Polyblends. III. Correlation of the viscoelastic data for polyblends of NBR and plasticized vinyl chloride compositions with theories of polycomposite behavior

Viscoelastic data obtained on the polyblends described in the previous two papers together with some new data have been correlated with various theories derived for the viscosity and continuum properties of polycomposites, to gain insight into the nature of compatible domain interactions. Unmodified theories of Mooney, Eilers and Van Dyck, Guth and Smallwood, and Kerner did not correlate with the observed viscoelastic data. However, when the Kerner relation was substantially altered (after allowing for phase inversion following procedures of Halpin and Tsai as modified by Nielsen), an adequate description of torsional modulus behavior at ambient temperature was obtained. To characterize tensile modulus (100%), however, a new expression was necessary. Both procedures invoked in a critical modulus for the blend with respect to composition at which phase inversion was initiated. The critical volume fraction associated with this modulus increased inversely with the T g of the filler; when the filler T g was below the ambient temperature, the blends behaved as mixed rubbers, and torsional modulus ratios followed the lower Kerner relation at all blend compositions. It was concluded that polyblends having isochronal modulus–temperature curves that shift with composition over the temperature scale yet are anomalously broad as in the present work should be classified as systems exhibiting restricted molecular mixing. The restricted molecular mixing character exhibited by the polyblends could be explained by a plurality of mixed‐phase responses to deformation produced in a morphology of interlocking microdispersions. Favourable polarity effects and high filler ductility were considered responsible for the domain interactions. No evidence was found for true molecular compatibility in the blends. An analysis of temperature effects on the blend viscoelasticity resulted in a temperature analog of the composition behavior.