Recycling glass fibers from thermoset epoxy composites by in situ oxonium-type polyionic liquid formation and naphthalene-containing superplasticizer synthesis with the degradation solution of the epoxy resin

Glass fibre-reinforced thermoset (GFRT) epoxy composites with permanent cross-linked polymer networks are difficult to recycle, leading to the production of large amounts of waste. Developing an efficient approach to reuse both the high-value fibre and the resin matrices is thus imperative. In this work, we explored the application of H2SO4 (98%) to react with ether and benzene groups in the epoxy backbone at room temperature. As a result, a new family of poly(ionic liquid)s (PILs) comprising cationic oxonium was produced. The in situ oxonium PIL formation enables clean glass fibres to be released with well-maintained surface microscopic morphology, chemical structure and tensile modulus close to the virgin glass fibres (vGFs). Furthermore, the dissolved matrix solution functions as a synergistic sulfonation agent in the synthesis of naphthalene containing superplasticizer. The obtained additive is superior to the fresh H2SO4 sulfonated naphthalene formaldehyde condensate (SNF) in reducing water content (33% vs 19%) and improving compressive strength of cementitious materials by 29%. Therefore, this novel eco-friendly strategy provides an open-loop solution for GFRT composites recycling at ambient conditions producing no new waste.