Showing papers on "Rheometer published in 1978"

Studies on structural foam processing I. The rheology of foam extrusion

Abstract: An experimental study was carried out to investigate the flow behavior of gas-charged molten polymers in foam extrusion. For the study, a rectangular slit die with glass windows was constructed to permit visual observations, from the direction perpendicular to flow, of the dynamic behavior of gas bubbles when a gas-charged molten polymer flows between two parallel planes. Pictures were taken of gas bubbles in the flow channel with the aid of a camera attached to a microscope, and these were later used to determine the position at which gas bubbles start to grow. Using three melt pressure transducers mounted on the short side of the rectangular slot, pressure distributions were measured along the longitudinal centerline of the die. The polymeric materials used were high-density polyethylene and polystyrene, and the chemical blowing agents used were a proprietary hydrazide which generates nitrogen, and sodium bicarbonate which generates carbon dioxide. It was observed that the gas-charged molten polymer shows a curved pressure profile as the melt approaches the die exit, whereas the polymer without a blowing agent shows a linear pressure profile. The visual observations of the bubble growth in the flow channel, together with the pressure measurements, permitted us to determine the bubble inflation pressure, often referred to as the critical pressure for bubble inflation. It was found that the critical pressure decreases with increasing melt extrusion temperature, and increases with increasing blowing agent concentration. It was also found that the bulk viscosity of gas-charged molten polymers decreases with increasing blowing agent concentration and with increasing melt temperature. A general remark is made concerning the precaution one should take when an Instron rheometer is used for determining the bulk viscosity of gas-charged molten polymers.

Nonlinear shear creep and constrained elastic recovery of a LDPE melt

Abstract: Shear creep and constrained elastic recovery experiments on a well characterized low-density polyethylene melt are reported. The temperature dependence of the shear strain and the primary normal stress difference is discussed in detail. Comparison is made with predictions of a strain-dependent single integral constitutive equation, which has already been successfully used for the same polymer melt to describe the stress growth after sudden imposition of a constant shear rate flow and stress relaxation after cessation of steady shear flow. It should be emphasized that this constitutive equation contains no adjustable parameters. The linear-viscoelastic part of the memory function is related to the linear-viscoelastic relaxation spectrum, while the nonlinear, strain-dependent part was determined from rapid-strain experiments. In the case of a prescribed shear stress history the resulting integral equation cannot be solved by closed integration but has to be inverted by numerical methods. Agreement between theoretical predictions and experimental data is rather encouraging for shear strain and primary normal stress difference during creep and retardation tests. Within experimental error, the strain and shear rate dependence of the recoverable portion of the total strain can be correctly predicted.

Observations on shear-induced textures and rheology of a smectic-A phase

Abstract: Observations are reported of the behaviour of a smectic-A liquid crystal, 4-n-octyl-4’-cyanobiphenyl (8CB), as it is sheared in two geometries. In the first an initially-homeo-tropic sample is sheared in a planar shear flow cell, and it is observed that the shear creates textures which resemble those caused by dilating a smectic. The same textures are seen in the second geometry, where the sample is placed in a transparent cone-and-plate rheometer. The apparent viscosity of the smectic material measured in this geometry is found to increase with the fraction of the sample which contains a certain disordered focal conic texture induced by the shear. It appears that the presence of this texture gives the smectic a finite yield stress.

The extensional flow capillary as a new method for extensional viscosity measurement

Abstract: THE behaviour of non-newtonian fluids in extensional flow is of both theoretical and practical importance. However, because of the difficulty of imposing a purely extensional deformation on a fluid material, very few experimental measurements of extensional viscosity have been obtained in well defined kinematic conditions. All of the experimental techniques currently available which utilise constant extension rate kinematics involve the application of a tensile stress to a cylindrical sample, and thus require the assumption of uniform deformation of material which is bounded by a free surface. These techniques are applicable only for very high viscosity materials (> 105 P), and are difficult to use in the study of materials whose resistance to extensional deformation is ‘tension thinning’ because of a tendency of the sample to neck and fail. We describe here an extensional flow capillary rheometer which we have evaluated for the measurement of extensional flow properties of a wide variety of materials over a broad range of extension rates. Recent discussion1 of a ‘speculative rheometer’ of apparently similar design emphasises the value of such a device.

