Fabrication and characterization of carbon foams using 100% Kraft lignin

Abstract

Carbon foams have been prepared using Kraft lignin as the solely resource. No catalysts, foaming/blowing agents, surfactants, and/or crosslinking agents are used for the foam preparation. The process includes pressing carbon foam precursors into molds followed by formation of lignin foam through heating and carbonization/graphitization of the lignin derived foams. The resultant lignin carbon foam (LCF) has an open-cell structure with densities ranging from about 0.18 g/cm3 to 0.68 g/cm3. The compressive strengths of LCFs increase with increasing of bulk density, from 7.03 ± 1.25 MPa of LCF1 to 30.16 ± 2.41 MPa of LCF7, and thermal conductivity is strongly influenced by the bulk density with increase from 0.21 ± 0.02 W/(m·K) to 0.75 ± 0.01 W/(m·K). The bulk electrical conductivities of LCF samples increase with increasing of bulk densities from 701 S/m to 2031S/m. The LCF samples were evaluated for resistance to fire and native subterranean termites. LCF samples exhibit excellent fire resistance, no damage occurred when the LCF sample was exposed to an oxyacetylenic flame in air over 1050 °C for more than 3 min. Termite testing showed no degradation to the LCF samples after the evaluation.