Esterification of Cellulose with Betaine using p-Toluenesulfonyl Chloride for the in-situ Activation of Betaine

A novel synthesis method was developed for betaine-modified cellulose ester using a mixed N,N-dimethylacetamide/lithium chloride solvent system; p-toluenesulfonyl chloride was used for the in-situ activation of the betaine. The influence of the reaction temperature and time, as well as the anhydroglucose unit to p-toluenesulfonyl chloride to betaine mass ratio on the degree of substitution of the product was evaluated. Increasing the proportion of betaine and p-toluenesulfonyl chloride was beneficial to the esterification reaction. The degree of substitution was 1.68 at 90 °C for 32 h with an anhydroglucose unit to p-toluenesulfonyl chloride to betaine molar ratio of 1 to 2 to 3. The physicochemical properties of the betaine-modified cellulose were closely related to the degree of substitution. Major changes in the morphologies, crystallinity, thermal properties, porosity, and the average degree of polymerization resulted from the modification. The introduction of betaine made cellulose esters thermally less stable than neat cellulose but more difficult to completely degrade. The crystalline structure of the cellulose esters was destroyed, and the products exhibited a porous nature. Dye sorption studies demonstrated that the betaine-modified cellulose holds the potential of adsorbing anionic substances, which is the premise of its application.