Search

The fiber‐windup technique, developed by Macosko and Lorntson [SPE Tech. Papers 19, 461–467 (1973)] for rotational shear rheometers, was re‐examined to obtain transient uniaxial extensional viscosity data. Macosko and Lorntson used a special force transducer to measure the tension in the filament being pulled. In contrast, in this study commercial rotational shear rheometers (Rheometrics Mechanical Spectrometer‐800 and Rheometrics Fluids Spectrometer‐II) with torque transducers were used to obtain the extensional viscosity. One end of the sample is clamped, while the other end is wound around a drum at a constant rotational speed, to achieve a given extension rate. Tests were conducted with a polyisobutylene sample at room temperature to verify reproducibility and were compared with published studies. Results for polyisobutylene and IUPAC‐X low density polyethylene were found to be in good agreement with published results. Hencky strains of up to 6 could be achieved. The technique can provide valuable ext...

Corn meal and commercial low density polyethylene (LDPE) were extruded through a slit die using a laboratory model single‐screw extruder at various extrusion conditions. Flow curves for the corn meal showed severe shear thinning behavior (n≲0) at lower moisture contents; molecular degradation, pressure dependence of viscosity, viscous dissipation, slip, and yield stress were identified as the possible factors. Survey of the available literature and the behavior observed in this study indicates that molecular degradation is the major factor responsible for n≲0. A modified viscosity model that includes the die entrance pressure (barrel pressure) for molecular degradation effects was developed; such a model also accounts for the pressure dependence of viscosity. Negative exit pressures for LDPE and both positive and negative exit pressures for corn meal were obtained. Statistical analysis indicated large errors in the exit pressures predicted by the linear extrapolation. These errors originate from several s...