Constructing a gradient modulus interface layer on the surface of carbon fibers to enhance the mechanical properties of carbon fiber/epoxy composites at different temperatures

A gradient modulus interface layer was designed between the carbon fiber and the epoxy by grafting the rigid polymer PPENK and the flexible polymer PEI. The influence of the interfacial modulus on the mechanical performance of carbon fiber/epoxy composite at different temperatures was analyzed. At room temperature, compared with the desized CF composite, the mechanical properties (interfacial shear, interlaminar shear, flexural strength, flexural modulus, and impact strength) of CF-PPENK-PEI composites were increased by 32.2 %, 11.4 %, 34.8 %, 24.2 % and 20.3 %, respectively. This improvement was attributed to the interfacial phase PPENK-PEI, which improved the roughness and polarity of the CF surface, increased wettability with the matrix, and buffered and balanced the modulus discrepancy between the CF and the epoxy. Atomic force microscopy (AFM) was confirmed the existence of a gradient modulus interface layer in CF-PPENK-PEI/epoxy composites. Notably, at 180 °C, the interlaminar shear strength (ILSS), flexural strength and flexural modulus of the CF-PPENK composite increased by 86.7 %, 92.5 % and 113.0 %, respectively, compared with the commercial CF composite, indicating better thermomechanical stability due to PPENK rigid heteroaromatic structures, which can maintain a high modulus at elevated temperature. Additionally, the dynamic thermomechanical properties of the composites were demonstrated the outstanding thermomechanical stability of the CF-PPENK/epoxy composites interface. Overall, this work provides a theoretical basis for preparing CF composites for use in high-temperature fields.