Antimicrobial film from PLA/NR-grafted-modified chitosan-chelated-silver ions blend

New antimicrobial packaging films made from poly(lactic acid) (PLA) and natural rubber -graft-modified chitosan (chitosan-graft-polyacrylamide-2-methyl propane sulfonic acid (chitosan-g-PAMPS, Cg) loaded with different Ag+ concentrations (NR-g-Cg:Ag+, NCg:Ag) were prepared via a melt mixing process. After mixing NCg:Ag with PLA, the morphology of the compounds showed coarse surface with small particles of NCg:Ag dispersed in the PLA matrix. The size of the NCg:Ag particles found in the blends became smaller than that of the initial particles indicating partial compatibility of the blend between NCg:Ag and PLA. In addition, the compatibility of NCg:Ag and the remaining NCg:Ag particles may contribute to the improvement of the elongation at break, toughness and oxygen barrier properties of PLA films. The release of Ag+ on the order between 5 and 500 ng/cm(2) was observed depending on the pH value of the solution and immersion time. However, the optimum concentration of the released Ag+, which was approximately 100 ng/cm(2), affected the inhibition of microbial growth. The antimicrobial activity of the final materials was tested using colony count method with 5 bacterial species, both gram-negative and gram-positive bacteria. The blended film exhibited more than 99% reduction in numbers of all bacterial cells during 0-48 h of cultivation.

Automated summary

New antimicrobial packaging films were prepared using a blend of NCg:Ag and PLA, resulting in smaller particle size and improved mechanical and oxygen barrier properties. The released Ag+ at approximately 100 ng/cm(2) demonstrated effective inhibition of microbial growth. The blended film exhibited more than 99% reduction in bacterial cell numbers, showing strong antimicrobial activity.