Capillary viscosimeter

Viscosities of the blends and composites were measured in shear flow with a Gottfert Rheograph 2002 capillary viscosimeter. The shear rate was investigated from 100-10000 s" . The L D ratio of the capillary die was 30 mm 1 mm. Rabinowitch correction was made to the measurements, but Bagley correction was not applied. 

The on-line viscosimeters currently available are adaptations of the classical dilute solution capillary viscosimeters. They work on the principle of measuring the pressure drop across a capillary with a differential pressure transducer. The pressure drop can be related to the reduced or inherent viscosity of the sample via Poiseuille s law.84 Intrinsic viscosity is determined using the equation ... 

Oil viscosity is measured in a rolling-ball viscosimeter or a capillary viscosimeter, either designed to simulate differential liberation. Measurements are made at several values of pressure in a stepwise process. The liquid used in each measurement is the liquid remaining after gas has been removed at that pressure. See page 6 of Table 10-1. 

The experimental part of the viscosimetric method used in this study is based upon an automatization of the FIP method (49). A calibrated capillary viscosimeter of the Ubbelohde type (nr. 2453723 Jenaer Glas-werk, Schott Gen., Mainz) is used. The length of the capillary is 13 cm and its diameter is 0.096 cm, determined experimentally by filling the capillary with Hg. The volume of the bulb is 0.71 cm3. 

The viscosity of copovidone in water depends on its average molecular weight. This can therefore be calculated from the viscosity, to give the viscosity average of the molecular weight (see Section 4.2.3.3). Figure 90 shows the viscosity of solutions in water and in 2-propanol as a function of their concentration. The measurements were done in a capillary viscosimeter. It can be seen that solutions of about 10% have a low viscosity, which is an advantage in practice. 

Molecular-mass distribution of SKEPT samples was determined by spectra of relaxation times of polymers solutions pressure (SRTP). Method is based on the use of experimental data of pressure fall in capillary viscosimeter s cylinder imder non-stationary polymer melt outflow through capillary after piston stop (automatic capillary viscosimeter MPT "Monsanto" with capillary size n = 1,5mm at 398K and initial shear rate 3,6 sec" ) [270,271]. 

For the liquid samples, the viscosity in mmVs has been measured using a capillary viscosimeter (system Cannon-Fenske ASTM D 2515) at 50 °C and 100 °C, according to DIN 51 366. 

Einstein s formula, according to its derivation, holds only for Couette flow. Its usefulness for capillary viscosimeters and the probability of its general validity was proved by R. Simha, Kolloid Z., 76, 16 (1936). 

For partial Brownian motion of small rods, there is, as yet, no satisfactory solution. In any case, the viscosity will decrease with the flow gradient and increase with increasing Brownian motion (i.e. with kT), Because of the variable gradient in a capillary viscosimeter, different results are to be expected for Couette and Poiseuille flow. 

Viscosity measurements were carried out by Ubbelohde-type capillary viscosimeter. The surface tension and kinetic energy corrections were neglected. 

Spectra of electron spin resonance (ESR) were recorded using ESR-spectrometer Bruker EMX in the X-wavelength range. Viscosity of amylose samples before and after treatment was measured by capillary viscosimeter previously dissolved them in dimethyl sulfoxide (0.6 g of polymer or products in 10 cm of DMSO). 

The viscosity fj was measured with a capillary viscosimeter. The correlation radius of the concentration fluctuations was determined from the radiation dizigram (hxjua-tions 100-102). 

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... 

Capillary viscosimeters belong to the type of effluent viscosimeters. They are the most commonly used viscosimeters for the determination of the intrinsic viscosity. 

Fig. 3.2. Velocity profile in a capillary viscosimeter.The fluid velocity v has a parabolic profile with a maximum in the middle of the capillary the shear rate f and the shear stress rhave a maximum at the capillary wall and are zero in the middle of the capillary...

