Effect of hybrid sizing with nano-SiO2 on the interfacial adhesion of carbon fibers/nylon 6 composites

Polyurethane/nano-SiO2 hybrid sizing agents were deposited on the surface of carbon fibers to improve their interfacial adhesion with nylon 6. To obtain homogenous sizing agents, the nano-SiO2 surface was grafted with 3-glycidoxypropyltrimethoxy silane (GPTMS) and the most appropriate mass ratio of nano-SiO2 to coupling agent was determined by dynamic light scattering. Transmission electron micrograph (TEM) and scanning electron microscope (SEM) images of sizing agents showed modified nano-SiO2 was distributed more uniformly than the original SiO2. The effect of incorporation of nano-SiO2 in the polyurethane sizing on thermostability and hydrophobicity were studied by thermogravimetric analysis and static contact angle measurement, respectively. The chemical characteristic and morphologies of carbon fibers were researched using fourier transform infrared spectroscopy (FTIR), SEM and atomic force microscope (AFM). The results showed the roughness of the carbon fiber surface was improved when they were coated with PU/SiO2 hybrid sizing agents. Interfacial adhesion between carbon fibers and nylon 6 under dry conditions and after hygrothermal treatment was measured by transverse fibers bundle (TFB) test. For carbon fibers coated with polyurethane sizing incorporated with nanoSiO(2), a remarkable increase of more than 40% and a mild increase of TFB strength were observed at dry and after hygrothermal treatment, respectively, compared with carbon fibers coated with pure polyurethane.