Polymer Degradation and Stability 44 (1994) 9-15 ~ %/I ELSEVIER Effect of some current antioxidants on the thermo-oxidative stability of poly(ethylene terephthalate) George P. Karayannidis, Irini D. Sideridou, Demetris X. Zamboulis, George A. Stalidis, Demetris N. Bikiaris Department of Chemistry, Aristotle University of Thessaloniki, GR-54006 Thessaloniki, Greece & Aioyse Wilmes Du Pont de Nemours (Luxembourg) S.A., L-2984 Luxembourg (Received 6 July 1993; accepted 8 October 1993) Four current commercial antioxidants (Naugard 445, Ethanox 330, Irganox 1098 and a blend of Irganox 1098 and 1019) were added during synthesis of poly(ethylene terephthalate) in order to test their thermo-oxidative stability and eventually to obtain more thermostable products during synthesis and processing. Their stabilization effect was evaluated by DSC analysis in nitrogen and air, using as criteria the stabilization coefficient and the induction period of oxidation. At low concentrations (0.03% and 0.10%), under the conditions used, better results were obtained with Naugard 445 and Ethanox 330, while at higher concentrations (0.5% and 1-0%) Irganox 1098 and the blend of Irganox 1098 and 1019 were better than the others. 1 INTRODUCTION Poly(ethylene terephthalate) (PET) is one of the most widely used polymers for the manufacture of films (supports for magnetic tapes or insulation layers for capacitors), textile fibres and soft drink bottles. It is usually prepared in two stages from dimethyl terephthalate (DMT) and ethylene glycol (EG). In the first stage (transesterifica- tion), the diglycol ester of terephthalic acid is mainly formed with a certain amount of oligomers. Transesterification is catalyzed by metallic ions such as Zn 2+, Mn 2+, Mg 2+, etc. In the second stage, the above precondensate is polycondensed to PET by heating at high temperature under high vacuum. Polycondensa- tion is catalyzed by a heavy metal compound, Polymer Degradation and Stability 0141-3910/94/$07.00 © 1994 Elsevier Science Limited. usually antimony trioxide. However, during transesterification and mainly polycondensation I 3 degradation reactions occur simultaneously, le- ading to the formation of various side products such as acetaldehyde4 and diethylene glycol. 5.6 The carboxy end group content of PET also increases by these reactions and strongly affects the thermal and hydrolytic stability of the polymer. 7 Moreover, as PET degrades its colour changes from white to yellow, then to brown and finally to black; 8 this is a serious problem since the consumer of white polyester goods demands a brilliant white colour. PET also degrades during its melt processing in the presence of air (thermo-oxidative degradation), 8~ but in comparison with other polymers, e.g. polyolefins, is more stable against auto-oxidation. In general, in order to prevent the thermo-oxidative degradation, antioxidants are added during polycondensation or process-