Bark-based functional wood coatings for indoor air remediation

Indoor air quality can be improved by coatings that adsorb harmful volatile organic compounds (VOCs). In the present work, bio-based and VOC-adsorbing wood coatings were fabricated from polyphenols extracted from spruce bark, biochar produced from mixtures of spruce and pine bark, and a polyamine crosslinker. The bark-based biochar was doped with a catalyst (MnO 2 ) to enable continuous elimination of the adsorbed VOCs so that the coatings would not become saturated. The coatings formed a homogenous and smooth layer that covered the whole surface of the wood and showed excellent adhesion to the substrate, while their VOC removal efficiency was dependent on the pollutant type and the coating weight. The best performance was achieved toward formaldehyde, followed by chloroform and methyl ethyl ketone. Thick coatings (200–220 g/m 2 ) reached a formaldehyde removal of 62%, with the coating base and the biochar contributing nearly equally to the VOC removal. Overall, the bark-based coatings showed good potential for improving indoor air quality, but the surface wettability of the coated spruce wood was high. Despite the presence of biochar and nitrogen-containing aromatic compounds, the coatings did not appear to improve the reaction to fire of the wood.