Impact of Sustainable Binders Based on Lignin and Collagen on the Volume Stability and Mechanical Properties of MgO‐C Refractories with MgO‐C Recyclates

This study investigates sustainable binders based on lignin and collagen hydrolysate as substitutes for conventional binders in MgO‐C refractories, with a particular focus on volume stability after thermal treatments. Collagen hydrolysate undergoes thermally induced decomposition of peptide chains while simultaneously forming a cross‐linked network, accompanied by the release of H ₂ O, CO ₂ , and NH ₃ . During coking, this network forms a partially ordered carbon network that provides high oxidation resistance, bulk density, and strength of the MgO‐C material both at room and elevated temperatures, comparable to reference samples bonded by a conventional mixed binder based on novolak and Carbores P. However, the combination of gas formation and cross‐linking leads, in small laboratory samples, to a volume increase without structural damage. In large‐format bricks the longer diffusion paths cause an increase of internal gas pressure, resulting in macroscopic cracking. The variation of the graphite grade, the partial replacement of virgin fused MgO and graphite with MgO‐C recyclate, and lignin addition reveals that porous channels facilitate gas release and thereby significantly improve volume stability.