Use of atomic force microscopy to detect wavelength dependent changes in wood veneers, and spin coated lignin and cellulose films exposed to solar radiation

Abstract

We examined whether spin coated lignin and cellulose films could act as material models for wood exposed to solar radiation. Films and wood were exposed to sunlight under filters that transmitted different parts of solar radiation. Changes in surface roughness, hardness and polarity of the films were analysed with atomic force microscopy and compared with those occurring on wood. All properties changed after exposure and the magnitude depended on the wavelength and substrate. The roughness of wood and lignin films increased after exposure, whereas it decreased on cellulose. The surface hardness of all three substrates increased more after exposure to less energetic radiation. Lignin films became more hydrophilic, whereas polarity changes of wood and cellulose were wavelength dependent. We conclude that lignin and cellulose films can act as material models for wood exposed to solar radiation and discuss how they might be used to develop new photoprotective wood treatments.