RELATION BETWEEN DRAWING TEMPERATURE AND CRITICAL NECKING TENSION ON ZONE DRAWING FOR POLY(ETHYLENE-TEREPHTHALATE) FIBERS

The relation between the drawing temperature (T-d) and the critical ne cking tension (sigma(c)) has been investigated for amorphous unoriente d Poly(ethylene terephthalate) (PET) fibers. The sigma(c) was defined as the minimum tension needed to generate a necking at a given T-d. Th e sigma(c) varied inversely with T-d in the temperature range below T- g: 75 degrees C. It was found that the temperature difference between T-g and T-d was proportional to the sigma(c):sigma(c)=C(T-g- T-d). Whe re C has a value of 0.546 MPa/degrees C. The birefringence and the cry stallinity in the temperature range below T-g increased steadily with decreasing T-d, but those in the temperature range above T-g were very low and hardly depended on T-d The fiber zone-drawn at 65 degrees C h as a high birefringence of 0.150 and a crystallinity of 17%, respectiv ely. However, the fiber zone-drawn at 102 degrees C has a low birefrin gence of 0.008 and a crystallinity of 4%. No strain-induced crystalliz ation occurred at temperatures above T-g. The viscoelastic behavior of the fibers zone-drawn below T-g is markedly different from that of th e fibers zone-drawn above T-g; the fibers obtained at the drawing temp erature above T-g show no rubber-like region. The dynamic modulus incr eases with decreasing drawing temperature.