Capillary Viscosity Research Articles

Nonlinear viscoelastic behavior of butadiene–acrylonitrile copolymers filled with carbon black

Various viscoelastic measurements including dynamic mechanical measurements in tension at 110 Hz from −60° to 160°C, tensile stress relaxation measurements with 100% elongation at 25°, 54°, and 98°C, capillary flow measurements at 70°, 100°, and 125°C, and high-speed tensile stress–strain measurements carried to break at 25°, 56°, and 98°C were performed on four samples of carbon black-filled butadiene–acrylonitrile copolymers. All the data were treated with the same equation for time–temperature conversion. The capillary viscosity–shear rate curves were significantly lower than the complex viscosity–angular frequency curves, indicating “strain softening” with extrusion. The viscosity was estimated from the stress–strain relationship at the yield point. The viscosity as a function of the strain rate is significantly higher than the complex viscosity as a function of angular frequency, indicating “strain hardening” with extension. The strain softening and strain hardening are attributable to the structural changes upon deformation of the carbon black-filled elastomers. With the unfilled elastomers, neither strain softening nor strain hardening were observed in similar measurements.

Rheology of Elastomer Blends

Abstract The melt flow properties of certain elastomer blends are shown to be a function of the mixing history and the morphology of the blends. And, more significantly, the melt flow properties are found to be non-additive functions of the melt flow properties of the homopolymers comprising the blends. Mixing studies using a Brabender Plastograph show that blends of certain elastomers generate much higher temperatures while, simultaneously, generating much higher torques than either of the homopolymers over time cycles of practical interest in elastomer processing operations. A sharp minimum in the early stages of the torque/time relationship in the mixing operation, followed by an abrupt maximum, is correlated with abrupt changes in the morphology of the blends as determined by electron microscopy. The morphological structure of certain well mixed elastomer blends consists of domains of the lesser component dispersed into a matrix of the major component. For well mixed blends near 50/50 weight per cent composition the morphological structure appears to consist of two continuous interpenetrating phases. Mooney values as well as Plastograph torque values are observed to be non-additive functions of the corresponding properties of the homopolymers. A minimum in the Mooney/blend ratio relationship over a rather narrow range of blend compositions is observed for certain systems. In contrast, the Plastograph torque values for the identical compositions are observed to be higher in all instances than those for the homopolymers. A phenomenological description of these apparent contradictions is obtained from a simple analysis of capillary melt viscosity measurements carried out on the same blends. These melt viscosities are also a non-additive function of the viscosities of the homopolymers. Minimum and/or maximum viscosities for specific blend ratios are observed for a given rate of shear. The minimum or maximum shift (s) to different blend ratios with changes in the rate of shear. Viscosity/composition plots similar to the Mooney/composition plot are observed at low rates of shear and plots similar to the torque/composition plot are observed at high rates of shear. These behavior patterns remain unexplained at this time.

Influence of shearing history on the properties of polymer melt. I.

The flow pattern of molten polymer through capillaries was studied by using a tracing method. An incompatible polymer was added to polypropylene as a tracer, and the influence of shear in a capillary rheometer on the tracer particle size as well as on the distribution of the particles in the extrudate in relation to flow was studied. It was found that the particle size varied inversely with shear rate of extrusion, capillary aspect ratio, polymer viscosity, and extrusion temperature. The flow was found to be of the telescopic type, and the tracer particle size was independent of position along the radius of the cylindrical extrudate. It is assumed that the supermolecular structure of a polymer melt is of the cluster type suggested by Busse, and it is postulated that spherical clusters of molecules in the melt are modified by shear analogously to the spherical particles of the incompatible tracer polymer. The large spectrum of melt properties obtainable, by various shearing treatments, from a polymer of constant molecular structure suggests that a wide range of supermolecular structures must be possible in the polymer melt.

