Structural analysis of residual lignin in Eucalyptus kraft pulp by pyrolysis gas-chromatography

It is important to obtain the information about residual lignin (RL) in kraft pulp ill order to clarify the mechanism of formation nf organic chlorine compounds in the bleaching process and to develop a non-chlorine bleaching method. The RL was isolated from eucalyptus (Eucalyptus camaldulensis) kraft pulp (screened yield: 47.3%. kappa number: 14.4) by enzymatic treatment. From 100 g of the pulp, 1.36 g of RL was obtained after the first treatment. The decrease of the yield was only 0.3%, by the second treatment. Analysis of carbohydrate composition of the RL showed that the ratio of glucose to xylose was about 1. and that the ratio of lignin to carbohydrate was about 1. The RL were characterized by pyrolysis gas-chromatography; The pyrogram showed C-6-C-3 pyrolysis products (eugenol, propioguaiacone, coniferaldehyde, t-coniferyl alcohol, propenylsyringol, propiosyringone. dihydrosinapyl alcohol, sinapaldehyde. t-sinapyl alcohol) as well as C-6-C-2, C-6-C-1, and C-6 products. The ratio of syringyl to guaiacyl units was estimated to be 2 on the basis of the pyrolysis products. It was suggested that the lignin-carbohydrate complex in the RL may include C-6-C-3 lignin units.