New developments in vegetable oil materials science
By Rebecca Guenard
- Long before petrochemicals became the dominant starting material, manufacturers used vegetable oils to make coatings, adhesives, and other types of polymers. Researchers are now optimizing vegetable oil chemistry with an eye toward making sustainable products with properties that gain the same level of customer satisfaction as their petrochemical counterparts.
- Electrolysis and ozonolysis are manufacturing methods that reduce reagent use and unwanted side reactions. A major vegetable oil company has brought ozonolysis technology online to make plant-based products quicker and cleaner.
- Before the pandemic, the bio-based polymers market was projected to have huge growth in the next five years. COVID-19 has caused unemployment and plummeting petroleum prices; how will these factors affect the bio-based sector?
In 1941, Henry Ford produced a new type of car body. It was made of a metal frame surrounded by soybean-based plastic panels. The company never documented the formula for the panels on the Soybean Car, so there is no way to know if Ford made the bio-plastic by manipulating the oil’s chemistry the way it is done today (https://tinyurl.com/soybeancar).
“Making natural resin is not a new idea,” says Jonathan Curtis, associate professor and principle investigator at the University of Alberta’s, Biorefining Conversions Network, in Edmonton, Canada. Protective coatings for furniture and wood floors were once sourced from conifer sap and insect exudate. But synthetic materials made from petrochemicals significantly outperformed natural polymers, and natural materials fell out of vogue.
Some materials scientists want to make natural products mainstream again. By addressing technical problems and considering the mechanical properties needed for a given application, they are developing novel chemical formulations to turn vegetable oils into a range of polymer materials.
Vegetable oils are a mixture of unsaturated fatty acids with double bonds that act as reactive sites where the molecules can be chemically modified. Oleic acid, linoleic acid, and linolenic acid contain one, two, and three double bonds, respectively. Since different vegetable oils have different fatty acid compositions, researchers have an opportunity to create different materials. The potential for a new variety of vegetable oil-derived materials coincides with growing consumer interest in environmentally friendly, sustainable products in the past decade. Will the post-COVID economy threaten their chance of success?
According to market research, the projected global market value for epoxy resins will exceed $11 billion in the next two years, a nearly 70% increase (https://tinyurl.com/resinsmarket). Petrochemical products currently dominate the market, but vegetable oil epoxides continue to battle for a share. Analysts believe that recent regulatory mandates for non-phthalate plasticizers, coupled with consumer demand for eco-friendly materials, will give naturally based polymers a boost.
“Producing vegetable oil epoxides is a low-cost, well-established process using simple chemistry that is relatively benign,” says Curtis. The reaction uses formic or acidic acid and peroxide with only water as a waste product (Fig. 1) and is fairly clean, he says.
However, linking the epoxides together to form a hard plastic involves overcoming inherent challenges. The organic acids, commonly used as curing agents, do not mix with oil oxides and no reaction occurs. A solvent can be added, but that introduces toxicity to a reaction that is intended to be clean.
“There are more technical problems using vegetable oil-based epoxides because of their poor solubility with some of the more polar crosslinking agents,” Curtis says.
In an effort to address these problems, scientists have studied the kinetics of common curing agents to understand how they influence the physical and mechanical properties of resulting resins (https://doi.org/10.1002/aocs.12260). Some researchers found that using bio-based curing agents (Fig. 2) improved the properties of a polymer made from epoxidized vegetable oil (https://doi.org/10.1016/j.cej.2017.06.039). Whatever the approach, materials scientists now understand that to create a valuable vegetable oil-based polymer they must consider each aspect of the polymer: the monomers, curing agents, and additives.
“Nobody is going to have great commercial traction on the vegetable oil epoxy materials front without addressing the whole package,” Curtis says. “You cannot just work on the oil epoxides; you have to design the whole system.” Part of working with natural products is thinking about the chemistry in a different way, he explains. A synthetic plastic is made from one monomer and leads to one type of polymer. When you start with a mixture of fatty acids from vegetable oils you cannot identify a single polymer, just the overall properties you want the end product to have.
