CNRE of VT pioneers biodegradable plastic bags
December 3, 2020
Plastic waste is consistently in the news for its damaging effects on the environment. As a consequence, many stores worldwide, especially grocery chains, are beginning to switch back to using paper bags at the check-out registers for their customers. However, several private sector companies have recently begun to explore the development of plastic bags made from biodegradable materials.
With the help of Wolfgang Glasser, Professor Emeritus of the Department of Sustainable Biomaterials at Virginia Tech, CycleWood Solutions, LLC, a start-up company located in Arkansas has teamed up with BASF of Ludwigshafen, Germany. The partnership is producing and testing prototype compostable bags made out of a combination of modified, wood-derived substances called lignin, and a biodegradable polyester polymer called ecoflex which is manufactured by BASF. These XYLO bags (s. Figure) have already met all of the usual requirements of mechanical strength and compostability. Their success is based, in large part, on the research of Glasser and his many graduate students since 1972. Throughout the years, their research made the necessary chemical modifications to isolated lignin so that it was miscible with man-made polymers.
It turns out that lignin, the second most abundant polymer on the planet (after cellulose), contributes the same desirable material properties to plastics as it does to wood, namely stiffness and longevity. Without lignin, plants would be unable to lift their solar energy-collecting crowns off the ground. Lignin also contributes to the resistance to rapid biodegradation in wood. In short, adding lignin helps the product last longer, and then lignin helps convert the product to humus in a natural environment. Hence, XYLO bags decompose quickly, which has been tested successfully by a large distributor in Arkansas.
While technically successful in multi-ton, prototype-scale experiments, project development was stopped on account of odor. Even though lignin in nature is as odorless as wood, the only commercially available lignin comes from pulp & paper mills. They use the Kraft process to separate the lignin which is an operation that uses reduced sulfur compounds, and sulfer is notoriously malodorous. Unfortunately, this odor follows the lignin all the way through the isolation and melt processes!
In the advent of biorefineries, industrial companies are converting to the use of sustainable bioresources (wood and/or agricultural harvesting residues) which use non-chemical harvesting methods, such as ethanol or other carbohydrate-derived substances. This advancement holds the promise of someday generating odor-free isolated lignin for use in commercial plastics. Unfortunately, Glasser’s patience, as well as the validity of his 24 patents, will have expired by that time! While Glasser helped pioneer the field, it will be up to future researchers to continue the work towards creating commercially available, odor-free, biodegradable plastic bags using lignin.