Investigation of a Widely Applicable Process for Extracting Carboxyl-rich Cellulose Nanocrystal (CNC)

Herein, carboxyl-rich cellulose nanocrystals (CNC) were obtained through a designed TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) mediated oxidation process without any subsequent mechanical treatment, which was proved to be widely suitable for commonly used cellulosic sources, including fibril-like fibers and lignocellulose biomasses. CNC prepared from the acid-free process showed better dispersion stability, less aggregation, higher aqueous UV transmittance and crystallinity compared with that from sulfuric acid hydrolysis process. Furthermore, the residuals in the insoluble precipitate were further conducted ultrasonic treatment and extra CNC was obtained from the oxidized cotton and ramie cellulose while cellulose nanofibril (CNF) was extracted from rice straw and pine powder, attributing to their different native structures. The total yields of nanocelluloses (NCs) were up to 63.2–68.3 %, improving the utilization ratio of the raw materials. This work provided a widely applicable acid- and mechanic-free route in fabricating CNC with inherent carboxyl groups and described an understanding of the relationship between the native structure of raw materials and their products, which is beneficial for improving the application of NCs.