The cover is made from an epoxy resin that uses 30 percent vegetable oil to partially replace the petroleum-based ingredients. Flax fiber has been added to the plastic to give it more strength and stiffness. The combination is called a reinforced composite, and it could be used in a number of applications including parts for automobiles and agricultural equipment such as tractors, says Dennis Wiesenborn, one of a multidisciplinary team of researchers at NDSU’s Bio Energy and Products Innovation Center, or BioEPIC. “When you talk about composites, fibers are used to provide structural strength but you need some kind of binder or matrix to hold them,” Wiesenborn says. “There are a number of possibilities, including using a polymer-type material. The polymer we used was a chemically modified vegetable oil.”
Wiesenborn’s lab has developed a method for converting unsaturated fats into epoxy compounds. Epoxies are highly reactive compounds characterized by a ring made of two carbon atoms and an oxygen atom. The chemical bonds in this three-member ring are highly strained, which makes it easy for them to react with other compounds to form polymers. Composite materials made with epoxy resins are versatile and are used as adhesives and as structural resins in applications ranging from electronics to automotive to industrial uses. Fibers, typically fiberglass, are added to epoxy resins to give them strength and stiffness.
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Currently, Wiesenborn is working with a blend of 30 percent epoxidized vegetable oil and a petroleum-based epoxy that is mixed with fiberglass and a chemical catalyst called a hardener. To convert the oil into an epoxy, Wiesenborn reacts vegetable oil with hydrogen peroxide and acetic acid in the presence of a catalyst. The double bond in unsaturated fatty acids is converted to an epoxide group. “The epoxy groups then become the active group in cross-linking the fatty acids into the hardened polymeric material,” he says.
Saturated fats, such as those found in animal fat or palm oil, are essentially inert in this process. Wiesenborn found that canola oil, being a highly unsaturated fat, was extremely
well-suited for producing epoxys. “It’s high in monounsaturated fatty acids and quite low in saturated fatty acids,” he says.
Wiesenborn’s work is still in the early stages. The batches of resin he is creating measure only about 100 grams. His next challenge is to scale up the process to make kilogram-sized batches. He is also looking for ways to lower the cost of the process such as recycling the catalyst. “We would like to show that we can make some finished types of products—paneling for agricultural equipment, for example—simply to raise awareness that these kinds of things are possible,” he says.
Protein Power
Another bioplastic project is also taking shape at NDSU. Rather than converting oil into epoxy, Scott Pryor, an assistant professor in agricultural and biosystems engineering at NDSU, is using the canola meal left over after oil extraction and converting that into a biodegradable bioplastic. “It’s been done quite a bit with soy proteins,” Pryor says. “We have been using soy for many decades to make adhesives, polymers and composites. We’re interested in seeing how proteins from other sources might function in these applications. Hopefully, different proteins might lend themselves to improved properties for certain applications.”
He became interested in using canola meal because canola oil is used as a feedstock for biodiesel production in North Dakota. He was approached by a biodiesel producer about other value-added opportunities for canola meal, which is currently sold as animal feed. A surprising number of polymers can be made out of proteins. Pryor listed panels for automobiles or farm equipment as just one example of a potential product.
A mixture of different proteins, called an isolate, can be extracted from oilseed meal. Pryor started by taking canola meal isolate and separating it into its component proteins and examining their properties. One property that is important is water absorbtion. “One problem with protein-based polymers is that they can absorb too much water,” he says. “We see that if we can extract the portions of the protein that have higher water solubility, we can decrease the solubility of the final mix of proteins.” Proteins can also be modified with heat, enzymes or chemicals to modify their properties.
Pryor’s work is also in its beginning stages so he isn’t sure for which applications canola-based bioplastics will be best suited. “We didn’t go into this research with a specific application in mind,” he says. “We saw that there was a hole in the research in that we didn’t know what functionality these canola proteins would give for industrial products. We want to explore the possibilities of canola proteins.” Pryor will be looking at using the proteins to make composites, but will be keeping an eye open for other applications such as adhesives.
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