TRANSIENT EXTENSIONAL VISCOSITY FROM A ROTATIONAL SHEAR RHEOMETER USING FIBER-WINDUP TECHNIQUE

The fiber-windup technique, developed by Macosko and Lorntson [SPE Tec h. Papers 19, 461-467 (1973)] for rotational shear rheometers, was re- examined to obtain transient uniaxial extensional viscosity data. Maco sko and Lorntson used a special force transducer to measure the tensio n in the filament being pulled. In contrast, in this study commercial rotational shear rheometers (Rheometrics Mechanical Spectrometer-800 a nd Rheometrics Fluids Spectrometer-II) with torque transducers were us ed to obtain the extensional viscosity. One end of the sample is clamp ed, while the other end is wound around a drum at a constant rotationa l 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 agreeme nt with published results. Hencky strains of up to 6 could be achieved . The technique can provide valuable extensional viscosity data for hi gh viscosity liquids. (C) 1996 Society of Rheology.