- A new type of wood reflects sunlight and radiates away excess heat.
- The mechanical strength per weight of this new wood is 3 times stronger than steel.
- It could drop a building’s temperature up to 10°C, slashing 60% cooling costs.
In the United States, buildings account for nearly 70% of electricity use, generating an annual national energy bill of over $430 billion. Cooling and heating alone account for 48% of this energy use.
According to the 2nd law of thermodynamics, cooling is more challenging than heating. So far, scientists have come up with various techniques about how to handle concrete and steel production and various passive cooling schemes to reduce cooling costs.
Now, researchers at the University of Maryland and the University of Colorado have discovered a single solution that seems to manage everything using a wood material which reflects sunlight and radiates away excess heat.
Making The New Wood
Most materials absorb heat and emit it as near-infrared (IR) photons. These photons are then absorbed by surrounding air molecules, which makes the area hot. In the last couple of years, scientists have developed paints and plastic films that capture heat and emit it at longer mid-IR wavelengths. In this case, photons dump their heat into deep space, and since air does not absorb these wavelengths, the surrounding area remains cool.
Instead of using any paint or plastic sheet, the research team tried to mimic such behaviors in wood materials. Wood comprises of two major elements:
- Cellulose that forms long straw-like structures
- Lignin that behaves like an adhesive holding the straw strands together.
Lignin strongly emits IR photons, thus researchers chose to remove this element from the wood. To do this, they soaked the wood in a solution of hydrogen peroxide. They then compressed the chemically treated wood which led to the formation of a dense hydrogen bonding mesh.
This resulted in a material 8 times stronger the natural wood. In fact, the mechanical strength per weight of this new material is more than 3 times stronger than steel. Scratch test proved that the wood cannot be easily damaged while compression test showed that it can bear more weight than natural wood.
By removing lignin, the wood turns white, reflecting almost all incoming rays. Although it does not radiate heat away as efficiently as plastic sheets, it could really make a big difference.
Sample of new wood | Credit: UMD
If fixed on a building’s exterior, the wood could reduce the temperature up to 10°C, slashing 60% cooling costs. What’s more impressive is the nanotechnology is solely based on wood; there is no other components (such as polymers) involved.
However, the new wood is flammable and far less durable than standard roofing materials, such as asphalt shingles. Moreover, it could be costly and potential energy saving may not offset the expense.