Stereological and Chemical Analysis of Paper Cross-Sections, 1998 Papermakers Conference Proceedings
Embedding and polishing cross-sections of coated and uncoated papers now take on the order of only ten to twenty minutes of entirely manual work per sample to produce a finished specimen (not including the time for curing of the embedding resin). Slight etching in KOH solution removes most of the polishing defects and a small part of the surface epoxy, leaving the section standing slightly above the surrounding resin surface. In addition, the resin that had been in the internal porosity is also removed. The resulting sections provide a visually impressive and easy- to-display image of the paper structure. Several small changes to the methods published by Williams and Drummond (1994) make the sample preparation easier and in some ways more effective. The full X-Z section of the sheet is available for examination, as is a small strip of the X-Y section.
This paper’s major contribution is in development of the methods of chemical and stereological analysis of the resulting sections. Standard energy- dispersive x-ray spectroscopic maps of the important elements in the paper filler and coatings are produced. These usually include Al, Si (as clay), calcium (as calcium carbonate), Ti (as titania) and Mg, Si (as talc). The apparent paper thickness of images of the sections is made constant by adjusting the magnification. The x-ray intensities are summed within each row in every map. Then, since all maps of the same sample have the identical apparent thickness, these row-sums can be added, producing a cumulative sum for as many maps as desired. These data can be plotted to show the cumulative filler distributions for all the elements across the sheet.
These techniques allow as much cross- sectional length to be examined as desired or necessary to obtain truly representative data on the various paper samples, a technique not possible with microtomed sections. The cumulative elemental distributions can be obtained in this way, as well as such stereological characteristics as coating thickness, base sheet thickness variation, and base sheet as a percentage of total sheet thickness, using a digitizing tablet and the Sigma-Scan measuring program. This is considerably simpler and faster than any image analysis program based on image segmentation.
These techniques have been used to examine lightweight contour-coated paper, several heavier basis-weight coated stocks, newsprint and linerboard, producing data which enable a more thorough knowledge of paper structure than ever before possible.