Rheology of starch–clay nanocomposites

The effects of incorporating various montmorillonite nanoclays into wheat, potato, corn, and waxy corn starch samples were examined by rheology and X-ray diffraction. The nanoclays included the hydrophilic Cloisite Na+ clay as well as the more hydrophobic Cloisite 30B, 10A, and 15A clays. Frequency sweep and creep results for wheat starch–nanoclay samples at room temperature indicated that the Cloisite Na+ samples formed more gel-like materials than the other nanoclay samples. X-ray diffraction results showed no intercalation of Cloisite Na+ clays at room temperature, suggesting that starch granules interacted only with the clay surface and not the interlayer. When the various wheat starch–nanoclay samples were heated to 95 °C, the Cloisite Na+ samples exhibited a large increase in modulus. In contrast, the more hydrophobic nanoclay samples had comparable modulus values to the neat starch sample. These results suggested that during gelatinization, the leached amylose interacted with the Cloisite Na+ interlayer, producing better reinforcement and higher modulus values. X-ray diffraction results supported this interpretation since the data showed greater intercalation of Cloisite Na+ clay in the gelatinized samples. The samples containing wheat and corn starch showed comparable elastic modulus values during gelatinization. However, the potato and waxy corn samples had modulus values that rapidly decreased at higher temperatures.