An edible fungus could make paper, fabric liquid-proof

As an alternative to single-use plastic wrap and paper cup coatings, researchers in ACS’ Langmuir report a way to waterproof materials using edible fungus. Along with fibers made from wood, the fungus produced a layer that blocks water, oil and grease absorption. In a proof-of-concept study, the impervious film grew on common materials such as paper, denim, polyester felt and thin wood, revealing its potential to replace plastic coatings with sustainable, natural materials.

“Our hope is that by providing more ways to potentially reduce our reliance on single-use plastics, we can help lessen the waste that ends up in landfills and the ocean; nature offers elegant, sustainable solutions to help us get there,” says Caitlin Howell, the corresponding author of the study from the University of Maine.

Fungi are more than their mushroom caps; underground they form an extensive, interwoven network of feathery filaments called mycelium. Recently, researchers have been inventing water-resistant materials made from these fibrous networks, including leather-like, electrically conductive gauze and spun yarn, because the surface of mycelium naturally repels water. Additionally, films made from the fluffy wood fibers used in paper-making — specifically, a microscopic form called cellulose nanofibrils — can create barriers for oxygen, oil and grease. Howell and colleagues wanted to see if the edible “turkey tail” fungus (Trametes versicolor) would grow with cellulose fibrils into a protective coating on various materials. Their goal was to develop a food-safe, natural film with water-, oil- and grease-resistant properties.

To create the film, the researchers first blended T. versicolor mycelia with a nutrient-rich solution of cellulose nanofibrils. They applied thin layers of the mixture to denim, polyester felt, birch wood veneer and two types of paper, letting the fungus grow in a warm environment. Placing the samples in an oven for one day inactivated the fungus and allowed the coating to dry. It took at least three days of fungal growth for an effective water barrier to develop. And after four days, the newly grown layer didn’t add much thickness to the materials (about the same as a coat of paint), but it did change their colors, forming mottled yellow, orange or tan patterns.

Water droplets placed on the fungus-treated textiles and paper formed bead-like spheres, whereas similar droplets on untreated materials either flattened out or soaked in completely. In addition, the fungal coating prevented other liquids from absorbing, including n-heptane, toluene and castor oil, suggesting that it could be a barrier to many liquids. The researchers say this work is a successful demonstration of a food-safe fungal coating and shows this technology’s potential to replace single-use plastic products.

The authors acknowledge funding from the University of Maine Sea Grant, funded by the National Oceanic and Atmospheric Administration’s National Sea Grant Program; a UMaine Flagship Fellowship; the National Science Foundation; and The Specialized Materials and Manufacturing Alliance for Resilient Technologies (SM²ART) program between Oak Ridge National Laboratory and the University of Maine.

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