Paperboard Middle Ply Furnish Compression Mechanics under Static Bench Conditions
Middle ply CTMP bulk provides structural moment of inertia, while short-span compression bench testing quantifies network collapse risks under load.
Compression Index
Performance Metric
Structural measurement of the load bearing capacity of a material relative to its grammage provides a standardized way to compare different grades of containerboard. To determine the structural efficiency, compression index is calculated by dividing the short span compressive strength by the basis weight of the paper. This value allows for an objective evaluation of how efficiently a specific fibre blend or manufacturing process uses raw material to achieve strength.
It eliminates the influence of thickness or weight when comparing the inherent quality of the substrate.
Testing Protocol
Measurement occurs using a short span compression tester that grips a small strip of paper and pushes the ends together until it buckles. The compression index relies on the peak force recorded during this failure. Because the distance between the clamps is very short, typically 0.7 millimeters, the test focuses on the fibre-to-fibre bonding and fibre stiffness rather than the global stability of the sheet.
The results are highly sensitive to the orientation of the fibres, with the machine direction typically showing substantially higher values than the cross direction. Maintaining consistent moisture and temperature during testing is essential because these factors directly influence the elastic modulus of the cellulose.
Operational Impact
Mill managers use this value to optimize the refining process and chemical additions in the wet end. A higher compression index indicates that a lighter board can provide the same stacking strength as a heavier, lower quality grade. This optimization reduces transport costs and material waste for the end user.