Structural Rearrangement
Shear forces applied to moist cell walls shift tiny sub-micron cellulose elements within paper fibres during mechanical refining or creasing operations. Structural paperboard testing analyzes internal web deformation, where micro-fibrillar displacement describes the permanent physical movement of secondary wall fibrils relative to adjacent cellulose chains. High-resolution electron microscopy and atomic force microscopy quantify these structural shifts across individual fibre cross sections.
The phenomenon governs micro-scale mechanical rearrangements within cell walls, excluding macro-level fibre sliding across sheet surfaces.
Deformation Mechanism
Mechanical refining induces internal fibrillation that enhances inter-fibre bonding areas during web consolidation. Fibrils dislodge from primary cell walls and create high surface area contact points that boost tensile strength upon drying. Excessive mechanical action weakens individual fibre walls and reduces tearing resistance.
Fibre Interaction
Deep creasing and embossing operations apply severe shear strains to paperboard layers, forcing cellulose structures to realign under compression. Fibrils shift past each other within swollen cell walls, dissipating mechanical energy without inducing catastrophic linerboard fracture. Micro-fibrillar displacement enables paperboard substrates to undergo sharp ninety-degree folding without face cracking or surface delamination.
Moisture content during converting operations acts as a lubricant between micro-fibrils, increasing displacement capacity and improving fold flexibility. Chemical additives like wet strength resins lock micro-fibril structures in place, altering web response during subsequent converting steps.
