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The engineering thermoplastic poly(ether ether ketone) (PEEK) has a rigid backbone that crystallizes relatively slowly upon cooling the melt. In this study, fast scanning chip calorimetry (FSC) was used to analyze isothermal crystallization between 170 and 285 °C, a range from about 27 K above the glass transition temperature up to the melting temperature. Incorporation of carbon nanotubes (CNT) enhances nucleation at all crystallization temperatures, including low temperatures. FSC also was employed to study crystallization at cooling rates spanning 0.33 to 8000 K/s, important as PEEK is subject to these conditions during melt processing. The critical cooling rate to produce a vitrified sample was increased from 500 K/s in the neat PEEK to 4000 K/s in a 5% CNT/PEEK nanocomposite due to faster nucleation rate caused by heterogeneous nucleation. 

Both heterogeneous nucleation and flow‐induced entropy reduction are the two well‐known factors that accelerate polymer crystallization. However, the interplay of nucleation and flow‐induced acceleration is still poorly understood. This work investigates the nucleating effect of carbon nanotubes (CNT) on both the quiescent and flow‐induced crystallization kinetics of polyamide 66 (PA 66). The quiescent crystallization study indicates that CNT acts as a powerful nucleant, as suggested by the fact that the critical cooling rate to bypass crystallization and create the amorphous glassy state changes from 1000 K s⁻¹in PA 66 neat resin to a rate faster than 4000 K s⁻¹in the PA 66 nanocomposites. The flow‐induced crystallization study indicates PA 66 onset crystallization time and morphology depend on the shear work introduced by rotational rheometry. A combined acceleration effect from CNT nucleants and flow‐induced crystallization (FIC) persists when the CNT loading is under the saturation limit. However, if CNT loading meets the saturation limit, specific shear work shows no impact on the crystallization time, providing evidence that the role of the FIC acceleration effect no longer exists when nucleant acceleration dominates the crystallization of PA 66.