Miscibility, crystallization and phase structure of poly(3-hydroxybutyrate)/cellulose acetate butyrate blends

Blends of poly(3-hydroxybutyrate) (PHB) with cellulose acetate butyrate (CAB) were prepared by solution casting from chloroform solutions at different compositions. The miscibility, crystallization behavior and phase structure were investigated using differential scanning calorimetry, optical microscopy and small-angle X-ray scattering (SAXS). CAB/PHB blends were found to be miscible in the melt state as evidenced by the deduction of a single glass transition (Tg) for each composition, a depression in the equilibrium melting point of PHB, and a marked reduction in the spherulites growth rate of PHB in the PHB/CAB blends. The Flory–Huggins interaction parameter (χ12), obtained from melting point depression data, is composition dependent, and its value is always negative. The nucleation factor, Kg, was determined using Lauritzen–Hoffman model. The Kg values for the PHB in the blends are considerably lower than the Kg value in the pure homopolymer. The phase structure of the blend in the solid state as revealed by SAXS is characterized by the presence of a homogeneous amorphous phase situated mainly in the interlamellar regions of crystalline PHB and consisting of CAB molecules and uncrystalline PHB chains.