Characterization and antimicrobial activity studies of polypropylene films with carvacrol and thymol for active packaging

Antimicrobial active films based on polypropylene (PP) were prepared by incorporating thymol and carvacrol at three different concentrations: 4,6 and 8 wt.% of both additives as well as an equimolar mixture of them. A complete thermal, structural, mechanical and functional characterization of all formulations was carried out. SEM micrographs showed certain porosity for films with high additives concentrations. A decrease in elastic modulus was obtained for the active formulations compared with neat PP. The presence of additives did not affect the thermal stability of PP samples, but decreased PP crystallinity and oxygen barrier properties. The presence of thymol and carvacrol also increased stabilization against thermooxidative degradation, with higher oxidation induction parameters. Finally, thymol showed higher inhibition against bacterial strain present in food compared with carvacrol, leading to higher antimicrobial activity. The obtained results proved the permanence of certain amounts of the studied additives in the polymer matrix after processing making them able to be used as active additives in PP formulations. (C) 2011 Elsevier Ltd. All rights reserved.