Balancing stiffness and ductility in starch–lignin bioplastics using binary and ternary deep eutectic solvents (ChCl:Gly:MEA)

Abstract

Deep eutectic solvents (DESs) offer a green route to tailor starch–based plastics, yet how composition controls the interphase and aging in corn starch-lignin (CS–Lig) matrices remains unclear. Binary and ternary DESs were prepared from choline chloride (ChCl), glycerol (Gly), and monoethanolamine (MEA). In this study, CS–Lig was melt-processed with Gly (control) or with binary (ChCl:Gly 1:3; ChCl:MEA 1:3) and ternary ChCl:Gly:MEA DESs (1:1:1; 1:1:2; 1:2:1). We combined dynamic mechanical analysis (DMA), tensile testing, Fourier transform infrared (FTIR), Xray diffraction (XRD), scanning electron microscopy (SEM), and Owens–Wendt– Rabel–Kaelble (OWRK) wettability; we also integrated 0–56-day retrogradation assays. Relative to glycerol, DESs systematically enhanced performance: tensile strength (TS) rose to ≈ 2.97 MPa (CS–Lig–C.G.M 1:2:1) and elongation (εb) to ≈ 184 % (CS–Lig–C.G.M 1:1:2). One-way ANOVA (p < 0.001) and Tukey HSD separated ternary DESs from the control. FTIR showed broadened, red-shifted –OH/–NH envelopes; XRD indicated reinforced V-type order; SEM revealed tighter lignin encapsulation. Surface polarity was tuneable (γ ≈ 41–58 mN m⁻¹), and specific DESs mitigated aging-related losses. This composition–property map provides practical design rules to target strength/stiffness (e.g., 1:2:1) or ductility (e.g., 1:1:2) in greener CS–Lig bioplastics.