Recycled rubber material developed by Toyoda Gosei is now being used in components for the popular Toyota vehicle model, the RAV4.
Specifically, the opening trim weatherstrip installed around the vehicle doors incorporates 20% recycled rubber blended with newly produced rubber material.
Rubber products derive their elasticity from rubber molecules that are cross-linked with sulfur. Unlike plastics and metals, which can be melted and reused when heated, rubber does not melt under heat, making it inherently difficult to recycle. As a result, much of the waste rubber generated to date has been used as fuel.
However, as societal priorities have shifted, the CO₂ emissions produced during combustion have come under scrutiny, and reductions are increasingly being demanded. Recycling rubber not only reduces waste volume, but also helps prevent the release of chemical substances such as hydrogen sulfide that are generated during combustion.
Transforming rubber—long considered difficult to recycle—into a high-quality material suitable for automotive components is no easy task. Toyoda Gosei has taken on this challenge for more than 30 years.
In this article, we trace that long journey through conversations with Kenji Kobayashi from materials development, Yoshinobu Yamada and Naoto Kuriyama from planning, and Kentaro Adachi from product design.
Specifically, the opening trim weatherstrip installed around the vehicle doors incorporates 20% recycled rubber blended with newly produced rubber material.
Rubber products derive their elasticity from rubber molecules that are cross-linked with sulfur. Unlike plastics and metals, which can be melted and reused when heated, rubber does not melt under heat, making it inherently difficult to recycle. As a result, much of the waste rubber generated to date has been used as fuel.
However, as societal priorities have shifted, the CO₂ emissions produced during combustion have come under scrutiny, and reductions are increasingly being demanded. Recycling rubber not only reduces waste volume, but also helps prevent the release of chemical substances such as hydrogen sulfide that are generated during combustion.
Transforming rubber—long considered difficult to recycle—into a high-quality material suitable for automotive components is no easy task. Toyoda Gosei has taken on this challenge for more than 30 years.
In this article, we trace that long journey through conversations with Kenji Kobayashi from materials development, Yoshinobu Yamada and Naoto Kuriyama from planning, and Kentaro Adachi from product design.
1.
Late-1990s Challenges—and Their Limits
In the 1990s, as awareness of environmental issues grew and the Kyoto Protocol was adopted, a joint rubber recycling development initiative was launched by three organizations: Toyoda Gosei, Toyota Motor Corporation, and the Toyota Central R&D Labs.
At the time, the only rubber recycling method considered viable was the so-called “Pan process,” which involved pressurizing and heating waste rubber with chemicals for more than five hours. However, this method caused significant damage to the rubber, leading to degraded quality and strong residual odors. As a result, its application was limited to only a narrow range of uses.
At the time, the only rubber recycling method considered viable was the so-called “Pan process,” which involved pressurizing and heating waste rubber with chemicals for more than five hours. However, this method caused significant damage to the rubber, leading to degraded quality and strong residual odors. As a result, its application was limited to only a narrow range of uses.
The rubber recycling process at Toyoda Gosei’s plant in Mori Town, Shizuoka Prefecture
At that point, Toyoda Gosei set out to develop a completely new devulcanization technology based on a twin-screw process.
To recycle rubber products, it is necessary to break the sulfur cross-links—the “sulfur bonds” that allow rubber to stretch and return to its original shape. However, if the molecular chains that form the rubber itself are damaged in the process, material quality deteriorates.
This approach selectively cuts only the sulfur cross-links while preserving the polymer chains. Engineers pursued the optimal shapes and combinations of dozens of individual screw elements, testing countless configurations. After more than six months of trial runs, the mass-production line finally began operation.
At the time, however, the technology could be applied only to products made from a single type of rubber. It was not suitable for products composed of multiple rubber types or those containing metal components. While technical improvements continued, the cost of maintaining and managing the equipment mounted, and at one point, the possibility of shutting down the line was even considered.
Kuriyama from the planning team recalls what he heard from those involved at the time.
To recycle rubber products, it is necessary to break the sulfur cross-links—the “sulfur bonds” that allow rubber to stretch and return to its original shape. However, if the molecular chains that form the rubber itself are damaged in the process, material quality deteriorates.
This approach selectively cuts only the sulfur cross-links while preserving the polymer chains. Engineers pursued the optimal shapes and combinations of dozens of individual screw elements, testing countless configurations. After more than six months of trial runs, the mass-production line finally began operation.
At the time, however, the technology could be applied only to products made from a single type of rubber. It was not suitable for products composed of multiple rubber types or those containing metal components. While technical improvements continued, the cost of maintaining and managing the equipment mounted, and at one point, the possibility of shutting down the line was even considered.
Kuriyama from the planning team recalls what he heard from those involved at the time.
