Development of a Cellulose Nanofibril Production Process from Sea Squirt Tunics

This study aimed to develop a production process for cellulose nanofibrils (CNFs) derived from sea squirt tunics and to evaluate the feasibility of their surface modification for functional applications.Sea squirt tunics, which contain highly crystalline animal cellulose known as tunicin, were utilized as a sustainable marine biomass resource for CNF production.To enhance nanofibrillation efficiency, enzymatic pretreatment with cellulase was performed at varying enzyme dosages, and the effects on fiber morphology and physicochemical properties were systematically investigated.The results revealed that increasing the cellulase dosage progressively loosened the entangled fiber network of the tunic fibers and reduced the fine content.Among the tested conditions, a cellulase dosage of 5.0% was identified as the most effective for promoting nanofibrillation and was subsequently selected for high-pressure homogenization at 30,000 psi for 50 passes.The resulting enzymatically treated CNF (EN-CNF) exhibited nanoscale fiber dimensions, with an average fiber width of 18.21 nm.To further enhance the functionality and industrial applicability of the produced CNFs, quaternization and carboxymethylation reactions were performed to prepare cationic quaternized CNF (Q-CNF) and anionic carboxymethylated CNF (CM-CNF), respectively.Field-emission scanning electron microscopy (FE-SEM) analysis confirmed successful nanofibrillation in all samples, with average fiber widths of 17.36 nm for Q-CNF and 15.61 nm for CM-CNF.Zeta potential measurements further confirmed the successful introduction of surface functional groups, as Q-CNF exhibited a strong positive surface charge (+41.1 mV).In contrast, CM-CNF displayed a negative surface charge (-22.0 mV).Although the carboxymethylation efficiency of tunicate-derived cellulose was lower than that typically reported for plant-derived cellulose, likely due to its high crystallinity and the presence of residual protein components, the results demonstrated the feasibility of