A new study by researchers at Oregon State University details a key advance in turning apple waste into an environmentally friendly packaging material that could serve as an alternative to plastic. The researchers report their advance in a paper in Food and Bioproducts Processing.

Recycled newspaper has traditionally been the main ingredient of so-called molded pulp packaging products, which have become increasingly popular because they are compostable. But the supply of recycled newspaper is in decline, creating a market for substitute materials.

Yanyun Zhao, a professor at Oregon State University who leads a research team focusing on sustainable food packaging and processing, has investigated replacing the recycled newspaper in molded pulp packaging with apple pomace and other by-products from processing fruit and vegetable juice. She has received a patent for this research.

“Right now, apple pomace is typically just composted or used for animal feed,” said Zhao, whose research aims to reduce food loss and waste across the food supply chain. “We thought why not turn it into an environmentally friendly product that meets an industry need.”

Zhao envisions apple pomace being the main ingredient for molded pulp packaging products such as take-out containers, flowerpots, beverage cartons and bottles, and clamshell packaging used for fruits and vegetables.

She is focused on apple pomace, in part, because it is readily available in the Pacific Northwest. When apples are processed for juice, about 70–75% of the apple goes into the juice, leaving the remaining 25–30% as pomace.

One of the key problems to solve for pomace- and paper-based packaging is improving its water resistance so the packaging can deal with high moisture, liquid food or non-food items, and products stored under high humidity conditions. This inspired the team to create eco-friendly, bio-based, compostable and cost-effective solutions that would improve the hydrophobicity, or water resistance, of the apple pomace-based molded pulp products.

They pursued two strategies: incorporating polymers and compounds that will improve water resistance, including lignin, chitosan and glycerol, into the pulp formulation; and applying superhydrophobic coatings to the surface of apple pomace-based molded pulp products.

Lignin is a polymer that forms key structural materials in the support tissues of most plants. Rhubarb pomace, which is particularly rich in lignin, was used in this study. Chitosan is a bio-based polymer commonly used in the papermaking industry. A previous study by Zhao’s team found that chitosan significantly reduced the water absorption of cellulose nanofiber (CNF) films through its adsorption onto CNF fibers via hydrogen bonds.

Finally, glycerol is an organic compound often added to a material to make it softer and more flexible. Previous studies have shown that at low levels glycerol can decrease water absorption. The researchers determined the optimal amounts of these polymers and compounds, while also adding a small amount of cardboard fiber to enhance the stability of the molded pulp packaging products.

Zhao’s team also has a long history of studying food coatings as a barrier to water and gases. The team had previously created a two-step preparation process for a superhydrophobic coating that is resistant to heat, cold and water. They applied a simplified, one-step coating on the surface of the apple pomace-based product to enhance its water resistance.

The researchers concluded that their study demonstrated the feasibility of using fruit pomace as a new source of fiber in producing molded pulp packaging and identified effective approaches for enhancing water resistance in those packaging materials.

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

Yanyun Zhao with flowerpots made from apple pomace-based molded pulp packaging. Photo: Oregon State University.
Yanyun Zhao with flowerpots made from apple pomace-based molded pulp packaging. Photo: Oregon State University.