Modified cellulose from chemical kraft fiber and methods of making and using the same

Abstract

A modified kraft pulp fiber with unique properties is provided. The modified fiber can be a modified bleached kraft fiber that is almost indistinguishable from its conventional counterpart, except that it has a low degree of polymerization (DP). Methods for making the modified fiber and products made from it are also provided. The method can be a one step acidic, iron catalyzed peroxide treatment process that can be incorporated into a single stage of a multi-stage bleaching process. The products can be chemical cellulose feedstocks, microcrystalline cellulose feedstocks, fluff pulps and products made from them.

We claim: 
     
       1. A bleached kraft fiber exhibiting an aldehyde content ranging from about 1 meq/100 g to about 9 meq/100 g, a carboxyl content of at least about 3 meq/100 g, a 0.5% capillary CED viscosity of less than about 10 mPa·s, an ISO brightness of at least about 88, and a length-weighted average fiber length of at least about 2 mm. 
     
     
       2. The fiber of  claim 1 , wherein the carboxyl content is from about 3 to about 6 meq/100 g. 
     
     
       3. The fiber of  claim 2 , exhibiting a ratio of total aldehyde content to carboxyl content ranging from about 0.3 to about 1.5. 
     
     
       4. The fiber of  claim 1 , exhibiting a ratio of total carbonyl content to aldehyde content ranging from about 0.9 to about 1.6. 
     
     
       5. The fiber of  claim 1 , wherein the ISO brightness is at least about 89. 
     
     
       6. The fiber of  claim 1 , wherein the ISO brightness is at least about 90. 
     
     
       7. The fiber of  claim 1 , wherein the length-weighted average fiber length is at least about 2.3 mm. 
     
     
       8. The fiber of  claim 7 , exhibiting a wet zero span breaking length greater than about 4 km. 
     
     
       9. The fiber of  claim 1 , exhibiting a Canadian standard freeness of at least about 700 mls. 
     
     
       10. The fiber of  claim 1 , exhibiting a kappa number less than about 1.9. 
     
     
       11. The fiber of  claim 1 , exhibiting a hemicellulose content from about 16% to about 18%. 
     
     
       12. The fiber of  claim 1 , exhibiting ketone functionality. 
     
     
       13. The fiber of  claim 1 , exhibiting a length-weighted curl index in the range of about 0.11 to about 0.23. 
     
     
       14. The fiber of  claim 1 , exhibiting an iron content of less than 5.5 ppm. 
     
     
       15. The fiber of  claim 1 , wherein the length-weighted average fiber length is at least about 2.5 mm. 
     
     
       16. The fiber of  claim 15 , exhibiting a wet zero span breaking length greater than about 6 km. 
     
     
       17. The fiber of  claim 1 , wherein the 0.5% capillary CED viscosity is less than about 7 mPa·s. 
     
     
       18. The fiber of  claim 17 , wherein the aldehyde content is at least about 2 meq/100 g. 
     
     
       19. The fiber of  claim 18 , exhibiting a Canadian standard freeness of at least about 730 mls. 
     
     
       20. The fiber of  claim 18 , exhibiting a ΔR of at least about 3. 
     
     
       21. The fiber of  claim 1 , wherein the 0.5% capillary CED viscosity is less than about 4 mPa·s. 
     
     
       22. The fiber of  claim 21 , wherein the aldehyde content is at least about 4 meq/100 g. 
     
     
       23. The fiber of  claim 22 , exhibiting a copper number of at least about 3. 
     
     
       24. The fiber of  claim 23 , exhibiting a ΔR of about 6 or greater. 
     
     
       25. The fiber of  claim 22 , wherein the fiber absorbs from about 5 to about 10 ppm ammonia per gram of fiber. 
     
     
       26. The fiber of  claim 25 , wherein the fiber absorbs from about 7 to about 10 ppm ammonia per gram of fiber. 
     
     
       27. The fiber of  claim 22 , wherein the fiber is compressible to a density of at least about 0.130 g/cc, upon compression at 10 psi gauge pressure. 
     
     
       28. The fiber of  claim 27 , wherein the fiber is compressible to a density of at least about 0.150 g/cc, upon compression at 10 psi gauge pressure. 
     
     
       29. The fiber of claim 1, wherein the fiber does not comprise an optical brightening agent. 
     
     
       30. The fiber of claim 2, wherein the fiber does not comprise an optical brightening agent. 
     
     
       31. The fiber of claim 11, wherein the fiber does not comprise an optical brightening agent.