4,4‐Diphenylmethane diisocyanate coating modified short‐cut carbon fiber enhances the interlaminar shear properties of carbon fiber/epoxy resin composite laminates

The brittleness of epoxy resin (EP) and the smooth, inert surface of carbon fiber (CF) affects their interfacial interaction, making the composite exhibit poor interlaminar shear properties that significantly limit its practical application. In this paper, a 4,4‐diphenylmethane diisocyanate (MDI) layer was uniformly coated on short‐cut carbon fiber (SCF) by chemical bonding and physical cladding. The reaction of the isocyanate group of MDI with the active hydrogen in the epoxy system was used to form a strong chemical bond between EP and SCF to enhance the interfacial interaction. Moreover, the introduced SCF as filler can play a better connecting and anchoring role in the CF/EP composite, enabling better stress transfer and enhancing the integrity inside the composite. The coating of MDI on the surface of SCF and the efficient synergistic effect that it brings were successfully demonstrated by Fourier‐transform infrared, thermogravimetric analyzer, dynamic mechanics analyzer, scanning electron microscopy, and interlaminar shear strength characterization. Compared with the untreated SCF reinforced CF/EP composite, MDI@SCF enhanced the interlaminar performance of the material by 10.06%. When the concentration of MDI treatment solution and SCF content was adjusted to the optimal value, the interlayer performance of the material increased by 17.01% compared to the pure CF/EP composite.