Crystallization behavior and morphological characterization of poly(ether ether ketone)

•The double melting peaks phenomenon observed in conventional DSC work originates from the reorganization of PEEK crystals.•A refined crystallization model to describe PEEK crystal structure formation is proposed.•The refined crystallization model can help reconcile the discrepancy found between the crystallinity measured by DSC and SAXS.

The crystal structure and morphology of poly(ether ether ketone) (PEEK) was investigated using standard differential scanning calorimetry (DSC), flash DSC, optical microscopy, atomic force microscopy, and small angle X-ray scattering tools. The flash DSC results suggested that the double melting peaks phenomenon observed in conventional DSC work originated from the reorganization of PEEK crystals, which was due to the much faster recrystallization rate of PEEK than the DSC heating and cooling rate. A refined crystallization model to describe PEEK crystal structure formation was proposed. The refined crystallization model could help reconcile the discrepancy found between the bulk crystallinity measured by DSC and the linear crystallinity obtained from SAXS experiments by taking into account possible variation in crystal perfection within the lamellar structure. Simplified molecular dynamic modeling was carried out to support this model. Implications of the above findings to the fundamental understanding of structure-property relationships in PEEK were discussed.

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