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. |