Akın Odabaşı, Essam Bkkur
The demand for materials with flame-retardant and electromagnetic shielding properties has increased research on sustainable and multifunctional composites. Thermoset-based hybrid composites containing Fe3O4 and activated carbon obtained from solid waste were investigated for flame retardancy and electromagnetic shielding. Activated carbon produced by pyrolysis of buckwheat hulls (agricultural waste) exhibited a BET surface area of 714.33 m2/g and a conductivity of 69.5 S/m, and was used as a filler to enhance electrical conductivity, while Fe3O4 was added to promote electromagnetic absorption. Composites with 1, 3, 5 and 7 wt% activated carbon at a constant 15 wt% Fe3O4, together with a complementary series at 5 wt% activated carbon with 10, 15, 30 and 45 wt% magnetite, were characterized by limiting oxygen index and thermal analysis. LOI values clustered between 32.31% (Nov-5-15) and 33.71% (Nov-3-15), a 1.40-percentage-point spread around the 34.31% reference Novolac. The 850 °C char yield peaked at 56.38% (Nov-3-15) and 55.34% (Nov-7-15), with T50% reaching 898 °C and 882 °C, respectively, while DTA replaced the 529 °C Novolac exotherm with endothermic Tmax values of 485-501 °C. Electromagnetic shielding effectiveness over the 8-12 GHz range varied from 2.97 ± 0.3 dB (unfilled Nov-0) to a maximum of 9.19 ± 1.46 dB (Nov-5-45, 5 wt% activated carbon and 45 wt% Fe3O4), with an intermediate value of 7.43 dB for Nov-7-15. These hybrids are thus candidate materials for fire-safe phenolic-thermoset applications, where magnetic-dielectric coupling and a percolated char-barrier network govern flame-retardant performance, demonstrating the potential of waste-sourced carbon in sustainable composite production.