Submitted to: American Chemical Society Abstracts
Publication Type: Proceedings
Publication Acceptance Date: August 30, 2001
Publication Date: N/A
Interpretive Summary: Starch, widely used in food and non-food applications, is composed of two components known as amylose and amylopectin. When dispersed in water, the properties of starch depend on the relative amounts of these two com- ponents. Under most conditions of practical interest, the two components of starch do not intimately mix, but separate into two phases, with one component dispersed as droplets in the other component. The behavior of phase-separated starch solutions is highly dependent on the processing history, but has not been systematically investigated. Solutions of potato starch were prepared and subjected to different processing condi- tions (ie, shear). The structure of the dispersed phase was characterized during processing by a custom-built optical instrument. Under strong processing conditions (ie, high shear), the starch solutions formed aggregates. Milder processing conditions resulted in deformation (or elongation) of the dispersed droplets into string-like structures. When shearing was stopped, the deformed droplets returned, or relaxed, to their static (round) shape. These initial results provide insight into the development of structure in starch solutions, and provide fundamental knowledge which can be used to develop starch-based materials with desired properties through control of processing conditions.
Technical Abstract: When potato starch granules are dissolved in aqueous medium, the two major components, amylopectin and amylose, do not mix together and form two separate layers like oil and water. This property of starch solutions can be used to isolate each component for industrial use. Study of starch solutions that includes the construction of "phase diagram" allows us to replace old techniques that required long and tedious steps to obtain purified form of starch components. In this report, the "phase diagram" of potato starch is presented. When polymers are blended commercially, the processing conditions usually subject these materials to complicated flows. Polymers are returned to the quiescent state after processing has been completed. The application of simple shear offers the possibility of modeling the behavior under flow in a more controlled environment. Monitoring the relaxation of the blend after the cessation of shear allows one to obtain insight into the kinetic processes during the approach of the final equilibrium state. Since it is already known that the behavior of polymer blend under flow is similar to that of polymer blend solution, we employed potato starch solution as a model system and studied the behavior under flow and compared with that of synthetic polymer solutions.