Showing papers on "Rheometer published in 1975"

Nonlinear Viscoelasticity of Polymer Melts

Abstract: Large amplitude oscillatory shear has been employed to study the nonlinear viscoelastic properties of three polymer melts. The resins studied included a DuPont high‐density polyethylene, a Union Carbide low‐density polyethylene, and a Dow polystyrene. The equipment used consisted of a small‐gap, concentric cylinder rheometer with a controlled‐speed motor unit and a rack‐pinion, oscillating drive mechanism. The torque was monitored by means of a torquemeter based on magnetic stress anisotropy in a steel tube and the strain was monitored by means of a displacement transducer. A signal proportional to the rate of strain was generated by integrating the strain with respect to time. Strain amplitudes up to 10 and frequencies between 0.5 and 30 sec−1 were employed. For purposes of material characterization, plots of stress versus rate‐of‐strain are employed. This is a closed stationary curve. Its “openness” is an indication of elasticity and its deviation from an elliptical shape is an indication of nonlinearit...

A method for the measurement of the true die swell of polymer melts

Abstract: A new device has been designed for the measurement of the die swell of extruded polymer melts. According to the proposed procedure, samples can be collected, annealed, and photographed. The device may be used in conjunction with any capillarytype rheometer. It can accommodate simultaneously as many samples as it is needed. The samples are suspended in a thermostated liquid, carefully selected for each polymer. The liquids must be thermally stable and of proper density and thermodynamic and interfacial properties. The device was used in conjunction with the Instron capillary rheometer, ICR. Three types of polymer were tested: polystyrene (PS), polyethylene (PE), and a semirigid poly(vinyl chloride) formulation (PVC). The swelling of the extrudates was followed for ca. 40 min; the equilibrium dimensions were usually reached within the first 2 min. Parallel with these measurements, the samples were tested in the Weissenberg rheogoniometer (WR) recording both shear and normal stresses. For PS and PE, the flow curves determined in these two rheometers overlapped, while they differed for PVC. The swell ratio, Bexp = D/D0 (where D and D0 are the equilibrium diameter of the extrudate and diameter of the capillary, respectively), was converted to recoverable shear strain, s, as follows. First, Bexp and s were determined in ICR and WR, respectively, for a PS sample over wide and overlapping ranges of rate of shear. This experimental dependence was found to follow Tanner's theoretical relation. Consequently, this relation was used to compute s from Bexp for all the other samples. Excellent agreement was observed between the s values calculated from Bexp and s values determined in WR.

Nonlinear effects in the shear viscosity of fluids near the critical point

Abstract: We present a microscopic theory for the nonlinear shear viscosity of fluids near the critical point, and find that dependence on shear gradients should be observable in capillary viscometer experiments. We suggest that the leveling off (cusplike behavior) of viscosities that has been observed experimentally may be a result of shear gradient effects. Further experiments to test our theory are suggested.

Rheological Properties of Disperse Systems of Spherical Particles in Polystyrene Solution at Long Time‐Scales

Abstract: The dynamic and steady flow properties of disperse systems of styrene–divinylbenzene copolymer particles in a polystyrene solution have been measured over wide ranges of frequency, shear rate, and strain amplitude by means of a cone‐and‐plate type rheometer. The main results may be summarized as follows. 1) These systems show Newtonian behavior at extremely low rates of shear, that is, the apparent viscosity is approximately constant. This fact indicates that the systems have no yield stress, although they appear to show one if only the behavior at high shear rates is considered. 2) They show linear viscoelastic behavior at strain amplitudes less than 0.5%, but striking nonlinearities at larger strains. However, at very long time‐scales, these systems are linearly viscoelastic and independent of the strain amplitude. 3) The nonlinear viscoelastic functions G1′ and G1″ decrease with increasing strain amplitude, but they are almost independent of strain for strains larger than 50%, over the entire frequency...

Development of an extrusion rheometer suitable for on‐line rheological measurements

Abstract: A new type of extrusion rheometer has been designed which employs dual slit geometry with a double valve. The double valve concept allows a change in flow rates through the slits, while the total extruder flow rate remains constant thus leaving extruder operating conditions unchanged. Electronic pressure transducers are mounted along the slit to record axial pressure distribution. Flow rates are measured by weighing polymer output and wall shear stresses are calculated from the axial pressure profiles. Exit pressures are derived from extrapolating the pressure profile to the slit exit and from this information the normal stresses can be determined.

Dynamic properties of some polymer solutions subjected to a steady shear superimposed on an oscillatory shear flow

Abstract: Measurements in which a steady shear flow is superimposed on a small amplitude oscillatory shear flow were performed by means of aWeissenberg Rheogoniometer. Solutions of polystyrene and poly-(ethylene oxide) in Acroclor-1248 and also ethylcellulose in a solvent mixture were investigated. By means of special electronical devices we were able to measure accurately at low frequencies when high rates of shear were superimposed. In this range of frequencies and rates of shear, the following effects were noticed for all the investigated solutions: the dynamic viscosity, as a function of the frequency, shows a minimum, the phase shift between the oscillatory stress and strain increases with the increase of the rates of shear even to values larger than 90°, therefore the real part of the dynamic modulus (G′) becomes negative.

