Research On Polypropylene Filled And Modified With Wollastonite Powder Covered With Nano SiO₂

In this paper, six wollastonite fillers with different kinds of surfaces characteristics were designed to modify properties of polypropylene and the effects on the mechanics performance, interfacial effect and crystallizing behavior of composite material were studied.In order to optimize the surface modality of the wollastonite, an idea in which a kind of new-fashioned nano-coated particle has been produced via coating wollastonite with nano SiO2 particle was brought forward in this research.Compared with the normal wollastonite, the coated wollastonite had many advantages. Firstly, the specific surface area of nano-coated particle is much larger than that of ordinary wollastonite, and the edges formed in comminuting is passivated, which made the slippy crystal surface coarsened. At the same time, the color of nano-coated particle became whiter, which fit for light ware. Secondly, if the coated wollastonite hasn't been modified by coupling agent, the toughness of PP/ wollastonite composite couldn't be improved. For example, when the amount of the untreated-nano-coated filler was 25% and more, the toughness of the composite was worse than with ordinate wollastonite filler. However, after the coated wollastonite modified by coupling agent, the intensity and toughness of the composite would be improved observably, especially the toughness. Even if the content of coated wollastonite is as much as 20%, the impact strength of composite was still higher than pure polypropylene, which shows coated wollastonite could toughen PP, and the shortcoming of making composite brittle by filling ordinate wollastonite in polypropylene could be overcome.Some analysis such as SEM, DSC and WXAD were made to further discuss the toughening mechanism. Research showed that the nano-coated wollastonite modified by coupling agent, compared with the other surface disposal methods, could improve the disperse state of the filler in PP, by which the adequate integration with PP interface was built up, owing to the decrease of surface disfigurement and the increase of specific surface. Moreover, as a kind of nucleating agent, the fillers would enhance the crystalloid temperature of the composite material, and debase the crystallinity as well as minish the crystalloid size, and besides, it could partially lead α-PP phase changing into β-PP phase. These influences varied with the different surface characteristic of the fillers, which is the cause why composite systems with different fillers have varied macroscopically mechanics performance.