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-screwC. W. Brabender laboratory-scale extruder with a slit capillary die attached in-line. Shear stress at wall, shear rate atwall, shear viscosity, and exit pressure of the blends melted at different die temperatures (403, 413, 423, and 433 K) weredetermined at various flow rates and pressure gradients within the slit capillary die. Shear stress at wall increased at agiven screw speed with decreased die temperature; whereas, shear rate at wall decreased. At each screw speed and dietemperature, shear stress at wall and shear rate at wall of blend melts containing normal wheat starch were higher thanthose of blend melts containing hydroxypropylated wheat starch. The blend melts transformed from dilatant topseudoplastic fluid when temperature increased from 403 to 433 K. The blend melts containing normal wheat starchexhibited dilatant behavior at 403 and 413 K and pseudoplastic behavior at 423 and 433 K. The blend melts containinghydroxypropylated wheat starch exhibited dilatant behavior at 403 K and pseudoplastic behavior at 413, 423, and 433 K.
No takes yet. Share an insight, caveat, or question.
Cha et al. (1999) studied this question.