Owing to its hydrophilicity, the internal interaction and morphology of starch will be readily changed
by water molecules, and thereby its glass transition temperature (Tg), the dimension and mechanical properties depend on the water content. Tg of native starch can be as low as 60 to 80°C when the weight fraction of water is in the range 0.12 to 0.14, which allows starch to be successfully injection moulded to obtain thermoplastic starch polymers in the pres- ence of water [15]. On the other hand, the hydro- philicity of starch can be used to improve the degradation rate of some degradable hydrophobic polymers, which will be shown in 3.1.1.
Starch is totally biodegradable in a wide variety of environments. It can be hydrolyzed into glucose by microorganism or enzymes, and then metabolized into carbon dioxide and water [16]. It is worth not- ing that carbon dioxide will recycle into starch again by plants and sunshine. Starch itself is poor in processability, also poor in the dimensional stabil- ity and mechanical properties for its end products [17]. Therefore, native starch is not used directly.