Preparation And Properties Of POM/TPU/Modified Nano-ZnO Composites

Polyoxymethylene (POM) easily forms larger spherulites in the molding process due to the regular structure of the molecular chain, leading to its notch sensitivity and low impact strength, so its application has been limited. Toughening POM using thermoplastic polyurethane (TPU) sacrifices its mechanical properties. In order to improve the overall performance of POM, POM/TPU/modified nano-ZnO composites were prepared by mechanical blending and nano-ZnO surface-modification technology with the coupling agent on the foundation of TPU toughening POM, in order to improve the strength of the POM/TPU blends. Effects of modified nano-ZnO content on mechanical properties of POM/TPU/modified nano-ZnO composites were studied by universal testing machine controlled by a computer. Crystal morphology and crystallization characteristics of the composites were analyzed by polarizing microscope (PLM), differential scanning calorimeter (DSC) and X-ray diffractometer (XRD). Rheological properties of the composites were studied by rotational rheometer, capillary rheometer, melt flow rate meter and HAAKE torque rheometer. In addition, we studied the non-isothermal crystallization kinetics, fracture mechanism, the heat distortion temperature and shape memory properties of the composites.The results showed that appropriate modified nano-ZnO uniformly dispersed in POM matrix, enhanced and toughened POM matrix. When the content of modified nano-ZnO was 0.3 wt%, POM/TPU/modified nano-ZnO composites demonstrated favourable comprehensive mechanical properties. Modified nano-ZnO acted as heterogeneous nucleating agent in the composites, could promote the crystallization of POM, and diminish the spherulite size of POM. When the content of modified nano-ZnO was 0.3 wt%, composites had the best crystal properties.Jeziorny method and Mo’s equation could better describe the non-isothermal crystallization kinetics of POM/TPU blends and POM/TPU/modified nano-ZnO composites, which showed that the crystallization process were greatly influenced by cooling rate, both homogeneous nucleation and heterogeneous nucleation were existed in crystallization, the addition of modified nano-ZnO accelerated the crystallization rate of POM, improved crystallization temperature.Effects of notches and holes on tensile properties of POM/TPU blends and POM/TPU/modified nano-ZnO composites were tested. Fracture mechanics were analyzed by J-integral of three point bending test. The resistance to crack initiation (Jc), the resistance to steady state crack propagation (Rp) and the resistance to crack growth at maximum load (Rmax) were calculated. The results showed that the addition of modified nano-ZnO improved notch fracture toughness of POM.The heat distortion temperature of POM could be improved with an appropriate amount of modified nano-ZnO, but the addition of modified nano-ZnO increased melt viscosity, slightly reduced flowability and deformation recovery rate of POM/TPU/modified nano-ZnO composites.