Determination of paper filler Z-distribution by low-vacuum SEM and EDX

Paper, mainly constituted of cellulose fibres, often contains mineral fillers. These fillers increase some of the properties of the paper (whiteness, printability, etc.) and are cheaper than the cellulose fibres. Nevertheless, the fillers reduce the mechanical properties of the sheet. Paper presents an anisotropy corresponding to three main directions. This anisotropy characterises the sheet mechanical properties, structure and filler distribution. Analyses of the cross section of the paper sheet with a low-vacuum scanning electron microscope with an energy dispersive spectrometer analysis module can show this distribution. The procedure developed consists in analysing discrete profiles to build the mean profile known as filler Z-distribution for each of the fillers. To develop this method, problems such as determination of the surface points, the number of points to analyse to define a cross section profile and the time required for the test, have been solved. Paper is sensitive to electron irradiation. In order to avoid deterioration of the material and to obtain satisfactory results, the time span for analyses is restricted to 40 s with a 12 kV electron beam accelerating voltage. Monte Carlo simulations are used to determine the diffusion cloud size and thus to determine the number of points that constitute a profile. The samples are gold sputtered and, with the aid of backscattered imaging, the coated surface allows determination of the sample surface points.