Virgin Hardwood Pulp Sizing Chemistry and Fibre Hydrogen Bonding Properties
Virgin hardwood sizing requires balancing high surface hydroxyl density against AKD and ASA steric interference to maintain internal bond and Cobb holdout.
Hydroxyl Density
Polymer Adhesion
Surface active groups determine how strongly a cellulose sheet holds a water based coating during extrusion lamination. Hydroxyl density measures the exact concentration of available alcohol groups per square nanometre of dry fibre. Converters track this metric to predict boundary layer bonding before molten polyethylene contacts the primed paperboard web.
Excess moisture alters the reaction kinetics, so mills regulate drying temperatures to preserve functional sites.
Coating Rheology
Viscosity profiles shift when reactive binders encounter high surface concentrations of active hydrogen atoms. Shear thinning behaviour depends on molecular interactions between the aqueous pigment suspension and the cellulose matrix. Formulators adjust additive packages to prevent premature gelation inside the coating pan during high speed application.
Crosslinking agents react with these specific surface sites to build final barrier integrity against grease and moisture vapour.
Print Uniformity
Ink transfer efficiency relies on uniform wetting across a substrate containing varying populations of active sites. Surface energy gradients cause microvoids in the printed film when local concentrations fluctuate wildly across the web. Printers compensate for these variations by modifying fountain solution chemistry or adjusting nip pressures on the impression cylinder.
Final print density depends directly on how evenly the substrate distributes liquid absorption across every square millimetre.