Influence of Sulfuric Acid Bath on Morphological Structure and Mechanical Properties of Poly(p-phenylene-1,3,4-oxadiazole) Fibers

Poly(p-phenylene-1,3,4-oxadiazoles) (p-PODS) spinning solution was prepared by one-step polycondensation, and p-POD fibers were obtained by wet spinning method using dilute sulfuric acid as coagulation bath. The morphology and mechanical properties of p-POD fibers under different coagulating conditions, such as bath concentration and temperature, were qualitatively and quantitatively studied by microscopes, ultrasonic orientation measurement, WAXD, and other traditional methods. The microscopic observation indicated that the p-POD fibers were of three-layer structure which consisted of outer skin, inner skin, and the core. The skin-core structure and surface feature of the fibers were greatly affected by the coagulating conditions. At the same time, the results of WAXD and ultrasonic orientation measurement demonstrated that the crystallinity and orientation of the fibers also varied with the change of bath conditions. The tests of mechanical properties showed that the tensile strength, elongation at break, and maximum draw ratio of the p-POD fibers were determined by their solid-phase structures, which were largely influenced by coagulation conditions. According to the structure analysis and the mechanical tests, the optimal coagulation parameters were chosen to obtain p-POD fibers with denser and more regular structure and better mechanical properties. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1485-7493, 2009