Kinetic analysis, Friedman method

In order to assess the activation energy for development of a reasonable model for kinetic analysis of pristine PE and PE-n-MMT thermal degradation processes, a few evaluations by model-free methods have been done as the starting point. As an example, the results of a model-free Friedman analysis for thermal degradation of PE, where the activation energy is a function of partial mass loss change [24], are shown in Figure 5. 

Model-free methods evaluations were chosen as the starting points in kinetic analysis of neat PP and PP-mPP with 7% Cloisite 20A for determining the activation energy in the development of the model. Figure 6 shows a corresponding Friedman analysis, where the activation energy is a function of partial mass loss change [16]. 

Friedman s isoconversional method [14] involves an Arrhenius analysis at constant levels of conversion, and we determined the apparent first-order frequency factor and activation energy at 1 % intervals using both LLNL and AKTS kinetics analysis programs. 

Budrugeac et al. [123] examined the kinetics of the non-isothermal crystallization of (GeS2)o.3(Sb2S3)o.7 by employing the methods of Friedman and of invariant kinetic parameters and demonstrated that the process can be treated as a single step. A more complex kinetic situation has been encoimtered by Thomas and Simon in re-crystallization of nickel sulfide from the a- to P-form. Their analysis yielded evidence of at least two steps involved in the overall process [124]. 

To evaluate the apparent activation energy, the isoconversional methods are use as suitable analysis procedures. These methods are based on the assumption that at a constant extent of conversion degree (a), the decomposition rate da/dt is a function only of the temperature. In methods developed by Friedman and Flynn-Wall-Ozawa, linear functions are obtained from which slopes the apparent activation energy at constant conversion a is achieved. In the free kinetic method set by Kissinger is calculated from the slope of the linear function takes into consideration the relationship between the heating rate and peak temperature of the first-derivative thermogravimetric curve [97]. 

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