Photo-oxidative degradation of poly(ethylene-co-vinyl acetate)/nisin antimicrobial films

The photo-oxidative behaviour of different antimicrobial blown films based on poly (ethylene-co-vinyl acetate) (EVA) was studied. In particular, two samples of EVA containing different level of vinyl acetate comonomer (namely 14% and 28%) were used as matrices while nisin at different concentrations was used as antimicrobial agent. The degradation was followed by analyzing the changes in the spectroscopic behaviour and of the elongation at break measured in tensile tests. Moreover, changes in the antimicrobial activity of the films were followed by measuring the inhibition halo in agar diffusion tests. The results indicate that nisin acts as an excellent UV stabilizer for both samples of EVA used and especially for the sample with the higher vinyl acetate content. The protective effect of nisin is accompanied by a progressive decrease of the antimicrobial properties as a function of the photo-oxidation time due to the photo-degradation of the additive, which causes the inactivation of the additive. (C) 2012 Elsevier Ltd. All rights reserved.