Exploration of pros and cons of polyetherimide solutions with varying concentrations as the sizing agents for graphite fibers in graphite fabric-PAEK composites

Some specialty polymers such as polyetheretherketone (PEEK), Polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherimide (PEI), polyamideimide (PAI), and polyimide (PI) are the ideal choices for developing high performance bidirectionally reinforced composites that would excel in specific strength performance. However, these polymer composites are extremely challenging from a processing point of view and have limited choices. Most of the time, a lot of compromises are to be made on the fiber-matrix wetting issues. The current research elaborated on a method to exploit two techniques together to opt for advantages from both. Polyetherimide (PEI) solutions of various concentrations/viscosities were used as sizing agents for the fibers so as to wet the cross-over points on graphite fabric and inter-tow filaments. It was expected that the PEI and PAEK would form a blend at the interface, although fiber would necessarily be covered with only PEI. It was also anticipated that there could be an optimum amount of PEI on the fibers' surface for the best performance properties. Based on the in-depth studies on the performance properties, it was concluded that PEI solution in the range of 5–10 wt. % would lead to the best combination of performance properties. Compared to the classical method of developing PAEK-graphite fabric composites by film technique, the current method of combination of impregnation and film technique led to excellent results.