Crystal structure transformations in extruded starch plasticized with glycerol and urea
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Cornstarch was processed on an extruder with glycerol and different contents of urea giving rise to samples named as SGU-0, SGU-1, SGU-5, and SGU-10. The gelatinization enthalpy ΔHgel, calculated by DSC, indicated that the mixture of glycerol and urea seems to better plasticize the starch than glycerol alone. XRD was used to identify the changes in the crystal structure of native starch after extrusion processing. XRD diffractograms indicated the presence of both residual native crystallinity and processing-induced crystallinity. The morphology observed by SEM was compatible with the presence of residual crystals and recrystallization, as suggested by XRD analysis. SAXS experiments pointed out the minute amount of B-type crystallites in the samples with urea, probably due to the hydrophilic character of urea, which contributes to starch hydration.
KeywordsThermoplastic starch Urea Extrusion Crystal structure XRD SAXS
The authors acknowledge financial support from the Brazilian Research funding agencies: National Council for Scientific and Technological Development (CNPq), Coordination for the Improvement of Higher Education Personnel (CAPES), and Foundation for Research Support of the State of Minas Gerais (FAPEMIG).
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