Synthesis of core–shell ZnO nanoparticles and their effect on mechanical and antibacterial properties for PLLA/ZnO nanocomposites

Abstract

AbstractTo overcome the inherent brittleness of renewable poly(l‐lactide) acid (PLLA) and enable it for use in a wide application, we successfully synthesized the toughening agent of ZnO nanoparticles grafted by poly(caprolactone‐co‐d‐lactide) (ZnO‐g‐PCLDLA) via sequential open‐loop polymerization. First, ZnO was silanized to produce hydroxyl groups on the surface of the nanoparticles. Initiated by hydroxyl groups on the ZnO core, the rubbery PCLDLA composed of caprolactone‐d‐lactide co‐polymeric segments and d‐lactide homo‐polymeric segments was successively polymerized, forming ZnO core–shell nanoparticles. PLLA/ZnO‐g‐PCLDLA nanocomposites were prepared by solution blending. The nanocomposites with 10 wt% ZnO‐g‐PCLDLA exhibited superior ductility, whose elongation at break was about 54 times higher than that of neat PLLA. This considerable increment of toughness was attributed to the rubbery shell of PCLDLA and the enhanced interfacial interaction from the interfacial stereocomplex crystallites, formed by co‐crystallization of the PLLA matrix and d‐lactide homo‐polymeric segments of the PCLDLA shell on ZnO. The PLLA/ZnO‐g‐ PCLDLA nanocomposite films possessed outstanding antimicrobial properties against Staphylococcus aureus and Escherichia coli. Positive ZnO produces an electrostatic force to interact with the negatively charged membrane of bacteria, thereby damaging the cell membrane and achieving significant antibacterial effects.Highlights ZnO‐g‐PCLDLA core–shell nanoparticles were constructed by sequential ROP. The ZnO core provided high rigidity and antimicrobial properties. The rubbery PCLDLA shell provided high elasticity and ductility. Interfacial interaction was greatly enhanced by the SC crystallites. The PLLA nanocomposite films exhibited outstanding antimicrobial activity.