Rheological properties of liquid crystalline solutions of ethyl celluloses with different molecular weight in m-cresol

Steady-state shear rheological properties of liquid crystalline solutions of four ethyl celluloses (ECs) were determined at a low shear rate (1 s^?1) and at relatively high shear rates by using two rheometers (cone-plate and capillary types), and were compared with those of liquid crystalline hydroxypropyl cellulose (HPC). The effect of molecular weight (MW) on the viscoelastic behavior was also determined. The viscoelastic behavior was also determined. The viscometric behavior of EC solutions was similar to that of HPC solutions: (1) with respect to temperature, the shear viscosity (η) at shear rate of 1 s^?1 exhibited a minimum (η_min) and a maximum (η_max), and the concentration–temperature superposition for η could be applied; (2) the behavior of η at relatively high shear rates as a function of shear rate or polymer concentration was typical of lyotropic liquid crystals. The MW dependence of η_min was greater than that of η_max for EC solutions. The behavior of the elastic parameters such as Bagley correction factor (v), entrance pressure drop (ΔP_ent), and die swell (B) at relatively high shear rates for EC solutions was essentially similar to that for HPC solutions: (1) the shear rate or stress dependence of the elastic parameters was greatly dependent on whether the polymer solution was in a single phase or biphase; (2) with respect to concentration the elastic parameters showed a maximum and a minimum and the maximum or minimum point for each parameter was not always identical to each other. η for the isotropic or fully anisotropic solutions at a given concentration (C) increased, whereas η for the solutions in the vicinity of the biphasic region showed a minimum, with respect to MW. The slope of η at a given shear rate vs. CM _w depended on shear rate, and this slope for the isotropic solutions appeared to be greater than that for fully anisotropic solutions. ΔP_ent and v at a given concentration showed either a monotonical increase or a maximum or minimum with MW, and this behavior was not fully consistent with that of η. B for the isotropic solutions increased and B's for both biphasic and fully anisotropic solutions were almost constant, with MW.     

VIscometric behaviour of Kevlar fibre filled liquid crystalline solutions of ethyl cellulose in m-cresol

Liquid crystalline solutions of ethyl cellulose in m-cresol were mixed with Kevlar® fibres, and the viscometric behaviour with respect to temperature of those filled systems was determined with a cone-plate type viscometer. The viscosity of the systems exhibited a maximum and a minimum at temperatures denoted by T_max and T_min' respectively. The effects of fibre on the critical temperatures (T_max and T_min) and critical concentrations (C_a and C_b) and on the viscosity enhancement are discussed. T_max and T_min decreased with fibre concentration for single-phase anisotropic solutions, whereas they increased for the biphasic solution. The critical concentrations increased with fibre concentration and C_b was more sensitive to the fibre than C_a. The viscosity enhancement due to the fibre depended on the phase of solution. In the single-phase (isotropic and anisotropic), the viscosity enhanced with fibre; however, in the biphasic solution, the effect was not simple. The viscosity enhancement for the single-phase anisotropic solutions with fibre was lower than that for the isotropic solutions.     

Rheological behavior of ethylene–octene copolymer vulcanizates: Effect of blowing agent and precipitated silica filler

An experimental study of the rheological behavior of ethylene–octene copolymer vulcanizates in extrusion containing blowing agent has been carried out. The cell morphology development has been studied through a scanning electron microscope. Rheological properties of unfilled and precipitated silica‐filled systems with variations of blowing agent, extrusion temperature, and shear rate have been studied by using a Monsanto processibility tester (MPT). The total extrusion pressure (P_T), apparent shear stress (τ_wa), apparent viscosity (η_a), and die swell (%) of the unfilled and silica‐filled compounds have been determined by using MPT. The effect of blowing agent (ADC) on the rheological properties of the vulcanizates has also been investigated. There is a reduction of stress and viscosity with blowing agent loading. It was observed that the incorporation of a blowing agent led to decreased shear thinning behavior resulting in an increase in power law index. The viscosity reduction factor (VRF) of unfilled vulcanizates is found to be dependent on the concentration of the blowing agent, shear rate, and temperature, whereas VRF of silica‐filled vulcanizates is found to be dependent on shear rate, temperature, and blowing agent concentration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1132–1138, 2003     

Flame retardation of polypropylene: Effect of organoantimony compounds on the melt flow behavior

The melt flow behaviour of polypropylene filled with organoantimony compounds, triphenylstibinedibromide and its derivatives with tribromo-, trichloro-, and pentachloro-phenols, as flame retardants has been studied in the temperature range of 180 to 220°C, and at shear rates of 29.5 to 588.8's^?1, using a capillary rheometer. A decrease in the melt viscosity at all shear rates and temperatures was noticed on addition of these flame retardants, The melt viscosity further decreased upon increasing the concentration (from 5 to 20 phr) of the flame retardants. The die swell was measured in order to determine the melt elasticity of the filled systems. The minimum melt viscosity of filled propylene was observed approximately where the maximum die swell (melt elasticity) occurred.     

