Abstract: A polybenzazole fiber obtained through heat treatment, which has a high tensile modulus of not less than 300 GPa and a tensile strength of not less than 5.0 GPa, said fiber being characterized by an X-ray analysis by a fine structure thereof of at least one of the following (1) and (2):(1) a crystal orientation parameter <sin.sup.2 .PHI.> of not more than 0.

Abstract: A polybenzazole fiber characterized by having an elastic modulus of not less than 1350 g/d and requiring not longer than 10 minutes to reduce its water content from 2.0% to 1.5%, when determined using a thermogravimetric analyzer at 110.degree. C. after moisture absorption of not less than 2.0% of a fiber, and a method for manufacturing such a polybenzazole fiber, comprising extruding a spinning dope comprising polybenzazole and a polyphosphoric acid from a spinneret to give a dope filament, and cooling the dope filament to not more than 50.degree. C., followed by coagulation and washing. According to the method of the present invention, a polybenzazole fiber showing less decrease in strength by rapid heating can be provided.

Abstract: The present invention provides processes for producing polybenzazole fibers where a spinning dope containing a polybenzazole polymer in an acid solvent is extruded through a spinning nozzle, followed by coagulation in a coagulating medium and washing with a fluid capable of dissolving the acid solvent; thereafter, in one process, the fiber obtained by the coagulation under specific conditions and the subsequent washing is dried in a heating zone with at least 80% part based on the total length thereof being set at a temperature of 240.degree. C. or higher, and in the other process, the fiber obtained by the coagulation under the conventional conditions and the subsequent washing is neutralized with a basic solution, followed by washing with a fluid capable of dissolving the basic solution, and then dried at a specific temperature set depending upon the residual moisture content in the fiber.