Time-temperature superposition principle applicability for blends formed of immiscible polymers

In this work, the linear viscoelastic behavior of PP/PS and PP/HDPE blends modified with SEBS and EPDM, respectively, was studied. Small amplitude oscillatory shear measurements were carried out at different temperatures, ranging from 190degreesC to 240degreesC. The storage (G') and loss (G") moduli curves obtained were horizontally shifted and curves of angle delta (delta) (delta = atan (G"/G')) as a function of complex shear modulus (G*), known as van Gurp plots, were obtained at several temperatures, to test the applicability of time-temperature superposition principle RTS) to these blends. The results showed that successful application of TTS depends on the flow energy of activation and horizontal shift factors of the individual components of the blend, on the interfacial properties of the blend and on the concentration of compatibilizer added to the blend. TTS application failed for PP/PS blend, but held for PP/HDPE blend. Addition of SEBS to PP/PS blends promoted successful TTS application at specific concentrations that corresponded to interfacial saturation of the dispersed phase. Addition of EPDM did not imply sensitive change on TTS application for the PP/HDPE blends.