Review - Properties of blends and composites based on poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) copolymers

Poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) ( PHBV) copolymers are microbial polyesters presenting the advantages of biod egradability and biocompatibility over other thermoplastics with useful mec hanical properties. However, their costs and performances must be adjusted by blending with suitable polymers. In this article the miscibility, morpho logy, mechanical behaviour and other prominent characteristics of a represe ntative number of blends and composites of PHB and PHBV are summarized. In particular, blends with a few polyethers, polyesters, polyvinylacrylates an d polysaccharides are illustrated. Furthermore, a brief paragraph deals wit h PHB/vegetal fiber composites. A wide range of properties emerges by blend ing with polymers having very different molecular structures and characteri stics, such as crystallinity, glass transition and melting temperatures. Th e microstructure of the blends, resulting from thermodynamic and kinetic fa ctors, is regarded as an important factor in controlling the mechanical and the biodegradation behaviours. Moreover, some considerations upon the natu re of the "driving force" of the miscibility have been made in order to exp lain miscibility behaviour differences. (C) 2000 Kluwer Academic Publishers .