Wood chemical modification based on bio-based polycarboxylic acid and polyols – status quo and future perspectives

Novel approaches for a non-toxic protection of timber have been investigated and referred to as "wood modification". Especially, chemical impregnation modifications show promising opportunities to improve a wide range of wood properties. Yet, most of the available treatments resort to technically synthesized oil-based chemicals. Therefore, new ways of wood modification based on citric acid (CA) and bio-based low-molecular-weight polyols (CA-PO) – both originating from renewable resources – are under test and appear to be a promising alternative to available processes. The mode of action is expected to be a combination of both a cell wall bulking, and a cross-linking between CA-PO polyesters and wood cell wall polymers. However, the treatment process requires optimization with regard to the impregnation system and parameters for an industrial scale implementation. This paper provides a general background about CA-based solid wood treatment and its effects on the characteristics of wood. Moreover, it discusses current developments in this area and points out existing research gaps, with one focus being the process of development on an industrial scale.