Rheology of Elastomer Blends

Abstract

Abstract The melt flow properties of certain elastomer blends are shown to be a function of the mixing history and the morphology of the blends. And, more significantly, the melt flow properties are found to be non-additive functions of the melt flow properties of the homopolymers comprising the blends. Mixing studies using a Brabender Plastograph show that blends of certain elastomers generate much higher temperatures while, simultaneously, generating much higher torques than either of the homopolymers over time cycles of practical interest in elastomer processing operations. A sharp minimum in the early stages of the torque/time relationship in the mixing operation, followed by an abrupt maximum, is correlated with abrupt changes in the morphology of the blends as determined by electron microscopy. The morphological structure of certain well mixed elastomer blends consists of domains of the lesser component dispersed into a matrix of the major component. For well mixed blends near 50/50 weight per cent composition the morphological structure appears to consist of two continuous interpenetrating phases. Mooney values as well as Plastograph torque values are observed to be non-additive functions of the corresponding properties of the homopolymers. A minimum in the Mooney/blend ratio relationship over a rather narrow range of blend compositions is observed for certain systems. In contrast, the Plastograph torque values for the identical compositions are observed to be higher in all instances than those for the homopolymers. A phenomenological description of these apparent contradictions is obtained from a simple analysis of capillary melt viscosity measurements carried out on the same blends. These melt viscosities are also a non-additive function of the viscosities of the homopolymers. Minimum and/or maximum viscosities for specific blend ratios are observed for a given rate of shear. The minimum or maximum shift (s) to different blend ratios with changes in the rate of shear. Viscosity/composition plots similar to the Mooney/composition plot are observed at low rates of shear and plots similar to the torque/composition plot are observed at high rates of shear. These behavior patterns remain unexplained at this time.