Hemicelluloses hygroscopicity

The surface wettability of heat-treated wood decreases due to a reduction in the hydroxyl content of the modified wood (Pdtrissans etal., 2003). There is a reduction in the water-sorption capacity, which is related to a reduction in the number of primary sorption sites (OH groups) within the wood cell wall, largely as a result of the removal/degradation of the hemicellulosic component. As remarked upon earlier, hygroscopic properties are strongly influenced by the treatment method employed. Podgorski etal. (2000) heated... 

Effect of Wood Species and Extractives. The sorption isotherms of all woods are generally similar in shape. However, there may be considerable variations among them with respect to the absolute values of hygroscopicity. This variation may be because of differences in the proportion of the primary wood constituents, such as cellulose, hemicellulose, and lignin in different woods or more importantly, because of differences in the kind and quantity of ex-... 

Cellulose, the hemicelluloses, and lignin sorb moisture to different extents (Figure 1). The hemicelluloses are more hygroscopic than cellulose, which is more hygroscopic than lignin (5). This means that lignin (noncrystalline and probably totally accessible), the hemicelluloses (all noncrystalline and nearly totally accessible), the noncrystalline portion of cellulose, and the surfaces of the cellulose crystallites are responsible for moisture uptake by the wood cell wall. 

The plant cell walls of bast fibers consist mainly of cellulose, hemicellulose, and lignin. The uptake of water by a hygroscopic material as cellulose or hemicellulose is a hydration process involving accessible hydroxyl groups, or in this case -CH2OH groups of the host material. Water molecules absorbed by dry cellulose form a true cellulose hydrate, and the reaction is exothermic, which provides the driving force (Pizzi 1987). 

Water acts as a plasticizer and increases the mobility of the hygroscopic hemicellulose macromolecules, and this leads to a lower glass transition temperature under moist conditions. Measurements (4) as well as calculations (6) show a decrease to approximately 50 C at 20% water content. In other carbohydrates water also shows a strong softening effect (12,13). 

This paper has presented a method of studying the softening, or glass transition, of hygroscopic polymers by using humidity scans at constant temperatures. In extracted hemicelluloses, here xylan and glucomannan, a... 

Woody biomass, either gymnosperms (softwoods) or angiosperms (hardwoods) is inherently anisotropic and hygroscopic it is porous material, with the porosity caused by the hollow fibers that make up the woody material. Any number of wood technology texts (see, for example, Haygreen and Bowyer [13]) describe the physical structure of woody biomass. The porosity or void volume of wood exists as macropores—tracheids, rays, resin canals and related structures useful in moving moisture and nutrients within the tree. Chemically, woody biomass is comprised of cellulose, the hemicelluloses, one or another type of lignin, and extractives such as pinoresinol, catechin, pinosylvin, and related compounds. 

Wood is a hard, fibrous tissue found in many plants. It is an organic natural material and can be treated as a natural composite of cellulosic fibers embedded in the lignin matrix. It is a heterogeneous, hygroscopic material composed of cells and cell walls. It contains 40-50% cellulose, 15-25% hemicellulose, and 15-30% Hgnin. 

According to Spinace et al. [27], due to the opened structure, that contains many hydroxyl and acetyl groups, hemicellulose is partially water soluble and hygroscopic. 

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