Aromatic poly(1,4-phenylene-1,3,4-oxadiazole) fibers by dry jet-wet spinning

Fibers of poly(1,4-phenylene-1,3,4-oxadiazole) have been prepared by dry jet-wet spinning sulfuric acid solutions of the polymer. Polymer was prepared by polymerizing terephthalic acid and hydrazine dihydrochloride in 30% fuming sulfuric acid and directly spinning the resulting solution. Dry jet-wet spinning allows greater flexibility in conditions than does wet spinning in that spinneret temperature and coagulation bath temperature are independent of one another. Therefore, coagulation may be at temperatures well below those needed at the spinneret to maintain a flowing, extrudable solution. Another common advantage of dry jet-wet spinning is application of draw to the extruded fiber before coagulation, but in this system, drawing the fiber before coagulation was shown to be a disadvantage. Fiber properties were maximized by spinning with a spinneret temperature of 58–73°C into a coagulation bath at 3–4°C and with an air gap of 1/4 in. Water as a coagulation medium allowed operation at speeds up to 40 m/min, while with 50% sulfuric acid less than half that speed was reached. Application of draw ratios of 3/1 on the coagulated but still swollen fiber combined with high-temperature treatments at low draw ratios (1.05/l) gave maximum fiber properties–tenacity 6 g/denier, elongation 20–25%, and modulus 200–240 g/denier.