Recycling of polycarbonate from optical lens manufacturing waste via solvent-targeted recovery and precipitation: A process feasibility and sustainability assessment.

Polycarbonate (PC) is widely used in optical lenses, and lens manufacturing generates a heterogeneous waste stream known as swarf that contains PC, polyurethanes, thermoset resins, coatings, and process debris and is currently unrecyclable. This preliminary feasibility study evaluates swarf as a potential feedstock for PC recycling via solvent-targeted recovery and precipitation (STRAP™). Solvent selection was guided by COSMO-RS modeling to identify solvents that dissolve PC under mild conditions (65-120 °C, ambient pressure) while minimizing urethane-resin dissolution. Among the solvents tested, tetrahydrofuran (THF) gave the highest PC yield (89 wt%), outperforming toluene (74 wt%) and xylenes (63 wt%). Spectroscopic (FTIR), thermal (TGA, DSC), and chromatographic (GPC) analyses confirm the THF-recovered fraction is PC, with no detected contamination from other polymers. A reduction in glass transition temperature (135.4 °C versus 145.6 °C for virgin PC) and a 20 °C decrease in degradation onset measured by TGA suggest the possible formation of a minor low-molecular-weight in the recovered PC. Further development is needed to optimize the process and validate end-use performance at scale. A technoeconomic analysis of small-scale STRAP operations (2000-10,000 t yr⁻1) indicates that, under favorable assumptions for feedstock logistics, solvent-based PC recovery from swarf can be economically viable. Specifically, a 5000 t yr⁻1 plant selling recycled PC at $2.50 kg⁻1 achieves a 15 % IRR. Life cycle assessment shows an 79 % reduction in greenhouse gas emissions (kg CO2 eq.) versus virgin PC production. Further development is needed to address polymer performance at scale.