LIQUID He3, LIQUID MIXTURES OF He3 AND He4, AND DILUTION REFRIGERATION

Basic properties of pure liquid He3 and of dilute solutions of He3 in superfluid He4 are reviewed as they relate to the design and operation of dilution refrigerators. Brief discussions are given both of the intrinsic limitations of the dilution refrigerator and of instabilities which can degrade performance. Finally some characteristics of a new generation of practical dilution refrigerators are displayed and discussed. I. Basic Properties of Liquid ~e~ and of Dilute Mixtures of He3 and He4 as They Relate to the Dilution Refrigerator. We have already discussed elsewhere [I] the essence of this section, so we will confine ourselves to a few remarks in review. Pure, or concentrated, liquid He3 can be regarded as a normal Fermi liquid with sufficient accuracy for the present purposes. That is, we can ignore the very interesting departures [2] at low temperatures of the specific heat from a linear dependence on T, of the thermal conductivity from a T-' law, and of the viscosity from a T ~ law. Dilute solutions of He3 in superfluid He4 have thermal properties very similar to those of the ideal FermiDirac gas. Transport phenomena in the dilute solutions at temperatures below 10 to 20 m OK are also rather like those in a dilute Fermi gas. They may be deduced from an effective interaction [3] dependent on momentum transfer in a mutual collision of quasiparticles and attractive for low values of momentum transfer. Above about 10 m OK the contribution of He4 phonons to the thermal conduction in dilute solutions is already important. By 100 m OK He4 phonons, scattered by He3 quasiparticules and by boundaries, carry essentially allthe heat [4]. There are no measurements of capillary viscosity at low temperatures in dilute solutions. At low temperatures the capillary viscosity has been estimated by Roach [5]. Above 100 m OK we can use the effective viscosity measured by Webeler and Allen [6] to estimate viscosity as a function of temperature and concentration. In addition to the properties individually of concentrated He3 and dilute solutions, the solubility of He3 in He4, and vice versa, is of great importance. A number of measurements have been made, particularly by Edwards and collaborators, [7] and these have been reviewed in reference 2. The principal qualitative point is that at T = 0 a single He3 atom is more strongly bound to liquid He4 than it is to liquid He3, so that even at T = 0 He3 will dissolve in He4. The solubility is limited, however, by the Fermion nature of ~e~ quasiparticles in superfluid He4 which requires additional He3 atoms to enter the liquid in higher translational energy states. Similarly, a single He4 atom is also more strongly bound to liquid ~e~ than to liquid He3 so that as T approaches zero the concentration of He4 in He3 tends rapidly to zero. Certainly below 100 m OK an accurate picture of a mixture of He3 and He4 is that, assuming excess He3, essentially pure He3 will float over a dilute solution containing near T = 0 a He3 molar concentration of about 6.5 %. At higher temperatures the increase in solubility of He3 in superfluid is proportional to T 2 . In the most common type of dilution refrigerator, the refrigeration is produced by dilution of He3 by the superfluid in the mixing chamber. The refrigeration rate at constant temperature is of the form n3 TAs , or

Measurements of the relaxation spectra of unplasticized poly(vinyl chloride) melts

AbstractWe have measured the relaxation modulus in the temperature range 150–220°C of two samples of poly(vinyl chloride) resin with different molecular weights. The data were treated by the principle of reduced variables to yield composite curves. The shift factors (aT) when plotted against reciprocal temperature gave good straight lines from which apparent activation energies were obtained. An apparent activation energy of 50 kcal/mole was obtained for both samples. A relaxation spectrum for each resin was calculated from the relaxation modulus data. These spectra showed a marked molecular weight dependence. The spectra were in the range characteristic of the terminal zone of the entanglement plateau. Zero‐shear‐rate viscosities were obtained from the integration of relaxation modulus plots. From extrapolation of capillary viscosity data it is shown that the viscosity of the higher molecular weight resin used in this study does not approach its zero‐shear value until shear rates less than 10−3 sec−1 are reached. The effect of supermolecular flow units is briefly discussed.

455. Calibration of capillary flowmeters and viscosity measurements at pressures below 10 torr

455. Calibration of capillary flowmeters and viscosity measurements at pressures below 10 torr

Rheology of Dispersions of High Aspect Ratio Submicroscopic Whiskers

An unusual form of single crystal whiskers of β SiC was in vestigated in terms of the rheological properties of its suspensions in several fluids. Individual whiskers could not be separated intact from the fiber mass produced in the reactor. Capillary viscosity measurements were used to estimate the length of the fibers. An aspect ratio of 10,000 is obtained by the use of Burgers' equation for the viscosity of suspensions of rigid rods. The fibers are shown to be remarkably effective at low concen trations (<0.1%) in increasing the viscosity of a silicone, a hydro carbon and an alkylphosphonate fluid. The suspensions also exhibited pseudoplastic flow behavior.

Calibration of gel permeation chromatographic columns for measuring the molecular size of poly(vinyl chloride) in tetrahydrofuran

AbstractA calibration plot of the intrinsic viscosities of poly(vinyl chloride) fractions against elution volumes gives a good correlation between the first moments, i.e., mean elution volumes, and intrinsic viscosities of poly(vinyl chloride) whole polymers. This is evidence that column permeation of chain macromolecules is governed by some sort of hydrodynamic size in a manner akin to that in which hydrodynamic size affects capillary viscosity measurements.

High‐shear capillary viscosity studies on concentrated copolymer solutions

High‐shear capillary viscosity studies on concentrated copolymer solutions

High‐shear capillary viscosity studies on concentrated copolymer solutions

AbstractFlow behavior of ten copolymer solutions of polyacrylonitrile and polymethyl methacrylate in concentrations up to 16% was studied at 30°C. with the use of capillaries of constant diameter but different lengths. The shear rate and shear stress range covered were up to 200,000 sec.−1 and 800,000 dynes/cm.2, respectively. A rheological model of the form log D = A0 + A1 (log τ)β + A11 (log τ)2β was employed in determining the inflection point of the flow curve by computer analysis. A marked dependence of the flow curve upon the lenght‐to‐diameter ratio was observed when l/d ratio decreased to below 300. At shear rates above 50,000 sec.−1 the capillary “end effect” corrections and the kinetic energy corrections were found to be large for the concentrated and dilute solutions, respectively. The flow curves were characterized in terms of the inflection point in accordance with the treatment of Schurz. An upper Newtonian viscosity η* was observed at shear rates above 150,000 sec.−1. Up to a concentration of about 1%, the value of the upper Newtonian viscosity was such that the calculated ηsp/C was essentially independent of C and equal to [η*] obtained by extrapolation to infinite dilution. The values of the heat of activation for viscous flow were found to be dependent upon the applied shear stress.