This article reports the results of studies on the photooxidative and thermooxidative degradation of linear low-density polyethylene (LLDPE) in the presence of cobalt stearate. Various amounts of cobalt stearate (0.1-0.9% w/w) blended with LLDPE and films of 70 +/- 5 mu thickness were prepared by a film-blowing technique. The films were subjected to xenon arc weathering and air-oven aging tests (at 70 degrees C) for extended time periods. We followed the chemical and physical changes induced as a result of aging by monitoring changes in the mechanical properties (tensile strength and elongation at break), carbonyl index, morphology (scanning electron microscopy), melt flow index, and differential scanning calorimetry crystallinity. Cobalt stearate was highly effective in accelerating the photodegradation of LLDPE films at concentrations greater than 0.2% w/w. The kinetic parameters of degradation, as determined by nonisothermal thermogravimetric analysis, were estimated with the Flynn-Wall-Ozawa isoconversion technique, which was subsequently used to determine the effect of cobalt stearate on the theoretical lifetime of LLDPE. (c) 2008 Wiley Periodicals, Inc.