An automated high pressure capillary rheometer with hydraulic drive

A new capillary rheometer design is described, in which a hydraulic device is used to produce the pressure driving the sample fluid through capillaries. The device is fully automated and controlled by a PC unit. Various measuring modes can be preselected and are automatically executed. Some preliminary results with New tonian fluids and with polymer solutions show the functioning of the new rheometer.     

Dynamic rheological behavior of polypropylene melts with pulsatile pressure flow in a dynamic capillary rheometer

A self‐made dynamic capillary rheometer (DCR) was designed to investigate the dynamic viscoelastic characteristic of polypropylene (PP) melt during the pulsatile pressure extrusion. A vibration force field was parallel superposed upon steady shear flow in this DCR by means of a vibration driven piston. During the pulsatile pressure extruding process in DCR, the PP melt displayed apparent viscoelasticity. The experiment results proved the pressure pulsatile extrusion could reduce the viscosity of polymer melts effectively. The phase difference between the shear stress and the shear rate decreased with the superposed vibration. But, at large amplitude conditions, the viscosity has an increasing tendency. This maybe illuminated that large amplitude could be harmful for the vibration‐assistant polymer processing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1834–1838, 2006     

毛细管流变仪在聚烯烃加工中的应用

采用毛细管流变仪测定聚烯烃的流变行为,得到一系列剪切速率与剪切应力、剪切速率与剪切黏度的流变数据.利用该流变数据可进行专用料配方优化及加工条件筛选等工作,同时,还根据不同批次产品的流变曲线的偏离情况,监控产品质量。     

Measurement of the pressure dependence of viscosity of polymer melts using a back pressure‐regulated capillary rheometer

The effect of pressure on the melt viscosity was experimentally investigated for five polymers: polycarbonate (PC), acrylonitrile‐butadiene‐styrene (ABS), polystyrene (PS), polypropylene (PP), and low‐density polyethylene (LDPE). Measurements were carried out using capillary rheometer modified to allow regulation of back pressure. To enable correction for the entrance pressure drop, two round‐hole dies were used: a 1‐mm diameter die of length 10 mm and an orifice die of the same diameter. For determining the pressure coefficient from the experimental viscosity data, time‐pressure superposition was applied to generate a master curve to which the Carreau‐Yasuda model was fitted. The resulting pressure coefficients revealed that for the polymers studied the order of the degree of the pressure dependence is as follows: PS > ABS > PC > PP > LDPE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Determination of true flow curves from capillary rheometer data

The evaluation of polymer melt viscosity versus shear rate has been customarily done by a time-consuming graphical method, which corrects for non-Newtonian behavior and pressure losses at flow transitions. It is shown by mathematical analysis that the flow data in terms of applied pressure and apparent shear rate can be treated by a semigraphical method, in which calculation of the true flow curve can be done with a computer. Moreover, it is possible in some cases to program the data treatment entirely for computer calculation. Results obtained by the proposed method are in excellent agreement with those obtained by the older graphical method.     

Rheological properties of carbon mixes at low shear rates using a capillary rheometer

A capillary rheometer is used to measure the rheological properties of green carbon mixes consisting of petroleum coke and carbon black as filler and pitch tar as binder. It has been shown that in the low shear rate range (0·3 to 2·0 sec^?1), the carbon mixes behave as Bingham body with yield stress of 6 × 10⁵ dyn/cm² and plastic viscosity of 2 × 10⁶ poise.     

An experimental study of flow patterns in polymer fluids in the reservoir of a capillary rheometer

Flow patterns in the reservoir of a capillary rheometer have been measured for several different polymer fluids including low density and high density polyethylene, polystyrene, polymethyl methacrylate, polypropylene, nylon 66, polybutadiene and a polyisobutylene solution. Measurements have also been made on glycerine. The experimental results are interpreted in terms of the theory of viscoelastic fluids and the dependence of the flow patterns upon the Weissenberg number is considered.     

Steady flow and dynamic viscoelastic behavior of nylon 1313 using parallel‐plate rheometer and capillary rheometer

In this study, a novel nylon with long alkane segments (also called nylon 1313), which was synthesized using 1,13‐tridecanedioic acid in our laboratory, has been characterized. Different rheological behaviors of nylon 1313 have been presented using steady shear, creep recovery, and dynamic tests. The time‐temperature effects have also been investigated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1643–1651, 2005     

The application of a capillary extrusion rheometer to the determination of the flow characteristics of lard

A capillary extrusion rheometer was designed, and techniques were developed to obtain basic information on the flow behavior of lard. Since constant and adjustable shearing rates are a necessary feature for the study of the basic rheological behavior of a material, the rheometer was designed for use in conjunction with a tensile tester having a wide selection of crosshead rates. Techniques were developed for accurately measuring the flow variables and for treating the data. A comparison study on a Newtonian liquid sample proved the validity of the approach. Lard at 23.4C was tested, and its flow parameters (fluid-consistency index and flow-behavior index or degree of non-Newtonian behavior) were obtained. Presented at the AOCS Meeting, Cincinnati, October 1965. E. Utiliz. Res. Dev. Div., ARS, USDA.     

