Antibacterial activity of sustainable composites derived from epoxidized natural rubber/silver-substituted zeolite/poly(lactic acid) blends

Abstract : Sustainable composites derived from epoxidized natural rubber (ENR)/silver-substituted zeolite (AgZ)/poly(lactic acid) (PLA) blends possessing antibacterial activity were reported. ENR, herein, acted as an antibacterial promoter providing more hydrophilicity to the composites and facilitating water diffusion. Two methodologies were used to prepare composites, including solution casting (S) as well as solution casting followed by roll milling (SR). Both composites were compared in terms of morphology, AgZ dispersion, water absorption, and antibacterial activity. The shift of Tg and tan δ toward lower temperature of PLA composites consistently confirmed the compatibility between ENR and PLA by DSC and DMA results, respectively. The good AgZ distribution was observed in composites-SR, as confirmed by SEM/EDX. The results of agar disk diffusion susceptibility test showed that PLA, AgZ/PLA, and even ENR/AgZ/PLA composites-S showed no or less inhibition zone; meanwhile, ENR/AgZ/PLA composites-SR showed the significant inhibition zone against both Escherichia coli and Staphylococcus aureus. Besides, the antibacterial activity of the composites was required at least 5 wt% of AgZ. More than 98% inhibition of S. aureus growth by the composites-SR was observed during 2–24 h of cultivation, whereas AgZ/PLA provided the highest inhibition of only 75% at 24 h of cultivation. Hence, the incorporation of ENR enhances the bactericidal activity of the composites. In terms of mechanical properties, incorporating ENR into the composites decreased tensile modulus and strength, but increased the impact strength significantly. Therefore, the developed composites could be promising materials in food and biomedical fields in which antibacterial and impact resistance properties are required.