Factors Affecting Solvent Retention due to Gel Formation during Dissolution-Based Plastic Recycling

Solvent-targeted recovery and precipitation (STRAP) is a dissolution-based plastic recycling process that allows the selective recovery of polymers from mixed plastic waste, but removing the residual solvent from polymer gels remains a major challenge. In this study, we investigate factors affecting the residual solvent in gels during dissolution-based recycling. Experimental measurements show that the precipitation method, cooling rate, and extended filtration time do not have a significant effect on solvent retention. We investigated six variables (solvent vapor pressure, polymer molecular weight, initial polymer-to-solvent mass ratio, predicted solubility, the total Hansen solubility parameter, and the Flory-Huggins interaction parameter) that influence solvent retention. The six variables were used to build a support vector regression-based model to predict solvent retention and determine feature contribution for six polymers commonly used in recycling and nine solvents. Our analysis reveals that solvent vapor pressure is the most influential factor, followed by polymer molecular weight, while the Flory-Huggins interaction parameter has a weaker influence. The predictive framework established in this work provides a foundation for selecting polymer-solvent systems that minimize solvent retention in dissolution-based plastic recycling.