Molecular dynamics simulation and properties of thermoplastic starch -- effect of water content on starch plasticization

Abstract

To investigate the impact of water content on starch plasticization, the molecular dynamics (MD) simulation method was employed to investigate the hydrogen bonding energy, radial distribution function (RDF) and mean square displacement (MSD) of the starch/glycerol/water system at various water contents (ranging from 8% to 14%, based on the dry starch weight). Additionally, Glycerol-plasticized thermoplastic starches (GTPSs) were prepared using a twin-screw extruder with precise material proportions according to the simulation ratio. Subsequently, DSC, XRD, FT-IR, SEM and mechanical properties of GTPSs were evaluated. By conducting an analysis on the correlation between simulation results and TPS performance, it has been demonstrated that water molecules play a pivotal role in the plasticization process of starch. GTPS exhibits challenges in processing due to its inadequate melt fluidity at lower water content (≤11%). Conversely, excessive water content (≥13%) leads to a decline in the mechanical properties of GTPS. Considering both processing stability and material’s mechanical properties, a starch water content of 12% is deemed suitable for TPS preparation.