Extensional Rheometers for molten polymers; a review☆

Abstract: The various techniques which have been devised to study uniform stretching flows in molten polymers are described briefly, and their advantages and disadvantages are noted. Techniques involving non-uniform deformation such as melt spinning and converging flows are not included as these are not subject to unambiguous interpretation in terms of traditional material functions. Uniaxial extensiometers are either of the controlled stress or controlled strain-rate types. End effects, non-uniformities in temperature and deformation, measurement of very small forces, and limitations on maximum strain are the principal experimental problems. A recent design which seems to keep the effects of these difficulties within reasonable bounds is to be manufactured commerically in the near future. Techniques for the study of biaxial extension have all been based on the inflation of a flat sheet of polymer into a contour approximating a spherical cap. Only one of these techniques is suitable for the study of melts with viscosities less than 105 Pa s. An additional method has been proposed which involves the compression rather than stretching of a sheet. Finally, procedures for generating planar extension (“pure shear”) and more general extensional flows are described.

Viscosity, modulus, and die swell of glass bead filled polystyrene-acrylonitrile copolymer

Abstract: Flow curves were obtained at 190°C over the shear rate range 0.1 to 100 sec−1 for polystyrene-acrylonitrile copolymer containing up to 36 percent by volume glass beads, using a capillary extrusion rheometer. The addition of glass beads always increased shear stress and viscosity at a given shear rate, with the increase being more pronounced at low shear rates. The addition of glass beads decreased die swell, which also depended on shear-stress and capillary length-to-radius ratio. At low shear rates a lower limiting value of die swell ratio of about 1.1 was achieved. Values of recoverable shear derived from end correction data by the technique of Philippoff and Gaskins and from die-swell data by the method of Bagley and Duffey are compared. A fairly good agreement was found for low concentration blends at low shear, However, the values differed by a factor of up to 3 at higher shear stresses. In all cases, recoverable shear was found to increase with shear stress at a fixed filler loading and to decrease with increased filler loading at a fixed shear stress. Values of shear modulus calculated from the recoverable shear measurements decreased rapidly with increasing shear stress.

Mechanical spectroscopy of colloidal dispersions

Abstract: The mechanical properties of colloidal dispersions are closely related to their stability parameters. Unfortunately, the rheological characteristics which are normally used, such as viscosity and static elasticity, measure the global behaviour. It is extremely difficult to extract from such characteristics detailed information about the structure. Therefore, there is a need for more adequate experimental techniques.The construction and the potential applications of a rheometer, in which an oscillatory movement is superimposed perpendicular to a steady shear flow, are discussed. Measurements on carbon black dispersions are carried out, and the relaxation spectra obtained for the sheared dispersions are compared with theoretical predictions based on a chain-like structural model. In this way, information concerning interaction forces and structural parameters is obtained.

A study of melt density of flowing linear polyethylene

Abstract: Linear polyethylene was extruded from a capillary rheometer with the driving piston operated at fixed speed and at fixed pressure. Apparent viscosity and melt density were measured in both extrusion modes. Apparent density decreased at shear rates approaching the melt fracture region in fixed piston-speed operation. Flow of other polymer melts was essentially incompressible in fixed piston-speed operation, and all polymers exhibited incompressible flow in fixed-pressure extrusion. The oscillating portion of the flow curve of linear polyethylene reflects alternating periods in which the polymer exits faster and slower than the rate at which the advancing piston clears the rheometer reservoir. Linear polyethylene behaves differently from most other polymers in fixed piston-speed extrusion and during melt fracture because of the existence of a more extensive entanglement network in the melt. It is suggested that melt fracture in general results from a tensile failure of the entanglement network, which may occur at the die inlet and in the orifice.

European Activity Concerning Engine Oil Viscosity Classification –Part III

Abstract: As a follow up to earlier publications, this paper reports on recent work carried out in Europe, within CEC, in the field of high shear rheology aimed at defining a simple method to measure viscosity as seen by the engine. Seven SAE 15W-50 calibration oils were tested in a large number of high shear viscometers, engine tests and rigs in order to determine if any correlation was possible. The work has shown that the low shear viscosity does not correlate with the behaviour of the oil in the engine and that the viscosity under high shear conditions is from 70 to 90% of the low shear viscosity. Correlation was found between high shear viscometers and power loss/oil-flow in engines. Further work on lower viscosity oils is underway.

