Method of making regenerated cellulose microfibers and absorbent products incorporating same

1. A method of making microfibers of regenerated cellulose comprising:

a) preparing a first cellulosic dope having a first composition;

b) preparing a second cellulosic dope having a second composition which differs from the first composition of the first cellulosic dope;

c) spinning the first and second cellulosic dopes into composite nascent fibers each having a length and a segmented cross-section comprising a plurality of segments across the cross-section of the nascent fiber, the segments also extending along the length of the fiber and the nascent fibers including at least one longitudinally-extending segment formed from the first cellulosic dope juxtaposed with at least one longitudinally-extending segment formed from the second cellulosic dope;

d) regenerating the nascent fibers to splittable composite regenerated cellulose fibers each having a plurality of regenerated cellulose segments across the cross section of the regenerated fiber, the segments also extending along the length of the fiber and including at least a first longitudinally-extending regenerated cellulose segment formed from the first cellulosic dope juxtaposed with at least a second longitudinally-extending regenerated cellulose segment formed from the second cellulosic dope, wherein the first longitudinally-extending regenerated cellulose segment is joined to the second longitudinally-extending regenerated cellulose segment along a splittable interface; and

e) splitting the composite regenerated cellulose fibers into microfibers of smaller cross-section along the splittable interface between segments,

wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are cellulosic dopes without other fiber-forming components, and are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into micro fibers with a coarseness between 0.05 mg/100 m and 10 mg/100 m with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e) and said microfibers have a length weighted average length of from about 20% to about 50% of said larger splittable regenerated cellulose composite fibers.

2. The method according to claim 1 , wherein the composite regenerated cellulose fibers are split into microfibers with coarseness between 0.1 mg/100 m and 6 mg/100 m with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

3. The method according to claim 2 , wherein the composite regenerated cellulose fibers are split into microfibers with coarseness less than 1 mg/100 m with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

4. The method according to claim 2 , wherein the composite regenerated cellulose fibers are split into microfibers with coarseness less than 0.5 mg/100 m with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

5. The method according to claim 2 , wherein the composite regenerated cellulose fibers are split into microfibers with coarseness less than 0.25 mg/100 m with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

6. The method according to claim 1 , wherein the composite regenerated cellulose fibers are split into microfibers with a length weighted average length between 0.1 mm and 10 mm.

7. The method according to claim 1 , wherein the composite regenerated cellulose fibers are split into microfibers with a length weighted average length between 0.2 mm and 6 mm.

8. The method according to claim 1 , wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into microfibers with a coarseness between 0.05 mg/100 m and 10 mg/100 m with a microfiber yield of more than 60% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

9. The method according to claim 1 , wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into microfibers with a coarseness between 0.05 mg/100 m and 10 mg/100 m with a microfiber yield of more than 70% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

10. The method according to claim 1 , wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into microfibers with a coarseness between 0.05 mg/100 m and 10 mg/100 m with a microfiber yield of more than 80% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

11. The method according to claim 1 , wherein the first cellulosic dope comprises dissolved cellulose at a first concentration and the second cellulosic dope comprises dissolved cellulose at a second concentration different from the first concentration of cellulose in the first cellulosic dope.

12. The method according to claim 1 , wherein the first cellulosic dope comprises dissolved cellulose of a first purity and the second cellulosic dope comprises dissolved cellulose of a second purity different from the first purity of the cellulose dissolved in the first dope.

13. The method according to claim 12 , wherein at least one of the cellulosic dopes comprises purified alpha-cellulose and at least one of the cellulosic dopes comprises dissolved Kraft pulp.

14. The method according to claim 12 , wherein at least one of the cellulosic dopes comprises dissolved high yield pulp.

15. The method according to claim 1 , wherein the first cellulosic dope contains dissolved cellulose having a first average degree of polymerization different from a second average degree of polymerization of dissolved cellulose in the second cellulosic dope.

16. The method according to claim 1 , wherein the first cellulosic dope has a connatural saccharide content different from the connatural saccharide content of the second cellulosic dope.

17. The method according to claim 1 , wherein the first cellulosic dope has a constituent not present in the second cellulosic dope.

18. The method according to claim 1 , wherein the splittable composite regenerated cellulose fibers have at least 2 longitudinally-extending regenerated cellulose segments formed from the first cellulosic dope alternately juxtaposed with at least 2 longitudinally-extending regenerated cellulose segments formed from the second cellulosic dope such that juxtaposed segments formed from the cellulosic dopes of different compositions are joined along splittable interfaces therebetween.

