Interfacial crystallization behavior of poly(ether-ether-ketone) on polyimide-modified CCF300 carbon fibers

Thermostable polyimide (PI) was synthesized and used as a sizing agent to modify carbon fiber (CF) surfaces. In order to investigate the influence of the PI sizing agent on interfacial properties of continuous CF reinforced poly(ether-ether-ketone) (CF/PEEK) composites, a comparative investigation on the interfacial crystallization behavior of PEEK on CF surface with and without PI modification was performed by in situ polarized optical microscope (POM) and differential scanning calorimetry (DSC) analysis. The POM images showed that the unsized CFs acted as heterogeneous nucleating agents to accelerate the formation of transcrystals, whereas CFs with PI sizing agents reduced nucleation site density, inducing nonuniform crystal layers. Quantitative investigation on the kinetics of interfacial crystallization growth also revealed that the PI sizing agent was an obvious obstacle to nucleation and subsequent crystallization growth. Based on the Jeziorny-modified Avrami model, nonisothermal crystallization kinetics was studied over a large range of cooling rates, whose results were found consistent with the results in POM observation. Moreover, a theoretical model was proposed to reveal the mechanisms for the considerable influence of the PI sizing agent on the interfacial crystallization behavior of PEEK in CF/PEEK composites, and the predication for other systems was also performed.