Rheological properties of blend melts for starch-based foams in extrusion processing
1999
Cha, J.Y. | Chung, D.S. | Seib, P.A.
Blends composed of 49% wheat and corn starch (dry solid basis), 33% synthetic polymers, 10.5% total water, 7% blowing agents, and 0.5% nucleating agent were extruded at different screw speeds (70-130 rpm) using a single-screw C.W. Brabender laboratory-scale extruder with a slit capillary die attached in-line. Shear stress at wall, shear rate at wall, shear viscosity, and exit pressure of the blends melted at different die temperatures (403, 413, 423, and 433 K) were determined at various flow rates and pressure gradients within the slit capillary die. Shear stress at wall increased at a given screw speed with decreased die temperature; whereas, shear rate at wall decreased. At each screw speed and die temperature, shear stress at wall and shear rate at wall of blends melts containing normal wheat starch were higher than those of blend melts containing hydroxypropylated wheat starch. The blend melts transformed from dilatant to pseudoplastic fluid when temperature increased from 403 to 433 K. The blend melts containing normal wheat starch exhibited dilatant behavior at 403 and 413 K and pseudoplastic behavior at 423 and 433 K. The blend melts containing hydroxypropylated wheat starch exhibited dilatant behavior at 403 K and pseudoplastic behavior at 413, 423, and 433 K.
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