Preparation And Characterization Of Polypropylene/Magnesium Borate Whisker Composites

Polypropylene (PP) is one of the most popular and widely used thermoplastics, with many advantages such as rich in raw materials, simple composite processing, low price. However, its further application is restricted for its low mechanical strength, poor impact strength and fracture toughness at relatively low temperature and high strain rate. Thus, the challenge of increasing the tensile strength and thoughness of PP has provoked considerable interest of scientists. Magnesium borate whiskers (MBOw) are expected to widely used in polymer such as PP matrix composites for its low price, high tensile strength and high elastic modulus. However, there have not yet seen the reports on MBOw reforce and toughened PP.In this paper, KH-550and borate ester (BE) coupling agents were used to treat the MBOw. The effect of two coupling agents on the surface properties of MBOw were studied comparatively. MBOw and BE coupling agent treated MBOw filled PP composites were prepared by melt blending. And then, the influence of MBOw on properties of PP/MBOw and PP/BE/MBOw composites has been systemically investigated. Moreover, the interface bonding mechanism of PP/BE/MBOw was studied by FT-IR, meanwhile, the reinforcement and thoughening mechanisms of MBOw filled PP composites were discussed, the major results are listed as follows:(1) The surface properties of BE-treated MBOw were changed radically in comparison with untreated MBOw, however, KH-550did not have any influence on the surface properties of MBOw. Thus, it has determined that the BE is better than KH-550coupling agent to treat MBOw, and the best surface coating is about2%of the quality of MBOw.(2) The compatibility between untreated MBOw and non-polar PP is very poor. The surface properties of BE-treaed MBOw are similar to PP, which results in a good compatibility of BE-treated MBOw and PP.(3) The non-isothermal crystallization kinetics of PP and its composites can be well described by Mo Zhishen function. MBOw has the heterogeneous nucleation effect in PP composite, which accelerates the crystallization speed of PP, BE strengthens the heterogeneous nucleation ability of MBOw which is more conducive to the improvement of the crystallization speed of PP. The tensile strength and tensile modulus of PP/MBOw composite increased as with MBOw content, but then MBOw content over a certain range (≥15wt%), the tensile strength and modulus decreased; The tensile strength and modulus of PP/BE/MBOw composite increased as with MBOw content, and the improve trend is significant. The elongation at break of PP/MBOw and PP/BE/MBOw composites decreased as with MBOw content, and PP/BE/MBOw composites decreased more obvious. With increased of MBOw content, the notched impact strength of PP/MBOw composite showed a linear downward trend, however, the impact strength of PP/BE/MBOw composite increased first, when the MBOw content increased to5wt%, the impact strength reached the maximum, futher increasing MBOw content but lead to decrease in impact strength of the composite system. Thermal deformation temperature of the improvement trend of PP/BE/MBOw composite is more significant compared with PP/MBOw.(4) The interface bonding mechanism of PP/BE/MBOw composite can be explained as follows. On the one hand, hydrophilic groups at one side of BE react with-OH on MBOw surface with physical adsorption and chemical reaction. On the other hand, hydrophobic groups at the other side of BE with macromolecular chains of PP have a better affinity. BE plays a good "bridge" role between MBOw and PP.(5) The reinforcement and thoughening mechanisms of MBOw filled PP can be explained as follows. MBOw forms a skeleton strengthening in PP matrix, and BE-treated MBOw with PP have a good interface bonding, which result in high efficiency of transfer stress between PP matrix and MBOw, so the effect of MBOw reinforce PP significantly. MBOw can be uniformly distributed in PP which lead to the interface bonding improve obviously, stress can effectively transfer and uniformly dispersed, and the effect of pull-out can not only consume a lot of impact energies, but also can induce plastic deformation of the PP matrix, which makes the toughness of material improved.