Development of paraffin and paraffin/bitumen composites with additions of B2O3 for thermal neutron shielding applications

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

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.

Epoxy Phase-Change Materials Based on Paraffin Wax Stabilized by Asphaltenes

The usual problem of meltable phase-change agents is the instability in their form upon heating, which can be solved by placing them into a continuous polymer matrix. Epoxy resin is a suitable medium for dispersing molten agents, but it is necessary to make the obtained droplets stable during the curing of the formed phase-change material. This work shows that molten paraffin wax forms a Pickering emulsion in an epoxy medium and in the presence of asphaltenes extracted from heavy crude oil. Theoretical calculations revealed the complex equilibrium in the epoxy/wax/asphaltene triple system due to their low mutual solubility. Rheological studies showed the viscoplastic behavior of the obtained dispersions at 25 °C, which disappears upon the heating and melting of the paraffin phase. Wax and asphaltenes increased the viscosity of the epoxy medium during its curing but did not inhibit cross-linking or reduce the glass transition temperature of the cured polymer. As a result of curing, it is possible to obtain phase-change materials containing up to 45% paraffin wax that forms a dispersed phase with a size of 0.2-6.5 μm. The small size of dispersed wax can decrease its degree of crystallinity to 13-29% of its original value, reducing the efficiency of the phase-change material.

Simulation of Neutron/Self-Emitted Gamma Attenuation and Effects of Silane Surface Treatment on Mechanical and Wear Resistance Properties of Sm2O3/UHMWPE Composites

This work reports on the simulated neutron and self-emitted gamma attenuation of ultra-high-molecular-weight polyethylene (UHMWPE) composites containing varying Sm₂O₃ contents in the range 0–50 wt.%, using a simulation code, namely MCNP-PHITS. The neutron energy investigated was 0.025 eV (thermal neutrons), and the gamma energies were 0.334, 0.712, and 0.737 MeV. The results indicated that the abilities to attenuate thermal neutrons and gamma rays were noticeably enhanced with the addition of Sm₂O₃, as seen by the increases in µ_m and µ, and the decrease in HVL. By comparing the simulated neutron-shielding results from this work with those from a commercial 5%-borated PE, the recommended Sm₂O₃ content that attenuated thermal neutrons with equal efficiency to the commercial product was 11–13 wt.%. Furthermore, to practically improve surface compatibility between Sm₂O₃ and the UHMWPE matrix and, subsequently, the overall wear/mechanical properties of the composites, a silane coupling agent (KBE903) was used to treat the surfaces of Sm₂O₃ particles prior to the preparation of the Sm₂O₃/UHMWPE composites. The experimental results showed that the treatment of Sm₂O₃ particles with 5–10 pph KBE903 led to greater enhancements in the wear resistance and mechanical properties of the 25 wt.% Sm₂O₃/UHMWPE composites, evidenced by lower specific wear rates and lower coefficients of friction, as well as higher tensile strength, elongation at break, and surface hardness, compared to those without surface treatment and those treated with 20 pph KBE903. In conclusion, the overall results suggested that the addition of Sm₂O₃ in the UHMWPE composites enhanced abilities to attenuate not only thermal neutrons but also gamma rays emitted after the neutron absorption by Sm, while the silane surface treatment of Sm₂O₃, using KBE903, considerably improved the processability, wear resistance, and strength of the composites.

Rare-Earth Oxides as Alternative High-Energy Photon Protective Fillers in HDPE Composites: Theoretical Aspects

This work theoretically determined the high-energy photon shielding properties of high-density polyethylene (HDPE) composites containing rare-earth oxides, namely samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), and gadolinium oxide (Gd₂O₃), for potential use as lead-free X-ray-shielding and gamma-shielding materials using the XCOM software package. The considered properties were the mass attenuation coefficient (µ_m), linear attenuation coefficient (µ), half value layer (HVL), and lead equivalence (Pb_eq) that were investigated at varying photon energies (0.001–5 MeV) and filler contents (0–60 wt.%). The results were in good agreement (less than 2% differences) with other available programs (Phy-X/PSD) and Monte Carlo particle transport simulation code, namely PHITS, which showed that the overall high-energy photon shielding abilities of the composites considerably increased with increasing rare-earth oxide contents but reduced with increasing photon energies. In particular, the Gd₂O₃/HDPE composites had the highest µ_m values at photon energies of 0.1, 0.5, and 5 MeV, due to having the highest atomic number (Z). Furthermore, the Pb_eq determination of the composites within the X-ray energy ranges indicated that the 10 mm thick samples with filler contents of 40 wt.% and 50 wt.% had Pb_eq values greater than the minimum requirements for shielding materials used in general diagnostic X-ray rooms and computerized tomography rooms, which required Pb_eq values of at least 1.0 and 1.5 mmPb, respectively. In addition, the comparisons of µ_m, µ, and HVL among the rare-earth oxide/HDPE composites investigated in this work and other lead-free X-ray shielding composites revealed that the materials developed in this work exhibited comparable X-ray shielding properties in comparison with that of the latter, implying great potential to be used as effective X-ray shielding materials in actual applications.

Cellular Bi2O3/natural rubber composites for light-weight and lead-free gamma-shielding materials and their properties under gamma irradiation

This work investigated the effects of a radiation-protective filler, namely bismuth oxide (Bi2O3), and blowing agents, namely azodicarbonamide (ADC) and oxy-bis (benzene sulfonyl) hydrazide (OBSH), on gamma attenuation and the mechanical, physical, and morphological properties of cellular natural rubber (NR) composites for potential use as light-weight and lead-free gamma-shielding materials. The contents of Bi2O3 were varied from 100 to 300 and 500 parts per hundred of rubber by weight (phr) and the contents of ADC or OBSH were varied from 0 to 8 and 16 phr. The results indicated that the addition of Bi2O3 enhanced the overall gamma-shielding ability, density, tensile modulus, and hardness (Shore OO), but lowered the tensile strength and elongation at break. On the other hand, the addition of ADC or OBSH resulted in decreases in the density, linear attenuation coefficient ( μ), and overall tensile properties but an increase in the mass attenuation coefficient ( μm), with ADC producing better mechanical properties than samples with OBSH. In addition, investigations on the properties of the cellular Bi2O3/NR composites under additional 35 kGy and 70 kGy gamma irradiation revealed that the irradiated samples had increased density, tensile modulus, and hardness (Shore OO), but decreased tensile strength, elongation at break, and μm after such ageing. In conclusion, the overall results suggested that the developed cellular Bi2O3/NR composites not only had efficient and promising gamma-shielding and mechanical properties but also offered comfort and light-weight to users, which could potentially reduce discomforts caused by wearing heavier conventional radiation-protective equipment.