The effect of the interfacial assembly of nano-silica in poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends on morphology, rheology and mechanical properties

This work studies the effect of the interfacial assembly of spherical nano-silica particles on the morphology, rheology and mechanical properties of heterophase poly(lactic acid), PLA, and poly(butylene adipate-co-terephthalate), PBAT, blends. Through a controlled mixing strategy, nano-silica particles could be assembled in a stable fashion at the PLA-PBAT interface. Rheological analysis indicates that the interfacial assembly of nano-silica significantly diminishes the relaxation of the dispersed PBAT phase and 3 wt.% of nano-silica particles shifts the co-continuity region to a lower PBAT volume fraction. At co-continuity, the assembly of nano-silica at the interface changes the rheological behaviour of the co-continuous PLA/PBAT from a liquid-like to a gel-like behaviour. The interfacial assembly of nano-silica reduces the co-continuous phase size but maintains co-continuity. The results of thermal annealing indicate a remarkable stabilization effect of interfacially assembled nano-silica on the co-continuous morphology. A conceptual model is proposed to explain the observed effects of interfacially assembled nano-silica on the morphology which emphasizes the critical role of nano-silica content, the relaxation time of the dispersed phase and the migration time of nano-silica to the interface. The mechanical properties of the PLA/PBAT blends are clearly influenced by the observed shift in co-continuity in the presence of nano-silica. Most importantly, the mechanical properties of co-continuous PLA/PBAT are very sensitive to annealing due to morphological coarsening. Interfacially assembled nano-silica has the effect of completely stabilizing the co-continuous morphology without any diminishing of the mechanical properties. These results clearly indicate the significant potential of the interfacial assembly of nano-particles as a promising strategy toward achieving polymer blends with highly robust and stable co-continuous morphologies.