Towards a greener future: using COSMO-RS to select eutectic solvents for complex polymer mixtures recycling

The global production of synthetic polymers now exceeds 400 million tons annually, yet limited recycling efforts are projected to result in 12,000 million tons of plastic waste in landfills by 2050. Among the various recycling approaches, dissolution/precipitation methods offer promising potential, particularly for complex, hard-to-recycle polymer mixtures. Despite this, these methods are often overlooked and commonly rely on traditional organic solvents. Eutectic solvents (ES) represent a promising, greener alternative, though their development is complicated by the vast diversity of potential hydrogen bond acceptors (HBA) and donors (HBD).

This study leverages the COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) to identify selective and effective ES for dissolving complex mixtures of fossil-based polymers—such as polyethylene (PE), poly(ethylene terephthalate) (PET), polypropylene (PP), and poly(vinyl chloride) (PVC)—as well as commercial bio-based polymers like poly(lactic acid) (PLA). Using COSMO-RS, infinite dilution activity coefficients were calculated for 40 HBA and 59 HBD, generating 2,360 ES at 100 °C. These predictions were validated with experimental solubilization tests.

The results indicate hydrophobic ES with long-chain alcohols effectively dissolve PE and PP, while ES with phenolic monoterpenes dissolve PET and PLA efficiently. Overall, this work highlights the critical role of rational ES selection in advancing sustainable recycling processes for complex polymer mixtures as for multilayer films.

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI:10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI:10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI:10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC). This work is funded by national funds through FCT – Fundação para a Ciência e a Tecnologia, I.P., under the project GREEN-PATH (Ref. 2023.15169.PEX, DOI:10.54499/2023.15169.PEX). MISA acknowledges FCT for the Ph.D.grant PRT/BD/154714/2023. AMF and AFS acknowledge FCT for the research contracts CEECIND/00361/2022 (DOI:10.54499/2022.00361.CEECIND/CP1720/CT002) and CEECINSTLA/00002/2022, respectively.