Strength and biodegradability—these are the benefits of using cellulose to make plastics and other packaging materials. The cellulose can be harvested from plant materials, such as byproducts of agricultural processing and production, as well as forestry residues.
However, scientists must first figure out how to extract cellulose in an efficient, safe and sustainable manner. That is what assistant professor Srinivas Janaswamy of South Dakota State University’s Department of Dairy and Food Science is doing.
He is extracting cellulose from a model feedstock, corn stover—the stalks, leaves, cobs, husk and tassels left after harvesting, and then using inorganic salts to dissolve the cellulose. “We are establishing protocols to extract cellulose from renewable agricultural residues and then solubilizing it to make strong, biodegradable films,” Janaswamy explained. “This will allow us to use our nation’s abundant supply of cellulose to create environmentally friendly products.”
He gathered preliminary data on the extraction process through support from the North Central Regional Sun Grant Center. Graduate student Cecilia Wambui Wanjuu, who completed her master’s degree this summer, also worked on the project.
Janaswamy then used the results of the Sun Grant project to secure a three-year, $481,618 U.S. Department of Agriculture National Institute of Food and Agriculture grant to continue improving the extraction process and to evaluate the technology’s economic feasibility. Work on the project will begin in early 2021.
Producing sustainable, biodegradable product
“Cellulose can potentially be extracted from several types of biomass and used to make biofilms. This will generate extra income for farmers,” Janaswamy said. Using cellulose to create biodegradable products that can replace petroleum-based plastics will reduce the impact these packaging materials have on the environment.
In 2018, a little more than 8% of plastics were recycled, but more than 26.8 million tons of plastic wound up in landfills, accounting for 13.4% of municipal solid waste, according to the Environmental Protection Agency. Furthermore, scientists estimate more than 8 million tons of plastic wind up in the ocean each year.
Professor Stephen Gent, director of the North Central Regional Sun Grant Center, said, “This cutting-edge research can help open new markets for value-added agricultural products while reducing the impact of petroleum-derived plastics have on our environment, landfills and water bodies.”
Cellulose can also be extracted from wheat and oat straw, switchgrass and prairie cordgrass and soybean biomass. Nearly 205 million dry tons of plant biomass are produced each year, according to a 2011 U.S. Department of Energy report. By 2030, that is expected to increase to 320 million dry tons.
Professor Bill Gibbons, associate dean for research in the College of Agricultural, Food and Environmental Sciences, agreed: “Developing new technologies to process plant biomass is key to developing new biodegradable products from sustainable agricultural resources.”
Cellulose must be broken down, or solubilized, before it can be made into functional products, Janaswamy explained. However, the same characteristics that give cellulose its sturdy structure also prevent it from dissolving in water.
While at Purdue University’s Whistler Center for Carbohydrate Research, Janaswamy and research assistant professor Qin Xu developed a cost-effective method of solubilizing cellulose. They used a zinc chloride solution to break down the cellulose network and then added calcium chloride to crosslink the cellulose chains, thus helping to develop strong films.
Janaswamy applied this technique to cellulose extract from corn stover at SDSU. In the pilot study, the researchers optimized the zinc chloride solution and the processing temperature. Adding the calcium chloride thickened the liquid to form a nanofiber gel.
Then the researchers used the gel, along with a small amount of glycerol, to make flexible films.
To test the film’s biodegradability, the researchers buried approximately 3-inch-square pieces in soil. “After a month, the film was entirely degraded—and it will not harm the environment,” Janaswamy said. The next step will be to evaluate microbial degradation.
Tensile tests were also performed to evaluate the film’s strength. “Results showed the films have high tensile strength” Janaswamy said.
“This is a sustainable, green process,” noted Janaswamy, pointing out the solvents can be reclaimed and used again. Furthermore, the same process can be used for other agricultural biomass.