Polypropylene (PP) has been widely used in various industrial fields because of its wide variety of characteristics. However, the oxidative degradation of PP easily proceeds, which leads to poor mechanical properties. Generally, the degradation starts from the reaction by alkyl radical, and proceeds according to the 'auto-oxidation mechanism'. Once radical is formed, it reacts with oxygen to make peroxide radical and re-generate new radicals. The oxidative degradation mechanism of PP has been studied by many researchers. However, the mechanism of initial radical formation still remains unclear. If it becomes clear, it can be expected to get quite effective information on PP stabilization. The objective of this study is about the initial radical formation. Propylene polymerization was carried out using industrial Ziegler-Natta catalyst under various conditions to find the possibility. The oxidation induction time (OIT) of PP was evaluated by chemiluminescence (CL) analysis because CL analysis is one of the most sensitive techniques to detect the initial stage of the oxidative degradation. Increased concentration of cocatalyst causes decrease of OIT . In addition, triethylaluminum (TEA) having short alkyl groups compared with triisobutylaluminium (TIBA) and tri(n-octyl)aluminium (TNOA) showed the lowest OIT due to high reactivity of TEA for the catalyst . It is highly possible that the initial radical formation is caused by the reaction of catalyst and cocatalyst during polymerization.

Influence of polymerization conditions and cocatalyst structure on polypropylene stability

248th National Meeting (2014)

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