The majority of plastic products pose a serious environmental hazard because they don't degrade in landfills and cannot be composted. Soybeans are a sustainable source of protein and oil, and soy protein and oil are not solely a food source for humans and animals. They also have an increasing role in industrial applications, including the production of soybean plastics. Soybeans, when produced by sustainable farming, reduce carbon dioxide emissions, and biodegradable soybean plastics can replace petrochemical products for a "greener" solution for some applications.
The two major types of soybean-derived plastics are polyurethane products and polyester thermoset products. Soy polyols, made from soybean oil, are used to make toner, adhesives, sealants, coatings, newspaper ink, automobile panels and urethane foam, including rigid urethane foam insulation. When combined with the appropriate chemicals, soy polyols rival their petroleum counterparts in durability, strength and often cost. But many of these soybean plastics are not biodegradable because they are made from nonbiodegradable polymer molecules, which give these products strength and durability. In contrast, disposable soybean plastics tend to be biodegradable or compostable.
Biodegradation Vs. Compostability
Biodegradable plastics break down at the same rate as paper, producing water, carbon, oxygen and bio-products, called "biomass." The biodegradation is carried out by bacteria, fungi and other microorganisms. The technical definition of biodegradation differs from compostability in requirements of time limits for breakdown and toxicity issues. Biodegradable plastics that are also compostable have to break down in a specified time period and cannot leave any residual toxicity. Future goals are to create soybean plastics that are not only biodegradable but also compostable.
Biodegradable Soybean Plastics
Most biodegradable soybean plastics consist of disposable food service and tableware products and packaging, including grocery and trash bags. They can be produced from soybean protein and are sensitive to high temperatures and humidity or water. Soy protein plastics are processed at significantly lower temperatures than synthetic plastics, providing energy savings. These soybean plastics look and feel like petroleum-based plastics and usually are freezer safe and may handle hot foods up to 93 degrees Celsius (200 degrees Fahrenheit), according to World Centric.
The development of new plastic products, produced from soybeans and other agricultural crops, is ongoing. Soy-based adhesives can reduce the use of formaldehyde, which is a cancer-causing pollutant. Products that use soy proteins or soy flour are an expanding market. While some products like soy-based ink and adhesives are biodegradable, many soy plastics are not. The development of soy plastics that are biodegradable or compostable and cost-competitive, other than disposable cutlery and packaging plastics, requires more research.
- United Soybean Board: Soy Plastics: Versatile and Cost Effective
- World Centric: Compostable Plastics
- R & D Magazine: Soy Materials Make a Green Mark
- U.S. Environmental Protection Agency: Final Report: Sustainable Plastics: Designing and Demonstrating Renewable, Biodegradable Products Made of Soy Protein-Based Plastics
About the Author
Based in Connecticut, Marie-Luise Blue writes a local gardening column and has been published in "Organic Gardening" and "Back Home." Blue has a Ph.D. in biological sciences from the State University of New York at Stony Brook and wrote scientific articles for almost 20 years before starting to write gardening articles in 2004.
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