EFFECTS OF SOLVENT TREATMENT ON COLD CRYSTALLIZATION BEHAVIOR AND MORPHOLOGY OF POLY(ETHER ETHER KETONE)

Isothermal crystallization kinetics at temperatures between 160-194 de grees C and the morphology of virgin and solvent-treated poly(ether et her ketone) (PEEK) were investigated by using differential scanning ca lorimetry, scanning electron microscopy (SEM), and wide-angle X-ray sc attering analysis. Kinetic analysis showed that the cold crystallizati on of virgin (untreated) PEEK proceeds with an Avrami exponent of n = 2,5-2,6, and the SEM results revealed a grainy-texture morphology with no regular spherulites, suggesting a planar growth. The X-ray charact erization revealed low to medium crystallinity, which is consistent wi th the SEM results. This is quite different from the typical impinged spherulitic morphology of high crystallinity in melt-crystallized PEEK . Post cold-crystallization annealing at temperatures near the melting point (300-320 degrees C), however, induced a spherulitic morphology resembling that produced from melt crystallization. Furthermore, methy lene dichloride treatment on PEEK was found to significantly affect th e cold-crystallization kinetics and the resulting morphology. The cold crystallization of solvent-desorbed PEEK samples proceeds with n = 1, 0-1,2, reflecting probably an irregular line growth with heterogeneous nucleation. Additionally, SEM examination revealed a highly porous te xture in the desorbed/cold-crystallized PEEK that hindered direct obse rvation of the actual crystalline morphology; nevertheless, neither sp herulites nor planar lamellar crystals were observed.