Case study 3 Kinetic studies by TGA

Ahmad N.

et al. (2014) study thermal stability and kinetic parameters of Sodium

carboxymethyl cellulose and kinetic investigations of polymeric materials by TGA

techniques to analyze the data. The kinetics of the thermal transformation of a

solid state chemical reaction is usually described by the general equation.

(3)

Where ? is a degree of conversion/reacted fraction, t is the time, T

is the process temperature and k(T)

is a temperature dependent constant and f(?)

is the reaction kinetic model, accounts for the reaction rate dependence on ?.

The kinetic model is an algebraic expression, which is frequently associated

with a physical model that describes the kinetics of the solid state reaction. k(T

) is usually approximated by the Arrhenius equation.

(4)

Where A, E, R and T are the pre?exponential

factor, the apparent activation energy, the universal gas constant (R = 8.314 J/mol. K), and the absolute

temperature, respectively. For a dynamic thermogravimetric process, Equation 1

can be modified using the definition of the constant heating rate, ? = dT/dt, as in the equation 5.

(5)

This is a

fundamental equation of solid kinetics. One of the few difficulties encountered

in using Equation 3 is the determination of the E of a reaction without

having any previous knowledge about the reaction model. There are several

methodologies to evaluate the thermal degradation kinetics 21.

Ahmad N. et al. (2014) study nonisothermal decomposition

behavior of NaCMC and their mass

losses, the onset temperature of

degradation (Tonset), maximum degradation rate temperature (Tmax),

mass loss percentage at Tmax and residue mass loss at

different heating rates are evaluated. The results are listed in Table

3.