Photon shielding and neutron interaction behaviour in natural rubber composites reinforced with hybrid oyster shell–derived CaCO₃/BaCl2 fillers

The development of flexible, lightweight, and sustainable radiation-shielding composites is important for medical and portable protection. Here, we design a lead-free natural rubber (NR) composite reinforced with a ball-milled hybrid filler derived from oyster shell CaCO3 and barium chloride (BaCl2·2H2O). The hybrid particulate design combines a bio-waste mineral phase with a high-atomic-number component to enhance attenuation while retaining elastomeric deformability. Photon attenuation was evaluated at 81, 122, and 342 keV using Co-57 and Ba-133 sources. With increasing filler loading (0–150 phr), the mass attenuation coefficient increased by around 8–9× at 81 keV, around 5× at 122 keV, and around 2× at 342 keV, while the half-value layer decreased by up to around 90%, 80%, and 50%, respectively. These trends are consistent with increased effective atomic number and electron density, promoting photoelectric absorption at low energies and Compton scattering at higher energies. SEM/EDX confirms the incorporation and microscale distribution of Ba- and Cl-containing domains, while high loadings introduce porosity/agglomeration that moderates density and mechanical reinforcement. Neutron measurements further show complementary shielding behavior, where hydrogen-rich NR moderates fast neutrons and chlorine-containing phases contribute to thermal neutron capture. The results demonstrate a sustainable multifunctional elastomer composite for dual photon–neutron shielding.