A molecularly designed “rigid-flexible” synergistic polyimide sizing agent for enhancing the interfacial performance of CF/PEEK composites

Synthesis of a A-PAAS sizing agent featuring a “rigid-flexible” synergistic structure. • The flexural strength and ILSS of 0.5-CF/PEEK were largely increased by 59.8% and 35.0%. • The possible interfacial modification and thermal properties is comprehensive analyzed. • The as-prepared A-PAAS sizing agent is environmentally friendly. Polyimide (PI) has attracted increasing attention in recent decades for interfacial optimization of carbon fiber/polyether ether ketone (CF/PEEK) composites owing to its outstanding thermal resistance. This study effectively incorporated a novel polyimide sizing agent (A-PAAS) by introducing non-coplanar alicyclic rings, amide functional groups, and ammonium ions into the polymer backbone through molecular design. This structural design effectively reduces the packing density of molecular chains, facilitating easier spreading during the sizing process and thereby enhancing penetration into fiber pores. Furthermore, the prepared A-PAAS exhibited outstanding thermal stability, with a 5% weight-loss temperature (T 5% ) of 435.0 °C, which exceeds the processing temperatures of most commercially available thermoplastic resins. The work shows that the CF/PEEK composite, after sizing, exhibits effectively enhanced mechanical properties; the interlaminar shear strength and flexural strength increased by 35.0% and 59.8%, respectively, compared to the unsized composite. This work introduces non-coplanar aliphatic rings, ether bonds, and amide bonds into the sizing agent, thereby establishing a synergistic reinforcement bridge at the CF-PEEK interface. Improving the surface interfacial adhesion and wettability of CF, whilst establishing a hydrogen-bond cross-linking network within the sizing agent and PEEK, makes a key contribution to enhancing the composite's macroscopic mechanical properties. In brief, this efficient and environmentally friendly A-PAAS sizing agent provides an innovative strategy for the interfacial modification of CF/PEEK composites. Download: Download high-res image (459KB) Download: Download full-size image