Anasthasia Shilov, Illustrations Editor

New research conducted by scientists at Yale, the University of Wisconsin and the University of Maryland could help phase out traditional plastics.

Researchers at the Yale School of the Environment, the Biological Systems Engineering Department at the University of Wisconsin and the Department of Materials Science and Engineering at UMD have created a lignocellulosic bioplastic that is a promising alternative not just to plastics derived from petroleum but also to existing bioplastic materials. Research on the bioplastic’s properties, manufacturing process and environmental impacts are outlined in a study published on March 25 in the journal Nature Sustainability.

“This is a promising technology for circular economy and a great demonstration of industrial ecology approach,” Yuan Yao, professor of industrial ecology and sustainable systems at the Yale School of the Environment and one of the senior authors of the study, wrote in an email to the News.

Wood powder, a cheap wood processing residue, is the raw material that forms the basis of the bioplastic, according to the study. To deconstruct the wood powder, which has a loose structure composed of cellulose, hemicellulose and lignin, the researchers used a deep eutectic solvent, or DES, specifically composed of choline chloride and oxalic acid. In the paper, the researchers explained that they used a DES because of its biodegradable and recyclable properties.

The DES performs two functions: It dissolves the lignin, and it splits the cellulose from the wood cell walls into micro/nanofibrils, the paper explains. Then, it is possible to regenerate or “deposit” the lignin by adding water. Lignin is hydrophobic, or repelled by water, so when water is added, the lignin quickly regenerates from the DES and binds the micro/nanofibril network, yielding a lignin-cellulose “slurry,” according to the study. The bioplastic is then formed from the slurry by way of a simple casting process.

“The modification of the lignin is the key,” UMD senior author and professor of materials science and engineering Liangbing Hu wrote in an email to the News.

The paper explains that the in-situ lignin regeneration process eliminates the need for the separation and isolation of the lignin and cellulose, a process that is costly and energy intensive. As a result, the bioplastic is inexpensive to produce. High manufacturing costs are a significant obstacle to the widespread adoption of bioplastics, according to the study, making this innovation an important breakthrough. Furthermore, the in-situ lignin regeneration process can be performed for various types of materials, and the study found that lignocellulosic bioplastic can be made from grass, wheat straw or bagasse, in addition to wood.

The study found that the lignocellulosic bioplastic exhibited a high tensile strength of about 128 MPa. This figure means the material is stronger than two widely used plastic films: acrylonitrile butadiene styrene, or ABS, and polyvinyl fluoride, or PVF.

The bioplastic also demonstrated “excellent” water stability, a common weak point for other bioplastics derived from hydrophilic cellulose and hemicellulose. In one of the study’s experiments the lignocellulosic bioplastic retained its shape without any fractures after spending 30 days submerged in water. By contrast, a cellulose film submerged for the same amount of time disintegrated completely. The bioplastic also exhibited good heat stability, with a thermal degradation temperature of 357 degrees Celsius.

In addition to being a strong material, the lignocellulosic bioplastic is highly biodegradable. The study found that a sheet of the bioplastic buried at a soil depth of 5 centimeters biodegraded completely after three months. The material was also placed in the grass outside for “several months,” where it again biodegraded completely, according to the paper. By contrast, the commonly used plastic polyvinyl chloride, or PVC, did not decompose at all in a similar environment over the course of three months.

The bioplastic can also be broken down by mechanical stirring and returned to its slurry state, from which it can be recycled. The DES used to create the slurry can also be recycled by saving the filtrate produced during processing and evaporating the water, the paper explains. The DES remains effective at deconstructing the wood even after being recycled several times.

The researchers also undertook a life-cycle assessment of the lignocellulosic bioplastic to determine its environmental impact, looking at factors such as the amount of electricity used during manufacturing. They found that it generally had a lower environmental impact than ABS, PVF and several other bioplastics.

“What is remarkable about the study is how the research team was able to address so many of the challenges that had previously frustrated other efforts to make conventional plastic waste more recyclable,” Marian Chertow, professor of industrial environmental management at the Yale School of the Environment and director of the Yale Center for Industrial Ecology, wrote in an email to the News. “Even when something sounds so promising there is always the question of how do we know that this new solution is better in environmental terms than other competing technologies. The authors, therefore, chose to do a life-cycle assessment, led by Prof. Yuan Yao, who was able to make the comparisons and confirm the benefits of this bioplastic.”

Some questions remain about the scalability of the technology, according to Hu, although the study indicates that the manufacturing processes used to produce the bioplastic can be performed on a larger scale than in their experiment. Hu also suggested that future research might look at how the bioplastic can be produced in different shapes.

“The [Yale] Center for Industrial Ecology is very proud of Dr. Yuan’s involvement in this project, and we look forward to the next research steps on this bioplastic, and eventually seeing it scaled up and commercialized,” Chertow wrote.

According to the Environmental Protection Agency, 27 million tons of plastic were deposited in American landfills in 2018.

Sam Panner | sam.panner@yale.edu

SAM PANNER