Thermogravimetric Analysis of Polymethylmethacrylate and Polytetrafluoroethylene
Kinetics is of fundamental importance in the understanding of the mechanism of thermal decomposition of high polymers. Since most thermal decomposition reactions are associated with weight changes, thermogravimetry is being employed to a great degree in kinetic studies of polymer decomposition. Two approaches are commonly used to obtain the various kinetic Chapaumeters of these reactions. The static method or “isothermal thermogravimetry” produces precise weight loss curves for various single temperatures as a function of time. Thus the rate Chapaumeters are obtained directly. This method is inherently time consuming and the results are sometimes questionable due to experimental uncertainities arising from the initial thermal lag of the sample. More recently, “dynamic thermogravimetry” data has been used for kinetic studies. In these, a single weight loss curve obtained by means of programmed heating is used to provide information equivalent to an entire family of isothermal weight loss curves. The new approach is time saving, being able to cover a wide range of temperatures in a relatively short time. For this work the kinetics evaluation procedure by Freeman and Carroll1 and its extension by Anderson and Freeman2, is applied to dynamic thermogravimetric data in order to evaluate the rate Chapaumeters.
KeywordsActivation Energy Heating Rate Thermal Decomposition Atmosphere Pressure Inert Atmosphere
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