The increased use of fibre reinforced polymer composites in the industry, coupled with increasingly stringent European regulations, has resulted in a need to develop effective recycling technologies for composites. Such sociotechnical pressure will continue to grow in the coming years, driving the development of advanced End-of-Life solutions. Recycled carbon fibres, if properly treated, can indeed have a reduced global warming potential and require less energy compared to the production of virgin fibres. This thesis investigates supercritical solvolysis, an innovative chemical recycling technique, within the framework of the European EuReComp project, with a specific focus on water diffusion in thermoset polymers. A multiscale modelling strategy is adopted to provide insights into transport phenomena across different length scales, combining continuum-based Finite Element analysis with atomistic Molecular Dynamics simulations.