SynopsisThe emission of visible light during the tensile deformation of medium-and high-tenacity nylon 66 yarns in air has been studied a t strain rates of 0.63-200%/min and a t temperatures of 20-110OC. Emission is observed only in an oxidative atmosphere and increases with temperature according to an Arrhenius relation. The activition energy decreases with applied stress. The intensity at any temperature can be described by the sum of a component linear with stress and another exponential in stress above -60% of the ultimate strength. These results and the measured spectral distribution suggest that light emission arises from bimolecular termination of alkyl peroxy macroradicals. The chemiluminescence growth curves indicate that the applied stress increases the oxidation rate of the fiber due to internal and external frictional heating while, at high strains, stress-induced mainchain scission occurs up to fiber failure. The growth curve is sensitive to the load history of the fiber. The chemiluminescence decay curves are a sensitive probe of radical reactions such as cage termination and stabilizer scavenging in the amorphous region of the polymer.