Precipitated Mineral
Synthetic calcium carbonate synthesized into trigonal crystal clusters provides high optical scattering and structural bulking when utilized as a wet-end papermaking additive. Manufactured via controlled gas-liquid carbonation, scalenohedral PCC features rosettes of elongated, pointed crystals that resemble aggregated calcite scalenohedrons. This specific crystal geometry creates substantial internal particle porosity, which scatters visible light with exceptional efficiency relative to ground limestone or rhombohedral morphologies.
Papermakers add this synthetic mineral to chemical and mechanical pulps to boost sheet opacity, whiteness, and brightness while preserving bulk in wood-free printing and packaging papers. Its application ends where extreme mechanical shear or high-pressure calendering occurs, as the delicate rosette clusters break down under intense compressive forces.
Gas Carbonation
Production occurs primarily in satellite plants situated adjacent to paper mills, utilizing quicklime slaked into calcium hydroxide slurry and carbonated with carbon dioxide recovered from boiler flue gases. Process operators maintain the reaction temperature between thirty and fifty degrees Celsius while regulating gas flow and agitation rates to guide crystallization along the scalenohedral pathway. As calcium carbonate precipitates, calcite seeds cluster into porous, hollow rosettes possessing average particle sizes between one point eight and two point eight micrometres.
The resulting high specific surface area, typically measuring between eight and twelve square metres per gram, produces excellent optical properties. Excessive surface area, however, increases retention chemical demand and impairs sizing efficiency by adsorbing alkyl ketene dimer or alkenyl succinic anhydride sizing agents onto the mineral faces.
Wet End Dynamics
Incorporating scalenohedral PCC into the papermaking furnish alters drainage, formation, and web consolidation on the fourdrinier wire. The bulky rosette structure resists wet pressing, which helps folding boxboard mills preserve caliper and bending stiffness at reduced basis weights. Fine paper machines run filler loadings up to twenty-five percent scalenohedral PCC, securing high sheet opacity for lightweight offset printing grades.
The steep, irregular particle edges interfere with inter-fibre hydrogen bonding, requiring retention aid optimization and dry-strength starch additions to maintain z-directional tensile strength and surface linting resistance during high-speed printing.
