Examining the effects of simulated Low Earth Orbit on the viscoelasticity and strain behaviour of deployable polybenzoxazine nanocomposites

Thin polybenzoxazine (PBZ) nanocomposite laminates containing polyhedral oligomeric silsesquioxane (POSS, 5 and 10 wt%) and reinforced with carbon and Kevlar^® fabrics are prepared on a large (350 mm x 290 mm x 0.4 ± 0.05 mm) scale. Composite specimens are exposed separately to progressive amounts of atomic oxygen (AO), gamma radiation, and vacuum ultraviolet radiation (VUV) to simulate up to 18 months of exposure in low Earth orbit, before being analysed by a range of techniques to examine the thermal, thermo-mechanical, and surface characteristics. The inclusion of POSS leads to the development of a protective silica rich layer (1-2 μm) in response to AO and significantly reduces the surface roughness compared with the same blend in the absence of POSS, while the T_g of the blend containing 10 wt% POSS is raised by up to 26°C over 18 months of simulated exposure. In contrast, gamma radiation has little effect on the T_g (increase of 2.5°C over the same exposure period) and effects less roughening, particularly where POSS is present. Exposure to VUV results in a loss in reflectance properties, but this is reduced as the POSS content is increased.