Dielectric relaxation spectroscopy of poly[(R)-3-hydroxybutyrate] (PHB) during crystallization



The dielectric response of poly [(R)-3-hydroxybutyrate] (PHB) was investigated as a function of time after quenching a film from the melt to a crystallization temperature of 20 °C. In the frequency range investigated (20 to 106 Hz) a relaxation maximum was observed–attributable to the glass transition–which could be analysed by the Havriliak–Negami relation. Changes in the complex dielectric constant were monitored both during spherulite growth (primary crystallization) and subsequently during a period of progressive crystallization (secondary crystallization) at room temperature. The relaxation strength changed only slightly during primary crystallization and its peak position remained at a constant frequency. Subsequently a continuous decrease in relaxation strength occurred, indicating considerable changes in molecular mobility after spherulite growth had been completed. The results provide further evidence that molecular mobility in the amorphous regions decreases significantly with time, and that this would be the reason why PHB shows embrittlement on ageing at room temperature. Copyright © 2004 Society of Chemical Industry