Preparation of amino cellulose nanofiber via ε-poly-L-lysine grafting with enhanced mechanical, anti-microbial and food preservation performance

A green and effective method was proposed for producing amino cellulose nanofibers (ε-PL-TOCNs) with a yield of > 60%, which was obtained via ε-poly-L-lysine-grafting of 2, 2, 6, 6-tetramethylpiperidine-N-oxyl (TEMPO)-oxidized cellulose (TOC). The different carboxyl group content of TOC, EDC/NHS molar ratio and their adding ways, ε-poly-L-lysine concentration on the yield, amino content and physicochemical properties of ε-PL-TOCNs were systematically investigated and optimized. The ε-PL-TOCNs with the characteristics of enhanced thermal stability, improved mechanical strength, and fluorescence properties was successfully produced. Moreover, the ε-PL-TOCNs was zwitterionic with both anionic and cationic charges due to the co-existence of carboxyl and amino groups, thus showed excellent dispersion stability in a wide pH range except for the isoelectric point around pH 9. Notably, the ε-PL-TOCNs possessed an excellent anti-microbial effect (>99%) against Escherichia coli and Saccharomyces cerevisiae at 200 μg/mL loading dosage because of the positive role of amino groups, which made it applicable to extend the freshness of fruits. This preparation approach of amino cellulose nanofibers was advantageous over traditional methods owing to green and efficient methods, which expanded the application of cellulose nanofibers in anti-microbial agent and food preservation.