Particle Ratio
Proportional presence of small cellulosic elements within a pulp slurry establishes the fines distribution and morphological balance of paper stock. Determining the short fiber fraction evaluates the percentage of fibers falling below specified length thresholds, typically under zero point two millimeters or zero point five millimeters depending on the classifier mesh. Optical fiber analyzers or Bauer-McNett screen classifiers separate fiber length populations through fluid flow or mechanical screening stages.
Hardwood pulps naturally exhibit a higher proportion of short elements compared to long softwood kraft pulps. Higher short fiber proportions increase sheet density and surface smoothness, while simultaneously reducing tear resistance and wet web strength. The metric excludes non-fibrous filler pigments, chemical additives, and dissolved organic solids.
Classification Process
Fractionation screens segregate pulp slurries into distinct length classes using hydrocyclones or wire mesh barriers. Longer fibers remain on primary screens, while shorter fragments pass through to secondary recovery systems. Image analysis cameras capture individual fiber dimensions in dilute suspensions to compute the short fiber fraction of the pulp.
Stock Performance
Paper machine runnability depends on maintaining consistent fiber length distributions in the headbox stock. Excessive short fiber fraction slows water drainage on the forming wire, requiring reduced machine operating speeds and increased vacuum pressure at wet suction boxes. Recycled fiber repulping progressively shortens fibers through mechanical cutting, increasing the need for virgin long fiber blending or strength additives.
Good bonding between short fibers improves printability and surface opacity in graphic printing papers.
