Dynamic Strain Rate Modeling for Multi Ply Boxboard under Rapid Compression
Dynamic strain rate modeling predicts multi-ply boxboard Z-direction compression and interlayer shear collapse during high-speed converting and package drops.
Groundwood Core
Internal Layer
Multi-ply paperboard often contains a central layer made from mechanically ground wood fibres to provide bulk and thickness at a lower cost. This component is the groundwood core, which is positioned between the outer layers of bleached chemical pulp. This configuration is commonly used in folding boxboards.
Mechanical Strength
The use of mechanical pulp in the center of the board offers different performance characteristics than chemical pulp. The groundwood core contains high amounts of lignin, which makes the fibres stiff and resistant to compression but also susceptible to yellowing when exposed to light. Because this layer is shielded by the brighter, white chemical pulp on the outside, its color instability does not affect the print quality.
It provides the bulk that keeps the carton from bulging under the weight of its contents.
Bending Stiffness
Separation of the outer plies by a thick, lightweight center is the primary method for maximizing the bending resistance of the board. The groundwood core acts like the web of an I-beam, holding the high-tensile outer layers apart to maximize the moment of inertia. When the thickness of this central layer is increased by ten percent, the overall stiffness of the board increases by nearly thirty percent.
This design allows brand owners to reduce the overall basis weight of their packaging while maintaining high structural performance.