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Cold plasma is an emerging technology offering many potential applications for food packaging. While it was originally developed to increase the surface energy of polymers, enhancing their adhesion and printability, it has recently emerged as a powerful tool for surface sterilisation of both food and food packaging materials. The food packaging industry is still dominated by petroleum derived polymers but in the past few decades there has been significant interest in the development of environment friendly, biodegradable green polymers. In this study, the interaction and effects of cold plasma with biopolymer based packaging materials (polylactic acid, zein, sodium caseinate, starch, chitosan and gelatin) and its potential for active and intelligent packaging was investigated. DBD (Dielectric Barrier Discharge) plasma increased the surface roughness of all the treated polymers films. DBD plasma treatments did not induce significant changes in the thermal profile of the polymers, but significant increases in the initial degradation temperature and maximum degradation temperature was observed for poly(lactic acid) and starch. DBD plasma also increased the equilibrium moisture content of both protein films: zein and sodium caseinate, but no significant increases in the water vapour and oxygen permeability was noticed for any of the films. An increase in overall migration was observed in PLA for various food simulants however they were below the EU regulatory limits. Plasma treatment increased the polar component of the total surface energy of all the polymers. The increase in the O/C atomic ratio shows the formation of new oxygen-containing polar groups on the film surface of the plasma treated films. Plasma treatments of both zein and sodium caseinate film lead to a change in the protein conformation which was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. Plasma treatment of antimicrobial films (zein and chitosan) also increased their surface roughness. A significant increase in the diffusion coefficient was observed which lead to an accelerated release of the active compound into the food simulant. Phosphorescent optochemical oxygen sensors (Optech™ and PP based) were also evaluated for compatibility with DBD in-package plasma treatment under different gaseous environments. Both sensors worked well under the modified atmospheric condition (devoid of any oxygen) during plasma treatment. However, the PP based sensor was found to be largely degraded after plasma treatment when packed under atmospheric air. Optech™ sensors were found to be compatible with the plasma treatment under both gaseous environment tested, although, a re-calibration was required for sensor accuracy.
Pankaj, S. (2015). Cold plasma treatment of biodegradable films and smart packaging.Doctoral Thesis. Technological University Dublin. doi:10.21427/D7QS45