ORIENTATION CHANGES DURING THE COLD DRAWING AND SUBSEQUENT ANNEALING OF PEEK

Two-dimensional wide- and small-angle X-ray scattering (WAXS and SAXS) patterns have been recorded at the Daresbury Synchrotron Radiation Source in time-resolved studies of changes in orientation and crystallinity during annealing of cold drawn samples of poly(aryl ether ether ketone) (PEEK). An amorphous PEEK film drawn uniaxially to a draw ratio of 2.0 was observed to give a well oriented non-crystalline WAXS pattern. The drawn film was then held at constant length and diffraction patterns recorded while the sample temperature was raised at 15 degrees C min(-1) from ambient to the glass transition temperature (T-g = 145 degrees C) and beyond. WAXS patterns were recorded with an exposure time of 5 s. Close to T-g there was a sudden loss of orientation so that the diffraction pattern resembled that given by the specimen before cold drawing. This absence of crystallinity and orientation persisted for similar to 45 s after which the unoriented non-crystalline pattern began to be gradually replaced by a highly crystalline oriented pattern. This loss of orientation within a non-crystalline specimen close to T-g is consistent with a change from a molecular orientation associated with pseudo-affine deformation to an orientation associated with a stretched rubbery network. From parallel studies, the dramatic changes in the WAXS pattern were found to be correlated with changes in the small angle diffraction. Significant features in the SAXS pattern were not observed until the temperature was similar to 150 degrees C when the meridionally oriented central maximum began to develop. With increasing temperature this maximum gradually broadened in the meridional direction until at similar to 160 degrees C it developed into a distinct meridional peak at a spacing of 140 Angstrom. During subsequent annealing the intensity of this peak increased but its spacing did not change. Also, the half width of this peak in the direction parallel to the equator did not vary during annealing, suggesting that the lateral dimension of the crystalline regions within the specimen does not change during crystallite growth.