Study On The Preparation, Properties And Structure Of Nano-CaCO₃/PP/EVA Compsites

It is an important means to enhance properties of PP with PP physical blend modification. PP/elastomeric blend is apt to cause a sharp decline in inflexibility and PP/RIF composite has low toughness. In this paper using nano-CaCO3/EVA on modifying of PP toughening is studied to avoid the question above.In experiment the proportion of matrix for PP and EVA is 80:20, and the proportion for nano-CaCO3 and PP is 100:1,100:3,100:5,100:7 respectively. A series and B series nano-CaCO3PP/EVA composite is prepared by extrusion graining with twin-screw extruder method. The preparing process includes one step method and two step method. In A series composite, the microstructure of nano-CaCO3 and EVA shows mainly separation structure. And in B series composite, the microstructure shows coexistence for coating structure and separation structure.Then the notched impact strength, drawn characteristic, young modulus and thermal properties(DSC) are tested. Results show addition of nano-CaCO3 can raise the room temperature impact strength, yield strain, rigid and thermal resistance for PP. However the effect on low temperature(-35℃) toughness is very limited. From the comparison, composite property preparing by two step method process is superior than one step method. When the usage amount of nano-CaCO3 is 1 portion, the room temperature impact toughness of Al and B1 composite achieves the maximum,6.92KJ/m2 and 7.5KJ/m2 respectively. They have risen notably compared to PP(3.5K J/m2); when the usage amount of nano-CaCO3 is 3 portion, the yield strain of A1 and B1 composite achieves the maximum,6.92KJ/m2 and 7.5KJ/m2 respectively. They are higher than PP/EVA(23.7MPa).From observation of polarized-light microscopy, effect of EVA on PP grain refinement is not apparent. Nano-CaCO3 has apparent heterogeneous nucleation. As the usage amount increasing, PP spherulite size decreases. Spherulite size in B series composite is bigger than A series composite. DSC shows the melting temperature, crystallization temperature and crystallinity of composite are all increased. The crystallinity of PP in B series composite is lower than A series composite because of too much coating structure in B series composite. Reunion phenomenon because of excessive nano-CaCO3 result in the derceasing of crystallinity in A and B composite. From DSC of melting and crystallization process, new crystalline phase is generated in nano-CaCO3/PP/EVA composite. Especially the usage amount of nano-CaCO3 is 1 portion, it will encourage new crystalline phase growth. From observation of microstructure by SEM, nano-CaCO3 has good distribution in matrix when usage amount is low. In A series composite, the microstructure shows mainly separation structure. And microstructure of composite preparing by two step method shows coexistence for coating structure and separation structure. Comparison A and B composite on property and structure, coating structure has positive effect on toughness for nano-CaCO3/PP/EVA composite.In paper, on the basis of the best quantity(1 portion) of nano-CaCO3,the effect of EVA content on mechanical property and structure of nano-CaCO3/PP/EVA composite is studied. Results show when EVA content decreases properly, the strength of composite raises and toughness loss decreases. Nano-CaCO3 and EVA has cooperative effect on PP spherulite refinement. And they has positive effect on toughness of composite.