Controlled sulfuric acid alcoholysis of cellulose in a medium of primary monohydric alcohols (СnH2n+1OH, n=5-8) for obtaining cellulose nanocrystals

Abstract

The lack of a universal method for isolating cellulose nanocrystals (CNCs) has encouraged researchers to look for new methods and approaches as alternatives to traditional sulfuric acid hydrolysis. Moreover, acid alcoholysis has long been actively used in cellulose depolymerization processes to obtain a variety of alkyl glycosides and further alcoholysis products. In the present article, the authors continue their earlier research on the synthesis of CNCs by cellulose alcoholysis in an alcoholic environment. In this work, CNCs were obtained by controlled sulfuric acid alcoholysis of sulfate cellulose in a medium of primary monohydric alcohols (СnH2n+1OH, n = 5–8). A maximum CNC yield of 60% was achieved with pentanol-1 at a sulfuric acid concentration of 50%. The paper showed that in descending order of both the acid concentration corresponding to the maximum CNC yield and the yield itself, the alcohols studied can be arranged as follows: pentanol-1, hexanol-1, heptanol-1, and octanol-1. For 1-octanol, the maximum CNC yield was 20% at an acid concentration of 40%. The physicochemical properties of the isolated CNCs were studied. No surface alkylation of the synthesized CNCs was found to occur during cellulose alcoholysis in the media of the alcohols studied, as the properties of the CNCs, in general, were similar to those of CNCs obtained by standard sulfuric acid hydrolysis.