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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2026

Universal Approach for the Depolymerization of Polyamides via Photothermal Conversion

Polyamides (PAs) exhibit excellent chemical stability and mechanical resistance, yet these same characteristics lead to their widespread accumulation in the environment as pollution. In this work, we developed an inclusive and operationally simple photothermal strategy to recycle PAs, overcoming the high energy barriers necessary to break down these materials. PAs can be depolymerized using photothermally mediated ring-closing depolymerization and acidic hydrolysis to afford cyclic and linear monomers using carbon black as a photothermal agent (PTA) under visible light irradiation. We showed that polyamide 6 is efficiently depolymerized to ε-caprolactam with 74% yield in 10 min. Similarly, in 1 h, the photothermal acidic hydrolysis of polyamide 6,6 afforded hexamethylene diamine and adipic acid with 97 and 96% yields, respectively. This method was further applied to a variety of aliphatic and aromatic PAs and mixed PA waste. Both photothermally promoted processes effectively depolymerize pigment-containing postconsumer waste by leveraging existing black pigments as PTAs. Here, photothermal conversion provided a general and rapid route for PA depolymerization under visible light irradiation, enabling high monomer yields with inexpensive reagents and a general tolerance to additives, demonstrating this approach’s potential for a circular plastic economy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Selective Sequential Depolymerization of Mixed Plastics Mediated by Photothermal Conversion

Chemical recycling of plastics into monomers is a promising strategy to achieve a circular economy. However, selective depolymerization methods for mixed plastics are still underdeveloped. Herein, we report a selective and sequential depolymerization strategy for mixed plastics, including poly(L-lactide) (PLLA), polystyrene (PS), and poly(ethylene terephthalate) (PET), using photothermal conversion. We were able to selectively depolymerize PLLA into L-lactide in the presence of PS and PET. Then, PS was selectively depolymerized to styrene, followed by the depolymerization of PET into its monomer. Our protocol was carried out in one pot without any additional purification of the unreacted plastics at each stage. This method was successfully applied to mixtures of post-consumer waste plastic.

carbon black↗

DOE OSTI2024

Recycling of Post-Consumer Waste Polystyrene Using Commercial Plastic Additives

Photothermal conversion can promote plastic depolymerization (chemical recycling to a monomer) through light-to-heat conversion. The highly localized temperature gradient near the photothermal agent surface allows selective heating with spatial control not observed with bulk pyrolysis. However, identifying and incorporating practical photothermal agents into plastics for end-of-life depolymerization have not been realized. Interestingly, plastics containing carbon black as a pigment present an ideal opportunity for photothermal conversion recycling. Herein, we use visible light to depolymerize polystyrene plastics into styrene monomers by using the dye in commercial black plastics. A model system is evaluated by synthesizing polystyrene–carbon black composites and depolymerizing under white LED light irradiation, producing styrene monomer in up to 60% yield. Excitingly, unmodified postconsumer black polystyrene samples are successfully depolymerized to a styrene monomer without adding catalysts or solvents. Using focused solar irradiation, yields up to 80% are observed in just 5 min. Furthermore, combining multiple types of polystyrene plastics with a small percentage of black polystyrene plastic enables full depolymerization of the mixture. This simple method leverages existing plastic additives to actualize a closed-loop economy of all-colored plastics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Demonstration of Complete Recycling Processes of Reversible Epoxies Using Solar Energy Conversion

Reversible epoxies using the Diels–Alder chemistry enables recycling processes through depolymerizing the polymer at higher temperature and then repolymerizing upon cooling. Compared to conventional bulk heating, photothermal heating can save time and resource and, consequently, reduce costs to reach an elevated temperature for recycling processes of the reversible epoxies. In previous studies, self‐healing of cracks and reattachments of two broken pieces have been presented using a laser; however, recycling of a sample as a whole is not feasible by using such a point light source. Herein, complete recycling processes are demonstrated utilizing an area light source, i.e., sunlight. Reversible epoxies are incorporated with carbon black and refractory plasmonic titanium nitride nanoparticles (NPs). Under concentrated (10 times) sunlight, they can generate sufficient heat (≈140 °C) to completely liquefy, reprocess, and reshape the samples multiple times. Recycling processes are validated by evaluation of mechanical properties for each cycle. Using an integrated experimental and theoretical approach, photothermal performance is investigated in terms of the dispersion and loading of photothermal NPs in the matrix, as well as the sample thickness. In this study, an insight is provided into the design of polymer/photothermal nanomaterial composites which can be sustainably recycled using abundant solar energy.

14 SOLAR ENERGY↗