Method for preparation of cellulose nanocrystals and nanofibrils

Abstract

A method for producing nanocellulose is described herein. The method includes contacting a cellulosic material with an oxidizing agent, and a compound selected from the group consisting of an alkali metal bromide, an alkali metal iodide, an alkali metal fluoride, an alkali metal chloride, or a combination thereof, in an aqueous solution to provide an oxidized cellulose mixture. The nanocellulose prepared according to the method is also described.

1 . A method for producing nanocellulose, the method comprising,
 contacting a cellulosic material with
 an oxidizing agent, and 
 a compound selected from the group consisting of an alkali metal bromide, an alkali metal iodide, or a combination thereof, 
   in an aqueous solution to provide an oxidized cellulose mixture comprising an oxidized cellulose precipitate, and   mechanically treating the oxidized cellulose precipitate to provide oxidized cellulose nanofibrils.   
     
     
         2 . The method of  claim 1 , wherein the method excludes a nitroxyl radical compound. 
     
     
         3 . The method of  claim 1 , wherein mechanically treating comprises sonicating. 
     
     
         4 . The method of  claim 1 , wherein the oxidized cellulose nanofibrils have an average diameter of 1 to 10 nanometers and an average length of 500 to 2500 nanometers. 
     
     
         5 . A method for producing nanocellulose, the method comprising,
 contacting a cellulosic material with
 an oxidizing agent, 
 a compound selected from the group consisting of an alkali metal bromide, an alkali metal iodide, or a combination thereof, and 
 a nitroxyl radical compound, 
   in an aqueous solution to provide an oxidized cellulose mixture comprising oxidized cellulose nanocrystals having an average diameter of 1 to 10 nanometers and an average length of 50 to 500 nanometers,   wherein the nitroxyl radical compound is of the formula   
       
         
           
           
               
               
           
         
         wherein R 1  and R 2  are independently at each occurrence a C 1-6  alkyl group. 
       
     
     
         6 . The method of  claim 5 , further comprising isolating the oxidized cellulose nanocrystals. 
     
     
         7 . The method of  claim 6 ,
 wherein isolating the oxidized cellulose nanocrystals comprises centrifuging the oxidized cellulose mixture to provide an aqueous dispersion comprising the oxidized cellulose nanocrystals and an oxidized cellulose precipitate, and   wherein the method further comprises mechanically treating the oxidized cellulose precipitate to provide oxidized cellulose nanofibrils.   
     
     
         8 . The method of  claim 7 , wherein mechanically treating comprises sonicating. 
     
     
         9 . The method of  claim 7 , wherein the oxidized cellulose nanofibrils have an average diameter of 1 to 10 nanometers and an average length of 500 to 2500 nanometers. 
     
     
         10 . The method of  claim 1 , wherein the aqueous solution comprises a pH adjusting compound in an amount effective to provide a pH of 9 to 12. 
     
     
         11 . The method of  claim 10 , wherein the pH adjusting compound is sodium hydroxide. 
     
     
         12 . The method of  claim 5 , wherein each occurrence of R 1  and R 2  are methyl. 
     
     
         13 . The method of  claim 1 , wherein the oxidizing agent is a hypohalite or an alkali metal salt thereof. 
     
     
         14 . The method of  claim 1 , wherein the oxidizing agent comprises sodium hypochlorite. 
     
     
         15 . The method of  claim 1 , wherein the cellulosic material is contacted with the oxidizing agent, the alkali metal bromide wherein the alkali metal bromide is sodium bromide, and optionally the nitroxyl radical compound. 
     
     
         16 . The method of  claim 1 , wherein the cellulosic material is cellulose pulp. 
     
     
         17 . The method of  claim 1 , wherein
 the cellulosic material comprises cellulose pulp;   the oxidizing agent comprises sodium hypochlorite;   the cellulosic material is contacted with the oxidizing agent and the alkali metal bromide;   the alkali metal bromide comprises sodium bromide;   the aqueous solution has a pH of 10 to 12; and   contacting the cellulosic material with a nitroxyl radical compound is excluded from the method.   
     
     
         18 . The method of  claim 5 , wherein
 the cellulosic material comprises cellulose pulp;   the oxidizing agent comprises sodium hypochlorite;   the cellulosic material is contacted with the oxidizing agent, the nitroxyl radical compound, and the alkali metal bromide;   the alkali metal bromide comprises sodium bromide;   the nitroxyl radical compound has the formula   
       
         
           
           
               
               
           
         
       
       and
 the aqueous solution has a pH of 10 to 12. 
 
     
     
         19 . An oxidized nanocellulose prepared by the method of  claim 1 . 
     
     
         20 . The oxidized nanocellulose of  claim 19 , wherein the oxidized nanocellulose is an oxidized cellulose nanofibril, an oxidized cellulose nanocrystal, or a combination thereof.