19. The method according to claim 1 , wherein the splittable composite regenerated cellulose fibers have at least 4 longitudinally-extending regenerated cellulose segments formed from the first cellulosic dope alternately juxtaposed with at least 4 longitudinally-extending regenerated cellulose segments formed from the second cellulosic dope such that juxtaposed segments formed from the cellulosic dopes of different compositions are joined along splittable interfaces therebetween.

20. The method according to claim 1 , wherein the splittable composite regenerated cellulose fibers have at least 8 longitudinally-extending regenerated cellulose segments formed from the first cellulosic dope alternately juxtaposed with at least 8 longitudinally-extending regenerated cellulose segments formed from the second cellulosic dope such that juxtaposed segments formed from the cellulosic dopes of different compositions are joined along splittable interfaces therebetween.

21. The method according to claim 1 , wherein the splittable composite regenerated cellulose fibers have at least 16 longitudinally-extending regenerated cellulose segments formed from the first cellulosic dope alternately juxtaposed with at least 16 longitudinally-extending regenerated cellulose segments formed from the second cellulosic dope such that juxtaposed segments formed from the cellulosic dopes of different compositions are joined along splittable interfaces therebetween.

22. The method according to claim 1 , wherein the splittable fiber is a hollow segmented fiber.

23. The method according to claim 1 , wherein at least one of the first and second cellulosic dopes comprise cellulose dissolved in a solvent comprising N-methyl morpholine-N oxide (NMMO).

24. The method according to claim 1 , wherein the first and second cellulosic dopes comprise cellulose dissolved in a solvent comprising N-methyl morpholine-N oxide (NMMO).

25. The method according to claim 1 , wherein at least one of the first and second cellulosic dopes comprise cellulose dissolved in a solvent comprising an ionic liquid.

26. The method according to claim 1 , wherein the first and second cellulosic dopes comprise cellulose dissolved in a solvent comprising an ionic liquid.

27. The method according to claim 1 , wherein at least one of the first and second cellulosic dopes comprise cellulose dissolved in a solvent comprising an ionic liquid, wherein the ionic liquid comprises an imidazolium salt.

28. The method according to claim 27 , wherein the first and second cellulosic dopes comprise cellulose dissolved in a solvent comprising an ionic liquid, wherein the ionic liquid comprises a dialkylimidazolium salt.

29. A method of making microfibers of regenerated cellulose comprising:

a) preparing a first cellulosic dope comprising cellulose dissolved in a solvent including an ionic liquid, the first cellulosic dope having a first composition;

b) preparing a second cellulosic dope comprising cellulose dissolved in a solvent including an ionic liquid, the second cellulosic dope having a second composition which differs from the first composition of the first cellulosic dope;

c) spinning the first and second cellulosic dopes into composite nascent fibers each having a length and a segmented cross-section comprising a plurality of segments across the cross-section of the nascent fiber, the segments also extending along the length of the fiber and the nascent fibers including at least one longitudinally-extending segment formed from the first cellulosic dope juxtaposed with at least one longitudinally-extending segment formed from the second cellulosic dope;

d) regenerating the nascent fibers to splittable composite regenerated cellulose fibers each having a plurality of regenerated cellulose segments across the cross section of the regenerated fiber, the segments also extending along the length of the fiber and including at least a first longitudinally-extending regenerated cellulose segment formed from the first cellulosic dope juxtaposed with at least a second longitudinally-extending regenerated cellulose segment formed from the second cellulosic dope, wherein the first longitudinally-extending regenerated cellulose segment is joined to the second longitudinally-extending regenerated cellulose segment along a splittable interface; and

e) splitting the composite regenerated cellulose fibers into microfibers of smaller cross-section along the splittable interface between segments and having a length weighted average length of from about 20% to about 50% of said larger splittable regenerated cellulose composite fibers,

wherein said first cellulosic dope and second cellulosic dope are cellulosic dopes without other fiber-forming components.

30. The method according to claim 29 , wherein at least one of the cellulose dopes comprises an ionic liquid which includes an imidazolium salt.

31. The method according to claim 30 , wherein the imidazolium salt is 1-allyl-3-methylimidazolium chloride.

32. The method according to claim 29 , wherein the first and second cellulosic dope each comprise the same ionic liquid.

33. The method according to claim 29 , wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into microfibers with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e).

