Abstract
A slit rheometer, mounted on a square cross section barrel extension, was attached to the exit of a single screw extruder to facilitate the simultaneous measurement of steady shear viscosity (ηsh), apparent planar extensional viscosity (ηpa), and the first normal stress differences (N1). The hole pressure method was used to determine N1 and the entrance pressure drop method with Cogswell’s analysis for abrupt planar contraction flow was used to determine ηpa. The effect of slot dimensions on N1 was investigated using low density polyethylene. Increasing the depth and width of the slot by 50% produced no significant change in the hole pressure. N1 predicted using the Higashitani–Pritchard–Baird (HPB) equation compared favorably with extrapolated N1 values obtained on a cone and plate rheometer. Addition of salt and sugar to corn grits affected the rheological properties of the melt, as observed by the changes in ηsh, N1, and ηpa. Of the three material functions, N1 and ηpa were more sensitive to the addition of ingredients. Corn grits exhibited thinning behavior in shear and planar extensional flows.
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