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United States Department of Agriculture

Agricultural Research Service

Title: Melt Rheology and Molecular Weight Degradation of Amylopectin During Multiple Pass Extrusion of Starch

Authors
item Willett, Julious
item Millard, Merle
item Jasberg, Brian

Submitted to: American Institute of Chemical Engineers Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: November 10, 1996
Publication Date: N/A

Technical Abstract: The degradation of starch during extrusion and the role of specific mechanical energy (SME) in this process have been widely studied for single pass extrusion. Multiple extrusion histories are not uncommon in the plastics industry, but little if any has been reported on their effects on starch. Native waxy maize starch (app. 98% amylopectin) was initially converted to a thermoplastic by twin screw extrusion. This extrudate was equilibrated to either 18% or 23% moisture content, and subsequently re-extruded in a single screw extruder (3:1 compression screw) at 110 deg C or 130 deg C. Melt viscosity data were calculated using the output-pressure data from the second pass. The melts exhibited shear thinning behavior; the power law index increased with temperature, and slightly with moisture content. Molecular weights of selected second-pass extrudates, as well as the native starch and the first-pass extrudate, were measured by light scattering in dimethyl sulfoxide/water. The initial extrusion pass reduced the molecular weight from 300 million to 50 million. Molecular weight reductions in the second pass increased with increasing SME. A first order expression was shown to fit the MW-SME data with a correlation coefficient of 0.91. Implications of the degradation on extrusion processing of starch and the use of single screw extruders for rheological characterization will be discussed. ____________________

Last Modified: 12/18/2014
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