リグニンの色に関する研究(VIII)

サルファイト蒸解におけるリグニンの着色について

抄録

In order to clarify how cooking time affects the color of lignosulfonate, six fractions of fir lignosulfonate were isolated from acid sulfite waste liquor withdrawn at regular intervals. In this connection, it should be emphasized that each fraction of lignosulfonate is isolated very soon after dissolution into the cooking liquor, in other words it is not much influenced by heating after dissolution. The color, the amounts of functional groups and the molecular weight distribution curve of each lignosulfonate were compared each other, and the changes of molecular weight distribution curve by recooking with acid sulfite cooking liquor were also discussed. The results are summarized as follows :
1. The amounts of methoxyl and non-conjugated phenolic hydroxyl groups show no significant difference among lignosulfonate, obtained at various cooking stages. However, the amount of α-carbonyl group in lignosulfonate at the earlier cooking stages is higher than that at the later cooking stage.
2. The chromophoric structures in lignosulfonate are not practically formed inthe solid state of protolignin, but formed after the dissolution from wood. The rate of coloration of lignosulfonate obtained at the earlier stage is more remarkable than that at the later stage.
3. The molecular weight distribution curve of lignosulfonate was obtained by gel filtration. At the earlier cooking stage, lignosulfonate of lower molecular weight fraction dissolves from wood more easily than that of higher molecular weight fraction. The peaks of these gel filtration curves which correspond to the fractions of higher molecular weight, are located at the same amount of elution volume. This means that the pore size of cell wall determine the rate of delignification.
4. The molecular weight distribution curve of lignosulfonate changes to the lower side of the molecular weight during recooking with acid sulfite cooking liquor, and this tendency is especially remarkable in the case of lignosulfonates obtained at the earlier cooking stage. This shows that the different accessibilities of lignosulfonates to the acid hydrolysis are present even among specimens which are obtained at various cooking stages and then fractionated at the same elution volume.