Paperboard coated with the sustainable biomaterial exhibited strong oil and water barrier properties. The coating also resisted toluene, heptane and salt solutions, and exhibited improved wet and dry mechanical and water vapor barrier properties. Photo: Penn State.
Paperboard coated with the sustainable biomaterial exhibited strong oil and water barrier properties. The coating also resisted toluene, heptane and salt solutions, and exhibited improved wet and dry mechanical and water vapor barrier properties. Photo: Penn State.

An inexpensive biomaterial that can be used to sustainably replace plastic barrier coatings in packaging and many other applications has been developed by researchers at Penn State, who predict that its adoption would greatly reduce pollution.

Completely compostable, the material – a polysaccharide polyelectrolyte complex – is comprised of nearly equal parts treated cellulose pulp from wood or cotton, and chitosan, which is derived from chitin – the primary ingredient in the exoskeletons of arthropods and crustaceans. The main source of chitin is the mountains of leftover shells from lobsters, crabs and shrimp consumed by humans.

These environmentally friendly barrier coatings could have numerous applications, said lead researcher Jeffrey Catchmark, professor of agricultural and biological engineering in Penn State’s College of Agricultural Sciences. The potential applications range from water-resistant paper, to coatings for ceiling tiles and wallboard, to food coatings to seal in freshness.

"The material's unexpected strong, insoluble adhesive properties are useful for packaging as well as other applications, such as better performing, fully natural wood-fiber composites for construction and even flooring," said Catchmark. "And the technology has the potential to be incorporated into foods to reduce fat uptake during frying and maintain crispness. Since the coating is essentially fiber-based, it is a means of adding fiber to diets."

The amazingly sturdy and durable bond between carboxymethyl cellulose and chitosan is the key, he explained. The two very inexpensive polysaccharides – already used in the food industry and in other industrial sectors – have different molecular charges and lock together in a complex that provides the foundation for impervious films, coatings, adhesives and more.

The potential of these coatings for reducing pollution is immense. They could replace millions of tons of petroleum-based plastic associated with food packaging that is used every year in the US – and much more globally, Catchmark noted.

He pointed out that the global production of plastic is approaching 300 million tons per year. In a recent year, more than 29 million tons of plastic became municipal solid waste in the US and almost half was plastic packaging. It is anticipated that 10% of all plastic produced globally will become ocean debris, representing a significant ecological and human health threat.

The polysaccharide polyelectrolyte complex coatings performed well in research, the findings of which are published in a paper in Green Chemistry. Paperboard coated with the biomaterial, comprised of nanostructured fibrous particles of carboxymethyl cellulose and chitosan, exhibited strong oil and water barrier properties. The coating also resisted toluene, heptane and salt solutions, and exhibited improved wet and dry mechanical and water vapor barrier properties.

"These results show that polysaccharide polyelectrolyte complex-based materials may be competitive barrier alternatives to synthetic polymers for many commercial applications," said Catchmark, who, in concert with Penn State, has applied for a patent on the coatings. "In addition, this work demonstrates that new, unexpected properties emerge from multi-polysaccharide systems engaged in electrostatic complexation, enabling new high-performance applications."

Catchmark began experimenting with biomaterials that might be used instead of plastics a decade or so ago, out of concerns for sustainability. He became interested in cellulose, the main component in wood, because it is the largest volume sustainable, renewable material on earth. Catchmark focused on studying its nanostructure – how it is assembled at the nanoscale.

He believed he could develop natural materials that are more robust with improved properties, allowing them to compete with synthetic materials that are not sustainable and generate pollution. Examples include the low-density polyethylene laminate applied to paper board, Styrofoam, and the solid plastic used in cups and bottles.

"The challenge is, to do that you've got to be able to do it in a way that is manufacturable, and it has to be less expensive than plastic," Catchmark explained. "Because when you make a change to something that is greener or sustainable, you really have to pay for the switch. So it has to be less expensive in order for companies to actually gain something from it. This creates a problem for sustainable materials – an inertia that has to be overcome with a lower cost."

Funded by a Research Applications for Innovation grant from Penn State’s College of Agricultural Sciences, Catchmark is currently looking for commercialization partners in different industry sectors for a wide variety of products.

"We are trying to take the last step now and make a real impact on the world, and get industry people to stop using plastics and instead use these natural materials," he said. "So they (consumers) have a choice – after the biomaterials are used, they can be recycled, buried in the ground or composted, and they will decompose. Or they can continue to use plastics that will end up in the oceans, where they will persist for thousands of years."

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.