Physico-chemical analysis of a silane-grafted polyethylene stabilised with an excess of Irganox 1076®. Proposal of a microstructural model

Abstract

This work focuses on the physico-chemical analysis of a silane-grafted polyethylene stabilised with an excess of Irganox 1076® as phenolic antioxidant before and after surface cleaning using acetone as a polar solvent. The non-uniform distribution of Irganox 1076® in this polymer matrix was investigated with several complementary characterisation techniques including FTIR spectroscopy (in both ATR and transmission modes), DSC analysis, OIT measurements, and optical microscopy. Initially, the presence of antioxidant crystals at the polymer surface was confirmed. Surface cleaning showed to be effective to remove all antioxidant crystals present at the polymer surface, as confirmed by FTIR spectroscopy in ATR mode, DSC analysis, and optical microscopy. The remaining concentration of antioxidant in the polymer matrix was estimated by FTIR spectroscopy in transmission mode and OIT measurements using preliminary established OIT and FTIR calibration curves. It was found that this concentration corresponds to the solubility threshold at 25 °C of about 0.9 wt% (i.e. ≈ 1.6 × 10−2 mol.L−1) determined in a previous publication. Hence, all experimental results suggest that antioxidant crystals would only be present at the polymer surface, and not within the polymer bulk, which finally allows proposing a simplified microstructural model for this heterogeneously stabilised polymer. It was also found that antioxidant crystals efficiently participate to the stabilisation process of the polymer matrix during oxidation, thus significantly increasing the OIT. This important result might constitute an interesting stabilisation route for industry, still unexplored to date, obviously depending on the intended final application of the polymer.