Flexsys to work with USDA to look for 6ppd alternatives

AKRON—The 6ppd and 6ppd-quinone conundrum has not changed: How does the tire industry come up with a way to replace the essential chemical 6ppd with an environmentally friendly filler that continues to provide tire safety for consumers?

Flexsys America L.P. is partnering with the U.S. Department of Agriculture in the effort, as the Northeast Ohio chemical supplier explores potential bio-based alternatives for 6-para-phenylene-diamine.

The issue has become especially pressing, as the California Department of Toxic Substances, under the auspices of the California EPA, approved tires containing 6ppd as "priority products" earlier this year.

And on July 1, the rulemaking documents concerning 6ppd alternatives took effect with the California Office of Administrative Law, a CDTS spokesperson told Rubber News July 11.

"Within 60 days of this date of the regulation, anyone who manufactures motor vehicle tires containing 6ppd for sale in California must submit a 'Priority Product Notification' and determine how they will choose to comply with the Safer Consumer Products requirements," Russ Edmondson, director of media relations for the DTSC, told Rubber News.

Flexsys said it is doing everything it can to assist in what has become a global issue.

"We are maximizing our efforts to bring the right scientists and researchers together to explore possible molecular structures to protect tires, people and the environment," said Neil Smith, Flexsys chief technology and sustainability officer.

The chemical 6ppd is an antidegradant used in tire manufacturing that prevents breakdown and cracking due to oxygen and ozone exposure, as well as from wide temperature swings.

By design, 6ppd migrates to the tire surface during use to create a protective film against degradation.

However, 6ppd can morph into 6ppd-quinone as tires wear, and tire road wear particles (TRWP) containing 6ppd-quinone have found their way into the waterways of the Pacific Northwest.

The U.S. Tire Manufacturers Association, which has supported state and federal research into 6ppd alternatives and 6ppd-quinone, has cautioned that TRWPs contain 50 percent tire tread and 50 percent road surface—so, in many ways, the USTMA believes, the jury still is out on how 6ppd-quinone forms.

Regardless, in the urban streams and creeks of the Pacific Northwest, 6ppd-quinone has proven fatal to coho salmon—a fish that is key to Native American culture.

And the studies make Flexsys' collaboration and exploration of a bio-based 6ppd replacement a critical undertaking.

Flexsys will work with the U.S. Department of Agriculture's Agricultural Research Service on fundamental chemistry, bio-based materials and applications testing, the chemical supplier said.

Very little basic research has been performed in the past 50 years on 6ppd alternatives, as the troublesome and transformational chemical 6ppd-quinone had not been identified until three years ago.

Therefore, there are no known, commercially viable replacements "that exhibit equivalent or better passenger safety, tire performance and anti-degradation properties," according to Flexsys.

"While the problem of replacing 6ppd is challenging, it also represents an exciting opportunity to develop urgently needed bio-based antidegradants for tires," said Colleen McMahan, a research chemist at the U.S. Department of Agriculture's ARS bioproduct research unit in Albany, Calif.

Here, she said, computational and laboratory expertise will be implemented to develop bio-based and bio-degradable chemicals, including a replacement for 6ppd.

The first hurdle is to develop an understanding of the basic science, lab-level identification, synthesis and evaluation of the 6ppd molecule, McMahan said.

The California Department of Toxic Substances Control finalized its listing of motor vehicle tires that contain 6ppd as "priority products" in the first quarter of this year.

Public comments have been received and evaluated, and the rulemaking documents have been completed.

The California Office of Administrative Law approved them July 1.

For the USTMA, the scope of possible alternatives for 6ppd include a "drop-in replacement;" a redesign of the product to reduce exposure; a reduction in the use of the chemical; or infrastructure mitigation measures.

But issues around tire wear are now topping the agenda of the tire manufacturing industry across the world, with great effort among leading players and industry bodies to establish standardized measurement protocols to guide future regulation in this increasingly critical area.

While much of the attention is on quantifying the rubber "dust" and TRWPs generated by abrasion on road surfaces, and how driving behavior affects this, another topic—toxicity—could soon take center stage.

According to Nick Molden, founder and CEO of United Kingdom-based Emissions Analytics, each car generates 4 kilograms per year (about 8.8 pounds) of abraded rubber, equivalent to 6 million metric tons per annum globally.

The nearly three-year-old Tian et al. study (December 2020) is the root motivation for the process that put 6ppd in the crosshairs of the California Environmental Protection Agency, which oversees the DTCS.

"While heavy metals and polycyclic aromatic hydrocarbons have long been regulated pollutants in stormwater, recent studies have reported numerous emerging organic contaminants such as various pesticides, pharmaceuticals, plasticizers, and vehicle and tire rubber-related contaminants," the Tian study states.

Calling it "stormwater-linked urban runoff mortality syndrome," death rates for coho salmon across Pacific Northwest sub-basins correlated with road density and traffic intensity, according to the study.

The academic researchers ultimately used juvenile coho salmon provided by the Puyallup Tribe of Indians to conduct the "in-house" studies.

Five outdoor sites were used, with two roadway runoff sites measured in Seattle and one in Los Angeles; and one site "receiving water" in Seattle (Puget Sound) and another in San Francisco.

In specific northern California areas, coho salmon are declining to a fraction of what they were at their peak in the 1960s, at around 55,000 "new individuals" per year counted through fish ladders in the Pacific Northwest.