Wet spinning of poly-m-phenylene isophthalamide (PMIA)/N-methylpyrrolidone (NMP) and PMIA/NMP containing calcium chloride was investigated using aqueous solutions of calcium chloride as coagulating medium. Void fractions, cross-sectional shapes and amounts of residual solvents in as-coagu-lated fibers were studied, and moisture contents in the fibers were estimated for the as-coagulated fibers obtained under wide range of conditions of salt concentration and temperature of the coagulation bath. Every spinning solution had a respective region of the optimum coagulating conditions in which uniformly coagulated fibers were obtained. In the case of spinning solution without salt, uniform as-coagulated fibers were obtained in the widest range of temperature at salt concentrations of 30-35%, and the region of optimum coagulating conditions was shifted to higher-temperature side and narrowed in the case of spinning solution containing salt. The as-coagulated fibers obtained in the region of optimum coagulating conditions were successively drawn in hot-water to give molecular pre-orientation and then drawn on a hot-plate (heat-treated) to afford PMIA fibers with high molecular orientation and crystallinity, The estimated moisture content in the as-coagulated fiber, used as a measure of reverse diffusion of coagulant during the coagulating process, depended upon the salt concentration in the coagulation bath. The moisture content in the as-coagulated fiber was estimated to be about 10% in the case of a coagulation bath with high-salt content of at least 30%. These results suggested that the reverse diffusion of coagulant into the spun fibers was suppressed in coagulation bath with high-salt concentration. On the other hand, the amount of residual solvent in the as-coagulated fiber strongly depended upon bath temperature rather than salt concentration in the range of 20-45% salt concentration and decreased with the rise in bath temperature. This result was attributed to the acceleration of the removal of solvent (normal diffusion) from the spun solution at higher temperatures.
