Starches crystalline properties

Svensson E. Crystalline Properties of Starch. Sweden Lund University 1996. [Ph.D. Dissertation],... 

J.J.G. Van Soest, and J.F.G. Vliegenthart, Crystallinity in starch plastics consequences for material properties. Trends Biotechnol. 15,208-213 (1997). 

Native starch granules give distinct X-ray diffraction patterns of three types [30c,30d] an A-pattem characteristic of cereal starches such as maize, wheat, and rice starches, a B-pattem characteristic of tuber, fruit, and stem starches such as potato, banana, and sago starches and a C-pattem that is obtained from some starches and is intermediate between the A- and B-pattems and may be due to mixtures of A-type and B-type granules (see Fig. 6,6), X-ray diffraction indicates that the starch granules have crystalline properties. However, they are only partly crystalline and vary in their degree of crystallinity [31]. Waxy starches that are 100% amylopectin showed a crystallinity of 40%, and high-amylose starches showed a crystallinity of only 15%. 

Chemical modification of natural polymers such as starch, dextran, cellulose and proteins represents an attractive alternative route to totally synthetic polymers for producing biodegradable polymers. Early modification of polysaccharides resulted in hydrophobic materials such as cellulose acetate and cellulose nitrate. Both are degradable by microorganisms. Hydroxyalkylcelluloses should be of interest because of their liquid crystalline properties.The only question is whether their biodegradability is unified. Polysaccharides react with small carboxylic acids to produce derivatives that are biodegradable. " ... 

Propylthiouracil. This compound is a white, powdery, crystalline substance of starch-like appearance with a bitter taste. It is slightly soluble in water, chloroform, and ethyl ether, sparingly soluble in ethanol, and soluble in aqueous alkaline solutions (53). An extensive compilation of its chemical, spectral, and chromatographic properties is available (43). It is assayed titrimetrically with NaOH (53). 

More than a century elapsed between the discovery of the hydrolysis of starch and the successful large scale manufacture of crystalline dextrose of high purity. Examination of some less familiar properties of dextrose will indicate the difficulties which have been encountered in developing the processes used today. 

Blends of starch and a hydrophobic polymer make it possible to overcome the disadvantages described above. Starch compounds with Ecoflex are used to enhance hydrophobicity as well as the mechanical and thermal properties of compounded products. To obtain high quality film products, the starch has to be treated before being blended with Ecoflex . The crystalline structure of starch granules has to be destroyed because starch granules are as large as the film thickness of typical film applications and would therefore reduce the mechanical properties of the films. 

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