Switchable deep eutectic solvents as efficient and sustainable recycling media for carbon fiber reinforced polymer composite waste

Carbon fiber reinforced polymer composite (CFRP) waste has posed a great environmental challenge due to the unavailability of efficient and environmentally benign recycling processes, and otherwise valuable CFRP components (i.e., carbon fibers and epoxy resin) are ending up as waste. Therefore, CFRP waste recycling, which is both environmentally friendly and economically wise, is urgently needed. Herein, effective recovery of both valuable long carbon fibers and epoxy resin from CFRPs has been realized by a novel recycling route with a mixture of deep eutectic solvents (DESs) with switchable-hydrophilicity and metal salt catalysts (e.g., ZnCl 2 , FeCl 2 , and FeCl 3 ). Complete epoxy resin matrix decomposition was achieved under ordinary pressure and mild temperature (180 °C for 1.5 h) in hydrophobic DESs composed of thymol and decanoic acid ([Thy][C10] (1:1)) with ZnCl 2 catalyst (3.3 wt%). The [Thy][C10] DES efficiently swelled densely cross-linked epoxy resin, facilitating the diffusion of the catalytic Zn 2+ ions into the polymer matrix for achieving cleavage of the C–N bonds and C–O–C bonds of the epoxy resin. The recovered long carbon fibers retained 94.5% of their original strength, which was ascribed to the superior swelling features, hydrogen bonding ability, and highly active Zn 2+ ions of the ZnCl 2 /[Thy][C10] system. The reusable ZnCl 2 /DES media offer a novel platform for the recycling of CFRPs by using a sustainable concept and facilitate the recycling of CFRP waste on a large-scale implementation. • A DES with switchable-hydrophilicity is used as a green solvent in CFRP recycling. • Clean and long carbon fibers are recovered via an environmentally benign route. • Zn 2+ ions in a hydrophobic [Thy][C10] DES system exhibit high catalytic activity. • Higher swelling ability driven by [Thy][C10] DES facilitates the diffusion of Zn 2+ . • The crosslinked epoxy resin was decomposed by the cleavage of C–N and C–O–C bonds.