Specific Structural Features of Crystalline Regions in Biodegradable Composites of Poly-3-hydroxybutyrate with Chitosan

Differential scanning calorimetry and X-ray diffraction at wide and small angles were used to examine the biodegradable composites of poly-3-hydroxybutyrate with chitosan, produced by mixing of these polymers in a rotor disperser at 150 degrees C. Samples of individual polymers and composites with 80, 40, and 20 wt % poly-3-hydroxybutyrate were studied. It was found that the presence of chitosan in the composites leads to a change in the crystallite size of poly-3-hydroxybutyrate and to an increase in the large period in this polymer. Mixing of poly-3-hydroxybutyrate with chitosan affects the structural rearrangement in crystalline regions of poly-3-hydroxybutyrate under a high-temperature treatment. The effect of a high-temperature treatment of the composites via alternation of melting-crystallization cycles in the nonisothermal mode, when a sample is heated and cooled at the same constant rate of 8 deg min(-1) in the range from 20 to 200 degrees C and is annealed at a temperature of 150 degrees C, was analyzed. This analysis suggests that, in composites of this kind, the intermolecular interaction between the components is a factor strongly affecting the structure of the crystalline regions and the mechanism of their rearrangement in the course of annealing. The mechanism of this interaction is discussed.