As a building material, glass is inefficient in terms of energy management and poses safety risks as it can easily shatter. Materials with greater thermal insulation and better light management than glass would significantly contribute to increasing the energy efficiency of buildings, considering that over 50% of the energy used in buildings is used for lighting and air conditioning. Liangbing Hu and colleagues at the University of Maryland, College Park, US, have now shown that wood can be processed into a transparent composite with superior optical and mechanical properties to glass, making it a promising candidate for use as a building material.
A wood composite with a transparency of 85% of the visible range is obtained by removing the lignin from the wood cells, which are then filled with a polymer that has the same refractive index as cellulose and hemicellulose — the compounds making up the cell walls. The cell walls, naturally vertically aligned, act as a waveguide for the light which is transmitted through the wood panel and scattered with a haze greater than 95%, resulting in uniform indoor lighting insensitive to the Sun direction. The composite has a thermal conductivity three times lower than that of glass, helping to maintain a constant temperature, and is much more ductile than glass, and thus better able to absorb impact energy.