Chemoselective depolymerization of polyurethane via solvent-engineered glycolysis

Area of Science:

• Chemical Engineering
• Materials Science
• Green Chemistry

Background:

• Chemical upcycling of polyurethane (PU) is crucial for sustainability but challenged by toxic toluene diamine (TDA) byproduct formation during high-temperature glycolysis.
• Preventing secondary thermolytic pathways while selectively cleaving urethane bonds is a key engineering hurdle.

Purpose of the Study:

• To develop a chemoselective depolymerization strategy for PU upcycling that minimizes toxic TDA formation.
• To identify optimal solvent systems and process conditions for efficient and safe PU feedstock recovery.

Main Methods:

• Systematic evaluation of binary-glycol solvent systems to balance nucleophilicity and solvation.
• Kinetic window optimization including glycol-to-PU ratio, catalyst concentration, and temperature threshold.
• Toxicological modeling to assess the safety of the upcycled product.

Main Results:

• A 6:4 monoethylene-to-diethylene glycol ratio was identified as optimal for the solvent system.
• A constrained kinetic window (1:1 glycol-to-PU ratio, 1 mM diethanolamine, 160 °C) maximized urethane scission and minimized TDA (<2278 mg kg⁻¹).
• The resulting glycolysate allows up to 40% substitution into secondary PU formulations without exceeding aquatic toxicity thresholds.

Conclusions:

• The developed strategy offers a scalable, low-toxicity pathway for polyurethane circularity.
• Integrating molecular solvent design with process control enhances the commercial viability of PU upcycling.
• This approach significantly reduces hazardous byproducts, paving the way for sustainable materials.