Carboxylated nanocellulose obtained through ultrasonication using an alternative acid mixture solvent

The growing concern for a safer chemical industry has spurred research towards replacing strong acid solvents, because of the significant hazards they cause, such as issues related to effluent treatment and high corrosiveness. In the production of nanocellulose, sulfuric acid stands out as an example, being highly corrosive, yet widely used. This study aimed to investigate a more ecological acid mixture solvent, specifically comprising hydrochloric acid (HCl) and citric acid (CA), for obtaining carboxylated nanocellulose from kraft cellulose pulp. Distinct methodologies were employed based on three different durations, corresponding to each methodology (30 minutes, 60 minutes, and 90 minutes). FTIR analysis confirmed the occurrence of chemical modification. Among these methodologies, ultrasonication for 60 minutes yielded the best carboxylated nanocellulose, as determined through morphological analysis, with an average diameter of 8.4 nm and an average length of 123 nm. X-ray diffraction (XRD) revealed a decrease in crystallinity; however, both kraft pulp and carboxylated nanocellulose exhibited the cellulose Iβ allomorph. This surface modification paves the way for incorporating new functional properties into the design of composites, hydrogels, Pickering emulsions, drug delivery systems, food packaging, and biofilms.