Mechanochemical and molecular analysis of organic binders in charcoal briquetting for enhanced cold mechanical strength

Charcoal briquettes often fracture during handling because their fine particles require a binder that is both strong and low in ash. This study presents the first integrated analysis that couples full-scale briquetting trials with molecular docking simulations to guide binder selection. Industrial hardwood-charcoal fines were blended with five organic binders—native starch, citric-acid-modified starch, lignosulfonate, polyvinyl acetate (PVA), and flour—at 2.5–25 wt %. Each formulation was compacted using either a 5 MN hydraulic press or an industrial roller press and evaluated by proximate analysis, drop-impact testing (Impact Resistance Index, IRI), and axial compression. Mechanical testing showed that modified starch outperformed all other binders, achieving compressive strengths up to 7 MPa and IRI values exceeding 3600 at 15–20 wt % loading under hydraulic pressing. Lignosulfonate, despite its high calculated adsorption energy (−6.1 kcal/mol), yielded weaker briquettes due to moisture uptake and higher ash, whereas PVA displayed the weakest surface affinity (−1.8 kcal/mol) and lowest mechanical strength. Across all formulations, hydraulic pressing improved strength two- to four-fold compared with roller pressing. Docking simulations on an oxidised-graphite model surface revealed that polysaccharides form extensive hydrogen-bond networks with oxygenated carbon edges, explaining their superior adhesion. These findings confirm that binder molecular structure and densification pressure jointly govern briquette integrity. When normalised for cost, modified starch remains the most efficient and sustainable option. The combined mechanochemical–molecular framework thus provides a transferable, molecularly informed roadmap for selecting sustainable binders and optimising compaction in commercial charcoal-briquette manufacturing.