Mechanical Pulp Distribution in Folding Boxboard Core Layers
Core layer mechanical pulp distribution controls folding boxboard bulk and bending stiffness, enabling weight reduction while preserving box structural integrity.
TMP
Mechanical Defibration
Thermomechanical pulp arises from wood chips processed through high pressure disc refiners where thermal softening precedes mechanical shear. Steam injection raises wood temperature above the lignin glass transition point before the material enters revolving plates that separate individual fibres without complete chemical degradation. High yield operation characterizes the method because most original wood components remain in the final fibrous network rather than dissolving into liquid liquor streams.
Residual lignin stiffens cell walls and reduces bonding potential compared to chemical pulping, which demands higher refining energy inputs to achieve required surface area development. Refiner segment geometry and plate clearance dictate fibre length distribution and tear strength retention across the production run.
Opacity Control
Printing substrates containing thermomechanical pulp achieve superior light scattering coefficients because retained lignin and short fines create micro voids within the sheet structure. High bulk properties allow manufacturers to reduce basis weight while maintaining caliper standards required for catalog and magazine production. Surface smoothness improves during calendering as coarse fragments collapse under nip pressure, but brightness reversion occurs upon ultraviolet light exposure due to quinone formation from residual aromatic structures.
Bleaching sequences utilizing hydrogen peroxide restore brightness without removing lignin, preserving high yield advantages while mitigating discoloration risks in commercial print applications.
Drainage Resistance
Stock preparation systems process thermomechanical pulp with careful attention to freeness reduction because excessive refining generates fines that impede water removal on the paper machine wire. Hydrostatic pressure gradients across forming fabrics determine sheet consolidation rates and influence final porosity levels. Wet web tensile strength depends on mechanical entanglement rather than chemical bonding, leaving the web vulnerable to open draw breaks at high running speeds.
Closed white water circuits concentrate dissolved solids and colloidal substances that interact with retention aids, requiring precise charge neutralization to maintain drainage performance and prevent press section deposits.