There is no observable difference between pure Hevea and blends with up to 40 percent guayule, she said. “Adding curatives to 50-50 blends creates continuity with 100 percent Hevea,” Tardiff said.
Concurrent with its guayule research, Ford is experimenting with using eggshells as a partial replacement for carbon black, she noted. Eggshells can replace up to 20 percent of the carbon black in a tire, Tardiff said.
Next, Ford plans to test the dynamic properties of guayule and work with the firm's auto parts suppliers so that they can provide prototype guayule auto parts, she said.
Zachary Walters, an engineer in the Innovative Technology Department of Cooper's Global Technical Center, spoke of Cooper's continuing research into the use of guayule rubber in tires.
“Guayule can completely replace Hevea and synthetic rubber in most tire areas,” he said, though he added that the impact of strain-induced crystallization in the bead and sidewall areas still is being studied.
Cooper is the leader of the five-year, $6.9 million Biomass Research and Development Initiative funded by the departments of Agriculture and Energy. The goal of the BRDI is to assess the feasibility of guayule rubber as an ingredient in commercially produced tires.
Cooper Senior Scientist Howard Colvin presented a paper on BRDI's progress at the International Tire Exhibition & Conference in Akron in September, and Walters' paper was an update on that research as it relates to guayule's performance in various parts of a tire.
“We have been testing guayule in one tire component at a time,” Walters said. “In the end, we will put everything together to have an all-guayule concept tire by 2017.”
The last all-natural-rubber tire was built in the 1940s, and the obvious differences between tire construction then and now makes it an enormous challenge to make an all-guayule tire that meets modern performance standards, he said.
There are minimal cure differences between guayule and Hevea, though additional specifications are necessary for guayule because of its higher resin content, according to Walters.
The dynamic and static properties of guayule/Hevea and SR/Hevea compounds are markedly different, he said.
“There's a reason we use synthetic rubber in tires,” he said.
In most areas, including bead and filler assembly, body plies, belt coatings, sidewalls, rim cushions and tread caps/bases, guayule passed all relevant tests, including high speed, endurance and bead unseating, according to Walters. It also passed Cooper's proprietary endurance and aging/oxidation tests, he said.
The only problem area for guayule was in innerliners, with the strict requirement to maintain inflation pressure, he said.
“It's challenging to make innerliners without halobutyl, especially because of permeability,” he said. “Factory processing is a challenge when you replace synthetic rubber with guayule.”
On the other hand, guayule had a lower mixing time than Hevea or SR in all areas, Walters said.
“A 10 percent energy savings on each batch would be a huge savings,” he said.