Modification via preparation for poly(3-hydroxybutyrate) films: Water-transport phenomena and sorption

The effect of the preparation technique on the sorption-diffusion parameter s of poly(3-hydroxybutyrate) (PHB) films was studied. The films formed by a single-stage technique have an axial texture of the crystalline phase, wit h the polymer chain oriented predominantly perpendicularly to the film plan e. Moreover, the crystallites in PHB are preferably ordered in stacks in th e course of diffusion; the alignment of the crystallites noticeably decreas es the "sites" of PHB (polar groups) which are accessible to water molecule s. As a result, the sorption capacity decreases but the rate of diffusion i ncreases. On the contrary, PHB films prepared by a two-stage technique are characterized by a poor ordering of crystallites without texture organizati on. Here, the sorption/immobilization on the polar groups of PHB is increas ed, but diffusivities are decreased. Concentration dependencies of the wate r-diffusion coefficient are discussed. Additional information on the existe nce of protein impurities in the PHB samples obtained by the above two prep aration techniques was obtained by FTIR spectroscopy and H-D exchange metho ds. (C) 2000 John Wiley & Sons, Inc.