Preparation of Reactive Organic–Inorganic ZnO Core-Shell Structure Sizing Agents and Their Effects on Carbon Fiber Composite Properties

In this paper, five self-emulsifying organic–inorganic ZnO core-shell structure sizing agents with different amounts of coupling agent KH570 bonding on their shells were synthesized. These agents exhibited uniform particle size in the range of 90–250 nm, excellent storage stability and enhanced thermal stability up to 300°C, while also demonstrating an effective reactivity with carbon fibers (CF). The reactive sizing agents modified by KH570 not only significantly increased the monofilament tensile strength, the surface roughness and the surface energy of the sized CF, reaching 6837.35 MPa, 23.81 nm and 80.2 mJ/m 2 , but also prominently enhanced the interlaminar shear strength (ILSS) and flexural strength of the sized CF/epoxy resin (CF/EP) composites, approaching 141.43 and 2087.86 MPa, corresponding improvement of 26.49%, 297.50%, 89.20%, 60.81%, and 40.22%, respectively, compared to the unmodified sizing agents with KH570. The improvements in mechanical properties are mainly attributed to the increased wetting of EP matrix on the sized CF and the enhanced interfacial adhesion between CF and the sizing agent, facilitated by chemical bonding of the KH570 modified ZnO particle shell on the CF surface and their crosslinking of the sizing agents among themselves, and efficient stress transfer at the CF/EP interface through the interlocking mechanism of the organic–inorganic ZnO core-shell particles. Highlights The sizing is modified by KH570 to form a reactive sizing. The reactive sizing undergoes surface reactions on CF to enhance their adhesion. The crosslinking on sizing surface affects composite mechanical properties. The composite has a maximum ILSS of 141.43 MPa. The composite has a maximum flexural strength of 2087.86 MPa.