Crystallization kinetics of glass fiber reinforced PBT composites

The effect of glass fibers on the crystallization of poly(butylene terephth alate) (PBT) was investigated by crystallization kinetics analysis under is othermal and nonisothermal conditions. From the crosspolar optical microgra phs of melt- and solvent-crystallized PBT composites, the glass fibers were found to increase the number density and decrease the size of crystallites . The glass fibers provided heterogeneous nucleation sites, and thus enhanc ed the overall rate of PBT crystallization in isothermal experiments. Howev er, the Avrami exponent and the regime transitions were not significantly a ffected by the presence of glass fibers. For the nonisothermal kinetics of PBT composites, the model prediction was excellent in most ranges of crysta llization, but it deviated above 70% of crystallization especially at fast cooling rates (>40 degrees C/min). This discrepancy of the model seemed to result from the growth. regime transitions, which were clearly observed esp ecially at high undercoolings. (C) 2000 John Wiley & Sons, Inc.