No abstract

The melt viscosity of thermoplastic starch has been investigated as a function of temperature, moisture content, and processing conditions. The effects of various low molecular weight additives have also been studied. Starch melts exhibit power law behavior over the range of shear rates studied. Melt viscosity decreased with increasing temperature and moisture content (MC). The power law index m increased with increasing temperature. The consistency K decreased with increasing temperature and increasing moisture content. Moisture content during the pelletizing step influenced melt viscosities measured after equilibration to different MCs. All additives studied except glycerol monostearate (GMS) significantly lowered the melt viscosity of starch, some more effectively than water relative to starch with 15% MC. Starch with GMS had viscosities essentially the same as, or slightly higher than, starch/water. This behavior may be due to the presence of unmelted helical inclusion complexes of starch and GMS. Starch formulations at 160°C exhibited melt visocosities similar to an LDPE of melt index 1.8.

The elastic and loss moduli of fiue types of wheat flour doughs were measured in an eccentric rotating disc (ERD) rheometer. G’ and G”, determined from the linear portions of the response curve, were very sensitive to water content, decreasing as water content increased. Differentiation among samples was greatest at the highest water content. Results also depended on protein level, with higher moduli being observed at higher protein level. Samples mixed in a Farino‐graph to constant consistency showed differing values of both storage and loss moduli. The ERD geometry thus appears suited to characterization of doughs and to study of component interactions in such systems.