Green cinnamaldehyde and thymol modified zinc oxide with double synergistic antibacterial effects in polypropylene

The green cinnamaldehyde (CA) and thymol (THY) separately or successively modified O‐ZnO (O‐ZnO‐CA, O‐ZnO‐THY, and O‐ZnO‐CA‐THY) were prepared after (3‐aminopropyl) triethoxysilane (KH550) was grafted to the surface of ZnO (O‐ZnO) and characterized by FTIR, TGA, and SEM. Polypropylene composites (PP/O‐ZnO‐CA, PP/O‐ZnO‐THY, and PP/O‐ZnO‐CA‐THY) were prepared by melting the modified O‐ZnO and PP. The antibacterial tests showed that the antibacterial rate of PP/O‐ZnO‐CA and PP/O‐ZnO‐THY against S. aureus and E. coli was obviously enhanced. It indicated an excellent synergetic antibacterial effect of O‐ZnO and the little CA or THY grafted on the surface of O‐ZnO. The antibacterial effect of O‐ZnO‐CA and O‐ZnO‐THY was related to the hydrophobic and hydrophilic groups contained in CA and THY. Importantly, CA and THY in O‐ZnO‐CA‐THY exhibited another excellent synergetic antibacterial effect against both S. aureus and E. coli. The antibacterial rate of three PP composites containing 4 phr O‐ZnO‐CA‐THY against S. aureus and E. coli reached 95% and 90%, respectively. The mechanism was regarded as that CA and THY grafted onto the same O‐ZnO improved the contact probability between antibacterial agents and bacteria. Moreover, O‐ZnO‐CA, O‐ZnO‐THY, and O‐ZnO‐CA‐THY had excellent migration resistance in the PP matrix. One kind of highly efficient compound antibacterial agents was prepared by grafting green natural organic antibacterial agents to the modified zinc oxide sheets. The polypropylene composites with the compound antibacterial agents have excellent antibacterial effect on both the Escherichia coli and Staphylococcus aureus, due to the double synergistic antibacterial effects.