Fibre Architecture
Long-fibre chemical pulp provides structural strength and reinforcement in paper and paperboard formulations. Papermakers utilize bleached softwood kraft to build strong internal fiber networks capable of enduring mechanical stress during converting. The substrate classification applies to wood pulps derived from coniferous species processed through alkaline sulfate cooking followed by multi-stage bleaching sequence operations.
The definition excludes mechanical pulps, unbleached kraft grades, non-wood plant fibers or recycled pulps.
Chemical Delignification
Alkaline cooking liquor dissolves native lignin bonds while preserving long cellulose chains during digestion. Coniferous wood chips undergo high-temperature digestion with sodium hydroxide and sodium sulfide before entering elemental chlorine-free or totally chlorine-free bleaching sequences. Chemical bleaching removes residual chromophores to reach target ISO brightness values above eighty-eight percent without severe cellulose degradation.
Digester control parameters determine ultimate yield and preserve individual fiber length distributions across production lots. Bleached softwood kraft maintains web wet strength on high-speed paper machines due to high individual fiber length and strong inter-fiber bonding potential.
Tensile Performance
Reinforcing pulp fractions increase tear resistance and tensile energy absorption in packaging substrates. Incorporating bleached softwood kraft into packaging grades enables lower total grammage without sacrificing Mullen burst resistance or folding endurance. Recycled packaging mills add virgin softwood fractions to offset strength loss from repeated repulping.
