International audienceA space-used filled silicone rubber (silica and iron oxide fillers) and its polysiloxane isolated matrix were exposed to high energy electrons in order to determine their ageing mechanisms from a structural point of view. Physicochemical analysis evidenced that both filled and unfilled materials predominantly crosslink under such irradiation. Solid-state 29Si NMR spectroscopy allowed the identification of T-type SiO3 units as the main new crosslinks formed in the polymer network. It also revealed an increase in Qtype SiO4 units in the irradiated filled sample. Thanks to the combination of NMR spectroscopy and ammonia-modified swelling tests, these Q-type units were associated with new crosslinks formed at the silica fillers-matrix interface. While the main interaction between the polysiloxane network and the fillers was shown to proceed mainly through hydrogen bonding in the pristine filled samples, it was suggested that the hydrogen bonds were progressively replaced with SiO4 chemical bonds. These additional chemical crosslinks induced evolutions of the shear modulus on the rubber plateau and crosslink density that were significantly more pronounced in the filled material than in the neat one
This work investigates the possibility of using cellulose nanocrystals (CNCs) as biobased nanoadditives in protective polydimethylsiloxane (PDMS) space coatings, to improve the thermal and optical performances of the material. CNCs produced from wood pulp were functionalized in different conditions with the objective to improve their dispersibility in the PDMS matrix, increase their thermal stability and provide photoactive functions. Polysiloxane, cinnamate, chloroacetate and trifluoroacetate moieties were accordingly anchored at the CNCs surface by silylation, using two different approaches, or acylation with different functional vinyl esters. The modified CNCs were thoroughly characterized by FT-IR spectroscopy, solid-state NMR spectroscopy and thermogravimetric analysis, before being incorporated into a PDMS space coating formulation in low concentration (0.5 to 4 wt %). The cross-linked PDMS films were subsequently investigated with regards to their mechanical behavior, thermal stability and optical properties after photoaging. Results revealed that the CNC additives could significantly improve the thermal stability of the PDMS coating, up to 140 °C, depending on the treatment and CNC concentration, without affecting the mechanical properties and transparency of the material. In addition, the PDMS films loaded with as low as 1 wt % halogenated nanoparticles, exhibited an improved UV-stability after irradiation in geostationary conditions.
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 (Td 5%). 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.
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