In wood hemicelluloses

In wood, hemicelluloses and lignin act as amatrix bonding the cellulose fibers into a composite structure. It is a puzzle that the stiffest, strongest, and cheapest of the biological polymers is not used at all in animals. 

Hemicellulose is a collective name for the non-cellulosic polysaccharides, which are a large constituent in the structure of the wooden cell wall. Hemicelluloses are generally considered to cover the elementary cellulose fibrils and function as an amorphous glue binding the cellulose fibrils together. Hemicelluloses comprise typically 25-35% of the wood, and are thus the second most abundant component group in wood. Hemicelluloses have only a very weak surface activity but are, nevertheless, of scientific and technical interest because of their ability to function as emulsion stabilizers through a steric stabilization mechanism. 

What functions do the polymers cellulose, lignin and hemicellulose play in the construction of the cells in wood ... 

Brown rot fungus Fungus that attacks cellulose and hemicellulose in wood, leaving dark-colored lignin and phenolic materials behind. 

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... 

The basic structure of all wood and woody biomass consists of cellnlose, hemicelluloses, lignin and extractives. Their relative composition is shown in Table 2.4. Softwoods and hardwoods differ greatly in wood stmctnie and composition. Hardwoods contain a greater fraction of vessels and parenchyma cells. Hardwoods have a higher proportion of cellulose, hemicelluloses and extractives than softwoods, but softwoods have a higher proportion of lignin. Hardwoods ate denser than softwoods. 

The FP cellulose per unit (ml) volume and enzyme yield per unit (g) cellulose or substrate obtained on wheat straw, wood, and CTMP in SSF were higher than those obtained in LSF on wheat straw and wood (Tables I, II, and III). And wheat straw proved to be a better substrate than wood for cellulose production in SSF. This could be attributed to the polysaccharides (cellulose and hemicelluloses) of wheat straw being more readily available for the organism s growth and cellulose synthesis than those of wood. The hemicelluloses and cellulose were presumably not as available in wood, because of its high lignin content and high cellulose crystallinity, as in wheat straw. 

Cellulose is found in nature in combination with various other substances, the nature and composition of which depend on the source and previous history of the sample. In most plants, there are three major components cellulose, hemicelluloses, and lignin. Efficient utilization of all three components would greatly help the economics of any scheme to obtain fuel from biomass. Hemicelluloses, lignocellulose and lignin remaining after enzymatic degradation of the cellulose in wood would require chemical or thermal treatment - as distinct from biochemical - to produce a liquid fuel. 

We should note, also, that the lignin in the S2 layers is chemically bonded to the polysaccharide moiety (87-92). Such bonds occur not only in wood but may be formed during chemical pulping (93,94). Even if the lignin-carbohydrate bonds are restricted to the hemicelluloses (95), the regularity of these chain molecules will probably impose some non-randomness on the lignin structure. 

The steam explosion process is a recent development in wood processing (1,2). Much attention has been paid to this process from the viewpoint of total wood utilization. Cellulose and hemicellulose from this process can be converted into sugars of commercial value by enzymatic methods (3). However, the conversion of lignin from this process (steam explosion lignin) into useful materials continues to present difficulties. Preparation of adhesives from it is considered to be a feasible way to solve this problem. 

Finishing wood cellulose. The finishing process is made to obtain a higher a-cellulose content and to endow the wood pulp with a shape conducive to easy nitration. This is the last operation prior to nitration. It consists in removing hemicelluloses, pentosans, and hexosans, which are undesirable ingredients of wood pulp. An insufficiently purified wood pulp may contain 5-6% of pentosans, straw cellulose even as much as 20%, whereas cotton does not contain more than 0.5-0.6%. 

The network structure of lignin, which is made of phenol units, coagulates the cell wall in wood tissue, which is composed of cellulose and hemicellulose. Lignin is currently a waste product because of its complicated structure [1-4], It is produced by an oxidative polymerization of coniferyl alcohol, sinapil alcohol, and cumarol alcohol (Figure 1) catalyzed by metalloenzymes such as laccase and peroxidases. Laccase is a protein whose active center contains four coppers per one subunit [5-20],... 

Cellulose is found in wood, along with hemicellulose and lignin, and in cotton, linen, hemp, and other similar products. It is a polymer of glucose. It can also be made from sucrose by bacterial means [8]. This bacterial cellulose has high mechanical strength and may become an important material if the cost can be brought down. 

Analyses of the hemicelluloses of woods indicate the presence of a high proportion of D-xylose residues in association with those of a methyl ether of a hexuronic acid.64 The first evidence for the chemical structure of such wood xylans came from the isolation of xylobiose, xylotriose,65 and the aldobiouronic acid 0-(4-0-methyl-a-D-glucosyluronic)-(l —> 2)-D-xylose acid (IX)22 from partial hydrolyzates of aspen wood. The role of such oligosaccharide fragments in wood xylans became more apparent as the result of a study of a xylan from European beechwood,26 in which it was shown... 

By far the most abundant reactive chemical sites in wood are the hydroxyl groups on cellulose, hemicellulose, and lignin. The types of covalent chemical bonds of the carbon-oxygen-carbon type that are of major importance are ethers, acetals, and esters. 

The major chemical changes in wood caused by fiberboard manufacture are secondary side reactions which are both beneficial and detrimental to the final properties achieved. Defibering is accomplished by hydrolytic breakdown of lignin and hemicelluloses under wet acidic conditions combined with high process temperatures. Board conversion and consolidation is attended by pyrolytic reactions which... 

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