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.