The effect of transition metal stearates on the photodegradation of polyethylene

The effect of a series of transition metal (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) stearates on the photodegradation of a high‐density polyethylene was examined mainly by changes in the carbonyl IR absorption of the sample films. Electron spin resonance (ESR) and luminescence spectra of the samples containing the copper stearate were measured. The photochemical reaction of the copper stearate was examined by IR and UV‐visible spectroscopies. The iron stearate was the most effective at an early stage of the photodegradation of the polymer, and vanadium and manganese stearates accelerated it, while the copper stearate retarded it. The other metal stearates showed no applicable effect on the photodegradation. The relative intensity of the ESR spectra of the photoirradiated samples and that of the emission spectra of the unirradiated samples at ca. 350 nm decreased with increasing concentration of the copper stearate. An absorption peak at 1580 cm −1 decayed, and a new peak at 1740 cm −1 appeared with photoirradiation of the copper stearate. Absorption peaks of the copper stearate at 252 and 665 nm decayed also rapidly with photoirradiation of the copper stearate in THF solution. The results suggest that one of the main retardative functions of the copper stearate in the photodegradation of polyethylene was an ultraviolet absorber.