Comparative X-ray Shielding, Mechanical, and Morphological Properties of Single-Layered and Multi-Layered Bi2O3/NR Composites

This work compared mechanical, X-ray shielding, and morphological properties of single-layered and multilayered natural rubber (NR) composites containing bismuth oxide (Bi₂O₃). The single-layered sample was prepared with the Bi₂O₃ content of 200 phr and the multi-layered samples were prepared such that the same amounts of Bi₂O₃ per unit area were achieved in all samples, i.e. theoretically having the same shielding abilities in all designs. To fabricate the specimens, NR and other chemicals were mixed using a kneader mixer, rolled into sheets of different thicknesses using two roll mills, and then compressed using a compression mold. The mechanical and physical properties, including tensile strength, elongation at break, surface hardness (shore A), and swelling ratio, were tested for all samples. The X-ray shielding properties, including the linear attenuation coefficient (μ), half-value layer (HVL), and lead equivalence (Pbeq), were also determined at varying X-ray supplied voltages of 60, 100, and 150 kVp. Furthermore, the surface morphologies and filler distributions of the composites were conducted using a scanning electron microscopy (SEM). The results indicated that the multilayered Bi₂O₃/NR composites generally exhibited higher overall mechanical properties than those of a singlelayered sample, while all designs in this work could attenuate X-rays with approximately the same efficiencies as initially intended. Specifically, the multi-layered sample having 5 layers with an arrangement of N-BiN-N-BiNN, where N represents a neat NR and BiN represents Bi₂O₃/NR composites, exhibited the highest tensile strength and elongation at break among other designs. This could have been due to a neat NR on the outer layer being more efficient at resisting heavy loads and/or transferring external forces than those of Bi2O3 /NR layers, which had visible filler agglomeration, determined using a SEM analysis. However, after simultaneous consideration of tensile strength and X-ray shielding properties, the sample having 4 layers with an arrangement of N-BiN-BiN-N
exhibited the most preferable overall properties, evidenced by the relatively high values of μ (6.54, 2.56, 3.24 cm-¹ for X-ray supplied voltages of 60, 100 and 150 kVp, respectively) and tensile strength (9.28 MPa). In summary, the overall results suggested that the multi-layered design could preserve the mechanical properties of the NR composites, which would be beneficial for actual uses in radiation protection.