Chemically cross-linked cellulosic fiber and method of making same
The present invention relates to cross-linked cellulosic fiber having improved absorbency characteristics when compared to conventional cross-linked fibers. The cross-linked cellulosic fiber is obtainable by reacting pulp in the sheet or fluff form with one or more reagents selected from organic molecule having acid and aldehyde functional groups “acid aldehydes.” The invention also relates to a method of producing the cross-linked fiber. The method includes heating the treated cellulosic fibers to promote intrafiber cross-linking. The cross-linked fibers are characterized by having an improved centrifuge retention capacity, fluid acquisition rate, resiliency, absorbent capacity, absorbency under load, and other absorbent properties. The inventive cross-linked fibers are useful in forming absorbent composites, and in particular absorbent cores for use in absorbent articles.
1. A method of making chemically cross-linked cellulosic fibers comprising:
forming a wet laid sheet of caustic-treated cellulosic fibers;
applying an acid aldehyde cross-linking agent to the cellulosic fibers in the sheet form to form a sheet of impregnated fibers;
fiberizing the sheet in a hammermill to form fluffed fiber impregnated with a cross-linking agent; and
curing the cross-linking agent impregnated in the fluffed fiber to form intra-fiber cross-links, wherein curing takes place at a cure temperature within the range of from at least 320° F. to about 435° F.;
wherein the cross-linked fibers produced thereby have a centrifuge retention capacity of not more than 0.6 g saline/g fiber.
2. The method of claim 1 , wherein the cellulosic fiber is a wood pulp fiber selected from the group consisting of hardwood pulp, softwood cellulose pulp obtained from a Kraft or sulfite chemical process, and combinations or mixtures thereof.
3. The method of claim 1 , further comprising drying the sheet of impregnated fibers prior to fiberizing the sheet in a hammermill.
4. The method of claim 1 , wherein the sheet of impregnated fiber produced in step is not dried prior to fiberizing the sheet in a hammermill.
5. The method of claim 1 , wherein the acid aldehyde cross-linking agent is at least one acid aldehyde organic molecule containing aldehyde and carboxylic acid functional groups.
6. The method of claim 5 , wherein the acid aldehyde cross linking agent is selected from the group consisting of glyoxylic acid, succinic semialdehyde, and mixtures and combinations thereof.
7. The method of claim 5 , wherein the acid aldehyde cross-linking agent is applied to the fiber in an aqueous solution.
8. The method of claim 5 , wherein the acid aldehyde cross-linking agent has a pH from about 1.5 to about 4.0.
9. The method of claim 1 , wherein the cross-linking agent is applied to fiber in an amount from about 0.5 to 10% by weight, based on the total weight of the fiber.
10. The method of claim 9 , wherein the cross-linking agent is applied to the fiber in an amount from about 2 to 5% by weight, based on the total weight of the fiber.
11. The method of claim 1 , wherein curing takes place for about 0.5 minutes to about 8 minutes at a cure temperature within the range of from at least 320° F. to about 435° F.
12. The method of claim 1 , wherein the cross-linked fibers produced thereby have an absorbent capacity of at least about 9 g saline/g fiber.
13. The method of claim 1 , wherein the cross-linked fibers produced thereby have a dry bulk of at least about 12 cm 3 /g fiber.
14. The method of claim 1 , wherein the cross-linked fibers produced thereby have a free swell of at least about 10.0 g saline/g fiber.
15. The method of claim 1 , wherein the fibers are cross-linked with a mixture of cross-linking agents selected from the group consisting of: a mixture of glyoxylic acid and citric acid; a mixture of glyoxylic acid and polymaleic acid; and a mixture of glyoxylic acid, citric acid, and polymaleic acid.
16. The method of claim 1 , wherein the fibers are cross-linked with a mixture of cross-linking agents selected from the group consisting of: a mixture of glyoxylic acid and citric acid; a mixture of glyoxylic acid and a terpolymer of maleic acid, vinyl acetate, and ethyl acrylate; and a mixture of glyoxylic acid, citric acid, and a terpolymer of maleic acid, vinyl acetate, and ethyl acrylate.
17. A method of making a cross-linked cellulosic fiber, comprising:
treating individualized cellulosic fibers with caustic;
forming a non-woven mat or fluff of the caustic treated individualized fibers;
supplying a cross-linking agent to the non-woven mat or fluff of the caustic treated individualized fibers to form an impregnated non-woven mat or fluff impregnated with the cross-linking agent; and
curing the cross-linking agent on the impregnated non-woven mat or fluff to form intra-fiber cross-links;
wherein the cross-linked fibers produced thereby have a centrifuge retention capacity of not more than 0.48 g saline/g fiber.
18. The method of claim 17 , wherein the fibers are cross-linked with a mixture of cross-linking agents selected from the group consisting of: a mixture of glyoxylic acid and citric acid; a mixture of glyoxylic acid and polymaleic acid; and a mixture of glyoxylic acid, citric acid, and polymaleic acid.
19. The method of claim 17 , wherein the fibers are cross-linked with a mixture of cross-linking agents selected from the group consisting of: a mixture of glyoxylic acid and citric acid; a mixture of glyoxylic acid and a terpolymer of maleic acid, vinyl acetate, and ethyl acrylate; and a mixture of glyoxylic acid, citric acid, and a terpolymer of maleic acid, vinyl acetate, and ethyl acrylate.