The rheology of polysulfone

The viscosity-shear rate functions for polysulfone (PSF) condensates ranging from 0.4RV to 0.95RV were determined using capillary rheometry, The most probable distribution of molecular weights of these resins allowed facile comparison with the polydisperse Bueche theory for viscosity, The agreement in shape of the viscosity function with theory was good but the data were displaced by a factor of 3 to 4 to higher reduced shear rate, a fairly common occurrence for melts. The high absolute value of PSF viscosity was explained with existing empirical correlations as a combination of low critical molecular weight and strong intermolecular interactions. The temperature dependence of viscosity was found to be close to that for polystyrene in the temperature range, T_g + 90 to T_g + 190°C. The die swell, end corrections, and melt fracture characteristics were also determined. The latter was found to occur at a constant wall shear stress of about 6 × 10⁶ dynes/cm² while the die swell and end corrections were found to be small.     

Rheological properties of phenophthalein poly(ether ether ketone)

The rheological properties of the novel engineering thermoplastic phenophthalein poly(ether ether ketone) (PEK-C) have been investigated using both a rotational and a capillary rheometer. The dependence of the viscosity on the shear rate and temperature was obtained. The activation energy was evaluated both from the Arrhenius and the Williams-Landel-Ferry (WLF) equation. An estimate for the proper E_η (dependent only on the chemical structure of the polymer) has been found from the WLF equation at temperatures about T_g + 200°C. Measurements of the die swell have been performed. The first normal stress differences were evaluated from the die swell results and compared with the values obtained from the rotational rheometer at low shear rates.     

Viscometric behavior of ternary concentrated solutions of hydroxypropyl cellulose and ethyl cellulose in m-cresol

The shear viscosity of blend solutions of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) in m-cresol (both HPC/m-cresol and EC/m-cresol systems form lyotropic liquid crystals) was determined by cone-plate-type and capillary-type viscometers. The textures for the same systems at rest and undergoing shear were also observed with a polarized microscope. At shear rate of 1 s^?1, viscosity exhibited a maximum and a minimum with respect to temperature, and this suggested that the phase of the matrix dominated the viscometric behavior of the ternary systems; the blend composition dependence of the viscosity was not additive, and this suggested that HPC and EC were immiscible. At relatively high shear stress, the blend composition dependence of the viscosity greatly depended on the total polymer concentration of the solutions and was quite different from that at low shear rate; the texture of the anisotropic solutions was also different from that at low shear rate. Our findings suggested that the dependence of viscosity on shear and concentration for pure HPC solution was different from that for pure EC solution.     

Observation of melt fracture of polypropylene resins in capillary flow

Melt fracture, shear viscosity, extensional viscosity, and die swell of two polypropylene resins were studied using a capillary rheometer. A modified Bagley plot with consideration of pressure effects on melt viscosity and end effect was used. From the true wall shear stress the shear viscosity was calculated. Extensional viscosity was calculated from the end effect. Both shear and extensional viscosities of different molecular weights and temperatures correlated well under the time-temperature Williams-Landel-Ferry (WLF) superposition. Die swell increased when shear stress increased, and was higher for shorter dies at a given shear rate. When shear rates increased the extrudate staged from smooth to gross melt fracture with regular patterns (spurt), and then turned into irregular shapes. In the regular stage the wavelength of extrudates was measured, and corresponding frequency was calculated. The frequency increased when molecular weight decreased and when melt temperature increased. The shift factor based on shear viscosity also brought frequency data of different molecular weights and temperatures into master curves. The frequency decreased slightly when die lengths increased from L/R=10 to 60. A small maximum was observed when shear rates increased.     

Rheological behavior of highly filled ethylene propylene diene rubber compounds

The rheological behavior of highly filled ethylene propylene diene rubber (EPDM) compounds was studied with respect to the effect of curative system, grafted rubber, shear rate, temperature and die swell using a Monsanto Processability Tester (MPT) to gain an understanding of the molecular parameters that control the surface finish. All systems show pseudoplastic behavior. At a particular shear rate, shear viscosity increases with blend ratio. The dependence of flow behavior on extrusion velocity indicates a surface effect. The extrudate die swell and maximum recoverable deformation are related by a linear relationship, which is independent of sulfur/accelerator ratio, extrusion temperature and shear rates and blend ratio. The principal normal stress difference increases nonlinearly with shear stress. Activation energy decreases with shear rate in most cases. The faster relaxing system produces extrudate of better surface quality.     

