Laboratory-Scale Life-Cycle Assessment: A Comparison of Existing and Emerging Methods of Poly(ε-caprolactone) Synthesis

Abstract

Poly(e-caprolactone) (PCL) is a widely employed biodegradable polymer synthesized commercially using stannous octoate-mediated ring-opening polymerization (ROP) of e-caprolactone (e-CL). It needs to be revisited in alignment with green chemistry principles, such as less hazardous chemical syntheses. We identified and optimized two emerging methods—Route A: acid-catalyzed ROP of e-CL using hydrogen chloride (HCl) in diethyl ether; and Route B: free-radical ROP using cyclic ketene acetal (CKA) monomer, 2-methylene-1,3-dioxepane (MDO), which are essentially solvent-free, metal-free, and organic-catalyst-free. They were then compared with the laboratory-scale reproduction of Route C: stannous octoate-mediated ROP of e-CL. Laboratory-scale life-cycle assessment (LCA) is employed to analyze the potential environmental profiles of these three routes by employing a cradle-to-gate system boundary, starting from extraction of raw materials and ending with production of 1 g of PCL homopolymer. The overall findings showed that Route A, the low-temperature acid-catalyzed approach, was more power-efficient and less hazardous compared to Routes B and C, with consideration of sensitivity and uncertainty analysis results. Route A was demonstrated to be the most environmentally sustainable route with environmental impact reductions of 79.46% (climate change), 54.53% (fossil fuel depletion), 45.10% (terrestrial acidification), and 66.36% (water depletion) per 1 g of PCL, in contrast to Route B. In comparison to Route C, Route A achieved 43.54% (fine particulate matter formation) and 98.41% (human toxicity) impact reductions per 1 g of PCL. Route B contributes largely to climate change, whereas Route C has the most significant influence on human toxicity.