Fully bio-based ternary polymer blends: structural characterization and mechanical behavior

In this work, ternary immiscible blends based on poly (lactic acid) (PLA) as major phase and polybutylene succinate (PBS) and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHH) as minor phases were prepared through melt blending, aiming at obtaining fully biobased materials with enhanced ductility and toughness as compared to the inherently brittle matrix. Thermodynamic considerations based on the calculation of the interfacial tensions predicted the achievement of a partial encapsulation between the domains of the two minor components embedded in the PLA matrix. The rheological characterization revealed higher melt viscosity and elasticity for all the ternary blends as compared to the PLA matrix and a growing level of interfacial interactions between the different phases when increasing amounts of PBS are incorporated. This last was confirmed through morphological observations, which allowed demonstrating the achievement of an improved homogeneous microstructure for the blends containing 30 and 40 wt% of PBS, notwithstanding the relatively good interfacial adhesion obtained in all the explored materials. The combined effect of the strong established interfacial interactions and of the uniform morphology resulted in the obtainment of dramatic increments of ductility, tensile toughness and impact strength for all formulated ternary blends as compared to the PLA matrix, and especially for those containing 30 or 40 wt% of PBS, while maintaining satisfactory levels of stiffness and tensile strength.