Transmission electron microscopy (TEM) at high magnification of thin c
ross-sections of drawn multifilament poly (ethylene terephthalate) yam
and of this yarn after heat-setting in the slack state at 250 degrees
C and in the taut state at 258 degrees C is shown to provide evidence
for the existence of crystallites whose lateral dimensions are consis
tent with those measured from wide-angle X-ray diffraction (WAXD). The
denser, crystalline microfibrils appear to be separated by interfibri
llar material of lower density in all the samples examined. The electr
on micrographs bring out the important differences in the morphologies
of the three samples, the implications of which are critically examin
ed. (C) 1997 Elsevier Science Ltd.