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1.
Summary The rheological properties of vinylon fiber suspensions in polymer solutions were studied in steady shear flow. Shear viscosity, first normal-stress difference, yield stress, relative viscosity, and other properties were discussed. Three kinds of flexible vinylon fibers of uniform length and three kinds of polymer solutions as mediums which exhibited remarkable non-Newtonian behaviors were employed. The shear viscosity and relative viscosity (
r
) increased with the fiber content and the aspect ratio, and depended upon the shear rate. Shear rate dependence of
r
was found only in the low shear rate region. This result was different from that of vinylon fiber suspensions in Newtonian fluids. The first normal-stress difference increased at first slightly with increasing fiber content but rather decreased and showed lower values for high content suspensions than that of the medium. A yield stress could be determined by using a modified equation of Casson type. The flow properties of the fiber suspensions depended on the viscosity of the medium in the suspensions under consideration.With 16 figures and 1 table 相似文献
2.
Mahmoud Rajabian Charles Dubois Miroslav Grmela Pierre J. Carreau 《Rheologica Acta》2008,47(7):701-717
Rheological properties of suspensions of fibers in polymeric fluids are influenced by fiber–polymer interactions. In this
paper, we investigate this influence from both experimental and modeling standpoints. In the experimental part of this investigation,
we have changed the fiber–polymer interactions by treating the surface of the fibers. The resulting effects are observed using
scanning electron microscopy and dynamic mechanical analysis techniques and quantified from the measurements of the viscosity
in the start-up of shear flows and dynamic tests in the linear viscoelastic range region. The results are interpreted with
the help of a mesoscopic rheological model developed for suspensions of fibers in viscoelastic fluids. 相似文献
3.
Manish K. Tiwari Alexander V. Bazilevsky Alexander L. Yarin Constantine M. Megaridis 《Rheologica Acta》2009,48(6):597-609
Rheological behavior of concentrated suspensions of chemical vapor deposition carbon nanotubes in uniaxial elongation and
simple shear is studied experimentally and theoretically. Nanotubes are suspended in viscous host liquids—castor oil or its
blends with n-decane. The elongational measurements are performed by analyzing self-thinning (due to surface tension effect) liquid threads
of nanotube suspensions. A quasi-one-dimensional model is used to describe the self-thinning process, whereas corrections
accounting for thread nonuniformity and necking are introduced a posteriori. The effects of nanotube concentration and aspect
ratio, viscosity of the suspending liquid, and initial diameter of the self-thinning thread in uniaxial elongation are elucidated.
The results for uniaxial elongation are compared with those for simple shear. The correspondence in the results of the shear
and elongational measurements is addressed and interpreted. The results conform to the Herschel–Bulkley rheological constitutive
equation (i.e., power law fluids with yield stress). However, the yield stress in elongation is about 40% higher than in simple
shear flow, which suggests that the original Herschel–Bulkley model need modification with the yield stress being a function
of the second invariant of the deviatoric stress tensor. The present effort is the first to study capillary self-thinning
of Herschel–Bulkley liquids, which are exemplified here by suspensions of carbon nanotubes. 相似文献
4.
An attempt is made to incorporate into a quasilinear viscoelastic constitutive equation of the Boltzmann superposition type the two mirror relations of Gleissle, as well as his relation between the steady-state first normal-stress difference and the shear viscosity curve. It is shown that the three relations can hold separately within this constitutive model, but not simultaneously, because they require a different nonlinear strain measure, namelyS
12 () = – a ( – 1) (a = 0 for 1,a = 1 for 1) for the mirroring of the viscosities,S
12 () = – a (–k
2/) (a = 0 for k, a = 1 for k) for the mirroring of the first normal-stress coefficients, and
for the third relation. Here denotes the shear strain and erf the error function. Experimental data on melts of a low-density polyethylene, a high-density polyethylene and a polypropylene show that the mirror relations are passable approximations, but that the third relation meets reality surprisingly close if the right value ofk is used. 相似文献
5.
This is the second part of a study examining the mechanical properties and capillary flow of fiber suspensions in Newtonian fluids and in polymer solutions. In part I results for the viscous and elastic properties of the fiber suspensions were presented and it was shown that the fiber suspensions exhibited normal stresses in Newtonian as well as in viscoelastic suspending media. It was thus expected that circulating secondary flows would occur near the entrance to a capillary. Four types of fillers (glass, carbon, nylon and vinylon fibers) suspended in glycerin, HEC solutions and Separan solutions were investigated. The entrance flow patterns were visualized and the pressure fluctuations measured. The visualization enabled the eddies occurring in the fiber suspensions in Newtonian fluids to be analysed and classified into two tpyes. The results from the flow visualization were correlated with the pressure fluctuations. Empirical equations for the tube length correction factor due to the elasticity were obtained. 相似文献
6.
In-line measurement of rheological properties of polymer melts 总被引:1,自引:0,他引:1
Shear viscosity (), first normal stress difference (N
1), and extensional viscosity (
E
) of polymer melts measured under processing conditions are important in process modeling, quality control, and process control. A slit rheometer that could simultaneously measure , N
1, and the planar extensional viscosity (
p
) was designed and tested by attaching it in-line to a laboratory model single-screw extruder. A tube (circular cross-section) rheometer to measure and the uniaxial extensional viscosity (
u
) simultaneously was also designed and tested. Two commercial grades of LDPE (low density polyethylene) with melt index values of 6 and 12 were used as test materials for the study. Exit and hole pressure methods were used to estimate N
1, and the entrance pressure drop method using the analyses of Cogswell, Binding, and Gibson (the last analysis used with the axisymmetric case only) was used to estimate
E
.The hole pressure method was considered better than the exit pressure method to estimate N
1 (due to the greater susceptibility of the latter to experimental errors). From the hole pressure method N
1 was obtained from 100 kPa to 500 kPa over a range of shear rates from 40 s–1 to 700 s–1. Among the analyses used to estimate the extensional viscosity, Cogswell's is recommended due to its simpler equations without loss of much information compared to the other analyses. The range of extension rates achieved was 1 to 30 s–1. The combination of the hole pressure and entrance pressure drop methods in a slit rheometer is a feasible design for a process rheometer, allowing the simultaneous measurement of the shear viscosity, first normal stress difference and planar extensional viscosity under processing conditions. Similarly, combining the entrance pressure drop measurements with a tube rheometer is also feasible and convenient. 相似文献
7.
