It will be shown that when polyether-b-amide (PEBA) is added to a PLA/PA11 blend, it tends toward the interface and results in a significant increase in the impact strength when all three phases are fully percolated. The addition of the elastomeric PEBA phase to the binary PLA/PA11 blend replaces a rigid PLA/PA11 interface with a much more deformable one. The further addition of PEO to PLA results in an ultratough material with an impact strength of ∼750 J/m, which is approximately 40 times greater than the original co-continuous PLA/PA11 blend. The tensile toughness and notched Izod impact strength are significantly influenced by the critical co-continuous composition region of the PLA/PA11 binary system and a minimum concentration to form a fully percolated PEBA layer at the co-continuous PLA/PA11 interface. The added PEO is also found to enhance the interfacial interactions and the chain mobility of PLA. The combined effects of co-continuity, strong interfacial interactions, a deformable interface, and sufficient PLA chain mobility are all essential to achieving ultratough behavior in PLA/PA11. Examination of the fracture surface of the ultratough material after impact indicates significant voiding. It is suggested that the stress-field overlap within the deformable PEBA phase in conjunction with suitable interfacial adhesion changes the failure mode from crazing to shear yielding. These results establish a strategy for the toughening of multiphase polymer blends, especially in the vicinity of the co-continuous region.

It will be shown that an interfacially percolated rubbery phase in a cocontinuous polylactide (PLA)/linear low-density polyethylene (LLDPE) blend results in a significant increase in the impact strength. All blends possess a tricontinuous phase morphology in which poly­(ε-caprolactone) (PCL), poly­(ethylene–methyl acrylate) (EMA), and ethylene–methyl acrylate–glycidyl methacrylate (EMA-GMA) percolate at the interface of PLA/LLDPE but offer different toughening and compatibilization effects. Among these components, the addition of EMA-GMA to the binary PLA/LLDPE blend reduces the cocontinuous PLA/LLDPE phase thickness from about 25 to 5 μm and yields a very tough material with an impact strength of about 515 J/m, which is approximately 13 times greater than the original cocontinuous PLA/LLDPE blend and more than 32 times that of PLA. The ternary blends show significant improvements in the impact strength within the tricontinuous region; however, the principal differences in the toughening effects are attributed to interfacial interactions between the phases. The interconnected network of the rubbery phase is expected to percolate the stress field throughout the tricontinuous system and reduce the detrimental dilatational stress in the bulk blend.

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In this study it is shown that the three different intermediate phases in melt blended ternary PLA/PHBV/PBS, PLA/PBAT/PE and PLA/PE/PBAT systems all demonstrate partial wetting, but have very different wetting behaviors as a function of composition and annealing. The interfacial tension of the various components, their spreading coefficients and the contact angles of the confined partially wet droplets at the interface are examined in detail. A wetting transition from partially wet droplets to a complete layer at the interface is observed for both PHBV and PBAT by increasing the concentration and also by annealing. In contrast, in PLA/PE/PBAT, the partially wet droplets of PE at the interface of PLA/PBAT coalesce and grow in size, but remain partially wet even at a high PE concentration of 20% and after 30 min of quiescent annealing. The dewetting speed of the intermediate phase is found to be the principal factor controlling these wetting transitions. This work shows the significant potential for controlled wetting and structuring in ternary polymer systems.