Residual lignin distribution in bleached kraft pulp fibres

The distribution of residual lignin across the cell wall of kraft pulp fibres was measured after a variety of single bleaching stages. Measurements of brominated fibre sections were taken using scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDXA). The powerful oxidants ozone and isolated dimethyldioxirane,] reacted more rapidly with outer cell wall material [(P+S-1) and S-3 layers], while reaction with lignin in the interior wall (S-2) appeared to be slowed by mass transfer limitations. Peroxide, monoperoxysulphate, chlorine dioxide, and in-situ-generated dimethyldioxirane produced uniform residual lignin distributions Following oxygen bleaching, the residual lignin in the (P+S-1) and S-3 layers were higher than in the S-2 layer; with a ratio very close to that of the original kraft pulp.