Evaluation of the thermal stabilization behavior of hydrotalcite against organic stabilizers for plasticized PVC films

This study focuses on the systematic comparison of the thermal stabilization behavior of the hydrotalcite which is present in the nature and is non-toxic, with organic stabilizers (mixed metal salts, maleimide and tri-nonyl phenyl phosphite) having high stabilizing efficiency. For the purpose of this study, first plastisols were prepared by mixing plasticizer and thermal stabilizers into the PVC resin. Then films were obtained from plastisols, which were applied on a glass plate as 150 mu thick films with the help of a film applicator. The films were cured for 15 min in oven at 160 degrees C to produce plastigel films. The stabilization behavior of these films was measured by applying various stabilization testing methods: thermal aging test, oxidation index, polyene formation measurement and discoloration. Thermal aging studies for these plastigel films were carried out at 100 and 150 degrees C up to 420 min. Oxidation index values are associated with oxidized surface layer that is formed after the aging and degradation of the films, which are determined by FTIR spectroscopy. Thermal stability behavior in terms of concentration of polyenes formed due to the released HCl has been investigated by UV-visible spectroscopy. Color changes of the degraded films were followed by observed colorimetry. According to the results, number of the polyenes for all degraded films increased with increasing time and temperature. The results have proved the greater stabilizing efficiency of hydrotalcite relative to that of the thermal stabilizers in terms of the number of the conjugated double bond, polyene concentration, polyene formation rate and change in color. It is believed that the results will contribute to the thermal stability of PVC by different stabilizers and blends, and an effort has been made in this article to throw light on this issue.