Small angle X-ray scattering study of the phase structure of poly (D (-) 3 hydroxy butyrate) and atactic poly (epichlorohydrin) blends.

Isothermally crystallized and annealed blends of poly(D-(-)-3-hydroxybutyrate) (PHB) and atactic poly(epichlorohydrin) (aPECH) were examined by wide-angle X-ray diffraction and small-angle X-ray scattering (WAXD and SAXS). The lateral crystal dimensions of PHB increased with annealing treatment and with increasing aPECH component in the blends, while the long-period distances of the blends were slightly smaller than for pure PHB. The scattering observed for the blends resulted from the superposition of the scattering arising from the crystalline regions (made up by alternate stacking of lamellae and thin amorphous layers) and from the aPECH inhomogeneity present outside them. The structural information was obtained, from the SAXS curves, on the basis of Glatter and Debye-Bueche approaches. The results suggest that, during melt-crystallization of PHB, segregation ofaPECH occurs within the growing spherulite with its dispersion in the interfibrillar zones that are larger than the interlamellar regions but smaller than the overall spherulite. The aPECH molecules are dispersed at the molecular level in the interfibrillar zones where they can assume a random-coil conformation. The detection of a glass transition temperature (Tg) close to the aPECH Tg value indicates low interactions at the segmental level between the two polymers. The annealing treatment produced a general perfectioning and rearrangement of the sample morphology, enhancing the crystallinity and the crystal dimensions of PHB in the pure state and in the blends, and probably favouring the trend of the aPECH molecules to assume a globular conformation.