Thermodynamic State
Liquid wetting and adhesion on a paper substrate are governed by the interfacial forces present at the boundary. The fiber surface energy determines how readily water, inks, coatings or adhesives will spread across and penetrate the paper structure. This property is split into polar and dispersive components.
Wetting Behaviour
Water spreads on a solid surface when the surface energy of the solid exceeds the surface tension of the fluid. To optimize the fiber surface energy, papermakers use chemical treatments such as internal sizing agents or surface starches. These materials modify the chemical groups exposed on the cellulose surface, lowering the thermodynamic attraction for water while allowing specific solvent interactions.
This balance dictates whether an offset ink will wet the sheet or bead up, controlling the subsequent dot gain and drying rate. Precise measurement of the contact angle of probe liquids provides the values for calculating these energy components.
Adhesion Potential
Packaging converters rely on predictable chemical bonding when applying extrusion coatings or water-based adhesives to board. If the fiber surface energy falls below the critical threshold, the laminate or adhesive will fail to wet the surface, leading to delamination during convertor runs. Maintaining this property within specified limits ensures robust structural performance of the completed package.
