Compatibilization and toughening of co-continuous ternary blends via partially wet droplets at the interface

This work reports that a partially wet phase can compatibilize and toughen a co-continuous PLA/PA11 blend. Four different polymers: PBS, PBAT, EMA and EMA-GMA are examined for their capacity to partially wet the PLA/PA11 interface in a melt-blending process. All the blends exhibit a partial wetting morphology, but offer very different compatibilization efficacies and toughening effects. EMA-GMA demonstrates the best compatibilization effect as it reduces the co-continuous thickness to 5-6 mu m, which is about half that of the original binary PLA/PA11 blend, followed by EMA while PBS and PBAT result in the least changes in morphology and properties. Despite the enhanced compatibilization effect obtained with EMA-GMA, it is the self-assembled droplets of EMA at the PLA/PA11 interface which result in a major increase in the ductility of the blend with an elongation at break of 260% as compared to 4% for the binary blend. A substantial increase in the notched Izod impact strength is also achieved with partially wet droplets of EMA with a value of 73 J/m, a four-fold increase as compared to the impact strength of the pure PLA and the PLA/PA11 binary blend. This difference is attributed to the limited internal cavitation of the very fine droplets of EMA-GMA at the interface whereas the blends with partially wet EMA demonstrate significant interfacial cavitation after the impact fracture test. This work shows that self-assembled rubbery EMA droplets at a co-continuous PLA/PA11 interface combine to compatibilize the system, improve interfacial adhesion and interfacially cavitate through the continuous system upon fracture. The percolation of the stress field around these interfacially cavitated partially wet droplets results in the shear yielding of the matrix and a significant toughening effect ensues. These results indicate the potential of partially wet droplets to compatibilize and toughen co-continuous structures. (C) 2017 Elsevier Ltd. All rights reserved.