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 - 14 . (canceled)  
   
   
       15 . Cellulose derivatives, including cellulose ethers or cellulose esters produced by the method of  claim 17 .  
   
   
       16 . (canceled)  
   
   
       17 . 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;    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; and    d) converting the cellulose obtained in step c) to a cellulose ether or ester,    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.    
   
   
       18 . The method of  claim 17 , wherein the cellulose ether or ester is characterized by an increased viscosity and an increased brightness over cellulose ethers or esters prepared from cellulose that is not subjected in the terminal step of the multi-stage bleaching process to said agent capable of reducing carbonyl groups.  
   
   
       19 . The method of  claim 17 , wherein the cellulose ether or ester is characterized by an increased viscosity and an increased brightness over cellulose ethers or esters prepared from cellulose that is not subjected in the terminal step of the multi-stage bleaching process to said agent capable of reducing carbonyl groups.  
   
   
       20 . The method of  claim 17 , 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).  
   
   
       21 . The method of  claim 17 , wherein the aqueous slurry has a cellulose content of from 1 to 40% by weight based on the total weight.  
   
   
       22 . The method of  claim 17 , 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.  
   
   
       23 . The method of  claim 17 , 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.  
   
   
       24 . The method of  claim 17 , wherein the step of adding at least one agent capable of reducing carbonyl groups is performed at temperatures from ambient to 90° C.  
   
   
       25 . The method of  claim 17 , wherein the step of adding at least one agent capable of reducing carbonyl groups is performed at a pH value from 8 to 14.  
   
   
       26 . The method of  claim 17 , 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.  
   
   
       27 . The method of  claim 26 , wherein the post-processing step is a step of drying.  
   
   
       28 . The method of  claim 17 , wherein an oxidizing agent is added concurrently with the reducing agent.  
   
   
       29 . An improved method for preparing an cellulose ester or ether derivative wherein the method comprises 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 prior to conversion of the cellulose to the cellulose ester or ether derivative.  
   
   
       30 . The method of  claim 29 , wherein the multi-stage bleaching process is performed in batch mode or continuously.  
   
   
       31 . The method of  claim 29 , wherein an oxidizing agent is added concurrently with the reducing agent.  
   
   
       32 . Cellulose obtainable by a process comprising the steps of: 
 a. providing the mixture containing cellulose 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.    
   
   
       33 . The cellulose of  claim 32 , wherein the cellulose when converted to a cellulose ether has an increased brightness of 5% to 80% of the brightness of a cellulose ether that has not been treated with at least one agent capable of reducing carbonyl groups.  
   
   
       34 . The cellulose of  claim 32 , wherein the cellulose when converted to a cellulose ether has a viscosity that is increased by at least 8% to 50% over the viscosity of cellulose that has not been treated with at least one agent capable of reducing carbonyl groups.