Mechanical properties of polymer mixtures: Effect of compatibility

Abstract

The effect of compatibility on the mechanical properties of polymer mixtures is discussed. From solution thermodynamics we conclude that for compatible mixtures of high molecular weight polymers the excess internal energy of mixing must be negative. For most polymer mixtures, this results in a negative excess volume of mixing. The excess entropy of mixing is therefore also negative. These general conclusions point to a stiffening of the solid lattice and a reduction in chain mobility. In dynamic mechanical behavior, the relaxation of molecular moieties responsible for the specific interaction should be shifted to intermediate temperatures, and the relaxation of other moieties should be shifted to higher temperatures if the potential well is inter-molecular. In finite deformation behavior craze initiation stress and shear yielding stress should both be higher than a linear combination of the properties of the pure components.