Universal Approach for the Depolymerization of Polyamides via Photothermal Conversion

Area of Science:

• Materials Science
• Polymer Chemistry
• Environmental Science

Background:

• Polyamides (PAs) are durable but persistent environmental pollutants due to their stability.
• Recycling PAs is challenging due to high energy requirements for depolymerization.
• Existing PA waste contributes significantly to global plastic pollution.

Purpose of the Study:

• To develop an efficient and accessible photothermal strategy for polyamide recycling.
• To overcome the high energy barriers associated with traditional PA breakdown methods.
• To enable the recovery of valuable cyclic and linear monomers from PA waste.

Main Methods:

• Utilized photothermal conversion with carbon black as a photothermal agent (PTA) under visible light.
• Employed ring-closing depolymerization and acidic hydrolysis for PA breakdown.
• Applied the method to various aliphatic, aromatic, and mixed PA waste streams, including pigmented postconsumer waste.

Main Results:

• Polyamide 6 was depolymerized to ε-caprolactam with 74% yield in 10 minutes.
• Polyamide 6,6 yielded hexamethylene diamine and adipic acid with 97% and 96% yields, respectively, in 1 hour.
• The photothermal method effectively depolymerized pigmented PA waste by using existing pigments as PTAs.

Conclusions:

• Photothermal conversion offers a general, rapid, and energy-efficient route for polyamide depolymerization under visible light.
• The method achieves high monomer yields using inexpensive reagents and tolerates additives, supporting a circular plastic economy.
• This approach presents a viable strategy for recycling diverse PA waste, mitigating environmental pollution.