Groundbreaking method to produce renewable PU without toxic precursors


NREL researchers have developed a groundbreaking method for producing renewable polyurethane without toxic precursors, using nontoxic resources like linseed oil, waste grease, or even algae. It is a breakthrough with the potential to green the market for products ranging from footwear, to automobiles, to mattresses, and beyond.

Natural Oils to Produce Renewable PU

NREL’s chemistry reacts natural oils with readily available carbon dioxide to produce renewable, nontoxic polyurethanes—a pathway for creating a variety of green materials and products. The real challenge was figuring out how to speed up that reaction to compete with conventional processes. Researchers 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. So, we needed to make sure we had reactivity comparable to conventional chemistry,” Tao Dong, an expert in chemical engineering, NREL explained.

The Epoxidation Process

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, researchers combined 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, researchers have managed to synthesize polymers with properties comparable to conventional polyurethane. In other words, they have developed a viable renewable, nontoxic alternative to conventional polyurethane. And the chemistry had an added environmental benefit. “As much of 30% by weight of the final polymer is CO2,” said Phil Pienkos, a chemist who recently retired from NREL. He also added 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.

Boosting the Value of CO2

CO2, a ubiquitous greenhouse gas, is often considered an unfortunate waste product of various industrial processes, prompting many companies to look for ways to absorb it, eliminate it, or even put it to good use as a potential source of profit. By incorporating CO2 into the very structure of their polyurethane, Pienkos and Dong had provided a pathway for boosting its value. “That means less raw material per pound of polymer, lower cost, and a lower overall carbon footprint. It looks to us that this offers remarkable sustainability opportunities,” Pienkos continued.

Meeting the Demand of the Market

The next step was to see if the process could be commercialized, scaled up to meet the demands of the market. After all, renewable or not, polyurethane needs to demonstrate the properties that consumers expect from brand-name products. The process to create it must also match companies’ manufacturing processes, allowing them to “drop in” the new material without prohibitively costly upgrades to facilities or equipment. “That’s why we need to work with industry partners to make sure our research aligns with their manufacturing processes,” Dong explained. In the two short years since the researchers 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.

Tunable Chemistry

By controlling the epoxidation process or amount of carbonization, for example, the process can be suited to meet the performance needs of a product. That may give the outsoles of a pair of running shoes enough flexibility and strength to endure many miles pounding into hot or cold asphalt. Or it may give a mattress a balance of stiffness and support. “It’s got regulation push. It’s got market pull. It’s got the potential to compete with non-renewables based on cost. It’s got a lower carbon footprint. It’s got everything. This became the most exciting aspect of my career at NREL. So, when I retired, I decided that I want to make this real. I want to see this technology actually make it into the marketplace,” Pienkos said of the opportunities for commercialization. “I think this is a great opportunity to solve the plastic pollution problem. We need to save our environment, and part of that begins with making plastic renewable,” Dong said.

Source: NREL, 30 September 2020