Toughening\nImmiscible\nPolymer Blends: The Role of\nInterface-Crystallization-Induced Compatibilization Explored Through\nNanoscale Visualization

This study explores\nthe novel approach of interface-crystallization-induced\ncompatibilization (ICIC) via stereocomplexation as a promising method\nto improve the interfacial strength in thermodynamically immiscible\npolymers. Herein, two distinct reactive interfacial compatibilizers,\npoly(styrene-<i>co</i>-glycidyl methacrylate)-<i>graft</i>-poly(l-lactic acid) (SAL) and poly(styrene-<i>co</i>-glycidyl methacrylate)-<i>graft</i>-poly(d-lactic\nacid) (SAD) are synthesized via reactive melt blending in an integrated\ngrafting and blending process. This approach is demonstrated to enhance\nthe interfacial strength of immiscible polyvinylidene fluoride/poly l-lactic acid (PVDF/PLLA) 50/50 blends via ICIC. IR nanoimaging\nindicates a cocontinuous morphology in the blends. The blend compatibilized\nwith SAD exhibits a higher storage modulus, as unveiled by small amplitude\noscillatory shear (SAOS) in the melt state at a temperature below\nthe melting temperature of the stereocomplex (SC) crystals and by\nDMTA measurements in the solid state. This increase is attributed\nto the formation of a 200–300 nm thick rigid interfacial SC\ncrystalline layer that is directly visible using AFM imaging and chemically\ncharacterized via IR nanospectroscopy. This ICIC also results in a\nsignificant toughening of the blend, with the elongation at break\nincreasing more than 20-fold. Moreover, the fracture toughness factor\nobtained from single edge-notch bending (SENB) tests is doubled with\nICIC as compared to the uncompatibilized blend, indicating the strong\ncrack-resistance capability as a result of ICIC. This improvement\nis also evident in SEM images, where thinner and longer fibrillation\nis observed on the fractured surface in the presence of ICIC.