Derivative thermal gravimetry

The thermogravimetry is an experimental technique based on registration of loss in weight carried out for isothermal or tempera-ture/time programmed conditions and can be displayed in cumulative Thermal Gravimetric Analysis (TGA) or derivative Differential Thermal Gravimetry (DTG) forms. 

To be able to compare thermal stabUity between polymers of different structures, it is necessary to rely on some standardized system, sucdi as the temperature of half-decomposition Tyi). The temperature of halfdecomposition is defined as the temperature at whicJi the polymer loses half of its weight when heated in vacuo for 30 min. Experimentally, Ty2 can be conveniently determined by thermal gravimetry (TG). From the TG curves obtained at different scan speeds, an Arrhenius plot at constant weight-loss ratio is derived. The pre-exponential factor and activation energy determined are then used to calculate Ty2. 

Figure 9. Thermal analysis of levoglucosenone samples (a) neat, (b) +5% zinc chloride, (c) +5% diammonium phosphate, and (d) +5% diphenyl phosphate (D.t.a., differential thermal analysis T.g., thermo gravimetry D.t.g., derivative of thermogravimetry)...

Mass loss is measured in the course of the thermal decomposition by means of thermobalances. A very small sample is placed on the beam of a sensitive balance extending into an oven which can be heated at different rates. A recorder actuated by the balance beam depicts the mass change as a function of temperature thermo-gravimetry, TG curve). Some thermobalances also record the rate of mass change derivative thermogravimetry, DTG curve). 

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