Rheological measurements on two uncrosslinked, unfilled synthetic rubbers

Abstract: For two uncrosslinked rubbers (EP and polybutadiene) measurements of viscosity, velocity profiles and flow birefringence in stationary shear flow are compared with dynamic moduli for oscillatory shear in the linear region. At a low temperature (20°C) slip at the wall was sometimes found, but not at higher temperatures (above 70°C). The flow behaviour of the two rubbers at higher temperatures does not differ essentially from that of thermoplastics such as polyethylene or polystyrene. The dynamic shear moduli can give a fair prediction of normal and shear stresses in stationary shear flow.

Nonlinear viscoelasticity of polystyrene solutions. II. Non-Newtonian viscosity

Abstract: The steady shear viscosity η(k) and the stress decay function (the shear stress divided by the rate of shear k after cessation of steady shear flow) were measured for concentrated solutions of polystyrene in diethyl phthalate. Ranges of molecular weight M and concentration c were 7.10 × 105 to 7.62 × 106 and 0.112–0.329 g/cm3, respectively. Measurements were performed with a rheometer of the cone-and-plate type in the range 10−4 τ2 > …, and the values of τ1, τ2 η1 and η2 were determined for some solutions. The relaxation times τ1 and τ2 were found to be independent of k and equal to the relaxation times of linear viscoelasticity. At the limit of k → 0, η1 and η2 were approximately 60 and 20–30%, respectively, of η and the non-Newtonian behavior was due to large decreases of η1 and η2 with increasing k. It was shown that η1(k) may be evaluated from the relaxation strength G1(s) for the longest relaxation time of the strain-dependent relaxation modulus with a constitutive model for relatively high c–M systems as well as for low c–M systems.

Further Studies of Fluid Nonlinearity: The Orthogonal Rheometer and the Oscillating Sphere

Abstract: Nonlinear effects have been considered in computations of orthogonal rheometer flow and in flow caused by the oscillation of a sphere in an unbounded fluid. Predictions of fluid response, based on a Bird‐Carreau constitutive model, are qualitatively different from those which follow from linear theory. Of particular interest are the corrections to force components in the orthogonal rheometer analysis and the generation of a steady secondary flow in the oscillating sphere problem. Magnitudes of these nonlinear effects are presented for a variety of fluid and flow parameters.

A rotational rheometer with a drag‐cup torque transducer

Abstract: A rotational cone-and-plate rheometer incorporating a drag-cup torque transducer and a frictionless, wire suspension has been designed and constructed. The instrument design provides for a controlled atmosphere for the sample, including anhydrous conditions necessary for studies on solutions of polymers in strong acids. The rheometer can be used to determine the shear deformation in response to an applied stress, including creep, recovery, and the shear stress in response to an applied steady shear. Both transient and steady-state measurements are possible. Illustrative examples of the instrument performance are given.

A new approach to capillary extrusion rheometry

Abstract: . A capillary extrusion rheometer has been developed which circumvents many of the problems of traditional hypodermic principle rheometers. The capillary is enclosed in a hollow plunger driven at a series of fixed rates into a barrel containing the test sample. Drawbacks observed with traditional viscometers have been obviated, for example, entrapment of air between the sample and the plunger leading to gas compression effects, gross motion of the fluid in the barrel leading to fluid structure breakdown and difficulties in determining plunger/barrel friction contributions. With strict temperature control, it has been shown that absolute values for fluid flow properties could be determined on small samples quickly and easily with an accuracy of ±0.5%.

Studies of time effects in the flow of polymer melts using a biconical viscometer

Abstract: The variation of viscosity of various polymer melts under constant shear rate conditions has been investigated using a biconical viscometer, a cone-plate viscometer, and a capillary rheometer. The validity of the biconical viscometer edge-zone correction was investigated. Comparisons between the three types of viscometer showed that sample fracture at the material boundary contributed to the decrease of viscosity with time of shearing occuring in the cone-plate viscometer. Polymer melts are subjected to hydrostatic pressure within the biconical viscometer and fracture appears to be prevented. Shear stress–shear rate–time relationships were obtained for the materials studied with the biconical viscometer at shear rates up to a few reciprocal seconds. There was good agreement with capillary data at high shear rates and cone-plate data at low shear rates. A recoverable decrease of viscosity with time of shearing was found to occur. Both the fractional decrease in viscosity and the time taken to recover the original viscosity become smaller as the temperature is increased.

