Miscibility and Mechanical Properties of Blends of (l)-Lactide Copolymers with Atactic Poly(3-hydroxybutyrate)

Poly( l -lactide- co -glycolide) (PLLAGA) copolymers and poly( dl -lactide) (PDLLA) were synthesized using the low toxicity compound zirconium(IV) acetylacetonate. Blends with synthetic atactic poly(3-hydroxybutyrate) (a-PHB) were prepared in film form by solvent casting. The solid-state properties of the plain polymers and of the blends were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA−MS), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and stress−strain measurements. The a-PHB/PDLLA blends are miscible over the whole composition range. On the other hand, blends of a-PHB with PLLAGA copolymers containing 5 and 16 mol % of GA units show partial miscibility. The solubility limit of a-PHB in PLLAGA is around 20 wt % in both cases. In the blends, the a-PHB in excess to this value segregates as a pure phase. The mechanical properties of blend films of either PDLLA or PLLAGA containing up to 50 wt % of a-PHB can be modulated by changing blend composition. The tenacity progressively increases by the addition of a-PHB not only in the miscible amorphous a-PHB/PDLLA system but also in the partially miscible a-PHB/PLLAGA blends.