Scientists have found a way to make strong wood even stronger—removing the hollow tubes that run through its cellulose structure—paving the way for timber to replace metals in more construction applications and potentially in aircraft and cars. Known as the “lumen,” scientists from China’s Nanjing University claim the tubes have, until now, limited wood’s natural strength, which is the root cause of its low tensile strength relative to metal and alloy equivalents.
Published in the Journal of Bioresources and Bioproducts, the scientists have invented a new chemical method for making wood denser by filling these tubes uniformly. Treated this way, the wood “exhibits ultra-high tensile strength (496.1 MPa), flexural strength (392.7 MPa) and impact toughness (75.2 kJ/sq m), surpassing those of compressed densified wood and traditional metal materials like aluminium alloys”.
This process of “self-densification” is caused by boiling the wood in a mixture of caustic soda and sodium sulphite to remove some of its lignin. It is then soaked in a mixture of lithium chloride and a solvent known as dimethylacetamide, causing the cellulose and lignin to swell and eliminate the lumen tubes before being left to dry and shrink.
Led by Dafang Huang from Nanjing’s Department of Material Science and Engineering, the technique’s main attraction is that it causes “uniform shrinkage,” which is far superior to the “hot pressing” method, which can only mechanically compress wood on a single axis: “This uniform shrinkage leads to an order-of-magnitude enhancement in the overall mechanical performance of the wood, presenting a significant advantage over compressed densified wood,” Huang said, adding that super-strong wood has “great potential for application as a sustainable engineering material, replacing traditional structural materials as metals and alloys.”
Scientists’ secret for making untreated wood as strong as aluminium!
Last year, Wood Central reported that scientists in Maryland, in the United States, have created a new type of poplar wood that is as strong as chemically treated wood and on par with aluminium for strength. They accomplished this by using base editing to affect a key gene in poplar trees that deals with lignin production, reducing the amount of lignin in poplar trees by about 13%.
“Typically, when you engineer wood to be stronger and more durable, you do that by chemically reducing the amount of lignin in the wood,” said Professor Yiping Qi, one of the lead authors in the study. “The process is energy-intensive and involves the use of a plethora of chemicals that could harm the environment.”
