Kinetic Analysis by Curve Shifting (TG): An Approach Based on Experimental Design

Abstract

Thermogravimetric analysis (TGA) is widely employed for determining kinetic and thermodynamic parameters, with non-isothermal methods such as Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Friedman requiring multiple heating rates. However, the need for numerous heating rates is a limiting factor in many laboratories due to time constraints, instrumental availability, and operational costs. This study proposes an alternative methodology based on a single experimental TG curve, from which simulated curves are generated by a controlled shift along the temperature axis, thereby mimicking different heating rates. The procedure is structured using a multilevel full factorial design to evaluate the influence of the temperature shifts on the activation energy (Ea). High-density polyethylene (HDPE) and chitosan (CS), materials with distinct natures, were evaluated using the KAS method. The Ea values ranged from 80–230 kJ.mol⁻¹ for HDPE and from 16–130 kJ.mol⁻¹ (1st stage) and 60–350 kJ.mol⁻¹ (2nd stage) for CS, showing a systematic reduction as the applied shift level increased. The 1–1 level provided the closest results to the values reported in the literature. The findings indicate that the TG curve shifting methodology may represent a viable alternative for kinetic estimations in situations with experimental constraints.