The Effect of Filler Content on the Pore Structure and the Mechanical Strength of Filler-Loaded Paper

Abstract

The pore structure and mechanical strength of filler-loaded papers were studied for a wide range of filler contents. The handsheets with filler contents of 6% to 90% were prepared by mixing fossil sea-shell with softwood pulp. The tensile strength and the folding endurance were measured by a Schopper-type and the bursting strength by a Mullen machine. The pore structure of these sheets was measured by a scanning electron microscope and a mercury penetration porosimeter. The pore diameter of fiber sheet (filler content 0%) was mostly 20100 pm. The pore of 2-10 pm in diameter increased abruptly in the sheet with 14% filler content and further increased with an increasing filler content. When the filler content was more than 14%, the pore smaller than 2 pm increased. The pore with diameter of 2-.40 pm decreased in the sheets with 71%, and 90% filler content as compared with the sheets with lower filler contents. The filler particles looks like condensing at the network portions of pulp fibers and making their bonding weak. So, the mechanical strength was remarkably reduced even for the sheets with the lowest filler content. The filler content affected most significantly the folding endurance among three types of mechanical strength. By these experiments, the effect of filler content on the pore structure and the mechanical strength was clarified for highly filler-loaded papers. Key words: Filler-loaded paper, Filler content, Pore structure, Mechanical strength, Fossil sea-shell