X-ray investigation on melt-crystallized bacterial poly(3-hydroxybutyrate)

Films of bacterial poly(3-hydroxybutyrate), obtained by crystallization from the melt at different temperatures up to 120 degrees C, were investigated by powder X-ray diffraction analysis and optical microscopy. With increasing crystallization temperature (T-c) the diffraction patterns differed more and more from that of the `'as received'' powder in both relative intensity of the reflections and peak width. The relative peak intensities also varied in response to temperature changes of the melt from which the polymer was quenched to a selected T-c. The differences in the X-ray diffraction patterns were correlated with changes of average spherulite size (0.1 mm to 2 mm) in films with limited thickness. When the spherulites were large the lamellar crystals were strongly oriented parallel to the film plane. Full profile Rietveld analyses allowed to quantify the preferred orientation effect and to extract additional morphological and structural informations.