Effects of spinning process on morphology of polyimide fibers

Polyamic acid (PAA) fibers were prepared via traditional wet spinning process with methanol as a coagulation bath. The as-spun PAA fibers showed good mechanical properties that the tensile strength and the initial modulus of the fibers reached 2.21 cN/dt and 40.7cN/dt, respectively. The SEM photographs also indicated that the fibers had the most solid morphology with the heart-shaped cross-sections. Two processes were applied to prepare polyimide (PI) fibers. One was direct heat-treatment with the fibers undergoing a certain process under 370 degrees C in the N-2 atmosphere; the other was chemical/heat-treatment in which the fiber dipped into the chemical imidization agents, and then followed the heat-treatment. In comparing the two methods, solid PI fibers were obtained by the direct heat-treatment, while the chemical/heat-treatment caused voids in the fibers. Correspondingly, the PI fibers obtained by the direct heat-treatment showed better mechanical properties with the tensile strength and the initial modulus increasing to 2.8 cN/dt and 43 cN/dt, respectively.