A Plastic System Born from CO₂, Returning to Fertilizer and Raw Materials: Demonstrating a New Polymer Resource Cycle for Carbon and Nitrogen

A research group led by Rikuto Niki (at the time of research) from the Graduate School of Science and Engineering at Chiba University, Associate Professor Daisuke Aoki from the university's Faculty of Engineering (also affiliated with the Center for Space Gardening Research), and Professor Tatsuo Taniguchi, in collaboration with Associate Professor Takehiro Kamiya from the University of Tokyo, and Program-Specific Associate Professor Yusuke Kita and Professor Masazumi Tamura from Kyoto University, has directly synthesized a monomer and a cross-linking agent from carbon dioxide (CO₂) to create a cross-linked aliphatic polycarbonate material. This material is not only usable as a soft material but can also be decomposed into the plant fertilizer urea and precursors for the monomer and cross-linking agent by treating it with ammonia water after use. They also succeeded in regenerating the original monomer and cross-linking agent from the obtained decomposition products using CO₂ again. This study demonstrates a new polymer resource circulation system that integrates a "carbon cycle" for using and recycling CO₂-derived carbon as a polymer material and a "nitrogen cycle" for utilizing nitrogen components as urea fertilizer through ammonia-based polymer decomposition.

The research results were published online in the academic journal Journal of CO2 Utilization on June 18, 2026.

■ Research Background
Plastics are indispensable in modern society, but their increasing waste, reliance on fossil fuels, and CO₂ emissions are societal challenges, creating a strong demand for the development of sustainable, resource-circulating plastics and their decomposition/recycling technologies. In nature, carbon is converted from atmospheric CO₂ into organic compounds, and nitrogen is taken up by plants from the soil as ammonia or ammonium salts, circulating as a nutrient source. This research aimed to introduce such carbon and nitrogen cycles into polymer materials, focusing on CO₂-derived cross-linked aliphatic polycarbonate materials. While it was known that aliphatic polycarbonates themselves could be synthesized from CO₂, most studies targeted linear polymers. However, by introducing a cross-linked structure, it's possible to develop polymer materials usable as soft materials, leading to the effort of directly synthesizing a cross-linking agent using CO₂. This aimed to create a soft material using CO₂ as a raw material from monomer to cross-linking agent and to build a resource circulation system for its post-use phase.

■ Key Research Findings
1. Successful direct synthesis of monomer and cross-linking agent from CO₂: By using a cerium oxide (CeO₂) catalyst, they succeeded in efficiently synthesizing the monomer and cross-linking agent while suppressing side reactions.
2. Creation of a flexible and transparent free-standing film: The cross-linked body obtained by ring-opening polymerization of the monomer and cross-linking agent formed a transparent and flexible free-standing film, showing promise for use as a soft material.
3. Decomposition into urea fertilizer via ammonia treatment and reconversion to raw materials using CO₂: Decomposing the cross-linked polymer with ammonia water produced urea and precursors for the monomer and cross-linking agent. Furthermore, plant experiments showed that the decomposition products exhibited a fertilizer effect even as a mixture, and the original monomer/cross-linking agent could be re-synthesized from the precursors using CO₂ and the CeO₂ catalyst. This demonstrated a new polymer resource circulation system for carbon and nitrogen.

■ Future Prospects
In the future, further optimization of the ammonia decomposition conditions and recycling process is expected to lead to the development of more practical chemical recycling technologies. Additionally, applications as soft materials with adjustable flexibility and strength are anticipated by appropriately designing the cross-linked structure and monomers. Furthermore, as this study also succeeded in material formation using light, future expansion into photocurable materials such as 3D printer resins is also expected.