Preparation of semi-aliphatic polyimide for organic-solvent-free sizing agent in CF/PEEK composites

The inert structure and high molding temperature of thermoplastic resin bring new challenges to carbon fiber (CF) sizing agents. Herein, an easily purified semi-aliphatic polyimide (SA-PI) was synthesized as CF sizing agent. The SA-PI has no significant decomposition before 300 degrees C and a 5% decomposition temperature of 442 degrees C. Based on the solubility of its polyamic acid ammonium salt, the SA-PI is configured as an aqueous solution for CF sizing. The results show the surface of sized carbon fiber (SCF) is covered with a sizing coating. At the same time, the polar group of the sizing coating increases the surface energy by 28.45%. Compared with bare CF, the tensile strength of SCF is increased by 11.43%, the ILSS and flexural strength of SCF/PEEK increased from 55.71 MPa and 485.34 MPa to 68.98 MPa and 523.33 MPa, respectively. In addition, the micro-morphology at the fracture of the composite clearly proves that the sizing agent improves the interface performance of the composites effectively.

Automated summary

A semi-aliphatic polyimide (SA-PI) was synthesized and used as a sizing agent for carbon fiber. The sized carbon fiber surface was covered with a coating, increasing its surface energy. Tensile strength, ILSS, and flexural strength were improved after applying the sizing agent.