Comprehensive Utilization Strategy of Cellulose in a Facile, Controllable, High-Yield Preparation Process of Cellulose Nanocrystals Using Aqueous Tetrabutylphosphonium Hydroxide

Cellulose nanocrystals (CNC) have attracted great attention due to their excellent physical properties, abundant functional groups, and extensive use in many fields. However, how to facilely and efficiently prepare CNC and utilize the cellulosic raw materials comprehensively are still major challenges. Herein, a comprehensive utilization strategy of cellulose is implemented by facile, high-yield, controllable CNC preparation and effective enzymatic hydrolysis of the cellulosic residue. CNC with a mixed crystal form of cellulose I and cellulose II was successfully prepared through the partial dissolution of cellulose in an aqueous tetrabutylphosphonium hydroxide (TBPH) solution under mild conditions followed by regeneration, short-term ultrasonic dispersion, resulting in a high CNC yield of up to 72.2%, high crystallinity of up to 72.1%, and tunable dimensions and crystal structure of CNC. The characterization results confirmed that the present method produced a nonderivative form of cellulose and changed its crystalline structure to varying degrees, and CNC exhibited thermal stability comparable to that of the raw materials. A partial dissolution/regeneration/ultrasonic dispersion mechanism was proposed for this CNC preparation process. Cellulose residue obtained from the CNC production process led to a high enzymatic hydrolysis rate of up to 89.1%, which was twice as high as that of the raw material. The overall process finally resulted in a comprehensive cellulose utilization rate of more than 95%. The present strategy provides a candidate approach for the comprehensive utilization of cellulose through the synchronous production of advanced high-performance materials and fine chemicals.