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.
BCTMP Shive Content
Particle Purity
Metric for quantifying the presence of unrefined wood fragments or bundles of fibres that have survived the bleaching and mechanical pulping stages. High bctmp shive content indicates a deficiency in the screening or refining process at the mill. These particles usually consist of several fibres still bonded together by lignin, which prevents them from flattening or bonding effectively during sheet formation.
Excessive levels of these fragments degrade the surface smoothness and printability of high yield paperboard grades.
Operational Impact
Large particles create visible defects known as fish eyes or pick outs when the board passes through a coating station or a printing press. Because bleached chemi-thermomechanical pulp relies on chemical softening and mechanical force, the shive count serves as a measure of how efficiently the mechanical energy was applied to the wood chips. Physical strength properties like tensile index and burst strength suffer when large bundles disrupt the uniformity of the fibre network.
Process control systems often monitor this value in real time to adjust the gap in the primary refiners.
Measurement Technique
Laboratory analysis involves passing a diluted pulp sample through a slotted screen plate with a specific opening size, typically 0.15 millimetres. The resulting shive count dictates the suitability of the pulp for high quality graphic papers.