Cone-plate Rheometer Research Articles

Measurement of the first normal-stress difference at high shear rates for a polyisobutylene/decalin solution ?D2?

Reasonable agreement is found between values of the first normal-stress differenceN 1 for samples of “D2”, a polyisobutylene/decalin solution, measured in steady shear flow using three different instruments: a Weissenberg Rheogoniometer (a cone-plate rotational rheometer), a Torsional Balance (plate-plate rotational) Rheometer, and a Stressmeter (a transverse-slot slit-die rheometer). Viscosity values are also in reasonable agreement. Ranges of variables common to at least two rheometers include values of shear stressσ up to 3,700 Pa and shear rate $$\dot \gamma $$ up to 20,700 s−1 near 25 °C. The agreement supports the approximate validity of the semi-empirical “HPBL equation” used to calculateN 1 from Stressmeter data over a range of shear rates up to 20,700 s−1 near 25 °C. Time-temperature superposition behavior exhibited by Stressmeter data at temperatures in the range 21 °C to 111 °C suggest that the range of validity of the Stressmeter method for determiningN 1 approximately may extend up to shear rates of 290,000 s−1 at 111 °C.

The viscoelastic properties of PP/glass fiber composites in molten state

The molten viscoelastic behavior of polypropylene/glass fiber composites (FRPP) were investigated under steady state and dynamic state. The steady viscosity was measured from both cone-plate rheometer and capillary flow tester. The dynamic viscoelastic properties were measured from cone-plate rheometer. The variation of molten viscoelastic behavior of FRPP with the composition, temperature, shear rate, and coupling agent are examined and discussed in this paper. Die swell phenomena of FRPP at different temperatures, shear rates, and compositions were also observed. The results were that the viscosity and modulus of FRPP increased with increasing the fiber content in FRPP. Pretreatment of glass fibers with coupling agent would enhance the interfacial adhesion between polypropylene and fibers, and the fiber length in FRPP was longer on the average. Die swell of FRPP significantly decreased by the presence of glass fibers.

Elasto-thixotropic properties of bronchial mucus and polymer analogs. I. Experimental results.

The non-newtonian viscous and elasto-thixotropic properties of native and lyophilized pathological bronchial mucus and of polymer solutions (3% and 6% PIB in decalin) used as mucus analogs were analyzed using a cone-plate Carri-Med rheometer and a Couette viscoelastometer that we have specifically developed for measuring the rheological properties of bronchial mucus in clinical practice. The master curves obtained for apparent viscosity under steady conditions as a function of shear rates (gamma: 2.6 X 10(-3) to 6.9 X 10(1) sec-1) were fairly similar, whatever the apparatus used. Under transient conditions, at low shear rate (gamma less than 1.4 sec-1), PIB and mucus exhibited a typical viscoelastic behavior: the shear stress increased slightly up to a steady-state value. At higher gamma, a transitory overshoot of sigma characteristic of the elastothixotropic systems appeared. Such a behavior can be interpreted as resulting from structural changes such as formation and rupture of the three-dimensional network present in bronchial mucus as in polymer solutions.

A linear model of the stick-slip phenomena in polymer flow in rheometers

A linear approach was employed for the qualitative theoretical study of the stick-slip phenomena in polymer flows in rheometers. For this purpose, the familiar three-constant rheological equation and a linear wall friction law (i.e. wall stress — slip velocity dependence) were used with some additional hypotheses about the onset of the stick-slip behaviour. The friction law used was derived from a crude molecular approach. On the basis of these equations the inertialess stickslip behaviour of a viscoelastic liquid flowing through a capillary at a constant flow rate was considered. To be able to describe some transient phenomena in this problem, inertial effects (as an example) were taken into account. Furthermore, the distortions on the extrudate surface due to the slip phenomena inside the capillary were described theoretically within the framework of a linear approximation. In the final part of the study the possibility of rapid stochastization was discussed for rotational stick-slip flow of polymers in a cone-plate rheometer.

