Sustainable Upcycling of Expanded Polystyrene for Use in Coatings

Expanded polystyrene (EPS) is widely used in packaging and insulation due to its low density, excellent thermal properties and impact resistance. However, these very properties make it an environmental challenge: it is bulky, difficult to compact, has low biodegradability and contributes to the formation of persistent microplastics. Globally, only a small fraction of the EPS produced is recycled, and traditional methods, such as landfill, incineration or mechanical recycling, prove to be insufficient, energy-intensive or environmentally problematic.

In recent years, several studies have shown that dissolution recycling is a promising alternative, capable of reducing the volume of EPS by more than 95 per cent and producing polymer solutions with potential for new applications. Other studies have also revealed that terpenoid solvents, such as d-limonene, extracted from citrus peel, dissolve polystyrene efficiently without degrading the polymer chains and with a lower environmental impact when compared with petrochemical solvents such as toluene or xylene. Furthermore, limonene is renewable, biodegradable and highly compatible with polystyrene, enabling the formation of homogeneous solutions suitable for coatings, adhesives and protective films.

Inspired by these advances, the project Sustainable Upcycling of Expanded Polystyrene for Coating Applications aims to transform EPS waste generated on the Alameda campus of Instituto Técnico into a functional and sustainable varnish, formulated by dissolving the polymer in limonene. This approach incorporates principles of Green Chemistry, the Circular Economy and Materials Engineering, demonstrating that hard-to-manage waste can be converted into value-added products.

The project is carried out in several stages: collection and preparation of EPS, optimisation of dissolution conditions, physico-chemical characterisation of the polymer solution (viscosity, solids content, stability), preliminary formulation of the varnish, application tests on wood and other substrates, evaluation of properties such as adhesion, water resistance, gloss, drying time and durability, and, finally, comparison with commercial varnishes. The formulation will also be explored using natural additives, such as waxes, biological plasticisers or pigments derived from organic waste, to improve performance and provide new functionalities, such as UV protection or specific shades.

In addition to its direct environmental impact, the project reinforces Técnico’s commitment to sustainable practices, reducing waste generation, promoting the reuse of materials and involving students in applied research with tangible results. By transforming common waste into a useful coating for furniture and other applications on campus, the project demonstrates how science and engineering can generate practical, efficient solutions that address contemporary environmental challenges.

This project positions the DEQ as an active player in sustainable innovation, capable of integrating research, training and real impact within the academic community, and paves the way for future initiatives in waste recovery and the development of green materials.

You can find out more about the project here.