Molecular Rebar, Goodyear bringing big innovations in nano-packages

AUSTIN, Texas—The level of innovation required for the tires of the future is both magnificent and minuscule.

The ever-stubborn performance triangle never has been asked to be more flexible, especially in the tire wear corner, as electric vehicles are expected to increase abrasion by more than 30 percent compared to internal combustion engine vehicles.

While this makes for an enormously complex rubber compounding problem, Molecular Rebar L.L.C. and Goodyear are going small for what could be a remedy.

Austin-based Molecular Rebar, the awardee of a $1.15 million Department of Energy grant to develop, test and produce an EV tire tread, is banking on its carbon nanotube technology as a filler (with a carrier agent, like silane) in the tread to provide a solution.

Thus far, results look promising.

"We are aware of other nanotechnology Phase I projects focused on composites, but are not aware of any that focused on using nanotechnologies in tires," said August Krupp, director of rubber development for MRD. "We are the only carbon nanotube company focused on dispersing functionalized carbon nanotubes for use in rubber, and we think that this organosilane functional Molecular Rebar product is an innovative expansion of our core competency and business focus.

"We believe that carbon nanotubes are more effective and reinforcing on a loading basis than other currently available reinforcing fillers."

Goodyear, considered a Phase II contractor as part of the DOE pact, ultimately will test the EV tires with the prototype tire tread. The project will look to commercialize the Molecular Rebar (as the patented carbon nanotubes are called) for passenger vehicles first.

"As a leader in the world of new mobility, Goodyear has responded to the increasing electrification of vehicles with tires customized to the unique load, torque, noise, range, rolling resistance and performance requirements of EVs," said Eric Mizner, director of material science at Goodyear. "We're excited to work with MRD to help continue to advance the performance of EV tires."

Implications of the project are far-reaching, as success with the prototype development and demonstration represent key steps toward commercialized tire production. The project, which began in August 2022, will look to an August 2024 completion date, when the grant period expires.

"The tire industry is risk-averse, for good reason, and we see challenges in the timing of development for EV tires," Krupp said. "The EV industry is moving at a rapid pace, and we believe an inherent challenge is the pace at which the tire industry and its suppliers innovate versus the pace at which the EV industry is innovating."

To be clear, Molecular Rebar is being used in the tire tread for this research and development project, not the rubber in the carcass.

But Krupp said there is no reason that carbon nanotubes, combined with a carrier agent (like silane) and dispersed "pristinely," cannot work in other portions of the tire and in combination with other fillers, like carbon black and silica.

"At this point, that is correct," Krupp said. "We believe that the use of the silane-MR in the tire tread minimizes some of the typical risks associated with tire development. The carcass is not being modified, the fiber-polymer connection is unaltered. Only the tread compound itself has a different composition.

"This may allow tire manufacturers to optimize tread design with new tread compound properties, but that is out of our hands. Long term, there is no reason that the Molecular Rebar could not be used in the carcass of the tire, but that is not currently our focus."

Goodyear's Robert Dennis-Pelcher, principal scientist in the tire maker's Global Materials Science division, told Rubber News that EV tire demands can be met—despite the heavier weights and higher torques.

"Compared to internal combustion engine vehicles, EVs are heavier and have higher, more instantaneous torque," Dennis-Pelcher said. "Consequently, EV tires may wear up to 30 percent more quickly than tires on their ICE counterparts.

"The demands of today's EV tires can be met, (and) Goodyear, the U.S. Department of Energy and MRD recognize the opportunity for continuous enhancements, especially with the tradeoff between treadwear, rolling resistance and weight, as EVs grow in popularity. (These are) the greatest challenges associated with the development and performance requirements for EV tires."

Partnerships will be required to solve these complex chemistries and material applications.

In addition to Goodyear, the LARTA Institute is a subcontractor on the project, which will assist Molecular Rebar Design with some business development and commercial planning later in Phase II.

There are no other formal partners, though Krupp noted that support letters for Phase II came from Bridgestone, Goodyear, Agora Tire, Arlanxeo and Thomas Swan.

Electric vehicles are growing in popularity, but current tire technology is inadequate for their performance needs, according to the DOE's EV tire tread project, known as "Game-Changing Technologies for Polymer Composites."

While the 30-percent increase in tire wear (on EVs) has been noted, potentially driving up cost and micro-rubber pollution (tire wear particles that gather in urban runoff), CNT tech has been shown to increase abrasion resistance and lower rolling resistance, reducing operating costs for both consumers and commercial fleets and increasing energy efficiency, Krupp said.

