Lignin Adsorption on Wood Fibre Surfaces, 2002 International Pulp Bleaching Conference Proceedings

Kecheng Li and Douglas W. Reeve

Lignin is highly concentrated on the surface of fibres after kraft pulping. To better understand this phenomenon, lignin adsorption experiments were devised using pine kraft lignin as the adsorbate and fully bleached pine kraft pulp as the substrate. Pulping and pulp washing conditions such as temperature and lignin concentration were simulated, and lignin adsorption isotherms and kinetics were investigated. It was found that lignin adsorption takes place on both the fibre surface and in the bulk of the fibre under both kraft pulping and pulp washing conditions. Compared with the lignin adsorption in the fibre bulk, lignin adsorption on the fibre surface reaches maximum more quickly. The predominant factor affecting surface lignin adsorption is the lignin concentration in the solution. Adsorbed lignin on the fibre surfaces appears to be a monolayer, corresponding to a surface lignin concentration of 15-18%. When calcium ions are present, the maximum concentration of surface lignin increases dramatically due to the coagulation and precipitation of lignin aggregates on the fibre surfaces.