**1. Introduction**

56 Thermoplastic Elastomers

Williams, P.C. & Lesselleur, G.C. (1970). Determination of damaged starch in flour, a comparative study of present day procedures. *Cereal Science Today*, Vol.15, 4. Wurzburg, O.B. (1989). *Modified starches: properties and uses*. CRC Press, Boca Raton, 277. Guan, J.& Hanna, M.A. (2006). Selected morphological and functional properties of extruded acetylated starch–cellulose foams. *Bioresource Technology*, Vol. 97, 1716–1726. Yaĝci, S. & Göĝůş, F. (2009) Effect of incorporation of various food by-products on some

Yanniotis, S.; Petraki, A.& Soumpasi, E. (2007). Effect of pectin and wheat fibers on quality attributes of extruded cornstarch. *Journal of Food Engineering*, Vol. 80, 594–599. Yunos, M.Z.B. & Rahman, W.A.W.A. (2011). Effect of glycerol on performance rice straw/starch based polymer. *Journal of Applied Sciences*, Vol. 11, No.13, 2456-2459.

*International*, Vol. 15, No.6, 571-581.

nutritional properties of rice-based extruded foods. *Food Science and Technology* 

For the last few decades, the usage of plastic increased because of its specific properties such as low cost, light weight, high strength, non-biodegradability, durability, non corrosive nature, process ability and high energy effectiveness. Hence these plastics can be used for various application which includes household articles to aeronautic sector. Now a day it's difficult to imagine a life without plastic which are mostly derived from crude oils and natural gas. Among the various polymers, polyethylene, polypropylene and polystyrene are used greatly for food packaging, biomedical field and in agriculture. According to statistics, from 1950 onwards, 9% of growth can be seen globally, in the production and consumption of plastics. In 1950 the overall production of plastic was 1.5 million tones while it reached 245 million tones in 2008.

In these polyethylene is one of the most dominant packaging material, creating the real problems in the disposal of one-trip packaging. These polymers will take millions of years to degrade under natural weathering conditions. Hence careless dumping of these plastics after its usage creates severe problems to the environment. Also during combustion it produces toxic materials which eventually pollute the atmosphere. The land filling results in the contamination of water, thereby adversely affecting the soil's biological balance. 'Recycling' is another solution for reducing the amount of waste polyolefin materials. But recycling has its own limitation in regard to compatibility of different polyolefins which adversely affects the processability and final properties. Subsequently the problems created by plastic wastages to the environment triggered the interest in the development of biodegradable disposable plastics. So that the onetime use items can be disposed off with the hope that they will not remain for centuries in a landfill, or as litter, which is one of the tenets driving the recent interest in "green" technologies. The current biodegradable plastics, such as PLA, PHBV, Mater-Bi etc are very costly and the processing and mechanical properties of these materials are not good enough for the production of consumer products. Hence several studies were conducted to modify the current commodity plastics such as

Properties and Biodegradation Nature of Thermoplastic Starch 59

Studies show that the structures of native and thermoplastic wheat starch are totally different. Scanning Electron Micrograph (SEM) reveals that the native wheat starch has a

These granules are spherical or oval and have different domain sizes. They are smooth, free from pores, cracks, or fissure around to lenticular and polyhedral shapes and are relatively thick. For both starch granules there exists a wide distribution of granule size. This wide distribution is a common feature of cereal starch [Buleon et al., 1998; Charles et al., 2003]. During plasticization (the transformation of granular morphology into a homogeneous polymeric film), the destruction of hydrogen bonds between the starch molecules occurs synchronously with the formation of the hydrogen bonds between the plasticizer and starch

The extrusion method is a combination of thermal and mechanical input. During this process, starch was plasticized and a homogeneous molten phase characteristic of

The X-ray diffraction (XRD) patterns for native and plasticized starch based on wheat flour (with 9% water and 12.8% glycerol) are displayed in Figures 4 A and B, respectively [Saiah et al., 2007]. The signal obtained from XRD, for native starch shows the semi-crystalline nature of this material. The diffraction peaks were obtained at 2θ values equal to 11.3, 15.2, 17.3, 18.1, 20.1, 23.3, and 26.7°, leading to the conclusion that these raw materials present Atype crystalline structure. This general characteristic of cereal starches was already observed in many other studies [Katz and Van Italie, 1930; Le Bail et al., 1993; Krogars et al., 2003]. For the extruded thermoplastic films, the peak appears at 2θ = 7.2°, 12.9°, 19.8°, and 22.6° (Figure

thermoplastic polymeric material was obtained (Figure 3) [Saiah et al., 2009].

Fig. 3. SEM of extruded wheat starch based thermoplastic film

**3. Properties of thermoplastic starch** 

granular structure (Figure 2) [Leblanc et al., 2008].

Fig. 2. SEM micrographs of native wheat starch

molecules [Yang et al., 2006].

**3.2 Structure** 

**3.1 Morphology** 

polyethylene, polypropylene into biodegradable type. One method to achieve this goal was blending of plastics with biodegradable agricultural feed stocks to meet the requirements of responsible and ecologically sound utilization of resources. This will reduce our dependence on depleting petrochemical resources.
