Dottorato in INGEGNERIA AERONAUTICA E SPAZIALE

Titolo della tesi: Multifunctional poly(vinyl alcohol) gel systems for radiation protection and sensing in space environment

Protecting astronauts from the extreme radiation environment during long duration missions to the Moon or Mars is a fundamental challenge. Space agencies are currently evaluating the possibility of establishing permanent lunar bases as staging points for crewed missions into deep space, where exposure to solar particle events (SPEs) and galactic cosmic radiation (GCR) poses critical health and safety risks. In this context, the development of lightweight, flexible, hydrogen-rich materials with high stopping power for radiation protection has become a key priority. This doctoral research focuses on the design, fabrication and characterization of poly(vinyl) alcohol (PVA)-based gelled systems designed for various space applications. Two main experimental approaches were used for the fabrication of PVA-based gels. First, physically cross-linked PVA gels were fabricated through controlled freeze-thaw (FT) cycles to study the influence of water content on structural and mechanical properties. Subsequently, gels chemically cross-linked with boric acid (BA) were synthesised to improve radiation attenuation. Comprehensive experimental characterization was conducted to assess mechanical, thermal, electrical, and spectroscopic properties, confirming the potential of these gels as multifunctional materials. This study pursues three main objectives: the development of self-healing, thermally insulating layers for extravehicular spacesuits, the enhancement of neutron shielding performance for radiation protection in space, and the fabrication of electrically conductive gels capable of supporting embedded sensing for structural health monitoring. First, PVA/BA gels were studied as intermediate layers between the pressure bladder garment (PBG) and the liquid cooling and ventilation garment (LCVG) of spacesuits, with the aim of improving radiation shielding during extravehicular activities (EVA) on the Moon without altering the ergonomics or geometry of the suit. Thanks to their high-water content, these gels combine softness and ductility with strong radiation attenuation. Experiments demonstrated comparable density and thermal conductivity, but markedly superior flexibility in the gels, highlighted by higher local strain under tensile stress with elongations up to ∼ 65%. Simulations with NASA’s On-Line Tool for the Assessment of Radiation in Space (OLTARIS) confirmed effective protection against SPE protons on the lunar surface. To improve neutron attenuation in long-duration missions, PVA/polyethylene glycol (PVA/PEG) composite hydrogels filled with boron carbide were fabricated through physical cross-linking. Characterization by infrared spectroscopy and thermal conductivity measurements confirmed good structural integrity and stability. Numerical simulations performed with OLTARIS tool and NGCal software showed that these gels achieve dose reductions comparable to water and superior to aluminum, owing to the high hydrogen and boron concentrations. Finally, multifunctional PVA–MWCNTs gels were designed for combined radiation shielding and strain sensing. Compression tests and quasi-static tensile tests coupled with impedance monitoring were used to evaluate electromechanical stability.