3.5. Scanning electron microscopy (SEM)
The SEM morphologies of thermoplastic starch pellet was investigated by SEM Zeiss type Evo50
which showed an homogeneous surface, indicating that the starch granules were completely disrupted. All
the thermoplastic materials produced from all of the treatments showed a smooth surface. It seems that
corn hominy, tapioca and glycerol concentration did not effect the surface morphology. When samples
were investigated by cross section, there were some differences between the different treatment. SEM
images of cross section showed that the images were not as smooth as surface images. This condition was
probably caused by surface section that got more pressure and heat from the plate when moulded byhydraullic press. There were some starch granules that were not fully disrupted. Higher ratio of corn
hominy gave smoother surface than tapioca, meanwhile glycerol content did not give the same effect.
These results were on contrast with Matthew and Dufresne [36] that if the plasticizer content is increased
there will be a strong decrease in melt viscosity, which made the plasticization of starch difficult, due to
the decrease in the shear during processing