Tensile stress relaxation behavior of a mechanical mixture of two polymer components

Abstract

AbstractAs one in a series of studies relating the rheological properties of mechanical mixtures of two polymer components to the degree of mixing, the temperature dependence of tensile stress relaxation behavior of two types of mixed systems, i.e., poly(methyl methacrylate)–poly(vinyl acetate) system and lightly crosslinked poly(methyl methacrylate–poly(vinyl acetate)) system, was investigated over a temperature range covering the glass transition temperatures of both polymer components. The time–temperature superposition procedure was carried out for comparison of several parameters, such as fractional free volume and its thermal expansion coefficient, which were determined on the basis of the free volume concept from the viscosity in relation to the William‐Landel‐Ferry equation, with those of the individual polymer components. Although the fractional free volume and its thermal expansion coefficient thus determined for the mixed systems were apparent values, the results may, at least qualitatively, deny the simple additivity of the free volumes of the two‐polymer mixed phases and suggest the existence of a sort of physical interaction between the phases, i.e., the internal pressure induced by one phase or the other due to a difference in thermal expansion coefficient between the phases.