Comparative study on effects of covalent-covalent, covalent-ionic and ionic-ionic bonding of carbon fibers with polyether amine/GO on the interfacial adhesion of epoxy composites

Delicate design and reasonable utilization of interfacial interaction is important for improving interfacial adhesion of composites, however, how exactly the different interfacial interactions and their interaction degree affect the interphase of composites still needs further exploration. Herein, to make the impact of the interactions more prominent, two layers of combined polyether amine/graphene oxide (GO) were built on carbon fiber surface via covalent-covalent, covalent-ionic and ionic-ionic bonding. The effects of different bonding forces on surface physicochemical properties of carbon fiber and on interfacial shear strength (IFSS) of corresponding epoxy composites were compared in-depth. Compared with hybrid bonding acted fibers, same bonding acted fibers have higher IFSSs. Covalent-covalent bonded fibers show 48.3% improvement than untreated fibers due to the strong covalent bonding, more GO content and uniform coverage of smaller and decumbent GO. Ionic-ionic bonded fibers present 38.3% enhancement mainly because of the improved mechanical interlocking by upright GO sheets and abundant ionic and hydrogen bonds. While for covalent-ionic bonded fibers, the weak interface at fiber/surface coating and uneven distribution of GO lead to lower IFSS. This work provides valuable guidance for interphase design in order to obtain high performance composites with good interfacial adhesion.