Transient extensional viscosity from a rotational shear rheometer using fiber‐windup technique

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...