New process makes wood stronger than many titanium alloys

Researchers from the University of Maryland have developed a type of “super wood” that has the strength of many titanium alloys while being both lighter and cheaper. Their process for treating wood makes it 12 times stronger than natural wood and 10 times tougher, offering a potential alternative to a range of structural materials.

With natural wood being cheap and abundant, this is could be a promising way to design lightweight, high-performance materials that improve on those currently used. The research, which was published in the journal Nature [Song et al. Nature (2018) DOI: 10.1038/nature25476], demonstrates a simple strategy for transforming bulk natural wood directly into a high-performance structural material with a more than tenfold increase in strength, toughness and ballistic resistance.

While a range of methods have been developed to pre-treat wood before densification, such as steam, heat, ammonia and cold-rolling, they tend to only soften the wood structure without altering its chemical composition, resulting in incomplete densification and only a modest enhancement its mechanical properties. However, this technique is based on a two-step process that combines chemical modification, involving the partial removal of lignin and hemicellulose from the natural wood via a boiling process, with hot-pressing. The resulting wood offers a highly dense and laminated structure with intertwined cell walls that are fully collapsed without gaps, demonstrates a record high tensile strength, and being very stable under moisture attack.

“The findings of this research not only demonstrate remarkably enhanced mechanical properties of natural wood, but also shed light on a promising solution toward high-performance, low-cost and sustainable structural materials”Teng Li

On measuring the dense wood's mechanical properties, the team found it as strong as steel, but six times lighter. It also takes 10 times more energy to fracture than natural wood, and it can even be bent or molded during the processes early stages. They also compared the new treated wood material with natural wood by shooting projectiles at them – while these went straight through the natural wood, the densified wood partly stopped them.

Synthetic structural materials can be too heavy, not good for the environment, or difficult to produce and therefore not cost-effective, but this approach was shown to be beneficial for different types of wood. As co-leader Teng Li said, “The findings of this research not only demonstrate remarkably enhanced mechanical properties of natural wood, but also shed light on a promising solution toward high-performance, low-cost and sustainable structural materials”.

The densified wood could find uses as a structural material in lightweight vehicles, CO₂-free building with wood structures, advanced furniture and in aerospace applications, providing better performance and less of a carbon footprint. The team are now exploring its potential integration into a range of applications that require the material to meet the complete performance matrix.