In recent years, the increase in fibre production has intensified the societal and environmental challenges associated with the end-of-life management of textile waste. The complexity of these waste streams remains one of the major limitations, mainly due to the simultaneous presence of different fibre types and possible contaminants, such as dyes, pigments, and additives. As a result, many recycling solutions have been developed primarily for homogeneous industrial streams with known composition. This limited recyclability represents a critical issue from a circular economy perspective, as it reduces material recovery. In this context, this thesis investigates hydrothermal liquefaction (HTL) as an innovative synthetic fibre-to-monomer recycling technology for recovering high-quality monomers from mixed streams.