A barista slides a white paper coffee cup toward the outer edge of a coffeeshop counter.

Coating strengthens paper packaging without harmful plastics and chemicals

A lot of people think they are choosing an environmentally friendly bag or packaging material if they use paper instead of plastic. But that’s not always the case because today’s paper packaging is not the same as it was a couple of decades ago. 

The microplastic problem

Paper packaging now contains chemicals and plastics to make it less likely to tear under stress or disintegrate when wet. Without these coatings, paper coffee cups and juice boxes would leak, for example. Alternatives to plastic coatings present other problems — many contain PFAS, or forever chemicals.

That creates a problem at the packaging’s end of life: The plastic coatings prevent the paper from breaking down in the trash or in waterways. The plastic eventually breaks down into microplastics that enter the environment and can end up in the seafood people eat. Integrated plastic also prevents items like paper coffee cups from being recycled.

A soluble solution

Michigan State University researchers developed a new coating that protects paper packaging from oil and water, but it is made from environmentally friendly, biodegradable materials. 

“The question we asked was can we get rid of the plastics that become microplastics without using PFAS,” Muhammad Rabnawaz, assistant professor at Michigan State University, said in a news release.

Two brown paper cups, the right labeled "control" with visible liquid leakage, and "coated" on the left with none.
A paper cup coated with the new MSU material on the left holds liquid without leaking, unlike its uncoated counterpart on the right. Credit: Muhammad Rabnawaz / Sustainable Materials Group
  • The coating is made from an oil used in contact lenses, a water-soluble polymer called polyvinyl alcohol, and chitosan, a natural starch-like polymer that comes from shellfish. It does not contain the shellfish proteins that cause an allergic reaction in some people. 
  • Chitosan is naturally abundant, but not much of it is prepared in the U.S. for manufacturing purposes. Therefore, the research team incorporated the polyvinyl alcohol into their coating to reduce the amount of chitosan needed. Polyvinyl alcohol is more readily available and less expensive; it is used as the outer coating for laundry pods.
  • The soluble polymers are strong but not as resilient as the thermoplastics currently used as paper coatings, so they break down over time when exposed to moisture and UV light. “All plastics are polymers, but not all polymers are plastic,” Rabnawaz said.
  • The coating can be removed when the paper is repulped, making the paper recyclable. “The paper becomes just like pristine paper and you can use it over and over again,” Rabnawaz said.

The team is working to commercialize this coating. Rabnawaz already has filed two patents for it and started sharing samples with companies that might be interested in using it in their products.

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