A new analysis of filler effects on paper strength

Information about the disruption of fibre/fibre bonds by fillers was derived from measurements of the peel force required to delaminate two-ply handsheets with a sparse layer of fillers between the plies. The smallest filler particles have the greatest negative effect on delamination strength. A surprising finding was that polystyrene spheres had little effect on strength. Electron microscopic evidence suggests that the particles rolled away from fibre/fibre bonding regions during sheet lamination. From a modeling perspective, the decline in peel force with filler content follows a simple exponential decay with an exponent-βΓ, where Γ (g/m²) is the filler coverage and β is the specific debonding index - a measure of the fillers' tendency to weaken paper. A model based on the Poisson deposition of disks on a surface indicates that each filler particle disrupted a fibre/fibre bonding area between 4 and 10 times its own projected area.