Effects of Thymolphthalein on Thermo-Oxidative Stability of High-Density Polyethylene in Melt and Solid States

The present work aimed to evaluate capability of a new molecular structure to stabilize polyethylene against thermal oxidation. Hence, effects of 3,3-bis(4-hydroxy-2-methyl-5-propane-2-ylphenyl)-2-benzofuran-1-one (thymolphthalein) on the thermo-oxidative stability of high-density polyethylene (HDPE) in both solid and melt states were investigated and compared with those of SONGNOX 1010, a commercially used phenolic antioxidant for the polymer. Oven aging experiments at 90 °C followed by Fourier Transform Infrared (FT-IR) spectroscopy showed that thymolphthalein at concentrations of 0.1-1.0 wt% improves thermo-oxidative stability of the polymer strongly in the solid state so that its stabilization efficiency is comparable to that of SONGNOX 1010. Furthermore, measurements of Oxidation Onset Temperature (OOT) and Oxidative Induction Time (OIT) of the polymer samples revealed that thymolphthalein modifies thermo-oxidative stability of the polymer in the melt state remarkably. So that, an increase in OOT value of the polymer as large as 36 ○C was obtained by addition of 0.1 wt% of thymolphthalein. It was also confirmed that thymolphthalein does not interfere with the stabilization action of the phenolic antioxidant in the polymer neither in the melt or in the solid state. Finally, a mechanism for the stabilization action of thymolphthalein in the polymer was proposed.