Nanoparticle-induced co-continuity in immiscible polymer blends - A comparative study on bio-based PLA-PA11 blends filled with organoclay, sepiolite, and carbon nanotubes

Different amounts of organoclay, sepiolite, and carbon nanotubes are added to an immiscible blend of poly(lactic acid) (PLA) and polyamide 11 (PA11) with drop-matrix morphology aiming at elucidating the mechanisms through which unevenly distributed nanoparticles may induce co-continuity. Morphological and dynamic-mechanical analyses show that the three fillers, preferentially located inside the minor PA11 phase, are all able to convert the drop-matrix morphology of the blend into a stable, highly co-continuous one provided a critical nanoparticle loading is exceeded. The cross-checking of the experimental results reveals that co-continuity occurs when the strength of the particle network encapsulated inside the PA11 is sufficient to balance the inclination of the stretched polymer domains to retract back towards lower aspect ratio shapes driven by interfacial tension. A single dimensionless group that combines the yield stress of the filled PA11, the bending resistance of the nanoparticles, and the PLA-PA11 interfacial tension, seems able to rationalize our data, providing a general criterion for the optimal selection of fillers suitable to induce co-continuity in immiscible polymer blends.