Filtration Efficiency
Short suspended cellulose fragments and colloidal fillers remain suspended in the dilute liquid slurry during paper formation unless controlled by chemical retention aids. Fines retention measures the proportion of these sub-micron fragments captured within the forming sheet on the wire mesh rather than passing through into the white water loop. Paper makers target a specific balance between mechanical drainage and chemical flocculation to prevent sheet two-sidedness and reduce biological oxygen demand loads in effluent treatment plants.
Drainage Resistance
High capture rates of microscopic material frequently restrict water removal speed on the Fourdrinier table by blinding the forming fabric openings. Excess polyelectrolyte addition blocks interstitial channels between longer pulp fibres, which forces operators to apply higher vacuum levels at the flat boxes to achieve target dryness before the press section. Coagulation dynamics dictate that cationic polymers bridge negatively charged colloidal particles into larger flocs, but overdosing causes steric stabilization and redisperses the fines into the suspension.
Coating Holdout
Surface smoothness depends heavily on maintaining an even distribution of fine pigments and fillers across the upper and lower faces of the raw paper base. Poor fines retention leaves microscopic voids in the outer sheet structure, which causes excessive binder absorption during subsequent pigment coating operations and produces mottled print density. Print houses evaluate this property by measuring ink gloss uniformity and pick resistance across high-speed offset lithography runs.
