Method for removing sulfur from fiber using monovalent salt ion exchange
View Patent ↗The present invention concerns methods for removing sulfur from a fiber made from a polymer comprising imidazole groups, said method comprising: a) contacting never-dried sulfate anion containing polymeric-fiber with aqueous salt having monovalent anions to displace at least a portion of the sulfate anions; and b) rinsing the fiber to remove displaced sulfate anions.
1. A method for removing sulfur from a fiber made from a polymer comprising imidazole groups, said method comprising:
a) contacting never-dried sulfate anion containing polymeric-fiber with aqueous salt solution comprising monovalent anions to displace at least a portion of the sulfate anions; and
b) rinsing the fiber to remove displaced sulfate anions.
2. The method of claim 1 , wherein said polymer comprises derivatives of 5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamine, and aromatic diacid-chloride.
3. The method of claim 2 , wherein said aromatic diacid-chloride is terephthaloyl dichloride.
4. The method of claim 2 , wherein said aromatic diamine is para-phenylenediamine.
5. The method of claim 2 , wherein the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is in the range of from 30/70 to 85/15.
6. The method of claim 5 , wherein the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is in the range of from 45/55 to 85/15.
7. The method of claim 1 , wherein said monovalent anions comprise one or more of fluoride, chloride, bromide, iodide, acetate, formate, nitrate, nitrite, and perchlorate.
8. The method of claim 7 , wherein said monovalent anions comprise one or more of chloride, bromide, acetate, and nitrate.
9. The method of claim 1 , wherein in step b), at least a portion of residual monovalent anions is removed.
10. The method of claim 1 , wherein after step b), the fiber has less than 3.0 weight percent sulfur based on the weight of the fiber.
11. The method of claim 10 , wherein after step b), the fiber has less than 2.5 weight percent sulfur based on the weight of the fiber.
12. The method of claim 11 , wherein after step b), the fiber has less than 1.0 weight percent sulfur based on the weight of the fiber.