Surface modification of aramid fiber meshes - the key to chemically recyclable epoxy composites

The higher chemical sensitivity of aramid fibers, compared to carbon or glass fibers, adds to the challenge of designing recyclable aramid fiber reinforced polymer composites. Our study sheds some light on this endeavor through a surface functionalization approach. Twaron (R) aramid fibers were surface modified by self-polymerization of dopamine followed by the condensation of a silane coupling agent, bearing an epoxy group (PDA-Si). Thanks to the mild modification process, the fibers retained their thermal and mechanical properties. At the same time, the functionalization enhanced the adhesion strength between the meshes and a partially bio-based epoxy thermoset, which was demonstrated by a peeling adhesion test and lap-shear bonding test. Chemical recycling of the epoxy thermoset and epoxy composites reinforced with PDA-Si aramid meshes was achieved by mild solvolysis in ethylene glycol. The recycled thermoset was rich in hydroxyl groups, which promoted the adhesion with PDA-Si meshes. Furthermore, high-quality PDA-Si aramid meshes were recovered after the chemical recycling. The recovered meshes showed 82% removal of the thermoset matrix and the retention of the surface functionalization as suggested by thermogravimetric and spectroscopic analyses, respectively. This enabled 78% recovery of the initial interface strength between the recycled PDA-Si meshes and virgin thermoset matrix. This unveils the role of surface functionalization not only as a performance enhancer but also as a useful aid in the development of circular FRPCs. Fiber surface functionalization can play a dual role in the development of fiber reinforced polymer composites; improving the overall performance and enabling recovery of high-quality fibers.