"There is a want from customers to use sustainable materials, and this proves a challenging environment for us to keep an advantage over our competitors. Sustainability has come into focus as a key thing customers are looking for."
Rolling resistance, wet and dry performance (in the snow, sun and rain) and treadwear form the "performance triangle" for tire makers, and in the past increasing one meant weakening another.
Through compounding and modifications, Goodyear has seen success with petroleum-based oils such as distillate aromatic oils and medium extracted solvates (heavy naphthenic oils), but there always has been a trade-off.
DAEs provided excellent compatibility with tire compounds, however the environmental impact was significant. Goodyear phased out the use of these oils years ago, according to Woloszynek.
Medium extracted solvates then replaced DAE oils, but are less compatible with tire compounds.
"As we move to high performance materials, with higher levels of fillers and higher surface levels, these are often more difficult to process," Woloszynek said. "Expanding the performance triangle requires new technology that we need to account for."
Since the key focus is to reduce petroleum-based oils, driven by demands for sustainability and fuel efficiency, Goodyear has found soybean oil to be "domestic, abundant and renewable" and possess the key attributes of naphthenic oils, such as thermal stability and compatibility with rubber compounds.
"It is a renewable resource, compound adjustments are possible and various grades are available," Woloszynek said. "This is a growing trend with one of the lowest environmental impacts for raw materials in industrial-use applications."
Specifically, he noted that soybean oil possesses better miscibility with SSBR compared to naphthenic oils, as soybean oil is a better plasticiser with the same viscosity.
"This means better manufacturing capacity and a reduction in the energy needed in overall production," he said. "A lower amount of soybean oil (roughly half) is required to provide the same level of extension. And there is no penalty in terms of processing."
In addition, soybean oil has a very low Tg, or glass transition temperature, remaining softer at lower temperatures than naphthenic oils. While petroleum oils transition at about -50°C , soybean shifts this Tg to about -90°C.
Soybean oil is not entirely a polymer pollyanna, however, as Woloszynek said that improvements in one corner of the performance triangle still can come at the expense of another.
"Soybean oil is good for wet traction, compounded with high styrene and high vinyl, but it took a hit in treadwear when we improved the others," he said. "We can adjust by compounding and we are able to balance the properties and in many cases see an improvement in performance."
The novel soybean oil extended polymer was developed into an industrialised material in Akron, and Goodyear's chemical operations business supplies synthetic elastomers, latex products, antioxidants and isoprene monomers around the globe.
The tire maker's emulsion plants in Houston and Beaumont, Texas, provide 1 billion pounds of synthetic rubber annually for both tire and non-tire applications, Woloszynek said.
So how is Goodyear leveraging soybean oil to give the proper performance in these spaces?
"With petroleum oils, stiffness goes up as temperature goes down – it's why your sports car gets no traction in the winter," he said.
"The key is to acquire lower stiffness across the entire temperature range, and soybean oil is softer at lower temperatures."
And this is one crux of the problem, Woloszynek said, perhaps the toughest trade-off – getting both wet and snow performance at the same time.
"We have a lot of levers we can pull with soybean oil," he said. "Soybean oil allows a compound to remain flexible across a broad temperature range, improving the balance of wet and snow traction."
Such benefits have found their way to the commercial front lines for Goodyear, as soybean oil has replaced petroleum oil entirely in the company's popular Assurance WeatherReady tire, introduced in 2017.
"We have replaced petroleum oil 100% with soybean oil, which has provided a 60% overall reduction in petroleum products," Woloszynek said.
The achievement earned Goodyear the Environmental Achievement of the Year from Tire Technology International in 2018.