Prediction of outdoor weathering performance of polypropylene filaments by accelerated weathering tests

The effects of both accelerated and outdoor weathering tests on polypropylene filaments are studied to seek the possible relationship between weathering performance of the material under the two weathering conditions. Three intensities of Ultraviolet (UV) irradiation were provided in accelerated weathering tests to study the influences of UV irradiation intensity on photo-oxidation of the filaments. These are 81.58, 162.58 and 325.25 W/m2 using 2, 4 and 8 UV fluorescent lamps, respectively. One year of outdoor weathering tests was also conducted. The tensile strength of the filament samples under different weathering conditions was then measured. Also, the intrinsic viscosity of the corresponding samples was measured to examine molecular weight reduction of the filaments in various stages of the arranged weathering conditions. In addition, Fourier transform infrared spectrometry was used to analyze the samples. Formation of carbonyl group of “chain end” carboxylic acids has observed from the samples under both outdoor weathering test and accelerated one with the lower intensities of UV irradiation (81.58 and 162.58 W/m2), indicating a decomposition reaction of hydroperoxides. However, carbonyl group of esters and some lower molecular weight acids have been observed from the samples by the accelerated weathering test with the higher intensity of UV irradiation (325.25 W/m2), indicating different degradation mechanism of the samples from the outdoor test. The study shows that the lower intensities of UV irradiation in accelerated weathering tests could offer a compatible condition with the outdoor ones for photo-oxidation of the material, and consequently, provide a possible way to predict weathering performance of polypropylene filaments used outdoors.