Cohesive Separation
Material rupture occurring within the internal structure of paper or paperboard represents a breakdown of the adhesive forces holding cellulose fibers together. During fiber bond failure, the individual fibers pull apart under tensile or shear stress, causing the sheets or plies to delaminate. This separation occurs when the external pulling force exceeds the internal bonding strength of the pulp matrix.
It is a parameter in multi-ply boards where different fiber layers are pressed together during wet forming. This internal integrity determines how well the material handles subsequent converting operations.
Mechanical Tension
High-speed offset printing presses exert substantial surface forces on the paper substrate. When tacky inks pull on the surface, fiber bond failure occurs if the internal cohesive strength is too low. This rupture ruins the print run and fouls the printing blankets with loose paper fibers.
Press operators measure this property using wax pick tests or high-speed tack testers.
Structural Protection
Papermakers adjust the refining of pulp and the addition of starches to enhance internal bonding. To prevent fiber bond failure, chemical bonding agents such as cationic starch are introduced to the fiber furnish. Refining the pulp increases the surface area available for natural hydrogen bonding.
These interventions ensure that the board can withstand folding and scoring without splitting.
