Engineering: Knock on (denser) wood

A simple way to transform bulk natural wood into a high-performance structural material - with impressive strength, toughness and ballistic resistance - is described in a paper published in this week’s Nature. This densified (compressed) wood is intrinsically light and delivers a specific durability higher than almost all structural metals and alloys.

Synthetic structural materials with exceptional mechanical performance are often heavy and environmentally harmful (steels and alloys) or expensive (polymer-based and biomimetic composites) to produce. Conversely, natural wood is a low-cost and abundant material that has been used for millennia as a structural material for building and furniture construction. However, its mechanical performance is unsatisfactory for many advanced engineering structures and applications.

Liangbing Hu and colleagues developed a method of treating wood before densification that substantially enhances its dimensional stability and mechanical properties - even in humid conditions where wood densified using existing processes is susceptible to weakening. The authors show that by partially removing lignin and hemicellulose components before hot-pressing it, they can compress the wood more effectively, with an 80 per cent reduction in thickness and around three times the density. Complete removal of lignin and hemicellulose produces a poor-quality material, so the authors suggest that some of the lignin must be retained to bind the wood. The resulting material shows impressive strength, toughness and ballistic resistance while being humidity-resistant, lightweight, simple and inexpensive to process, and less environmentally damaging to produce than many other structural materials.