Wall slip and compressibility like effects in capillary rheometer tests on complex polymer systems

Abstract

Using an appropriate set of capillary dies, the applicability of the Mooney wall slip method has been investigated with several filled compounds. Inconsistent results were obtained, for example, ‘negative’ slip velocity. With respect to data measured in practical capillary rheometry, a model was developed for treating (barrel) pressure data versus die length/diameter ratio at fixed applied apparent shear rate, i.e. the so called Bagley plots. A very simple equation was obtained

P _meas = 2P _ends - 1/β ln [exp (P _ends β) - 4σ_w0 β L/D ]

which yields the wall shear stress at zero pressure σ_w0 , the ends pressure loss P _ends , and a factor β when fitted to experimental data by non-linear regression. Experimental results show that the factor β accounts for both wall slip and compressibility like effects. Negative β values indicate dominating wall slip effects, while positive values demonstrate compressibility like effects. Slip velocity is thus pressure dependent and consequently the combination of wall slip and a pressure dependent viscosity can mask the expected gap dependence in the analysis by Mooney.     

Rheological properties of carbon mixes at very low shear rates using a capillary rheometer—III

A capillary rheometer has been used to determine the rheological properties of carbon mixes consisting of petroleum coke as filler and coal tar pitch as binder. It is shown that carbon mixes behave as Bingham materials with definite yield stresses. The yield stress was found to be a general property of all carbon mixes and its value is independent of the size of the capillary die. It was also seen that extrusion at low shear rates through big diameter capillaries results in slipflow. The slipflow occurs when the applied stress is somewhat below the yield stress, the material then extrudes without the formation of a core which otherwise would cause cracks in the product after baking. This explains why big diameter rods are generally extruded at very low speeds in usual manufacturing process. The modified Buckingham-Reiner equation has been applied to the case of slipflow and the values of yield stress and plastic viscosity calculated. These values agree well with those obtained from the consistency curve.     

Study of polymer powder and melt rheology using a constant pressure,non-isothermal rheometer

A rheological analysis is proposed on a non-conventional, constant pressure, non-isothermal rheometer. The test usually starts with a polymer powder and ends with melt extrudate. The volume- (or displacement of plunger) temperature curve of the test is analyzed according to the following model: (1) at a temperature below the glass transition temperature, the test is related to the packing and/or compaction of powders, and also the compressive deformation of powders; (2) as the temperature is raised to where polymer flow begins, the test is analyzed according to melt viscous flow. The activation energy of flow of a polymer may also be estimated using this rheometer. Comparison and correlation of data using other techniques (e.g. torsional pendulum dynamic measurement, capillary rheometer, Rheometric dynamic spectrometer) will also be discussed.     

Flow visualization and extrudate swell of natural rubber in a capillary rheometer: Effect of die/barrel system

An investigation was carried out to examine the effect of die/barrel system on the flow patterns and extrudate swell of natural rubber in the barrel of a capillary rheometer, using a colored tracer as the visualization technique. The capillary rheometer used in this work had two dies located along the barrel, which is novel in rheometer design. The flow of the rubber in the upper barrel was dependent on the piston/barrel action and changed with piston displacement, whereas the complexity of the flow in the lower barrel was dependent not only on the piston displacement, but also on the geometry of the upper die design. The flow patterns that developed in the whole barrel were independent of the die located at the bottom of the barrel. In addition, the change in extrudate swell was associated with the flow occurring in the barrel, residence time, elastic characteristic, and the temperature rise during the flow. It was concluded that the general style of the flow patterns of natural rubber was greatly dependent on the die geometry that the material had previously moved past. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2525–2533, 2001     

Flow analysis of natural rubber in a capillary rheometer. 1: Rheological behavior and flow visualization in the barrel

Capillary rheometers have been widely used in the study of the rheological behavior of thermoplastics but their application to rubber has so far been limited. An investigation was therefore carried out to determine the effect of mastication and temperature on the rheological properties of natural rubber using a capillary rheometer. The flow of the rubber in the barrel of the capillary rheometer was observed at various test conditions such as die geometry, piston speed, and test temperature using layers of pigmented rubber compound, this involving the use of a split barrel system. It was found that the flow patterns in the barrel of the capillary rheometer used were very complex and were a function of piston displacement.     

