Submitted to: Society of Plastics Engineers Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 2, 1997
Publication Date: 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 flow 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 increase in solution viscosity and the consequent stable, flow-induced structure formation of waxy maize starch solutions. The rise in viscosity was observed for waxy maize starch but not for normal maize starch at the same concentration. The increase in viscosity was observed to occur at temperatures ranging from 25 to 80 deg C. Physical models were used to distinguish the flow 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 shear-thickening behavior exhibited by semidilute solutions of waxy maize starch during a repeated thixotropic-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 thixotropic-loop experiment. For waxy maize starch, the power law exponent, n, 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 n was found to be equal to 0.751 +/ 0.015 and only shear-thinning behavior was observed. The values of n for both waxy maize and normal maize starch were found to be temperature independent within the precision of the experimental measurements. Oscillatory shear measurements indicated the presence of a highly-entangled network formed during the shear-thickening regime.