Effect of filler on rheologic and thermodynamic characteristics of binary polymeric mixture melts

Rheologic, thermodynamic, and mechanical loss tangent properties of a binary polymeric mixture were studied. The system was a mixture of poly(vinyl acetate) (PVA) with ethylenevinyl acetate copolymer (EVC) with varying concentrations of the polymer components and filler. A correlation between the above characteristics of the PVA/EVC two‐phase mixture was found. This mixture was thermodynamically unstable (positive values of the interaction parameter, χ) practically over the entire range of compositions at temperatures of rehologic studies. The presence of a disperse filler raised the thermodynamic stability, that is, parameter χ decreased. Reversal of the sign of the temperature dependence of χ of a mixture with increasing concentration of filler was found. The variations of viscosity with the composition, temperature, and shear for the PVA/EVC mixture are ascribed to different levels of heterogeneity occurring in the process of the shear straining in the working unit of the rheometer.