New materials based on recycled rubber for domestic, industrial and transport applications

Currently, cooling devices used in domestic, industrial and transport equipment are based on the compression of hydrofluorocarbon (HFC) vapour, which has a high global warming potential (GWP). The rapid growth of the cooling sector has meant that the release of HFCs is responsible for 3% of global emissions of greenhouse gases.

Current regulations, aimed at eliminating HFCs progressively, have encouraged the development of new cooling alternatives with less atmospheric warming potential (AWP). The most promising and environmentally friendly processes are those of heat exchange associated with mechanical transitions in solid materials, related with the mechanocaloric effect (MC), the elastocaloric effect (EC) and the barocaloric effect (BC). The EC and BC effects are induced through a phase transition (crystallisation/fusion), which generates heating/cooling through changes in deformation due to traction (EC) or hydrostatic pressure (BC) on the material, respectively. Recently, natural rubber has emerged as an excellent material with an MC effect, and EC and BC effects at a low or moderate applied tension in an optimal range of temperatures for domestic applications.

Unlike most caloric materials, rubber is soft, low-cost and of biological origin. These characteristics simultaneously resolve some of the main engineering and sustainability problems of artificial cooling. However, despite the enormous potential of natural rubber, this has not been used to date efficiently in protocols for advanced cooling technologies.

In this context, a project is being undertaken with the participation of research group Eco-Friendly Plastics and Composites (e-PLASCOM) at the Universitat Politècnica de Catalunya - BarcelonaTech (UPC), and the Catalan Plastics Centre (CCP). The aim is to design new materials ad hoc based on rubber, with specific compositions and geometries, to be integrated in an optimal way in EC and BC technologies at prototype level.

To achieve this, the proposal was to process materials with the right composition, mixed with waste rubber from tyres to gain high fatigue life and high crystallisation capacity, so as to achieve the expected EC and BC properties.

As part of the project, processing methods at laboratory and pilot plant scale were worked on to design materials for fundamental research and for the commercialisation of EC and BC devices. The trials based on natural rubber are tested in traction and compression modes in the laboratory and for ad hoc use in EC and BC prototypes.