New Chemical Method Turns Used Rubber into High-Value Resins

Rubber is a highly valuable material with a massive global market. Although its use dates back hundreds of years, it was primarily restricted to natural rubber from trees. The modern process of vulcanization, which makes rubber durable and versatile, wasn’t developed until 1839. 

Chemist Charles Goodyear invented vulcanized rubber, which is natural or synthetic rubber improved by treating it with sulfur, among other chemicals, and heat.

Unique properties like elasticity, flexibility, toughness, tensile strength, resistance to aging, impermeability, shock absorption, and heat resistance are what make rubber so valuable in automotive, construction, industrial, healthcare, consumer goods, and packaging.

However, rubber waste is a major issue contributing to the massive waste crisis, which poses challenges to the environment, human health, and the economy. The rising waste generation problem is a product of urbanization, economic development, and population growth.

Tires, in particular, are the primary contributor of rubber waste. The total worldwide production of waste tires accounts for 2% of the total annual solid waste.

The Grievous Rubber Waste Problem 

About a billion tires are discarded each year worldwide, and millions end up in landfills. In the UK alone, an estimated 37 million car and truck tires are discarded annually. Meanwhile, in the US, more than 274 million tires were discarded in 2021, with about 20% of them tossed in disposal sites. 

It’s not just a space issue, though. The accumulation of these waste materials introduces environmental hazards. 

Rubber products contain various chemicals, including antioxidants and antiozonants, which can leach into the environment and pose health risks. The improper disposal of rubber waste, especially tires, in landfills can even lead to groundwater contamination from leaching of harmful substances and heavy metals. 

Being non-biodegradable in nature means they persist in the environment for extended periods, contributing to pollution and visual blight for centuries. Also, rubber is highly flammable, and stockpiles of waste tires can pose a significant fire hazard, releasing harmful pollutants into the air. 

A 2020 UK government-funded research study suggested that tire particles are a major and additional source of microplastics and could, in fact, be a largely undocumented source of microplastics in water bodies.

The study was the first to identify this, demonstrating that tire particles can either be transported straight to the ocean through the atmosphere or carried into sewers and rivers by rainwater, where they can pass through the water treatment process.

“Scientists have long suspected that tyre debris is posing a hidden threat to the marine environment,” but few studies have measured their abundance in aquatic environments, said Professor Richard Thompson OBE. The study provides “real insight into the importance of tyre wear as a source of microplastics.”

All these factors demand urgent action and a shift towards sustainable waste management practices.

Need for Efficient Rubber Waste Management Solutions

Rubber waste, particularly from tires, is a growing problem globally due to increasing production and limited lifespans, creating a need for effective waste management and recycling solutions. 

“Tyre particles are thought to be among the greatest sources of microplastic pollution worldwide,” and we need “more systemic solutions perhaps via improved vehicle tyre design,” says Professor Richard Thompson OBE FRS, Director of the Marine Institute.

Research from last year, conducted by the University of Plymouth and Newcastle University and funded by UK National Highways, shows that retention ponds can help tackle tire pollution. The study also noted that tire wear particles outweighed other forms of microplastics and were removed in far greater quantities.

Now, the presence of retention ponds and wetlands has been found to reduce the amount of particles released by tires entering the waters by an average of 75%, in turn, offering protection for rivers and the ocean.

As such, the researchers recommended the maintenance of wetlands and retention ponds to be made a major priority to reduce the flow of tire particles from roads to rivers.

“Retention ponds and wetlands are constructed as part of highways projects primarily to attenuate flow and prevent downstream flooding, but also to remove pollutants. These existing drainage measures in place along parts of the UK’s strategic road network have the potential to halt the spread of tyre pollution.”

— Mrs Florence Parker-Jurd, Associate Research Fellow

To get hard numbers on the total amount of tire wear particles collected in the influent, effluent, and sediments of the wetlands and retention ponds, the study used the pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) method developed by Geoff Abbott from Newcastle University. The method was developed to identify particles derived from tires in the environment.

Another promising solution is recycling, which can reduce the environmental impact of rubber waste disposal and create new products from recycled materials. 

One application of recycled rubber is construction, where it can be used in asphalt and concrete mixes, paving stones, and playground surfaces. Other applications include artificial turf infill, sports surfaces, floor tiles, and acoustic insulation. Using thermal processes, waste rubber can even be converted into fuel or other energy sources. 

Pyrolysis is a popular process that turns rubber waste into something useful. In this chemical process, rubber is recycled through high-temperature decomposition. It separates covalent bonds in organic matter in the absence of oxygen. 

By subjecting rubber waste to thermal decomposition, recycled carbon black nanoparticles (RCBN) and oil/gas are produced, which can be used as an alternative fuel in cement kilns.

