Improvement of the Mathematical Model for Quality Assurance in the Determination of Kinetic Parameters of Thermal Degradation of Polypropylene Through Thermogravimetric Analysis

Abstract

Robust mathematical treatment of the Ozawa/Flynn/Wall isoconversion method is conducted to determine the value and uncertainty of the activation energy and pre-exponential factor for the degradation of polypropylene in thermogravimetric analysis experiments at constant heating rates. The present work employs mathematical models and uncertainty propagation techniques based on the Guide to the Expression of Uncertainty in Measurement to estimate the Arrhenius activation energy and pre-exponential factor due to the uncertainty of the integration constant b, both in a linear and a third-degree reciprocal polynomial model with respect to x. The error arising from Doyle's linear approximation in the improper integral of temperature in the Arrhenius equation is examined, and an alternative method is proposed to correct this error, reducing it to 0.032% in the working interval of −200 ≤ x ≤ −15, where x = −E/RT. Given the increased sensitivity of modern thermogravimetric analysis equipment, these improvements are considered essential for obtaining reliable results that align with experimental precision limits compared to previous works. Thus, this allows for the development of an enhanced quality assurance framework by providing more robust uncertainty estimation and a better understanding of the method. Moreover, this approach can be applied to other similar polymer system.