Flexsys has narrowed its search for a replacement for 6PPD to two final candidate molecules and entered a Cooperative Research and Development Agreement with the U.S. Geological Survey for independent aquatic toxicity testing. The company says both candidates are outside the PPD chemical family, do not form quinone transformation products during use and have met internal and external targets for tire performance, scalability, safety and environmental sustainability. The USGS will now conduct independent testing on the candidates and their transformation products, including effects on Pacific salmon and other aquatic species. Flexsys says the program has moved beyond identifying possible substitutes and is now focused on final validation, regulatory approval, manufacturing scale-up and tire industry adoption. The company is also optimizing process chemistry so that the eventual replacement can be produced using much of the existing intermediate chemistry and manufacturing infrastructure currently used for 6PPD, potentially reducing investment requirements and accelerating commercialization.

Two candidates remain after screening program

Flexsys said it has completed the screening phase of its 6PPD replacement program and selected two molecules for expanded evaluation. The development follows the company’s November 2025 announcement that it had identified what it described as the first viable alternative to 6PPD for tire applications.

Both remaining candidates fall outside the PPD chemical family. According to Flexsys, neither forms a quinone transformation product during use, and both have met the company’s performance, safety and environmental benchmarks during testing conducted internally and with external industry partners.

USGS to conduct independent aquatic toxicity testing

Flexsys has signed a Cooperative Research and Development Agreement with the U.S. Geological Survey to independently assess the potential effects of the two candidates on aquatic life.

The work will involve the USGS Western Fisheries Research Center, supported by the California Water Science Center and Columbia Environmental Research Center. Researchers will examine the candidate molecules and their transformation products for potential effects on Pacific salmon and other aquatic species.

Research will go beyond standard chemical registration testing

Flexsys said the testing program is intended to go beyond the level typically required for registration of a new chemical. USGS scientists will use both existing and newly developed methodologies to build a broader aquatic toxicity profile for the candidates.

The agreement builds on research already underway between Flexsys and USGS scientists and formalizes expanded testing. It also follows a separate 2023 research agreement between Flexsys and the U.S. Department of Agriculture’s Agricultural Research Service.

New methods could support wider chemical toxicity assessment

The USGS work will include development of cell-line-based approaches for aquatic toxicity assessment. Flexsys said these methods could ultimately be applicable not only to 6PPD alternatives but also to evaluation of other chemicals.

Independent testing is particularly important because any replacement for 6PPD must satisfy both the technical requirements of tire manufacturers and concerns from regulators, environmental organizations, tribes and other stakeholders regarding potential effects on aquatic ecosystems.

6PPD replacement must maintain tire performance

6PPD is an antidegradant used in tire compounds to protect rubber against degradation caused by ozone and oxidation. Any replacement must therefore provide comparable protection over a tire’s service life without introducing unacceptable safety, environmental or processing issues.

Flexsys said its remaining candidates continue to meet targets for in-rubber performance alongside toxicity, environmental sustainability and manufacturing scalability. Selecting a replacement therefore requires balancing environmental characteristics with the demanding durability and safety requirements of tire compounds.

Scale-up becomes next major challenge

With candidate identification largely complete, Flexsys says its development program is increasingly focused on process optimization and manufacturing scale-up. The company is refining the chemistry needed to manufacture both candidate molecules efficiently at world-scale volumes.

This stage is particularly important for a chemical used throughout global tire manufacturing, where even a technically successful substitute must be available in sufficient quantities, at suitable cost and with consistent quality before widespread adoption becomes practical.

Existing chemical infrastructure could support faster adoption

Flexsys said both candidate molecules use substantially the same intermediate chemistry currently employed in 6PPD production. This could allow existing manufacturing assets to be adapted rather than requiring entirely new chemical production infrastructure.

The company views this compatibility as an important advantage because it could lower capital requirements, simplify industrial scale-up and allow tire manufacturers and chemical suppliers to transition more quickly once a final molecule is selected and regulatory approvals are obtained.

Regulatory approvals still required globally

Flexsys is working with regulatory authorities in multiple jurisdictions while testing continues. Even after a final candidate is selected, commercial introduction will depend on completion of required chemical registrations, safety reviews and other approvals.

Tire manufacturers will also need to qualify the new antidegradant in their own compounds and products before broad commercial use. This means the transition from candidate selection to widespread tire production is expected to involve additional technical testing and validation.

Intellectual property could shape commercialization

The move from laboratory development to industrial-scale production also introduces commercial and intellectual property considerations. A successful replacement for a widely used tire additive such as 6PPD could require substantial investment in manufacturing, qualification and global regulatory approvals, increasing the importance of patent protection and licensing strategies.

Industry adoption will therefore depend not only on whether the chemistry performs successfully but also on whether production can be scaled economically and whether manufacturers can secure reliable access to the technology and material under commercially workable terms.

Flexsys shifts focus toward final selection and market adoption

Flexsys Chief Executive Officer Carl Brech said the program has progressed from searching for a viable replacement toward validation, regulatory approval, scale-up and adoption. Chief Technology and Sustainability Officer Neil Smith said the final molecule must remain reliable and safe over the long term while also meeting practical manufacturing requirements.

The company has not yet announced which of the two candidates will ultimately replace 6PPD or when commercial volumes could become available. The results of independent USGS toxicity testing, continued tire performance evaluation and manufacturing scale-up work will be important factors in the final selection.

Original announcement by Flexsys via PR Newswire.