Improving mechanical properties of high-temperature resistant carbon fiber/phthalonitrile composites via surface modification: a comparative study on modification methods

The interfacial bonding is of essential importance for the mechanical properties of high-temperature resistant carbon fiber/phthalonitrile composite materials. To promote the interfacial adhesion of carbon fiber/phthalonitrile composites, three surface modification methods, namely HP302 sizing, diazotization modification, and oxidation-diazotization modification, were applied and compared. The results showed that the de-sizing treatment barely affected the mechanical properties of the composites. Both re-sizing with HP302 agent and diazotization modification improved the mechanical properties, while the mechanical properties were drastically decreased via the oxidation-diazotization modification. Among these surface modification methods, the diazotization treatment derived the best mechanical properties of carbon fiber/phthalonitrile composites both at room and high temperature. Specifically, the flexural strengths were 345 MPa (RT), 525 MPa (300 degrees C), and 442 MPa (400 degrees C), which were 47%, 302%, and 281% higher than those of the pristine composites. The interlaminar shear strengths were 33 MPa (RT), 26 MPa (300 degrees C), and 27 MPa (400 degrees C), which were all over twofold than those of the original counterparts.{Graphical abstract}