Development of SiO₂-reinforced natural rubber vulcanizate composite with Gd₂O₃ additions for neutron shielding...

Flexible composite materials with excellent mechanical properties that exhibit neutron moderation and absorption are required for effective neutron shielding in various applications. However, the addition of neutron absorbers may be detrimental to the overall mechanical properties of the materials. In this study, SiO₂-reinforced natural rubber (NR/SiO₂) vulcanizate with addition of Gd₂O₃ (NR/SiO₂-Gd₂O₃) was investigated to develop a flexible material with good mechanical and neutron attenuation properties. NR/SiO₂ and NR/SiO₂-Gd₂O₃with Gd₂O₃ concentrations of 5-15 phr were fabricated and characterized for their curing, mechanical, physicochemical, and thermal neutron attenuation properties. The results show that the vulcanizates retained acceptable hardness, tensile strength, elongation at break, and tear strength despite the addition of Gd₂O₃, with only moderate decreases observed. SEM-EDS mapping confirmed that Gd₂O₃ and SiO₂ were dispersed within the vulcanizate, although micro-agglomeration of Gd₂O₃ was observed in all samples. The beam hardening correction was applied to estimate the effective neutron attenuation value (Σ_eff) by linear regression of the experimental values (Σ_exp) against sample thickness. The Σ_eff for NR/SiO₂ was 2.02 cm^-1, whereas the values for NR/SiO₂-Gd₂O₃ were 5.20-9.33 cm^-1. These values correspond to an increase in Σ_eff by a factor of 2.5-4.6 with the addition of Gd₂O₃ at the investigated concentrations. The value for NR/SiO₂ was in close agreement with the theoretical total macroscopic cross section, whereas NR/SiO₂-Gd₂O₃ exhibited smaller values, likely due to the micro-agglomeration of Gd₂O₃. Nevertheless, the Σ_eff values were still greater than those of other reported NR vulcanizates.