Morphology development in poly (lactic acid)/polyamide11 biobased blends: Chain mobility and interfacial interactions

Abstract

In this study, the interfacial tension, morphology, PLA phase continuity and thermal behavior are studied for poly (lactic acid)/bio-polyamide11 blends. This blend combines the very unusual characteristics of high static interfacial tension, 5.8 ± 0.6 mN/m and 5.4 ± 0.4 mN/m as measured by the breaking thread (BT) and fiber retraction (FR) methods respectively, with the fine dispersed morphology and low level coalescence of a highly interacting system after melt mixing. The dispersed phase size at 1 vol% is 750 and 700 nm for dispersed PLA and PA11 respectively with no coalescence whatsoever up to 20 vol% minor phase. A coalescence study during annealing shows that the 50PLA-50PA11 blend behaves as if it were an interfacially modified system. Furthermore, the half time of crystallization of PA11 increases in the presence of PLA, an indication of significant interfacial interactions. A study using plasticizers for both PA11 and the PLA shows that this discrepancy between the static interfacial tension and the observed morphology after dynamic mixing can be attributed directly to the limited chain mobility of the stiff PLA molecule, particularly under quiescent conditions, which inhibits the available functional groups from interacting at the interface. Plasticized PLA in PLA-PA11 serves to significantly reduce the static interfacial tension as well as the phase size and coalescence in the dynamically mixed system at high concentrations of 30 and 40 vol% PLA. These results underline that the stiffness and borderline mobility of PLA chains can have a significant influence on its capacity for interfacial interactions and could be dependent on the flow conditions.