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Literature is strongly contradictory about the molecular reasons for yellowing and brightness reversion of pure (lignin- and hemicellulose-free) celluloses, such as in highly bleached pulps, bacterial cellulose, or cotton linters. While oxidized groups—carbonyls (CO) and carboxyls (COOH)—have been recognized as the initiators of yellowing, they are generally always found together; thus, their effects...
The chemistry of cellulosic key chromophores is challenging because of the usually very low concentration of the colored compounds in real-world cellulosic matrices. It offers many surprises and positive outcomes; unfortunately there are also pitfalls and disappointments. This report discusses eight examples or surprising chemistry out of the realm of cellulosic key chromophores. The reactions have...
5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores occurring in all types of aged cellulosics. This study investigates the degradation of DHNQ by chlorine dioxide at moderately acidic (pH 3) conditions, corresponding to the conditions of industrial bleaching (“D stage”). The degradation involves three major pathways. As initial reaction, a hydrogen transfer from DHNQ to chlorine...
The chromophore release and identification method isolates well-defined chromophoric substances from different cellulosic matrices, such as highly bleached pulps, cotton linters, bacterial cellulose, viscose or lyocell fibers, and cellulose acetates. The chromophores are present only in extremely low (ppm to ppb) concentrations. The concept of primary and secondary chromophores is introduced, with...
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