Fiber Morphology Characterization in Recycled Packaging Substrates
Automated optical morphology testing under ISO 16065-2 quantifies fiber shortening and hornification to control secondary substrate strength and yield.
Curl Index
Shape Measurement
An optical dimension that quantifies the deviation of pulp fibres from a straight line determines the dimensional stability and runnability of paper. Known as the curl index, this value is calculated by dividing the actual contour length of a fibre by its projected length and subtracting one. A higher value indicates that the fibres are highly convoluted, which directly impacts the structural behaviour of the formed sheet.
Drying Impact
Fibre deformation occurs during pulping and refining, often exacerbated by high consistency mixing. When these deformed fibres dry, they release localized stresses unevenly across the sheet, causing curl and twist in the final paper product. Controlling this parameter helps mill operators prevent curls that disrupt high-speed converting lines.
Mechanical Recovery
Alleviating the effects of deformed fibres typically involves low consistency refining, which straightens the pulp before it reaches the headbox. Automated analysers measure this property dynamically by tracking wet fibres through a capillary tube with a high-speed camera. This real-time testing allows packaging manufacturers to adjust their refining energy or furnish blend to maintain flat sheets during offset printing and folding.
If the fibre straighten process is neglected, the resultant paperboard suffers from poor stiffness and erratic feeding on high-speed carton converting lines.