Studies On High Performance Modification Of Polypropylene

Polypropylene (PP) is an excellent thermoplastic with versatile application. However, it has low impact strength and large mold shrinkage, which greatly limits its application. In order to extend the application of PP, we study high performance modification of PP in this paper.In order to prepare polypropylene (PP) blends with higher toughness, lower strength and hardness, higher melt flow rate and transmittance, the effects of elastomer type and content, and processing agent on the toughness, strength, hardness, processing properties and transmittance of PP were studied. The results show that, in comparison with other elastomers, ethylene propylene elastomer (EPR1) and polyethylene wax are the best choices. Moreover, color change due to soaping was studied by means of wide-angle X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscope (SEM). The results show that, the addition of polyolefin ealstomer (POE) made PP second crystallize, leading to the decrease of transmittance, while the addition of EPR did not affect PP crystallization, resulting in no change in transmittance.PP/ POE/wollastonite composites were prepared by means of melt blending, and the effects of the types and contents of wollastonites on related properties of composites were studied. The results of mechanical properties and scanning electron microscopy (SEM) analysis show that, the tensile strength of the composites increases first and then decreases, and the notched impact strength and elongation at break decrease gradually with increasing wollastonite content. Moreover, the mechanical properties of needle-like wollastonite system are better than those of ultra-fine wollastonite system. Through the melt index (MFR) test, with the increase of wollastonite content, the melt index of PP/POE/wollastonite composites increases gradually at first, and then decreases gradually with increasing wollastonite content. In comparison with the processing performance of ultra-fine wollastonite system, that of needle-like wollastonite system is better. The results of XRD and DSC measurements show that, the addition of wollastonite does not change the crystal type of PP, but crystallite size of the composite becomes smaller. Moreover, the heterogeneous nucleation function of needle-like wollastonite is more obvious than that of ultra-fine wollastonite. The Vicat heat resistance analysis shows that the addition of wollastonite improves the heat resistance of the composites; moreover, the heat resistance of needle-like wollastonite system is better than that of ultra-fine wollastonite system.PP/ POE/magnesium sulfate whisker (MOS) composites were prepared by means of melt blending, and the effect of the contents of MOS on related properties of composites was studied. The results of mechanical properties and scanning electron microscopy (SEM) measurements show, the tensile strength of the composites increases first and then decreases, while the notched impact strength and elongation at break decrease gradually with increasing MOS content. The result of limited oxygen index (LOI) measurement shows that, the flame-retardant properties of composites improve greatly with increasing MOS content. The Vicat heat resistance analysis shows that, the addition of MOS improves the heat resistance of the composites.