Extraction of Cellulose Nanocrystals with a High Yield of 88% by Simultaneous Mechanochemical Activation and Phosphotungstic Acid Hydrolysis

An efficient approach for extracting cellulose nanocrystals (CNCs) was put forward through phosphotungstic acid (PTA) hydrolysis of cellulose raw materials under mechanochemical activation. Response surface methodology was employed for experimental design to determine the optimum conditions of CNCs preparation with software Design Expert. The results showed that quadratic polynomial model was qualified to represent the relationship between the response and independent variables and the regression model defined well the true behavior of the system. Under the optimal conditions, a high yield of up to 88.4%, crystallinity index of 79.6%, and a higher thermal stability can be achieved by combining mechanochemical activation and phosphotungstic acid hydrolysis. This process can improve effectively the hydrolysis efficiency, avoid a lengthy separation process, and reduce the preparation time. Meanwhile, compared to other techniques, mechanochemical activation is an energy-intensive method, and the process is environment-friendly. Phosphotungstic acid hydrolysis is easier to handle than liquid acids; meanwhile, the catalyst causes fewer corrosion hazards and can readily be recycled. Thus, an efficient green high-yield approach for the preparation of CNCs was achieved in the study.