Investigation of morphology, mechanical, dynamic mechanical and thermal behaviour of blends based on ethylene vinyl acetate (EVA) and thermoplastic polyurethane (TPU)

Abstract

Novel blends based on ethylene vinyl acetate/thermoplastic polyurethane (EVA/TPU) at different ratios were prepared via the melt blending technique. Scanning electron microscopy (SEM) studies revealed primarily a two phase morphology in which the minor TPU phase was dispersed in the major continuous EVA matrix. However in the 50/50 blend EVA and TPU appear as a co-continuous phase. The influence of blend ratio on the mechanical properties and hardness was investigated. An 80/20 EVA/TPU blend was observed to exhibit optimum tensile strength and elongation at break. Various models have been applied to predict the change in modulus with blend composition. The Veenstra B model was found the best to correlate the experimental modulus values. All the blends show a single T_g and a shift in T_g with change in blend composition was observed through differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), indicating technological compatibility. Thermogravimetric analysis (TGA) was performed to study the thermal stability of the EVA/TPU blends. Incorporation of TPU has also been found to improve the oil resistance properties of the blend system.