34. The method according to claim 29 , wherein the splittable fiber is a hollow segmented fiber.

35. The method according to claim 29 , wherein the first cellulosic dope contains dissolved cellulose having a first average degree of polymerization different from a second average degree of polymerization of dissolved cellulose in the second cellulosic dope.

36. The method according to claim 29 , wherein the first cellulosic dope has a connatural saccharide content different from the connatural saccharide content of the second cellulosic dope.

37. A method of making a wet-laid absorbent sheet comprising:

(a) preparing regenerated cellulose micro fibers fibers by way of:

i) preparing a first cellulosic dope having a first composition;

ii) preparing a second cellulosic dope having a second composition which differs from the first composition of the first cellulosic dope;

iii) spinning the first and second cellulosic dopes into composite nascent fibers each having a length and a segmented cross-section comprising a plurality of segments across the cross-section of the nascent fiber, the segments also extending along the length of the fiber and the nascent fibers including at least one longitudinally-extending segment formed from the first cellulosic dope juxtaposed with at least one longitudinally-extending segment formed from the second cellulosic dope;

iv) regenerating the nascent fibers to splittable composite regenerated cellulose fibers each having a plurality of regenerated cellulose segments across the cross section of the regenerated fiber, the segments also extending along the length of the fiber and including at least a first longitudinally-extending regenerated cellulose segment formed from the first cellulosic dope juxtaposed with at least a second longitudinally-extending regenerated cellulose segment formed from the second cellulosic dope, wherein the first longitudinally-extending regenerated cellulose segment is joined to the second longitudinally-extending regenerated cellulose segment along a splittable interface; and

v) splitting the composite regenerated cellulose fibers into microfibers of smaller cross-section along the splittable interface between segments, wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into microfibers with a coarseness between 0.05 mg/100 m and 10 mg/100 m with a microfiber yield of at least 50% based on larger splittable regenerated cellulose composite fibers subjected to step (a)(v), and having a length weighted average length of from about 20% to about 50% of said larger splittable regenerated cellulose composite fibers;

(b) preparing an aqueous furnish incorporating the regenerated cellulose microfibers made by step (a) as well as pulp-derived papermaking fibers;

(c) depositing the aqueous furnish on a foraminous support to form a nascent web and at least partially dewatering the nascent web; and

(d) drying the web to provide absorbent sheet,

wherein said first cellulosic dope and second cellulosic dope are cellulosic dopes without other fiber-forming components and micro fibers.

38. The method according to claim 37 , wherein the aqueous furnish comprises a pulp derived fiber selected from Kraft hardwood fiber, Kraft softwood fiber, high yield fiber, recycle fiber and mixtures thereof.

39. The method according to claim 37 , wherein the sheet has a basis weight of from about 5 lbs/3000 ft 2 ream to about 50 lbs/3000 ft 2 ream.

40. The method according to claim 37 , wherein the sheet has a basis weight of from about 7.5 lbs/3000 ft 2 to about 35 lbs/3000 ft 2 ream.

41. The method according to claim 37 , wherein the sheet comprises from about 1 wt % to about 30 wt. % of regenerated cellulose microfibers prepared by step (a).

42. The method according to claim 37 , wherein the sheet comprises from about 10 wt. % to about 75 wt. % of regenerated cellulose microfiber prepared by step (a).

43. The method according to claim 37 , wherein the sheet comprises from about 20 wt. % to about 70 wt. % of regenerated cellulose microfiber prepared by step (a).

44. The method according to claim 37 , wherein the sheet comprises from about 30 wt. % to about 65 wt. % of regenerated cellulose microfiber prepared by step (a).

45. The method according to claim 37 , wherein the sheet comprises from about 40 wt. % to about 60 wt. % of regenerated cellulose microfiber prepared by step (a).

46. The method according to claim 37 , wherein the sheet exhibits a wet/dry CD tensile ratio greater than 30%.

47. The method according to claim 37 , wherein the sheet exhibits a wet/dry CD tensile ratio of between about 35% and about 60%.

48. The method according to claim 37 , wherein the sheet exhibits a wet/dry CD tensile ratio of at least about 40%.

49. The method according to claim 37 , wherein the sheet exhibits a wet/dry CD tensile ratio of at least about 45%.