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 com-ponents (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., ZnCl2, FeCl2, and FeCl3). Complete epoxy resin matrix decomposition was achieved under ordinary pressure and mild temperature (180 degrees C for 1.5 h) in hydrophobic DESs composed of thymol and decanoic acid ([Thy][C10] (1:1)) with ZnCl2 catalyst (3.3 wt%). The [Thy][C10] DES efficiently swelled densely cross-linked epoxy resin, facili-tating the diffusion of the catalytic Zn2+ 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 Zn2+ ions of the ZnCl2/[Thy][C10] system. The reusable ZnCl2/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.

Automated summary

This study presents a novel recycling method for carbon fiber reinforced polymer composites (CFRPs) using a mixture of deep eutectic solvents and metal salt catalysts. The method allows for the effective recovery of both carbon fibers and epoxy resin from CFRPs, with the recovered carbon fibers retaining a high strength.