Blending of polyhydroxybutyrate-co-valerate with polylactic acid for packaging applications - reflections on miscibility and effects on the mechanical and barrier properties

Biopolymers for packaging applications offer many advantages and are therefore of increasing interest. In order to develop a sustainable alternative for petrochemical-based polymers the biobased and biodegradable polymers, the focus of this work are polyhydroxybutyrate-co-valerate (PHBV) and polylactic acid (PLA) (and copolymers). Blending of these two biopolymers was reviewed under thermodynamic aspects and backed with own results. Additionally, different ways of improving the miscibility were performed by compatibilisers, peroxides, transesterification catalysts, and by blending PHBV with modified molecular weight. These blends were extruded as cast films, and characterised by means of mechanical and barrier properties. This study analyses the miscibility of PLA and PHB-copolyester (with approximately equal molar masses) and reports on the unusually high barrier properties in PLA and PHBV blends. However, the quality of blending, especially regarding barrier properties to interphase boundaries, depends on the compatibility of the components and the morphology of the blend. Our results suggest that a PHBV content of 20-35 % in PLA is the most suitable blend system in terms of compatibility and high barrier properties.