Polydimethylsiloxane/Additive Systems for Thermal and Ultraviolet Stability in Geostationary Environment

The development of radiation resistant materials is an ongoing challenge for space industry. High-energy irradiation (ultraviolet, electrons, neutrons, protons) induce damage to materials and electronic components in spaceships. Silicone resins are often used and play a key role as coatings and adhesive materials for satellites. Polydimethylsiloxanes show material exhaustion after long-term exposure to ultraviolet irradiation. Consequently, solutions are required to increase their thermo- and photostability under solar irradiation. Three different families of additives, namely ultraviolet absorbers, hindered amine light stabilizers, and a carbazole derivative are investigated. Those ultraviolet stabilizers were mixed with polydimethylsiloxane, then a cross-linking process was run by hydrosilylation. When ultraviolet absorbers could not be used due to a miscibility problem, addition of 0.5 wt % of bis(2,2,6,6-tetramethylpiperidin-4-yl)decanedioate (hindered amine light stabilizer 1) was shown to increase the thermal stability, measured by thermogravimetric analysis, from 360 to 395°C (Td5%). Using visible near-infrared spectroscopy and after 450 equivalent solar hours of ultraviolet irradiation, an average increase of 2.6% in the ultraviolet stability was also obtained in the wavelength range from 250 to 400 nm. A polydimethylsiloxane/dibromocarbazole 1.0 wt% did not improve the ultraviolet stability but exhibited a strong increase (about 100°C) of the degradation temperature of the polydimethylsiloxane.