Using Chemistry in Compositional Analysis by Thermogravimetry

Many of the compositional analysis applications involving thermogravimetry have focused on the determination of concentrations of one or two additives to a polymeric matrix. Paramount to the utility of such a thermogravimetric approach for filled polymers is that the matrix pyrolyzes repeatably, if not completely. Equally important is the understanding of the components constituting the high temperature residue (ash) and how they are derived. Two examples will be addressed in which controlling or understanding the chemistry of the experiment highlights the significance of the above-mentioned factors in achieving useful compositional analyses. In the first example, an ammoniated atmosphere is employed to achieve repeatable pyrolysis of silicone rubber to measure the carbon black filler content. The second example emphasizes the understanding of decomposition chemistry to distinguish two inorganic fillers retained as ash. In this example the evolution of CO₂ from CaCO₃ is used to identify the calcium oxide portion of the ash in a polystyrene + carbon black + silicone oil + calcium carbonate + titanium dioxide system.