Sorption behavior and swelling of citric acid and sorbitol (SorCA) treated wood

Citric acid together with sorbitol (SorCA) have been used to modify wood and improve its properties, such as dimensional stability and biological durability, which partly result from its swelling and sorption behavior. However, the underlying mechanism of water interaction with SorCA-treated wood is very complex and not fully understood. Previous research confirmed cell wall bulking and suggested cross-linking, however the extent of their contribution to moisture-induced changes has not been researched. This study investigated the effect of SorCA treatment on sorption properties of wood in the hygroscopic range (0-95% RH). Scots pine sapwood (Pinus sylvestris L.) was chemically modified with an aqueous SorCA solution at different treatment levels and measured by dynamic vapor sorption (DVS). The observed permanent increase in oven dry dimensions did not result in a decreased swelling compared to untreated specimens. It was ascribed to the excessive expansion of cell wall matrix caused by a degradation of cell wall constituents by the acidic impregnation solution. However, a reduction in moisture content in comparison to untreated reference was detected. Present findings suggest that the SorCA polyester structure is altered after impregnation inside the wood and affects its sorption behavior by covalent bonding and, presumably, cross linking with wood polymer constituents.

Automated summary

The study investigated the effect of SorCA treatment on the sorption properties of wood and found that while it increased the dimensions of the wood, it did not decrease swelling compared to untreated specimens. This was attributed to the excessive expansion of the cell wall matrix caused by degradation of cell wall constituents by the impregnation solution. However, a reduction in moisture content compared to untreated wood was observed, suggesting that the SorCA structure is altered and affects the sorption behavior of the wood through covalent bonding and potentially cross linking with wood polymer constituents.