1.9 GPa), respectively, were obtained for the drawn fibers from the HD system. These values were 15%–20% higher than those achieved for the drawn fibers from the NB system. The difference was explained on the basis of the morphological differences of asspun fibers and the extent of molecular degradation during processing observed between the two series.