Proper oxidation modeling is essential in developing useful tests performed in a reasonably short time. It is shown that one of the assuptions utilized in modeling, called the constant substrate concentration hypothesis (CSCH), is a weak, unrealistic proposition that is incompatible with the generally accepted basic autoxidation scheme. More reliable results can be achieved when the CSCH is replaced by the inherent, easily understandable relation between the substrate and hydroperoxide concentrations. Furthermore, utilization of the latter relationship plays a key role in the development of the chemiluminescence (CL) methodology for the experimental assessment of two major oxidation parameters - the induction time and the oxidation rate constant. The intrinsic connection between the former parameter and the commonly used in practice graphically acquired oxidation induction time is demonstrated. The procedures presented in the study are applicable to both unstabilized and stabilized systems. Conducting the isothermal CL experiment on a series of the phenolic-stabilized PP samples at somewhat higher temperature (160<sup>0</sup>C) than the standard oven temperature (150<sup>0</sup>C) and under pure oxygen allowed us to keep good correlation with the oven testing results and, at the same time, essentially shorten duration of the test. Comparative study of a great variety of the ABS formulations revealed CL superior sensitivity and permitted experiments at significantly lower temperatures than differential scanning calorimetry (DSC). Consequently, the DSC oxidative stability data can be related to resistance to oxidation during processing while the CL results are expected to be useful in evaluating durability at service conditions.

Oxidation modeling and evaluation of the thermal oxidative stability by means of chemiluminescence

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ACS Fall 2022

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