Investigation on spent coffee ground-epoxy resin composite as a sustainable radiation shielding material

Growing interest in bio-based fillers offers a sustainable alternative to toxic, heavy metal-based radiation shielding. However, biomass often compromises mechanical integrity, limiting practical structural applications. This study investigates the mechanical and radiation shielding properties of epoxy resin composites reinforced with spent coffee grounds (SCG). The influence of SCG content (0, 10, 20, and 30 wt%) on tensile, flexural, and impact strength was evaluated, alongside neutron and gamma attenuation. Composite samples were fabricated using a fixed epoxy-hardener ratio and tested for mechanical properties following ASTM standards. Neutron and gamma shielding performance was evaluated using a²⁴¹Am-Be neutron source and a¹³⁷Cs gamma source, respectively. FIB-SEM was used to assess the internal morphology, while EDX mapping provided elemental analysis. Results showed that increasing SCG content led to a decline in mechanical properties: tensile strength decreased from 27.0 MPa to 12.0 MPa, flexural strength from 62.4 MPa to 38.0 MPa, impact strength from 3.4 kJ/m² to 2.2 kJ/m² due to particle agglomeration, void formation, and weak interfacial bonding. However, neutron shielding efficiency improved with higher SCG loadings, with the macroscopic removal cross-section rising from 0.1752 cm^-1 to 0.1878 cm^-1 due to high carbon and hydrogen content in SCG that enhances neutron moderation and scattering. Gamma attenuation varied minimally across all formulations, with linear attenuation coefficients ranging from 0.0832 cm^-1 to 0.0987 cm^-1. Calculated Half-Value Layer (HVL) results ranged from 3.69 to 3.96 cm for neutrons and 7.02-8.33 cm for gamma rays. Notably, 10 wt% SCG delivers the optimal balance between gamma-ray attenuation effectiveness and mechanical structural integrity, making it the most suitable formulation for practical low-dose radiation shielding applications. This study demonstrates that spent coffee grounds can serve as a promising sustainable filler in radiation shielding composites, particularly for neutron attenuation.