A model for the yield strength of binary blends of thermoplastics

Abstract

A model procedure has been proposed to predict the yield strength of binary blends of thermoplastics on the basis of the information on the continuity of phases acquired from the Hill model for the elastic properties of two-component systems. Utilizing this information in an equivalent box model and assuming either ‘perfect’ or ‘zero’ interfacial adhesion, the upper and lower bounds of the yield strength can be calculated. The upper bound may be close to (but lower than) the dependence corresponding to the additivity (rule of mixtures). The lower bound passes through a minimum at a composition of about 50 50 (by volume), which corresponds to the phase-inversion point in the Hill model. The minimum yield strength is linked to the minimum of the sum of the continuity parameters of the components in the blends. Predicted dependences of the yield strength on the blend composition are in reasonable accord with the experimental data for blends with good or poor interfacial adhesion. If the model is to be employed for the appraisal of the interfacial adhesion in polymer blends, other factors affecting the phase structure should be taken into account, e.g. relative melt viscosities, particle size, orientation during processing, cavitation, etc.