Indoor accelerated and outdoor field weathering of styrene-ethylene-butadiene-styrene block copolymer have been studied by Fourier transform infrared (FTIR) spectroscopy. In the indoor accelerated experiments, specimens are exposed to ultraviolet-visible light with wavelengths ranging from 295 nm to 600 nm and one of four environments involving the combinations of temperatures and relative humidity (RH): (a) 30C at < 1 % RH, (b) 30C at 80 % RH, (c) 55C at < 1 % RH and (d) 55C at 80 % RH. Outdoor field exposure is conducted in Gaithersburg, MD. The specimens are placed in a chamber that is tilted at 5 degree from the horizontal plane and facing south. Two independent sets of specimens having different starting dates, May 2006 and July 2006, respectively, are examined. In the case of the accelerated exposure, the IR spectra indicate that the formation rate for carbonyl and hydroxyl oxidation products at 55C is faster at a higher RH; while no substantial changes are observed for 30C. Further, a higher temperature led to faster degradation rate at a given RH. The ultimate acceleration obtained from the combination of two independent exposures with high RH at low temperature and with high temperature at low RH is not equivalent to that obtained from a single exposure at high temperature and high RH. For outdoor exposures, FTIR revealed that specimens exposed to outdoor field conditions exhibited a degradation mechanism similar to that seen in indoor testing. Multiplicative shift factors are determined using an approach analogous to the time-temperature superposition. Acceleration in degradation ranged from two to eight times in comparison to the outdoor field exposures, depending on the indoor accelerated conditions.
Citation: Polymer Degradation and Stability
Pub Type: Journals
Acceleration, thermoplastic elastomers, accelerated aging, correlation, degradation, mechanism, outdoor exposure, SEBS, weathering.