The heavy-duty composite bioplastics designed to be dismantled
Thermoset composites(opens in new window) are widely used in applications that must stand up to significant mechanical and thermal pressures, such as structural components of aircraft and wind turbines. These materials owe their robustness to their unique structure, which combines a thermosetting polymer matrix and reinforcing fibres, typically glass or carbon. Once irreversibly ‘cured’, this three-dimensional crosslinked structure confers strength and rigidity on products, allowing them to maintain shape and prevent melting. However, production relies on fossil-based raw materials, which can be toxic. They are also hard to recycle, with annual carbon and glass fibre composite waste from the aircraft and wind turbine industries alone, projected to be 840 300 tonnes by 2050(opens in new window). “The available recycling techniques are typically either energy-intensive, so costly and unsustainable; or significantly degrade quality, limiting applications. Moreover, these techniques frequently focus on the recovery of the valuable fibres, while discarding the polymer matrix, limiting their reuse,” explains ESTELLA(opens in new window) project coordinator Laura Matesanz, from the Cidaut Foundation(opens in new window) in Spain. To offer a more sustainable alternative, ESTELLA adopted bio-based recyclable covalent adaptive networks(opens in new window) (CANs) to redesign the crosslinked structure of traditional thermosetting materials.
The CAN-do approach
Comprising 13 research institutions and companies from eight European countries, ESTELLA’s first challenge was to incorporate the CANs into epoxy resins to form the thermosetting three-dimensional matrices. CANs are ideal, as these polymer structures are made up of chemical bonds which can break and reform under specific stimuli, such as heat, UV light or changes in acidity – meaning they can be more easily manipulated for both production and recycling. Diels-Alder chemistry(opens in new window) was first used to ‘unlock’ the chemical bonds of the CANs and integrate them into the epoxy resins. The next task was to find the most compatible bio-based fibres for the matrices. After exploring a range of options, hemp and nanocellulose(opens in new window) fibres were chosen. To ensure the right configuration of materials, the resulting composites have been manufactured into a series of plates and subjected to a range of tests to ensure relevant properties such as tensile strength and flexibility. To explore how the materials would withstand real use cases, the team are now working on the production of prototypes, initially for mobility and construction applications. A footrest for scooters using a composite of hemp fibres, and a window profile(opens in new window) with a composite based on nanocellulose fibres, are currently being manufactured. To identify optimum recycling options, the team is also adapting various pre-existing techniques. Primarily focused on chemical approaches to modifying the molecular structure of composites, mechanical recycling is also being explored. “Keeping the original mechanical and thermal properties of recycled materials makes them more reusable, so we are fine-tuning our recycling techniques to retain fibres and the polymer matrix,” adds Matesanz.
Ensuring sustainability and competitiveness
Recyclable bio-based thermosetting composites will help reduce European dependence on virgin fossil resources while minimising waste, supporting prominent EU initiatives such as the European Green Deal(opens in new window) and circular economy action plan(opens in new window). To help quantify ESTELLA’s environmental contribution, the team will conduct life cycle analyses of their solution’s impact on climate change, fossil depletion and terrestrial acidification, compared to conventional processes. Economic feasibility studies, including on the scalability of the manufacturing and recycling processes required, will also be undertaken. “Making more sustainable materials available to European sectors such as transport and construction will lead to more responsible industrial practices. This will not only create products that benefit people and planet but help position European companies at the global front line of the green transition,” says Matesanz.
Keywords
ESTELLA, polymer, fibres, turbine, aircraft, thermoset, recycle, composites, waste, epoxy resin, hemp, nanocellulose, bio-based, scooter, window