Recycled rubber waste obtained by pyrolysis from waste tires can also be used to produce electrically conductive concrete. Conductive rubber waste is being used in the aerospace, military, and automobile industries.

Rubber waste management, however, faces serious challenges. For starters, the sheer volume of rubber waste generated globally makes it extremely difficult to manage and recycle efficiently. 

Then there’s the variety of rubber products and their complex chemical compositions that make recycling and reuse difficult. Even the widely used process (pyrolysis) has its disadvantages — it generates harmful byproducts like dioxins and benzene that pose health and environmental risks.

There’s also a lack of infrastructure and technology for effective rubber waste collection, sorting, and recycling. Traditional waste management methods focus on collecting, burning, and disposing of rubber waste in landfills.

Against this backdrop, it is essential that we develop efficient waste management techniques to tackle the growing problem of rubber waste effectively.

Click here to learn if a ‘Sustainability Metric’ can help curb plastic pollution.

A New Chemical Process to Repurpose Rubber Waste

A new study, funded by the U.S. Department of Energy (DOE) and published in Nature¹, has introduced a new technique for tackling rubber waste.

Due to the lack of strategies for the chemical recycling of commodity diene polymers, like those found in tires, a novel chemical method has been developed to break down the rubber waste. 

A team of researchers led by Dr. Aleksandr Zhukhovitskiy, an assistant professor in the Department of Chemistry at UNC-Chapel Hill, applied C-H amination along with a polymer backbone rearrangement strategy to transform the disposed rubber into precursors for epoxy resins. 

This deconstruction of materials offers an innovative, practical, and sustainable alternative to traditional recycling methods. It also aims to overcome challenges in traditional approaches to breaking down rubber.

Rubber is made of polymers that are cross-linked together into a three-dimensional network. This extensive cross-linking within the polymer structure makes rubber a tough, flexible, and durable material, but this also makes it resistant to degradation.

There are two main conventional techniques for breaking down rubber: de-vulcanization, a process that breaks down sulfur cross-links but erodes the polymer’s mechanical properties, and cleavage of the polymer backbones using catalytic or oxidative methods, which tends to result in low-value byproducts.

Neither of the methods provides an efficient and scalable solution to repurpose rubber waste. To get past these obstructions, the research developed “a method that breaks down rubber into functional materials that possess value even as a mixture,” said senior author Dr. Zhukhovitskiy.

For this, the researchers developed a sulfur diimide reagent, which is an imine of sulfur dioxide, that allows as much as 35% allylic amination of diene polymers and rubber. The cationic 2-aza-Cope rearrangement was then applied to deconstruct polymers.

Introducing the sulfur diimide reagent enables the positioning of amine groups at particular locations in the polymer chains and sets the stage for the ensuing backbone rearrangement. The chemical reaction is what restructures the polymer backbone. This reorganization involves the deconstruction of rubber into soluble amine-functionalized materials. This two-step process, as shown by the researchers, works superbly. 

When tested in a model polymer, the researchers were able to break it down considerably. The molecular weight of the polymer was reduced to about 400 g/mol from 58,100 g/mol.

On applying their method to used rubber, they were able to break it down in its entirety in a matter of six hours. The aminated post-consumer rubber turned into a soluble material with amine groups that can be utilized to produce materials like epoxy resins.

Epoxy resins are known for their excellent bonding properties. They are used in adhesives, coatings, sealants, electrical insulation, and civil engineering repairs. Epoxy resins are typically made from petroleum-based chemicals like bisphenol A and curing agents. 

According to the research, the epoxy thermosets prepared using the resulting soluble amine-functionalized polymers have similar strength to commercial bisphenol A-derived resins.

According to co-author Maxim Ratushnyy, a former postdoc scholar at UNC-Chapel Hill:

“In moments like this, I come to appreciate the power of organic synthesis. It is fascinating to see the ease with which the developed sequence of simple, yet powerful, organic transformations can take on a stubborn C—C bond and convert polybutadiene and polyisoprene-based rubbers into potentially valuable epoxy resins.”

Furthermore, the novel chemical recycling of post-consumer materials is highly efficient compared to conventional recycling methods, which often require expensive catalysts or extreme temperatures.

In this study, researchers got their results under mild temperatures, 35-50°C (95-122°F) in aqueous media, making the process cost-effective and environmentally friendly.

The environmental impact of the process was evaluated using the Environmental Impact Factor (E-factor), “a simple but powerful metric,” that calculates the actual amount of waste by measuring waste generated relative to the product yield.

Besides comparing the impact of a new process to the existing ones, Dr. Geoff Lewis, a research specialist at the Center for Sustainable Systems at the University of Michigan, explained that E-factor also highlights “process steps that can be improved as we work to transition this process out of the lab and into practice.”

