## 3 Results
### Thermal Properties
#### 3.4.1 Thermo-Oxidation
The main stage of the thermal decomposition under thermo-oxidation conditions was subjected to kinetic analysis. The activation energy values of the decomposition process were calculated using the Coats-Redferm method [37]. The results of the analysis are shown in Table 4. \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **Activation Energy (kJ/mol)** \\ \hline BBW & 84.1 \\ MBW & 69.9 \\ UBW & 41.9 \\ BBD & 46.6 \\ MBD & 36.4 \\ UBD & 39.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Activation energy of thermo-oxidation process of okra fibers (standard deviation 5%). Based on the data shown in Table 4, the activation energy values at the given conditions (kinetic parameters significantly depend on the heating rate, as well as on the assumptions adopted in a given calculation method [45]), are at the 36-84 kJ/mol level. The large range of spread suggests that the assumptions associated with this method [37] cause a moderate adaptability of this method to the tested samples. However, while elaborating on the results of thermal tests in air, a coefficient of determination at the 98-99% level was found with the Coats-Redfern method. The authors of that method used an integration procedure. They obtained the following equation:  
\[\ln\ (\frac{\alpha}{\mathrm{T}^{2}})=\ln\frac{\mathrm{AR}}{\beta\mathrm{E}}(1- \frac{2\mathrm{RT}}{\mathrm{E}})-\frac{\mathrm{E}}{\mathrm{RT}} \tag{2}\]  
where:  
A--Pre-exponential factor (min\({}^{-1}\))  
\(\alpha\)--Degree of conversion or fractional mass loss  
Figure 8: Alpha s–alpha r dependence of okra best fibers. Figure 9: Alpha vs. temperature relationship for okra best fibers. \(\beta\)--Heating rate (K min\({}^{-1}\))  
E--Apparent activation energy (kJ mol\({}^{-1}\))  
R--Gas constant 8.3136 (J mol\({}^{-1}\)K\({}^{-1}\))  
T--Temperature (K)  
By plotting ln (\(\alpha\)/T\({}^{2}\)) = f(1/T), E value can be calculated. It must be remembered that the equation is only true for zero reaction order, which results from the former simplifications. The results obtained by this method are true for low \(\alpha\), but they can be generalized for the whole process assuming that the reaction mechanism does not change during the reaction. From a practical point of view, this method is moderately laborious. It requires taking the \(\alpha\) values from the thermogram and doing the necessary calculations to obtain the plot. Researchers have used this method, among others, to investigate poly (tetrafluoroethylene) [37] and poly (3-dimethyloacryloyloxyethyl) ammonium propanosulfate [46], and the results correspond to the results obtained from other calculation methods. In comparing the values of the activation energy obtained for samples processed by the water- and dew-retting methods, we found an interesting relationship between the average EA results, which were 65.5 and 40.8 kJ/mol, respectively. The results of the thermal decomposition analysis of okra fiber samples from different parts of the plant in the presence of oxygen have not yet been published. From the results presented in this study, it can be concluded that regardless of the origin of the material, okra fibers can be used in composites up to a temperature of 290 \({}^{\circ}\)C. The activation energy of the decomposition process varies depending on how the fiber is pretreated.