Balancing free-volume and hydrogen-bond/ion-pair interactions: Plasticisation of cassava starch with glycerol-monoethanolamine deep eutectic solvents

Abstract

Thermoplastic cassava starch was plasticised with deep eutectic solvents (DES) based on choline chloride (ChCl), glycerol (Gly), and monoethanolamine (MEA) to balance free-volume creation and hydrogen-bond/ion-pair junctions. Binary (ChCl:Gly 1:3; ChCl:MEA 1:3) and ternary ChCl:Gly:MEA (1:1:1; 1:1:2; 1:2:1) DES at 25 wt% were melt-compounded and assessed by processing metrics, FTIR-ATR, Dynamic Mechanical Analysis (DMA), Scanning electron microscopy (SEM), X-ray diffractometry (XRD), wettability (Owens-Wendt-Rabel-Kaelble (OWRK)), and 56- day ambient aging (23±2°C, 50±5% RH). Gly-rich systems enhanced flow but depressed cohesion, whereas MEA-rich systems strengthened interchain junctions. The ternary ChCl:Gly:MEA 1:1:2 delivered the best process-structure-property balance, combining high melt processability with TS≈2.9 MPa and _εb≈195% (n=5) and displaying the lowest 56-day ductility loss (Δ_εb≈-17%) compared with glycerol controls (≈-50%). FTIR (O-H/N-H red-shift and broadening), together with SEM fracture morphology and OWRK-derived surface energetics, supports a dual-mode plasticisation mechanism in which MEA-enabled junctions counterbalance Glyinduced free volume, thereby stabilising the amorphous phase and retarding retrogradation without sacrificing strength. This composition-structure map identifies ChCl:Gly:MEA (1:1:2) as a composition window that stabilises TPS mechanical performance during ambient aging.