Reactivity of Waterlogged Archeological Elm Wood with Organosilicon Compounds Applied as Wood Consolidants: 2D 1H–13C Solution-State NMR Studies

Abstract

Some organosilicon compounds, including alkoxysilanes and siloxanes, proved effective in stabilizing the dimensions of waterlogged archaeological wood during drying, which is essential in the conservation process of ancient artifacts. However, it was difficult to determine a strong correlation between the wood stabilizing effect and the properties of organosilicon compounds, such as molecular weight and size, weight percent gain, and the presence of other potentially reactive groups. Therefore, to better understand the mechanism behind the stabilization effectiveness, the reactivity of organosilicons with wood polymers was studied using a 2D 1H–13C solution-state NMR technique. The results showed an extensive modification of lignin through its demethoxylation and decarbonylation and also the absence of the native cellulose anomeric peak in siloxane-treated wood. The most substantial reactivity between wood polymers and organosilicon was observed with the (3-mercaptopropyl)trimethoxysilane treatment, showing complete removal of lignin side chains, the lowest syringyl/guaiacyl ratio, depolymerization of cellulose and xylan, and reactivity with the C6 primary hydroxyls in cellulose. This may explain the outstanding stabilizing effectiveness of this silane and supports the conclusion that extensive chemical interactions are essential in this process. It also indicates the vital role of a mercapto group in wood stabilization by organosilicons. This 2D NMR technique sheds new light on the chemical mechanisms involved in organosilicon consolidation of wood and reveals what chemical characteristics are essential in developing future conservation treatments.

Organosilane-modified wood materials: A review of research and applications

“…In their study, (3mercaptopropyl) trimethoxysilane provided the best shrinkage resistance by penetrating CWs to strengthen the wood structure. In more in-depth studies, demethoxylation of lignin was observed in the case of alkoxysilane treatment, whereas (3-mercaptopropyl) trimethoxysilane treatment was most effective in stabilizing the wood, and severe changes in wood composition, such as decomposition of lignin, could be observed (Broda and Yelle 2022).…”

Modification Mechanisms and Properties of Poplar Wood via Grafting with 2-Hydroxyethyl Methacrylate/N,N′-methylenebis(acrylamide) onto Cell Walls

“…The curve in Figure 5 shows that the main characteristic peak of HEMA is a reaction with wood at 133.36, 88.77, 83.78, and 74.8 ppm. The characteristic peaks at 133.36 ppm belong to the structure of R-CH = C and R-C = C, mainly due to the introduction of C = O [26]. The characteristic peaks of 83.78 ppm and 88.77 ppm indicate that the crystalline structure of cellulose is not damaged, but an etherification reaction occurs in the amorphous region of cellulose, leading to -OH decreasing in the cellulose [27].…”