Decoupling interfacial compatibilization and chain extension in polymer blends using rheology: PBAT/EVOH with MDI

Abstract

The rheological models were employed to distinguish dual elasticity effects of a compatibilizer in a polymer blend with a droplet-matrix morphology. Polymeric methylene diphenyl diisocyanate (MDI) acts as a reactive compatibilizer in immiscible blends of Poly(butylene adipate-co-terephthalate) (PBAT)/ poly(ethylene vinyl alcohol) (EVOH). Therefore, it alters elasticity of the blend through interface compatibilization. It also acts as chain extender in PBAT and increases its elasticity. The blends of PBAT/EVOH with a ratio of (70/30) wt% containing MDI were prepared by melt mixing. The FE-SEM images showed that by adding MDI the radius of EVOH droplets decreases from 0.34 to 0.12 µm. The interphase viscosity of the blends, estimated by Lee-Park model, was lower than the viscosity of PBAT-MDI as matrix, revealing a greater chain-extending effect of MDI as compared to its interfacial compatibilization effect. The shear-thinning behavior of the interphase, PBAT-grafted-EVOH, was stronger than the matrix i.e. chain extended PBAT. Coran model was modified by considering the interphase's elasticity, which improved the fitted curve's accuracy to the experimental data. Pal model revealed a decrement in the interfacial tension when adding MDI to the blend, confirming an effective compatibilization role of MDI in the PBAT/EVOH blend.