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ARS Home » Research » Publications at this Location » Publication #84006


item Carriere, Craig
item Loffredo, Armand

Submitted to: Polymer Engineering & Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Starch is an industrially-important polymer which is used in numerous applications including paper coatings and foods. Despite its widespread use, many unanswered questions remain regarding the basic rheological properties of starch. In order to process starch effectively, an understanding of the flow behavior of starch-based systems needs to be developed. This work discusses the unexpected shear-thickening behavior and consequent stable, flow-induced structure formation of waxy maize starch in semidilute solutions. Shear-thickening behavior was observed for waxy maize starch, but not for normal maize starch at the same concentration. The flow-induced structure was observed to occur at temperatures ranging from 25 to 80 deg C. Once formed, the flow-induced structure was stable with respect to time and temperature. Physical models were used to distinguish the rheological behavior of waxy maize starch from normal maize starch. The model parameters indicated the unique behavior of waxy maize in comparison to normal maize starch.

Technical Abstract: The effect of temperature on the unexpected shear-thickening behavior exhibited by semidilute solutions of waxy maize starch during a repeated shear-loop experiment was evaluated. Shear-thickening behavior, characterized using power law models, was observed for waxy maize starch, but not for normal maize starch at the same concentration. The shear-thickening region was observed for waxy maize starch at temperatures ranging from 25 to 80 deg C and shear rates from 20-100 s**1 during the initial part of the shear-loop experiment. For waxy maize starch, the power law exponent, eta, was found to be 1.22 +/ 0.06, and 0.545 +/ 0.051 in the shear-thickening and shear-thinning regions, respectively. For normal maize starch, the value of eta was found to be equal to 0.751 +/ 0.015 and only shear-thinning behavior was observed. The values of eta for both waxy maize and normal maize starch were found to be temperature independent within the precision of the experimental measurements. The differences in eta indicate the differences in the conformational dynamics of waxy maize and normal maize starches in solution.