Impact of natural antioxidant (silybin) on the thermal stability of ultra high molecular weight polyethylene: a thermogravimetric study

The natural antioxidant (Silybin), with different concentrations, is introduced in Ultra High Molecular Weight Polyethylene (UHMWPE) and impact on thermal stability is observed. For this, thermograms are recorded at 5 ℃/min heating rate in temperature region 50–600 ℃ through Thermogravimetric Analysis (TGA) technique. The model fitting (Coats and Redfern) kinetic approach is adopted to determine activation energy of each recorded thermograms to identify optimum silybin concentration. UHMWPE, with optimum silybin concentration, are further subjected to three other heating rates (10, 15 and 20 ℃) in the same temperature region. By employing deconvolution (bi-Gaussian asymmetric function) approach, two iso-conversional kinetic models (Starink (SR) and Friedman (FR)) are utilized to obtain activation energies of the deconvoluted peaks. Further, the reaction mechanism involved in thermal decomposition, change in entropy \(\left({\Delta \text{S}}^{\#}\right)\) $\left({\mathrm{\Delta }\text{S}}^{\#}\right)$ , change in enthalpy \(\left({\Delta \text{H}}^{\#}\right)\) $\left({\mathrm{\Delta }\text{H}}^{\#}\right)$ and change in Gibbs free energy \(\left(\Delta {\text{G}}^{\#}\right)\) $\left(\mathrm{\Delta },{\text{G}}^{\#}\right)$ are determined.