Materials derived from a sulfur vulcanization of biochar

Abstract

The pyrolysis of lignocellulosic biomass yields biochar consisting of high-carbon scaffolds bearing a variety of functional groups. As produced, the biochar is mechanically fragile and lacks the structural cohesion needed for making structural materials. To enhance both its chemical stability and mechanical strength, elemental sulfur is here introduced to induce a vulcanization reaction with biochar. Heating a biochar–sulfur (BS) mixture up to 185 °C under pressure induces effective crosslinking within the carbon network of biochar, a reaction attributed to free-radical sulfur polymerization and addition to functional groups attached to the carbon network of biochar. The synthesis method yields a crosslinked biochar with markedly enhanced mechanical strength. Depending on the synthesis conditions, the compressive strength and Young's modulus can reach values between 22–382.5 MPa and 6–165 GPa, respectively. With the density of only 1.4 g cm⁻³, the mechanical properties of the best synthesized materials closely match that of structural steel. The BS materials can potentially be used as sustainable materials in parts and products for human infrastructure and transport. Alternatively, this method may also provide an alternative pathway for biomass-derived carbon storage contributing to climate change mitigation.