PLLA/PMMA blends: A shear-induced miscibility with tunable morphologies and properties?

Polymer blends and alloys represent an interesting approach to implement bio-based poly(l-lactic acid) (PLLA) into high-value applications. Here, a re-evaluation of the miscibility extent between both biobased PLLA and petro-based poly(methyl methacrylate) (PMMA) is proposed in order to tune morphologies and properties of resulting blends upon either a solvent-casting method or a twin-screw extrusion. The solvent-casting process proved only able to produce immiscible blends with matrix–droplet or co-continuous morphologies in function of the blend composition and the immiscibility–miscibility transition is not observed for temperature lower than 250 °C. When melt-processed via extrusion technique, only miscible PLLA/PMMA blends were recovered all over the composition range, as observed by a single glass transition and a single α-relaxation transition at intermediate temperature between pure PLLA and pure PMMA as determined by DSC and DMTA, respectively. Miscibility was also observed at low shear rate with a phase-reversibility, demonstrating the absence of any reactions between PMMA and PLLA phases and the existence of a shear-sensitive clarity point. Homogenous and transparent PLLA/PMMA blends were easily produced with tunable thermomechanical and barrier properties against the blend composition. Glass transition temperature, α-relaxation temperature, thermal resistance and gas permeability were accurately controlled by the PMMA content, while maintaining impact strength and storage modulus in the same range than PLLA itself.