The rheology of suspensions of vinylon fibers in polymer liquids. I. Suspensions in silicone oil

The steady shear flow properties of suspensions of vinylon fibers in silicone oil were measured by means of a cone-plate type rheometer. Three kinds of vinylon fibers used had no distributions of length and were more flexible than glass fibers and the like. The content of the fibers ranged from 0 to 7 wt.%. Shear viscosity, the first normal-stress difference, yield stress, and relative viscosity were discussed. Shear viscosity and relative viscosity increased with the fiber concentration and the aspect ratio, and depended upon the shear rate. The applicability of Ziegel's equation of viscosity for fiber suspensions was investigated. The first normal-stress difference increased with the fiber concentration, aspect ratio, and shear rate and its relative increase was much larger than for shear stress and viscosity depending on the properties of the characteristic time,\(\bar \tau \) The yield stress could be determined by Casson plots for large aspect ratio fiber suspensions even in low concentration comparing with the suspensions of spherical particles or powder. The influence of the flexibility of the fibers for the rheological properties of the fiber suspensions can not be ignored.

Rheological Properties of Disperse Systems of Photosensitive Particles

Relations between the rheological properties and the degree of aggregation of dispersed particles were investigated for suspensions of photosensitive particles. Photosensitive particles were prepared by introducing cinnamoyl group _??_ into styrene-divinylbenzene copolymer particles through the reaction with sodium cinnamate. The photocrosslinking reaction between particles, i. e. the degree of aggregation of photosensitive particles, was controlled by adjusting the irradiation time of a light.The steady-flow and dynamic viscoelastic properties of disperse systems of these particles in diethylphthalate were measured by a cone-plate type rheometer, and the degree of aggregation of particles was measured by the light scattering method. The latter is based on the increase in intensity of forward scattering with increasing aggregation.Shearing stress and dynamic viscoelastic functions increase with increasing degree of aggregation, and the so-called second plateau, which corresponds to the relaxation of the aggregate structure, begins to be observed with it. The relaxation time of disperse systems was also related quantitatively to the degree of aggregation.

The measurement of the second normal stress difference for some polymer solutions

The second normal stress difference N 2 can be determined by measuring the free surface shape of fluids flowing down a semicircular channel. A photograph is taken of a graduated straight edge and its reflection in the fluid surface. The shape of the surface is then calculated from the shape of the straight edge reflection using geometrical optics. We show that the surface shape can be measured to an accuracy of ±0.01 mm by this photographic method, leading to a value of N 2 which is accurate to about ±0.1 N m −2. A study was made of a number of moderately concentrated polymer solutions. The shear stress τ and the first nomral stress difference N 1 were measured on a cone—plate rheometer while the second normal stress difference N 2 was determined from the pipe flow experiment. The normal stress ratio N 2/ N 1 was found to be negative and independent of shear rate in the range 1 < γ . < 100 s −1. The ratio N 2/ N 1 is weakly dependent on concentration and our values are consistent with those obtained by other investigators using different methods to measure N 1 and N 2.

Non-Newtonian Behavior of Low Density Polyethylene Melts

Non-Newtonian behavior of low density polyethylene melts was studied at 190°C in a wide range of shear rate γ, namely from 1×10-2 to 3×103 sec-1. Three types of commercial low density resins were fractionated carefully to obtain sharp fractions of branched polyethylenes, AF, BF and CF series, respectively, and one type of commercial high density resin to obtain a series of linear polyethylenes, HDPE fractions, as reference materials. The weight-average molecular weight of low density polyethylene fractions was determined by light scattering. The melt viscosities η of low and high density polyethylene fractions were measured by using a cone-plate type rheometer in the range of low shear rate and a capillary type rheometer in the range of high shear rate. The zero shear viscosity η0 of the high density polyethylene fractions was proportional to Mv3.53. The zero shear viscosities of two series (AF and BF series) of branched polyethylene fractions were higher than that of the linear polyethylene fractions of the same molecular weight in the range of molecular weight higher than 5×104, while η0 of the third series (CF series) of branched polyethylene fractions was always lower than that of the linear polyethylene fractions of the same molecular weight. The reduced viscosity η/η0 of branched polyethylene fractions was not a unique function of τBγ, but was a function of g1τBγ. Here τB is the Bueche relaxation time and g1, is the branching index calculated by the Zimm-Kilb equation. The dependence of η/η0 on the quantity g1τBγ was given by the modified Bueche-Harding equation, η/γ0=1/[1+0.6 (g1τBγ)0.75] for AF and BF series, and by a slightly different form for CF series.