While sustainably-grown wood can be an economical and eco-friendly building material, its relatively low tensile strength limits its potential applications. That could soon change, however, thanks to a new self-densifying technique for creating super-strong wood.
Individual wood fibers are made up mainly of cellulose, along with a binder material known as lignin. This mixture forms the wall of what is essentially a long hollow tube – the fiber – which runs lengthwise within the larger piece of wood. The hollow space inside the tube is called the lumen, and it is what limits wood's strength.
A team from China's Nanjing University recently set out to address that shortcoming, by developing the new process.
It begins by boiling a block of wood in a mixture of sodium hydroxide (lye) and sodium sulfite, removing some of the lignin. That block is then immersed in a heated blend of lithium chloride salt and a solvent known as dimethylacetamide. This causes the cellulose (and remaining lignin) to swell, expanding inwards to fill the lumen.
In a final step, the processed wood is left to air-dry at room temperature for 10 hours. As it does so, it uniformly shrinks inwards from all sides, but maintains its original length.
The resulting material is claimed to exhibit "ultra-high" tensile strength, flexural strength, and impact toughness – much more so than natural wood. It even surpasses wood which has been compressed by traditional methods, in which the fibers are just mechanically flattened in one direction.
And unlike other methods of uniformly densifying wood, it doesn't require an energy-intensive hot-pressing process.
It is hoped that once the technology is developed further, the self-densified wood could be used as an alternative to traditional metals in building construction and other possible applications.
A paper on the research, which was led by Dafang Huang and Jie Li, was recently published in the Journal of Bioresources and Bioproducts.
Source: Journal of Bioresources and Bioproducts via EurekAlert
