Time-resolved X-ray study of poly(aryl ether ether ketone) crystallization and melting behaviour: 1. Crystallization

Time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) experiments using synchrotron radiation were made in order to study the isothermal crystallization behaviour of poly(aryl ether ether ketone) (PEEK). Two types of long period (L_B and L^M_C), the scattering invariant Q, and the linear degree of crystallinity within the lamellar stacks x_CL were estimated from the Lorentz-corrected plot and the correlation function. As a result, the average lamellar thickness l_C was calculated as the product of L^M_C and x_CL during crystallization at temperatures of 230-310°C. The bulk degree of crystallinity (by weight), ψ_C, was determined by WAXD. It was found that both long periods decreased, Q increased and l_C remained approximately constant with time. The decrease in the long period was explained by the lamellar insertion within the lamellar stacks, whereas the increase in Q was attributed to the increase in the bulk-volume degree of crystallinity x_C, rather than x_CL. In addition, the values of the long period and of Q were found to increase with temperature as a result of the thicker lamellae. Finally, our results support the model of two populations in lamellar thickness, namely the primary lamellae which are developed first in bundle-like stacks, and the narrower, secondary lamellae (as a small fraction) that are inserted later between the primary lamellae under various spatial restrictions.