Tensile Strain Measurement in Recycled Paperboard Grades
Recycled paperboard strain measurement requires direct optical extensometry under ISO 1924-3 to isolate true sheet elongation from clamp slippage.
Score Line Strain
Material Resistance
Internal tension within a paper substrate characterizes score line strain as the measurement of molecular displacement resulting from permanent deformation during the folding process. This score line strain emerges when the mechanical force applied by a creasing rule exceeds the elastic limit of the paperboard fibres. Fibres located at the outer apex of the fold experience significant elongation, whereas those at the interior radius undergo compression.
Excessive deformation leads to surface cracking or fibre separation that compromises the structural integrity of the container.
Folding Integrity
Production consistency relies upon the precise adjustment of the creasing rule width relative to the substrate thickness and moisture content. High strain values indicate an mismatch between the die geometry and the material density that prevents a clean fold. Optimal folding performance requires a delicate balance between rule depth and the clearance within the counter channel.
Operators regulate these parameters to prevent the rupture of the outer ply while ensuring that the hinge remains flexible for automated filling machinery.
Structural Limit
Failure thresholds represent the absolute point where the tension within the substrate overcomes the internal bonding energy of the cellulose matrix. Beyond this boundary, the physical connection between individual fibres breaks down and creates a failure site known as a fracture. Material composition significantly alters this limit, as recycled pulp with shorter fibre lengths sustains less deformation than virgin kraft.
Lower moisture levels within the paper stock exacerbate the brittleness of the fold by limiting the ability of the material to stretch under stress. The ultimate strength of a folding carton depends entirely upon the ability of the score geometry to distribute strain across a sufficient volume of the paperboard.