The process’s complete E-factor, which includes solvent use, was high. However, its simple E-factor was much lower, excluding solvents. This highlights the areas of the process that can be optimized for sustainability.

So, the team is now exploring greener solvent systems and alternative reaction conditions to reduce waste generation.

Calling it “a paradigm shift in how we approach the problem of rubber waste,” study co-author Sydney Towell, who’s a Ph.D. candidate at UNC-Chapel Hill, explained that:

“By harnessing the power of C–H amination and backbone rearrangement, this method provides a new pathway to transforming post-consumer rubber into high-value materials, reducing reliance on landfills and minimizing environmental harm.”

Innovative Company

Goodyear Tire & Rubber Co (GT +5.12%) 

Founded in 1898, Goodyear is a major tire manufacturer that is investing in sustainable rubber alternatives and recycling initiatives.

In January 2022, the company released a demonstration tire made of sustainable material. The tire includes 13 featured ingredients across nine different tire components and delivers strong overall performance. 

This includes carbon black, which is used to increase tire life and is made by burning various types of petroleum products. However, to reduce circularity and carbon emissions, four drift types are now featured, produced from plant-based oil, carbon dioxide, methane, and end-of-life tire pyrolysis oil (TPO) feedstocks. 

Soybean oil in the sustainable tire helps maintain the flexibility of its rubber compound in changing temperatures, while high-quality silica, made from rice husk waste residue, improves grip and reduces fuel consumption. 

Polyester used in tires is recycled from post-consumer bottles, while pine tree resins, which are bio-renewable, have replaced traditional ones that are based on petroleum. 

At the time, the sustainable-material content of Goodyear’s tires was 70%, which was reported to be increased to 90% in 2023, bringing it closer to its goal of creating the first tire made completely from sustainable materials.

The company has reported that the demonstration tire passed all applicable regulatory and internal testing. Compared to tires made with traditional materials, the demonstration tire was also found to have lower rolling resistance, which means better fuel savings and reduced carbon footprint. 

A few months ago, the company unveiled an ElectricDrive Sustainable-Material (EDS) Tire, which marks a pivotal step in its goal to introduce the industry’s first 100% sustainable-material tire by 2030.

Amidst the boom of electric vehicles (EVs) and focus on sustainability, these EDS tires are engineered specifically for EVs, delivering long mileage, lower rolling resistance, reduced noise, and superior wet braking and handling.

When it comes to company financials, the $2.5 billion market cap Goodyear, whose shares are currently trading at $8.85, down 2.33% YTD, announced a net income of $76 million or 26 cents per share, compared to a net loss of $291 million a year ago, and $114 million in adjusted net income or 39 cents per share for Q4 2024.

During this period, the company’s sales were $4.9 billion, with tire unit volumes totaling 43.6 million. For the full year, sales were $18.9 billion, with tire unit volumes totaling 166.6 million.

In 2024, Goodyear reported a net income of $70 million or 24 cents per share, compared to a net loss of $689 million a year ago, and an adjusted net income of $302 million or $1.05 per share.

Cash flows from operating activities during this period were $698 million, down from $1.032 billion in the previous year. Last month, the company successfully closed its off-the-road tire business sales to The Yokohama Rubber Company, while the sale of the Dunlop brand to Sumitomo Rubber Industries is anticipated to close by mid-year.

Talking about his first year at Goodyear, CEO Mark Stewart shared satisfaction with the progress made in 2024, during which the company exceeded expectations, grew earnings, and reached agreements to divest non-core assets.

“Moving forward, we remain committed to achieving our expanded Goodyear Forward targets, including further margin expansion and meaningful debt reduction.” 

– CEO Stewart

For 2025, the company expects “significant deleveraging,” margin expansion, and optimization of its portfolio to drive shareholder value. Goodyear is projected to deliver gross proceeds surpassing $2 billion and a net leverage ratio of 2.0x to 2.5x by the end of the year.

Latest on Goodyear Tire & Rubber Co

Conclusion

Rubber waste, mainly from tires, presents a big challenge that demands our urgent attention and efficient solutions. Existing methods like pyrolysis, while broadly used, produce hazardous byproducts. Meanwhile, traditional recycling methods struggle with efficiency and scalability.

Given that rubber waste is a growing and critical problem, researchers are exploring new ways, such as retention ponds for microplastic filtration and chemical processes involving C-H amination and backbone rearrangement for rubber deconstruction, offering promising and greener solutions.

With continued research and industry adoption, these advancements can help minimize rubber pollution, reduce landfill waste, and transform rubber waste into valuable materials!