Applying ultrasound-assisted processing to obtain cellulose fibres from rice straw to be used as reinforcing agents

Abstract

Rice straw (RS) is one of the most globally abundant agro-industrial residues. For its valorisation, a green combined ultrasound-reflux heating method was applied to obtain cellulose fibres (CF) from RS. The new method produced CF with a higher yield (37%) than the alkaline process (29%), more hydrophilic, and with a lower tendency to aggregate. Despite the slightly different degree of purification detected by the chemical and FTIR analysis, both fibres exhibited similar crystallinity, thermal behaviour, morphogeometric characteristics, and aspect ratio distributions (20–60). Both CF showed similar reinforcing capabilities in methylcellulose/gum Arabic films, enhancing the film stretchability and resistance to break by about 33% and 20%. Non-noticeable changes in water vapour permeability and the light internal transmission were observed, indicating good compatibility CF-polymer matrix. Therefore, using the ultrasound-heating method to obtain CF is an eco-friendlier process than the alkaline treatment, supplying suitable fibres as industrial reinforcing agents. Industrial relevanceUltrasound, an emerging technology in food processing, combined with reflux heating, can be a green alternative for obtaining cellulose microfibres for industrial applications. The new combined method was faster than the alkaline process (1.5 h vs. 6 h) and was more environmentally-friendly since it does not require a strong alkaline solution. Besides, both cellulose microfibres exhibited similar performances when incorporated into a polymer matrix. These results boost knowledge in the food packaging field, as well as the valorisation of agro-industrial wastes for industrial applications.