Generalized model representation relating the degree of mixing to the rheological behavior of a mechanical mixture of two polymer components

Abstract

AbstractOn assuming that the two polymer components are poorly compatible or incompatible and from semimicro heterogeneous systems composed of homogeneous phases of each component, two kinds of generalized models which relate the degree of mixing of the two phases to the mechanical behavior of the systems were proposed. In this phenomenological theory, the chemical interaction between the two polymer components was negelcted, and the stress or strain distribution along the boundaries between the two phases was much simplified. This might give serious error when the mixed phases become small and the surface effect, instead of volume effect, becomes significant. The mechanical mixtures can be classified by the manner of mixing of the two phases of A and B components as follows: A islands in B matrix, B islands in A matrix, A matrix‐B matrix, and A islands‐B islands mixing. The mechanical properties of the mixed systems are affected not only by those of each component and their volume fraction in bulk, but strongly by the manner of mixing. The terminology used here, as the degree of mixing, is one of the representations of the manner of mixing in terms of distribution function of partial volume fractions of each component in the mixed system.The analysis of some mixed systems of two polymer components gave the following results. The mixed systems cast from acetone solution of poly(vinyl acetate) and poly(methyl methacrylate) give mechanical mixtures of the islands‐in‐matrix type mixing. A phase conversion from PMMA islands in PVAc matrix to PVAc islands in PMMA matrix occurs at about 70% volume fraction of PMMA due to the hexagonal close packing of PMMA islands in PVAc matrix with increase of volume fraction of PMMA On the other hand, the systems cast from mixtures of acetone solution of PVAc and lightly crosslinked PMMA fine particles give mechanical mixtures of the matrix‐matrix type mixing. The mixed systems of polystyrene and 30/70 butadiene–styrene copolymer, which have been classified by Tobolsky as polyblends, might also be a type of mechanical mixture classifiable as matrix‐matrix mixing. However, the manner of mixing should be much modified by the chemical interaction between the two components.