Reprocessing Thermoset Polyurethane Foams Using Their Residual Polymerization Catalysts.

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Thermoset polyurethane (PU) foam recycling typically requires adding new catalysts, increasing costs and potential environmental hazards.
• Residual catalysts present in PU foams during synthesis may possess carbamate exchange activity, enabling reprocessing without additional agents.

Purpose of the Study:

• To investigate the potential of using residual tertiary amine catalysts, such as 1,4-diazabicyclo[2.2.2]octane (DABCO), for reprocessing thermoset PU waste.
• To evaluate the catalytic activity of DABCO in carbamate exchange reactions under various conditions relevant to PU recycling.

Main Methods:

• Model compound studies and crossover experiments were conducted to assess DABCO's catalytic mechanism and activity in carbamate exchange.
• Reprocessing of commercial thermoset PU foams was performed in a twin-screw extruder, examining the influence of shear force and residual catalysts.
• Characterization of reprocessed PU films included thermal analysis (glass transition temperature) and mechanical testing (tensile properties).

Main Results:

• DABCO was confirmed to catalyze both dissociative and associative carbamate exchange, with activity influenced by alcohol concentration.
• Microcompounding in a twin-screw extruder accelerated bond exchange compared to small molecule studies due to high shear forces.
• Three commercial thermoset PU foams were successfully reprocessed into films maintaining original thermal and mechanical properties, and composites were produced with tunable modulus.

Conclusions:

• Residual tertiary amine catalysts, like DABCO, can effectively facilitate the reprocessing of thermoset PU waste without altering commercial formulations.
• This method offers a cost-effective and environmentally friendly approach to PU foam recycling, preserving material properties.
• The findings highlight the potential for sustainable recycling of PU products by leveraging inherent catalytic activity.