Method for bleaching and color stripping recycled fibers

Abstract

A method for bleaching and color stripping recycled fibers by treating the fibers with a mixture of sodium borohydride and sodium bisulfite.

1 . A method for bleaching and color stripping recycled fibers; said method comprising steps of: 
 (a) adding sodium bisulfite to a recycled fiber slurry to produce a bisulfite-treated slurry; and    (b) adding to the bisulfite-treated slurry a mixture produced by combining: (i) an aqueous solution comprising sodium borohydride and sodium hydroxide; and (ii) an aqueous solution comprising sodium bisulfite.    
     
     
         2 . The method of  claim 1  in which an amount of bisulfite used for pretreatment ranges from 0.025% to 5% based on weight of dry fiber.  
     
     
         3 . The method of  claim 2  in which a ratio of (moles bisulfite-moles hydroxide)/moles borohydride combined to produce said mixture is from 0 to 25.  
     
     
         4 . The method of  claim 3  in which an amount of sodium borohydride used to produce said mixture is from 0.003% to 0.12%, based on the weight of dry fiber.  
     
     
         5 . The method of  claim 4  in which a ratio of (moles bisulfite-moles hydroxide)/moles borohydride combined to produce said mixture is from 3 to 15.  
     
     
         6 . A method for bleaching and color stripping recycled fibers; said method comprising combining: (i) an aqueous solution comprising sodium borohydride and sodium hydroxide; and (ii) an aqueous solution comprising sodium bisulfite, to produce a combined solution, and adding said combined solution to an aqueous slurry of recycled fibers; 
 wherein a ratio of (moles bisulfite - moles hydroxide)/moles borohydride is from 0 to 25.    
     
     
         7 . The method of  claim 6  in which an amount of sodium bisulfite added is from 0.05% to 5%.  
     
     
         8 . The method of  claim 7  in which the ratio of (moles bisulfite-moles hydroxide)/moles borohydride is from 2 to 7 or from 9 to 16.  
     
     
         9 . The method of  claim 8  in which an amount of sodium borohydride added is from 0.003% to 0.12%, based on the weight of dry fiber.  
     
     
         10 . The method of  claim 9  in which the ratio of (moles bisulfite-moles hydroxide)/moles borohydride is from 9 to 16.