Effects of Galbanic Acid on Thermal and Thermo-oxidative Stabilities of LLDPE

The effects of galbanic acid (GA) (a type of coumarin derivative) on the thermal and thermo-oxidative stabilities of LLDPE were investigated using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. It was shown that GA does not modify the onset of thermal degradation of the polymer. However, the thermo-oxidative stability of the polymer has been improved significantly in the solid state and moderately in the melt state by the additive. There is a proportional relationship between the stabilization effect of GA and its concentration in the polymer. Comparing the thermal resistance of LLDPE samples containing a combination of GA and a commercial antioxidant for polyethylene, Irganox 1010, and the samples containing Irganox 1010 alone confirmed that GA does not reduce the stabilization efficiency of the phenolic antioxidant in the polymer either in the melt or in the solid state. It was also observed that coumarin which was used in this study as a representative of the unsaturated lactone moiety of GA molecule has no contribution in GA stabilizing activity. On the basis of the obtained results, the thermo-oxidative stabilizing activity of GA was described in terms of the activity of allylic hydrogens present in the substituted moieties of GA molecules.