1. Introduction

Nuclear radiation has various useful applications in different fields such as industries, agriculture, food irradiation, defects detection in metal casting, nuclear reactors, medical diagnostic, imaging and therapy, nuclear power plants, aerospace, and radiation chemistry of polymers [1]. Nevertheless, exposure to ionizing radiation can result in radiation sickness, organ damage, cell mutation, cancer, component failure, and other negative effects, depending on the amount of radiation absorbed. Therefore, it is essential to use shielding to protect individuals from these harmful effects.

Radiation shielding is essential for protecting people and equipment from the harmful effects of ionizing radiation. Ionizing radiation can cause damage to living tissue and DNA, leading to an increased risk of cancer, radiation sickness, and other health problems. It can also damage electronic equipment and sensitive instruments, causing malfunctions or complete failure [2]. Radiation shielding works by absorbing or scattering the radiation, reducing its intensity and protecting the people and equipment behind the shield. Shielding materials can vary depending on the type and energy of the radiation being shielded. For example, bismuth and lead are commonly used for shielding against gamma and X-rays [3], while concrete or water can be used for shielding against neutron radiation [4,5]. Glass composites doped with heavy elements or mixed with cement are also used for gamma and neutron shielding [6,7,8,9].

Radiation shielding is critical in a variety of settings, including medical facilities, nuclear power plants, and research laboratories. Without adequate shielding, workers and the general public could be exposed to dangerous levels of radiation, leading to serious health consequences. Therefore, proper radiation-shielding design and implementation are crucial to ensure the safety of workers, the public, and the environment.

Polymers and rubber-based composites can also be used for radiation shielding. These composites are typically made by combining rubber with other materials, such as lead or tungsten, to create a material that can effectively block both beta and gamma radiation [10,11,12]. Polymers are an ideal option for radiation shielding because of their lightweight, strong, and flexible properties, as well as their resistance to physical, mechanical, and radiation damage. They are a superior alternative to concrete and lead for radiation shielding. Furthermore, by adding high atomic number materials, polymers can be easily transformed into composites that are more effective as radiation shields [13,14,15].

Silicone rubber doped with high-atomic-number materials such as lead, cadmium, and tungsten can be used in various applications such as medical imaging, nuclear power plants, and aerospace [16,17,18]. The effectiveness of the shielding material depends on the composition and thickness of the material, as well as the energy of the radiation being shielded. It is important to note that while silicone rubber doped with lead or tungsten can be effective for radiation shielding, it may not be the best choice for all applications. Factors such as weight, flexibility, and durability may also need to be considered. Ethylene propylene diene monomer (EPDM) rubber composites have the potential to serve as flexible, durable, and lead-free gamma-ray-shielding materials when metal oxides such as iron (II, III) oxide (Fe3O4), tungsten (III) oxide (W2O3), or bismuth (III) oxide (Bi2O3) are added to them [19]. Due to its high boron content, EPDM/Hexagonal boron nitride (hBN) samples are able to attenuate thermal neutron radiation up to 61.5% [20].

Recently, silica fillers have been introduced as a reinforcing filler for rubbers from economic factors as well as their ability to give major benefits, such as low thermal expansion, chemical resistance, hard surface, and high dielectric strength [21]. exposure to gamma radiation can lead to the creation of point defects in SiO2, such as oxygen vacancies or oxygen interstitials. These defects can induce structural changes in the material, altering its density, crystallinity, and morphology. Such changes can affect the shielding parameters of the NR/NBR blend. However, it is crucial to consider that the precise nature of this impact is contingent upon several factors, such as the concentrations of SiO2 and the shielding filler material such as Bi2O3, the radiation dosage, and the specific characteristics of the resulting point defects [22].

Nitrile rubber (NBR) is a synthetic elastomer that is commonly used in automotive applications due to its good resistance to oil and low gas permeability, but its limited ageing resistance may require careful consideration in certain situations [22]. Its good radiation resistance also makes it useful in certain specialized applications [23].

The objective of the present study is to create a novel composite material for shielding purposes using a blend of NBR and NR as the matrix. Bismuth oxide will be added to this blend as a filler, and its effect on the mechanical and shielding properties of the composite will be examined. The optimal concentration of bismuth in the blend will also be determined. The new composite material is expected to possess unique physical, mechanical, and attenuation characteristics, as well as being lightweight, affordable, and having reasonable radiation resistance. As a result, it has the potential to be utilized in the production of radiation protection equipment for use by medical, industrial, and military personnel.

2. Materials and Methods

2.1. Materials

All the rubber components were acquired from Aldrich Co. and were of commercial quality. Table 1 shows how all the used ingredients of the prepared NR/NBR/Bi2O3 composites. The chosen rubber matrix is acrylonitrile butadiene rubber (NBR) and natural rubber (NR). Acrylonitrile butadiene rubber (NBR) containing 32% acrylonitrile content with specific gravity 1.17 + 0.005 was supplied from Bayer AG, Germany. Natural rubber ribbed smoked sheet (Grade RSS 1) is obtained from Transport and Engineering, Alexandria company, Egypt. Its mass density is 0.913 ± 0.005 g/cm3 at 23 °C, Tg = ?75 °C, and Mooney viscosity in the range 60–90.

2.2. Preparation of Composites

The rubber blends were created using a two-roll mill that had a diameter of 470 mm and a working distance of 300 mm. The slow roller was set to rotate at 24 revolutions per minute, with a gear ratio of 1:1.4. The mixing process followed ASTM D3182 guidelines, with close attention paid to controlling temperature, nip gap, and the order of adding ingredients.

The vulcanization process was conducted using an electrically heated hydraulic press, which was equipped with an automatic control system. The temperature was maintained at 152 ± 1 °C, while the pressure was set at approximately 4 MPa. Standard methods were used to test the compounded rubber and vulcanizates, including ASTM D2084-11(2012) for determining rheometric characteristics using a Monsanto Rheometer model and an oscillating disc rheometer R-100 (MDR one moving Die Rheometer, TA instruments, New Castle, DE, USA).

2.3. Material Characterizations

The Zwick tensile testing machine (model Z010, Ulm, Germany) was utilized to determine the tensile strength and elongation at break. Compressed sheets were first cut into dumbbell-shaped specimens with appropriate punching dies, which had a width of 4 mm, a neck length of 15 mm, and a thickness of 1–1.5 mm, in accordance with ASTM D412 standards [24]. Mechanical property testing was carried out using a crosshead speed of 500 mm/min and a load cell of 10–20, as per the ASTM guidelines. Hardness measurements were obtained using a Shore A durometer (Bareiss, Oberdischingen, Germany), following ASTM D2240. The test specimens were at least 6 mm thick.

Mass density was measured at 25 °C using a standard Archimedes procedure, which was based on a given equation.


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