Susanne E. Mall-Gleissle Wolfgang Gleissle Gareth H. McKinley Hans Buggisch 《Rheologica Acta》2002,41(1-2):61-76
We investigate the variations in the shear stress and the first and second normal stress differences of suspensions formulated
with viscoelastic fluids as the suspending medium. The test materials comprise two different silicone oils for the matrix
fluids and glass spheres of two different mean diameters spanning a range of volume fractions between 5 and 25%. In agreement
with previous investigations, the shear stress–shear rate functions of the viscoelastic suspensions were found to be of the
same form as the viscometric functions of their matrix fluids, but progressively shifted along the shear rate axis to lower
shear rates with increasing solid fraction. The normal stress differences in all of the suspensions examined can be conveniently
represented as functions of the shear stress in the fluid. When plotted in this form, the first normal stress difference,
as measured with a cone and plate rheometer, is positive in magnitude but strongly decreases with increasing solid fraction.
The contributions of the first and the second normal stress differences are separated by using normal force measurements with
parallel plate fixtures in conjunction with the cone-and-plate observations. In this way it is possible for the first time
to quantify successfully the variations in the second normal stress difference of viscoelastic suspensions for solid fractions
of up to 25 vol.%. In contrast to measurements of the first normal stress difference, the second normal stress difference
is negative with a magnitude that increases with increasing solid content. The changes in the first and second normal stress
differences are also strongly correlated to each other: The relative increase in the second normal stress difference is equal
to the relative decrease of the first normal stress difference at the same solid fraction. The variations of the first as
well as of the second normal stress difference are represented by power law functions of the shear stress with an unique power
law exponent that is independent of the solid fraction. The well known edge effects that arise in cone-and-plate as well as
parallel-plate rheometry and limit the accessible measuring range in highly viscoelastic materials to low shear rates could
be partially suppressed by utilizing a custom- designed guard-ring arrangement. A procedure to correct the guard-ring influence
on torque and normal force measurements is also presented.
Received: 20 December 2000 Accepted: 7 May 2001 相似文献
8.
Frédéric Pignon Albert Magnin Jean-Michel Piau Gàbor Belina Pierre Panine 《Rheologica Acta》2009,48(5):563-578
The structure and orientation dynamics of sepiolite clay fibers about 1,000 nm long and 10 nm thick, suspended in an aqueous
poly(ehtylene oxide) matrix of 105 g/mol molecular mass, have been studied under control extensional and shear flow. A new extensional flow cell developed at
the “Laboratoire de Rhéologie” and the combined rheology and small angle X-ray scattering (Rheo-SAXS) setup available at the
European Synchrotron Radiation Facility have allowed access to in situ and time-resolved fiber orientations and structure
properties in the volume of suspensions under flow. In the volume fractions and shear rate domains for which the suspensions
exhibit shear-thinning properties, two regimes of orientation separated by a critical strain rate have been identified under
extensional flow. 相似文献
9.
This paper presents results on the rheological behaviour of suspensions of two kinds of TiO2 particles in two different polymer solutions. The particles differ in their hydrophilic or hydrophobic properties. The dispersing
media are a solution of high molecular weight polyisobutylene in decalin and a solution of a low molecular weight polybutene
in decalin. The concentrations of polymer are adjusted in order to get the same zero shear viscosity. The shear viscosity
measurements display an apparent yield stress in some cases. The existence and the values of the yield stress depend on the
volume fraction of solid particles and on the type of particles. The evolution of the intrinsic viscosity and of the maximum
packing fraction vs the shear rate is interpreted in terms of evolution of the size and of the shape of aggregates of particles
under shear. The effect of temperature on the development of the yield stress is also discussed. The results are completed
by microscopic observations. 相似文献
10.
Dr. Arthur S. Lodge 《Rheologica Acta》1996,35(2):110-116
A new slit-die rheometer (the Stressmeter) for on-line and sample measurement of the viscosity, , and the first normal stress difference, N
1, in steady shear flow for molten polymers and other high-viscosity liquids is described. Two liquid-filled transverse slots, located in one die wall near the center station, give pressures P
2 and P
3 from whose difference the wall shear stress is calculated. In the other die wall at a location opposite the center of the P
2 slot is a flush-mounted transducer, giving a pressure P
1. N
1 is calculated from the hole pressure P
* = P
1–P
2. A metering pump, used to measure the flow rate Q, is supplied with melt either from an extruder (online mode) or from a pressurized sample cylinder (sample mode). The wall shear rate is calculated from Q and ; the Weissenberg-Rabinowitsch correction and a new small-viscous-heating-correction algorithm (affecting ) are used. Viscous heating corrections are small; entrance and exit errors are negligible. The instrument is tested by comparing its results with those obtained from cone-plate and capillary rheometers. Measurement ranges extend to = 200 kPa, = 3000 s–1, and temperature = 250°C.Dedicated to Prof. Dr. J. Meissner on the occasion of his retirement from the chair of Polymer Physics at the Eidgenössische Technische Hochschule (ETH) Zürich, Switzerland 相似文献