EFFECT OF MOLECULAR-ORIENTATION ON THE MELTING BEHAVIOR OF HEAT-SET POLY(ETHYLENE-TEREPHTHALATE) FIBERS

Poly (ethylene terephthalate) (PET) filaments having a range of structure and morphology were prepared by heat-setting of commercial PET yarn at temperatures of 100-258°C for 5 min under two conditions, viz. while the yarn was free to relax and when it was held taut at constant length. Differential scanning calorimetric (DSC) measurements were made on these samples under two conditions, viz., while the sample was free to shrink and when it was constrained from shrinking in the DSC cell. X-ray diffraction studies were made to determine the degree of crystallinity, crystallite orientation, crystallite size, and crystal perfection. The overall trans content, trans orientation factor, and amorphous orientation factor were determined by infrared spectroscopy. The melting endotherm peaks appear between 254.6° and 256.3°C for the samples tested by DSC without constraint while they appear at temperatures between 261.4°. © 1990, Taylor & Francis Group, LLC. All rights reserved.