Chromophore in lignin

Reactions of Peracetic Acid with Chromophores in Lignin Preparations... 

In lignin, there are attendant ketone (sometimes, qninone) chromophoric moieties that give it a yellow/brown color. Cellulose is a white substance, which provides the desired strength and brightness properties to the paper products. The strength and whiteness of a paper product depends on the extent of removal of lignin from the pnlp fibers. Row woods contain as mnch as 20-30% lignin. 

The work described in this paper uses gamma rays to generate free radicals in situ in a pulp suspension. It is hoped that this proximity of radicals and chromophoric moieties in lignin will lead to enhanced bleaching and a better understanding of the bleaching and yellowing processes of TMP. 

Lee, D.Y. and Sumimoto, M., "Mechanochemistry of Lignin. V. An Intensive Chromophore in Mechanical Pulps Bleached With Alkaline Hydrogen Peroxide", Hokforschmg, 1991, 45 (Supplement), 15. 

The color of unbleached pulps is caused by certain unsaturated structures (chromophores). In addition, leucochromophores, which can be converted into chromophores by air oxidation may be present in the pulp. Most of the chromophores are presumed to be derived from lignin (Fig. 7-30) although some chromophoric groups can also be introduced into the polysaccharides, for example, carbonyl groups. 

Several color reactions form the basis for both the detection and estimation of specific structural elements in lignin. For example, coniferyl alcohol-type units (8) ultimately may be transformed to the reddish purple chromophore (10) through the series of reactions outlined below (Lindgren and Mikawa 1957). 

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