Methods of preparing polyimide fibers with kidney-shaped cross-sections

An integrated method for preparing polyimide fibers with kidney-shaped cross-sections, comprising:

• preparing a polyamic acid spinning solution by reacting an aromatic dianhydride with an aromatic diamine;
• filtering the polyamic acid spinning solution;
• degassing the filtered polyamic acid spinning solution under vacuum;
• wet-spinning the degassed polyamic acid solution through a spinneret having circular orifices at a spinning rate of about 0.1 m/min to about 100 m/min;
• entering as-spun polyamic acid fibers into at least one coagulation bath to form polyamic acid nascent fibers with kidney-shaped cross-sections by controlling process conditions associated with at least two of the spinning rate, a composition of the at least one coagulation bath, a coagulation temperature, and a depth of the coagulation bath, wherein the coagulation bath has the depth ranging from about 5 mm to about 800 mm, wherein the coagulation bath contains a solvent including water or a mixture of water and an organic solvent, and wherein the coagulation bath has the coagulation temperature ranging from about −10° C. to about 50° C.;
• washing the polyamic acid nascent fibers by water at a temperature of about 0° C. to about 100° C.;
• drying the polyamic acid nascent fibers at a temperature of about 60° C. to about 240° C.;
• thermally curing and stretching the polyamic acid nascent fibers at stepwise increased temperatures of about 120° C. to about 600° C. to convert the polyamic acid fibers to corresponding polyimide fibers with kidney-shaped cross-sections;
• thermally annealing the polyimide fibers with kidney-shaped cross-sections at a temperature of about 400° C. to about 800° C.;
• and
• winding the polyimide fibers with kidney-shaped cross-sections.