Viscosity and domain morphology in binary immiscible blends of poly(trimethylene terephthalate) and polyamide6,10

Poly(trimethylene terephthalate) (PTT) and polyamide6,10 (PA6,10) are polymers with significant biobased content that forms an immiscible blend system of high-value engineering materials with enhanced sustainability. Knowledge of the melt viscosity of these thermoplastic materials is critical, when processing blends to achieve optimum morphologies. We measured the viscosities of five extruded blends near the phase inversion composition, over a range of shear rates using both parallel plate and capillary methods. Based on the viscosities of the endmembers, Jordhamo co-continuity should be observed in the 21-44 volume percent PTT range, depending on the processing shear rate. Extruded blend viscosities were lower than the linear rule of mixtures and the phase inversion composition was identified near 55 volume percent PTT. SEM images showed clear indications of developing cocontinuity in the 55 volume percent PTT. We conclude that the viscosities of immiscible polymer blends in this system do not follow the rule of mixtures, due to slip between immiscible domain interfaces, but that the viscosity and the power law index are useful in locating the phase inversion composition. The empirical Jordhamo relationship, although generally useful in immiscible polymer systems, is not as valuable in this system.