Abstract: A continuous process for heating a polybenzazole or polybenzothiazole filament, which includes the step of heating the filament to a temperature of at least 100.degree. C. but no greater than 290.degree. C. while applying a tension thereto of at least 3.5 grams per denier, which is carried out at a line speed of at least 100 m/minute; and there is no prior or subsequent heating of the fiber to any temperature greater than 300.degree. C. It has been discovered that placing tension on the filament while it is dried increases its tensile modulus without a significant decrease in its tensile strength.

Abstract: A process for the preparation of polybenzazole filaments which comprises (a) extruding a solution of polybenzazole polymer in a mineral acid through a spinneret having at least 100 holes, which are arranged to form a annular pattern around the center of the spinneret, the center and at least two radial sections of the spinneret having no holes and an average width which is at least about 3 times the minimum pitch of the holes, thereby forming filaments of the polymer solution; (b) drawing the filaments of the polymer solution through a quench chamber while providing a substantially radial gas flow therein across the spinneret from at least two different directions; and (c) washing and drying the filaments of the polymer solution under conditions sufficient to form polybenzazole filaments.

Abstract: In a process for preparing polybenzoxazole or polybenzothiazole filaments by extruding a polybenzoxazole or polybenzothiazole dope, drawing the dope filament across an air gap, and coagulating the dope filament; the number of filament breaks can be reduced by placing a stress isolation device after extruding but before coagulating the filament.

Abstract: Improved polybenzoxazole fibers are made by a process for finishing a spun and drawn dope fiber, which contains polybenzoxazole polymer and polyphosphoric acid, including the steps of:(a) coagulating the dope fiber in an aqueous coagulant;(b) washing the coagulated fiber with an aqueous washing fluid for less than 72 hours under conditions such that the fiber contains no more than 8,000 ppm residual phosphorus (1 ppm=1 part per million, by weight);(c) drying the fiber at a temperature of no more than 300.degree. C. until it retains no more than about 3 weight percent residual moisture; and(d) heat-treating the fiber at a temperature of at least about 300.degree. C. under tension.

Abstract: Polybenzoxazole or polybenzothiazole polymer dopes are spun through a spinneret having an orifice density of more than 0.25 per cm.sup.2 to form filaments. The filaments formed then pass through an air gap which has a gas flowing into it at a temperature of between about 5.degree. C. to about 100.degree. C. and at a flow rate between about 0.1 meters/second and about 2.0 meters/second. The filaments cool in the air gap and are then coagulated. During or after coagulation the filaments are combined into one or more fibers. By this method of controlling the temperature in the air gap it is possible to stably spin polybenzoxazole or polybenzothiazole fibers at relatively high final line speeds.

Abstract: Polybenzazole polymer dopes are spun into fibers at high speed by passing through a spinneret with proper selection of hole geometry, followed by spin-drawing to a spin-draw ratio of at least 20, washing, taking up and drying. The take up speed is at least about 150 meters per minute, and the fibers are spun in at least 10 km lengths without a break.

Abstract: Polybenzazole polymer dopes are spun through a spinneret having more than 2 per cm.sup.2, of orifices in relatively close proximity. The dope filaments formed, then pass through an air gap which has a temperature of 50.degree. to 100.degree. C. and a gas flow sufficient to uniformly reduce the temperature of the dope filaments. The filaments cool in the air gap and are then coagulated.

Abstract: Improved polybenzoxazole fibers are made by a process for finishing a spun and drawn dope fiber, which contains polybenzoxazole polymer and a solvent acid, including the steps of: (a) coagulating the dope fiber in an aqueous coagulant: (b) washing the coagulated fiber with an aqueous washing fluid for less than 72 hours under conditions such that the fiber contains no more than 8,000 ppm residual solvent acid (1 ppm=1 part per million, by weight); (c) drying the fiber at a temperature of no more than 300.degree. C. until it retains no more than about 2 weight percent residual moisture; and (d) heat-treating the fiber at a temperature of at least about 300.degree. C. under tension.