Green systhesis of carboxymethyl cellulose

Abstract

Contemporary production of Carboxymethyl Cellulose (CMC) is carried out almost exclusively by the solvent slurry process which utilises large quantities of solvents such as isopropyl alcohol, ethanol and methanol. This study has focused on reducing the environmental impact of the CMC production by evaluating water as an alternative solvent and microwave energy as an alternative heating source. Due to poor reaction efficiency and product quality the historical dry/aqueous CMC manufacturing process was abandoned in the late 1950’s. To address these short comings the reaction conditions were optimised and the best reaction products then compared to those produced by the conventional solvent slurry process. Current investigations into the use of microwave technology for the carboxymethylation of cellulose focus mainly on solvent based reactions. The application of microwave technology for the dry/aqueous reaction was evaluated by comparing reactions where microwave and conventional heating were used respectively. X-ray diffraction (XRD) was used to evaluate the degree to which the cellulose was swelled during mercerisation, while the product quality and molecular characteristics of the CMC products were used to evaluate the results of the etherification reactions. By comparing the change in slope of the conformational plot, as determined by size exclusion chromatography with multi-angle light scattering (SEC-MALS), to the degree of thixotropy of the polymer solutions it was found that the slope could be used as new and novel method for estimating the uniformity of the substituent distribution along the cellulose backbone. This is a parameter which has a significant impact on the solubility and rheology of the CMC. This investigation concluded that water could be used as a viable alternative solvent for the industrial production of technical grade CMC’s. Comparable reaction efficiencies of 74.8% to the solvent slurry process were achieved for the low DS products and the use of microwave heating was found to significantly reduce the reaction time.