Lignin, complexes with cellulose

We have seen that lignin is a highly branched amorphous pol3rmer containing an extremely complex array of structures and that when in situ in the wood, it is a graft polymer with cellulose and hemicellulose to boot. Characterization of lignins thus becomes a problem. 

Tannins are water-soluble phenolic compounds which are usually extracted from plant material by hot water. After lignins, they are the second most abundant group of plant phenolics. Their tanning property is due to their capacity to combine with proteins. However, they can also complex with other polymers such as alkaloids, cellulose, and pectins. 

Figure 5.3 Schematic representation of the lignin-carbohydrate complex (LCC) and its interaction with cellulose...

Anhydrous ammonia also is known to cause temporary platicization of wood. The ammonia swells and plasticizes both the lignin and the cellulose, and the crystalline structure of the cellulose is converted to a different form in the process. To shape the wood, it is immersed in liquid ammonia or treated with gaseous ammonia under pressure until the cell walls have been penetrated and the wood becomes pliable and flexible. In this condition it is easily shaped and formed by hand or mechanically. The ammonia readily vaporizes and evaporates from the wood, so that the wood regains its normal stiffness but retains the new form into which it has been shaped. With this process the wood can be distorted into quite complex shapes without springing back to its original form. Treating plants have been developed on a pilot-plant scale, but the process has not been widely adopted. 

A thermo-analytical study of untreated and CCA treated wood samples (more or less cylindrically shaped with diameter less than 2 mm) was performed in order to examine the influence of the presence of CCA on the pyrolytic behaviour of wood samples (TG study), as well as the release of metals (Cu, Cr and As) during the pyrolysis process in the kinetically controlled regime. Since arsenic is the most problematic compound during pyrolysis of CCA treated wood and almost all arsenic is present in the treated wood as CrAs04 (precipitated on cellulose or complexed with lignin) [9], a... 

The products formed when CCA is reacted with wood are composed mainly of the CuCr04-lignin complexes, CrAs04-lignin complexes, and CrAs04 precipitates on cellulose. However, the actual proportions of various chemical species are dependent on the relative proportions of Cu, Cr, and As present in the formulation (40). 

When chromium is reduced from the hexavalent to the trivalent state it reacts readily with arsenic to form CrAs04, which, in turn, has the ability to complex with the lignin and cellulose. In treated wood, approximately 85% of the arsenic reacts with chromium the remaining arsenic forms fairly soluble complexes with lignin and cellulose (5J). 

The composition of organic inputs is as important as size in determining rates of microbial activity and differences in biogeochemical cycling. A complex microcrystalline cellulose base with various intercalated and distinct hemicelluloses, pectins and lignins, all of wbicb contain very little organic nitrogen, forms tbe bulk of terrestrial plant matter. Tbe typical ratio of C N in plant residues is more than 100 (see Table 3). 

Vanilla can also be extracted from plants other than Vanilla planifolia, such as potato peels and pine tree sap. The most economical source of the product, however, is waste material left over from the wood pulp industry. That waste material consists primarily of lignin, a complex natural polymer that, along with cellulose, is the primary component of wood. The wastes from wood pulping can be treated to break down and separate the lignin. This leaves behind a complex... 

Lignin is the third most abundant constituent of plant tissues, with cellulose and hemicellulose being first and second, respectively. In the process of decomposition most of the carbon of the two more abundant materials is released, as CO2, whereas lignin decomposes more slowly and less completely. The lignin residues and microbial transformation products become complexed with amino acids and other substances to form very resistant materials. 

Nitrogen is present in peat in various forms not well understood. A considerable portion is known to be in the form of protein, but not in a free state. It is complexed with lignin, cellulose and hemicellulose. In such forms it is not readily released as ammonia, but does undergo slow release as the peat decomposes. It is very fortunate that it is not readily released, because in this age of abundant supplies of commercial synthetic ammonia, the nitrogen is far more valuable to agriculture when present as complexes than if present as ammonia. 

In nature, hemicelluloses are found in the cell walls of woody and annual plants, together with cellulose and lignin.33 Hemicellulose is made up of a group of complex low-molecular-weight polysaccharides that are bound to the surface of cellulose microfibrils, but their structure prevents them from forming microfibrils by themselves. 

Retted fibers such as jute and kenaf have three principal chemical constituents, namely, a-cellulose, hemicelluloses, and lignin. The lignin can be almost completely removed by chlorination methods in which a soluble chloro-lignin complex is formed, and the hemicelluloses are then dissolved out of the remaining holocellulose by treatment with dilute alkali. The final insoluble residue is the a-cellulose constituent, which invariably contains traces of sugar residues other than glucose. 

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