Stepwise annealing of poly(butylene terephthalate)

Abstract

Annealing of poly(butylene terephthalate) (PBT) was studied by differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) measurement. A PBT sample was annealed at a recrystallization temperature where recrystallization occurs with a maximum rate in the heating process of the sample. In the subsequent annealing steps, the annealed sample was annealed repeatedly at the recrystallization temperatures, and the stepwise annealing sample was obtained. Peak melting temperature (Tm) and sharpness of DSC peak of the stepwise annealing sample increased with the annealing step. A high melting-temperature sample was obtained in a short time, and Tm increased up to 238.5°C which is higher than all the Tm values that appear in the literature. The long period calculated from SAXS curves of the stepwise annealing sample increased with the annealing step. The increase of crystallite size and perfection of the crystal in the stepwise annealing process is suggested. Annealing experiment indicated that T°m should be higher than about 235°C. Tm increased linearly with the annealing temperature of the final step in the stepwise annealing (Ta). The equilibrium melting temperature (T°m) for PBT was estimated to be 247°C by the application of a Hoffman–Weeks plot to the relation between Tm vs. Ta. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2420–2429, 1999