Residual Lignin in Unbleached Kraft Pulp. Part 2. -Analysis of Unbleached Kraft Pulp by New Permethylation Method-

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Abstract
Unbleached kraft pulp (UKP), its residue after extraction with concentrated alkali (α-UKP), bleached kraft pulp prepared from UKP (BKP) and its residue after extraction with concentrated alkali (α-BKP) were permethylated with powdered NaOH and CH3I in their SO2-diethylamine (DEA)-dimethylsufoxide (DMSO) solutions. The permethylated samples were separated into three fractions by gel filtration chromatography, according to molecular weights. Lignin contents and sugar compositions in the three fractions inidcated that: 1) the residual lignin in UKP had some alkali-stable chemical linkages with both hemicelluloses and cellulose, and certainly those linkages with cellulose cause the resistance of the residual lignin to further delignification reactions, and 2) the residual hemicellulose, at least in the fraction having the highest molecular weight, is most likely linked chemically to cellulose with direct and/or indirect linkages.

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