When Wood is Stronger Than Steel: Remove Some of the Lignin and Press for a Day

February 10, 2018 – Treated wood can be made to be stronger than steel these days. Through a combination of chemical baths and presses, new forms of wood represent an eco-friendly alternative to metal, plastic and other building materials. Soon we may see cars and buildings made of the stuff.

In an article published in Nature this last week, Teng Li, University of Maryland, describes a simple, effective way to transform natural wood into a “high-performance structural material with a more than tenfold increase in strength, toughness and ballistic resistance…with greater dimensional stability.”

The process involves the partial removal of lignin and hemicellulose by boiling natural woods in an aqueous mixture of sodium hydroxide and sodium sulfite followed by hot-pressing at 100 Celsius (212 Fahrenheit) degrees for a day. The end result, the total collapse of the wood’s natural cell walls and increased densification and highly aligned cellulose nanofibres. Using a scanning electron microscope they could see that the process crushed the cellulose tubes together until they crumpled and interlocked.

The key to strengthening wood involves removing the right amount of lignin (about 45%). When too much is removed it causes the wood to become brittle.

To test the modified wood strength, 9-millimeter lead pellets fired from a ballistic air gun were unable to penetrate a five-layer laminate of this new material, a mere 3 millimeters thick. The speed of the test firing although slower than a speeding bullet, was 30-meters (approximately 100 feet) per second, roughly equivalent to the speed of a car in normal traffic on a city street.

Using this treated wood, where today we currently use far more carbon-intensive materials, would help to reduce greenhouse gases. And I can imagine that cars like the old Ford Woody, (see image below) one that I remember from my childhood would still be around today.