In situ characterization of food and plastic waste carbonized under pressure

In situ investigations of soft-matter carbonization are essential to connect processing conditions with final carbon structure and function. Here we report time-resolved structural and chemical monitoring of autogenic pressure carbonization of non-recyclable commodity plastics performed directly inside sealed quartz capillaries. We also treated food waste-derived sugars through alkaline and neutral hydrothermal carbonization in water and ionic liquids. By combining synchrotron-grade WAXS and SAXS with in-situ Raman spectroscopy, and supporting ex-situ XPS surface analysis, we follow the transformation from disordered organic networks to carbonaceous solids under self-generated pressure in real time.

SAXS reveals the emergence and coarsening of nanoscale porosity and density inhomogeneities early in the heating profile, while WAXS captures the progressive development of short-range aromatic stacking (broadening and gradual appearance of 002-type scattering). Raman spectra recorded concurrently track the evolution of sp² domains and defect populations via the D and G bands, allowing kinetic comparison between plastic and sugar routes. Ex-situ XPS indicates contrasting heteroatom retention: hydrothermal-derived chars retain higher oxygen functionality, whereas plastic-derived carbons show lower O/C ratios and more pronounced graphitization signatures at equivalent processing stages.

Together the multimodal dataset supports a unifying mechanism in which precursor chemistry controls the balance between intramolecular rearrangement and intermolecular crosslinking, setting the pathway for pore formation and aromatic ordering under pressure.