Study Of PP/PA11/EPDM-g-MAH Composites

As one kind of general thermoplastics, polypropylene possesses perfect mechanical performances besides shortcomings of brittleness at low temperature, high shrinkage and aging. PA11 takes on excellent cold-resistance and endurance. Due to combination of performances of PA11 and PP, the impact property, anti-abrasion, dimensional stability and processibility of PP/PA11 blends can be improved. The different polarity between PA11 and PP resulted in bad compatibility. Therefore, the compabilizer was used to improve the compatibility. In this paper, malefic anhydride functional copolymer compatibilizer and elasticize EPDM-g-MAH were chosen to compatibilize PP/PA11 system. Morphology structure, rheological behaviors and crystallization behaviors were investigated by SEM, capillary rheometer, the polarizing microscope (POM) and DSC.The research of Mechanical properties and morphological structure of the compatibilized systems shows that the normal temperature Izod notched impact strength and low temperature impact strength of the blend was increased up to a maximum of 9.44KJ/m2 and 3.4KJ/m2 in the case of PP/PA11/EPDM-g-MAH =80/10/10, and was far higher than that of neat PP(2.03 KJ/m2). Meanwhile the tensile strength and the elongation almost kept the same. The morphology of the blends was studied by SEM. It is found that the PP/PA11 blend possesses an"island-sea"structure consisted of two phases incompatible thermodynamically. The addition of EPDM-g-MAH significantly improved the compatibility between PP and PA11 and enhanced the interfacial adhesion of the two phases. The composites exhibitted a morphology similar to a core-shell structure (PA11 core and EPDM-g-MAH shell) in the case of 10% of EPDM-g-MAH.The investigation of rheological behavior demonstrated that both PP and its composites are pseudo-plastic. The non- Newtonian indexes(n) are in the range of 0.4～0.6 corresponding to the variation of temperature and the apparent viscosity increases initially with the addition of EPDM-g-MAH and then decreases in the case of the constant shear stress and shear rate, the apparent viscosity of the blends reached a maximum for PP/PA11/EPDM-g-MAH =82/10/8.The crystallization kinetics of PP and its blends were investigated by DSC. The study on the isothermal crystallization shows that Avrami equation can describe isothermal crystallization process very well, the crystallization rate and the equilibrium melting point are higher than those of neat PP because of heterogeneous nucleation of PA11. The observation of the polarizering microscope reflected apperantly that the sizes of crystals reduce and the numbers of crystals increase from. The investigation on the Non-isothermal crystallization process revealed that both the Jeziorny and Mo methods could describe this system very well, but the Ozawa analysis failed. The addition of PA11 changes the nucleation and crystal growth of PP matrix as well as increases crystallization rate. The Hoffman-Lauritzen theory indicates that the addition of PA11 hinders the movement of PP macromolecule chain enter into the crystal lattice and increases the free energy of the molecular chain vertically.