Thoughening Of Polypropylene With Ethylene-propylene-diene Terpolymer

The polypropylene(PP) is one of three kinds of main general plastics. However, the poor impact properties at low temperature limit some of its application. In order to achieve improved properties , impact modifiers have been added to PP. Among the elastomers used, ethylene-propylene-diene terpolymer(EPDM) is the most widely employed.Two types of EPDMs which is synthesized by metallocene catalyst (mEPDM) and by conventional Ziegler-Natta catalyst (EPDM) were used to toughen PP.Process parameters were investigated by means of orthogonality experiment method to abtain optimum mixing conditions. The effects of process conditions on mechanical properties of blends were discussed. A rotor speed of 120rpm, temperature of 180 and mixing time of 9min were considered the optimum mixing conditions. With the increase of mixing time and rotor speed the impact strength of blends increases first, but at long time and high speed a decrease in impact strength was observed.The effect of mass fraction of elastomers on the properties such as the impact strength, the tensile strength, crystallization performance and Vicat softening point of the PP/elastomers blends was investigated. The results showed that compared with PP/EPDM blends, PP/mEPDM blends had lower critical rubber content when the brittle-ductile transition occurred and the elongation at break of PP/mEPDM blends was longer than PP/EPDM blends. It has been found that the brittle-ductile transition interval of PP/mEPDM blends is much narrower than PP/EPDM blends. With increasing the mass fraction of elastomers, the tensile strength and elastic modulus of blends decreased, but the decreasing amplitude of PP/mEPDM blends was minor. The blends were analyzed by of SEM and DSC and the results showed better compatibility between PP and mEPDM.On the basis of experiments, the influence of the diameter of particle and its distribution has been researched. It is found that the concept of critical matrixthickness is suitable for blends of PP/mEPDM. The critical matrix thickness of blends of PP/mEPDM is 2.18 times as thick as that of blends of PP/EPDM. To blends of PP/mEPDM, it is only 15wt% of elastomer concent while the brittle-ductile transition occurred, but to blends of PP/EPDM, it is 30wt% of elastomer concent.