Rosin modified cellulose nanofiber as a reinforcing and co-antimicrobial agents in polylactic acid /chitosan composite film for food packaging

•A solvent-free green synthesis route was applied for the functionalization of cellulose nanofibers by rosin.•Rosin modified cellulose nanofiber (R-CNF) was used as a reinforcement for polylactic acid (PLA) to prepare a R-CNF/PLA/chitosan composite film.•R-CNF reinforced composite film had better mechanical properties than those of CNF reinforced film when at the same reinforcing fiber load.•The R-CNF was found to have a synergistic antimicrobial effect with chitosan against E. coli and B. subtilis. Cellulose nanofiber (CNF) was modified by rosin and used as a reinforcement filler within a polylactic acid (PLA) matrix. The resulting film was then coated with chitosan (CHT) to prepare a two-layer composite film for antimicrobial food packaging. The FT-IR spectra of rosin modified CNF (R-CNF) displayed a clear peak at 1730cm−1, which confirmed the successful esterification of CNF by rosin. The R-CNF showed a better dispersion in PLA matrix than CNF and the loading of R-CNF had a significant effect on the mechanical properties of the resulting film. A percolation network was formed when the R-CNF loading was 8%, where the composite film displayed optimum mechanical properties. The antimicrobial test showed that the R-CNF/PLA/CHT composite film exhibited excellent antimicrobial performance against E. coli and B. subtilis, which could be attributed to the synergistic antimicrobial effect of CHT and rosin.