Tuning the interaction of an immiscible poly(l-lactide)/poly(vinylidene fluoride) blend by adding poly(methyl methacrylate) via a competition mechanism and the resultant mechanical properties

Abstract

In this work, a mutually miscible third polymer, i.e. poly(methyl methacrylate) (PMMA), was introduced into an immiscible poly(L-lactide) (PLLA)/poly(vinylidene fluoride) (PVDF) (60/40, wt/wt) blend. The interactions between PMMA and both components of the immiscible blend were first theoretically predicted by calculating the interfacial tensions and then experimentally proven by characterizing the glass transition and crystallization behaviors of the components. The results showed that although PMMA was miscible with PLLA and PVDF, it exhibited stronger interaction with PVDF and had a tendency to merge together with the PVDF component during the melt-compounding processing. There was a competition effect between PLLA and PVDF when they absorbed PMMA. Consequently, the interaction between PVDF and PLLA was enhanced by the bridge effect of PMMA. Furthermore, the migration and diffusion of PMMA carried a part of the PLLA component into the PVDF component (or carried some PVDF component into the PLLA component), forming a so-called occlusion structure. The mechanical properties were measured and the results showed that, at appropriate PMMA content (20–30 wt%), the ternary blends exhibited excellent fracture toughness. The enhanced interaction between components and the formation of the occlusion structure were suggested to be the main toughening mechanisms. This work demonstrated that the microstructure and mechanical properties of the immiscible polymer blends could be tuned by adding a mutually miscible third polymer via a competition mechanism and therefore it provided an alternative strategy for preparing microstructure-/property-controllable materials.