Ana M. FERREIRA1, José Pedro WOJEICCHOWSKI1, Mariana I. S. AGUIAR1, Andreia F. SOUSA1, João A.p. COUTINHO1
1CICECO - Aveiro Institute of Materials, University of Aveiro, Aveiro, Portugal
Plastics are ubiquitous synthetic polymers that have become an indispensable part of everyday life due to their many uses, ranging from packaging to electronic applications to biomedicine. It is therefore not surprising that their annual production exceeds 350 million. However, only a small fraction of all polymers produced annually are recycled and reused (18%), in part because the physical properties of the recycled material usually deteriorate significantly. Currently, precipitation-dissolution appears to be one of the most promising methods for recycling plastics, although the use of organic solvents is still the preferred choice. [1]. New solvents, such as bio-based solvents, have recently demonstrated their ability to selectively dissolve and precipitate polyethylene (PE) [2]. Other promising alternative solvents include the deep eutectic solvents (DES), however, the selection of the correct DES from the large number of possible hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) combinations can be quite challenging.
In this work, COSMO-RS (COnductor-like Screening MOdel for Real Solvents), a thermodynamic model based on quantum chemistry, was used to identify the most promising DES for the dissolution of polymers. The polymers evaluated were the four most representative of plastic wastes: polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polyvinylchloride (PVC). 29 HBA and 50 a HBD were selected and combined to give 1450 DES (molar ratio 1:1). The affinity of the polymer DES was evaluated by predicting the logarithmic activity coefficient of the four studied plastic wastes at 373.15 K. The results showed that the hydrophobic DES, especially those with tetraoctyl ammonium chloride as HBA, were the most suitable solvents for dissolving plastics. In addition, DES thymol: oxalic acid and thymol: carvacrol were the most promising for the dissolution of PET (Figure 1), but not for the other polymers studied. These results suggest that it is not only possible to develop a more sustainable recycling process, but also a selective dissolution process if the DES is properly chosen, which can be a great advantage in multilayer plastic packaging. Finally, the most promising results were validated in the laboratory. In summary, COSMO-RS enables rapid and qualitative in silico evaluation of polymer solubility in a wide range of unconventional solvents while reducing the number of experiments in the laboratory.
Acknowledgments
This work was partly developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MCTES (PIDDAC). This publication is supported by COST Action FUR4Sustain- European network of FURan based chemicals and materials FOR a Sustainable development, CA18220, supported by COST (Euro-pean Cooperation in Science and Technology).
References
1. Walker et al., Sci. Adv., 6, 47 (2020) eaba7599.
2. Ferreira et al., Mol., 1, 27 (2022) 98.