Verification of Post Consumer Recycled Content in Folding Boxboard Supply Chains
Verifying post-consumer recycled claims in folding boxboard requires cross-referencing FSC/PEFC credit accounts with deinking yield losses and MOSH/MOAH markers.
Middle Ply CTMP
Fibre Density
Chemithermomechanical pulp layers occupying the central interior of a multi-ply paperboard structure provide necessary bulk and compression resistance. Middle ply ctmp functions as a primary stiffening agent by introducing high-yield mechanical fibres that maintain internal spacing between the outer liners. This specific grade of pulp remains distinct from chemical pulps because it retains a higher portion of lignin, which increases the inherent thickness of the sheet relative to its weight.
The material serves to increase the bending stiffness of the final board while minimizing the total amount of furnish required to reach a target caliper.
Manufacturing Mechanics
Production of the internal substrate involves the mechanical refining of wood chips after a mild chemical treatment. High energy inputs separate the fibres while preserving lignin components that contribute to the structural rigidity of the paperboard matrix. Operators monitor the Canadian Standard Freeness of the slurry to ensure that the water drainage properties remain stable during the wet end formation.
Variations in the refining intensity change the fibre surface area, which governs the internal bonding strength between the middle ply and the adjacent plies. Proper control of the refining process prevents the formation of weak zones that could lead to delamination during high-speed converting operations.
Performance Constraint
Dimensional stability under heavy printing loads relies on the consistent mechanical properties of the central layer. Boards containing this material exhibit superior resistance to crushing when subjected to creasing or die-cutting pressures in a packaging line. The bulk provided by the fibres allows for the reduction of overall grammage without sacrificing the vertical strength required for protective cartons.
High stiffness-to-weight ratios represent the most reliable metric for evaluating the success of the internal composition in commercial packaging applications.