From Shrub to Rubber
Rubber is usually thought of as a substance made from petroleum or from rubber trees grown in Asia. But rubber can be also produced from a U.S. domestic plant called guayule. Guayule is a woody desert shrub cultivated in the southwestern United States as a source of natural rubber (latex), organic resins, and high-energy biofuel feedstock from crop residue.
ARS chemist Colleen McMahan and her lab colleagues, molecular biologists Grisel Ponciano, Niu Dong, and Dante Placido, and technician Trinh Huynh, in Albany, California, developed improved guayule for rubber production. In 2017, about 3,200 experimental guayule plants were delivered to Bridgestone Americas in Eloy, Arizona, for field testing.
“About 3 years ago, Bridgestone purchased 180 acres in Arizona and set up a state-of-the-art facility dedicated to developing guayule as a U.S. source of natural rubber,” says McMahan. At that time, Bridgestone Americas and ARS’s Bioproducts Research Unit entered into a research agreement to evaluate ARS genetically modified guayule that might provide increased yield.
“The genetic modification dramatically increased rubber content in the lab, and in partnership with Bridgestone, we will test if that translates to field conditions,” says McMahan.
This research technology demonstrated that a modern passenger tire can be made from U.S.-grown guayule natural rubber. Another partner, Cooper Tires, manufactured a demo tire, according to McMahan. In 2017, the group completed work under a 5-year USDA National Institute of Food and Agriculture (NIFA) awarded grant which was led by Cooper Tires, with significant ARS involvement.
“ARS did genome sequencing for guayule, rubber biochemistry studies, and agronomics work, including a major irrigation study,” says McMahan. “In 2017, another NIFA grant was awarded for work on guayule and guar. This one, led by the University of Arizona, is just starting. ARS scientists in Maricopa, Arizona, will be doing germplasm phenotyping, and our lab will be doing crop improvement.”
The tires have passed testing required by the U.S. Department of Transportation and more stringent internal industry tests. Guayule-rubber tires, with exceptional performance, have been established as meeting consumer requirements for a biobased rubber tire.
“Unfortunately, the supply of guayule-derived rubber is still limited, and we continue to focus on improving the yield of rubber from guayule and on sustainability,” says McMahan. “You need about 4 mature plants to yield enough rubber for a passenger tire, so with current yields, you can get about 500 guayule tires per acre. Both of those figures assume 100-percent guayule tires, which is unlikely. Commercialization would probably proceed with a lower percentage of guayule, which could get 1,000 tires per acre.”
Each of these sectors of bioproducing—food, fuel, and rubber products—aims to improve consumers’ future by adding healthy foods and reducing our dependence on petroleum.—By Sharon Durham, ARS Office of Communications.