Investigation of correlation of accelerated weatherings and natural weathering in Turkey for selected polymeric automotive exterior materials

In this study, PMMA, ABS+ASA and ABS surfaced materials, selected as automotive exterior materials were exposed to natural weathering for the first time in Bursa city in Turkey and accelerated weathering methods by xenon arc lamp and ultraviolet lamps to investigate the correlation between natural and accelerated weathering methods by analysis of molecular and macromolecular, determining of tensile strength and elongation, color difference and gloss properties on obtained samples from weatherings. As the first time in Turkey natural weathering test fixture was prepared according to EN ISO 877-1 in TÜBİTAK BUTAL. All samples were exposed to natural weathering conditions directly during one year (between November 11, 2019 and November 11, 2020). Six series of test samples were obtained by removing from the test fixture approximately in every two months. Accelerated weathering method by xenon arc lamp was carried out according to EN ISO 4892-2 (Method A, cycle no: 4) as totally 1920 hours. Six series of samples were obtained for periods of every 330 hours. Accelerated weathering method by ultraviolet lamps was carried out according to EN ISO 4892-3 (Method A, cycle no: 4) as totally 1512 hours. Six series of samples were obtained for periods every 252 hours. The effects of the weathering method on the changes in the molecular structure were determined by FTIR analysis, and the effects on the thermal degradation differences were determined by TGA analysis. The weathering resistance of the polymers was determined by changing properties of color and gloss, which are polymer surface properties. The performance parameter of polymers was determined by tensile strength test. Statistically PMMA did not undergo any change considerably, while significant changes were observed in ABS+ASA and ABS samples for all weathering methods. The noticeable change in PMMA polymer was in elongation at break and it was determined that this change was caused by the layer other than PMMA in layered structure. No noticeable change was detected in surface appearance, molecular structure and degradation behavior of PMMA samples. It was observed that ABS+ASA and ABS materials were affected by all three weathering methods and their properties changed and also both polymers showed similar weathering resistance. In the analysis of change in molecular structure by FTIR, it was observed that as a result of photooxidative degradation, new absorption bands belonging to carbonyl vibrations at 1600-1800 cm-1 and hydroxyl vibrations at 3000-3400 cm-1 were formed and the peak intensities in the vinyl structure decreased. This degradation state in molecular structure was also measured as the behavioral difference in thermal degradation by TGA analysis. Increasing of exposure time, which causes the degradation on molecular structure, resulted an acceleration of degradation of samples under heat. It has been found that surface properties are important in color measurement and the changes in surface texture cannot be detected by spectrophotometer, therefore it is appropriate to determine the color difference by visual color evaluation. Color change and decrease in gloss were observed on the surfaces of both polymer samples. As a result, PMMA was not affected by all three weathering methods, but ABS+ASA and ABS samples are significantly affected, the most affected polymer is ABS+ASA, and the most destructive weathering method is accelerated weathering by ultraviolet lamps and natural weathering has more mild effects. It was found that there was a correlation between the weathering methods on the basis of evaluation parameters as breaking strength, gloss and gray scale and color difference, and also the R2 coefficient in the regression-based curve estimation was high. The highest R2 value occurred in the gloss parameter. In correlation study for all data it was observed that correlation coefficient was higher than the correlation coefficients of each parameter. This study showed that correlation can be done between weathering methods for some parameters and the results of a weathering method can be converted to other methods. As a result of this determination, the time estimation for the natural weathering became possible when test results of the accelerated weatherings obtained by the laboratory by using transformation equations created by curve estimation.