Microstructure and mechanical properties of hot-air drawn poly(ethylene terephthalate) fibers

Hot-air drawing method has been applied to poly(ethylene terephthalate) (PET) fibers in order to investigate the effect of strain rate on their microstructure and mechanical properties and produce high-performance PET fibers. The hot-air drawing was carried out by blowing hot air controlled at a constant temperature against an as-spun PET fiber connected to a weight. As the hot air blew against the fibers weighted variously at a flow rate of about 90 l/min, the fibers elongated instantaneously at a strain rate in the range of 2.3 -18.7 s(-1). The strain rate in the hot-air drawing increased with increasing drawing temperature and applied tension. When the hot-air drawing was carried out at a drawing temperature of 220 degrees C under an applied tension of 27.6 MPa, the strain rate was the highest value of 18.7 s(-1). A draw ratio, birefringence, crystallite orientation factor, and mechanical properties increased as the strain rate increased. The fiber drawn at the highest stain rate had a birefringence of 0.231, degree of crystallinity of 44%, tensile modulus of 18 GPa, and dynamic storage modulus of 19 GPa at 25 degrees C. The mechanical properties of fiber obtained had almost the same values as those of the zone-annealed PET fiber reported previously. (C) 1999 John Wiley & Sons, Inc.