Hemicellulose-lignin complex, from

The chemical composition of wood is complex. Its main components consist of cellulose, hemicelluloses, lignin and extractives. The amount of each component varies with the tree species and tree part. For flame-retarded wood prepared by treating with a retardant, care should be taken in order to obtain homogeneous samples. Select a suitable amount of the sample from representative parts of the wood, then grind the sample... 

Fourth lesson - combination of different compounds in unique macrostructure provides unique performance properties. Starch is used extensively in nature to store carbon and energy. Starch is readily digested and must be protected from degradation by a resistant coating, for example, a seed (e.g. com, wheat or rice) or a skin (e.g. potato). Woody materials such as trees, soft plants and grasses are composed of a complex combination of aliphatic and aromatic compounds (cellulose, hemicellulose and lignin). 

Plant cell walls are complex, heterogeneous structures composed mainly of polymers, such as cellulose, hemicelluloses, and lignins. In spite of several decades of research, cell wall assembly and the biosynthesis and ultimate biodegradative pathways of individual polymers are still far from being fully understood. One simple example will suffice Even today, no enzyme capable of catalyzing cellulose formation in vitro has been obtained. 

The raw material that reaches the factory is a far cry from Avicel or Solka Floe that are used by many experimenters to simulate cellulosic products (Table I). In addition to the fact that the cellulose is tied up in a lignin-hemicellulose-cellulose (LHC) complex, it should be recognized that the terms lignin and hemicellulose are catchall terms covering a range of compositions and molecular weights. 

A problem but little discussed in the hterature is the possible association of polysaccharide molecules of various kinds with noncarbohydrate molecules. The association can be random, and a direct fractionation would then be impossible. Thus, it has frequently been observed in the authors laboratory that hemicelluloses containing lignin could not be separated into the pure components, but, after further dehgnification, they could be readily fractionated. It is possible that similar comphcations may also occur with other types of polysaccharide, for example, protein- or lipide-polysac-charide complexes. In this connection, it should be noted that the solution obtained on dehgnification of some materials may contain polysaccharide material of particular interest. For instance, the main part of the galactan present in spruce compression wood can be recovered from such a solution. ... 

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