Effect of high temperature desizing treatment of carbon fiber on thermal aging of polyimide composites

Abstract

The performance change and mechanism of polyimide composites with carbon fiber sizing and desizing states during thermal aging at 330 ℃ were compared and analyzed from the aspects of thermal oxidation mass loss, surface morphology and micro morphology, mechanical properties and glass transition temperature. The results show that carbon fiber desizing can reduce the mass loss rate of thermal oxidation of polyimide composites. The interface layer of the composites with sizing carbon fiber contains epoxy sizing agent, which has low temperature resistance. Therefore, the interface is easy to be damaged in the process of thermal aging, resulting in more cracks and rapid separation of edge fibers. Although the composites with sizing carbon fiber has high interlaminar shear strength before aging, it decreases rapidly in the early stage of thermal aging. On the contrary, the interlaminar shear strength of the composites with desizing carbon fiber is higher after aging for 200 h. The bending strength of the two composites before aging is basically the same, but the bending strength of the composites with sizing carbon fiber decreases rapidly in the early stage of aging; however, desizing has little effect on bending modulus. The glass transition temperature of the composites with desizing carbon fiber increases by about 15 ℃. After thermal aging, the glass transition temperature of the composites with sizing carbon fiber increases slightly, while the composites with desizing carbon fiber remain unchanged. Therefore, the high temperature desizing treatment of carbon fiber is conducive to improving the stability of polyimide composites for long-term use at high temperature.

Keywords

• carbon fiber
• epoxy sizing agent
• polyimide
• composites
• thermal aging