STRUCTURE AND PROPERTY STUDIES OF POLY(ETHYLENE-TEREPHTHALATE) POLY(ETHYLENE-2,6-NAPHTHALATE) MELT-BLENDED FIBERS

The effects of blend composition and take-up velocity on structural va riations and physical properties of poly(ethylene terephthalate) [PET] /poly(ethylene-2,6-naphthalate) [PEN] blend fibres were studied using WAXS, n.m.r., d.s.c., density, tensile and thermal shrinkage tests. Ov er the ranges studied, the structure and properties of the blend fibre s were significantly influenced by the composition and melt spinning v elocity. With the increase in content of any second component (PEN or PET), the crystallization process in the as-spun fibres becomes diffic ult, because of the formation of random copolymers via a transesterifi cation reaction occurring between PET and PEN. molecules. This reactio n also produces a miscible amorphous phase with the result that all bl end samples exhibit a single glass transition temperature intermediate to those of the two homopolymers. The WAXS results of annealed sample s, however, indicate separate crystals for the two components rather t han a co-crystallization. Room temperature mechanical properties, for fibres spun at constant take-up velocity, improved gradually with incr easing PEN content. The thermal shrinkage, however, is relatively high for blend fibres and reaches a maximum for the 50/50 PET/PEN blend, i ndicating that the copolymer chains are oriented fairly well, but exis t in the amorphous state. (C) 1998 Elsevier Science Ltd. All rights re served.