The ash is a measure of the mineral oxide content on a weight basis. Thermogravimetric analysis (TGA) in an oxidative atmosphere is a well-proven method to determine the inorganic residue, commonly referred to ash, in organic materials such as polymers, rubbers, etc. Therefore, the TGA measurement will identify if a material is filled and calculates the total filler content. However, it cannot identify individual percentages in multi-filled materials.
The determination is described in, e.g., ASTM E1131.
Usually in case of polymers and rubber, a few mg of the sample are placed in an open crucible (made of alumina or platinum) and heated in an inert nitrogen atmosphere up to approximately 800°C for investigating the sample composition. The following measurement segment is carried out under an oxidative atmosphere (air or oxygen).
In TGA measurements (thermogravimetric analysis), it is measured by converting the mineral constituents to the respective oxides above 800°C. The ash consists mainly of silica, alumina and/or other inorganics and the amount is dependent on the base raw material used to produce the product.