Accelerated UV degradation behavior of high tensile nylon 6, 6 webbings

The paper investigates the UV degradation behavior of high tensile nylon 6, 6 webbings used in military applications. Webbings of four colors (navy, black, tan, and white) were selected according to military specification MIL-DTL-4088. The webbings were then subjected to up to 15 days of continuous exposure using a modified ASTM D2565 test standard in xenon-arc Weather-Ometer with 1.5x narrowband irradiance or 0.83 W/m² ∙ nm at 340 nm under Arizona conditions (43 °C, 30% RH), a duration equivalent to 107 days of outdoor Arizona conditions. SEM analysis showed no morphological changes even after 15 days of continuous exposure, contrary to literature available on the degradation of nylon polymer. However, FTIR spectroscopy showed evidence of change in molecular structure of nylon webbings with increasing UV exposure duration. This finding showed that the peak at 1740 cm⁻¹ associated with -COOH bond energy increased as exposure increased, confirming that the hydrolysis phenomenon was initiated by UV radiation. This was also confirmed by tensile test results, which showed that the strength of the webbings decreased by 20% for all color except the white webbings (6% reduction) after 15 days in the weatherometer. A full factorial analysis confirmed that exposure duration had the largest effect on breaking strength (Partial η² = 0.67), followed by color (Partial η² = 0.54). A significant interaction effect (Partial η² = 0.37, p < .0001) confirmed that the rate of degradation was color-dependent, which could be the result of the dye chemistry associated with different colors. This study highlights the use of chemical characterization is essential for monitoring material integrity when surface changes are not visible due to UV degradation in nylon 6, 6 webbings. Future work should aim to quantify these chemical changes to develop a non-destructive method for predicting the residual strength of in-service webbings.

Graphical abstract