Highly Efficient and Eco-Friendly Thermal-Neutron-Shielding Materials Based on Recycled High-Density Polyethylene and Gadolinium Oxide Composites

Abstract

Due to the increasing demands for improved radiation safety and the growing concerns regarding the excessive use of plastics, this work aimed to develop effective and eco-friendly thermal-neutron-shielding materials based on recycled high-density polyethylene (r-HDPE) composites containing varying surface-treated gadolinium oxide (Gd₂O₃) contents (0, 5, 10, 15, and 20 wt%). The results indicate that the overall thermal-neutron-shielding properties of the r-HDPE composites were enhanced with the addition of Gd₂O₃, as evidenced by large reductions in I/I₀, HVL, and TVL, as well as the substantial increases in ∑_t and ∑_t/ρ of the composites. Furthermore, the results reveal that the values for tensile properties initially increased up to 5-15 wt% of Gd₂O₃ and then gradually decreased at higher contents. In addition, the results show that the addition of Gd₂O₃ particles generally increased the density (ρ), the remaining ash at 600 °C, and the degree of crystallinity (%XC) of the composites. This work also determined the effects of gamma irradiation on relevant properties of the composites. The findings indicate that following gamma aging, the tensile modulus slightly increased, while the tensile strength, elongation at break, and hardness (Shore D) showed no significant (p < 0.05) differences, except for the sample containing 5 wt% of Gd₂O₃, which exhibited a noticeable reduction in elongation at break. Furthermore, by comparing the neutron-shielding and mechanical properties of the developed r-HDPE composites with common borated polyethylene (PE) containing 5 wt% and 15 wt% of boron, the results clearly indicate the superior shielding and tensile properties in the r-HDPE composites, implying the great potential of r-HDPE composites to replace virgin plastics as effective and more eco-friendly shielding materials.

Keywords: attenuation; gamma aging; mechanical properties; neutrons; rare-earth oxide; recycled materials.

Figure 1

(a) Optical and (b) micrograph images of Gd₂O₃ particles and (c) distribution of Gd₂O₃ particle sizes.

Figure 2

Scope of work showing (a) Part I, optimization procedure for surface treatment of Gd₂O₃ particles using silane coupling agent (KBE903), and (b) Part II, preparation and investigation of properties for Gd₂O₃/r-HDPE composites with varying Gd₂O₃ contents.

Figure 3

Functional groups determined using FTIR of (a) silane coupling agent (KBE903) and non-treated Gd₂O₃ particles and (b) treated Gd₂O₃ particles with varying KBE903 contents (5, 10, 15, and 20 g/100 g Gd₂O₃).

Figure 4

SEM-EDX mapping showing the distribution of Gd elements in the 20 wt% Gd₂O₃/r-HDPE composites, with varying silane (KBE903) contents of (a) 5 g, (b) 10 g, (c) 15 g, and (d) 20 g per 100 g of Gd₂O₃. Dotted circles indicate areas with Gd agglomeration.

Figure 5

SEM images showing fractured surfaces of 20 wt% Gd₂O₃/r-HDPE composites with varying KBE903 contents of (a) 0, (b) 5 g, and (c) 20 g per 100 g of Gd₂O₃.

Figure 6

Thermal stability of Gd₂O₃/r-HDPE composites with varying Gd₂O₃ contents (0, 5, 10, 15, and 20 wt%), determined through TGA, with (a) correlations between remaining weight of r-HDPE composites and temperature and (b) correlations between derivative weight of r-HDPE composites and temperature.

Figure 7

Thermal stability of Gd₂O₃, determined through TGA. The dotted circle indicates the remaining weight (%) of Gd₂O₃ particles at 600 °C.

Figure 8

Neutron transmission ratios of (a) non-aged Gd₂O₃/r-HDPE composites and (b) gamma-aged Gd₂O₃/r-HDPE composites, with varying Gd₂O₃ contents and sample thicknesses, where error bars indicate ± standard deviation.

Figure 9

Thermal-neutron-shielding properties, consisting of (a) total macroscopic cross section (∑_t), (b) mass attenuation coefficient (∑_t/ρ), (c) half-value layer (HVL), and (d) tenth value layer (TVL) of non-aged Gd₂O₃/r-HDPE composites (solid lines) and gamma-aged Gd₂O₃/r-HDPE composites (dotted lines), where error bars indicate ± standard deviation.

Figure 10

SEM-EDX mapping of Gd distribution in Gd₂O₃/r-HDPE composites with varying Gd₂O₃ contents of (a) 5 wt%, (b) 10 wt%, (c), 15 wt%, and (d) 20 wt%. Dotted circles indicate areas with visible Gd agglomeration.

Figure 11

Mechanical properties, consisting of (a) tensile modulus, (b) tensile strength, (c) elongation at break, and (d) hardness (Shore D) of non-aged Gd₂O₃/r-HDPE composites (solid lines) and gamma-aged Gd₂O₃/r-HDPE composites (dotted lines), where error bars indicate ± standard deviation.

Figure 12

SEM images showing morphologies and particle distributions in (a) a pristine r-HDPE, and Gd₂O₃/r-HDPE composites with varying Gd₂O₃ contents of (b) 5 wt%, (c) 10 wt%, (d), 15 wt%, and (e) 20 wt%. Dotted circles indicate areas with visible particle agglomeration.