The Influence of PCC Morphology and Pulp Properties on Paper Delamination

Layered paper sheets consisting of two cellulose plies separated by a sparse filler layer were prepared by a handsheet-based process and by using a Dynamic Sheet Former. The delamination force was measured as functions of the concentration and morphology of precipitated calcium carbonate (PCC) with sheets based on softwood bleached kraft pulp (SBK) and based on pressurized stone groundwood (PGW). Delamination force decreased exponentially with the inter-ply filler content and scalenohedral PCC lowered strength more than prismatic PCC. The ability of filler to weaken the laminated sheets was more pronounced with the laminated handsheets than with the layered sheets made on a Dynamic Sheet Former. It was postulated that in the latter case there were more fines present in the interply region which partially compensated for the presence of filler. For both types of sheets the fraction of filler in ply 2 (the top side sheet) was less than 50% and the fraction was independent of the total filler loading. Although there was a pulp-dependent correlation between delamination force and conventional internal bond strength, the delamination force seemed to be a more sensitive measure of filler effects.