Bacterial poly(3-hydroxybutyrate): An optical microscopy and microfocus X-ray diffraction study

Two-dimensional spatially resolved microfocus X-ray diffraction has been used to investigate spherulites of pure bacterial poly(3-hydroxybutyrate) (PHB) and of a blend of natural and synthetic atactic PHB (a-PHB) crystallized at a relatively high temperature (T-c = 140 degreesC). Both samples investigated contained practically two-dimensional spherulites, characterized by wide extinction bands (band spacing > 80 mum). The X-ray diffraction patterns confirmed that the unit cell a-axis is oriented along the spherulite radius in PHB and that the same is true for the a-PHB containing blend. Comparison of the matrix of diffraction patterns with the polarized optical micrograph of the scanned sample area indicated a very clear correlation between pattern changes and banding, yielding a straightforward picture of the structural variations within the spherulite.