Statistical optimization of cellulose nanocrystal from cotton cloth waste using sulfuric acid hydrolysis and response surface methodology

A statistical optimization of cotton cloth waste-based cellulose nanocrystal production was carried out using sulfuric acid hydrolysis and response surface methodology. The three independent variables, including sulfuric acid concentration (58–64 wt%), hydrolysis temperature (50–70 °C), and hydrolysis time (40–80 min) were selected by Box–Behnken design. The findings indicated that the quadratic polynomial models used to predict cellulose nanocrystal yield, crystallinity index, and average particle size were highly reliable, indicating strong relationships between the independent variables and the responses. The optimized conditions for acid hydrolysis were identified as 61.27 wt% sulfuric acid concentration, a hydrolysis temperature of 50 °C, and a hydrolysis time of 56 min. At these conditions, the experimentally highest cellulose nanocrystal yield and crystallinity index were 44.57 and 86.29%, respectively, while the smallest average particle size was 160 nm. The analysis of interaction effects indicated that the crystallinity index tended to increase under strong hydrolysis conditions, but the strong hydrolysis conditions caused a decrease in yield and average particle size. Moreover, the obtained cellulose nanocrystal properties met the required specifications, indicating cotton cloth waste is a prospective cellulose source for bio-nanomaterial production on an industrial scale. Besides, effective optimization measures can potentially curtail excessive costs in cellulose nanocrystal preparation.