A Response Surface Methodology Study: Effects of Trivalent Cr Metal Ion-Catalyzed Hydrolysis on Nanocellulose Crystallinity and Yield

The preparation of nanocellulose via Cr(NO3)3-assisted sulfuric acid hydrolysis was optimized using response surface methodology (RSM). The experiment was performed using a five-level, four-factor central composite design coupled with RSM in order to optimize nanocellulose crystallinity and product yield. Four factors were evaluated for the preparation of nanocellulose: (1) reaction temperature, (2) hydrolysis time, (3) Cr(NO3)3 concentration, and (4) H2SO4 concentration. Based on the RSM model, the maximum yield and highest crystallinity of nanocellulose was obtained under hydrolysis conditions of 82.2 °C, 0.22 M Cr(NO3)3, and 0.80 M H2SO4 with 1 h of reaction. Furthermore, the physicochemical properties of the obtained nanocellulose were examined, revealing that the amorphous regions were successfully hydrolyzed, while the crystalline region remained unaltered. Morphology analysis also showed that the nanocellulose was an interconnected web-like network. Thus, both H2SO4 and Cr(III) metal salt concentration were important factors that influenced the nanocellulose yield and crystallinity index.