RAPID MECHANICAL DEFORMATION OF POLY(ETHYLENE-TEREPHTHALATE) FIBERS AT TEMPERATURES ABOVE THE GLASS-TRANSITION

The mechanical properties of poly(ethylene terephthalate) (PET) fibers at temperatures above the glass transition are investigated by means of a specially constructed device. Measurements of the deformation rat e and of the ''dynamic'' stress-strain curves of the fibers are perfor med in nearly isothermal regime (after initial rapid heating) in a tem perature interval 100-200-degrees-C. The results reported in the prese nt work demonstrate that the high-temperature mechanical characteristi cs of rapidly crystallizing polymers can be deduced to a satisfactory precision, while keeping the crystallinity development at low level. O ur investigations indicate that if the high-temperature deformation is sufficiently fast, the polymer behavior is similar to the deformation at sub-T(g) temperatures. Based on this similarity, a qualitative mod el of the deformation in the high-temperature region is proposed. The proposed model is fundamentally equivalent to the models describing me chanical deformation of glassy polymers at temperatures below the glas s transition. (C) 1995 John Wiley & Sons, Inc.