"Control of Generation and Decomposition of Modular Structures for Material Circulation - Sustainable Element Strategy-" is to enable flexible control of the stability and decomposition of inter-block bonds through the generation and decomposition of modular structures composed of multiple blocks, with the aim of realizing sustainable material circulation. This is a research and development concept that aims to develop materials with an awareness of the flow of materials after use. Here, "block" refers to the constituent unit of a Modular structure, such as the main phase (Nd-rich phase) and the sub-phase (grain boundary phase) in permanent magnets, the matrix (resin) and the filler (fiber) in composite materials, and the two-dimensional atomic layer thin film that constitutes layered materials. By carrying out research and development based on this concept, we aim to make it possible to make materials highly functional and multifunctional, which cannot be achieved with a single material phase (block), and to contribute to the realization of a circular society by solving waste disposal problems, reducing environmental impact, and reducing resource supply risks through decomposition controllability between blocks.

As we work toward the achievement of the SDGs and the realization of Society 5.0 proposed by Japan, and as digital transformation (DX) accelerates after the global pandemic of the new coronavirus infection (COVID-19) that broke out at the end of 2019, the requirements for various products are becoming increasingly sophisticated not only in terms of performance, but also in terms of environmental and energy impacts. The materials that make up the core components of these products are required not only to improve single performance but also to satisfy various functions simultaneously.

Highly functional or multifunctional materials have become indispensable, for example, for the acquisition of renewable energy sources that contribute to the reduction of CO2 emissions, one of the causes of global warming, and for the realization of various devices and products that are essential in the DX era. In these materials, many critical minerals are contained. For Japan, almost 100% of its mineral resources are imported, and supply risk is a continuous concern. In this context, the "Elemental Strategy" proposed by Japan to solve this problem is becoming increasingly important. With the recent changes in foreign countries' resource policies and the disruption of supply chains triggered by the expansion of COVID-19 infection, it is necessary to formulate a new materials development strategy in order to secure resources in a sustainable manner and to maintain the international competitive advantage of materials, devices, and manufacturing technologies in which Japan has an advantage.

While we pursue new functions and convenience in materials and products, there is a growing concern about the environmental impact of products made of new materials and general-purpose products manufactured and consumed in large quantities and their waste disposal problems. The growing social interest in these issues has led to the idea that we should break away from the conventional mass-production, mass-consumption, mass-disposal society and build a circulating society, which is about to change manufacturing drastically. Based on the concept of "inverse manufacturing" proposed in Japan in the 1990s, the construction of recycling systems for various products such as home appliances has progressed, but it can be said that it is just a shift from mass production, mass consumption, and mass disposal to mass production, mass consumption, and mass recycling, and the question remains whether this is the sustainable manufacturing that we should be aiming for. It is said that 5% of the energy consumed in the world is used for metal separation, of which 80% is for crushing and grinding. In order to reduce these energy consumptions and realize a circulating society with low environmental impact, it is necessary to pursue material circulation from the product level to the materials level. At present, however, both academia and industry are lacking in such efforts.

Looking at the scientific and technological trends, as society's demands for materials increase, they are evolving, for example, from single-element materials to multi-element materials in the case of inorganic materials, to control structures with complex combinations of multiple compositions, such as composite materials, and to control structures with higher-order hierarchy, such as polymer materials. In particular, materials science and technology for precise control of complex structures and higher-order hierarchical structures has not yet been established.

In separation and recycling technology, while physical separation technology developed from ore dressing and chemical separation technology developed from smelting (high temperature separation process and wet separation process) have been developed individually, the fusion of these two separation technologies is evolving into the development of localized, selective, and highly precise separation technology that concentrates energy only on the part that needs to be decomposed.

In the background above, this proposal focuses on the control of generation and decomposition of modular structures as a common target for materials creation (arterial side) and materials separation and recycling (venous side), and proposes to promote R&D toward the realization of a sustainable circulating society by targeting the flexible control of the stability and decomposition of inter-block bonds. By realizing this, in addition to satisfying the functions required by society at the time of materials use, we will show that there is a possibility of contributing to the reduction of environmental impact and material circulation after materials use.

The R&D issues to be addressed in implementing the R&D strategy include "designing new materials with new functions by controlling modular structures," and the "establishment of the science of the generation and decomposition of modular structures" and "advancement of common basic technologies" that are necessary to make this possible. In order to implement the "design of new materials with new functions by controlling modular structures," it is important to consider the following points: 1) how to combine multiple blocks to achieve the high functionality and multifunctionality required of materials, and 2) how to achieve a low-cost decomposition process to reduce environmental impact and achieve material circulation. In order to control the stability and decomposition of inter-block bonds, it is necessary to establish the "science of generation and decomposition of modular structures" through the elucidation of deterioration and destruction mechanisms in existing materials and scientific understanding of current separation and recycling processes. In addition, in promoting the above-mentioned R&D, it is necessary to advance simulation and measurement technologies in combination with data science that can handle more complex phenomena. In particular, it is necessary to develop simulation techniques for non-equilibrium and unsteady states, including decomposition processes, and to build a database of dynamic data that can track the time evolution of reactions and processes. In addition, it is necessary to develop new process technologies for the generation and decomposition of modular structures, as well as high-throughput experimental methods and real-time process measurement methods.

In promoting the research and development of this proposal, it is important that diverse researchers with different academic backgrounds and research motivations, such as materials science, chemistry, physics, computational science, process engineering, data science, recycling engineering, and separation engineering, collaborate and integrate their research to achieve the same goal. In addition, it is also important to consider social impact, technical feasibility, and economic rationality in parallel. In order to achieve this, it is necessary to create a policy framework that intentionally matches the academic curiosity and application orientation of each researcher, and to create a forum for sharing goals. For example, multiple research projects could be set up in a sequential manner to enable step-by-step implementation from the promotion of interdisciplinary and fusion research to industry-university collaborative research that considers the entire life cycle of materials and products. From the perspective of resource circulation, it is also necessary to involve human resources who can consider which resources should be circulated and which functions should be circulated after looking at the entire life cycle from natural resource development to disposal and recycling. In order to achieve this, it is also effective to set up a forum for exchanging opinions from diverse perspectives and from a bird's-eye view, involving specialists who have not been directly involved in materials development in the past, such as resource science, mineralogy, earth science, environmental science, environmental policy, and economics. In addition, the strategic use of standardization and regulations should be promoted in order to make material circulation take root in the proactive activities of industry.