“When discussions arose internally about freezing the project, one engineer kept saying, ‘As a leading company in rubber materials, Toyoda Gosei is the one that must develop recycling technologies. A time will definitely come when recycling technology is indispensable.’ Although the scale of the project was reduced, the technology itself was never abandoned and was steadily passed on.”（Kuriyama）
That conviction was finally rewarded in 2020. As climate change and marine pollution grew increasingly severe, Toyoda Gosei made a firm decision to accelerate recycling initiatives. The next challenge they took on was improving the quality of recycled rubber itself.
2.
Trial-and-Error R&D with No Precedents or Prior Research
The greatest obstacle to implementing the technology in society—and using it for interior automotive components—was odor. In particular, interior parts used inside the vehicle cabin must meet extremely strict standards, as even a faint smell can compromise passenger comfort. To be adopted as interior automotive components, the material therefore had to clear a very high quality threshold.
How could the strong, characteristic odor of recycled rubber be eliminated? Materials developers focused on the fact that odor-causing compounds readily bind with water. They established a technology in which a precisely controlled amount of water is injected into the screw, where high-temperature rubber is flowing. The odor components are dissolved, and as the water vaporizes, those components are carried away and removed.
How could the strong, characteristic odor of recycled rubber be eliminated? Materials developers focused on the fact that odor-causing compounds readily bind with water. They established a technology in which a precisely controlled amount of water is injected into the screw, where high-temperature rubber is flowing. The odor components are dissolved, and as the water vaporizes, those components are carried away and removed.
However, establishing this technology required countless rounds of trial and error. Injecting water into a screw where high-temperature rubber was flowing caused the temperature to drop sharply and the internal pressure to surge. The timing, volume, and temperature of the water injection—every parameter had to be precisely optimized. If even one condition was off, the equipment would not operate properly.
Simulation software was used to narrow down predictions, which were then tested on actual machinery. Yet rubber, as a viscoelastic material, exhibits highly complex behavior inside the screw, and the results rarely matched theoretical expectations. Even when consulting experts at research institutions, the response was often the same: “Rubber is extremely difficult to predict.”
Simulation software was used to narrow down predictions, which were then tested on actual machinery. Yet rubber, as a viscoelastic material, exhibits highly complex behavior inside the screw, and the results rarely matched theoretical expectations. Even when consulting experts at research institutions, the response was often the same: “Rubber is extremely difficult to predict.”
Recovered waste rubber from weatherstrips is cut and processed into recycled rubber, then blended with virgin material and reborn as new weatherstrips.
“There were no precedents and no reference materials. The only way forward was to keep experimenting—developing a feel for the gap between simulations and actual behavior, and gradually building our own body of knowledge.”（Kobayashi）
Kenji Kobayashi, Materials Development
Each time the screw configuration was changed, heavy components had to be disassembled, reassembled, and thoroughly cleaned. Engineers with expertise in chemistry worked hands-on with the equipment—often covered in oil—while developing new materials. It was a physically demanding process that required constant movement between theory and on-site practice, day after day.
Through these steady efforts and repeated trial and error, the team succeeded in establishing the deodorization technology and achieving high-quality recycled rubber. As a result, they were able to increase the recycled rubber content from less than 5% to 20%.
Through these steady efforts and repeated trial and error, the team succeeded in establishing the deodorization technology and achieving high-quality recycled rubber. As a result, they were able to increase the recycled rubber content from less than 5% to 20%.
Team members working with recycled rubber on a daily basis
3.
Building Allies and Proving Quality for Real-World Adoption
Even the most advanced technology has no value unless it is adopted as a product. Looking back on the process of introducing the technology into the RAV4, product design lead Adachi says that much of his work was about “building allies.”
As the automotive industry moves toward carbon neutrality, the use of recycled materials has been gaining momentum. However, priority has largely been given to plastics and metals, which account for a greater share of vehicle mass. Rubber, by contrast, remained a relatively minor material in this context.
As the automotive industry moves toward carbon neutrality, the use of recycled materials has been gaining momentum. However, priority has largely been given to plastics and metals, which account for a greater share of vehicle mass. Rubber, by contrast, remained a relatively minor material in this context.
“I’ve seen many cases—not just with rubber—where technologies are recognized as ‘essential and valuable for the next generation,’ yet never adopted,” Adachi explains. “I realized that it wasn’t enough for a materials supplier to make proposals. We needed people inside the automaker to say, ‘This is something we must do for the next generation.”（Adachi）
Adachi’s strategy was to launch a joint project with the automaker aimed specifically at adopting recycled rubber. Typically, automakers organize procurement and design teams by vehicle model. In this case, however, members from a department organized around components rather than specific models—known internally as a “component-based” team—were brought in. Adachi recalls feeling a strong sense of progress at this point.
At the same time, the team also had to confront the negative image often associated with “recycled” materials. They meticulously gathered data from individual part evaluations and full vehicle assessments, and even conducted sensory inspections at the automaker’s assembly sites to demonstrate ease of assembly.
At the same time, the team also had to confront the negative image often associated with “recycled” materials. They meticulously gathered data from individual part evaluations and full vehicle assessments, and even conducted sensory inspections at the automaker’s assembly sites to demonstrate ease of assembly.
