Oxidation lignin-containing papers

A related method involves measuring the solubility of the paper in 1% NaOH at 100°C after a period of time, e.g. 60 min. The solubility is proportional to the copper number (see below) that is itself proportional to the number of carbonyl groups in the paper, a measure of the oxidation and hydrolysis of the paper. This method has also been used on lignin-containing fibres of various kinds with some success. 

In a previous paper (21) we characterized aromatic acids trapped in lignite coal, and have found that these acids are quite similar qualitatively to those obtained from the present oxidation of the same pretreated coal. This indicated that the trapped acids were derived mainly from the hydrolytic degradation of lignin-like polymers. We also have observed that no trapped organic acid is isolated from the anthracite coal that no longer contains lignin-like polymers. 

The most important application of cellulosic materials is the production of paper. Thus wood is transformed first into pulp by mechanical or chemical modification. Hardwood trees such as eucalyptus, birch, and softwood trees like pinus and spruce are used. In the Kraft process woodchips are treated with sodium hydroxide and sodium sulfide to promote the breakdown of the linkage between lignin, some hemicelluloses, and cellulose. This produces cellulose containing residual lignin. The latter is removed by a bleaching process that can apply several oxidizing agents. White pulp is pure cellulose that is used to produce paper. 

Paper pulp used to make newsprint contains most of the lignin originally present in the wood, together with the cellulose. The oxidation of lignin is responsible for newsprint s yellowing with age (Figure 6.3). 

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