One-step surface grafting of organic nanoparticles: in situ deposition of antimicrobial agents vanillin and chitosan on polyethylene packaging films
Nanoparticles of natural antimicrobial agents, volatile vanillin and non-volatile chitosan, were deposited in situ from an aqueous/ethanol solution onto a polyethylene (PE) surface using the ultrasonic method. The modified PE films were comprehensively characterized in terms of their microscopic, spectroscopic, mechanical and physical properties, and the presence of stable organic nanoparticles on the polymer surface was established. The nanoparticle-grafted films showed specific antimicrobial activity against Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. The vanillin nanoparticles led to a total inhibition of E. coli and the chitosan nanoparticles led to a total inhibition of S. aureus. The antimicrobial effect of the prepared active PE films was also examined on a food model, fresh-cut watermelons. Contact with the active film significantly inhibits the fruit microbial spoilage, especially in the case of the vanillin nanoparticles on PE. As they are surface-grafted in a nanoparticle form, the active agents are fully utilized, allowing for a significant enhancement in their effectivity and a reduction in the amount required. The presented method is of general interest as a facile technique for the surface deposition of organic nanoparticles, and can potentially be applied as a feasible approach for the incorporation of active agents into polymer matrices.