A Low Shear, High Temperature Rotational Viscometer

To obtain accurate measurements of the limiting viscosity number of solutions of ultrahigh molecular weight polyethylene (UHMWPE), a low shear floating-rotor viscometer of the Zimm—Crothers type was developed to measure viscosities at elevated temperatures (135 °C) and essentially zero shear rate. The zero shear rate measurements for a set of UHMWPE samples were compared with viscosity measurements at moderate and high shear rates (up to 2000 s -1 ) carried out in a capillary viscometer. The limiting viscosity number of UHMWPE depends, as expected, on shear rate, and the higher shear rate data could not be extrapolated to yield the correct zero-shear rate viscosities.