Development of Novel Natural Deep Eutectic Solvent for Cellulose Nanofibrillation of Orange Peel via New Surface Functionalization

In this study, novel deep eutectic solvents (DESs) based on different ratios of glutamic and tartaric acids were used for the production of cellulose nanofibrils (CNFs). Orange peel (OP) was used as the cellulosic raw material. High-speed mechanical stirring and ultrasonication were applied in the nanofibrillation process to save energy and preserve the CNF crystalline structure. A high yield of CNFs, up to 95.8%, was produced without scarifying the cellulose crystalline structure. CNFs showed a diameter range of 10.55–15.32 nm and a length range of 211–451 nm. The functionalization of the CNF surface was evidenced by several techniques such as elemental analysis, Fourier-transformed infrared spectroscopy, zeta potential, and determination of the carboxyl content. The zeta-potential values of CNFs ranged from −17.77 to −37.97 mV and had a carboxyl content range of 0.40–0.61 mmol/g, indicating the surface functionalization of CNFs. The optimal CNFs obtained were those pretreated by DESs (G2T), having a glutamic acid/tartaric acid ratio of 2:1. The surface modification of CNFs by DESs (G2T) created antibacterial activity against Gram-positive bacteria.