Iterative method to improve calculation of the pre-exponential factor for dynamic thermogravimetric analysis measurements

The conventional isoconversional plot of ln(β/T²) versus 1/T usually has a large error of about -10% in calculation of the pre-exponential factor as a consequence of assuming h(x)=1. Iterative calculation using the plot of ln(β/hT²) versus 1/T is thus suggested. It is illustrated that the iterative method can greatly improve calculation for the pre-exponential factor. Success in calculation for the pre-exponential factor is accompanied by an enhanced accuracy in value of activation energy given by the iterative method in comparison with the conventional isoconversional plot of ln(β/T²) versus 1/T. One explanation is due to the compensation effect of the Arrhenius parameters. The iterative method has been applied to thermal degradation reactions of poly(methyl methacrylate) (PMMA) and polyethylene.