There’s still a lot of petroleum hanging onto electric cars, specifically around the rims. It takes about seven gallons of oil to make each standard car tire, and the world produces more than 2 billion tires every year. Now, some tire companies are turning to a desert shrub and a novel means of pulling natural rubber compounds out of it.
Bridgestone Americas has been working with guayule (Parthenium argentatum) since 2012. The tire company broke ground on a research facility in Mesa, Arizona, in 2012, started evaluating sample tires in 2015, and received multiple grants from the US Departments of Agriculture (USDA) and Energy for its research and molecular breeding work. Just last month, the company committed another $42 million to expanding its harvesting partnerships, with 350 acres in the short term and 250,000 more planned. That’s part of more than $100 million invested into guayule-based rubber, the company says.
“With guayule, we can reduce the environmental impacts that come with overseas sourcing while also realizing a more sustainable agricultural system for parts of this country that are facing persistent and worsening climate conditions, so it’s really something with many benefits for our environment and our economy,” said Nizar Trigui, chief technology officer for Bridgestone Americas, in a press release.
The US and its industries have looked into plant-based rubber supplies before, primarily in the early 1900s, during World War II shipping blockades, and when oil prices have risen so high as to make major manufacturers curious. Revolutions in synthetic petroleum-based rubber put an end to those avenues, although natural rubber is still 10–30 percent of a tire’s composition. Bridgestone, citing environmental goals, aims to get all-natural tires into the mainstream.
It helps that the rubber that comes from guayule is not some weaker, paper-straw alternative—it generally makes a better tire, especially in heavy-load applications like large trucks, airplanes, and race tires. Bridgestone’s Firestone brand debuted sustainable tires at a pre-Indy 500 pit stop challenge, and they were an alternate offering at a Nashville street race in August. Bridgestone tested its guayule-derived tires for over a year on Indy cars and found it provided “similar or better performance” than traditional race tires.
Natural rubber works better for high-stress tires due to properties in its polymer chain. When those chains are pulled under heavy load, they align, allowing reinforcing microcrystalline structures to form, according to Chemical & Engineering News.
Another boon for small-plant rubber is that while petroleum, and Pará rubber trees, are inconsistent rubber sources from often far-away locations, guayule wants to grow wherever it can and turn into strong, hypoallergenic rubber—with work. It’s a short, woody shrub that grows in dry areas of the Southwestern US and northern Mexico. Its bark cells contain latex, which prevent it from drying out, whereas rubber trees typically contain latex in long inner tubes. Guayule can grow with as little as half the water required for cotton or alfalfa, can be harvested with traditional crop equipment, and typically requires few or no pesticides.
The latex in guayule’s bark won’t come out easily, however. Organic solvents can dissolve latex from other plant material, creating a hard rubber mass ready for tires. An aqueous process, developed at the USDA’s Agricultural Research Service (ARS), runs plants through a centrifuge in an alkali solution, letting the rubber particles rise to the top in a latex emulsion, perfect for gloves, balloons, and other dipped latex products.
Other companies have made use of guayule rubber’s unique properties. Yulex, based in San Diego, capitalizes on the lighter, more flexible rubber produced by guayule, and the lack of allergy-trigger latex proteins, to make wetsuits, activewear, and other products.