Grafting of the hierarchical natural tannic acid and polyethyleneimine onto carbon fiber for significantly improved surface/interface properties

The interfacial adhesion between carbon fibers (CFs) and matrix is mainly controlled by inherent surface structures and mutual wettability. However, CFs, with superior properties, have the low of surface wettability and activity. Changing the fiber surface can enhance the quality of interface, which expands the engineering application of CFs composites. Noticeably, the most traditional procedures involve the deterioration of fiber structure by multistep manipulation to introduce active sites, toxic reagents, high energy consumption, as well as the poor interfacial interaction between the fibers and the modified materials by the coating or deposition. Herein, an environmentally friendly and mild strategy was facilely designed via firmly coating tannic acid (TA, a renewable plant‐based polyphenol, the versatile adhesive) and then covalently grafted branched polyethyleneimine (PEI) onto the fiber surface. The novel grafting significantly increased fiber surface polarity, roughness and interfacial wettability without destroying surface microstructure, resulted in the sharp improvements in interlaminar shear strength (ILSS, 51.34 MPa) and interfacial shear strength (IFSS, 66.21 MPa). Impact strength and hydrothermal aging resistance of the resulting composites were also greatly increased. The hierarchical reinforcement arising from a promising and green strategy is facile to be prepared advanced polymer composites in multifunctional applications with the demand of highly interfacial properties and the usages of energy conservation.