Copyright Interesting Engineering
Wood, long admired for its natural beauty and strength, has now inspired a carbon material tough enough to rival steel. Researchers at the University of Toronto have discovered that biochar derived from wood can achieve hardness levels comparable to mild steel if measured in the right direction. Their new study shows that the direction in which biochar is tested can make its hardness vary by more than twenty-eight times, revealing how the inner structure of wood influences the performance of carbonized materials. The finding could usher in a new era of sustainable carbon materials for energy devices, filters, and structural systems. Biochar, a carbon-rich solid produced by heating biomass without oxygen, has typically been prized for improving soil and cleaning up pollutants. But its mechanical potential has largely gone unexplored. This research turns that assumption on its head, positioning biochar not just as an environmental material, but as a future building block for green engineering. The study focuses on monolithic biochar, the solid blocks of carbonized wood that preserve the original grain and pore structure of the wood. These structures, the researchers found, are key to its remarkable strength and directional hardness. Nature’s blueprint for carbon Led by Professor Charles Jia at the Green Technology Laboratory, the team tested biochar from seven species of wood, including maple, pine, bamboo, and African ironwood. The samples were heated between 600 °C and 1,000 °C, with both temperature and wood type playing major roles in determining strength. African ironwood biochar reached an axial hardness of 2.25 gigapascals, on par with mild steel. Hemlock, on the other hand, showed extreme directional differences, with hardness along the grain exceeding that across it by 28.5 times. Using micro- and nano-indentation tools, the team measured hardness at multiple scales. They discovered that this striking anisotropy, or direction-dependent behavior, originated not from the carbon itself, but from the wood’s intricate pore network. At the nanoscale, the hardness of all samples was nearly identical, suggesting that cell-wall properties remain consistent across species and directions. From waste to wonder material The researchers also found a strong correlation between hardness, bulk density, and carbon content. Denser biochar with higher carbon fractions was more resistant to deformation, offering a roadmap for tailoring performance through feedstock selection and pyrolysis conditions. “These findings show that biochar is not just an environmental material, it is a structural one,” said Professor Jia. “By preserving the natural architecture of wood, we can design sustainable carbon materials with targeted mechanical properties suitable for specific industrial applications.” Possible applications range from high-strength electrodes in energy systems to lightweight composites and directional flow filters. Engineers could potentially design materials that are stiff in one direction yet flexible in another, mirroring the performance of natural wood. By decoding wood’s hidden architecture, the study provides the first quantitative framework for designing monolithic biochar with predictable mechanical behavior, bridging the worlds of materials science and sustainability. The research was published in Biochar X.
