Kraft wood fibers for carboxymethyl cellulose

Abstract

Disclosed is a method for producing kraft wood fiber having an alpha-cellulose content greater than 97% and a viscosity greater than 40 centipoise. The method involves prehydrolyzing hardwood chips with water, kraft cooking, bleaching and caustic treatment. The resulting pulp can be converted to carboxymethyl cellulose superabsorbents having improved properties, particularly a high “absorbency under load”.

We claim:  
     
         1 . A method for producing an absorbent carboxyalkyl polysaccharide composition comprising (a) prehydrolyzing hardwood chips with water; (b) kraft cooking the prehydrolyzed hardwood chips to reduce the hardwood chips to fibers; (c) bleaching the cooked hardwood fibers; (d) treating the bleached hardwood fibers with caustic to form a treated hardwood fiber pulp having an alpha-cellulose content greater than 97% and a viscosity greater than 30 centipoise; and (e) converting the treated hardwood fiber pulp to a carboxyalkyl polysaccharide having an AUL of about 20 or greater.  
     
     
         2 . The method of  claim 1  wherein the hardwood chips are prehydrolyzed at an H factor of from about 300 to about 1000 with a corresponding maximum chip yield of about 80 percent.  
     
     
         3 . The method of  claim 1  wherein the hardwood chips are prehydrolyzed at an H factor of from about 500 to about 800.  
     
     
         4 . The method of  claim 1  wherein the hardwood chips are prehydrolyzed at an H factor of about 600 to about 700.  
     
     
         5 . The method of  claim 1  wherein the prehydrolyzed hardwood chips were cooked in a cooking liquid of sodium hydroxide and sodium sulfide to obtain an unbleached pulp with a Kappa number of 5 or greater.  
     
     
         6 . The method of  claim 1  wherein the caustic treatment of the bleached wood fibers is carried out with a sodium hydroxide solution at from about 15 to about 65 degrees C. from about 10- to about 100 minutes.  
     
     
         7 . The method of  claim 1  wherein the AUL is from 20 to about 25.  
     
     
         8 . The method of  claim 1  wherein the viscosity of the treated hardwood fiber pulp is about 40 centipoise or greater.  
     
     
         9 . The method of  claim 1  wherein the water used to hydrolyze the hardwood chips of step (a) is drained from the hardwood chips without neutralization.