Enhancing Chlorine-Free Purification Routes of Rice Husk Biomass Waste to Obtain Cellulose Nanocrystals

Abstract

The global interest in sustainable production of chemicals and materials from lignocellulosic biomass is boosted by the need of replacing fossil derivatives. Cellulose nanocrystals may prove to be one of the most promising green materials of modern times due to its intrinsic properties, renewability and abundance. The preliminary steps to obtain pure cellulose fibers are crucial and must be performed carefully. Several chlorine-free treatments have been developed in order to decrease the environment impact of the pulping process. Among all, traditional pulping with sodium hydroxide and hydrogen peroxide is still the most viable method for industries. Based on that, this work is dedicated to propose and optimize chlorine-free purification routes for isolating cellulose nanocrystals from rice husk agroindustrial waste. The novelty addressed here is the application of mild industrially viable process conditions to perform the chlorine-free purification routes, previously unexplored for rice husk as a source of lignocellulosic raw material. Two routes were performed, reducing lignin from 20 to 2.91% and 4.65%. The formation of cellulose nanocrystals was confirmed by the significant increase in crystallinity, ranging from 40.87% of rice husk, to 77.45% for the first route and 66.21% for the second rout, both being cellulose II. Thus, it has been shown the viability to obtain cellulose nanocrystals using a totally chlorine-free technique to extract and bleach cellulose from rice husk under mild process conditions, in order to add value to this residue reducing its volume and impact on the environment.