Improving delamination resistance of 3D printed continuous fiber-reinforced thermoset composites by multi-scale synergistic toughening of mono-component polyetherketone-cardo

Continuous fiber-reinforced thermoset composites (CFRTCs) 3D printing offers a promising solution to fabricate lightweight, high-strength sophisticated composite structures. However, the delamination resistance of 3D printed CFRTCs is decreased by the weak fiber-matrix and interlayer adhesion caused by the process principle. To increase the interlayer toughness of 3D printed CFRTCs, this study developed a printing matrix toughened by various polyetherketone-cardo (PEK-C) forms by modulating its dissolution state. The results showed that the interlaminar toughening effects of the particle dispersion and dissolved dual form of PEK-C were superior to the insoluble particles or the dissolved PEK-C. As a result, the mode I and mode II interlaminar fracture toughness increased by 112.38 % and 189.01 %, respectively. And the synergistic effect of dual-form PEK-C was determined. Fractographic investigation revealed that the dissolved PEK-C experienced the reaction-induced phase separation initiating a nanoscale thermoplastic phase and developing a multi-scale PEK-C toughening system with the microscale PEK-C particles. Moreover, morphological observation of the particle and PEK-C phases demonstrate multi-scale synergistic toughening mechanisms of mono-component PEK-C. This study presents an innovative technique for interlayer toughening applicable to the CFRTCs 3D printing, illustrates the toughening principle, and shows its promise as a general strategy.