Applicability of non-isothermal model-free predictions for assessment of conversion vs. time curves for complex processes in isothermal and quasi-isothermal conditions

The non-isothermal model-free prediction procedures used for assessment of degradation isotherms of materials and products are presented and critical analyzed. To this end, these methods were applied to the following experimental data: thermo-oxidative degradation of poly (vinyl alcohol) (PVA) and thermal degradation of high density polyethylene (HDPE). The predicted conversion vs. time curves were compared with the experimental ones obtained in quasi-isothermal conditions as well as with those calculated using the degradation mechanisms and corresponding kinetic parameters obtained by Thermokinetics software package. The errors of predictions performed by model-free and model-based procedures were evaluated. Although the used software package considers relative simple reaction schemes containing maximum six steps, the predicted conversion vs. time curves by model-based procedure exhibit lower deviations from the experimental ones than those calculated by model-free procedures. The causes of the prediction errors are discussed. (C) 2013 Elsevier B.V. All rights reserved.