Railways are an important piece of infrastructure that supports our daily lives and logistics, and many of the cables (electrical wires) used there contain resource materials such as copper. However, with conventional processing technologies, it has been difficult to separate the conductors and coating materials from the cables with high purity, and the recovery of recyclable materials has therefore been limited.

Mitsubishi Materials, in collaboration with Tohoku University, Tokyu Corporation ("Tokyu"), and Tokyu Railways Co., Ltd. ("Tokyu Railways"), began research and development into railway cable recycling in April 2025. This research is being carried out with funding from the Environmental Research and Technology Development Fund (JPMEERF20253002) of the Ministry of the Environment and the Environmental Restoration and Conservation Agency.

We spoke with members of our research and development team about the background of this initiative, the technologies being utilized, and the goals to be achieved.

Mitsubishi Materials has established "Our Commitment" as "For people, society and the earth, circulating resources for a sustainable future." In particular, we are strongly committed to recycling copper—an important material at the core of our business. Our desire to contribute to the sustainability of society as a whole by ensuring the reliable recycling of copper in railroad operations is the driving force behind this research and development.

Since 2015, Tohoku University and Mitsubishi Materials have been jointly developing a technology called the "combined plastic swelling and ball milling method " ("the method"), which enables the separation of conductors and sheathing materials from cable components. The method involves immersing cables in an organic solvent to swell the coating materials, followed by impacting them with metal balls to separate the copper wires and coating without causing damage.
To achieve resource circulation, collaboration is essential not only with companies that produce materials but also with companies that use them. Tokyu Railways, which operate railroad businesses, have been facing challenges in recycling the materials they use, and as this coincided with Mitsubishi Materials' vision for resource circulation, a four-party collaboration based on university-developed technology was realized.

In its research on plastic recycling, Tohoku University (Yoshioka Laboratory) discovered that a swelling phenomenon caused by a combination of polyvinyl chloride and organic solvents is effective in stripping thin electrical wires.
Mitsubishi Materials took notice of this technology at an early stage and has supported the research.
In 2022, the basic technology was established, and research began on a recycling process using the method for automotive wire harnesses, with Mitsubishi Materials becoming fully involved in the research and development.

In our efforts targeting automotive wire harnesses, we have worked to develop the entire recycling process—including studying pre-treatment techniques for coated wires—to enable application of the method.
Furthermore, we are analyzing the quality of the recovered copper and reflecting the results in the optimization of stripping conditions, thereby improving the precision of the technology.
For our current expansion to railway cables, we will similarly continue to develop peripheral technologies and study recycling methods with the aim of establishing a practical process.

Railway cables often differ in material and structure from the coated electric wires that have been the subject of research to date, and new conditions must therefore be established to apply the method. Furthermore, because they contain materials other than conductors and insulating coatings, it is also essential to consider peripheral technologies such as pre-processing.
This initiative aims to separate, recover, and recycle not only copper but also resins such as coating materials at high purity. To achieve this, multiple technologies must be combined to build a practical process. Through collaboration among the four parties, we will combine the university's research capabilities, railway operators’ on-site knowledge, and material manufacturers’ technologies to overcome these challenges.

The knowledge gained from developing railway cable recycling technology can be applied not only to the railway industry but also to a wide variety of other cable products. Cables are essential components used in many industries, and advancing cable recycling technologies is expected to provide strong momentum toward realizing a circular economy.
Our first goal is to complete the recycling process for the targeted railway cables and build a resource-circulation scheme that clearly shows the flow through to material recovery.
Over the next three years, we plan to refine the technology and advance development to a level where we can move on to the practical application phase.