Up to 28 million tonnes of waste refractory materials are generated annually [1], of which only 7 to 30% are recycled into new refractory products. The remaining materials are typically sent to landfills or downcycled without the consideration to reprocess them into innovative and impactful applications [2]. As part of the European Union’s Horizon Europe-funded project ReSOURCE [3], CPI has characterised the physical properties of an end-of-life refractory material coming from furnace linings of cement manufacturing plants. This characterisation revealed a remarkable dielectric permittivity of such waste material.
In alignment with another Horizon Europe funded project, Sustain-a-Print (SaP) [4], which aims to develop sustainable printable electronic devices with end-of-life alternatives, CPI decided to bring forward a collaborative effort between the ReSOURCE and SaP projects. This collaboration uses the mentioned waste refractory material to create an electrically insulating dielectric ink designed to accommodate a printed crossover to complete multilayer circuits on the printing substrate. To target the rheology requirements of this dielectric ink for screen-printing of electronic switch devices and direct ink writing deposition (DIW) of biosensors, different loadings of this waste refractory material were incorporated into a recycled and hydrophobic polystyrene matrix. The result was a 99% sustainable and non-hazardous ink. The formulation process included a surface treatment of the waste refractory material to enhance dispersion stability, and the addition of bio-based plasticizers to ensure flexibility in printed films.
The primary challenge in formulating this sustainable ink was achieving good electrically insulative properties to prevent or delay the formation of silver dendrites in the dielectric layer, which could cause short circuits in the device. This issue is commonly observed with non-sustainable commercial dielectric inks, typically containing acrylates which are environmentally damaging and toxic for human health .
Initial trials of electronic switch devices were screen printed using our sustainable ink and a commercial ink, these were subjected to a harsh environment (85°C/85% relative humidity) for one week where performance remained consistent. Future work includes modification of the ink to achieve the desired rheological properties for DIW printing of biosensors.In summary, this collaborative initiative resulted in development of a highly sustainable and non-hazardous dielectric ink. It competes with the performance of conventional market options due to its insulative properties and durability, with enhanced environmental benefits. This innovative ink offers a viable alternative to traditional hazardous products and presents a new end-of-life solution for refractory materials leftovers.
References
[1] Horckmans, L. et al. (2019a) ‘Recycling of refractory bricks used in basic steelmaking: A Review’, Resources, Conservation and Recycling, 140, pp. 297–304. doi:10.1016/j.resconrec.2018.09.025.
[2] Recycling of refractory materials avoids 800,000 tons of co₂ – Fraunhofer ILT (2023) Fraunhofer Institute for Laser Technology ILT. Available at: https://www.ilt.fraunhofer.de/en/press/press-releases/2023/8-30-resource-project-recycling-refractory-materials.html (Accessed: 04 September 2024).
[3] https://www.project-resource.eu/
[4] https://www.sustainaprint.eu/
Funded by the European Union under the GA no 101070556. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or RIA. Neither the European Union nor the granting authority can be held responsible for them.