An improved Couette high shear viscometer

Abstract: The advantages of theCouette-type concentric cylinder viscometer have been cited for making viscosity measurements at high shear rates. Significant improvements in theBarber design are described which have resulted in the development of an instrument which can make measurements under laminar shear conditions at over several decades of shear rate. The range is over twice that of previous instruments demonstrating the achievement of shear rates to above 1 000 000 sec−1, and with minimum viscous heating and over a temperature range of over 100°C.

Influence of machine stiffness and shear rate on the friction behaviour of rock joints

Abstract: A new servo-controlled shear testing machine is described, which eliminates the influence of the stiffness of the testing machine The results of friction tests conducted on conventional shear machines are compared with those obtained with the new machine Further a dependence of frictional resistance on shearing rate is demonstrated

The flow behavior and impact strength of poly(butylene-terephthalate) as a function of several processing variables

Abstract: The flow behavior of poly (butylene-terephthalate) (PBT) has been investigated using a capillary extrusion rheometer. The behavior was measured as a function of temperature, moisture content, and residence time of the molten polymer in the rheometer barrel. The temperature and moisture dependence of PBT are compared with polycarbonate. The notched Izod impact strength of injection-molded PBT is also reported as a function of moisture content and residence time at processing temperatures.

Rheology of Lubricants in Real Bearing Contacts

Abstract: Experimental traction-slip and lubricant film-thickness data have been determined for selected lubricants to provide information for use in conjunction with the design of lubricated machine elements. The traction-slip experiments were performed using a rolling-disk rheometer which closely simulates those conditions existent in real lubricated contacts; the film-thickness data were obtained using an X-ray technique. The range of experimental conditions included two rolling speeds (5000 and 10,000 rpm), several contact pressures [(690 – 2400 MN/m2 ) (100 to 350 ksi)], and three temperatures [(338, 366 and 423 K) (150, 200, and 300 F)]. The slip conditions imposed on the lubricants ranged as high as 6 m/s (1200 fpm) which is equivalent to a shear rate of approximately 0.5 × 108 sec−1 . Interpretative analyses have been developed to infer basic lubricant properties from the experimental data. These analyses include time delay parameters and “dynamic” pressure-viscosity parameters. The analytical treatment of the data provides: (1) a generalization of the experimental data to apply over a wider range of conditions than those actually covered, and (2) a basis for comparing lubricants and obtaining a more fundamental understanding of lubricant behavior.

Shear flows of a liquid with a power-type rheological law in the presence of a constant transverse velocity component

Abstract: Plane shear flows of dilatant liquids are considered in the presence of a constant transverse velocity component of the liquid; this component arises from uniform injection (or suction) at the bounding surfaces. It is shown that the presence of transverse drift in the liquid influences the rate of propagation of the leading edge of the shear waves, and this has a number of effects on the flows.

Continuous recording of flow curves on a capillary rheometer using a new pressure transmission element

Abstract: In the capillary extrusion rheometer described, the speed of the hydraulically driven plunger and the pressure at the capillary wall are transmitted to the input terminals of an X-Y recorder. Continuous speed control of the driving unit enables automatic registration of the dependency among the consistency variables Gamma , tau in the range Gamma =0-3000 s-1, tau =0-2*104 Nm-2. A novel concept of a strain gauge transducer allows measurement of axial pressure profiles without disturbing the inner wall of the capillary with pickup holes.

Evaluation of Rheological Properties of Flame Fuels Using a Capillary Extrusion Rheometer

Abstract: : This report describes a research effort to develop methods to study the flow properties, such as viscosity and elasticity, of polymer solutions used as flame agents. Viscosity of the polymer formulations were studied at -3.89 C and 23.9 C using a capillary extrusion rheometer. Several brands of gasoline were used to prepare the polymer solutions, which gave varied flow curves under increased shear stresses. The flow curves exhibited considerable variation when different brands of gasoline were used to prepare the polymer solutions. The capillary length and die swell methods were used to study the elastic properties of the polymer solutions.

Some examples of the use of body coordinate systems in the kinematics of continuous media

Abstract: A detailed account of the usefulness of a bodytensor formalism in rheology has been given byLodge (1975). Here, we outline some of the more important results concerning shear flows and motions with constant stretch history (M.C.S.H.). We then discuss the relation between M.C.S.H. and the concept of a “perpetual rheological history” (P.R.H.) introduced byOldroyd (1965) and conclude that they are equivalent. The body-tensor formalism is applied to specific situations of practical interest, including certain new rheometers and an important class of nearly-viscometric flows. In much of the work, we use suitably chosennon-orthogonal coordinate systems. New results include (i) a method for deciding whether any given flow is a M.C.S.H. or not, and (ii) a proof that ‘Balance Rheometer Flow’ is not a M.C.S.H.

Viscosity of a Number of Oils Measured under Various Shear Stresses.

Abstract: : The viscosity of a number of oils has been found to fall at very high shear stresses over a large range of pressures. A limiting shear stress effect has been deduced. (Author)