Photo-oxidation at the exposed Surfaces of low-density polyethylene/montmorillonite composites was analyzed with attenuated total reflection/Fourier transform infrared spectroscopy. It was found that the clay particles were dispersed but not exfoliated in the polymer matrix. The extent of oxidative degradation of the low-density polyethylene matrix Was slightly greater when montmorillonite was present and was greatest for the blend of low-density polyethylene and organically modified montmorillonite. The Fourier transform infrared measurements demonstrated that the rate of photo-oxidation in the bulk was lower than that observed at the surface, but the oxidation chemistry was similar at the Surface and in the bulk. The distribution of the photo-oxidation products was somewhat modified in the presence of montmorillonite and organically modified montmorillonite in comparison With pore low-density polyethylene, with the yield of acidic products higher and the yield of double bonds lower. These observations were attributed to a slightly higher yield of radicals and some modification of the quantum yield for file processes leading to the formation of double bonds when the clay filler was present. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 112: 381-389, 2009