Thermally insulating robust carbon composite foams with high EMI shielding from natural cotton

Thermally insulating and fire-resistant carbon composite foams are prepared by consolidating natural cotton fibre dispersed in aqueous sucrose solution by filter-pressing followed by drying and carbonization. The compressive strength (5 kPa to 1.4 MPa) and thermal conductivity (0.069 to 0.185 W m − 1 K − 1) depend on the foam density (0.06 to 0.31 g cm−3) which is modulated by varying the sucrose solutions concentration (100 to 700 g L − 1). Partially flexible to the rigid transition of the carbon composite foams occurs at sucrose concentration above 200 g L − 1. The tubular carbon fibre formed from cotton is welded at their contact points by the amorphous carbon produced from sucrose leading to partial flexibility at low sucrose concentration and advancement of fibre- to- fibre bonding area at higher sucrose concentration results in rigid foam. The porosity in the inter-fibre space and lumen of the carbonized cotton fibre contributes to the low thermal conductivity. The carbon composite foams prepared at a sucrose solution concentration of 500 g L − 1 and above are amenable to machining using conventional machines and tools. The rigid carbon foams show EMI shielding effectiveness and specific shielding effectiveness in the ranges of 21.5 to 38.9 dB and 108–138 dB cm3 g − 1, respectively.