Thermal degradation studies of LDPE containing cobalt stearate as pro-oxidant

Abstract

The influence of a typical prooxidative additive, cobalt stearate, on the thermal stability, degradation kinetics and lifetime of low-density polyethylene (LDPE) was investigated using non-isothermal thermogravimetric analysis (TGA) in both nitrogen and air atmosphere. The derivative thermogravimetric (DTG) curves indicate single stage and multistage decomposition process in nitrogen and air atmosphere respectively. The kinetic parameters of degradation were evaluated using the Flynn-Wall-Ozawa iso-conversion technique. The apparent activation energies for decomposition have been cal- culated for degradation under nitrogen atmosphere. The lifetime of LDPE (time for 5% mass loss) was estimated to be 8.2·10 26 min in nitrogen and was found to decrease dramatically with increase in the concentration of cobalt stearate thereby revealing its pro-oxidative ability. Studies indicated that the service/process temperature also has a strong influence on the lifetime of all the formulations investigated. The effect of cobalt stearate on the air oven aging behavior of LDPE at two different temperatures (70°C and 100°C) was also investigated to demonstrate the pro-oxidative nature of cobalt stearate.