Application of mean-field theory in PP/EVA blends by focusing on dynamic mechanical properties in correlation with miscibility analysis

Multi frequency measurement of dynamic mechanical properties including storage modulus, loss modulus and loss tangent of binary blends of an isotactic polypropylene (PP) and ethylene/vinyl acetate copolymer (EVA) at varying blending ratios was performed. Molecular mechanisms of various transitions were explained. The effect of blend ratio on miscibility of the blends using different approaches was studied. It was found that miscibility of blends increases at around 60 wt. % of EVA loading. Also, molecular origins of this phenomenon were proposed. The Arrhenius relationship was used in order to calculate the apparent activation energy (Ea) for the glass transitions of blend components. The Ea were compared at different compositions. The composition dependency of Ea could be explained based on miscibility of the blend components. Morphological parameters such as particle size and its distribution were obtained from SEM micrographs. The differences observed in morphological parameters and also morphological evidence of increased miscibility near 60 wt.% of EVA loading could be explained. In order to predict the dynamic mechanical properties of blends from those of their pure components, mean-field theories developed by Kerner were applied and theoretical values were calculated by solving of the appropriate equations using iteration method. Comparatively, a good agreement between theoretical and experimental data, especially in the upper and lower temperature zones was obtained. It was found that differences between experimental and theoretical values are significant in transition zone. Finally, the different causes of deviations between theoretical and experimental results were discussed. (C) 2015 Elsevier Ltd. All rights reserved.