Bulk density measurement and coating porosity calculation for coated paper samples

During mercury intrusion at low pressure into uncoated and pigment-coated papers, irreproducible large pore volumes are frequently recorded which prevent detailed determination of total composite porosity by mercury porosimetry alone. A novel occlusion-correction procedure is reported here, in which the absorption volume of hexadecane into the void structures and its displacement by the skeletal structures are combined with the mercury intrusion data to allow the coating and the substrate to be separately assessed. This may be achieved either directly, in the case of a nonpermeable substrate, or by scaling the intrusion into the uncoated permeable substrate to that of the coated substrate intrusion curve. This is then scaled to an absolute porosity and bulk volume of the coated sample. The values so derived are compared to those obtained by the traditional method of approximating the intrusion volume into the coating and to the coating applied to an aluminium foil substrate. A method for estimating coating coverage derived from these analyses is described.