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• Eco-friendly recycling of CFRP composites in aqueous buffer solutions under mild conditions. • Straightforward separation of catalyst solution, decomposed resin and carbon fibers. • Innovative upcycling of CFRP waste by transforming decomposed matrix into recyclable vitrimers. • Fabrication of hydrothermally recyclable CFRP from waste, reinforcing the loop towards zero waste. • Pioneering a sustainable method contributing to a circular economy for CFRP. Carbon fiber-reinforced polymer (CFRP) composites have gained widespread adoption across diverse industries. However, their inherent stability, stemming from the crosslinked structure of the matrix resin, poses a significant challenge in managing the growing volume of CFRP waste. Consequently, there is a pressing need for an eco-friendly upcycling method that effectively recovers and reuses both the valuable carbon fibers and the polymer matrix from CFRP waste. This study presents a novel approach for upcycling CFRP waste under environmentally friendly conditions. Firstly, CFRP waste with an amine-cured epoxy matrix was completely decomposed in aqueous buffer solutions under mild conditions (≤ 220 °C, pH = 4.8). Further, decomposed matrix polymer (DMP) was employed to transform conventional epoxy resins into recyclable vitrimers. Lastly, new composites that can be hydrothermally recycled were fabricated using both DMP and recovered carbon fibers. This work proposes a novel strategy for achieving a circular economy within the CFRP industry. [Display omitted] [ABSTRACT FROM AUTHOR]

Conventional carbon fiber reinforced thermosetting polymers (CFRPs) are neither recyclable nor repairable due to their crosslinked network. The rapid growing CFRP market raises a serious concern of the waste management. In this work, a viable method to develop a readily recyclable CFRP based on epoxy vitrimer is introduced. First, a self‐catalytic epoxy prepolymer with built‐in hydroxy and tertiary amine groups is designed, which upon reaction with an anhydride formed a catalyst‐free epoxy vitrimer. The epoxy prepolymer is synthesized from a diamine and an excess of bisphenol A epoxy resin. The hydroxyls and tertiary amines of the epoxy prepolymer efficiently catalyze both curing and the dynamic transesterification of the crosslinked polymer without the need of a catalyst. Then, the epoxy vitrimer is used as the matrix resin to prepare CFRP. The resulting CFRP exhibited a tensile strength as high as 356 MPa. More interestingly, the matrix of the CFRP is efficiently degraded in pure water at above 160 °C. This is because the built‐in tertiary amines catalyze the hydrolysis of the ester bonds of the crosslinked network. The simple method developed in this work provides a framework for the development of recyclable CFRP. [ABSTRACT FROM AUTHOR]

This work proposes an approach to minimize surface energy deactivation of plasma-treated metal and carbon fiber-reinforced polymer (CFRP) surfaces by vacuum sealing. Plasma treatments enhance adhesive wettability on post-treated surfaces for adhesive joints, but the treated surfaces deactivate quickly in air. The surface energy of aluminum alloy AA6061 and carbon fiber-reinforced polymer-polyamide (CFRP-PA66) optimally treated by a blown air plasma instrument returns to the original surface energy within 1 h. Vacuum sealing of AA6061 and CFRP-PA66 reduced the surface energy deactivation over 7 days by at least 230 times and 970 times compared to in air. Double Cantilever Beam (DCB) tests performed on adhesively-bonded AA6061/CFRP-PA66 joints showed that the total energy release and energy dissipation before failure of plasma-treated and vacuum-sealed materials was up to 60% more than plasma-treated materials without vacuum sealing and up to 125% more than non-plasma-treated materials. • Vacuum sealing significantly slowed down the deactivation of plasma-optimized surface energy of AA6061 and CFRP-PA66. • Vacuum sealing preserved hydrogen-bonded carbonyl groups on the plasma-treated CFRP-PA66 surface. • Vacuum sealing protected over-oxidation of carbon to carbonate on AA6061 surface after the plasma treatment. • In the interface between adherend surfaces and adhesive, hydroxyl groups reacted with dicyandiamide to form amide bonds. • Vacuum sealing maintained the plasma-enhanced Mode I fracture energy of adhesively-bonded AA6061-CFRP-PA66 dissimilar joints. [ABSTRACT FROM AUTHOR]