A lightweight, strong material derived from wood works better than the heat-insulating substances used today, researchers report in the journal Science Advances. The insulator, which its developers call “nanowood”, is easy and cheap to make, biodegradable, and could slash the carbon footprint of homes and office buildings.
Insulation keeps heat from escaping out of structures in the winter and from seeping inside in the summer. It is key for making homes and buildings energy-efficient and comfortable. Insulating typically involves stuffing walls with materials like fiberglass or plastic-based foams. These contain potentially toxic chemicals and cannot be recycled. Insulating foams made from natural cellulose are also available on the market. But they are made using a series of mechanical and chemical processes, which is difficult, expensive and energy-intensive.
Researchers have been searching for low-cost, effective insulators that are sustainable. The team of scientists and engineers from the University of Maryland and the University of Colorado, Boulder came up with a simple way to make such a material from wood.
They immerse a piece of wood in a bath of cheap chemicals—sodium hydroxide, sodium sulphite and hydrogen peroxide—which wash away the lignin, a polymer that holds wood together. This leaves behind a porous, lightweight white material composed of tiny fibers of cellulose in their natural arrangement in wood: lined up parallel to each other.
Lignin is a good heat conductor, and without it, the nanowood reflects heat. The parallel arrangement of the cellulose fibers is also important for the materials insulating properties. The fibers channel heat along their length but it can’t cross through because of air gaps between the fibers.
The nanowood is about 50 times stronger than cellulose foam and more than 30 times stronger than common commercial insulating materials, while working just as well. It is also relatively cheap to make, costing $7.44 per square meter. The researchers picked fast-growing American basswood, but say any kind of wood could be used.
Source: Tian Li et al. Anisotropic, lightweight, strong, and super thermally insulating nanowood with naturally aligned nanocellulose. Science Advances, 2018.
Photo: Hua Xie, University of Maryland