Solvent-based separation of PA6 and PET using solubility data from Differential Scanning Calorimetry

To minimize plastic pollution and to prevent further extraction of fossil feedstock, circular economy (CE) for polymers offers a promising solution. As CE’s integral part to close material loops, solvent-based recycling enables the separation of mixed plastic waste into pure component streams without altering the polymer structure but requires reliable solubility data of polymers in solvents. We present a standardized differential scanning calorimetry (DSC) protocol to determine dissolution and precipitation temperatures of polymers in various solvents and apply it to the challenging separation of polyamide 6 (PA6) and polyethylene terephthalate (PET). The DSC method enables quantitative solubility analysis even above solvent boiling points and shows good agreement with a visual polythermal method, while offering higher objectivity and additional phase transition enthalpies. Temperature-dependent solubility data for nine solvents reveal that methanol, ethanol, 1,2-propanediol, dimethyl sulfoxide and water are selective solvents for PA6. A proof-of-concept PA6-PET separation using methanol yields recycled polymers with near-virgin properties under mild conditions (109 °C, ~4 bar), demonstrating the process relevance of the obtained DSC data for solvent selection in low-energy, solvent-based recycling processes.