Direct Carboxymethylation of Cellulose Fibers by Ternary Reactive Deep Eutectic Solvents for the Preparation of High-Yield Cellulose Nanofibrils

Carboxymethylation-modified cellulose nanofibrils (CMCNF) were prepared from bamboo fibers through a pretreatment process using a ternary deep eutectic solvent (DES) system consisting of chloroacetic acid, urea, and choline chloride. Grinding treatment was also employed. The properties of the resulting CMCNF were characterized using various analytical instruments including a fiber image analyzer, field-emission scanning electron microscope, X-ray diffractometer, and atomic force microscope. The results indicated that ternary DES pretreatment has the capability to carboxymethylate-modify the raw fiber material while maintaining the crystalline structure of cellulose. Additionally, it induced a wetting and swelling effect on the fibers, leading to the successful disruption of strong hydrogen bonds and the rapid production of cellulose nanofibrils during mechanical treatment. The carboxymethylation alteration enhanced the ability of the resultant CNF to disperse and increased the stability of the suspension. Furthermore, extending the duration of DES pretreatment enhances the process of fiber fibrillation and diminishes fiber polymerization. The CMCNF produced exhibited a high aspect ratio, with diameters ranging from 10 to 50 nm and lengths extending to a few micrometers. This study presents a novel approach and concept for producing carboxymethylated nanofibrillated cellulose. It also introduces a straightforward, environmentally friendly, and effective method for mass production of bamboo pulp nanofibrillated cellulose. This advancement is anticipated to enhance the processing and utilization of bamboo fiber resources, thereby contributing to an increased overall value.