Microstructure changes of on the extruded high-amylose bionanocomposites as affected by moisture content via synchrotron radiation studies

• Microstructure of starch nanocomposite was studied by Synchrotron measurements.
• Heterogeneity increased for the low moisture content samples.
• Two crystalline domains were found in low moisture and nanoclay presence samples.
• Retrogradation related to the formation of new emergence of the larger domain.

The crystalline domain changes and lamellar structure observations of sorbitol-plasticized starch nanocomposite had been investigated via synchrotron. Strong interactions were found between amylose–sorbitol, resulting in reduced inter-helix spacing of the starch polymer. Achievable dspacing of nanoclay was confirmed to be correlated to the moisture content (mc) within the nanocomposites. SAXS diffraction patterns changed from circular (high mc samples) to elliptical (low mc samples), indicating the formation of long periodic structure and increased heterogeneities of the electron density within the samples. Two different domains sized at around 90 Å and 350 Å were found for the low mc samples. However, only the ~90 Å domain was observed in high mc samples. Formation of the 380 Å domain is attributed to the retrogradation behaviour in the absence of water molecules. Meanwhile, the nucleation effect of nanoclay is another factor leading to the emergence of the larger crystalline domain.