Degradation of cotton cellulose treated with hydrochloric acid either in water or in ethanol

Cotton cellulose was acid treated either in water or in ethanol, containing 1.39% HCl, at 45 and 65 °C for 1–5 h. The morphology and molecular weight distribution of celluloses before and after acid treatments were observed, and the differences in the structure of celluloses treated at different conditions were compared. The soluble sugar contents of celluloses during acid treatment were lower than 6%. Native cellulose showed smooth surface, whereas tiny pin-holes (15–20 nm in diameter) and wrinkles were found on the surface of acid-treated cellulose. Cellulose tended to have pin-holes after treated in ethanol at 65 °C. When treated in the same media, the weight-average degree of polymerization (DPw) of cellulose decreased with increasing treatment time or temperature. The degradation rate of cellulose treated in ethanol was faster than that of cellulose treated in water, while the temperature effect on degradation rate was more profound for cellulose treated in water. Nevertheless, the crystallinity of cellulose after acid treatments remained constant or slightly increased. Results indicate that acid treatment in ethanol has more profound effect on the molecular degradation and surface structure of cellulose than the acid treatment in water.