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A porous material made by treating wood with sodium hydroxide could better insulate homes against cold and noise.

Wood is one of the most sustainable building materials available, but it is generally a poor insulator. Now, at the University of Maryland and his colleagues have worked out how to rapidly heat wood and then slowly cool it to remove polymers known as lignin and hemicelluloses, making it porous and therefore a more effective insulator.

The researchers call the resulting material insulwood. They say it makes an ideal material to use as insulation in buildings because it is much stronger than polystyrene foam and can double up as a structural element. It should also degrade safely at the end of its life.

The researchers used paulownia wood from Paulownia tomentosa聽because it is a fast-growing tree that is found around the world. But they say a wide range of woods, including balsa, basswood and pine would also be suitable.

Hu and his colleagues boiled the wood in a solution of sodium hydroxide 鈥� a strong alkali chemical already employed in the paper industry 鈥� to remove the lignin and hemicelluloses, and then dried the wood at an ambient temperature for 7 hours. This created numerous small voids less than 10 micrometres across in the wood, dropping its density from 0.27 grams per cubic centimetre to just 0.11 grams per cubic centimetre.

The process made insulwood about three times as good a thermal insulator as untreated wood, found the researchers, and, for a given thickness, it matched the insulation properties of expanded polystyrene (EPS) foam, which is commonly used in buildings.

Wrapping the new material in a plastic coating, creating a vacuum, made resulting panels of insulwood about 10 times as good as natural wood for preventing heat loss.

The researchers also found that the material retained much of the strength of the original wood. In tests, it was around seven times as strong as EPS foam, meaning that it could be used in buildings as a combined structural and insulating component.

The treated wood was also 10 times better at blocking sounds than untreated wood, when tested at frequencies of 500 and 2500 hertz.

Hu says the material has the potential to reduce the carbon emissions involved in building new homes, because it could replace foam made with oil, as well as cutting subsequent environmental damage.

鈥淭he disposal or landfilling of synthetic materials, especially polymer foams, at the end of use can cause environmental issues since it takes hundreds or even thousands of years for most plastics to degrade due to the stable long polymer chains,鈥� he says. 鈥淭he insulwood 100 per cent comes from natural woods and can be biodegradable in an ambient [environment] within several months.鈥