Mixed plastic waste poses a complex sustainability issue where reprocessed materials exhibit heavily diminished mechanical properties due to phase separation. Due to the difficulty with separating polyolefins, there is considerable need for developing solid-state upcycling methods that can directly incorporate mixed plastics wastes. This work demonstrates the manufacturing of three-dimensional carbon monoliths from various mixed polyolefin waste streams through fused filament fabrication 3D-printing followed by thermal stabilization and pyrolysis steps. Interestingly, phase separation present in the mixed waste precursors was found to promote reaction kinetics and lead to more efficient carbon manufacturing compared to polyolefin homopolymers. Moreover, the 3D-carbon structures were found to exhibit excellent Joule heating capabilities and were then utilized as catalyst supports to enable electrification of hydrogen production through ammonia decomposition. In comparison to a convection heated control, the Joule heated process displayed enhanced reaction conversions with improved reactor startup and shutdown speeds.
