DIELECTRIC INVESTIGATION OF COLD CRYSTALLIZATION OF POLY(3-HYDROXYBUTYRATE)

The dielectric behaviour of poly(3-hydroxybutyrate) (PHB) has been inv estigated for the glass (alpha) relaxation in the temperature and freq uency ranges of -60 to 100 degrees C and 10(3)-10(5) Hz, respectively. Also, the crystallization kinetics of PHB has been studied dielectric ally as a function of heating rate, time and temperature. Crystallinit y has a marked influence on the glass relaxation characteristics owing to the relative constraint imposed on the amorphous phase by the crys tallites. Furthermore, the results obtained showed that: (1) the optim um crystallization temperature is about 25 degrees C; (2) the time at which crystallization starts is a function of the working temperatures and apparently is reduced to just a few minutes at 40 degrees C; and (3) the crystallization process is completed within a period of less t han 1 h in the temperature range 20-40 degrees C. The bulk crystalliza tion phenomena could be also described by the Avrami equation with an exponent similar to 3.8. (C) 1997 Elsevier Science Ltd.