Fiber spinning from the nematic melt. II. Effect of thermal history on spinning of the copolyester of polyethylene terephthalate and <i>p</i>‐oxybenzoate

Abstract

Abstract 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 at the wall of 6.4 sec −1 , 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 and increased with increasing spinning temperature for a fixed 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 at 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.