Generation of a fibrillar core in PET fiber by cold drawing

Cold draw processing of poly(ethylene terephthalate) yarns has been discove red that yields a sheath/fibrillar core (s/fc) microstructure in the each f iber of a yarn. When aged, unoriented, noncrystalline spun yarns were cold drawn, high (>5.7 : 1) draw ratios could be achieved and an s/fc microstruc ture resulted. Cold drawing also generated a high oriented amorphous conten t. The tensile and shrinkage properties of yarns with the s/fc microstructu re and high oriented amorphous content were examined as function of process ing (drawing, annealing, and relaxing). The microstructure was examined by scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering, wide-angle X-ray scattering, and optical microscopy. The fibrillar microstructure survives all processing. Management of the orient ed amorphous component under heat and tension contributes to the greater st iffness (modulus) and dimensional stability of processed s/fc yarns. The pr operties of yarns with an s/fc microstructure are compared with more conven tional hot drawn yarns. (C) 1999 John Wiley & Sons, Inc.