Kentaro Adachi, Product Design
“From a technical standpoint, achieving performance on par with virgin material is already a significant accomplishment. At the same time, it also means that the performance itself hasn’t been enhanced beyond that level. In an industry where recycled materials are still not easily recognized as adding value, the automaker understood the significance of having established this level of technology and decided to adopt it. We expect that decision itself to have a major impact.”（Adachi）
Yamada adds that the decision to introduce the technology in the RAV4 was also the result of a deliberate strategy.
“We wanted a proven track record of adoption in a popular, high-volume vehicle. A model with large production volumes serves as clear evidence that mass production is feasible. In addition, receiving the Minister of Economy, Trade and Industry Award at the Chubu Industrial Technology Awards reinforced our sense that this technology has been recognized as one that responds to the demands of our time. We hope this will serve as a catalyst for expanding adoption to other vehicle models and other manufacturers.”
The Chunichi Industrial Technology Awards recognize outstanding industrial technologies and product developments, with the Minister of Economy, Trade and Industry Award representing the highest honor.
https://www.toyoda-gosei.co.jp/news/details.php?id=1475
https://www.toyoda-gosei.co.jp/news/details.php?id=1475
The material adopted for the RAV4 was recycled EPDM, a type of synthetic rubber. However, Toyoda Gosei’s challenge is already moving into its next phase. One example is the development of recycling technology for natural rubber, which accounts for a particularly large share of rubber usage. Because natural rubber has a different chemical structure, a new hurdle emerges in the form of differences in heat resistance compared with synthetic rubber. Further advances in devulcanization technology will be required, and Kobayashi and his team have already begun exploring these possibilities.
4.
Thirty Years of Responsibility and Technological Continuity
After the wave of recycling initiatives that peaked in the late 1990s and early 2000s, the project came close to being frozen. Even so, development continued on a small scale, and the technology has been carefully carried forward to the present day. What sustained this long-term effort was the identity of Toyoda Gosei itself.
The company traces its origins to the rubber research division of Toyoda Automatic Loom Works. Today, Toyoda Gosei takes pride in—and bears responsibility for—being the only company within the Toyota Group that engages in materials development.
The company traces its origins to the rubber research division of Toyoda Automatic Loom Works. Today, Toyoda Gosei takes pride in—and bears responsibility for—being the only company within the Toyota Group that engages in materials development.
“At present, waste rubber is being used as fuel, but that situation may not last forever. With the transition to green energy, it is also predicted that demand for fuel will decline. That’s why we are developing these technologies ahead of time,”says Kuriyama.
Naoto Kuriyama, Planning
Because social demand for the technology was not guaranteed, securing internal understanding and support—including development funding—was essential until the technology could be fully established. To that end, Yamada focused on creating mechanisms to “make the value of the technology visible,” both inside and outside the company.
The team first applied for public subsidies, obtaining official recognition for the project. They then acquired the international certification ISCC PLUS, enabling them to clearly demonstrate the environmental value of recycled materials. After the certification was obtained, external inquiries increased noticeably. These new connections led to opportunities for dialogue and exchange, allowing the team to gain fresh perspectives and ideas from other industries. As a result, support for the project continued to expand.
ISCC (International Sustainability & Carbon Certification) is a global certification program that verifies the sustainability of biomass and recycled raw materials.
These efforts contributed not only to the establishment of the technology itself, but also to increased employee motivation.
The team first applied for public subsidies, obtaining official recognition for the project. They then acquired the international certification ISCC PLUS, enabling them to clearly demonstrate the environmental value of recycled materials. After the certification was obtained, external inquiries increased noticeably. These new connections led to opportunities for dialogue and exchange, allowing the team to gain fresh perspectives and ideas from other industries. As a result, support for the project continued to expand.
ISCC (International Sustainability & Carbon Certification) is a global certification program that verifies the sustainability of biomass and recycled raw materials.
These efforts contributed not only to the establishment of the technology itself, but also to increased employee motivation.
“Younger employees, including those in their twenties, have a strong awareness of environmental issues and social challenges, and a strong desire to contribute through their work. Through rubber recycling technology and its implementation in society, we were able to deliver outcomes that directly contribute to environmental and social good. Both as a company and as individuals, we feel a strong sense of confidence in this technology,”says Yamada.
Yoshinobu Yamada, Planning
To other components, other vehicle models, and other manufacturers—the adoption of recycled rubber in this case marks a first step toward realizing a circular society.
Rubber recycling is a challenge that connects material life cycles, carries technologies forward, links generations, and ultimately helps build a sustainable future. The journey undertaken by the engineers who created this “unprecedented technology” has only just begun.
Rubber recycling is a challenge that connects material life cycles, carries technologies forward, links generations, and ultimately helps build a sustainable future. The journey undertaken by the engineers who created this “unprecedented technology” has only just begun.