Hemicelluloses chemistry

With discretion, the structural information on features in xylans from other, higher land-plants can be used to assist, as in the past, in the search for similar features in the hemicellulose of plantstuffs under examination—no matter how often they have been previously examined. If new facts suggest new interpretations, earlier studies should be re-examined to determine whether the newer interpretation accords with facts established earlier. It is a misfortune of hemicellulose chemistry that it is rarely possible to disprove a reported fact, as, unless total hemicelluloses30,31 are isolated from plants of the same variety or cultivar grown under very similar conditions to the plants studied earlier, the hemicellulosic material under examination may not contain molecules having detectable amounts of the structural features noted earlier. 

Mok, W. S. L. Jerry, M. Antal, J., Uncatalyzed solvolysis of whole biomass hemicellulose by hot compressed liquid water. Industrial and Engineering Chemistry Research 1992, 31,1157. 

Influence of Metal Ions on Oxygen Chemisorption and Ignition of Chars. We have carried out extensive studies of the influence of metal ions in wood on pyrolysis mechanisms (5.6) and this approach has now been extended to oxygen chemisorption of the chars. The metal ions occur in wood predominantly as the counterions of the uronic acid components of the hemicelluloses (12). We have shown that they can be almost completely removed by very mild acid treatment without any other major change in the chemistry of the wood. Table II shows that the major metal ions in cottonwood are Ca, K and Mg. The acid-washing process removed 98X of the metal ions in... 

In general, these chemical treatments reduce the percentage of lignin, hemicellulose and extractives and increase that of cellulose. The chemistry of these processes is discussed more fully in Chapter... 

Ramiah, M.V. and Goring, D.A.I. (1967). Some dilatomeric measurements of the thermal decomposition of cellulose, hemicellulose and lignin. Cellulose Chemistry and Technology, 1(3), 277-285. 

Complex pyrolysis chemistry takes place in the conversion system of any conventional solid-fuel combustion system. The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicellulose, and lignin. Pyrolysis of these biopolymers proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products which can be divided into char, volatile (non-condensible) organic compounds (VOC), condensible organic compounds (tar), and permanent gases (water vapour, nitrogen oxides, carbon dioxide). The pyrolysis products should finally be completely oxidised in the combustion system (Figure 14). Emission problems arise as a consequence of bad control over the combustion system. 

Streptomycin, chemistry of, 3, 337-384 Structural chemistry, of fungal polysaccharides, 23, 367-417 of the hemicelluloses, 14, 429-468 Structure, molecular, of cellulose, 19, 219-246 of dextran, 15, 341-369 of glycogens, 12, 261-298 of polysaccharide gels and networks,... 

No complete picture of biological materials can be given without reference to their original condition in their natural environment. Brief consideration will, therefore, be given to the biosynthesis of the hemicelluloses and to their relationship, in the plant, to cellulose and lignin. Since much of our present knowledge of the chemistry of the hemicelluloses is based upon examination of materials isolated by alkaline extraction from plant tissues which, in many cases, have been previously treated to remove lig-... 

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