Synergistic interaction between lignin and collagen during co-pyrolysis

Sustainable biomaterial binders developed from lignin plus collagen have offered effective binder systems for the fabrication of specialty graphites and graphite electrodes. To further chronicle collagen's synergistic effects and benefits, the authors appraised the formation and evolution of the chars pyrolyzed from lignin, collagen and their blends. Following pyrolysis in a vertical tube furnace at 1000 °C, the lignin-collagen blend yielded more char than did mere lignin or mere collagen. Elemental analysis indicated that along with the release of the oxygenated, nitrogenated, and hydrogen-containing gases, the collagen's presence facilitated carbon-enriched chars with more oxygenated polyaromatic structures. Collagen yielded an aryl (aromatic) carbon source in the aromatic condensation reactions, leading to the continuous cross-linking and growth of the lignin aromatic rings. Per Fourier-transform infrared spectroscopy (FTIR), during pyrolysis, collagen enhanced the hydrogen aromaticity index, and reduced the extent of aromatic substitution. The collagen presence facilitated more removal of functional groups, as indicated by bonded O–H stretching, symmetric CH₃ stretching in O–CH₃, and aliphatic C–H stretching. Scanning electron microscope (SEM) revealed that collagen served as a thermoplastic bio-binder that formed a thermally-fused framework with lignin. Thus, collagen induced significant differences in solidification behaviors and surface morphologies.