Influence of surface modification of zinc oxide on physical properties of high density polyethylene

Inorganic nanofillers have sparked important research in the field of polymer nanocomposites because they can improve the properties of polymers. Hydrophobic ZnO nanoparticles modified by oleic acid (OA) were designed and prepared to accelerate the dispersion state of ZnO in the high viscosity polyethylene (HDPE), and enhance the performance of HDPE. HDPE/ZnO nanocomposites with different kinds and fractions of ZnO were further prepared via melt mixing method. The result showed the hexagonal and spindle-like ZnO nanoparticles with size distribution of 150-300 nm was acquired in the absence and presence of OA. Compared with surface untreated ZnO (U-ZnO), ZnO nanoparticles modified by OA (O-ZnO) can disperse evenly into HDPE at the fraction of OZnO below 5 wt%. TG data showed the presence of nanosized U-ZnO and O-ZnO in HDPE can significantly enhance the thermal stability of HDPE through raising the activation energy of HDPE in thermal decomposition process. The thermal decomposition order (n) for HDPE/ZnO nanocomposites was mostly bigger than that of HDPE, demonstrating the decomposition mechanism for HDPE became more complicated because of the addition of ZnO nanoparticles. DSC data showed U-ZnO nanoparticles cannot accelerate nucleation of HDPE and seemed to postpone the crystallization process, and O-ZnO nanoparticles was heterogeneous nucleating agent for HDPE. Moreover, the tensile and impact strength of HDPE was improved by the addition of O-ZnO, and connected with the dispersion state of ZnO nanoparticles in HDPE. The improvement in thermal stability, crystallization and mechanical properties by adding ZnO into HDPE matrix significantly enhance the potential of HDPE in food packaging, electronic packaging, drug and pharmaceutical bottles.