Determination of hydroperoxides in ultraviolet-irradiated nylon 66

Abstract

According to mechanisms described in the literature, photodecomposition of nylon 66 proceeds through the abstraction of the hydrogen on the carbon α to the amide NH group by a free radical which has been activated by photo absorption. In the propagation phase, the α-carbon radical could readily react with atmospheric oxygen to form a hydroperoxide. The formation of a hydroperoxide in the photodecomposition scheme for nylon 66 has been detected but has not been measured quantitatively. With the colorimetric method described in this paper, it is now possible to determine the peroxide content in a polyamide to a level of 1 μmole/g. with a relative precision of less than 5%. The polyamide is dissolved in tetrafluoropropanol, to which aliquots of potassium iodide and glacial acetic solutions are added. The absorbance of the liberated iodine is measured in a 1-cm. cell at 400 mμ and the hydroperoxide concentration determined from a calibration curve constructed from hydrogen peroxide solution standards. The rate of peroxide formation, which is dependent on the wavelength of ultraviolet radiation, can be correlated to the strength loss exhibited by a nylon 66 yarn free from antioxidant and delustrant. In addition, an increase in the level of thermal degradation will accelerate yarn strength loss and peroxide formation under ultraviolet exposure. The hydroperoxide begins to decompose at about 100°C. Yarn finish will contribute to the peroxide formation during exposure.