Carbon fibre reinforced polymers are widely used in industrial applications due to their excellent properties. However, the weak matrix-dominated interlaminar properties limit its further application. With their unique properties, carbon nanotubes (CNTs) have great potential to improve the mechanical properties of composite materials. In this paper, carbon nanotube-modified carbon fibre/polyimide (CF/CNTs/PI) multi-scale composites were prepared by introducing amino-functionalized multi-walled CNTs into a PI resin matrix using an ultrasonic dispersion method. The interlaminar properties of the prepared composites were comprehensively evaluated by double cantilever beam (DCB), end-notched flexure (ENF), and short seam shear (SBS) tests. It is shown that the addition of 0.5wt.% CNTs increased the Mode I and Mode II interlaminar fracture toughness of the material by 50.21% and 61.74%, respectively, and the interlaminar shear strength (ILSS) by 42.85%. The CNTs bridging the crack tip and enhancing the fibre/matrix interface bonding ability were the dominating mechanisms for the improvement of interlaminar properties.

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