Most white papers contain fillers in the form of a fine powder of an inorganic material. Fillers are added to improve production economy and to contribute to some of the properties of the final product, such as surface smoothness, opacity and whiteness. In order to optimize the performance of fillers in the paper sheet, papermakers need measurement methods to decribe the distribution of fillers in the structure of the final product.

The paper testing laboratories at Innventia can characterize filler content in paper by a number of different methods, depending on the purpose of the investigation. Direct quantification of the total filler content in a sample is performed by ashing the sample in a high temperature oven (525°C or 900°C) and gravimetrically measuring the inorganic residues.

Ashing can be combined with one of the sheet splitting techniques available to obtain thin parallel splits from the original samples. In this way, it is possible to determine the local content of filler at different depth in the thickness direction of the sheet.

In its research activities, Innventia is developing a novel measurement technique based on splitting paper samples in very thin layers and selectively modifying the appearance of the organic material. In this way it is possible to obtain high-resolution images describing the local distribution of fillers in the sample.

Sample profile of local filler content determined by ashing indvidual layers after splitting of the sample.