Morphology and thermal behaviour of poly(3-hydroxybutyrate-co-hydroxyvalerate) starch valerate blends

The morphology, crystallisation and melting behaviour of binary blends prepared by extruding mixtures containing different amounts of starch valerate (SV) and a poly(3-hydroxybutyrate-co-hydroxyvalerate) copolymer have been investigated by optical and scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and mechanical tensile tests. The absence of apparent phase separation, the increase in spherulite dimensions and the decrease of radial growth rate with increasing SV content, as well as the presence of a single composition-dependent T-g value, evidenced a high degree of compatibility between the two components, up to 20 wt.-% of SV. For higher SV contents, phase separation occurred, confirmed by the appearance of the T-g values of the pure components in thermal analyses.