Properties of lead-free gamma-ray shielding materials from metal oxide/EPDM rubber composites

This work investigated the gamma-ray shielding, cure characteristics, physical, and mechanical properties of ethylene propylene diene monomer (EPDM) rubber composites with additions of metal oxides (either iron (II, III) oxide; Fe3O4, tungsten (III) oxide; W2O3 or bismuth (III) oxide; Bi2O3) for potential use as flexible, durable, and lead-free gamma-ray shielding materials. The results showed that increases in the metal oxide contents from 0 to 100, 300, and 500 phr (parts per hundred of rubber), respectively, improved the gamma-ray shielding properties of the EPDM rubber composites with the highest gamma attenuation in 500-phr Bi2O3. The results also showed initial decreases in the cure times at a 100-phr metal oxide content but subsequently increased at higher contents (300 phr and 500 phr). Furthermore, while tensile modulus at 100% elongation and hardness (Shore A) kept increasing with increasing metal oxide contents, tensile strength and elongation at break behaved differently as they initially increased at 100 phr but later decreased at 300 phr and 500 phr. In addition, after the accelerated-weathering studies, the tensile modulus at 100% elongation and tensile strength of the EPDM rubber composites increased but the elongation at break and hardness (Shore A) decreased. In summary, the overall properties suggested that these developed metal oxide/EPDM rubber composites could be effectively used to replace lead-containing materials as durable gamma-ray shielding materials.