Nonlinear Viscoelastic Properties of Very Dilute Drag Reducing Polymer Solutions

Abstract: Viscous and elastic rheological properties of three very dilute solutions (100 to 500 parts per million) of a polyacrylamide in distilled water which exhibit drag reduction in turbulent flow were determined. Apparent viscosity and first normal stress difference functions were determined using a Weissenberg rheogoniometer over a shear rate range of approximately 10−2–1500 sec−1. In addition, transient response characteristics were determined using a specially designed transient rheometer modified for increased resolution. A relatively simple five‐parameter nonlinear integral constitutive equation which was consistent with all steady and unsteady measurements was used to correlate the data. For comparison, Carreau's seven‐parameter model B, which has previously been found to be appropriate for such solutions, was also evaluated for its ability to represent the observed data. Although capable of a precise representation of the steady shear and normal stress data, this model is incapable of qualitative repres...

An Improved Rheometer Design Used to Measure Viscoelastic Properties of Polymer Melts

Abstract: A fixture consisting of a bob and a special cup was developed to ease the charging of polymer melt to the gap of a concentric‐cylinder rheometer Dynamic measurements with the improved rheometer for two polyolefins below melt temperatures were compared with results obtained on the Rheovibron and the torsion pendulum Shear moduli were generated for polypropylene, polyethylene,and poly(vinyl chloride) melts by oscillating the bob in the axial mode at amplitudes effecting relatively large strain Bob oscillations in the rotational mode were also investigated The phase angles and complex shear moduli differed slightly for different modes of oscillation At strains of 9%, the time‐temperature shift factor αT remained constant throughout the test‐frequency range for an isotactic polypropylene However, αT increased with increasing frequency for strains of 98% A time‐strain shift factor, αe, was found to satisfactorily superimpose polypropylene moduli data generated at high and low strain levels

Workability of flowing concrete. assessment by a free orifice rheometer

Abstract: Increased use of fresh very high workability concrete mixes in general construction practice has led to investigations into better 'on-site' methods of assessing its workability. The author describes a method using a free orifice rheometer to measure the rate of flow of the fresh mix. The design of the rheometer and its method of use are discussed in detail. A vertical casing pipe of constant diameter could not be used because a layer of cement paste or mortar would form along the inner surface of the pipe acting as a lubricant. The influence of the content of cement paste and the proportion of fine aggregate on the flow times was investigated experimentally. The results showed an optimum 50 per cent fine aggregate content of the total aggregate used. The influence of a plasticiser on flow times is also investigated. No correlation was found between rheometer flow times and initial spreads measured on the German flow table. The effect on rheometer sensitivity of orifice diameter and the influence of the time interval between the addition of water and the test results are also described. /TRRL/

Stability of coal-oil mixtures

Abstract: The settling behavior of both stabilized and nonstabilized coal-oil mixtures was investigated Thirteen stabilizers were tested under standardized conditions Several were found to be partially effective for the coal-oil combination studied The majority provided no improvement over the nonstabilized mixture and, in fact, decreased the stability in some cases The studies of nonstabilized mixtures considered five different oils and several coal concentrations Some effect, due to oil type, was found A fifty percent mixture was found to be stable in the oil used for the stabilizer tests Measurements of the shear stress/shear rate relationship were made for the oils and mixtures studied, using two types of viscometers: a concentric-cylinder device and an extrusion rheometer These data were used to examine the role of viscosity in establishing the settling rates found for the nonstabilized mixtures tested The viscosity data are also of value in predicting pressure drop in pipeline flow and may be used, in conjunction with the settling curves, to compare simple models of sedimentation, ie, free, hindered, compressive, to identify the mechanisms of settling in coal-oil mixtures

Prediction of diallyl phthalate molding performance from laboratory tests III. Correlation of data from capillary extrusion rheometer, mechanical spectrometer and differential scanning calorimeter

Abstract: The purpose of this work was to determine if capillary extrusion rheometer and mechanical spectrometer data can be used to predict the molding performance of a commercially available diallyl phthalate (DAP) compound. In addition, differential scanning calorimetry (DSC) curves of “good” and “bad” batches were statistically analyzed in order to determine if the DSC peak shape is related to the molding performance. It was found that the data obtained from all three techniques correlate very well with the molding behavior of the DAP material studied. Capillary rheometer and mechanical spectrometer results show that lower melt viscosities and lower curing rates are desirable for obtaining satisfactory molding performance. The mathematical moments analysis of DSC curves indicates that DAP batches which molded well give peaks of fairly high symmetry, while all peaks of “bad” batches are skewed to the left. The center of gravity of the former is at a higher temperature and the variance is smaller than the corresponding values of “bad” compounds.

