Preparation of Anti-Bacterial Cellulose Nanofibrils (CNFs) from Bamboo Pulp in a Reactable Citric Acid–Choline Chloride Deep Eutectic Solvent

In this study, bamboo pulp was simultaneously fibrillated and esterified in one-pot citric acid−choline chloride deep eutectic solvent treatment. The results indicated that increasing the temperature and time promoted esterification, yielding 0.19 to 0.35 mmol/g of the carboxyl group in CNFs. However, increasing the temperature and time resulted in decreases in yields and the diameter of CNFs from 84.5 to 66.6% and 12 to 4 nm, respectively. Analysis of the anti-bacterial activities of CNFs suggested that the high carboxyl group content corresponded to the effective inhibition of Escherichia coli and Staphylococcus aureus Taking yield, size, carboxyl group content, and anti-bacterial activate into consideration, treatment at 120 °C for 24 h was the optimal condition, yielding 76.0% CNF with 0.31 mmol/g carboxyl groups with a diameter of 8 nm and the inhibition fof E. coli (81.7%) and S. aureus (63.1%). In addition, effect of different CNFs on characteristics of polyvinyl alcohol (PVA) films were investigated. The results indicated that CNF obtained from the optimal condition was a favorable additive for the composite film, which enhanced (74%) the tensile strength of composite film compared with the pure PVA film due to its considerable size and carboxyl group content. However, the composite films did not show an anti-bacterial activate as CNF.