Even under normal ambient pressure relatively high shear rates occur at the wall of capillary viscosimeters (especially for small capillary diameters and low viscosity liquids), that can lead to a falsification of the results for so-called non-Newtonian liquids (see later in this monograph). In Tables 3.1 and 3.2 the maximum occurring shear rates for the admissible minimal running times tniin of the capillary are given for the standard Ubbelohde capillary viscosimeter (ISO 3105) and the Micro Ubbelohde capillary viscosimeter (DIN 51562). 

Table 3.1. Parameters for Ubbelohde Capillary Viscosimeters (ISO 3103 and DIN 51562) with Ref. numbers 501.., 530.., 532.., capillary number (No.), capillary diameter (D), capillary constant (K), minimum measurable flow time (fmin)> maximum shear rate at minimum flow time (fjnax) and kinematic viscosity range (v)...

However, in viscosimetry using a capillary viscosimeter normally the viscosity is not calculated from the maximum shear rate and the shear stress but rather from the Hagen-Poiseuille-Law (Eq. 3.1). 

The flow cup is a relative-capillary viscosimeter. The outlet nozzle is a very short capillary, and the propulsive force is the hydrostatic pressure of the liquid, which during the tests flows under its own weight from the central outlet nozzle on the bottom of the cup. The flow cup has a defined geometry with a given volume for the sample liquid. For the measurement, the nozzle is closed, the cup is filled with the sample liquid and then the time is measured that the Uquid takes to completely drain out of the cup. From that efflux time, the kinematic viscosity v is calculated. Up to this day many different flow cups are used around the world (see Fig. 3.3). 

This is in contrast to the capillary viscosimeter, where the shear stress always increases over the radius from zero to the maximum. The constant shear rate and therefore the viscosity can be calculated ... 

The most commonly used type of viscosimeter for the determination of the intrinsic viscosity or for single point measurements is the capillary viscosimeter. As the reproducibility with this type of viscosimeter depends on the clean execution of the measurement, a detailed description of the proceedings for a viscosimetric measurement is given below. 

The running times have to be corrected afterwards. For short running times this is to be done according to Hagenbach (see Capillary viscosimeter above). In practice, this is usually not done according to Eq. (3.6) though, but correction times are listed by the manufacturer for the particular capillary and have to be subtracted from the measured running times t ... 

Viscosimetric measurements of surface-active samples in capillary viscosimeters are often hindered by vesication. In addition to a variation of the running times by bubbles of air in the reservoir and the no longer existing laminar flow profile in the capillary, an exact determination of the running times is not possible, because the foam formation on the fluid meniscus interface is particularly strong. Especially fully automated viscosimeter systems with light barriers at the marks Mi and M2 provide no exact data in this case. 

The relative viscosities q of a dilution series (and therefore the relation of the running times of the solution and the pure solvent in a capillary viscosimeter according to Eq. (3.38)) should lie between 1.2 and 2.5, to assure an exact analysis. These limits of the relative viscosity are shown in Fig. 4.3. The data points below the critical value of the relative viscosity of 1.2 show deviations from the linear fit and should not be included in the extrapolation to the/-axis for the determination of the intrinsic viscosity. 

Viscosity measurements are often carried out with capillary viscosimeters because they are relatively cheap and give fast but exact results. Since capillary viscosimeters operate at higher shear rates (see Tables 3.1 and 3.2) it must be checked... 

It is possible that the zero-shear viscosity of polymer samples with very high molar mass and strong non-Newtonian flow behavior cannot be measured in a capillary viscosimeter. In case of a maximum shear rate in the capillary above the critical shear rate of the sample the calculated viscosity will be too low as one can see in Fig. 5.10 for different samples of high molar mass xanthan gum. 

Fig. 5.10. Intrinsic viscosity [q] determined at high shear rates Y with a capillary viscosimeter and at lower shear rates with a Zimm-Crothers viscosimeter for different xanthan gums in 0.1 mol/l sodium chloride (NaCI) solution at 25 C. Data from [93]. For strongly shear thinning polymer solutions, only low shear viscosimeters reach the shear rate independent viscosity region...

---