The race to make plastics renewable has led to bioplastics made from cornstarch, sugarcane, potatoes, coffee grounds, food waste, and algae. Researchers now introduce a new contender made of waste wood powder that they say could be a stronger, cheaper, and more sustainable alternative.
The bioplastic, reported in the journal Nature Sustainability, is strong: it can hold liquids without degrading and resist damage from UV light. Yet at the end of its life, it can be fully recycled or biodegraded.
As the environmental impact of the growing tide of plastics in oceans and on land becomes more obvious, scientists have been scrambling to make alternatives to petroleum-based plastics. But it has proven tricky to make bioplastics that are cheap, strong, water-resistant, and that can degrade quickly when their use is over.
Commercially available bioplastic cutlery, for instance, can last just as long as petroleum-based plastics in landfills and the natural environment. Bioplastics that are designed to degrade after a single use, meanwhile, might not fare well under heat and sunlight. Plus, making bioplastics often requires toxic chemicals and complicated processing steps. A recently reported plastic alternative made from wood and spider silk, for instance, requires processing wood pulp and mixing it with engineered spider silk proteins.
“It is critical to develop a simple and sustainable method of fabricating bioplastics from naturally abundant resources, in which the final product must be biodegradable at its end-of-life while at the same time being mechanically strong and robust during service,” researchers at Yale University and the University of Maryland write in the new paper.
The wood-based plastic they have made just might meet all these needs. The team starts with wood powder that’s a waste product from lumber mills. Wood is made of three components: the starchy fibers cellulose and hemicellulose that form cell walls, and the polymer lignin that glues them together.
They mix the powder in a green solvent that dissolves lignin and breaks the bonds between the cellulose fibers. After removing the hemicellulose, they get a thick slurry of cellulose and lignin in which lignin fills the spaces inside a 3D network of cellulose fibers.
Using a simple casting process, the researchers turn this slurry into solid bioplastic films. These films, which could be used to make bags and packaging, can be easily recycled by breaking it up mechanically in water to give a reusable cellulose–lignin slurry. Buried in soil, they are degraded by microorganisms and completely disappear in three months.
“That, to me, is what really makes this plastic good: It can all be recycled or biodegraded,” says Yuan Yao, a professor of industrial ecology and sustainable systems at Yale. “We’ve minimized all of the materials and the waste going into nature.”
Source: Qinqin Xia et al. A strong, biodegradable and recyclable lignocellulosic bioplastic. Nature Sustainability, 2021.