Low‐Dose Epoxy Compatibilization Amplified by <scp>ChCl</scp> : <scp>MEA</scp> Deep Eutectic Solvent: Balancing Strength–Ductility–Processability in Starch/Lignin Composites

ABSTRACT Reactive extrusion couples a choline–chloride:monoethanolamine deep eutectic solvent (DES) with a low‐dose epoxy compatibilizer (ECA) to deliver dual compatibilization of starch/lignin. The DES provides a hydrogen‐bonded/ionic microenvironment that preconditions the interphase, while epoxy ring‐opening forms C–O–C/C–N bridges across phases. Processing readouts (higher steady torque, lower melt‐flow index), FTIR trends within the DES–ECA series (a broader hydroxyl envelope and modest growth in ether/amine regions), void‐poor FE–SEM fracture surfaces, and an upshift of the main DTG peak (Δ T max,2 ≈ +14°C) together support enhanced interfacial coupling rather than crystallinity changes. At 0.75 wt% ECA, the DES route achieves a balanced property set (tensile strength: 4.1 ± 0.3 MPa; elongation at break: 307.7% ± 15%; melt flow index: 1.29 ± 0.09 g/10 min) with improved surface hydrophobicity and reduced moisture uptake, outperforming a glycerol benchmark at the same loading. A multicriteria performance map targeting irrigated nursery bag use identifies 0.75 wt% as a robust optimum, while higher loadings narrow the processing window by penalizing flow and ductility. The results establish a practical, scalable strategy—DES interfacial preconditioning combined with low‐dose epoxy bridging—to reconcile strength, ductility, and processability in biobased starch/lignin composites, and suggest straightforward extensibility to other DES/epoxy pairs and thin‐wall film operations.