Ultrasonic pretreatment of cellulose in ionic liquid for efficient preparation of cellulose nanocrystals
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Currently, cellulose nanocrystals (CNCs) are primarily prepared with acid-catalyzed hydrolysis process using strong mineral acid. However, it suffers from low yield and high dosage of acid. For high yield and low dosage of acid, we prepare CNCs by two steps method. Firstly, the cellulose was ultrasonically pretreated in ionic liquid (IL) at mild conditions. Secondly, the samples were hydrolyzed by H2SO4 with concentration of 20–23%. The results showed that during ultrasonic pretreatment at mild conditions, accessibility and susceptibility of the amorphous region in cellulose was substantially enhanced upon cooperative action of ultrasonication and ILs. Meanwhile, the crystalline region of cellulose was retaining untouched, and further results in the fact that enhanced reactivity of the amorphous region enabled acid-catalyzed hydrolysis to proceed smoothly. Experimental results show that the extracted CNCs exhibited rod-like shape with dimension of 220–300 nm in length and 15–22 nm in width. It’s also shown that thermostability of CNCs was greatly enhanced compared to that prepared by the traditional process. Ultrasonic pretreatment of cellulose in ILs offered a promising and efficient system for CNCs preparation with high yield, crystallinity and low dosage of acid.
KeywordsCellulose nanocrystals Ultrasonic pretreatment Selectivity on hydrolysis Ionic liquids Yield
The authors are grateful for the financial support from Natural Science Foundation of Shandong Province (ZR2017MC007), R&D Focus of Shandong Province (2017GGX80102).
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