The Study Of The Properties Of Modified PP Composites For Auto Bumper

In the thesis, the polypropylene (PP) resin was modified for toughness by these several methods, including blending with POE, usingβ-nuleating agent to modify the crystallization of PP, the adding of nano-SiO2 and using both nano-SiO2 andβ-nuleating agent to modify the PP/POE composites. The properties of the modified PP composites were studied, and the composites were characterized by the test of the mechanical properties, polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), as well as scanning electronic microscope (SEM), which in order to obtain the high toughness and high strength PP composites which meet the requirement of auto bumper.In the course of studying modified PP, the saturation ethylene-octylene copolymer (POE) produced by DOW chemistry company via ethylene and octylene original position polymerization catalysised by metallocene was adopted. The morphology of cross-sections, mechanical and crystallization properties of PP/POE composites were studied. The influence of addingβ-nuleating agent (TMB-5) on the mechanical properties of impact co-polypropylene modified by POE was also studied. The results indicated that the notched impact strength and the elongation at break of PP/POE composites increased gradually while the yield stress and bending strength decreased as the adding content of POE. The crystallization analysis shows that the crystallization degree of PP reduced by adding POE to damage the regulation of PP molecular chain and hind PP crystallization. POE had the function of decreasing the size of spherulite of the PP. With the add ofβ-nuleating agent, The tensile strength of PP/POE composites increased, and the brittle-ductile transition disappeared.The influence ofβ-nuleating agent (TMB-5) on the morphology of cross-sections, mechanical and crystallization properties of impact co-polypropylene were studied. The results indicated that the yield stress and bending strength of PP decreased while impact toughness increased by the addition ofβ-nuleating agent. When 0.4% ofβ-nuleating agent was added, the notched impact strength and the elongation at break came up to the highest level. POM showed that the size of spherulite decreased by the addition of TMB-5, and theβ-spherulites exhibited a sheaf-like structure. The adding of TMB-5 accelerated the crystallization velocity of PP, and increased the crystallization degree of PP.The impact co-polypropylene was modified by nano-SiO2, the influence of nano-SiO2 on the morphology of cross-sections, mechanical and crystallization properties of impact co-polypropylene were studied. And the influence of the blending procedures of nano-SiO2 on the mechanical properties of PP/nano-SiO2 composites was also studied. The results indicated that, the adding of nano-SiO2 had good toughening and reinforcing effects on PP/nano-SiO2 composites, and the adding of PP-g-MAH can enhance the interfacial interaction between nano-SiO2 and PP matrix. The masterbatch-blending enhanced the mechanical properties of PP/ nano-SiO2 composites ulteriorly. SEM showed that the nano-SiO2 particles can stop the crazes in PP matrix effectively when subjected to an impact loading, and absorb large amount of impact energy, so the impact toughness of composites increased. DSC showed that the addition of nano-SiO2 into PP had an obvious nucleating effect on the crystallization of PP, increased the crystallization temperature of PP, and also decrease its size of spherulite, meanwhile, PP-g-MAH enhances the nucleating activity of nano-SiO2. XRD showed that the adding of nano-SiO2 had the function of inducement ofβform PP, and increased the impact toughness of PP.The PP/POE composites was modified by multiplicity formulation of nano-SiO2 andβ-nuleating agent. The effects of nano-SiO2 andβ-nuleating agent on the properties of PP/POE composites were studied. The results indicated that, when the blend ratio of PP/POE/nano-SiO2 composites was 100/25/4, the mechanical properties of the composites were the best. The mechanical properties of masterbatch-blending composites was higher than that based on direct blending. The multi-step blending can improve the dispersion of nano-SiO2, and the mechanical properties of multi-step composites was higher than that based on masterbatch-blending. The size of spherulite of the PP/POE composites decreased by the addition of nano-SiO2, and there were no clear boundaries between the spherulites. The yield stress and bending strength of PP/POE/nano-SiO2 composites decreased while impact toughness increased ulteriorly by the addition ofβ-nuleating agent. When 0.4% ofβ-nuleating agent was added, the notched impact strength and the elongation at break came up to the highest level, and the tensile strength increased obviously. The PP composites can reach the require of auto bumper. XRD showed that theβ-nuleating agent had the function of inducement ofβform PP in the PP/POE composites filled with nano-SiO2.