Polyolefins and in particular polypropylene (PP) are intrinsically not inert enough to withstand the chemical attack of oxygen and subsequently degrade due to an auto-oxidative mechanism. In consequence, the need for the protection (stabilization) of this substrate from auto-oxidation was identified early-on. In further consequence, specific stabilizers, called antioxidants, were developed in the 1960s and 1970s during the industrialization of PP. Especially the Long Term Thermal Stability (LTTS) of PP homo polymer burdens since the late 1970s on the use of a high molecular weight hindered phenol (Songnox 1010) or its synergistic combination with an aliphatic sulphur compound (Songnox DSTDP). Based on its unmatched cost/performance, these two stabilization systems are used since more than 40 years and are still suitable for many applications. Nevertheless, those systems have clear performance limitations, which in selected cases need to be overcome. One of those limitations is the extension of the LTTS performance of thick section PP articles at a testing temperature of 150 °C; particularly in the presence of additives (like fillers and sizing agents) which impart strong antagonistic interactions with the antioxidant system. Another limitation is the LTTS performance at significantly lower (test) temperatures of around 80 °C (or lower). In both cases, new antioxidant packages which yield a significant improvement in LTTS performance were developed and are discussed in this publication.
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