Study of the partial wetting morphology in polylactide/poly[(butylene adipate)- co -terephthalate]/polyamide ternary blends: case of composite droplets

International audience; The prediction of the morphology of ternary polymer blends requires a good knowledge of the values of the three interfacial tensions. We selected three polymers, either biobased or biodegradable, PA, PBAT and PLA and we accurately measured their interfacial tensions using the retraction method, varying the molar mass or inverting the phases. The following values of interfacial tensions were obtained: = 3.3±0.7mN/m, = 5.6±0.3mN/m and = 3.0±0.4 mN/m. These values were used to calculate the spreading coefficients giving rise to two negative coefficients and one coefficient close to zero. Ternary blends with various compositions, two different levels of viscosity for the PBAT, different processing conditions were prepared. There was a very good agreement between the predictions of the spreading theory, when using the values of interfacial tensions in the right order of magnitude, and the observed morphologies, whatever the polymer serving as a matrix. When the PLA or PBAT was chosen as the matrix, the ternary blend morphology was composed of composite droplets, presenting a partial wetting morphology, dispersed in the polymer matrix. This morphology was observed whatever the composition, the viscosity level of the PBAT phase and the processing conditions. A further calculation of the free energy confirmed this 2 morphology. The formation process of this semi-encapsulated morphology was observed during blending.