Study On PP/POE/t-ZnOw Ternary Composites

Polypropylene (PP) is the most widely used thermoplastic. It has a good combination of physical and chemical properties, low yield cost, great recyclability and good processability. The main defect of polypropylene is its low toughness. Blending PP with elastomer such as POE (Polyolyaltha Olfin), EPDM (Ethylene-Propylene-Diene Monomer) as toughener is a prevailing way to overcome this problem. However, the incorporation of elastomer results to reduce the stiffness of the blends. Therefore, besides of POE as the toughener, tetrapod-shaped ZnO whisker (T-ZnOw) was also added into matrix to improve the mechanical properties of the blends via its unique stereostructure and high modulus and strength.The results of mechanical analysis showed that that the T-ZnOw treated by KH-570 improves the impact strength and tensile strength of the composite in comparison with that treated by KH-550. However the elongation at break was improved remarkably when the T-ZnOw was treated by 3 phr of KH-550.PP/POE/T-ZnOw ternary composites were prepared by melt extrusion. And their crystallization behaviors, rheological behaviors, mechanical properties were investigated using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and capillary rheometer.The analysis of isothermal crystallization behavior indicated that Avrami equation can perfectly describe the isothermal crystallization of PP and its composites. The T-ZnOw serves as nucleating agent and increases the crystallization rate of the composites. The mode of the nucleation and growth of PP and its composites may be a mixture of three dimensional spherulite growth and two-dimensional discotic growth. The equilibrium melting point of PP/POE andPP/POE/T-ZnOw composites obtained by the Hoffman-Weeks theory are lower than that of neat PP. All the isothermally crystallized samples exhibit one melting endotherms.The investigation of non-isothermal crystallization showed that Ozawa equation is not sutibale to describe the non-isothermal crystallization process, while the modified Avrami and Mo equations take great advantages over treating the non-isothermal crystallization kinetics. The incorporation of POE and T-ZnOw into matrix not only increases the crystallization rate of the matrix in the composites, but also influences the mechanism of nucleation and the growth of PP crystallites. The Hoffman-Lauritzen theory and its deduction reveal that the addition of T-ZnOw increases the folding surface free energy and the absolute values of effective activation energy, indicating that T-ZnOw restricts the movement of chain segments.The experimental research results of rheological behaviors revealed that both PP and its composites are pseudo-plasticity fluid. Apparent viscosity of PP/POE blends is low than PP. The incorporation of POE might reduce the temperature sensitivity of apparent viscosity. At the same shear rate, the apparent viscosity of ternary composites decreased initiately and then increased with the increasing content of T-ZnOw. The flow activation energy for PP/POE composite is higher than that for neat PP. The flow activation energy decreased initiately and then increased with the increasing content.