Method for producing anion-modified cellulose nanofiber dispersion

Abstract

Provided is a method which comprises a process of having an anion-modified cellulose nanofiber dispersion contain monovalent or divalent metal ions. Consequently, the fluidity of an anion-modified cellulose nanofiber dispersion obtained thereby is improved.

1 . A method for producing an anion-modified cellulose nanofiber dispersion, comprising the steps of:
 (A) preparing anion-modified cellulose; and   (B) defibrating the anion-modified cellulose into nanofibers to prepare the anion-modified cellulose nanofiber dispersion,   the method further comprising, after the step (B) or between the steps (A) and (B), the step of adding a compound containing a monovalent or divalent metal ion, wherein an amount of the added metal ion is 0.3 to 10% (w/w) based on anion-modified cellulose nanofibers contained in a final anion-modified cellulose nanofiber dispersion.   
     
     
         2 . The method according to  claim 1 , wherein the step of preparing anion-modified cellulose comprises introducing carboxymethyl groups into cellulose and a degree of substitution of carboxymethyl group per glucose unit of the anion-modified cellulose is 0.01 to 0.50. 
     
     
         3 . The method according to  claim 1 , wherein the step of preparing anion-modified cellulose comprises introducing carboxyl groups into cellulose and an amount of the introduced carboxyl groups is 1.0 to 2.0 mmol/g based on a bone dry mass of the anion-modified cellulose. 
     
     
         4 . The method according to  claim 1 , wherein the step of adding a compound containing a monovalent or divalent metal ion comprises the steps of:
 oxidizing a starting cellulosic material with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides and mixtures thereof to introduce carboxyl groups into cellulose to prepare anion-modified cellulose;   subjecting the anion-modified cellulose to alkaline hydrolysis using an oxidizing agent or a reducing agent under alkaline conditions;   subjecting a reaction mixture from the alkaline hydrolysis to solid-liquid separation to recover a liquid; and   adding the liquid.   
     
     
         5 . A method for producing an anion-modified cellulose nanofiber dispersion, comprising the steps of:
 oxidizing a starting cellulosic material with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides and mixtures thereof to introduce carboxyl groups into cellulose to prepare anion-modified cellulose;   subjecting the anion-modified cellulose to alkaline hydrolysis using an oxidizing agent or a reducing agent under alkaline conditions; and   defibrating the anion-modified cellulose contained in a reaction mixture from the alkaline hydrolysis into nanofibers, without washing the cellulose.