Lignin/collagen hybrid biomaterials as binder substitute for specialty graphites and electrodes

Abstract

Sustainable biomaterial binders were developed from lignin and collagen to replace the conventional petroleum pitch and coal tar pitch binders that have been used when making specialty graphites and graphite electrodes. The team prepared lab-scale graphite electrodes by first creating green composites, by hot-pressing together the lignin, collagen, petroleum coke, and other additives, followed by carbonization and graphitization. Response Surface Methodology (RSM) experimental design was employed, based on Box-Behnken Design (BBD). This was employed to optimize the recipes and processing protocols for the green composite hot-pressing of 3.5 cm diameter × 19 cm long cylinder specimens. Relative to density, the apparent optimum conditions occurred with 13.0% lignin, 3.6% collagen, 27.4% petroleum coke fines, and the balance of petroleum coke particles plus some additives. The green hot-pressing protocol employed 30 MPa pressure at 400 °C for 2 h. Baking peaked at 800 °C, ramped up and down over 13 days. This baked product hosted an apparent density of 1.67 g/mL, and exhibited 6.2% puffing. Another baked product hosted 1.56 g/mL and 1.67% puffing. After the baked product was graphitized, we achieved an apparent density of 1.51 g/mL and resistance of 25–30 μΩm. These results approached the specifications for specialty graphites.