Study on flexible composite materials for n-γ mixed radiation field protection based on boron nitride-lead acrylate hybrid filler

[Background] Neutron-gamma (n-γ) mixed radiation field protection is crucial for ensuring the safe utilization of nuclear energy and nuclear technology. The blending of different types of radiation shielding functional fillers with matrix materials is a commonly used method for preparing flexible n-γ radiation protection composite materials. However, constrained by challenges such as inhomogeneous dispersion of radiation-shielding elements and poor filler-matrix interfacial compatibility, the radiation shielding performance and mechanical properties of composite materials require improvement. There is an urgent demand for novel integrated fillers capable of providing simultaneous shielding against both neutron and gamma-ray. [Purpose] This study aims to develop a novel and high-efficiency hybrid functional filler for n-γ co-shielding, as well as high-performance flexible shielding composite material based on the filler. [Methods] Firstly, the thiol-functionalized boron nitride (BN) nanosheets were prepared via boric acid-assisted ball milling of BN followed by grafting with thiol-containing coupling agents, and lead acrylate (Pb(AA)2) was synthesized by the reaction of lead oxide and acrylic acid. Subsequently, BN-Pb(AA)2 hybrid fillers were prepared using thiol-functionalized BN nanosheets and Pb(AA)2 as precursors for neutron and gamma-ray shielding, via thiol-ene click chemistry reaction. Their microstructure and morphology were comprehensively characterized by using Fourier Transform Infrared Spectrum (FTIR), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction Analyzer (XRD), Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS), and the preparation mechanism was analyzed. Finally, flexible composite materials were prepared using ethylene propylene diene monomer (EPDM) as the flexible matrix material and BN-Pb(AA)2 hybrid filler as the functional filler, through open milling and vulcanization technology. Their neutron and gamma-ray shielding performance, as well as the mechanical properties, were tested and analyzed. [Results] Performance test results show that the 2-mm thick flexible composite material exhibits a thermal neutron shielding efficiency of 50%, mass attenuation coefficient of 3.494 cm2·g-1 for low-energy gamma-ray (39 keV), and tensile strength of 13.89 MPa when filled with 100 phr (parts per hundred rubber) of hybrid filler. Compared with mainstream commercial protective products, BN-Pb(AA)2/EPDM composite material achieves equivalent neutron shielding effectiveness while reducing thickness by over 30%, and additionally exhibits satisfactory gamma-ray shielding performance, demonstrating remarkable comprehensive n-γ shielding performance. [Conclusions] Results of this study provide technical support for the research and development of thermal neutron and low-energy gamma-ray protection materials. Constrained by challenges such as inhomogeneous dispersion of radiation-shielding elements and poor filler-matrix interfacial compatibility, the radiation shielding performance and mechanical properties of composite materials require further improvement, demanding for novel integrated fillers capable of providing simultaneous shielding against both neutron and gamma-ray.