Morphologies and Rheological Properties of Ethylene-Propylene Block Copolymer/Ethylene-Propylene Rubber Blends
Shuichi MAEDA, Eiichi KAMEI and Toshikazu TAKIGAWA
Abstract:The influence of heterogeneous structures of molten ethylene-propylene block copolymers (EPBC)/ethylene-propylene rubber (EPR) blends on rheological properties were investigated. A slow mechanical relaxation, characteristic of heterogeneous liquids, was observed in the long time region of the angular frequency versus dynamic modulus plots of the EPBC/EPR blends. The mechanism of the relaxation is associated with the shape recovery of the deformed dispersed phases. Stress undershoot in a course of stress development under steady shear flow is observed for EPBC/EPR blends with the EPR content of higher than 30wt%. The time required for the stress to reach the undershoot minimum increases with increasing EPR content in the blends. Comparing the blends with the same EPR content, the time required becomes longer as the molecular weight of EPR increases. The longest relaxation time of the blends, evaluated from the stress relaxation after cessation of steady shear flow, is the same as that of the pure EPBC, when the samples have lower EPR compositions than 30 wt% with a lower molecular weight EPR and all compositions with a higher one. The blends containing a lower molecular weight EPR with higher than 40wt % show the longer relaxation time than the pure EPBC. These results indicate that the change in the longest relaxation time for the blends originates from, whether or not the three-dimensional network structure is formed as a result of the elongation of dispersed EPR phases in the shear flow field, or the difference in morphology when the network structure is really formed. Key Words:Ethylene-propylene block copolymer, Ethylene-propylene rubber blend, Morphology, Dynamic viscoelastic properties, Steady shear flow properties, Stress relaxation, Slow relaxation mechanism