Ash content/Loss onignition

Purpose

Elevated temperatures cause the organic components of paper to be decomposed. The residual components are non-combustible minerals. The amount of ignition residues obtained depends on the temperatures applied.

Filler type	Loss on ignition in %
Calcium carbonate Kaolin Talc gypsum	40 – 43 12 – 14 4 – 6 9 – 10

The residue left after complete combustion of paper at high temperature. It is generally expressed as percent of original test sample and represents filler content in the paper. As it is ash content is not important property of paper but in some grade of papers such as filter papers are ash free and other such as cigarette tissue have certain level of filler to control cigarette burning rate. 

typical ash content (Grade)	Value (%)
Market wood pulp Newsprint LWC Fine paper	0.3 – 0.5 0 – 12 30 – 50 0 – 35

Principle

Incineration is normally performed at temperatures of 570 ºC and/or 920 ºC. This method enables the proportion of calcium carbonate in the filler to be calculated. Depending on its crystal shape, calcium carbonate is decomposed to CaO and CO2 at 825 ºC or 898ºC. For the dominant filler types, % loss on ignition at 920 ºC is shown in the figures. In view of these values, ash measurement only give an approximate determination of the filler content of paper.