Altering the characteristics of carbon foams synthesized by biomass liquefaction with bio-oil addition: influence of the surfactant ratio

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Carbon and graphite foams have recently been reported to be highly suited to a range of applications, such as high-temperature insulation, fuel cell electrodes, heat exchangers, brake discs, engine parts, and bone surgery materials. In this study, the effect of surfactant amount added during carbon foam synthesis on the structure of the foam produced through the liquefaction of spruce tree sawdust in the presence of pyrolytic oil (bio-oil) was studied. When a mixture of phenol and pyrolytic oil was used as a solvent during synthesis instead of just phenol, the foaming agent could not exit the polymer, leading to the production of a hard polymeric structure. Also, applying the standard amount of surfactant meant that the gas molecules could not overcome the high surface tension at the polymer surface and were therefore trapped within the polymer, causing relatively few pores to be generated during synthesis. Increasing the amount of surfactant led to successful foaming, as gas molecules could dissociate from the structure by overcoming the surface tension of the polymer matrix. When the combination of pyrolytic oil and phenol was utilized, adding extra surfactant caused the porosity to increase by 19–33% due to the 39–61% rise in the surface area, although the compressive strength of the foam decreased by 24–79%. This study, therefore, showed that the surface area, porosity, compressive strength, elemental carbon content, and crystalline structure of the carbon foam could be tailored to the application area of the foam by adjusting the conditions applied during synthesis appropriately.