Characterization and Processability of Blends of Polylactide Acid with a New Biodegradable Medium-Chain-Length Polyhydroxyalkanoate

In this work the processability and the mechanical performance of polylactide acid (PLA) based blends with a sample of a new biodegradable medium-chain-length poly (hydroxyalkanoate) (PHA) were investigated. The two polymers are incompatible with scarce adhesion and with the dispersed PHA particles size increasing with the PHA content. Rheological tests in shear flow indicate that adding PHA improves the processability of the matrix by increasing the content of this second component in the blend, as observed also for the torque curves, due to the very low viscosity of this new sample of PHA. The processability is only slightly worsened in non-isothermal elongational flow as the melt strength decreases, but accompanied by an increase of the melt stretchability that improves the ability of the pure PLA matrix to produce thin films. Mechanical properties put in evidence a brittle-ductile transition adding PHA to PLA matrix. The elongation at break significantly increases when PHA is added, while the elastic modulus is significantly reduced only at higher contents of PHA. This has been interpreted in terms of both plasticization action of the PHA and also in terms of lubricant action of the PHA macromolecules that allows a better sliding of the PLA macromolecules subjected to solid deformation.