Optimization of acid hydrolysis conditions to improve cellulose nanofibers extraction from wheat straw

Abstract

Cellulose nanofibers were isolated from wheat straw by a chemical-mechanical procedure. Chemical process eliminates non-cellulosic materials. This process includes acid hydrolysis, alkali treatment, and bleaching. Since the acid hydrolysis is a critical step in nanofiber extraction, its conditions were optimized based on the highest degree of crystallinity using the statistical response surface methodology. The chemical composition of fibers at different stages were analyzed and showed an increase in α-cellulose content. In the mechanical treatment, obtained chemical-purified cellulose microfibers were defibrillated into nanofibers employing a sonicator at 400 W power. The morphology of nanofibers was characterized using a scanning electron microscope and the average diameter of nanofibers was obtained to be 45 nm. In addition, the thermal properties of nanofibers and untreated fibers were studied by thermal gravimetric analyzer. The degradation temperature of nanofibers was reached beyond 300°C. These mentioned properties are suitable for cellulosic nanofibers used in polymeric nanocomposites.