Understanding the mode of action of sorbitol and citric acid (SorCA) in wood

In recent years, a wood treatment system based on sorbitol and citric acid (SorCA) has emerged as a promising alternative to already commercialized modification processes of European-grown wood species. The improvement of dimensional stability and biological durability have been reported. However, the mode of action behind the changes in wood structure leading to these improvements has not been well defined yet, as the research was based on the infrared spectroscopy, which cannot distinguish nor compare the effect of cell wall bulking (CWB), covalent bonding and cross-linking. Moreover, most of the assumptions regarding the reaction mechanism have resulted from the studies of citric acid reactions with wood and wood-based products. Therefore, in this study different analytical chemistry methods have been used to explain the interaction between SorCA and wood at two polymerization temperatures (120 and 140 degrees C). It has been confirmed that the curing temperature is a crucial parameter for achieving the desired fixation. Subsequently, liquid chromatography-mass spectrometry (LC-MS), cross-polarization/magic angle spinning (CP/MAS C-13-NMR) spectroscopy and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) have been used to determine the contribution caused by an in-situ formation of high molecular-weight SorCA polyesters (resulting in CWB) and a higher rate of esterification of wood polymers.

Automated summary

In recent years, a wood treatment system based on sorbitol and citric acid (SorCA) has emerged as a promising alternative to already commercialized modification processes of European-grown wood species. This study used different analytical chemistry methods to explain the interaction between SorCA and wood, confirming the crucial role of curing temperature in achieving desired fixation, and determining the contribution of high molecular-weight SorCA polyesters and increased esterification rate of wood polymers.