Plasticized starch prepared by a mixture of 6-hydroxy-N-[2-[(2-hydroxyethyl)amino]ethyl]hexanamide and glycerol: preparation, properties and plasticization mechanism

Abstract

The non-biodegradability of traditional plastics poses serious environmental challenges, while the high cost of biodegradable plastics limits their widespread application. Starch, due to its abundance, low cost, and biodegradability, represents a promising alternative. However, the strong intermolecular hydrogen bonding within starch impedes its processing. To address this limitation, a novel plasticizer, 6-hydroxy- N -[2-[(2-hydroxyethyl)amino]ethyl]hexanamide (HEEHA), was synthesized to enhance the thermoplasticity of starch. Thermoplastic starch (TPS) films were fabricated by blending HEEHA with glycerol at varying ratios, maintaining a total plasticizer content of 30 wt% relative to dry starch. Their properties were characterized using FT-IR, XRD, and mechanical testing, while molecular dynamics simulations were conducted to analyze mean square displacement (MSD), radial distribution function (RDF), and hydrogen bond energy, providing insights into the underlying plasticization mechanisms. The combination of HEEHA and glycerol exhibited synergistic effects, achieving optimal performance at a 10 wt% HEEHA/20 wt% glycerol ratio, where both tensile strength and elongation at break surpassed those of single-plasticizer systems. Simulations further revealed that, at this ratio, the plasticizers displayed the highest diffusion coefficients, the most uniform spatial distribution, and the strongest hydrogen bonding interactions. The resulting TPS retained moderate starch crystallinity, contributing to enhanced mechanical properties.