If you watched the 2022 Indy Car Music City Grand Prix, you might have noticed—between the multitude of crashes, that is—cars running Firestone tires with green stripes. The green denotes the use of guayule (pronounced why-YOU-lay) rubber in the sidewalls—a type of natural rubber extracted from a scrubby shrub in the Arizona desert. While not as argument-worthy as push-to-pass or as entertaining as Music City's eight collisions, there is an interesting story here—one that could be transformative for both Bridgestone (Firestone's parent company) and American farmers.
Today's tires are made from both natural and synthetic rubber, and it's the former that makes guayule such a big deal. Right now, most natural rubber comes from trees in southeast Asia, where it's subject to all sorts of issues: Political instability, natural predators, disease, farmers switching to less labor-intensive (and therefore cheaper) crops, plus the fact that the rain forests in which the rubber trees grow are shrinking. That's scary prospect for tire companies: Bridgestone alone uses well over a million tons of natural rubber per year, representing about a quarter of its raw-material purchases.
Why not switch entirely to synthetic rubber? First, because synthetic is a petroleum-based product, and second, because it doesn't have the strength of natural rubber, which is critical for high-stress tires for trucks, aircraft and racing cars. As Bill Naiura, Bridgstone's chief engineer for advanced and sustainable materials—the guayule project is his baby—puts it, "Nature is a better chemist than we are."
What Bridgestone wants is a more stable source of natural rubber, and they're established a research farm in Eloy, Ariz., midway between Phoenix and Tucson, to experiment with guayule as a possible answer. Guayule is a less labor-intensive crop than hevea brasiliensis (otherwise known as the rubber tree) and, more importantly, it can be farmed much closer to home, specifically in the deserts of Arizona, Texas, and northern Mexico.
Wait, wait—farming in Arizona? Yes, this is a thing, though one that gets more tenuous each year. Ever-intensifying water restrictions in Arizona are making farming more difficult, and that's another advantage in guayule's favor: It uses half as much water as Arizona crops like cotton and alfalfa, and Bridgestone's agricultural engineers are working on ways to grow it with significantly less. Guayule also has a different nutrient profile than other crops, so it's hard to over-farm—it can be grown continuously, or in a field normally used for other crops that would otherwise be lying fallow.
Bridgestone brought us out to their research farm, called Agro Operations, where a small team has spent just shy of a decade experimenting with guayule. Their goal is not only to find the best and most cost-effective way to grow and harvest guayule, but to develop the genetics of the plant to increase the rubber yield. The effort has expanded to include local farmers working under contract, who are pleased to have a low-water cash crop with a ready-made buyer.
Gathering guayule rubber is less labor-intensive than traditional rubber trees. Havea trees are planted and must grow for six years before they can be tapped; a specialist cuts the bark and the latex drips into pails, which are collected every two days. The trees have a lifespan of about 20 years (if pests and disease don't get them first), then must be cut down and re-grown.
Guayule is planted and left to grow for two years; they accumulate rubber in their bark as a stress response to cold, so it takes two winter chills (relatively speaking; we're talking about Arizona) to get sufficient rubber. After two years, the plants are harvested by cutting them right down to the soil; they'll be re-grown for another two years, cut again, then re-grown for another two. The third time they are harvested roots and all, and new seeds are planted to begin the cycle over again.
But farming guayle isn't as simple as it might appear: Bridgestone has had to engineer entirely new equipment to harvest it and gather seeds. Russ Prock, Operations Manager Agro Operations, has Frankensteined a variety of farm equipment for the purpose. One machine uses air to pull seeds from mature plants, while another employs a horror-movie array of saw blades to cut the plants. A specially modified baler gathers the plants into roughly 750-pound bales. On the side of the baler is a sticker that reads "GUAYULE WINS". "That slogan isn't just about racing," Prock told us. "It's also a reminder that guayule will tear up any farm equipment it goes through."
Extraction of the rubber isn't exactly straightforward, either, so Bridgestone has built another experimental facility—Bio-Rubber PRC, southeast of Phoenix—to develop that process. Here, the guayule bales harvested at Agro Operations are shredded, and a chemical process uses solvents to remove the rubber from the chopped-up plants. One of the niftiest things about guayule is that the rubber itself is chemically identical to havea rubber, to the degree that Bridgestone's tire factories can use havea and guayule rubber interchangeably.
Tire rubber isn't the only product that can be sourced from guayule. Along with rubber, guayule yields resins that are useful for pesticides, marine anti-fouling paint, and adhesives. It also produces hypoallergenic latex, which gives it high value in the medical industry (high enough, in fact, that such use might be more profitable than tires). The organic material with its rubber extracted, called begasse, can be used as a low-carbon fuel for power plants.
Guayule tires are not new—Henry Ford used them early on for the Model T—but their rebirth is going slowly. For now, Bridgestone has only built a few experimental run of truck and bus tires as well as the racing tires we saw at the Music City Grand Prix, which was the first time they were run at heat and speed in a competitive situation.
Even if the guayule tire experiments are successful—and profitable—chances are we won't see much of them in passenger-car tires, which lead a relatively low-stress life and can primarily be made from synthetic rubber. And no, guayule isn't likely to replace synthetics; tire engineers need the precise control they can exercise over synthetic rubber to engineer the best-possible grip surfaces.
Really, guayule is all about providing a cheaper and steadier source of natural rubber for Bridgestone, as well as a profit path to licensing or producing it for other tire manufacturers. Still, the potential for moving production of natural rubber to the United States, in the form of a flexible and drought-tolerant crop, is good news for American farmers and the American economy. Too bad it can't do much for those crashes at the Music City Grand Prix.
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