POLYMER BLENDS CONTAINING POLY(3-HYDROXYALKANOATE)S

The remarkable properties of poly(3-hydroxyalkanoate)s (PHAs) have resulted in a growing interest in these polymers. They offer a wide variety of useful mechanical properties and show excellent biodegradability. However, they are still expensive and poly(3-hydroxybutyrate) (PHB) in particular is quite brittle. Polymer blending offers interesting possibilities to prepare less expensive biodegradable materials with useful mechanical properties. In this review the literature concerning PHA-containing blends has been summarized. Blends incorporating either PHB or copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (P(HB-HV)) were discussed. The thermal and crystallization behaviour of the blends, their mechanical properties, morphology and biodegradability have been reviewed. Among the conclusions drawn from the literature, it is evident that PHAs can form miscible blends with polymers containing the appropriate functional groups via hydrogen bonding and/or donor-acceptor interactions. The crystallization behaviour of the PHAs is influenced by both the miscible and immiscible components. Immiscible PHA-containing blends show improved apparent biodegradability when compared to miscible blends. Their apparent biodegradability (weight loss) is mostly controlled by the blend morphology. Blends of PHA with other biodegradable polymers also usually show improved biodegradability when compared with pure PHAs.