A parallel coextrusion technique for simultaneous measurements of radial die swell and velocity profiles of a polymer melt in a capillary rheometer

This article proposes a new experimental technique to simultaneously measure radial die swell and velocity profiles of polystyrene melt flowing in the capillary die of a constant shear rate rheometer. The proposed technique was based on parallel coextrusion of colored melt‐layers into uncolored melt‐stream from the barrel into and out of the capillary die. The size (thickness) ratio of the generated melt layers flowing in and out of the die was monitored to produce the extrudate swell ratio for any given radial position across the die diameter. The radial velocity profiles of the melt were measured by introducing relatively light and small particles into the melt layers, and the times taken for the particles to travel for a given distance were measured. The proposed experimental technique was found to be both very simple and useful for the simultaneous and accurate measurement of radial die swell and velocity profiles of highly viscous fluids in an extrusion process. The variations in radial die swell profiles were explained in terms of changes in melt velocity, shear rate, and residence time at radial positions across the die. The radial die swell and velocity profiles for PS melt determined experimentally in this work were accurate to 92.2% and 90.8%, respectively. The overall die swell ratio of the melt ranged from 1.25 to 1.38. The overall die swell ratio was found to increase with increasing piston speed (shear rate). The radial extrudate swell profiles could not be reasoned by the shear rate change, but were closely linked with the development of the velocity profiles of the melt in the die. The die swell ratio was high at the center (～1.9) and low (～0.9) near the die wall. The die swell ratio at the center of the die reduced slightly as the piston speed was increased. Polym. Eng. Sci. 44:1960–1969, 2004. © 2004 Society of Plastics Engineers.     

FEM calculations of capillary rheometer flow for carbon‐filled liquid crystal polymer composites

There is an emerging market for conductive resins for use in fuel cell bipolar plates. This research focuses on developing a finite element model of a capillary rheometer. Comsol Multiphysics 3.2b was used to model the flow of a remeltable thermoplastic matrix material, Vectra A950RX Liquid Crystal Polymer, with varying amounts of either a carbon black or synthetic graphite filler, to obtain the velocity profile and pressure drop of these composites within the capillary. Previous experimental results have shown that the molten composites obey a shear‐thinning power law behavior. When comparing the model predicted pressure drops from the model with the experimental data, very good agreement was obtained. This signifies that the rheological behavior of the composites can be described by a power law relationship, using parameters specific to each composite. When comparing the modeled velocity profile with the theoretical profile, it was found for all composite formulations that the velocity becomes fully developed within a length of 0.05 times the diameter of the tube, independent of the power law parameters n and m. This work is a necessary first step in developing 2D or 3D mold filling simulations for fuel cell bipolar plate applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Determination of pressure drop for concentrated suspension in a capillary flow

The rheological behavior of concentrated suspension melts in a capillary die is investigated. Particle migration and wall slip are two major factors affecting the flow behavior. A numerical model is proposed to describe the coupling effect of particle migration and wall slip in a capillary tube flow, incorporating a power‐law model for binder viscosity and a concentrated suspension viscosity model proposed by Krieger. Wall slip of a non‐Newtonian concentrated suspension is characterized by a modified Mooney method for which the conventional Mooney method is not applicable. We characterized the flow behavior of a concentrated suspension of a non‐Newtonian binder, EVA 460 (ethylene vinyl acetate), mixed with spherical glass beads of 40% by volume. Predicted results were compared with experimental observations, with good agreement. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Exit pressure effects in capillary die data

The exit flow from a capillary is analyzed with the help of macroscopic mechanical energy and momentum balances. The analysis shows that primary normal stress differences cannot be determined from the exit pressures under the assumption that the flow is viscometric down to the exit. This assumption and the second one (made by Han [9]) that both slit and capillary exit pressures are the same would lead to unacceptable results. Published exit pressure data for polyethylene melts are shown to be unreliable because of large hole-pressure errors in the pressure measurements. Pressure profiles obtained with a thin tube technique for the flow of a poly(isobutylene) solution indicate that the flow does not remain fully developed near the exit. Moreover, it is shown that for this polymer solution the excess viscous dissipation at the exit contributes to approximately 90 percent of the exit pressure.