TIME-RESOLVED SIMULTANEOUS SAXS WAXS STUDIES OF PEEK DURING ISOTHERMAL CRYSTALLIZATION, MELTING, AND SUBSEQUENT COOLING/

Time-resolved simultaneous small- and wide-angle x-ray scattering (SAX S and WAXS, respectively) of poly(aryl ether ether ketone) (PEEK) duri ng isothermal crystallization, melting, and subsequent cooling were co nducted using synchrotron radiation. Unit cell parameters were determi ned using WAXS measurements, and the dimensions of lamellar-level moie ties were extracted from SAXS profiles. It was found that the changes in unit cell parameters were reversible on heating and cooling, and th ere were remarkable differences in the thermal expansion coefficients in different lattice directions. The long period L, the lamellar thick ness l(c), and the thickness of amorphous layers l(a) were calculated from the correlation function, and the changes of these dimensions dur ing the processes mentioned above were traced. Sharp decreases in L an d l(c) in the initial stage of isothermal crystallization and cooling from melt were observed, and a corresponding continuous distributed mo del is proposed. When cooling from the melt, the invariant Q exhibited a maximum. The maximum is attributed to a change in the difference of the densities of crystalline and amorphous phases (rho(c) - rho(a)) w ith decreasing temperature.