Fiber Spinning from the Nematic Melt. 2. Effect of Thermal History on Spinning of the Copolyester of Polyethylene Terephthalate and p-Oxybenzoate

摘要

Fibers were spun from the nematic phase of the copolymer of polyethylene terephthalate having 60 mol % of p-oxybenzoate units. A capillary rheometer was used for spinning with a shear rate and capillary (length/diameter) ratio of 14.1. The spinning temperature was varied from 250 to 300 C and, at each temperature, the spin-draw ratio was examined as a variable. Spinning was performed under two conditions. When spinning from the melt without preheating, the initial modulus of the fibers increased with spin-draw ratio. In the second case, the melt was preheated and then cooled to the desired temperature before spinning the fibers. The preheating temperature was 280 C for spinning 250 C, and 300 C for spinning at 280 C. Preheating increased the fiber modulus to the value obtained by spinning at the preheating temperature. A reduction of the viscosity due to the melting of poly(p-hydroxybenzoic acid) (PHB) crystallites produces better orientation and higher modulus. However, with increasing spin-draw ratio, the modulus of the preheated fibers decreased to the values expected for the spinning temperature. This decrease in modulus is due to recrystallization of PHB in the threadline.