Interface enhancement of carbon fiber reinforced unsaturated polyester composites with sizing agent containing carbon nanotubes

A liquid sizing agent containing carbon nanotubes was prepared for carbon fiber reinforced unsaturated polyester composite applications. The formation of chemical bonds among vinyl-functionalized carbon nanotubes, vinyl-functionalized carbon fibers, and unsaturated polyester in the coating was due to the radial polymerization process. Scanning electron microscopy images showed that a thin layer of unsaturated polyester coating containing carbon nanotubes was grafted on the surface of carbon fiber uniformly. Dynamic contact angle measurements, before and after sizing treatment, demonstrated an improvement in the surface energy and wettability that related to the increase of the polarity of sized fiber surface. X-ray photoelectron spectroscopy was used for surface functional group analysis of carbon fibers. Force modulation atomic force microscope (AFM) images indicated that an interface with local stiffness softer than that of carbon fiber and harder than that of matrix was gained. Results of the mechanical property tests showed that interlaminar shear strength increased from 46.7 to 64.5 MPa by 38% without sacrificing base fiber strength, and the impact resistance was increased simultaneously.