Lignin Color

Meshitsuka G, Nakano J (1978) Studies on the mechanism of lignin color reaction XII Maule color reaction Mokuzai Gakkaishi 24 563-568... 

Crocker EC (1921) An experimental study of the significance of lignin color reactions Ind Eng Chem 13 625 - 627... 

Migita N, Nakano J (1955) On the mechanism of color reaction of lignin. IV. Cross-Bevan color reaction of hardwood lignin. J Jpn For Soc 37 26-34 Nakamura T, Kitaura S (1957) Lignin color reactions. Ind Eng Chem 49 1388 Nakano J, Ishizu A, Sasaki A, Migita N (1960) On the mechanism of color reaction in lignin. 

Formation and Elimination of Multiple Bond Functionalities. Reactions that involve the formation and elimination of multiple bond functional groups may significantly effect the color of residual lignin in bleached and unbleached pulps. The ethylenic and carbonyl groups conjugated with phenoHc or quinoid stmctures are possible components of chromophore or leucochromophore systems that contribute to the color of lignin. 

The Wiesner Reaction. The reaction of lignified tissue and phloroglucinol—hydrochloric acid gives a visible absorption spectmm with a maximum at 550 nm. This has been attributed to coniferaldehyde units in lignin as the groups responsible for the color formation. 

Tall oil rosin is a by-product of paper manufacturing. Raw wood chips are digested under heat and pressure with a mixture of sodium hydroxide and sodium sulfide. Soluble sodium salts of lignin, rosin, and fatty acids are formed, which are removed from the wood pulp as a dark solution. The soaps of the rosin and fatty acids float to the top of the mixture, where they are skimmed off and treated with sulfuric acid to free the rosin and fatty acids. This mixture, known as cmde tall oil (CTO), is refined further to remove color and odor bodies fractional distillation separates the tall oil rosin acids from the fatty acids (see Tall oil). 

No residual guaiacol can be found in vanillin produced by the guaiacol process. In contrast to vanillin from lignin, vanillin from guaiacol is extremely consistent in quaUty owing to the consistency of the supply source, and shows no variation in taste, odor, or color. 

A final are we should discuss is color removal. This is perhaps the most difficult impurity to remove from waters. In surface waters color is associated with dissolved or colloidal suspensions of decayed vegetation and other colloidal suspensions. The composition of this material is largely tannins and lignins, the components that hold together the cellulose cells in vegetation. In addition to their undesirable appearance in drinking water, these organics can cause serious problems in downstream water purification processes. For examples ... 

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

When testing for a tannin reserve or tannin index, the presence of natural color aids detection. Testing for tannin is simple and relatively accurate using either a permanganate reduction test (development of permanent purple color) or lignin/tannic acid polymer test (tungstate blue color). 

Lignins are most usually employed as various types of sodium lig-nosulfonate and are products of sulfite pulping. (Kraft lignins from the Kraft pulping process are also available.) They are used as dispersants, binders, sequestrants, and emulsifiers. Sodium lignosulfonate product variables include color, MW, and the degree of carboxylation and sulfonation on the lignin backbone. 

Dissolved lignin and carbohydrates Color COD AOX Inorganic chlorine compounds (e.g., chlorate (C103 ))c Water... 

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