Process for preparing aramid copolymer yarn using an acid wash
View Patent ↗The present invention concerns methods for removing sulfur from yarn comprising the steps of: a) contacting never-dried polymeric yarn with an aqueous base, the polymer comprising imidazole groups and said polymer comprising sulfur atoms characterized as being in the form of sulfate anions; b) contacting the yarn with an aqueous acid solution of pH 5 or lower; and c) rinsing the yarn.
1. A process for removing sulfur from yarn comprising the steps of:
a) contacting never-dried polymeric yarn, comprising fiber made from polymer, with an aqueous base, said polymer comprising imidazole groups and said polymer comprising sulfur atoms characterized as being in the form of sulfate anions, followed by the step of;
b) contacting the yarn with an aqueous acid solution of pH 5 or lower to protonate the imidazole groups, ionically binding anions provided by the aqueous acid solution to the polymer; and followed by the step of
c) rinsing the yarn.
2. The process of claim 1 , further comprising rinsing the yarn after step a) but prior to step b).
3. The process of claim 2 , wherein the rinsing of the yarn in claim 2 is an aqueous rinse.
4. The process of claim 1 , wherein said polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamine, and aromatic diacid-chloride.
5. The process of claim 4 , wherein said aromatic diacid-chloride is terephthaloyl dichloride.
6. The process of claim 4 , wherein said aromatic diamine is para-phenylenediamine.
7. The process of claim 4 , wherein the molar ratio of 5(6)-amino-2-(p-am inophenyl)benzimidazole to aromatic diamine is in the range of from 30/70 to 85/15.
8. The process of claim 7 wherein the molar ratio of 5(6)-amino-2-(p-am inophenyl)benzimidazole to aromatic diamine is 45/55 to 85/15.
9. The process of claim 1 , wherein the aqueous acid solution is of pH 4 or lower.
10. The process of claim 9 , wherein the aqueous acid solution is of pH 3 or lower.
11. The process of claim 1 , wherein in step (c) the yarn is rinsed with water.
12. The process of claim 1 , wherein the aqueous acid solution comprises an acid having a pKa of 5 or lower.
13. The process of claim 12 , wherein the aqueous acid solution comprises an acid having a pKa of 3 or lower.
14. The process of claim 1 , wherein after step c), the yarn has 3.0 weight percent sulfur or less, based on the weight of the yarn.
15. The process of claim 14 , wherein after step c), the yarn has 2.5 weight percent sulfur or less, based on the weight of the yarn.
16. The process of claim 15 , wherein after step c), the yarn has 1.0 weight percent sulfur or less, based on the weight of the yarn.