Effects of solvent treatment on cold crystallization behavior and morphology of poly(ether ether ketone)

Abstract

AbstractIsothermal crystallization kinetics at temperatures between 160–194°C and the morphology of virgin and solvent‐treated poly(ether ether ketone) (PEEK) were investigated by using differential scanning calorimetry, scanning electron microscopy (SEM), and wide‐angle X‐ray scattering analysis. Kinetic analysis showed that the cold crystallization 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 characterization revealed low to medium crystallinity, which is consistent with 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°C), however, induced a spherulitic morphology resembling that produced from melt crystallization. Furthermore, methylene dichloride treatment on PEEK was found to significantly affect the 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 texture in the desorbed/cold‐crystallized PEEK that hindered direct observation of the actual crystalline morphology; nevertheless, neither spherulites nor planar lamellar crystals were observed.