Novel chemistry for greener polyurethane

Polyurethane is the go-to plastic for a range of products. Today, more than 16 million tons of polyurethane are produced globally every year.
“Very few aspects of our lives are not touched by polyurethane,” reflected Phil Pienkos, a chemist who recently retired from the National Renewable Energy Laboratory (NREL) after nearly 40 years of research.

But Pienkos—who built a career researching new ways for producing bio-based fuels and materials—said there is a growing push to rethink how polyurethane is produced.

Through a novel chemistry using nontoxic resources like linseed oil, waste grease, or even algae, Pienkos and his NREL colleague Tao Dong, an expert in chemical engineering, have achieved precisely that.

When polyurethane first became commercially available in the 1950s, it quickly grew in popularity for use in numerous products and applications. That was in no small part due to the dynamic and tunable properties of the material, as well as the availability and affordability of the petroleum-based components used to make it.

Through a clever chemical process using polyols and isocyanates—the basic building blocks of conventional polyurethanes—manufacturers could tailor their formulations to produce a stunning variety of polyurethane materials, each with unique and useful properties.

Producing from a long-chain polyol, for example, might yield flexible foams for a pillow-soft mattress. Another formulation might yield a rich liquid that, when spread on furniture, both protects and reveals the inherent beauty of wood grain. A third batch might include carbon dioxide (CO2) to expand the material, producing a sprayable foam that dries into rigid and porous insulation, perfect for holding heat in a home.

“That’s the beauty of isocyanate,” said Dong when reflecting on conventional polyurethane, “its ability to form foams.”

But Dong said that isocyanates bring significant downsides, too. While these chemicals have fast reactivity rates, making them highly adaptable to many industry applications, they are also highly toxic, and they are produced from an even more toxic feedstock, phosgene. When inhaled, isocyanates can lead to a range of adverse health effects, like skin, eye, and throat irritation, asthma, and other serious lung problems.

“We can do better than this,” thought Pienkos five years ago when he first encountered the predicament. Energized by the opportunity, he joined with Dong and Lieve Laurens, also of NREL, on a search for a better polyurethane chemistry.

Rethinking the Building Blocks of Polyurethane
The question becomes much the same for algae biorefining. Can the waste lipids and amino acids from the process become ingredients for a prized recipe for polyurethane that is both renewable and nontoxic?

For Dong, answering the question at the basic chemical level was the easy part—of course they could. Scientists in the 1950s had shown it was possible to synthesize polyurethane from non-isocyanate pathways.

The real challenge, Dong said, was figuring out how to speed up that reaction to compete with conventional processes. He needed to produce polymers that performed at least as well as conventional materials, a major technical barrier to commercializing bio-based polyurethanes.

“The reactivity of the non-isocyanate, bio-based processes described in the literature is slower,” Dong explained. “So we needed to make sure we had reactivity comparable to conventional chemistry.”

NREL’s process overcomes the barrier by developing bio-based formulas through a clever chemical process. It begins with an epoxidation process, which prepares the base oil—anything from canola oil or linseed oil to algae or food waste—for further chemical reactions. By reacting these epoxidized fatty acids with CO2 from the air or flue gas, carbonated monomers are produced. Lastly, Dong combines the carbonated monomers with diamines (derived from amino acids, another bio-based source) in a polymerization process that yields a material that cures into a resin—non-isocyanate polyurethane.

By replacing petroleum-based polyols with select natural oils, and toxic isocyanates with bio-based amino acids, Dong had managed to synthesize polymers with properties comparable to conventional polyurethane. In other words, he had developed a viable renewable, nontoxic alternative to conventional polyurethane.

And the chemistry had an added environmental benefit, too.

“As much of 30% by weight of the final polymer is CO2,” Pienkos said, adding that the numbers are even more impressive when considering the CO2 absorbed by the plants or algae used to create the oils and amino acids in the first place.

“That means less raw material per pound of polymer, lower cost, and a lower overall carbon footprint,” Pienkos continued. “It looks to us that this offers remarkable sustainability opportunities.”

In addition to partial funding by the U.S. Department of Energy’s (DOE's) Bioenergy Technologies Office, in the two short years since Pienkos and Dong first demonstrated the viability of producing fully renewable, nontoxic polyurethane, several companies have already contributed resources and research partnerships in the push for its commercialization.

A 2020 DOE Technology Commercialization Fund award, for example, brought in $730,000 of federal funding to help develop the technology, as well as matching “in kind” cost share from the outdoor clothing company Patagonia, the mattress company Tempur Sealy, and a start-up biotechnology company called Algix.

And Pienkos says companies from other industries have shown preliminary interest, too. “These companies believe there is promise in this,” he said.

Their interest could partly be due to the tunability of Pienkos and Dong’s approach, which lets them, much like conventional methods, create polymers that match industry standards.

“We’ve demonstrated that the chemistry is tunable,” Dong said. “We can control the final performance through our approach.”

After retiring last April, Pienkos went on to establish a company, Polaris Renewables, to help accelerate the commercialization of the novel polyurethane. So, while he continues with his responsibilities as an NREL emeritus researcher, he is also doing outreach to industry to find additional corporate partners, especially in the fashion industry through the international sustainability initiative Fashion for Good.

“In the fashion industry, customers are demanding sustainability,” he explained. “They will pay something of a green premium if you can demonstrate a lower carbon footprint, better end of life disposition.”

Indeed, for both Pienkos and Dong, the breakthrough in renewable, nontoxic polyurethane has become more than an exciting scientific venture. It offers the world a pathway for products that leave a lighter mark on the environment.

“I think this is a great opportunity to solve the plastic pollution problem,” Dong said. “We need to save our environment, and part of that begins with making plastic renewable.”

Pienkos, too, thinks that a commercial success in this venture could be a catalyst that spurs further growth and further success in bringing renewable, greener products to the market.

“This could be a success story for NREL,” he said. “A success here means a great deal to the world.”

In this case, success might be measured in more than the affordability of the production process or the carbon uptake of the polyurethane chemistry. In a world with NREL’s renewable, nontoxic polyurethane, success might be something we can truly feel in the durability of our clothing, in the comfort our shoes provide, or in the rejuvenation we feel after sleeping on a memory foam mattress.

Recently retired, Phil Pienkos (pictured) founded a new company, Polaris Renewables, to help accelerate the commercialization of the novel polyurethane, an idea that originally grew out of his algae biofuel research at NREL. (Photo by Dennis Schroeder, NREL)