Market and product

Compiled by Bao Hien

The global tire industry is accelerating efforts to find an alternative to 6PPD, an anti-aging additive used in most tires for nearly 50 years, after scientists discovered that its transformation product, 6PPD-quinone, is highly toxic to coho salmon.

Several companies have announced promising candidates. However, experts say that moving from a compound that performs well in initial tests to a commercially viable replacement for 6PPD on a global scale will still be a long process.

Growing pressure to replace a chemical used in most tires

6PPD is a standard antioxidant and antiozonant used in tire manufacturing. It helps protect rubber from degradation and cracking caused by exposure to ozone and oxygen, thereby extending tire life.

Environmental concerns surrounding the chemical intensified in 2020, when scientists identified 6PPD-quinone — a transformation product formed when 6PPD reacts with ozone during tire use — as a cause of acute toxicity in coho salmon.

As vehicles travel, tire-wear particles accumulate on road surfaces. During rainfall, these particles can be washed into drainage systems and eventually discharged into rivers and streams, carrying 6PPD-quinone into aquatic environments. Mass die-offs of coho salmon in urban streams across the Pacific Northwest of the United States have become one of the clearest signs of the problem.

The discovery quickly drew the attention of regulators. In California, the state's Department of Toxic Substances Control has identified tires containing 6PPD as a "priority product," triggering further efforts to assess the chemical's risks and identify safer alternatives.

The pressure is particularly significant given that the global 6PPD market is estimated at around $1 billion a year and the chemical is present in virtually all tires currently in use. The industry's challenge is therefore not simply to find a less toxic chemical, but to develop one that can provide comparable tire protection, meet safety requirements and be produced cost-effectively at the enormous scale required by the global tire industry.

Flexsys unveils a candidate but keeps its structure confidential

Among the companies pursuing an alternative, Flexsys — one of the world's major rubber-additive suppliers and a producer of 6PPD — attracted attention in November 2025 when it announced that it had developed what it described as the industry's "first viable alternative."

According to Neil Smith, Flexsys' Chief Technology and Sustainability Officer, the company began its research program in 2021 with several criteria established from the outset. The new chemical needed to have a better environmental and human-health safety profile than 6PPD and, ideally, should not belong to the p-phenylenediamine (PPD) family or generate quinones during use.

Notably, Flexsys has yet to disclose the candidate's specific chemical structure or molecular name.

Speaking to Chemical & Engineering News (C&EN), Smith said the company understood that, before a new chemical could be deployed on a large scale, the industry and regulators would need access to comprehensive information on its structure, performance, toxicity and transformation products.

Flexsys has so far confirmed only that the compound is not a PPD and does not form quinones during use. Another notable feature is that the candidate relies on many of the same chemical intermediates used in the current 6PPD manufacturing process. If its performance is confirmed, this approach could allow manufacturers to make use of existing production infrastructure, limit capital investment and shorten the industry's transition period.

More than one contender in the race

Flexsys is not the only company pursuing a 6PPD replacement. Tire and chemical manufacturers are exploring several approaches, ranging from complete substitution to reducing the amount of 6PPD required.

In the United States, the U.S. Tire Manufacturers Association (USTMA) is leading a program to evaluate potential alternatives. The initiative initially screened dozens of compounds before narrowing the field to 19 PPD molecules and 24 non-PPD molecules, based on data on antiozonant performance and hazard profiles from various sources, including the European Chemicals Agency (ECHA).

USTMA subsequently selected seven candidates for further evaluation and worked with the U.S. Geological Survey (USGS) to conduct toxicity testing on some of the most promising compounds. Flexsys' candidate is not included in this group.

In Germany, Lanxess is researching CCPD (N,N'-dicyclohexyl-p-phenylenediamine), representing another approach in the search for a replacement.

Japan's Asahi Kasei, meanwhile, is pursuing a mitigation strategy rather than complete replacement. The company has developed high-styrene butadiene rubber (HSBR), a synthetic rubber that could reduce the amount of 6PPD required in tire formulations. This could serve as an interim solution while the industry continues searching for a complete replacement.

Flexsys has also previously collaborated with the Agricultural Research Service of the U.S. Department of Agriculture (USDA-ARS), beginning in 2023, to investigate bio-based antioxidants.

The biggest challenge is proving both performance and safety

Flexsys says its testing results are "on track" to meet the initial targets, including short- and long-term tire protection, minimal changes to existing rubber formulations and compliance with the alternative-chemical assessment criteria developed by the Washington State Department of Ecology.

However, much of the evidence currently available comes from company testing combined with work by selected independent laboratories and industry partners. It has not yet developed into a comprehensive body of evidence that has been widely published and independently assessed through peer review.
For a chemical potentially destined for use across virtually the entire global tire industry, proving performance in the laboratory is only part of the challenge. Researchers and regulators must also determine what the chemical breaks down into, how long those substances persist in the environment and whether they pose risks to aquatic organisms or other species.

USTMA has also highlighted another complicating factor: tire-wear particles found in the environment do not originate entirely from tires. According to the association, roughly half of their mass may come from road surfaces. This makes it more difficult to determine precisely what these particles contain and how pollutants are formed under real-world environmental conditions.

Even so, debate over the relative contribution of tires and road surfaces does not diminish the pressure to develop safer alternatives.

From the laboratory to the market is still a long journey

The challenge facing the tire industry is not a lack of ideas. Numerous compounds have already been identified and are undergoing evaluation for performance, toxicity and manufacturability.

The difficulty is that 6PPD has become a critical component of the global tire supply chain. Any successful replacement will have to meet multiple requirements simultaneously: protect tires effectively, avoid generating hazardous transformation products, work with existing rubber formulations, be manufactured at scale and avoid pushing tire costs significantly higher.

For that reason, a company's announcement of a "viable candidate" is only an initial step. Independent testing, environmental and toxicity assessments, real-world durability trials, regulatory approval and, ultimately, large-scale production could all take years.

The search for a 6PPD replacement is therefore entering a critical phase: moving from identifying promising molecules to proving that one of them can actually replace a chemical that the tire industry has relied on for half a century.

With a global market estimated at around $1 billion a year and potentially far-reaching implications for the entire tire value chain, this is not merely a race to develop a new chemical. It is also a test of manufacturing technology, cost competitiveness and the industry's ability to transition to a safer alternative.

Source:
1. Chemical & Engineering News (C&EN), "Candidate antiozone molecules to replace salmon-killing 6PPD-quinone in tires are emerging, but development will still take years," 8/2026.
2. Chemical & Engineering News (C&EN), "Nov. 25 Business Watch: Flexsys readies safer tire additive," 25/11/2025.
3. Flexsys, thông cáo báo chí "Flexsys Announces It Has Developed the World's First Viable Alternative to 6PPD for Use in Tires," 18/11/2025.
4. European Rubber Journal, "Flexsys unveils 'world-first' 6PPD alternative for tire rubber," 21/11/2025.
5. Rubber News, "Flexsys to work with USDA to look for 6ppd alternatives," 7/2023.
6. Encyclopedia of Puget Sound, "Players in the race for 6PPD alternatives," 6/2026.