Poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] active bilayer films obtained by compression moulding and applying essential oils at the interface

Four active components, oregano essential oil (OR) and its respective main compound carvacrol (CA) and clove essential oil (CLO) and its respective main compound eugenol (EU), were used separately to obtain, using compression moulding, poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) bilayer films with antimicrobial activity. The active compounds were sprayed (15% w/w, polymer to active compound ratio) at the interface between two layers of PHBV, which were joined using thermo-compression. Tensile, barrier and optical properties, as well as thermal behaviour, of the films were characterized after one week at 25 degrees C and 53% relative humidity. Likewise, the antimicrobial activity of the films was evaluated against Escherichia coli and Listeria innocua. Although the tensile properties of the films were not improved with respect to pure PHBV films by the addition of the active compounds, more transparent materials with better water vapour barrier capacity were obtained. Thermogravimetric analyses showed that CA and EU slightly decreased the polymer thermal stability, while OR and CLO led to more thermally resistant material. Miscibility of actives with the polymer was assessed through the promoted decrease in melting temperature and degree of crystallinity. PHBV films allowed the release of the active compounds in adequate amounts and at adequate rates into culture media to control the microbial growth of the two tested bacteria. The films were significantly more effective against E. coli than against L. innocua. Both bacteria were more sensitive to OR and to its main compound, CA, due to the greater antimicrobial effectiveness of these components. (c) 2016 Society of Chemical Industry