Optimizing crystallinity and particle size of cellulose nanocrystals from rice straw biomass: an integrated sonication-assisted acid hydrolysis approach

This study focuses on producing cellulose nanocrystals (CNCs) derived from rice straw cellulose. It employs an integrated hydrolysis and ultrasonication approach to achieve an optimized balance between two crucial parameters, the crystallinity index (CI) and mean particle size (MPS), both vital for enhancing biopolymer reinforcement. The research investigates the effects of three key process parameters: sulfuric acid concentration (40 to 70%), ultrasound power (150 to 250 W), and ultrasound treatment time (30 to 120 min) using a Box-Behnken experimental design. The analysis reveals that both the crystallinity index and mean particle size data conform to a quadratic model with high coefficients of determination (R2 = 0.993 and 0.9922, respectively). The optimal conditions were identified through response surface optimization: sulfuric acid concentration of 51.62%, ultrasound treatment time of 48.55 min, and ultrasound power of 238.80 W. Under these conditions, CNC with a mean particle size of 65.87 nm and a crystallinity index of 90.01% were successfully obtained, resulting in a yield of 52.2% for optimized CNC. The ultrasonic cavitation process enhances crystallinity, leading to a pronounced peak sharpening in the nanocellulose spectra fingerprint region (893-1500 cm-1). Furthermore, the cellulose nanocrystals exhibit a rod-shaped structure with an average length of 190 +/- 6 nm and width of 35 +/- 3 nm.