Process for removing cations from polyareneazole fiber
View Patent ↗The present invention relates to processes for hydrolyzing polyphosphoric acid in a fiber and the removal of hydrolyzed polyphosphoric acid from the fiber.
1. A process for removing cations from a polyareneazole fiber, comprising the steps of:
a) providing a fiber comprising:
a polyareneazole polymer having pendant hydroxyl groups and at least 2 percent by weight of cations, said cations comprising one or more of sodium, potassium, or calcium,
b) contacting the fiber with an aqueous solution containing acid to release at least a portion of the cations, and
c) optionally, washing the fiber with water.
2. The process of claim 1 wherein the acid is a volatile acid.
3. The process of claim 2 , wherein the volatile acid includes acetic acid, propionic acid, or any combination thereof.
4. The process of claim 1 , wherein the aqueous solution contains from about 0.1 to about 10 percent by weight acid.
5. The process of claim 1 , wherein contacting the fiber with the aqueous solution includes spraying, coating, flowing, drawing, dipping, or any combination thereof.
6. The process of claim 1 , wherein the duration of the contacting step is up to about 30 seconds.
7. The process of claim 1 , wherein the duration of the optional washing step is up to about 30 seconds.
8. The process of claim 1 , wherein after the steps of contacting the fiber with an aqueous solution containing acid, and optionally washing the fiber with water, the fiber contains up to about 0.1 percent cations based on fiber weight.
9. The process of claim 8 , wherein the fiber contains up to about 0.05 percent cations based on fiber weight.
10. The process of claim 1 , wherein the fiber further comprises at least about 0.1 percent phosphorus based on fiber weight prior to contacting the fiber with the aqueous solution.
11. The process of claim 1 , wherein the fiber further comprises at least about 1 percent phosphorus based on fiber weight prior to contacting the fiber with the aqueous solution.
12. The process of claim 1 wherein the polyareneazole is a polypyridazole.
13. The process of claim 12 wherein the polypyridazole is a polypyridobisimidazole.
14. The process of claim 13 wherein the polypyridobisimidazole is poly(l,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′] bisimidazole.
15. The process of claim 1 wherein the polyareneazole is a polybenzazole.
16. The process of claim 15 wherein the polybenzazole is a polybenzobisoxazole.