Lightweight, highly durable fiber-reinforced epoxy composites, consisting of glass or carbon fibers embedded in a polymer matrix, are high-performance materials critical to the manufacture of automotive, marine, aircraft and wind turbine blades Material.
By 2025, approximately 25,000 tons of wind turbine blades will reach their operational limits each year. Traditionally, wind turbine blades have been difficult to recycle due to the chemical properties of epoxy, which is an elastic substance and is considered impossible to break down into reusable components. Epoxy resins are not biodegradable and emit toxic fumes when incinerated, eventually leading to landfills as the main way to dispose of them.
Landfilling of wind turbine blades has been banned in several European countries due to its inefficiency and unsustainability, and more are expected to follow. Therefore, there is an urgent need for feasible recycling strategies for epoxy resins and their composites.
The newly discovered process is a proof-of-concept recycling strategy that can be applied to the vast majority of existing wind turbine blades and blades currently in production, as well as other epoxy-based materials.
Specifically, the researchers showed that by using a ruthenium-based catalyst and the solvents isopropanol and toluene, they could separate the epoxy matrix and release one of the original building blocks of epoxy polymers, bisphenol A, and intact glass fibers in a single the process of.
However, the method cannot be immediately scaled up because the catalytic system is not efficient enough for industrial implementation—and ruthenium is a rare and expensive metal. The scientists at Aarhus University are therefore continuing to refine the method.
"Nevertheless, we believe this is a major breakthrough in the development of durable technologies that could create a circular economy for epoxy-based materials. This is the first published chemical process to selectively break down epoxy composites and isolate the most important materials One. One of the lead authors of the study "Epoxy polymers, as well as glass or carbon fibers, are an important component without damaging the latter in the process," says Troels Skrydstrup.
Troels Skrydstrup is a member of the Department of Chemistry and the Interdisciplinary Center for Nanoscience (iNANO) at Aarhus University. professor. The research was supported by the CETEC project (Circular Economy for Thermoset Epoxy Composites), a partnership between Vestas, Olin, the Technical Institute of Denmark and Aarhus University.
In this study, the researchers used a Ru-catalyzed dehydrogenation/bond-breaking/reduction cascade reaction to break the most common C(alkyl)-O bond in polymers, which can be used to break the phase with BPA matrix. adjacent C(alkyl)-O single bond. The researchers demonstrated the application of this approach to unmodified amine-cured epoxies as well as to commercial composites, including the casings of wind energy turbine blades. The researchers' results show that chemical recycling of thermoset epoxies and composites is feasible.
For the catalytic deconstruction experiment of epoxy resin, it is proved that 81% of BPA can be recovered in 4 days of catalytic reaction.
With a general approach available for the molecular decomposition of amine-cured epoxy resins, the researchers turned to investigate the applicability of this protocol to the deconstruction of fiber-reinforced epoxy composites containing a high weight percentage of fibers in addition to the polymer matrix. Without any preprocessing, the 3 After a few days, the composites visibly separated into loose fibers. The reaction mixture was decanted; after washing, 57 wt% of carbon fibers were recovered and 13 wt% of BPA was separated from solution.
A piece of the casing of a state-of-the-art decommissioned wind turbine blade was subsequently tested. This commercial composite sample was catalyzed and completely decomposed to yield 50wt% glass fibers and 19wt% BPA.
In conclusion, a circular economy can be considered for components recovered from end-of-life composite materials. The high-purity BPA obtained from recycling can theoretically be reused in existing production chains such as epoxy resin, polycarbonate or polyester, replacing virgin BPA produced from petroleum raw materials. The researchers' catalytic process can be seen as a proof-of-concept that achieving a circular economy for these valuable and relevant materials is feasible.
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