Study of antimicrobial and physicochemical properties of LDPE/propolis extruded films

Abstract

In this study, blended films of low-density polyethylene (LDPE) and different concentrations of propolis (5, 10, 15, and 20% w/w) were prepared by the extrusion method, and their antimicrobial and mechanical properties were investigated. Antimicrobial effects of the LDPE/propolis blended films were studied against Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Saccharomyces cerevisiae strains. The results indicated the inhibitory effects of these films against A. niger and S. cerevisiae, especially at propolis concentrations ≥ 15% w/w. The mechanical properties of the films such as tensile strength and elongation at break decreased with the addition of propolis, with the change in tensile strength being statistically significantly with respect to the control film (0% propolis). Incorporation of propolis into the LDPE films caused increased water vapor permeability and oxygen transmission rate (OTR) values compared with the control film. However, significant changes were only observed in the OTR values of the blended films containing 15 and 20% w/w propolis. Fourier transform infrared spectra, as well as thermal analysis data from thermal gravimetric analysis and differential scanning calorimetry, revealed that the addition of propolis (5–20% w/w) to the LDPE polymer matrix did not cause significant changes in chemical structure and certain mechanical properties. Field emission scanning electron microscopy images revealed that the morphological structures of the LDPE/propolis films were swollen and had island-like forms in comparison with the control, and this property progressed with rising propolis concentrations. These observations demonstrated the lack of strong interactions between LDPE and propolis.