Guayule rolling toward use in mass production

Akron, Ohio – Guayule rubber is passing all its physical tests with one year to go in a government-funded project to assess its feasibility as an ingredient in mass-produced tires, according to Howard Colvin, senior scientist at Cooper Tire & Rubber Co.

Colvin discussed Cooper's test results with prototype guayule rubber tires at the International Tire Exhibition & Conference in Akron 13-15 Sept.

Cooper is the leader of the five-year, $6.9 million Biomass Research and Development Initiative grant programme funded by the departments of Agriculture and Energy, according to Colvin.

The company's current partners in guayule research, Colvin said, include the Agricultural Research Service of the US Department of Agriculture; guayule development company PanAridus LLC.; and Cornell and Clemson universities.

Each of these entities is researching different aspects of the guayule commercialisation issue, according to Colvin. The objectives of BRDI are:

To develop genomic and agronomic tools to improve the rubber and biomass yield of guayule;

To develop technology to produce tire-grade guayule rubber;

To develop a concept tire using guayule or guayule-derived elastomers and compare it with a broadline control tire;

To utilise guayule crop residue as an energy source; and

To conduct a sustainability analysis to direct the future development of guayule.

“The idea is to provide tools to farmers to profitably grow guayule while providing the tire industry with a reliable source of raw material that benefits society economically, socially and environmentally,” Colvin said.

Guayule rubber is essentially Cis-1,4 polyisoprene, the same as Hevea rubber, he said.

But guayule rubber has much less gel content that Hevea, and its non-rubber content is primarily terpenes and terpenoids, whereas Hevea's non-rubber content is mostly proteins, he said.

Whereas Hevea rubber is highly allergenic to certain populations, guayule rubber is non-allergenic, Colvin said.

While guayule rubber is very similar to Hevea rubber, its differences present challenges in compounding, especially because each tire component requires a different formulation, he said.

“Tire Testing 101” consists of road testing, track testing and noise testing, Colvin said. There are high-speed, endurance, oxidative/ozone resistance and rolling resistance wheel tests, as well as tests for tire parameters including inflation pressure, load, speed and aging, he said.

Testing all portions of a tire, both pure guayule and guayule/synthetic rubber blends, passed all mandated government safety tests as well as Cooper's more stringent in-house testing, according to Colvin.

However, the guayule/synthetic blend performed best in Cooper's proprietary endurance testing, he said.

In rolling resistance testing, both the guayule and guayule/synthetic blend tires performed similarly to the control tire, Colvin said.

He said all of the challenges of compounding guayule rubber for use in tires have been overcome.

“Guayule can completely replace synthetic rubber and Hevea rubber in most areas of a tire,” he said. “That's not the same as saying it makes sense to do so. But it's a perfect fit in some areas.”

The BRDI programme is on schedule for completion of the final grant report in mid-2017, according to Colvin. Another paper from Cooper—on the economic aspects of using guayule rubber to build tires—is scheduled to be presented at the ACS Rubber Division's meeting in Pittsburgh 10-13 Oct he said.