Carboxymethyl cellulose with tailored degree of substitution obtained from bacterial cellulose

Abstract

Among the multiple industrial applications of carboxymethyl cellulose (CMC), those related to food and beverages industries (e.g. as thickener, stabilizer, emulsifier, binding agent), involve one fourth of the global CMC consumption. In the last years, a number of abundant and underutilized vegetable cellulose sources have been assayed as raw material for CMC production, as alternatives to cotton linters or cellulose feedstocks obtained from bleached pulps derived from wood. Alternatively, cellulose of microbial origin appears as a very promising highly pure raw material for CMC production. Together with molecular weight and substituents distribution, it is well established that the degree of substitution (DS) of CMC plays a key role in most food and beverages applications. In the current contribution, highly pure cellulose of bacterial origin was used to produce CMC with tailored DS in a two-stage process consisting of alkalinization with sodium hydroxide, followed by etherification with sodium monochloroacetate. Aiming to get insight into how the carboxymethylation extent conferred to BC can be easily tuned within the DS interval allowed for food uses (i.e. 0.2–1.5), the effects of NaOH concentration, molar NaOH/anhydroglucose unit ratio, molar etherifying reagent/anhydroglucose unit ratio, and etherification time, were systematically analyzed. By proper control of those variables, CMC samples with tailored DS within the 0.60–1.52 interval could be successfully obtained. Samples with varying DS were further characterized by means of FTIR, solid state 13C NMR, XRD and TGA. The suitability of using TGA data for estimating the carboxymethylation extent achieved is proposed.