Domestic, alternative NR critical to U.S. economy, security

AKRON—It's no secret the U.S. needs to establish a domestic, alternative source of natural rubber. And Katrina Cornish says this needed to happen yesterday.

"If you don't have natural rubber, you've got nothing," Cornish, endowed chair and Ohio research scholar in bio-emergent materials at Ohio State University, said during the first day of the International Tire Exhibition & Conference, held Sept. 13-15 in Akron.

In her presentation, "Sustainable Domestic Alternatives to Hevea and Synthetic Rubbers," Cornish emphasized just how critical it is for the U.S. to have a domestic, alternative source of natural rubber.

The world uses about 14 million tons of natural rubber per year in more than 50,000 different products. And without such a critical material, she said, the U.S. economy and defense would collapse.

And with today's global supply chain disruptions, China's control of about 80 percent of global production and the risk of tree diseases, she said, it's important now more than ever to establish a reliable source of natural rubber in the country—before a potential collapse of the hevea crop.

"The U.S. is terribly reactive," she said.

And while the supply chain woes that emerged because of the COVID-19 pandemic have made the U.S.—and the rubber industry—more proactive with material supplies, there's a heightened sense of urgency with natural rubber.

One of the biggest challenges with a reliance on hevea natural rubber (HNR), she said, is that the hevea tree is monoclonal and therefore lacks biological and geographical diversity.

And the risk of leaf blight impacting the HNR supply is far too great.

In 2020, 10 percent of global production of HNR was lost to leaf blight. This leaf disease, Cornish said, "spread to 500,000 hectares in seven countries in less than six months."

If this were to reach Southeast Asia, she added, there could be a severe loss of global natural rubber supply.

And an additional challenge associated with the reliance on HNR, Cornish pointed out, is the risk Americans face in developing a latex allergy, with more than 30 million Americans at risk for life-threatening reactions to current natural rubber products.

"These are people with IgE (Immunoglobulin E) antibodies in their bloodstream against hevea latex proteins or residuals," she said.

There are two "leading contenders" in the U.S. for domestic, alternative NR sources: Taraxacum kok-saghyz—also known the TKS dandelion—and the desert shrub guayule, which Cornish noted is becoming "really important" in the Southwest of the country.

"It's a desert crop, and so as water allocations are being just cut like there's no tomorrow because of the Colorado (River) drying up, this is one of the few crops that can still be grown in the Southwest," Cornish said.

With three species—hevea, guayule and the TKS dandelion—as a source of natural rubber, Cornish said, biological and geographical diversity can be achieved.

"We could basically grow (natural rubber) anywhere in the world," she said, adding that this would amend the issue with hevea's lack of biological and geographical diversity as a monoclonal crop.

"(With) guayule, the agronomics of that are pretty well sorted out," Cornish said.

Production of the shrub is "relatively mature," and it's suitable for targeting premium specialty markets, she said, noting Bridgestone's development of the Firestone Firehawk race car tire made with guayule-derived natural rubber (GNR).

She said production of dandelion-based natural rubber, currently, is further behind than guayule, so most focus in the industry is on developing the production and purification of the material. She added, however, that its properties are most like hevea natural rubber.

Currently, Goodyear is partnering with the Department of Defense to bring dandelion-derived natural rubber to the domestic U.S. market.

"You can certainly make any rubber product from either of these alternatives," Cornish said.

The U.S. must look not only at replacing the type of natural rubber production, but also reducing the carbon footprint of rubber products.

For a material to be a sustainable alternative, Cornish said, it must hit several benchmarks, including being bio-based, biodegradable, up-cyclable or recyclable, or energy saving during manufacturing.

Alongside this, she said, likely requirements for sustainable material alternatives include matching or exceeding a product's current performance, replacing toxic versions and offsetting potential increases in cost with improved performance.

Targets to achieve this, Cornish said, include alternative processing aids, waste-derived fillers and chemical modifications of natural rubbers.

Cornish said Ohio State University found liquid guayule natural rubber (LGNR)—made through thermal degradation of guayule natural rubber latex (GNRL)—to be an effective bioprocessing aid for HNR, GNR and SBR.

Unlike naphthenic or soybean oils, she said, the LGNR did not compromise product performance.

"When you use naphthenic oil, it's a dilutant as well as being a processing aid," Cornish said, noting the aid reduced the gel fraction in HNR, GNR and SBR.

But when using LGNR as an alternative aid, most of the gel fraction was maintained.

This also was reflected in tensile strength of rubber products, Cornish said.

"You don't get the same reductions (in performance) that you might see using naphthenic oil—or soybean oil for that matter," she said.

As for studies on sustainable fillers for HNR and GNR, Cornish said the university used a standard formulation with 35 phr carbon black filler loading and steadily replaced carbon black by weight until researchers ended up with 35 phr of an alternative, waste-derived filler—such as eggshells, tomato peels, carbon fly ash or guayule bagasse—at macro, micro and nano sizes.

"What we found is, if you have no carbon black at all, you get really, really crummy properties," Cornish said of the macro and micro sizes. "When you're trying to do 100-percent replacement (of carbon black), that's a mistake."

But a partial replacement, she said, "will get us a long way along the sustainability pipeline without having to try and force it into 100 percent."

When looking at a partial replacement of carbon black with eggshell as a filler with GNR, Cornish said hardness, elongation and strength of the rubber increased.

The findings were similar to rubber products with HNR, she said, but didn't have quite the same degree of change.

"Then we also found we got a lot of power savings when we used these alternative fillers," she added.

Cornish showed that as the studies gradually replaced carbon black as a filler in HNR and GNR, the composite mixing required less power, with GNR composites requiring up to 26 percent less power than HNR.

"And on large scales like a tire manufacturing plant, that can translate to a lot of money (saved)," Cornish said.

While trying to achieve 100-percent replacement of carbon black fillers at the macro and micro levels may be "a mistake," she said, 100-percent replacement could be achieved at the nano level.

Looking at examples of eggshell-GNR composites, tensile strengths remained mostly steady as elongation increased with complete replacement of carbon black at the nano level, she said.

The challenge with this, however, is that nano fillers are "really expensive," she added.

"I think that micro is the way to go," Cornish said, noting partial replacement of carbon black at the micro level with eggshell is the most promising overall when considering cost and performance of the final product.

She said about 30 rubber companies currently are testing the use of partial carbon black replacement with eggshell, "so there's a lot of interest" in the industry.

Cornish said GNR also can be chemically modified to increase oil resistance or to change its mechanical properties.

She said when the university epoxidized guayule-derived rubber, it found it had improved oil resistance, increased stiffness and increased predicted wet traction moreso than rolling resistance, making the natural rubber a sustainable alternative to some synthetic rubbers.

"This chemical modification would allow us in the long term to start to erode certain markets that the synthetic rubbers—which are petroleum-based—are dominant," Cornish said.

Taking inspiration from John F. Kennedy's "We Choose the Moon" speech, Cornish said the U.S. must establish domestic alternatives to HNR "not because it is easy, but because it is hard."

"We have to do this. This is not an option," she said.

"We can't always be reactive and wait for the hevea crops to collapse and then throw billions of dollars at it to try and fix it yesterday."

Cornish said the U.S. needs to build up its supply of alternative NR to where it can supply at least 10 percent of the country's requirements. And from there, she continued, the U.S. could quickly establish 100 percent in case of an emergency.

"If we can put a man on the moon, we can have a domestic rubber crop," she said.