Abstract
Efficient and comprehensive recycling of fiber-reinforced thermosets is particularly challenging, since the irreversible degradation of the matrix component is necessary in order to separate the fiber component in high purity. In this work, a new approach to fully recyclable thermoset composites is presented, based on the thermal reversibility of an epoxy-based polymer network, crosslinked through Diels–Alder (DA) chemistry. Carbon fiber composites, fabricated by compression molding, were efficiently recycled through a simple solvolysis procedure in common solvents, under mild conditions, with no catalysts. Specifically, the purity of reclaimed fibers, assessed by thermogravimetric analysis and scanning electron microscopy, was very high (>95%) and allowed successful reprocessing into second generation composites. Moreover, the dissolved matrix residues were directly employed to prepare smart, thermally healable coatings. Overall, DA chemistry has been shown to provide a convenient strategy towards circular economy of thermoset composites.
Highlights
The increasing global demand for lightweight materials is generating a continuous growth of the composite industry
Composite recycling methods are generally grouped into three categories: Mechanical, thermal, and chemical processes
Bisphenol A diglycidyl ether (DGEBA), N,N-diglycidyl-4-glycidyloxyaniline (DGGO), furfurylamine (FA), 1,10 -(methylenedi-4,1-phenylene)bismaleimide (BM), tetrahydrofuran (THF), propylene carbonate, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) were purchased from Sigma-Aldrich (Milan, Italy) while methanol was obtained from Fisher Chemical (Milan, Italy)
Summary
The increasing global demand for lightweight materials is generating a continuous growth of the composite industry. Carbon reinforced composites are progressively entering novel application sectors such as the automotive field, in addition to more established markets like aerospace and wind power. Beside the technological challenge of ensuring greater volumes at competitive costs, the composite industry has to address the recycling issue [1], as a dramatic increase in waste from end-of-life composites is foreseen in the few years, landfilling being progressively forbidden [2]. Available technologies for carbon composite recycling are mainly focused on the recovery of the fiber component, while the resin component is generally considered waste due to its lower market value [3]. Composite recycling methods are generally grouped into three categories: Mechanical, thermal, and chemical processes. The obtained powders can only be proposed as cheap, low-performing fillers for new composites [4]
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