Understanding leaching of amylopectin from cellulose/amylopectin/[Bmim][Cl] blends during regeneration from water and aqueous ethanol using molecular dynamic simulations

Abstract

The difference in amylopectin leaching from cellulose/amylopectin/1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) blends during regeneration in water and aqueous ethanol has been observed in experimental studies. To fully understand the above phenomenon, molecular dynamic simulation was adopted to illustrate the regeneration mechanism after dissolution to understand interactions responsible for the elution/leaching of amylopectin starch. Molecular dynamics (MD) simulations reveal that amylopectin dissolution in [Bmim][Cl] is similar to cellulose in ionic liquids (ILs). Strong hydroxyl-Cl- hydrogen bonding drives dissolution, with [Bmim]+ ions playing a stabilizing role through van der Waals interactions. Amylopectin regeneration in water and aqueous ethanol occurs through the initial disruption of weak hydroxyl-Cl- bridging bonds followed by the disruption of strong non-bridging hydrogen bonds. The water network intercalates amylopectin chains, forming a few “short-lived” interchain HBs. This leaves a very weak electrostatic interaction as the dominant intermolecular interaction between water-regenerated amylopectin chains. Water solvates and elutes low molecular weight amylopectin oligomers, with only 47.29 % amylopectin retained in the blend. In contrast, ethanol-water hydrophobic-hydrogen interactions disrupt the water network, create an ethanol-rich environment, shorten the intermolecular distance between chains, decrease diffusivity, increase hydrogen bonding lifetime between amylopectin, and regenerate amylopectin in aqueous ethanol. The regenerated amylopectin chains interact through improved but weak electrostatic interaction. Improved interaction between chains limits the erosion of low-molecular-weight amylopectin from films retaining 83.11 % amylopectin, approximately two times that in water. At a molecular level, we established that a very weak electrostatic interaction among amylopectin is responsible for leaching in water during regeneration. Ethanol enhances electrostatic interaction among amylopectin chains to limit amylopectin leaching in aqueous ethanol. These observations could apply to other polysaccharide blended materials prepared by the dissolution-regeneration method.