Optimizing Chemi-Thermomechanical Pulp Core Fractions for Lightweight Board
Balancing middle ply mechanical pulp freeness preserves sheet caliper and bending resistance while controlling delamination under high-speed scoring.
Reject Sulfonation
Fiber Modification
Chemical treatment process applied to the coarse or rejected fibers from a primary mechanical pulping stage to improve their bonding potential. Mills use reject sulfonation to soften stiff fiber fragments so they can be effectively refined and incorporated back into the main pulp stream. Treatment steps increase the overall yield and improve the strength properties of the final paper sheet.
Chemical Reaction
Sodium sulfite reacts with the lignin in the fiber walls to introduce sulfonic acid groups. By modifying the chemical structure at a molecular level, the reject sulfonation process increases the hydrophilicity and swelling capacity of the wood fibers. Flexibility improves.
As the fibers swell, they develop a larger surface area for hydrogen bonding during the drying process. The reaction is typically carried out at elevated temperatures in a separate vessel before the fibers pass through a secondary refiner. Adjusting the chemical dosage and reaction time allows the operator to target specific tensile and tear strengths.
Successful treatment transforms brittle shives into useful papermaking fibers.
Process Outcome
Improved flexibility in the treated fibers leads to better sheet formation and a smoother surface finish. Without reject sulfonation, the coarse fragments would create weak spots and reduce the surface quality of the printed product. The technique is a standard method for maximizing the utility of mechanical pulp.