The interfacial adhesion character highly depends on interactions of the interfacial molecules. Carbon fiber (CF) is sized by in situ polymerization of maleic acid and glycerol to form a hyperbranched polyester (HBPE) layer on the surface in an environmental and efficient technique. Vast hydroxyl groups are introduced to the CF surface with the presence of HBPE. Moreover, the HBPE sizing structure on 6 A/m2 moderately oxidized CF surface presents higher branch extent and more terminal hydroxyl groups than that on unoxidized or over‐oxidized CF surface. The interlaminar shear strength of polyamide 66 composite reinforced with HBPE sized oxidized‐CF under 6 A/m2 current density is optimal and remarkably enhanced to 77.9 MPa by 46% compared to that with the unsized one. The significant interfacial property improvement is attributed to the abundant terminal hydroxyl groups on HBPE sizing structure, which enhances the interaction at the interface of CF/sizing and sizing/matrix by constructing many covalent and hydrogen bonds.

The properties of carbon fiber (CF) reinforced thermoplastic resin composites depend on the physical and chemical interaction between the fibers and the resins. However, surface oxidation is not always necessary. In this study, the interaction between CF and Polyphenylene sulfide (PPS) is enhanced by using an emulsion of reactive sulfur to treat the CF surface. The interlaminar shear strength (ILSS) of CF/PPS composites is experimentally investigated and found to be up to 79.7 MPa, an increase of 36.1% compared to the untreated CF. The enhancement mechanism of the modification method established is inferred. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) results showed that sulfur etching on the surface of CF generated new functional groups, which improved the interfacial effect, and tightened the bond between CF and PPS. This indicates that sulfur treatment along with sizing must be a simpler method than surface oxidation to promote the interfacial bonding between CF and PPS.

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