Determination of Rotational Viscosity

Two main types of viscometers are suitable for the determination of the viscosity of a polymer melt The rotation viscometer (Couette viscometer, cone-plate viscometer) and the capillary viscometer or capillary extrusiometer. The latter are especially suitable for laboratory use since they are relatively easy to handle and are also applicable in the case of high shear rates. With the capillary extrusiometer the measure of fluidity is not expressed in terms of the melt viscosity q but as the amount of material extruded in a given time (10 min). The amount of ex-trudate per unit of time is called the melt index or melt flow index i (MFI). It is also necessary to specify the temperature and the shearing stress or load. Thus MFI/2 (190 °C)=9.2 g/10 min means that at 190 °C and 2 kg load, 9.2 g of poly-... 

The experimental methods for the determination of liquid viscosity are similar to those used for gases ( 8.VII F) (i) transpiration, through capillaries, (ii) torque on rotating cylinders, or the damping of oscillating solid discs or spheres, in the liquid, (iii) fall of solid spheres through the liquid, (iv) flow of liquid through an aperture in a plate, (v) capillary waves. Methods (i) and (ii) are mostly used for absolute, the others for comparative, measurements. 

Figure la-c shows the dependence of the apparent viscosity of the enzyme hydrolysis suspension on biomass concentration. It clearly demonstrates a dramatic decrease of viscosity at the reloading point (i.e., after the initial 4 h). The experimental determination of the viscosity-shear rate and shear stress-shear rate relationships of the various formulation suspensions with different concentrations was performed with a variable speed rotational viscometer (2 to 200 rpm). 

CEN EN 13302. 2010. Bitumen and bituminous binders — Determination of dynamic viscosity of bituminous binder using a rotating spindle apparatus. Brussels CEN. 

This rotating spindle viscometer is used for the determination of dynamic viscosity of a variety of bituminous binders modified and unmodified bituminous binders, bituminous emulsions, cut-back and fluxed bituminous binders by means of rotating spindle (coaxial viscometer) viscometer, at typical test conditions (temperatures and rate of shear). 

There are roughly three classes of viscosimeters available the capillary viscosimeter, the rotational viscosimeter, and the falling-ball viscosimeter. Both the capillary and the rotational viscosimeters are built in different versions that allow for the exact determination of the viscosity in well-defined flow fields. Especially rotational viscosimeters allow the exact adjustment of a constant flow profile, thus are available in high precision and expensive versions as rotational rheometers. Capillary viscosimeters are the best compromise between the exact determination of viscosity and a well-priced measurement device, and are therefore the most commonly found type of viscosimeters. Both rotational and capillary viscosimeters are available in simple and inexpensive versions as Brookfield viscosimeters and flow... 

Stormer Viscometer. A rotating cylinder viscometer of a type that has found considerable use in USA for the determination of the viscosity and thixotropy of clay slips. (Industr. Engng. Chem., 1,317,1909.)... 

The study of light scattered by a nematic sample allows the determination of the viscosities 7]j(q) and Tj Cg) (see Eqs. 17 and 18), which are mainly determined by the rotational viscosity coefficient yj, but also contain other coefficients because of the backflow. In principle, all coefficients can be determined with different accuracies by a suitable choice of the scattering geometry. The influence of the small coefficient Oi is normally neglected. For 4-n-pentyl-4 -cya-nobiphenyl, Chen et al. [93] found the following values at 25 °C 03=-0.086, a3=-0.004, a4=0.089, c%=0.059 and o = -0.031 Pa s. 

We note in conclusion that capillary and sHt rheometers are useful for the determination of melt viscosity at shear rates well above those accessible in rotational rheometer. However, at some shear rate, pressure and temperature variations become important and must be taken into account in the analysis of data. Also, the occurrence of slip may hmit the shear rate at which data can be obtained. 

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