Interface Properties of Epoxy and Polyurethane Mutually Sized Carbon Fiber Reinforced Composites

Anodized carbon fiber (OCF) is sized with epoxy sizing agent (EPS) and polyurethane sizing agent (PUS) to reinforce epoxy resin (EP) and polyurethane resin (PU) mutually. The dependence of interlaminar shear strength (ILSS) and failure strain on the sizing agent and amount is investigated. The ILSS of the as-received OCF reinforced EP composite is 59.5 MPa, while that of EPS sized OCF reinforced EP composite can be optimally increased to 66.7 MPa, and that of PUS sized OCF reinforced EP composite can be increased maximumly to 72.8 MPa. The ILSS of the as-received OCF reinforced PU composite is 39.5 MPa, while that of PUS sized OCF reinforced PU composite can be optimally increased to 50.5 MPa, and that of EPS sized OCF reinforced PU composite can be increased maximumly to 63.9 MPa. The results show the EPS is more suitable to size OCF for reinforcing PU while the PUS is more suitable to size OCF for reinforcing EP. Hence it is concluded that the law of similarity and intermiscibility does not always work, rather the chemical reactions are more important for strong interface formation. The sizing amount has a great influence on both the ILSS and failure strain.