Curtis says that genetic modification and controlled growth of oilseed plants can produce oils that are better suited for materials applications. “For example, castor oil naturally produces one hydroxyl fatty acid that is 95% of the oil,” he says. “Instead of canola or soybean, where you have 10 different fatty acids, you essentially have a pure compound coming out of the plant.” Biotechology can also produce high-purity designer oils that serve as better feedstocks for chemical processes.
Even if the challenges arising from different chemistries can be overcome, the existing manufacturing infrastructure of the petrochemical industry gives it an economic advantage over vegetable oil-based materials. To compete, natural materials manufacturers need innovative, low cost technologies that are easy to establish.
A simple, efficient way to produce oxidation products of free fatty acids is by reacting ozone across their double bonds. Manufacturers typically avoid this process because of the explosiveness of the bulk reagents. Now, a company has found a way to optimize the benefits of ozonolysis while avoiding the dangers.
The company P2 Science (https://www.p2science.com) in Woodbridge, Connecticut, USA, launched in 2011, with the mission of rethinking how to make specialty chemicals. Their goal: greener manufacturing using ozonolysis (Fig 3). “What we have done at P2 is make ozonolysis easier to control in an industrial setting,” says the company’s CEO, Neil Burns. Central to P2’s strategy, Burns says, is its continuous-flow technology, patented with the European engineering firm Desmet Ballestra.
In P2's continuous-flow reactor system, a thin film of reactant combines with ozone as it runs down the walls of a liquid-cooled tube. “We use very little reactant at any given time compared to the traditional process where tons are being used,” says Burns. “It is a continuous, controllable process where ozone enriched air and a vegetable oil or terpene flow concurrently.”
This summer, P2 Science and ADM (http://www.adm.com), based in Chicago, Illinois, announced a joint development agreement to commercialize plant-based monomers and polymers using ozonolysis. Initially, the companies will make high-value products like nylon and polyester for applications in paints and coatings, automotive, construction, and personal care and industrial cleaning industries, among others. Paul Bloom, ADM’s vice president of sustainable materials, says the partnership provides an opportunity for his company to broaden its plant-based portfolio.
Bloom says that for many years ADM has been interested in ozonolysis as a way to modify vegetable oils cleanly. “The end products are used everywhere—from intermediates for the agricultural industry to cleaning and personal care products,” he says. “These products are made more sustainably, because you can basically use air and electricity to generate ozone, and when you are done there is minimal waste.”
Burns also points out that the flow-through design of the process means that it is easily scalable. “This is a modular process that can go from tens to hundreds to thousands of tons of product produced with minimal change in the characteristics of the reactor,” he says. In that way, the process is more conveniently scaled than a process like fermentation where a complete recalibration would be necessary. “We will be able to adjust production effortlessly to meet demand,” says Burns.
Exploring the potential of electrolysis
As AOCS members certainly know, water is a very stable liquid. But with enough electricity running through it, water will break down into hydrogen and oxygen. A growing trend among chemical companies is testing whether renewable energy and cheap electrolysis can be used to make industrial chemicals from carbon dioxide and water. In late 2019, the German companies Evonik and Siemens built a facility together to test the technology (https://tinyurl.com/cenbusiness).
Now, there is a possibility that electrolysis could be used to epoxidize vegetable oils. Karthish Manthiram, engineering professor at Massachusetts Institute of Technology, in Cambridge, and his team recently published a paper in the Journal of the American Chemistry Society, describing the electrochemical epoxidation of olefins (https://doi.org/10.1021/jacs.9b02345). Manthiram says the conventional way of making epoxides creates surplus carbon dioxide. “When you try to drive that reaction using temperature and pressure there is a tendency for over oxidation,” he says.
