Cross-linked cellulose fibers and method of making same
View Patent ↗The invention provides a method for preparing cross-linked cellulosic fibers. A sheet of cellulosic fibers treated with a caustic solution under non-mercerizing conditions is cross-linked with a solution containing polymeric polycarboxylic acid cross-linking agents. The treated cellulosic fibrous material is dried and cured in sheet form to promote intrafiber cross-linking. Cross-linked fiber products of this method, which is economic, that possess good absorption and wet resiliency properties are also disclosed.
1. A method for preparing cross-linked cellulosic fibers in sheet form having less than 15% by weight knots, the method comprising:
(a) treating cellulosic fibers with a caustic solution under non-mercerizing conditions to make caustic treated cellulosic fibers with a hemicellulose content greater than 8%;
(b) forming said caustic treated cellulosic fibers into a sheet;
(c) applying a polymeric carboxylic acid cross-linking agent to said sheet of caustic treated cellulosic fibers; and
(d) curing the cross-linking agent on said sheet of caustic treated cellulosic fibers to form a sheet of caustic treated fibers with intrafiber cross-links and less than 15% by weight knots.
2. The method of claim 1 , wherein the hemicellulose content of the cellulosic fibers is greater than 10%.
3. The method of claim 1 , wherein the hemicellulose content of the cellulosic fibers is between 8–15%.
4. The method of claim 1 , wherein the sheet produced in step (c) is dried prior to step (d).
5. The method of claim 1 , wherein the fibers have been treated with less than 10% caustic solution strength.
6. The method of claim 1 , wherein the fibers have been treated with less than 8% caustic solution strength.
7. The method of claim 1 , wherein the polymeric carboxylic acid cross-linking agent comprises a homopolymer of maleic acid monomer, a copolymer of maleic acid monomer, a terpolymer of maleic acid monomer or a mixture thereof.
8. The method of claim 7 , wherein the polymeric carboxylic acid cross-linking agent has an average molecular weight from about 400 to about 10000.
9. The method of claim 7 , wherein the polymeric carboxylic acid cross-linking agent has an average molecular weight from about 400 to about 4000.
10. The method of claim 7 , wherein the polymeric carboxylic acid cross-linking agent has a pH from about 1.5 to about 5.5.
11. The method of claim 7 , wherein the polymeric carboxylic acid cross-linking agent has a pH from about 2.5 to about 3.5.
12. The method of claim 1 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbency under load greater than about 8.0 g/g.
13. The method of claim 1 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbency under load greater than about 9.0 g/g.
14. The method of claim 1 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbent capacity greater than about 9.0 g/g.
15. The method of claim 1 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbent capacity greater than about 10.0 g/g.
16. The method of claim 1 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have a centrifuge retention capacity less than about 0.6 g/g.
17. The method of claim 1 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have a centrifuge retention capacity less than about 0.55 g/g.
18. A method of preparing a sheet of cross-linked cellulosic fibers having superior absorbency properties and less than 15% by weight knots, the method comprising:
(a) treating cellulose fibers with a caustic solution under non-mercerizing conditions to make caustic treated cellulose fibers with a hemicellulose content greater than 8%;
(b) forming a wet laid sheet of said caustic treated cellulosic fibers;
(c) applying a polymeric polycarboxylic acid cross-linking agent to said sheet of caustic treated cellulosic fibers to form a sheet of caustic treated cellulosic fibers impregnated with the cross-linking agent; and
(d) curing the cross-linking agent on said impregnated sheet of caustic treated cellulosic fibers to form intrafiber cross-links and less than 15% by weight knots.
19. The method of claim 18 , wherein the impregnated sheet produced in step (c) is dried prior to step (d).
20. The method of claim 18 , wherein the hemicellulose content of the caustic treated cellulosic fibers is greater than 10%.
21. The method of claim 18 , wherein the hemicellulose content of the caustic treated cellulosic fibers is between 8–15%.
