Lightweight, high-opacity paper by fiber loading: filler comparison

SUMMARY:To comparetheeffects ofcommercialcalciumcar­ bonate fillers on handsheet properties with that of fiber loading, we obtained rhombohedral and scalendrohedral precipitated cal­ cium carbonates (PCCs) and wet and dry ground calcium carbo­ nates (GCCs). These commercial calcium carbonate fillers were selected to cover a wide range of particle diameter and shape. The properties of fiber-loaded handsheets, at 25% filler level, were compared to that of five commercial calcium carbonate samples at the same filler level for two fully bleached market pulps, eucalyptus and pine kraft pulps. Fiber-loaded pulps were shown to be stronger than similar direct -loaded pulps at the same calcium carbonate levels as a result of (1) precipitation of calci­ um carbonate within the fiber wall and lumen and (2) the low energy input refining of the pulp at high pH and consistency. Our results show that fiber loading results in somewhat higher free­ ness values than does direct loading along with higher strength. Brightness values were slightly lower or the same for fiber-loa­ ded handsheets compared to direct-loaded handsheets. Opacity and scattering coefficients were slightly lower for fiber-loaded handsheets, but the higher strengths of fiber-loaded pulps permit an increase in the filler level in the fiber -loaded pulps. Production of fiber-loaded PCC (FLPCC) pulp can be a key factor in develo­ ping lightweight, high-opacity printing papers.