Poly(vinyl alcohol) gels cross-linked by boric acid for radiation protection of astronauts

Abstract

Gels are soft materials composed of hydrophilic polymers cross-linked in water by physical or chemical bonds. Due to their lightweight and water-rich nature, these materials find application in various fields, including the space environment, for radiation protection purposes. In fact, thanks to their high hydrogen content, gels exhibit significant radiation stopping power, resulting in reduced fragmentation of incident particles. This suggests their potential utility in shielding electronic devices and safeguarding astronauts’ health. In this work, cross-linked gels based on poly(vinyl alcohol) (PVA) and boric acid (BA) were fabricated and their properties were investigated using different experimental and modeling techniques. The effect of parameters, such as time and temperature, used for fabricating the PVA/BA gels is assessed. Fourier transform infrared spectroscopy (FTIR) was employed to evaluate the ability of BA to form hybrid interpolymeric bonds with PVA macromolecules. To understand the thermo-mechanical properties and viscoelastic behavior of these gels, dynamic mechanical analysis (DMA) in compression mode was performed. The shielding properties were evaluated in different space radiation environments considering galactic cosmic rays, solar particle events, and low earth orbit radiation using deterministic transport codes. The High charge (Z) and Energy TRaNsport (HZETRN) code was employed to create different cross sections as first output for the selected materials, and then, propagate and transport the ionizing radiation inside the materials. The results highlight several advantages of PVA/BA gels fabricated at room temperature without heat treatments. Firstly, the incorporation of BA allows for a slight increase in water content compared to gels produced without the crosslinker. Additionally, an examination of elastic moduli reveals improved mechanical properties exhibiting approximately twice the elastic modulus of PVA gels. Moreover, the analysis of dosimetry quantities suggests that the radiation protection effectiveness of these gels is comparable to that of pure water, while heat-treated PVA/BA gels exhibit a reduced water content resulting in decreased shielding properties and decreased flexibility. Consequently, PVA/BA gels realized at room temperature appear to be the optimal material between PVA gels and the heat-treated counterparts, making them well-suited for integration into astronaut personal protective equipment.