Researchers Develop Environmentally Friendly Plastics

Environmentally conscious consumers know that plastic shopping bags crowd landfills, and sometimes end up in the ocean, but many don't know that those same bags are derived from oil and gas, the same fossil resources used to produce gasoline and other fuels. University of Minnesota researchers have developed a portfolio of degradable plastics derived from renewable resources that could serve as a viable alternative to plastics made from petroleum and natural gas. These materials have the potential to be safer, more sustainable alternatives to plastics currently on the market.

"Nearly all synthetic chemicals and materials are derived from fossil fuels," said Marc Hillmyer, Distinguished McKnight University Professor of chemistry and director of the Center for Sustainable Polymers in the College of Science and Engineering. "To wean ourselves from such products, we must develop alternatives based on renewable resources as a means toward a sustainable polymer industry."

According to a U.S. Department of Agriculture study conducted in 2008, bio-based polymers could account for up to 33 percent of the global polymer market by 2025.

Polylactides (PLA) are degradable polymers that can be used in a variety of products, from medical devices and sutures to food packaging and diapers. These polymers could reduce the country's reliance on materials derived from crude oil. However, PLA has a few property deficiencies in comparison to other polymers, such as its tendency to soften at higher temperatures, a feature that limits utility in food and beverage packaging applications. Hillmyer and his colleagues have developed new types of polyactide-based materials that have potential to solve these problems.

He envisions technologies based on these discoveries being useful for a wide range of applications that require high temperature stability and toughness. These include bottles, microwave trays, cell phone and other appliance cases and other durable household items.

"Sustainable polymers or 'green materials' can be durable or degradable, can be used in applications from adhesives to packaging to building materials, and can be produced efficiently and economically with low environmental impact," said Hillmyer. "These are the materials of tomorrow."

Dr. Dharma Kodali, a research professor in the department of bioproducts and biosystems engineering, discovered a method for developing plasticizers made from soy oil. Plasticizers are additives that change the properties of the plastic, making them useful for variety of applications.

"The currently used plasticizers, called phthalates, are petroleum-derived, non-renewable materials," said Kodali. "The new plasticizers synthesized in our lab could be a viable replacement for petroleum-derived plasticizers, as they are comparable in price and performance but are safer, are made from renewable resources and degrade readily if leaked into the environment."

Plastics containing plasticizers are used in construction, automobiles, packaging, computers, medical devices, house siding and other household items. The phthalates have suffered criticism because they can leach from plastic and be harmful to the environment and to people.

"There were numerous studies that have shown that some of these phthalates are carcinogenic and cause hormonal disruptions," Kodali said. "The use of renewable and natural resources to make alternate plasticizers that can substitute for phthalates, as is done in this project, provides a safer solution."

Although these technologies continue to undergo extensive application testing, the researchers hope the materials will make up an important piece of the rapidly growing bio-based polymer market.

"The global polymer market is hundreds of billions of dollars," Hillmyer said. "Our technologies could account for some fraction of this huge number."

Hillmyer's research has taken place over the past four years, supported by grants from the university's Initiative for Renewable Energy and the Environment, the USDA and Natureworks LLC, an independent company wholly owned by Cargill. Kodali's project is in its third year and is funded by United Soybean Board, a farmer association that promotes the value of soybean products.