Thermal stability of paper fillers: A strong case for a low temperature paper ashing

Methods for determination of ash in paper stipulate temperatures up to 900 degrees C. Lowering to 525 degrees C for the ashing of wood, pulp, paper, and paperboard would still give loses due to thermal decomposition of some fillers. A study of thermal stability of commonly used fillers showed that the most affected fillers are calcium carbonate, kaolinite, muscovite, and aluminosilicates. Ash values determined at temperatures higher than the filler decomposition temperature would therefore be substantially lower than the actual filler content in the paper sheet. The authors propose a 400 degrees C paper ashing method that leaves most fillers in their original, undecomposed form.