A coupling strategy for excellent mechanical properties and enhanced interfacial performance of polyimide/carbon fiber composite with metal-free catalyzed-curing route

The structure and properties of carbon fiber reinforced composites (CFRC) depend on main factors, especially the unpredictable interface. In this work, a kind of thiocarbonyl disulfide compound is introduced to achieve the catalyzed-cure of phenylethynyl terminated polyimide (PI) and plays the role of coupling medium to constitute covalent-bonded structure at the PI/CF interface. The organocatalyzed cure not only follows the free radical mechanism with an initial curing temperature down to 260.4 °C, but also endows the composite with reduced internal thermal stress and enhanced interface structure. Due to both CF surface-initiated free radical curing reaction and coupling reaction between thiocarbonyl-containing PI matrix and hydroxyl-rich sizing layer, the composite performs an improved interfacial shear strength (IFSS) of 123.9 MPa, being 2.47 times as the thermally cured ones, plus the anti-bacterial reinforcement of the PI matrix. Besides, the interface enhancement brings the CFRC specimen improved electrical properties, performing a 92.6% increase of transverse electrical conductivity to 367.6 S/m. This study gives perspective for improving the interfacial performance of high-temperature processed CFRC with “as-received” fiber reinforcers, plus a clear outlook to future research directions and open challenges to prepare high-performance CFRC.