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Starch

Notes

From 03/18/2015 through 6/6/2012

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Biodegradable Materials

Polysaccharides

Starch Applications.

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Notes

1. “Starch or amylum is a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store. It is the most common carbohydrate in the human diet and is contained in large amounts in such staple foods as potatoes, wheat, maize (corn), rice, and cassava.

Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.[1] Glycogen, the glucose store of animals, is a more branched version of amylopectin.

Starch is processed to produce many of the sugars in processed foods. Dissolving starch in warm water gives wheatpaste, which can be used as a thickening, stiffening or gluing agent. The biggest industrial non-food use of starch is as adhesive in the papermaking process.”

(Wikipedia, Starch, 6/6/2012)

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“Many starch materials have been used to make a variety of films, foams, and other industrial and food products. However, despite the variety of starch materials available, known starches generally can be somewhat unsuitable for use in these applications. For instance, native starches have two key limitations when used in films and coatings. Films made from unmodified or "reduced viscosity" starches generally are brittle, weak, cloudy, and opaque, and cooking is generally required to hydrate the starch polymers, inasmuch as native starches typically are water insoluble at temperatures at or below room temperature (25.degree. C.). The problems of brittleness, clouding and opacity can be mitigated somewhat with a low degree of hydroxyalkylation of amylose and/or amylopectin contained in the starch to form a hydroxyalkyl starch, but still the hydroxyalkyl starch will be cold-water insoluble. Thus, such starches are not useful where heating is not available.

To overcome the problem of cold-water insolubility, the starch may be physically or chemically modified, or may be enzymatically treated. One approach known in the art is to modify the starch by using alkylene oxide reagents, such as propylene, oxide, ethylene oxide, and the like. This process generally requires the use of organic solvents, such as ethanol, which are undesired due to the additional processing costs associated with such solvents.

The prior art also has taught to hydroxyalkylate the starch using an aqueous process. The hydroxyalkyl starch thus prepared is then cooked by drum-drying or spray-drying, and is ground to be marketed as a pre-gelled or "instant" starch. While such pre-gelled starches are suitable for some applications, such starches are difficult to disperse in water in low temperatures. Starches used in film and coating applications may contain intact starch granules, which can result in poor film clarity and increased film opacity. Particularly in the case of drum-dried starches, large lumps, sometimes referred to as "fish-eyes," are often formed. Also, the viscosity of these starches often is high, thus limiting the level of solids, which can be dispersed in an aqueous system without resulting in mixing and handling problems. Moreover, while occasionally additives such as borax, boric acid, gum arabic, and sulfate salts are added to improve wettability or dispersability, these solutions are somewhat unsatisfactory because of the additional costs required for such additional ingredients.”

[Wang et al, US Patent 8,192,660 (6/5/2012)]

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Interested!!
Bookmark this page to follow future developments!.
(RDC 6/5/2012)

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Roger D. Corneliussen
Editor
www.maropolymeronline.com

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Copyright 2014 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 6/6/2012.