The Morphology of Rubber/Plastic Blends

Abstract

Abstract This study considers the rheological and interfacial effects on the phase morphology of the rubber/plastic blends during molten-state mixing, cold pressing, and compression molding. We utilized a specially designed tool to take a sample from the mixer and quickly cool it with little chance for coalescence. The work of this report is mainly concerned with soft rubbery compositions, which contain large concentrations of elastomeric phases. The morphologies of rubber/plastic blends having low concentrations of plastic or rubber can be explained by the understanding gained from work previously reported by others. The viscosity-matched and polarity-matched rubber/plastic blend systems give the finer states of dispersion, especially during the early stages of mixing. At intermediate concentrations of rubber, (e.g., 60 vol. %) co-continuous and laminar structures are frequently formed. The determinants of the concentration where the phase inversion occurs and the determinants of phase-domain dimensions near this phase-inversion concentration (e.g., a thickness of a highly shaped structure) are complex and can only be rationalized qualitatively. However, we were able to quantitatively relate phase-morphological dimensions to interfacial tension, rheology, and the observed type of morphology. When the hot batch is cold pressed, then a striated or laminar phase morphology is formed. Even very small particles deform greatly if the interfacial tension is low. Higher viscosities in the dispersed phase give rise to lesser deformations during cold pressing. During compression molding, the laminar structure transforms itself into a random co-continuous structure of vastly increased textural dimensions. This coarsening is greatest when polarities are most divergent and when the viscosities of the polymers are lowest.