CRYSTALLIZATION KINETICS OF POLY(ETHER ETHER KETONE) (PEEK) FROM ITS METASTABLE MELT

After isothermal crystallization of the amorphous poly(ether ether ket one), double endothermic behaviour can be found through differential s canning calorimetry experiments. During the heating scan of semicrysta lline PEEK, a metastable melt, which comes from the melt of the thinne r lamellar crystal populations, can be obtained between these two endo therms. The metastable melt can recrystallize immediately just above t he lower melting temperature and form slightly thicker lamellae than t he original ones. The thickness and the perfection depend upon the cry stallization time and the crystallization temperature. By comparing th e TEM morphological observations of the samples before and after parti al melting, it can be shown that lamellar crystals, having different t hermodynamic stability, form during isothermal crystallization. After partial melting, only the type of lamellar crystal exhibiting the high er thermodynamic stability remains. Wide angle X-ray diffraction measu rements shows a slightly change in the crystallinity of the samples be fore and after the partial melting. Small angle X-ray scattering resul ts exhibit a change in the long period of the lamellar crystals before and after the partial melting process. The crystallization kinetics o f the metastable melt can be determined by means of differential scann ing calorimetry. The kinetic analysis showed that the isothermal cryst allization of the metastable PEEK melt proceeds with an Avrami exponen t of n = 1.0 similar to 1.4, reflecting that probably one-dimensional or an irregular line growth of the crystal occurred between the existi ng main lamellae with heterogeneous nucleation. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.