Process for removing phosphorous from a fiber or yarn

1. A process for removing phosphorus from a yarn spun from a polymer solution containing polyphosphoric acid, the yarn comprising at least about 1.5 percent by weight of the yarn of phosphorus, comprising contacting the yarn with a base and washing the yarn with an aqueous fluid, wherein the yarn is provided by heating a spun multifilament yarn comprising the polymer and polyphosphoric acid to at least 120 degrees Celsius for a time effective to hydrolyze polyphosphoric acid.

2. The process of claim 1 wherein the phosphorus content of the yarn prior to contacting the yarn with the base is in the range of from 2 to 20 percent based on yarn weight.

3. The process of claim 1 wherein the phosphorus content of the yarn prior to contacting the yarn with the base is 4 to 15 percent based on yarn weight.

4. The process of claim 1 wherein contacting the yarn with the base includes spraying, coating, flowing, drawing, dipping, or any combination thereof.

5. The process of claim 4 wherein the base includes sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium bicarbonate, or any combination thereof.

6. The process of claim 1 wherein the aqueous fluid contains an acid.

7. The process of claim 6 wherein the acid is a volatile acid.

8. The process of claim 7 , wherein the volatile acid includes acetic acid or propionic acid, or any combination thereof.

9. The process of claim 1 wherein the polymer comprises a polyareneazole.

10. The process of claim 9 wherein the polyareneazole is a polypyridazole.

11. The process of claim 10 wherein the polypyridazole is a polypyridobisimidazole.

12. The process of claim 11 wherein the polypyridobisimidazole is poly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole.

13. The process of claim 9 wherein the polyareneazole is a polybenzobisoxazole.

14. The process of claim 1 , wherein the yarn contains less than 0.1 percent phosphorus based on yarn weight after washing with the aqueous fluid.

15. The process of claim 1 , wherein the base is aqueous sodium hydroxide or the aqueous fluid contains acetic acid, or both.

16. The process of claim 1 , wherein the duration of the contacting step is no more than 30 seconds.

17. The process of claim 1 , wherein the duration of the washing step is no more than 30 seconds.

18. The process of claim 1 , wherein the step of contacting the yarn with a base begins before the step of washing the yarn with an aqueous fluid.

19. The process of claim 1 , wherein the time effective to hydrolyze polyphosphoric acid is up to about 120 seconds.