Correlation of rheology and morphology and estimation of interfacial tension of immiscible COC/EVA blends

Abstract

Rheology and morphology of cyclic olefin copolymer (COC) / ethylene vinyl acetate copolymer (EVA) immiscible blends with droplet and co-continuous morphologies were experimentally examined and theoretically analyzed using emulsion and micromechanical models. The blends showed an asymmetric phase diagram in which the EVA-rich blends had smaller dispersed size domains as compared to the COC-rich blends. This could be explained based on the higher melt elasticity and viscosity of COC as compared to EVA determined by the rheological investigations. The rheological tools were used to investigate the miscibility of the blends. From the melt viscosity data it is found that the COC/EVA blends show a positive deviation behavior at all compositions which is a hint for strong interaction between the COC and EVA. Analysis of Cole-Cole and Han diagrams revealed that COC/EVA blends, at high EVA contents, were more compatible than COC-rich blends. For the droplet morphology, Palierne model was more successful but, by increasing the dispersed phase content some deviation was observed. In the co-continuous region, the Coran model was in good correspondence with the experimental data as compared to the Veenstra’s model. The storage and loss modulus of EVA-rich blends had a better correspondence with the Palierne model than the COC-rich blends which further confirmed the morphological findings. Interfacial tension calculated for the COC/EVA blends using the Palierne model, were about 1.2 and 15 mN/m2 for EVA-rich (10/90) and COC-rich blends (90/10), respectively. In both EVA-rich and COC-rich systems the interfacial tension increased with increasing the dispersed phase content.