Finding low-toxicity biopolymer solvents with high melting temperature and thermally induced phase separation of poly(ε-caprolactone)†

This study focuses on identifying low-toxicity solvents for biopolymers such as poly(ε-caprolactone) (PCL) and polylactic acid (PLA) for applications in thermally induced phase separation (TIPS). Common solvents like dioxane and tetrahydrofuran, despite their effectivity, pose significant health risks. Therefore, this research aims to expand the available knowledge of safer solvent alternatives with melting temperatures above 0 °C to enhance the economic and environmental viability of TIPS. The Hansen solubility theory was applied to screen 846 chemicals for their compatibility with biopolymers, selecting those with favourable properties and experimentally testing their potential as TIPS solvents. Among the newly identified solvents, methyl-p-toluate (MPTOL) exhibited superior performance for PCL, showing high dissolution efficiency, low toxicity, and a melting temperature of 34 °C. The phase diagram of the PCL/MPTOL system was constructed using experimental data and computational modelling based on Flory–Huggins theory and PC-SAFT equation of state. Foams prepared through TIPS from this system demonstrated three distinct morphologies with increasing PCL concentration, aligning with expectations based on the phase diagram. These findings present methyl-p-toluate as a promising, safer alternative solvent for biopolymer processing in tissue engineering and membrane technologies, with potential to reduce energy costs and enhance process efficiency.