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US company Flexsys has narrowed its search for a tyre additive to replace 6PPD to two candidate molecules, after completing an initial screening programme. The Ohio-based tyre additives producer said both substances will undergo further testing before it makes a final selection.
The move gives tyre makers a clearer view of potential replacements, but regulatory acceptance and scale-up remain key hurdles before any switch from 6PPD.
N-(1,3-dimethylbutyl)-n'-phenyl-p-phenylenediamine (6PPD) is facing growing regulatory scrutiny after coho salmon deaths were linked to runoff contaminated by its oxidation byproduct, 6PPD-quinone. Last November, Flexsys said it had identified a potential replacement based on chemistry outside the PPD family.
In a 27 August press release, the company said both shortlisted molecules had met its safety, performance and environmental criteria in internal testing and work with industry partners. Flexsys has also signed an agreement with the US Geological Survey (USGS), which will independently assess the candidates' potential effects on aquatic life.
Any replacement must meet technical and environmental requirements, while also being made from readily available raw materials and produced economically at commercial scale, the company said.
Neil Smith, chief technology and sustainability officer with Flexsys, told Chemical Watch News & Insight that the company remains on track to begin commercial production of a 6PPD alternative in late 2030 or early 2031. "Our work aligns with the 2035 date that has been proposed to phase out 6PPD in tyres," he said.
Regulatory focus
As scrutiny of 6PPD intensifies, Flexsys said it is working with regulators including Washington state's Department of Ecology (Ecology), California's Department of Toxic Substances Control (DTSC), the US EPA and similar regional agencies, EU REACH authorities and Environment and Climate Change Canada (ECCC).
The company said engagement with regulators and government agencies is intended to support independent assessment of potential alternatives. "We recognise that any truly viable alternative will require global regulatory approval for production and use in tyres, and coordination with regulators is critical to achieve this," said Smith.
The announcement comes as scientists examine whether replacement chemicals could pose similar environmental risks to 6PPD. In an August bulletin, Ecology said researchers at the USGS Western Fisheries Research Center (WFRC) had launched studies to support efforts to identify safer tyre additives.
One project will examine whether chemicals derived from alternative PPDs, including 7PPD, 77PD and IPPD, affect coho salmon and coastal cutthroat trout in similar ways. The findings are expected to show whether these substances pose risks comparable with 6PPD and whether they offer meaningful environmental advantages.
CCPD option
Speciality chemicals company Lanxess is developing its own 6PPD alternative, focusing on a tyre anti-ageing additive containing n,n’-dicyclohexyl-1,4-phenylenediamine (CCPD).
In an 8 September press release, the German company announced the launch of Vulkanox 4060, its CCPD-based product. Lanxess said environmental studies so far found that CCPD quinone, the breakdown product formed from CCPD, showed no acute effects in coho salmon, unlike 6PPD quinone (6PPDQ).
Following the recent completion of its REACH registration, Vulkanox 4060 has been approved for use in the EU. Lanxess expects commercial production to begin later this year.