Formation mechanism of nanocomposites between starch and stearic acid via nanoprecipitation

Starch is one of effective host material for encapsulation of hydrophobic compounds using nanoprecipitation. In this study, stearic acid was encapsulated using starch, in which nanoprecipitation consisted of three phases such as the addition of an anti-solvent (ethanol) at 90 °C, the cooling procedure, and the addition of ethanol at an ambient temperature. To investigate the formation mechanism of composites between starch and stearic acid using nanoprecipitation, the changes in the physicochemical properties and crystalline structure of the composites for preparation phases 1, 2, and 3 were evaluated. During phase 1, the stearic acid content and complexation index of the sample mainly increased up to 2.8 mg/g composite and 83.4%, respectively. However, relatively minor changes were observed during the followed phases 2 and 3. The mean diameter of the composite gradually increased to 193.7 nm during phase 1, followed by a dramatic increase to 364.1 nm after phase 2. TEM revealed that individual particles with smaller sizes were mainly generated during phase 1; however, the particles formed larger aggregates by coagulation during phase 2. XRD and 13C NMR spectroscopy revealed that the V-type polymorph, in terms of short- and long-range crystalline structures, was mainly generated during phase 1.