The wetting properties and morphology of lignin adsorbed on cellulose fibres and mica

The wetting behaviour and the morphology of lignin on cellulose fibres and mica in the presence of cationic polyelectrolytes have been studied. Lignin was adsorbed from aqueous solution on the surfaces of mica and cellulose fibres. Static contact angles and residual drop volumes were measured on modified surfaces over time. Surface morphology was examined by AFM. Both the structure of the adsorbed layer as well as the hydrophobicity depended on the polymer addition strategy. Lignin adsorbed as granules on both smooth and rough cationised surfaces. Adsorbed and organised lignin was capable of weakening the adhesion of water to both nonporous and porous hydrophilic substrates. Maximum contact angles were found when the adsorbed lignin layer formed a granular structure. In contrast, polymer/lignin complexes that were formed in solution and then adsorbed on mica or cellulose were not as effective in lowering the adhesion of water. They adsorbed on mica and pulp fibres as either a thin film or as larger blobs, depending on the properties of the cationic polymer.