Boron Nitride Nanotube Reinforced Polyethylene Composite for Shielding Space Neutron Radiation for Human Space Flight

NASA's Artemis program aims to establish a sustained human presence on the Moon and, ultimately, on Mars, making astronaut protection from radiation a priority. Materials with spaceflight heritage, especially those high in hydrogen content like polyethylene (PE), represent the state-of-the-art in lightweight and effective radiation shielding. This effectiveness comes from hydrogen’s advantageous properties, including a high charge-to-mass ratio, minimal secondary radiation production, efficient energy absorption, and a high cross-section that increases the likelihood of interactions to decelerate or halt ionized particles. Boron nitride nanotubes (BNNTs) and other boron-enriched materials offer superior thermal neutron radiation shielding due to their high cross-section and strong neutron absorption abilities. BNNTs also enhance the mechanical properties of shielding materials due to their high strength-to-weight ratio. The addition of BNNTs to a wide range of spaceflight materials can enhance mechanical and radiation shielding properties for applications on the lunar and Martian surface. However, integrating high volumes of nanotubes (more than 15 wt%) in a matrix without defects, such as macro-voids and nanotube agglomerations, presents significant manufacturing challenges. Due to these challenges, state-of-the-art research has led to marginal improvements in mechanical and radiation shielding properties. To address this, a bulk nanocomposite laminate fabricating technique is utilized to integrate ~ 50 wt% of BNNTs in high density polyethylene (HDPE). This process involves synthesizing millimeter-long vertically aligned BNNTs, densifying the nanotubes to high-volume fractions, and infusing the nanotubes with HDPE while applying heat and pressure. The BNNT-HDPE nanocomposite was tested for its neutron radiation shielding properties at NASA Langley Research Center’s neutron radiation exposure lab. Radiation shielding properties of the BNNT-HDPE nanocomposite showed a ~10X improvement in neutron shielding compared to the same areal density/mass of HDPE.