Abstract
Wood is an increasingly important material in the sustainable transition of societies worldwide. The performance of wood in structures is intimately tied to the presence of moisture in the material, which directly affects important characteristics such as dimensions and mechanical properties, and indirectly its susceptibility to fungal decomposition. By chemical modification, the durability of wood in outdoor environments can be improved by reducing the amount of moisture present. In this study, we refined a well-known chemical modification with acetic anhydride and showed how the spatial distribution of the modification of Norway spruce (Picea abies (L.) Karst.) could be controlled with the aim of altering the wood-water interactions differently in different parts of the wood structure. By controlling the reaction conditions of the acetylation it was possible to acetylate only the cell wall-lumen interface, or uniformly modify the whole cell wall to different degrees. The spatial distribution of the acetylation was visualised by confocal Raman microspectroscopy. The results showed that by this targeted acetylation procedure it was possible to independently alter the wood-water interactions in and outside of cell walls. The cell wall-lumen interface modification altered the interaction between the wood and the water in cell lumina without affecting the interaction with water in cell walls while the uniform modification affected both. This opens up a novel path for studying wood-water interactions in very moist environments and how moisture distribution within the wood affects its susceptibility towards fungal decomposition.Graphic abstract
Highlights
Wood is an increasingly important material in the sustainable transition of societies worldwide
Regarding the cell wall moisture content, the results indicate that the interface modification of the lowest degree did not change the cell wall moisture content in the water-saturated state, but it was reduced for the interface modification of the highest degree (Fig. 6a)
The approximate positions of middle lamellas (ML), lumina and cell wall along the specific cell wall section (x) were estimated visually from the Raman image (Figure S4), while the longer reaction time gave chemical changes traceable up to approximately 5 lm both into the earlywood and latewood cell walls (Fig. 4, Figure S8). This indicates that the rate of acetic anhydride diffusion into the cell walls of earlywood and latewood was similar, but since earlywood has thinner cell walls than latewood, a higher proportion of earlywood cell walls was acetylated compared to latewood cell walls when subjected to the same treatment time
Summary
Wood is an increasingly important material in the sustainable transition of societies worldwide. Wood consists of cells that were already dead in the living tree, where one of their main functions was to transport water. These cells have a central empty void called the lumen which is surrounded by cell walls that are intricate micrometer-scale composite structures made from hygroscopic biopolymers (i.e. cellulose, hemicelluloses and lignin). Water in wood can be present both within cell walls and as capillary water outside of cell walls. Water outside of cell walls is present in larger voids such as cell lumina and pit chambers where water uptake occurs by capillary condensation (Fredriksson 2019) or by capillary action if placed in contact with liquid water
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