Comparison of methods for thermal analysis: Application to PEEK and a composite PEEK+CF

Abstract

This article applies and critically compares essentially all methods (based on Arrhenius temperature dependence and power law reduced mass) to deduce the degradation parameters of polyether ether ketone (PEEK) and its carbon fibre composites, PEEK + CF, from thermogravimetric analysis experiments in nitrogen. The methods used include classical (and variations) analytical approximate methods, a method applying the genetic algorithm for optimization and the Distributed Activation Energy Model, usually not discussed with the other methods. The analytical methods are fast and easy to implement but they are limited to degradation kinetics having a single peak or individual separated peaks in the mass loss rate. By contrast, the genetic algorithm gives good results if a postulated mechanism of several Arrhenius reactions of arbitrary order is considered. Moreover, the Distributed Activation Energy Model provides the possibility to assess the assumption of overlapping first-order reactions having various activation energies. The degradation of PEEK and its composite is basically characterized by two regimes, one fast degradation regime (570°C-630°C approximately) and one much slower degradation regime (630°C-800°C approximately) at a mass degradation rate with time being simply proportional to the heating rate, a very remarkable new result by itself. However, the focus of the modelling in this work lies in the first fast degradation regime. It is shown that the Distributed Activation Energy Model and the genetic algorithm can simulate well the experimental results noting, however, that the Distributed Activation Energy Model is based on more physically determined activation energies. By contrast, the classical methods (Kissinger and modified Ozawa methods) are not able to reproduce the mass loss rates in the initial fast degradation regime (570°C-630°C) of pure PEEK and PEEK + CF composite. Although a physical explanation of the degradation mechanisms is desirable, the end game is to find out whether a method even not including the whole truth about a process is yet capable of reproducing the measurements accurately.

Processing thermogravimetric analysis data for isoconversional kinetic analysis of lignocellulosic biomass pyrolysis: Case study of corn stalk

“…with increasing conversion (0.15~0.85). Other similar results were produced in the pyrolysis of tobacco waste [86], eucalyptus wood [47], polyether ether ketone and its carbon fiber composites [97], rice husk [98], rape straw [99], and microalgae [100].…”

On the determination of thermal degradation effects and detection techniques for thermoplastic composites obtained by automatic lamination

“…Most of them focused on the detection and explanation of the degradation mechanism from a physical-chemical point of view [16,[23][24][25][26] and a low number of works elucidate the kinetic model. Some of them, related to kinetics, are focused on pyrolytic tests [27], oxidative atmosphere tests [28], or both. In the particular case of oxidative degradation, the authors consider that there are only two mechanisms interacting from the beginning (0% mass loss) to the end (100% mass loss).…”

Thermal decomposition of flexible polyurethane foams in air

“…Due to the simplified assumptions and the difficulty in accurately determining the kinetic properties of extended, low magnitude reaction, the model has not been able to capture the final stage of decomposition involving char oxidation. The model also consistently shows oxidative thermal decomposition initiating and occurring over slightly higher temperature range compared to the experiment, and such inherent mismatch is not uncommon [24]. The likely causes of mismatch include the selection of data points analysed and the adopted graphical technique to determine the kinetic properties, the assumptions made to establish the derived oxidative reactions, and the exponential nature of Arrhenius equation where minor change of inputs translate into relatively greater change of outputs.…”