양갱의 물성(物性)에 관한 연구 - 제1보 양갱의 점탄성(粘彈性) -

Abstract: 【Rheological properties of Yangeng were studied by compression test with rheometer. The viscoel-asticity changed at strain 0.22 at the tested rate of strain. The optimum temperature and solid content for structure formation were $40^{\circ}C$ and Brix 70 respectively. The time-temperature dependency of rheological properties were empirically formulated.】

Rheometer and uses thereof

Abstract: A rheometer comprises adjacent surfaces moveable relative to one another e.g. a pair of rollers, means e.g. a motor for moving one or both surfaces and means for measuring the effect of or on the movement when a sample under test e.g. a sheet moulding composition is placed between and in contact with the surfaces.

The Characterisation of Viscous Flow. Viscosity, Shear Rate and Shear Stress

Abstract: When considering flow characterisation in what are commonly regarded as liquids it becomes necessary to examine a number of variables. The overall characterisation is attained when all the relationships—including the interdependent cross-relationships—of an all-embracing rheological equation have been evaluated. The most general rheological equation is $$\eta = F\left( {\gamma ,T,t,P,c,...} \right)$$ where η = coefficient of viscosity, ẏ = shear rate (itself a function of the shear stress), T = temperature, t = time, P = pressure (itself a function of volume), c = concentration, and where the multiple dots which follow include, for example, molecular parameters such as molecular weight (MW), molecular weight distribution (MWD), compositional variables such as crystallinity, the presence of additives (plasticisers, fillers, slip agents, mould release agents, pigments and dyes, stabilisers, products of decomposition and other impurities) and factors which relate to the processing history (orientation, residual stresses, etc.). Clearly such an equation is unrealistic and we shall therefore consider each of the principal variables in turn, assuming that the others remain constant.

Homogenisation of viscous liquids with different properties - by passing through oscillating shear field with specified frequency and shear stress

Abstract: Thick liquids are blended and homogenised by continuous passage through varying shear field. Here they are subjected to a shear frequency of 5 to 1000 Hz with a shear stress of >=103 N/m2. The portion of liquid subjected to shear at any moment should not exceed a total volume of 1-40%. The high shearing follows a zone of relaxation. The ratio of through put to shearing surface is 5.103 to 25.103 kg/m2h. The viscous liquid can contain up to 80% wt. of dispersed solids, and chemical reactions or crystallisation can occur during the process.

Mechanical spectroscopy of colloidal dispersions

Abstract: The mechanical properties of colloidal dispersions are closely related to their stability parameters. Unfortunately, the rheological characteristics which are normally used, such as viscosity and static elasticity, measure the global behaviour. It is extremely difficult to extract from such characteristics detailed information about the structure. Therefore, there is a need for more adequate experimental techniques.The construction and the potential applications of a rheometer, in which an oscillatory movement is superimposed perpendicular to a steady shear flow, are discussed. Measurements on carbon black dispersions are carried out, and the relaxation spectra obtained for the sheared dispersions are compared with theoretical predictions based on a chain-like structural model. In this way, information concerning interaction forces and structural parameters is obtained.

Dispersion of particulate additives in rubber using the batch operated internal mixer : a study of flow behaviour and properties of rubber mixes

Abstract: As an aid to understanding the mechanics of mixing in an internal mixer laboratory scale trials have been carried out using a mixer having a transparent plastics chamber. The use of a transparent rubber and coloured 'markers' then permitted direct viewing of the characteristic flow patterns deriving from the use of three fill factors. These mixing trials have indicated the rheological properties which must be measured in order to predict the mixing behaviour of a rubber. Also considerable information is contained in the visualisations which will aid further work into control and instrumentation strategies and into fundamental design/mathematical modelling studies. A laboratory Banbury mixer and Brabender Plastograph are used to prepare the rubber compounds which are then characterised for the dispersion of compounding ingredients. For carbon black dispersion studies several techniques are employed. Capillary rheometry is used to study their stress-strain rate relationships and to obtain die swell, shear and tensile properties. Creep and elongational tests are also carried out on uncured mixes. In addition measurements on Mooney viscometer, Monsanto rheometer and analysis of bound rubber are made. These tests for filler dispersion are supported by microscopic examination of microtomed sections. Work is also geared to examine properties that are not only sensitive to changes in levels of carbon black dispersion but also that which are readily measured and can be used in industry. Measurements of mechanical phase angle and electrical resistivity are considered. Dispersion of non-black compounding ingredients is studied by X-ray microradiographic technique and the analysis of vulcanisate properties. To relate the performance of the Plastograph and Banbury mix the concept of mixing energy per unit volume of material is used.