CONTROL OF THE MORPHOLOGY OF PLA/PBAT/PA TERNARY BLENDS THROUGH THE USE OF A PBAT-B-PLA COPOLYMER

Abstract : This work aims at achieving direct core-shell morphology in ternary PLA/PBAT/PA polymer blends by melt mixing. The final goal is to improve the toughness of polylactic acid (PLA). The morphology of multi-phase polymer blends is controlled by the thermodynamics of the system. The morphology of ternary blends can be predicted from the relative values of the three spreading coefficients characterising the triplet of polymers. Spreading coefficients are calculated from the values of interfacial tensions between binary components. The determination of interfacial tensions between a PLA, a poly(butylene adipate-co-terephthalate) (PBAT) and a copolyamide (PA) predicts a complex dispersed morphology in the PLA matrix where PA subinclusions are partly encapsulated in the PBAT phase. This morphology was obtained by melt mixing the three components, as observed by scanning electron microscopy (SEM). In a second step, selective compatibilization was used to modify the PA subinclusion location. To this end, a PBAT-b-PLA di-block copolymer was synthesized. The presence of the di-block copolymer enables us to modify the interfacial tension between PLA and PBAT. The modification of the interfacial tension balance was shown to successfully change the morphology from semi-encapsulation to full encapsulation of PA sub-inclusions in the PBAT drops.