Interlaboratory tests on polymers by differential scanning calorimetry (DSC): determination and comparison of oxidation induction time (OIT) and oxidation induction temperature (OIT∗)

Abstract

This report presents results obtained from two interlaboratory tests: 14 and 16 participants, respectively, mainly from industry and research institutes, measured oxidation induction times (OIT) and oxidation induction temperatures (OIT∗) on four different grades of polyethylene by differential scanning calorimetry (DSC). The measured data were collected by EMPA and evaluated using a robust statistical method. Repeatability and reproducibility data were of special interest. The results of the OIT tests indicate that the determination of OIT involves a high degree of uncertainty in respect of the measured data, particularly for low OIT values. This would seem to show that the significance of OIT measurements for quality control purposes or lifetime predictions of polyolefin parts has to be viewed critically. Determining OIT∗ could therefore be a valuable alternative for less stabilised polyolefins (low OIT values) in particular. However, OIT∗ measurement clearly indicates that the ability to distinguish between different samples decreases drastically as OIT∗ data increase. One interlaboratory test participant uses chemiluminescence instead of DSC to determine OIT values. In the context of this study it was shown that chemiluminescence could also provide OIT results within the range of DSC interlaboratory test data. Overall, the evaluated data can be used to estimate the significance of in-house and external OIT/OIT∗ measurements and their compatibility. This report should therefore support day-to-day work in analytical laboratories where oxidation induction values are measured by DSC.