Starch is one of the most studied natural polymers for plastic application, owing to its availability, biodegradability, and low cost3. Starch exists in a granular form in its natural state, but when subjected to shear forces at a temperature in the range 90-180 °C, in the presence of a plasticizer such as glycerol, starch loses much of its original granular structure and is transformed into a molten plastic state named thermoplastic starch4. Unfortunately, thermoplastic starch has two main disadvantages in comparison with most plastics currently in use, namely that it absorbs moisture and exhibits poor mechanical properties. Several approaches have been taied to overcome these drawbacks, such as reinforcement with fibers5 and inorganic materials6 and with both degradable7 and non-degradable polymers8.
Zein is a protein present in corn in the seeds of maize in large amounts, which has a high content of hydrophobic amino acids (leucine, proline and alanine)9.
The combination of thermoplastic starch and plasticized zein might have great potential in the field of biodegradable plastics, since both can be processed in the presence of plasticizers, similarly to most conventional synthetic thermoplastic polymers. Additionally, the low solubility of zein in water could increase the hydrophobic character of the corresponding thermoplastic starch compositions.
In this paper, we describe the preparation of starch/zein blends plasticized with glycerol by melt processing in an intensive mixer. The materials were characterized by differential scanning calorimetry (DSC), X ray diffraction, water-uptake tests and scanning electron microscopy (SEM). The morphology of the blends was analyzed as a function of zein/starch ratio.