Manthiram’s team set out to improve the mass balance of epoxide manufacturing while also developing a safe, sustainable process. They suspended electrodes in a mixture of water and acetonitrile that contained an olefin, and coated the negative electrode in magnesium oxide nanoparticles. Magnesium oxide is known to generate oxo-species during water oxidation, which they hoped would transfer to the olefin. The electrolysis reaction not only worked, it operated with an impressive 30% electron efficiency.
The group will work on improving the process and eventually expand the technology if it is successful. Currently, the reaction loses efficiency as the olefin chain length increases, but Manthiram sees a possibility for applying electrolysis to the epoxidation of vegetable oils in the future.
“We developed this process in the hopes of being able to apply it to starting material like ethylene and propylene,” Manthiram says. With the right combination of catalyst and a method for dispersing the vegetable oil in the desired solvent, he says long-term development could include the selective epoxidation of vegetable oils.
An economic curve ball?
Right now, demand for materials made from vegetable oils is uncertain. As with traditional polymers, the industry is cyclical, but the current market is unprecedented and difficult to read—although sustainability does seem to have a stronghold on consumer spending.
Plant-based polymers may only be a minor fraction of the industry, but they have enjoyed steady market growth as oil prices climbed, making them competitive against the price of synthetic polymers. At the same time, a growing number of major consumer goods companies partnered with green materials producers to create sustainable, eco-friendly packaging. Not every wrinkle had been smoothed out of vegetable oil-based polymers, but the industry was starting to gain traction. Now the coronavirus pandemic threatens to upend that progress.
The halt of transportation, global and domestic, from COVID-19 shutdowns resulted in a surplus of petroleum, and prices plunged. Meanwhile, the pandemic has sparked a demand for single-use packaging due to a rise in the number of people eating take out. In addition, retailers banned reusable bags fearing they could transmit the virus. Market analysts report that the natural plastics industry may be saved by these factors, but they indicate that the industry’s future will be determined in the next few months (https://www.plasticstoday.com).
This summer, Genomatica, an ingredient company in San Diego, California, USA, commissioned an independent survey within the United States that contradicts any negative forecast for bio-based polymers (https://tinyurl.com/sustainabilitysurverygenomatic). In an interview with Forbes, Genomatica’s co-founder and CEO, Christophe Schilling, explains how staying home made people realize their environmental impact more profoundly (https://tinyurl.com/sustainabilitysurveryforbes). Pollution cleared, and many people in the world experienced clean air and water for the first time in their lives.
Based on their survey results, Genomatica reports that amid the pandemic “sustainability has moved from a fringe preference to a core imperative across American life,” according to the Forbes article. The study found that 85% of Americans reported they have been thinking about sustainability the same amount or more during COVID-19 quarantine. And a third of participants said they were willing to pay a little more for sustainable products, even during an economic downturn. When the participants were categorized by generation, nearly half of the younger consumers (25–40 years old) said replacing synthetic products with alternatives containing natural ingredients was important. We will have to wait to see how these responses compare to the reality of the world economy in the next decade, but they do indicate that consumers are prioritizing the environment.
Curtis says, more and more researchers see the value in the extra effort required to make vegetable oil systems suitable for new applications; they just need manufacturers who are dedicated to sustainability. “If you can replace some portion of petrochemicals with vegetable oils, then that is a win for the people growing the beans and that is a win for the environment,” Curtis says.
In terms of performance and cost, petrochemical materials still outweigh vegetable oil materials. The petrochemical industry has had a 150-year head start. Its development and manufacturing infrastructure are well-established. But, Curtis says, it does not really make sense to directly compare products from the two industries. Just as milk jugs and grocery bags made of polyethylene were inconceivable before that material was developed, there are possible applications for vegetable oil materials that remain unknown. “Polymers are widely used in all kinds of places,” he says. “There are so many applications that surely we can find ones that work well with vegetable oil-based products.”
Rebecca Guenard is the associate editor of INFORM at AOCS. She can be contacted at firstname.lastname@example.org.
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