Chemiluminiscence Studies of Polypropylene Stabilized with Natural

PELTZER, M., JIMÉNEZ, A., MATISOVA-RYCHLÁ, L., RYCHLY, J.

Plejsy

Congreso; 2nd Bratislava Young Polymer Scientists workshop (BYPOS-2009); 2009

Polypropylene (PP) is sensitive to free radical degradation initiated by elevated temperature, light, mechanical forces and oxygen. Antioxidants from different sources are added to PP to limit such degradation processes. Natural compounds, such as α-tocopherol, have proven their antioxidant ability for polyolefins, combined with their very low toxicity. Of these hydroxytyrosol is a compound with high added value due to its excellent antioxidant abilities as well as other beneficial properties. Polypropylene (PP) is sensitive to free radical degradation initiated by elevated temperature, light, mechanical forces and oxygen. Antioxidants from different sources are added to PP to limit such degradation processes. Natural compounds, such as α-tocopherol, have proven their antioxidant ability for polyolefins, combined with their very low toxicity. Of these hydroxytyrosol due to its excellent antioxidant abilities as well as other beneficial properties present a high added value. Chemiluminescence (CL) has demonstrated to be a sensitive tool for in-situ studies in polymer degradation. One of the main advantages of this technique is the possibility to determine the oxidation induction time at temperatures below the melting temperature of the polymer, in contrast with DSC where at test temperatures the material is molten which might raise serious doubts on the applicability of results to real-life situations. The aim of this study is the use of CL to evaluate the antioxidant performance of two natural antioxidants: α-tocopherol and hydroxytyrosol in PP. A comparison with a synthetic phenolic antioxidant Irganox 1076 also is submitted. Concentrations of natural antioxidants used in this study were 0.01, 0.1 and 0.5 wt%. CL tests were performed in oxygen atmosphere and under isothermal conditions at 140, 150 and 160ºC. Non-isothermal measurements were performed at the heating rate of 2.5ºC/min from 30 to 180ºC. Pure polypropylene itself was studied also under isothermal conditions within temperature interval from 80 to 160ºC. In all cases under the isothermal study oxidation induction time (OIT) was determined and, as expected, OIT increased with increasing initial concentration of antioxidant. It was shown that concentrations of 0.1 wt% of both natural antioxidants are effective stabilisers of polypropylene. Tocopherol shows the better stabilising performance than Irganox 1076. On the other hand higher amounts of hydroxytyrosol are needed to obtain a similar stabilisation effect as with other antioxidants. However, it still appears to be a promising compound because of its absolutely natural origin.