Integrated and Sustainable Preparation of Functional Nanocellulose via Formic Acid/Choline Chloride Solvents Pretreatment

Abstract Formic acid/choline chloride (F-DES), one of high-efficiency deep eutectic solvents (DES) for lignocellulose pretreatment, has great potential in the production of nanocellulose (NC). In this work, the integrated preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) was developed using F-DES pretreatment and the followed ball milling. Then, the properties of the resultant NC products (F-NC) were comprehensively investigated. The NC samples obtained from direct ball milling and urea/choline chloride (U-DES) plus ball milling (i.e. B-NC, and U-NC, accordingly) were used for comparison. Characterization results showed that similar to U-DES, F-DES pretreatment could effectively enhance the fibrillation of cellulose and facilitate the followed ball milling for the production of NC, and the yields of NC (CNCs plus CNFs) were over 95%. Yet, compared with B-NC and U-NC, F-NC with surface ester groups had better ability to stabilize the oil/water interface for further preparation of oil-in-water Pickering emulsion. In addition, F-DES has lower viscosity than U-DES. The recovery rate of F-DES could reach 92% after three cycles, and the recycled F-DES without obvious increase of viscosity showed better reusability to make the whole process clean and sustainable.