Differential Thermogravimetry versus Differential Thermometry in studying the Pyrolysis of Polymers

Abstract

ORDINARY chemical methods of analysis are impractical for studying the pyrolysis of highly cross-linked polymers, because such materials are extremely infusible, insoluble and non-volatile. Techniques such as differential thermometry and differential thermogravimetry are therefore being used more and more for this purpose. Differential thermometry measures the net heats of reaction produced by chemical change as a function of temperature, whereas differential thermogravimetry measures loss of weight. Since the endothermic breaking of and the exothermic forming of bonds occur simultaneously in the pyrolysis of substances, differential thermometric information can be misleading. For example, if, at a given temperature, the heats of the endothermic reactions were exactly equal to the heats of the exothermic ones, a differential thermometric peak would be absent. This would lead to the false conclusion that no thermal decomposition had occurred. Changes in specific heat and in thermal conductivity of a polymer during pyrolysis also complicate the differential thermometric picture, especially when quantitative information is desired. Since differential thermogravimetry measures losses of weight during pyrolysis rather than heat changes, it is not subject to the above-mentioned complications, and should therefore give a more reliable quantitative estimate of the relative thermal stabilities of different polymers.