Treatment of cellulose during bleaching with agent capable of reducing carbonyl groups

Abstract

The present invention relates to a method for treating a mixture containing cellulose, comprising at least one step of adding at least one agent capable of reducing carbonyl groups. The invention further relates to a specialty cellulose pulp, obtained by a method comprising treatment. Furthermore, the invention relates to the use of the specialty cellulose pulp according to the invention or the specialty cellulose pulp obtained by a method according to the invention for the production of cellulose derivatives or materials containing cellulose molecules, including but not limited to, cellulose ethers or cellulose esters. Cellulose derivatives obtained from the specialty cellulose pulp according to the invention display increased viscosity and/or improved brightness over cellulose derivatives obtained from specialty cellulose pulp not subjected to the inventive treatment.

1 . A method for treating a mixture containing cellulose that has not been pulted or that has been pulped chemically or chemically and mechanically, characterized in that the treatment comprises at least one step of adding at least one agent capable of reducing carbonyl groups.  
   
   
       2 . A method according to  claim 1 , character ized in that the at least one agent capable of reducing carbonyl groups is added during at least one step of a multi-stage bleaching process.  
   
   
       3 . A method for treating a mixture containing cellulose that has not been pulped or that has been pulped chemically or chemically and mechanically, wherein the method comprises: 
 a) providing the mixture as an aqueous slurry;    b) subjecting the slurry to a multi-stage bleaching process; and    c) during at least one step of the multi-stage bleaching process, adding a sufficient amount of at least one agent capable of reducing carbonyl groups of the cellulose to produce at least a partially reduced cellulose;    wherein at least the terminal step of the multi-stage bleaching process comprises the addition of at least one agent capable of reducing carbonyl groups of the cellulose to produce at least a partially reduced cellulose.    
   
   
       4 . The method of  claim 3 , wherein the mixture containing cellulose is obtained from (i) chemically or chemically and mechanically pulping wood or is obtained from (ii) unpulped cotton linters or from any combination of (i) and (ii).  
   
   
       5 . The method of  claim 3 , wherein the aqueous slurry has a cellulose content of from 0.1 to 40% by weight based on the total weight.  
   
   
       6 . The method of  claim 3 , wherein the agent capable of reducing carbonyl groups is selected from the group consisting of borohydrides, dimethylamine borane (DMAB), lithium aluminum hydride (LiAlH), and mixtures thereof.  
   
   
       7 . The method of  claim 3 , wherein the sufficient amount of the agent capable of reducing carbonyl groups added to the slurry is from 0.1 to 200 gram·moles per ton of the mixture containing cellulose.  
   
   
       8 . The method of  claim 3 , wherein the step of adding at least one agent capable of reducing carbonyl groups is performed at temperatures from ambient to 80° C.  
   
   
       9 . The method of  claim 3 , wherein the step of adding at least one agent capable of reducing carbonyl groups is performed at a pH value from 8 to 14.  
   
   
       10 . The method of  claim 3 , wherein the method further comprises performing at least one step of post-processing of the cellulose, wherein said post-processing is selected from the group consisting of de-hydration, filtering, drying, pressing, vacuum drying, enzyme treatment and removal of fines.  
   
   
       11 . The method of  claim 10 , wherein the post-processing step is a step of drying.  
   
   
       12 . The method of  claim 3 , wherein the multi-stage bleaching process is performed in batch mode or continuously.  
   
   
       13 . The method of  claim 3 , wherein the multi-stage bleaching process comprises adding at least one oxidizing agent to the unprocessed cellulose prior to the terminal step of the multi-stage bleaching process.  
   
   
       14 . The method of  claim 3 , wherein an oxidizing agent is added concurrently with the reducing agent.  
   
   
       15 . The method of  claim 3 , further comprising delignification of the mixture containing cellulose.  
   
   
       16 . An improved method for conducting a multi-stage bleaching process with an aqueous cellulose slurry where the cellulose that has not been pulped or that has been pulped chemically or chemically and mechanically, wherein the improvement comprises during at least one step of the multi-stage bleaching process, adding a sufficient amount of at least one agent capable of reducing carbonyl groups of the cellulose to produce at least a partially reduced cellulose and further wherein at least the terminal step of the multi-stage bleaching process comprises the addition of at least one agent capable of reducing carbonyl groups of the cellulose to produce at least a partially reduced cellulose.  
   
   
       17 . The method of  claim 16 , wherein the multi-stage bleaching process is performed in batch mode or continuously.  
   
   
       18 . The method of  claim 16 , wherein the multi-stage bleaching process comprises adding at least one oxidizing agent to the aqueous cellulose slurry prior to the terminal step of the multi-stage bleaching process.  
   
   
       19 . The method of  claim 16 , wherein an oxidizing agent is added concurrently with the reducing agent.  
   
   
       20 . The method of  claim 16 , further comprising delignification of the aqueous cellulose slurry.