Amine-based deep eutectic plasticization opens a low-energy, high-flow processing window and improves ductility retention in banana fiber-reinforced thermoplastic starch composites

Abstract Plasticization of banana fiber (BF)-reinforced thermoplastic starch (TPS) must balance melt flowability during compounding with stability during service. Here, a stoichiometry-resolved processing map is established for an amine-based deep eutectic solvent (DES), choline chloride-monoethanolamine (ChCl:MEA; salt:donor 1:2–1:5), in composites containing 15 wt% BF, benchmarked against glycerol and reline (choline chloride:urea, 1:2). Processability was quantified by internal-mixer steady torque, specific mechanical energy (SME), and melt flow index (MFI). Solid-state response and early-life stability were assessed by dynamic mechanical analysis (DMA; glass transition temperature, T g ), scanning electron microscopy (SEM) fractography, and tensile testing after aging at 23 °C and 50 % relative humidity (RH) for up to 56 days. Replacing glycerol with ChCl:MEA halved the mixing load (torque: 9–10 N m; SME: 36–39 kJ/kg) and increased MFI from 0.89 to 1.67–2.01 g/10 min. A low-energy/high-flow window (SME ≤ 40 kJ/kg; torque ≤ 10.5 N m; MFI ≥ 1.8 g/10 min) occurred at ChCl:MEA = 1:3–1:4. T g (DMA tan δ peak) decreased from 109.2 °C (glycerol) and 97.3 °C (reline, ChCl:Urea 1:2) to 84.1–74.8 °C across ChCl:MEA (1:2–1:5) at BF = 15 wt%, and day-56 elongation retention reached 80–84 % for 1:4–1:5 versus 50–60 % for the controls. Stoichiometric tuning of ChCl:MEA therefore enables efficient compounding while preserving early-life ductility.