Hot surface hydrolysis of polyphosphoric acid in spun yarns

1. A process for removing residual polyphosphoric acid in a multifilament yarn, comprising:

a) spinning a bundle of dope filaments from a solution comprising polyareneazole polymer and polyphosphoric acid into a coagulation bath to produce a bundle of substantially solid polymer filaments;

b) removing the bundle of substantially solid polymer filaments of step (a) from the bath in the form of a multifilament yarn;

c) removing surface liquid from the filaments in the multifilament yarn of step (b);

d) contacting the multifilament yarn of step (c) with a hot surface to hydrolyze polyphosphoric acid; and

e) removing hydrolyzed polyphosphoric acid from the multifilament yarn of step (d), wherein the substantially solid polymer filaments remain substantially unfused.

2. The process of claim 1 , wherein removing the surface liquid from the filaments in the yarn comprises drying.

3. The process of claim 2 , wherein the drying is performed at a temperature of less than about 140° C.

4. The process of claim 3 , wherein the drying is performed on heated rolls at a temperature of less than about 120° C.

5. The process of claim 1 , wherein the multifilament yarn is rinsed with aqueous fluid prior to removing surface liquid from the filaments in the multifilament yarn.

6. The process of claim 1 , wherein the hot surface comprises heated rolls.

7. The process of claim 1 , wherein the hot surface has a surface temperature of at least 150° C.

8. The process of claim 7 , wherein the hot surface has a surface temperature of at least 180° C.

9. The process of claim 1 , wherein the removal of hydrolyzed polyphosphoric acid includes washing with base.

10. The process of claim 9 , wherein the yarn is washed with water prior to and after washing with base.

11. The process of claim 9 , wherein the base comprises sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium bicarbonate, or any combination thereof.

12. The process of claim 10 , wherein the base comprises sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium bicarbonate, or any combination thereof.

13. The process of claim 9 , wherein the yarn is subsequently washed with acid.

14. The process of claim 1 , wherein the multifilament yarn comprises filaments of a polyareneazole polymer.

15. The process of claim 14 , wherein the polyareneazole is a polypyridazole.

16. The process of claim 15 , wherein the polypyridazole is a polypyridobisimidazole.

17. The process of claim 16 , wherein the polypyridobisimidazole is poly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole.

18. The process of claim 14 , wherein the polyareneazole is a polybenzazole.

19. The process of claim 1 , wherein the polybenzazole is a polybenzobisoxazole.

20. The process of claim 1 , wherein substantially all of the polyphosphoric acid is hydrolyzed during the contacting of the yarn with a hot surface.