Interaction of Neutrons with Strain-Engineered Fibrous Boron-Doped Polyethylene Materials

Studies of materials interactions with neutron beams are important for developing a fundamental understanding of material properties, studying materials degradation in extreme environments, and for the development of new radiation shielding materials for terrestrial and space applications. When ionizing particles, such as energetic electrons, protons, and gamma-rays interact with materials or tissue, they produce secondary particles, including thermal neutrons. As a result, neutrons are dominant near planetary surfaces and in atmospheres, induce high biological damage and present a risk factor for space exploration. The development of new lightweight multifunctional materials with simultaneous flexibility in mechanical properties, radiation shielding capability, and form factors is of high interest for aerospace, healthcare, and nuclear industries as well as for military applications.<br/><br/>Hydrogen is the ideal particle for stopping broad-spectrum primary radiation while also providing protection against secondary neutrons. Hydrogen is highly concentrated in polyethylene (PE) and all-hydrocarbon olefin block co-polymers, making PE a popular choice of material for radiation shielding composites [1]. It is well known that doping hydrogenated polymers with Boron-rich nanomaterials can further improve their performance for shielding both primary and secondary ionizing radiation [2]. However, the role of nanomaterial size, form-factor, and orientation as well as the effects of the melt-spinning-induced crystallinity, alignment, and phase separations within blended polymer matrices are poorly understood as most modeling approaches often do not capture this information. Multiple and inelastic scattering of neutrons by the internal structure of fibrous composite materials can affect their radiation shielding performance and material degradation pathways.<br/><br/>Through a combination of computer modeling, additive manufacturing via Fused Deposition Modeling (FDM) 3D-printing, weaving, and knitting, we engineer composite fibrous materials composed of PE-based blended resins as well as of PE-based polymer matrix doped by Boron-rich nano- and micro-particles. These materials are then characterized with neutron spectroscopy. We aim to develop a fundamental understanding of the role of nano-dopants as well as material- and fabrication-process-induced crystallinity and phase separations in composite PE-based fibrous materials on their wavelength-dependent multiple scattering and inelastic scattering of neutrons.<br/><br/>FDM printing and fiber spinning enable control over the polymer strength, stiffness by shear and strain deformations during the melt-extrusion process, resulting in aligned polymer chains and control over the material crystallinity, allowing studies of a wide range of composite materials of identical chemical composition but different internal structure. Most intriguing, such composite 3D printed materials and textiles can be recycled and reused in different form factors at the end of the product lifecycle. The developed fundamental understanding of neutron-matter interactions can be useful for engineering new composite radiation shielding materials like those developed by the Cosmic Shielding Corporation (CSC) [3] as well as PE-based textiles for terrestrial applications [4].<br/><br/>DX and VK contributed equally. Correspondence should be addressed to LS and SVB. This research is funded by the Cosmic Shielding Corporation (CSC), Atlanta, GA (for the Boron-doped 3D printed PE materials development). We also thank the ORNL for awarding us beam time for neutron scattering measurements (Proposal IPTS-28797.1 for NScD 2022-A) and William Heller for his help in running the experiment.<br/><br/>[1] S.V. Boriskina, MRS Energy & Sustainability 6, E14, 2019.<br/>[2] M. Cai, et al, AAAS Space: Science & Technology, 9754387, 2022.<br/>[3] R.K. Kaul, et al, United States Patent (10) Patent No.: US 7,855,157 B1, Dec. 21, 2010.<br/>[4] M. Alberghini, et al. Nature Sustainability 4,715–724, 2021.