The Phase I goal was to produce a tire tread compound "with a reduced amount of total filler, density decrease of roughly 7 percent, making a lighter-weight tire possible."

The rolling resistance had the bar set at a 10-percent decrease. The heat buildup required a reduction of 7 percent, and the toughness required an increase of approximately 25 percent for the DOE project.

MRD surpassed these parameters, with the tire tread material with Molecular Rebar improving abrasion resistance by more than 25 percent, decreasing density by between 6 and 7 percent, and reducing rolling resistance and heat build-up by 20 percent each, as compared to a state-of-the-art tread compound.

"The successful development of new rubber composites with dispersed and chemically functionalized carbon nanotubes in Phase I improved tire tread performance," the DOE stated. "These results revolutionize rubber composites by reducing the use of typical materials and replacing them with a lesser quantity of the new, highly reinforcing functionalized carbon nanotubes."

The CNT additive could have future applications in aircraft tires, military tank track pads and mining equipment, according to the DOE.

One of the keys to the EV tire prototyping project happens to be one of Molecular Rebar Design's core competencies: the dispersion of CNTs within the treated rubber.

"We are exploring different methodologies of retaining both the functionality of the CNTs and their dispersion capability, while ensuring that any product form developed is adequate for typical industrial rubber compounding and tire manufacturing processes," Krupp said.

Previously, poor dispersion inhibited the commercial use of CNTs.

Improvements were achieved through the invention and use of individualized CNTs, functionalized with hydroxyl and carboxyl groups, chemically bound with an organosilane and the rubber itself, Krupp said.

It is a gap that is bridged with MRD's unique ability to produce discrete, surface-tailored carbon nanotubes at scale, called Molecular Rebar.

Outside of rubber, the technology has found use in batteries, electronics, 3D-printing and medical applications.

"The strength of our intellectual property portfolio reflects MRD's focus on both the dispersion and chemical functionalization aspects," Krupp said.

In Phase I, MRD invented an organosilane functional carbon nanotube (Molecular Rebar).

While the nanotube is physically similar to MRD's commercial products in (very tiny) size, length and aspect ratio, the chemical functionality is "quite different from our commercial products offered to the rubber industry currently," Krupp said.

"The time frame of nine months in Phase I forced rapid innovation, where we utilized hypotheses and theories from other MRD business units like batteries, coatings and biotechnology to assist in development of the organosilane functionalization," Krupp said. "We believe (our) proprietary processes enable better performance, and we can envision future applications with different functionalities for improved elastomeric goods, parts and tires."

Krupp added that the use of the silane-MR can be further improved with other innovative products and processing techniques.

"We see the effects of Molecular Rebar, in general, as additive to other innovative technologies," he said.

In other words, MR can be used in conjunction with other legacy fillers, like carbon black and silica.

"We found the best use to be a little bit of both," he said. "We find that using a mixed structure of filler is most effective in terms of performance and cost."

For its commercial products, MRD typically replaces smaller portions of carbon black with its MR (CNTs), resulting in the aforementioned improvements in abrasion and rolling resistance.

"The bulk of the carbon black loading is still present," Krupp said. "As seen in the Phase I results, we can replace portions of existing silica content (showcased as up to half replacement at the recent International Elastomer Conference).

"But by keeping some silica content, we have a 'backbone' of reinforcement that is improved with the Molecular Rebar."

The prototype EV tire will be developed in the second half of Phase II of the DOE project.

For MRD's part, this phase will determine the product form of the silane-MR material.

"The silane-MR composition itself is 99-percent complete," Krupp said. "We have some parameters to meet on the product form side."

First and foremost, the prototype tread must keep or allow a "pristine dispersion" of the silane-MR within the rubber. In addition, the tread must allow (or already have) the MR-silane-polymer coupling that provides for good filler-polymer interaction.

"And the product form must be both viable from a production standpoint and from a customer-use standpoint," Krupp said. "MRD must be able to make the material at scale and for a reasonable cost, while the tire manufacturers must be able to compound the product using typical techniques and throughput rates."

Innovations and partnerships are essential for the viability of the electric vehicle, the ultimate sustainable commercial product.

And small-scale innovations can make a very large difference.

"Our team is very well-suited to develop and then subsequently commercialize the new silane-MR technology into the tire industry, and thus the automotive industry," Krupp said. "We are very excited to continue the innovative project with the U.S. Department of Energy support.

"Electric vehicles pose a new set of performance requirements for the tire industry, and we feel that our new organosilane-modified Molecular Rebar can be used to meet or exceed those performance requirements."