Tree bark could hold the key to the next generation of timber treatments, with scientists using birch and spruce bark, abundant in European forests, to create the world’s first bark-based treatment free of chemicals.
Published in the Materials Horizons journal, “Fully bio-based, water-resistant wood coatings derived from tree bark,” Mika Sipponen, the lead author of the research, said that a 90/10 mix of suberinic acids extracted from birch bark and polyphenols from spruce bark holds the key to developing non-synthetic timber treatments free of hazardous organic solvents and polymers derived from fossil hydrocarbon resources:
“Here, we show a fully bio-based wood surface protection system using components sourced from birch bark and spruce bark, inspired by the natural barrier function of bark in trees,” said Mr Sipponen, an assistant professor at Stockholm University. “The uniqueness of this research lies in its formulation, which is entirely derived from renewable resources, contrasting with the industry’s reliance on fossil-based synthetic coatings.”
According to Mr Sipoonen, durability is a challenge faced by all timber-based construction materials, with outdoor environments exposing wood to moisture, heat, sunlight, and microorganisms. Whilst applying a protective coating can prolong the lifespan of materials, the processing industry relies on synthetic coatings that contain hazardous organic solvents and polymers derived from fossil hydrocarbon resources.
As it stands, tree bark, which is often turned into waste or burnt for biomass, is a chronically under-utilised resource in the wood processing industry – with the EU alone producing more than 23 million cubic tons of wood every year. Inspired by the natural barrier properties of bark, Sipoonen started exploring it as a resource for wood protection in outdoor environments:
“Such an application holds immense potential to revolutionise the forest industry, shifting away from the current practice of burning tree bark for energy recovery towards utilising it in carbon-storing materials.”
Mika Sipponen, the lead author of the research.
“Our work provides new insight and underlying concepts to the materials science by showcasing tree bark as a valuable resource for wood protection, achieving superior water resistance compared to traditional alkyd emulsion coatings,” according to Mr Sipoonen. “This research advances sustainable materials science and offers a practical solution for transforming waste into high-value products, thereby promoting resource-efficient use of forest resources.”
His team found that heating bark can turn suberinic acids into a tough, rubber-like, and water-resistant coating. And while supersonic acids are viscous and water-insoluble, their waxy nature makes it difficult to spread them evenly without adding organic solvents. Here, the material scientists used spruce polyphenols to stabilise the suberinic acids in an aqueous suspension, distributing them uniformly to deliver an even coating: “Varying the concentration of the spruce bark polyphenols also allows the mechanical properties of the cured coating to be adjusted,” they said.
- For more information, visit “Fully bio-based, water-resistant wood coatings derived from tree bark,” F Wang et al., Mater. Horiz., 2024, DOI: 10.1039/d4mh01010h.
