A modification to the Friedman and Ortega isoconversional methods for evaluation of the activation energy as a function of conversion and temperature

•Conventional isoconversional methods give activation energy as a function of conversion.•Modification to the Friedman and Ortega isoconversional methods.•Evaluation of the activation energy as a function of conversion and temperature. [Display omitted] The Friedman and Ortega isoconversional methods typically apply linear regression to the isoconversional kinetic data for calculation of activation energy solely as a function of extent of conversion. However, in complex reactions, activation energy depends on both conversion and temperature. Our modification involves quadratic curve fitting instead of linear regression, resulting in the determination of activation energy as a function of conversion and temperature. The new technique enables the calculation of the temperature dependence of activation energy for different heating rates, making it a valuable addition to isoconversional analysis. The conventional and modified approaches were utilized on the isoconversional kinetic data concerning polyethylene thermal degradation. The results provided a more detailed representation of the variations in activation energy when nonlinear regression was used.