Multi-scale Structural Features and Thermal Stabilities of Acylated Starch with Different Acyl Groups
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Abstract:
G50 corn starch was chemically modified using acid anhydrides with different chain lengths to yield starch esters in this study. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and thermogravimetry (TG) techniques were used to characterize the surface morphology, chemical structure, crystalline structure, ordered microdomain structure, and thermal properties of the starch esters. The results indicated that adding anhydride with a longer chain length could lead to a weaker esterification reaction. The starch particles were fragmented into small pieces after esterification reaction, and the butyrate starch (degree of substitution (DS)=1.38) and caproate starch (DS=1.37) tended to aggregate into clusters. All the starch esters presented an amorphous state. The highest degree of damage to the ordered microdomain was found in acetate starch with a high DS. With a similar DS, the starch esters obtained from the anhydride with a long chain length had periodic long-range ordered structures within the starch particles. Compared with the original starch, the starch ester showed enhanced thermal stability. Additionally, when the amount of added acid anhydride was same, the degree of enhancement of thermal stability of the starch ester samples showed a downward trend with increasing chain length of acid anhydride. These results could provide a reference for improvements in the application of starch esterification.
