Biochar materials engineered from wood demonstrate mechanical strength comparable to steel

Biochar materials engineered from wood demonstrate mechanical strength comparable to steel
by Riko Seibo
Tokyo, Japan (SPX) Nov 01, 2025

A team at the University of Toronto has found that the internal structure of wood allows biochar to achieve hardness matching mild steel, depending on how the material is measured. Their research shows monolithic biochar - carbonized wood blocks that maintain natural architecture - exhibits a hardness that can vary by more than 28 times based on orientation. This breakthrough enables targeted creation of carbon materials for energy, filtration, and technical uses.

Biochar, formed by heating biomass without oxygen, is commonly used for environmental purposes but has not previously been explored for its mechanical properties in engineering and energy applications. Led by Professor Charles Jia, the team analyzed biochar from seven wood species including maple, pine, bamboo, and African ironwood, heating samples between 600 and 1,000 degrees Celsius. Both wood type and processing temperature significantly influenced hardness. African ironwood biochar attained axial hardness values of 2.25 gigapascals, matching mild steel. Hemlock biochar demonstrated directional differences in hardness up to 28.5 times between axes.

Micro- and nano-indentation analysis mapped hardness at both structural and microscopic scales. The researchers determined that the unusual difference in strength depending on measurement direction is caused by the wood's hierarchical pore network. At the nanoscale, hardness was consistent across all samples, indicating natural cell-wall properties do not change based on species or direction.

The study identified strong links between biochar hardness, bulk density, and carbon concentration. Denser biochar with greater carbon resisted deformation more successfully. Manipulating feedstock selection and pyrolysis conditions provides a way to fine-tune performance for specific applications.

Professor Jia stated, "These findings show that biochar is not just an environmental material, it is a structural one. By preserving the natural architecture of wood, we can design sustainable carbon materials with targeted mechanical properties suitable for specific industrial applications."

Potential engineering uses for monolithic biochar include high-strength electrodes, lightweight carbon composites, and custom filters for directional flow. The ability to adjust material properties by orientation and production method enables better alignment of design with practical engineering needs.

The research creates a quantitative approach for engineering biochar with reliable mechanical behavior and bridges materials science with sustainability. Wood's natural grain structure offers pathways to develop advanced carbon technologies.

Research Report:Unlocking extreme anisotropy in monolithic biochar hardness