Homogeneous Synthesis And Characteristics Of Starch Acetates Using Ionic Liquid As Reaction Medium

The homogeneous chemical modification of normal corn starch, high amylose cornstarch, waxy corn starch with acetic anhydride was investigated in a solvent systemcontaining1-butyl-3-methylimidazolium chloride ionic liquid (BMIMCL) without anycatalysts. Furthermore, the molecular structure, crystallinity, morphology, and thermalproperties of starch esters were characterized by FT-IR,1H-NMR, XRD, SEM and TGAtechniques, respectively. The possible mechanism of the homogeneous esterification of starchin the ionic liquid BMIMCL was investigated. Finally, fibrous membranes were successfullyproduced via electro spinning of starch acetate solution, providing a theoretical basis forfurther preparation of bio-functional materials by using modified starch.The dissolution conditions of starches were performed as following, normal corn starchand high amylose corn starch was dissolved in BMIMCL at105℃for2h while waxy cornstarch was dissolved at135℃for the same time. The experimental results showed that thedegree of substitution(DS) of starch acetate could be varied depending on the processconditions(reaction temperature, acetic anhydride/starch molar ratio, etc.). In the optimumreaction condition, the achieved maximum DS of modified normal corn starch, high amylosecorn starch and waxy corn starch was2.11,2.0and2.96, at a reaction temperature of105℃for a reaction duration of2h,3h,4h, when acetic anhydride/anhydroglucose units (AGU)molar ratio was5:1,4:1,5:1, respectively.Results from FT-IR and1H-NMR spectroscopy suggested that the hydroxyl groups in thestarch molecules were converted into ester groups. Polarizing microscope and XRD studiesindicated that the morphology and crystallinity of starch esters were disrupted largely in theILs medium under the reaction conditions, which suggested that BMIMCL was effective insolubilizing starch. The consequence from XRD also showed that a typical wide peak ofacetylated starches which gave an amorphous pattern appeared at9°(2θ). SEM revealed thatshapes and structures of native starch granules were destroyed. TG analysis suggested thermalstability of starch acetates increased compared to native starch. And the thermal stabilityincreased with increasing DS.