Optical Light Scattering Variations in Highly Refined Secondary Fibre Furnishes
Intense refining of recycled fibres increases bonded area and collapses lumens, reducing optical scattering and requiring mineral fillers to restore opacity.
Primary Fines
Native Morphological Fraction
Non-fibrous particulate matter naturally present in raw lignocellulosic plant structures prior to mechanical beating represents a distinct morphological component of wood pulp. These biological remnants, recognized as primary fines, consist of ray parenchyma cells, epithelial fragments, broken vessel elements and parenchymal debris released during pulping processes. Standard fractionation separates them as unrefined pulp particles passing through dynamic drainage jars equipped with 200 mesh screens.
Unlike fibrillated particles generated by refiner bars, these biological fragments are chunky, blocky structures possessing low specific surface areas and negligible internal swelling capability. Ray cells and resinous fragments carry elevated extractives, pitch and ash, distinguishing them chemically from pure secondary cell wall fibrils.
Drainage Behavior
Unprocessed pulps release these small cellular components freely into suspension when chemical chips are washed and pumped into headboxes. During web formation, the blocky morphology of primary fines lets them pack tightly into inter-fibre spaces without forming flexible ribbons that bridge voids. This structural packing chokes drainage pathways on the fourdrinier wire, generating drainage resistance without providing compensating hydrogen bonding.
Capillary action remains low during mechanical pressing because these thick-walled fragments exhibit minimal consolidation flexibility. Their chemical composition often features elevated pitch, fatty acids and resin compounds that inhibit hydroxyl contact points between adjacent softwood tracheids.
Pulp Evaluation
Bleached hardwood kraft pulps, particularly eucalyptus and birch grades, contain high volumes of vessel elements and parenchyma cells that influence sheet smoothness and formation. Primary fines improve sheet opacity and light scattering by filling open pores with solid material, yet they lower overall burst indices and tensile strength compared to fibrillated fines. High concentrations in recycled pulp streams reduce retention aid efficiency, contaminate felt conditioning circuits and leave weak surface zones prone to picking during high-tack lithographic printing.
Sourcing specifications track this fraction to anticipate paper machine drainage rates and finished surface strength.