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Accelerated Weathering Parameters for Some Aromatic Engineering Thermoplastics

Published

Author(s)

Li Piin Sung, James E. Pickett, Olga Kuvshinnikova, Brett Ermi

Abstract

Samples of polycarbonate (PC), poly(butylene terephthalate) (PBT), a PC/PBT blend, and poly(styrene-co-acrylonitrile) (SAN), all containing 3 % TiO2 (by mass), were exposed in the NIST (National Institutes of Standards and Technology) SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) to determine the effects of UV intensity (irradiance), temperature, relative humidity (RH), and UV wavelength on yellowing and gloss loss. There was no effect of irradiance, meaning that the samples obeyed reciprocity and doubling the irradiance doubled the rate of degradation. The activation energy for yellowing was ≈ 20 kJ/mol for PC, PC/PBT, and SAN and ≈ 16 kJ/mol for PBT. The activation energy for gloss loss (9-16) kJ/mol. This means that a 10 °C increase in temperature results in a 20 % to 30 % increase in degradation rate. There was no consistent effect of RH on PC or PC/PBT yellowing or gloss loss. SAN degraded faster under very dry conditions, but there was little effect for RH > 10 %. PBT lost gloss more slowly under very dry conditions but there was no RH effect on yellowing. Shorter wavelength UV had a greater effect on PC/PBT than either PC or PBT alone. The results suggest that it is justified to operate a xenon arc weathering chamber using Atlas Right Light™ or Q-Lab Daylight-F filters up to an irradiance of 0.75 W/m2/nm at 340 nm, 30 % to 50 % RH, and preferably at as low of temperature as can be maintained. More work is needed to establish spray conditions that reproduce the effects of rain.
Citation
Polymer Degradation and Stability

Keywords

polycarbonate, poly(butylene terephthalate), SAN, weathering, reciprocity, activation energy, humidity

Citation

Sung, L. , Pickett, J. , Kuvshinnikova, O. and Ermi, B. (2019), Accelerated Weathering Parameters for Some Aromatic Engineering Thermoplastics, Polymer Degradation and Stability (Accessed May 24, 2024)

Issues

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Created May 24, 2019, Updated February 3, 2020