Influence of sample preparation of post-consumer and virgin polypropylene on the reproducibility of differential scanning calorimetry - Oxidation induction time and oxidation induction temperature results.

The "oxidation induction time/temperature" (OIT), measured with a differential scanning calorimeter (DSC), can be utilized as incoming feedstock characterization method, to classify virgin and post-consumer polypropylene (PP) concerning their oxidative stability using the ISO-11357-6 OIT standard, both isothermally and dynamically. Because the OITime is significantly dependent on different sample preparation methods, the results of oxidative stability with a time-dependent degradation exhibited great variability during testing. An increased variation in OITime measurement results was observed during investigation of films and samples with brought-in warpage through cutting compared to non-oriented materials. Therefore, the aim of this work was to propose an alternative, robust and easily reproducible preparation and testing method based on the norm to expand the scope and to find influences of reproducible measurability of virgin as well as post-consumer PP. The examined samples prepared for the isothermal OIT-measurements varied in geometry, preprocessing as well as the conducted DSC measurement program. Investigations show that a major factor of reproducibility is a uniform sample-to-oxygen surface, represented by the diameter. Thermostimulated deformation effects, commonly observed in oriented polyolefin products when heated, can lead to a temporary deformation of OIT samples during measurements inside the aluminum pan, followed by an altered sample surface exposed to oxygen. Concluding the experiments conducted, the ISO-OIT standard is capable of reproducible results but should be queried when effects altering the material surface are possible. Considering the consequent fluctuating results, an expansion of a reproducible OITime measurement is proposed. [ABSTRACT FROM AUTHOR]