Fiber Category
High-yield papermaking furnish produced through a combination of chemical pretreatment and mechanical refining offers high bulk and stiffness for packaging applications. Use of bleached chemi-thermomechanical pulp provides a cost-effective alternative to chemical pulps in the middle plies of folding boxboard. This material maintains the thickness required for bending stiffness while utilizing a higher percentage of the wood mass than kraft processes.
Production Process
Softwood or hardwood chips undergo mild impregnation with chemicals like sodium sulfite or hydrogen peroxide before entering a pressurized refiner. Softening the lignin allows the fibers to separate with less damage than purely mechanical methods, resulting in longer fibers and improved strength. These refined fibers then pass through a bleaching stage to reach the brightness levels required for high-quality printing surfaces.
Temperatures and chemical concentrations are carefully managed to prevent the yellowing associated with traditional groundwood. Refining energy is adjusted to balance the preservation of bulk against the need for surface smoothness.
Performance Attribute
Low density remains the defining physical characteristic that allows converters to achieve high caliper without increasing the grammage of the finished board. Stiffness increases when bleached chemi-thermomechanical pulp is layered between outer plies of strong kraft fiber. The mechanical nature of the process leaves some lignin intact, which provides the resilient structure needed for high-speed filling lines.
