| Polypropylene is a semi-crystalline polymer with some excellent properties, such as low relative density, thermal property, easy processability. However, its application is highly limited because of its brittleness at room and low temperatures. Elastomeric nano-particles have been used to enhance the toughness of PP with a small amount. Compared with traditional way, this method can achieve a good balance of toughness and stiffness of PP. In order to extend its application range, the stiffness of PP needs to be improved. Recently, carbon nanotubes have triggered considerable interest. Due to their unique structure, excellent properties and very high aspect ratio, they are used to improve the stiffness of polymer.The development and status of the modification of PP have been reviewed in this paper. The main purpose of this work is focused on preparing composites with better performance via blending PP with ENP or CNTs, studying the relationship between structure and properties. The major work of this paper is as follow:1. Two methods, dynamic packing injection molding and conventional injection molding, were used to prepare PP/ENP composites. The effect of processing method on the morphology and properties was investigated. Because the shear force introduced to the melt during packing stage can induce the molecular orientation, the mechanical property of dynamic samples was much higher than that of static samples. In addition, the shear force can help for good dispersion. At 2wt% of ENP content, both tensile strength and impact strength increased for dynamic samples, while the properties of static samples decreased. From the results of DSC and PLM, it can be seen that ENP could serve as nucleating agent, which increased the crystallizationtemperature and also caused the decreasing of crystal size.2. The viscosity of matrix and the processing method can affect the dispersion of ENP. Two kinds of PP with different MFI were used to blend with HDPE and ENP. The results showed that the impact strength keeps constant when ENP was added into the two kinds of PP/HDPE. It may be because that ENP can not have uniform dispersion and HDPE mainly act as toughening agent. Masterbatch and one-step methods were used to prepare the PP/HDPE/ENP blends. From the mechanical property of the blends, it can be seen that better dispersion of ENP could be achieved through masterbatch than one-step method.3. The brittle-ductile transition of PP/EPDM/Elastomeric Nano-Particle (ENP) was studied. Compared to PP/EPDM binary blends, the brittle-ductile transition of PP/EPDM/ENP ternary blends occurred at lower EPDM content. SEM results of the fractured surfaces of the composites indicated that at the same EPDM content, PP/EPDM/ENP ternary blends had smaller particle size, better dispersion and a smaller interparticle distance comparing to PP/EPDM binary blends, which promoted the brittle-ductile transition.4. The mechanical properties and morphology of the PP/CNTs composites were investigated, a simultaneous increase of tensile strength and impact strength has been achieved for dynamic samples of PP/CNTs composites containing only 0.6wt% CNTs. The dynamic packing injection molding could provide much strong shear force for better dispersion of CNTs in PP matrix. The result of PLM showed that the crystal size of PP decreases when CNTs was added into the matrix. It may be one of reasons that the mechanical property was improved. From the DSC result, it can be seen that the crystallization temperature increased by 10°C at 0.3wt% of CNTs content. |
