Oxonium Poly(Ionic Liquids) Enabled Thermoset Fluidization and Intact Carbon Fiber Recycling

Polymerized ionic liquids (PILs), especially N⁺-based PILs have been extensively studied as multifunctional materials. However, it remains challenging to synthesize O⁺-based PILs due to the fleeting characteristics of oxonium salts. Here, we describe a general method in obtaining oxonium PILs through post-polymerization treatment of oxy-polymers with concentrated sulfuric acid. The formation of O⁺-PILs induces dissolution of most oxygen-containing polymers, thus offering a novel strategy to recover carbon fibers (CFs) at ambient conditions from widely used epoxy thermosets characterized by insolubility and infusion. The recovered CFs show improved crystalline structure and enhanced strength than the virgin ones. The discovery of oxonium PIL is expected to significantly extend the research scope of traditional imidazolium-based PIL as oxygen-containing organic chemicals are far more common than nitrogen-containing compounds.