Inter-Ply Delamination

Shear Stress Action

Mechanical forces applied during creasing, folding, or printing can exceed the cohesive limits of the internal starch bonds. An inter-ply delamination occurs when the board is bent around tight radii, forcing the plies to slide past each other. This action is sometimes encouraged during creasing to make the board fold easier, but it must be tightly controlled to prevent the board from splitting entirely.

Moisture and temperature variations can weaken the inter-ply bonds, increasing the risk of failure during storage.

Preventative Mill Practice

Papermakers adjust the amount of starch spray applied between the plies on the forming wire to improve adhesion. Refining the pulp fibers also increases the number of hydrogen bonds, creating a more integrated multi-ply sheet. Standard testing methods, such as the Scott Bond test, measure the energy required to split the plies to verify consistent internal strength.

Ensuring uniform moisture distribution across the sheet further protects the board from localized stress concentrations during converting.