Tunable morphologies for ternary blends with poly(butylene succinate): Partial and complete wetting phenomena

Poly(butylene succinate) (PBS) is a promising polymer for the production of bio-based and biodegradable materials. This study focuses on the development of novel tunable morphological states based on ternary blends comprising PBS. The other biodegradable polymers are selected from a set of poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT), and polycaprolactone(PCL). Three completely different morphological states are observed here for the ternary blends and are reported for the first time including: partial wetting for PBS/PLA/PCL in which PLA droplets self-assemble at the interface of PBS and PCL; complete wetting tri-continuous morphology for PBS/PLA/PBAT; and a highly unusual state combining both partial and complete wetting cases for the PBS/PBAT/PCL blend. The dramatic variation of morphology for these blends is possible due to very low interfacial tensions between the polymer pairs. Within these morphological wetting states a significant variety of specific structures can be obtained through control of the relative compositions. For example, for the partially wet xPBS/yPLA/50%PCL blend, changing the volume fraction of PBS to PLA from φPBS/φPLA=10 to φPBS/φPLA=0.1 results in a transformation from PLA droplets at the PBS/PCL interface to PBS droplets at the PLA/PCL interface. From the thermodynamic standpoint, the observed partial and complete wetting cases are supported by Harkins theory. This work opens the door to a wide range of novel and stable PBS-based ternary blend structures comprising biodegradable polymers.