Calcium carbonate adhesion in paper

Two-ply laminated handsheets (LHS) with a sparse layer of precipitated calcium carbonate (PCC) particles at the ply/ply interface were prepared to investigate the influence of PCC filler on the strength properties of paper. It was found that the delamination strength reduced exponentially with the inter-ply PCC content. Scalenohedral PCC was found to impair paper strength more significantly than prismatic PCC of similar size. The strength of mechanical pulp sheets (pressurized ground wood pulp) was less sensitive to filler content than that of chemical pulp sheets (softwood bleached kraft pulp). The results from these laboratory sheets agreed with those of similarly structured layered sheets from a Dynamic Sheet Former.; The delamination strength of LHS in the presence of PCC filler can be increased by beating chemical pulp, high-pressure wet pressing the sheets, adding fines, or applying polymers. Fines either from chemical pulp or mechanical pulp were found to be extremely effective in promoting the delamination strength of LHS with filler. The ability of fines on strengthening paper strength was found to be proportional to the density of pure fines sheets. Flocculating PCC particles, with high molecular weight cationic polyacrylamide, increased the delamination strength more than treating fibre surface with strength agent (polyvinylamine), or coating PCC surface with carboxyl methylcellulose and phosphate-containing polymers. Wet pressing treatment produced slightly stronger sheets than beating treatment of fibres for LHS in the presence of PCC filler. Fines were found far more effective in promoting the strength of sheets with PCC fillers than polymer treatment, beating, or wet pressing.