22. The method of claim 18 , wherein the cellulosic fibers have been treated with less than 10% caustic solution strength.
23. The method of claim 18 , wherein the cellulosic fibers have been treated with less than 8% caustic solution strength.
24. The method of claim 18 , wherein the polymeric carboxylic acid cross-linking agent comprises a homopolymer of maleic monomer, a copolymer of maleic acid monomer, a terpolymer of maleic acid monomer, or a mixture thereof.
25. The method of claim 24 , wherein the polymeric carboxylic acid cross-linking agent has an average molecular weight from about 400 to about 4000.
26. The method of claim 24 , wherein the polymeric carboxylic acid cross-linking agent has a pH from about 1.5 to about 5.5.
27. The method of claim 24 , wherein the polymeric carboxylic acid cross-linking agent has a pH from about 2.5 to about 3.5.
28. The method of claim 18 , wherein the fibers in said sheet of caustic treated cellulose fibers with intrafiber cross-links have an absorbency under load greater than about 8.0 g/g.
29. The method of claim 18 , wherein the fibers in said sheet of caustic treated cellulose fibers with intrafiber cross-links have an absorbency under load greater than about 9.0 g/g.
30. The method of claim 18 , wherein the fibers in said sheet of caustic treated cellulose fibers with intrafiber cross-links have an absorbent capacity greater than about 9.0 g/g.
31. The method of claim 18 , wherein the fibers in said sheet of caustic treated cellulose fibers with intrafiber cross-links have an absorbent capacity greater than about 10.0 g/g.
32. The method of claim 18 , wherein the fibers in said sheet of caustic treated cellulose fibers with intrafiber cross-links have a centrifuge retention capacity less than about 0.6 g/g.
33. The method of claim 18 , wherein the fibers in said sheet of caustic treated cellulose fibers with intrafiber cross-links have a centrifuge retention capacity less than about 0.55 g/g.
34. A composition comprising a wet laid sheet of cellulosic fibers having a hemicellulose content greater than 8% and less than 15% by weight knots, said cellulosic fibers having been treated with a caustic solution under non-mercerizing conditions and having substantial intrafiber cross-linking formed from the application of a polymeric polycarboxylic acid cross-linking agent.
35. The composition of claim 34 , wherein the hemicellulose content of the cellulosic fibers is greater than 10%.
36. The composition of claim 34 , wherein the hemicellulose content of the cellulosic fibers is between 8–15%.
37. The composition of claim 34 , wherein the cellulosic fibers have been treated with less than 10% caustic solution strength.
38. The composition of claim 34 , wherein the cellulosic fibers have been treated with less than 8% caustic solution strength.
39. The composition of claim 34 , wherein the polymeric carboxylic acid cross-linking agent comprises a homopolymer of maleic acid monomer, a copolymer of maleic acid monomer, a terpolymer of maleic acid monomer, or a mixture thereof.
40. The composition of claim 39 , wherein the polymeric carboyxlic acid cross-linking agent has an average molecular weight from about 400 to about 4000.
41. The composition of claim 39 , wherein the polymeric carboxylic acid cross-linking agent has a pH from about 1.5 to about 5.5.
42. The composition of claim 39 , wherein the polymeric carboxylic acid cross-linking agent has a pH from about 2.5 to about 3.5.
43. The composition of claim 34 , wherein said caustic treated cellulosic fibers are cross-linked while they are in said sheet form.
44. The composition of claim 34 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbency under load greater than about 8.0 g/g.
45. The composition of claim 34 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbency under load greater than about 9.0 g/g.
46. The composition of claim 34 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbent capacity greater than about 9.0 g/g.
47. The composition of claim 34 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have an absorbent capacity greater than about 10.0 g/g.
48. The composition of claim 34 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have a centrifuge retention capacity less than about 0.6 g/g.
49. The composition of claim 34 , wherein the fibers in said sheet of caustic treated cellulosic fibers with intrafiber cross-links have a centrifuge retention capacity less than about 0.55 g/g.