Near-net-shape forming of carbon foams from rotten plantain fruit for thermal insulation and EMI shielding

Biomasses are widely used for the preparation of advanced functional materials. Herein, near-net-shape carbon foam bodies are prepared by casting of plantain fruit pulp slurry, freeze-drying, annealing, and carbonization. The amorphous nature of carbon foam is evidenced by the XRD and Raman spectra. A change in pore structure from lamellar to cellular type is observed by adding water to the slurry. The cell walls and struts of the carbon foams exhibit a hierarchical structure consisting of dense carbon platelets bonded by carbon. The density, compressive strength, thermal conductivity, and electrical conductivity of the carbon foams are modulated in the ranges of 0.367 to 0.180 g cm⁻³, 7.5 to 0.3 MPa, 0.27 to 0.112 Wm -1 K -1, and . 28.9 to 8.6 S.m⁻¹, respectively, by changing the water-to-plantain fruit pulp weight ratios in the range of 0 to 1. The carbon foams exhibit total EMI shielding effectiveness in the 66 to 34.6 dB range with an absorption contribution of 57.8 to 29.4 dB. The impedance matching due to the high porosity, multiple internal reflections within the pores, dielectric loss due to the polarizable functional groups, large area of carbon-carbon interfaces due to the structural hierarchy, and uniform distribution of metal oxides are responsible for the high EM wave absorption. Carbon foams show oxidation resistance up to 326 o C in air and excellent fire resistance when exposed to oxyacetylene flame. The carbon foams obtained are amenable to machining using conventional machines and tools.