Rheological behaviour of copoly(ethylene/octene) elastomer compunds: Effect of blowing agent and precipitated CaCO3 filler

Abstract

An experimental study of the rheological behaviour of ethylene/octene copolymer compounds in extrusion containing blowing agent has been carried out. The cell morphology development was studied using scanning electron microscopy. Rheological properties of unfilled and precipitated CaCO₃ filled systems with various blowing agents, extrusion temperatures, and shear rates were studied using a capillary rheometer. The total extrusion pressure, apparent shear stress, apparent viscosity, and die swell of the unfilled and CaCO₃ filled compounds were also determined and the effect of blowing agent on the rheological properties of the compounds studied. It was observed that there is reduction of stress and viscosity with blowing agent loading. Incorporation of blowing agent led to decreased shear thinning behaviour resulting in an increase in the power law index. The viscosity reduction factor of the unfilled compound was found to be dependent on the concentration of blowing agent, the shear rate, and the temperature.     

Extrusion die swell of carbon black-filled natural rubber

Extrusion die swell of natural rubber compounded with a wide variety of carbon blacks has been determined in a capillary rheometer using a long circular die. The range of variation of carbon black loading, surface area, and structure are, respectively, 10 to 60 phr, 44 to 124 m²/g, and 78 to 120 cc/100 g. The effective carbon black volume fraction φ_e not participating in the strain recovery leading to die swell is assumed to be the sum of the actual filler volume fraction and the fraction of unextractable rubber determined experimentally for each compound. Bagley and Duffey's analysis of extrusion die swell of unfilled polymers as unconstrained elastic recovery was adopted for a filled elastomeric system whose relative shear modulus (G/G₀) is assumed to vary as (1 ? φ_e)^?N. The matrix shear modulus G₀, originally introduced by Nakazima and Shida on the basis of a linearized approximation, will depend on the shear stress level because of nonlinear deformation. The power N will vary with shear stress which changes the orientation of carbon black aggregates. Except for these features, die swell data for a wide range of carbon black compounds fall on a single curve when plotted in the manner of the predicted relation between the wall shear stress, die swell, and φ_e. Replacing φ_e by Medalia's φ′ based on an equivalent sphere concept introduces a larger scatter around the mean curve.     

Melt fracture,melt viscosities,and die swell of polypropylene resin in capillary flow

The melt fracture, shear viscosity, extensional viscosity, and die swell of a polypropylene resin were studied using a capillary rheometer and dies with a 0.05‐cm diameter and length/radius ratios of 10, 40, and 60. A temperature of 190°C and shear rates between 1 and 5000 s^?1 were used. A modified Bagley plot was used with consideration of pressure effects on both the melt viscosity and end effect. The shear viscosity was calculated from the true wall shear stress. When the true wall shear stress increased, the end effect increased and showed critical stresses at around 0.1 and 0.17 MPa. The extensional viscosity was calculated from the end effect and it showed a decreasing trend when the strain rate increased. Both the shear and extensional viscosities correlated well with another polypropylene reported previously. The die swell was higher for shorter dies and increased when shear stress increased. When the shear rates increased, the extrudate changed from smooth to gross melt fracture with regular patterns (spurt) and then turned into an irregular shape. In the regular stage the wavelength of the extrudates increased when the shear rate increased. The frequency of melt fracture was almost independent of the shear rate, but it decreased slightly when the die length increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1587–1594, 2003     

Viscosity and die swell of acrylonitrile-butadiene-styrene filled with glass beads and glass fibers

Shear viscosity and die swell ratio of acrylonitrile-butadiene-styrene filled with glass beads and glass fibers were measured. The relative viscosity of the composites increased with filler content, but decreased with shear rate. At low shear rates, fiber filled systems had higher relative viscosities than bead filled systems. At high shear rates, the opposite was observed. The die swell ratio of the unfilled material increased linearly with the logarithm of the shear rate. Systems highly filled with glass beads or fibers showed a maximum in the die swell ratio at medium shear rates. The magnitude of the maximum in the die swell ratio increased with the filler content and the die length, up to a certain length, in a series of dies that had the same radius. The presence of a maximum in the die swell ratio of the filled melts is explained by an order-disorder phenomenon observed earlier by Wu.     

A Survey of Rheological Properties of One-Component Epoxy Adhesives

Flow characteristics of seven commercially available one-component epoxy adhesive pastes were measured using a controlled shear stress rheometer and a controlled shear rate rheometer over a temperature range from 5°C to 60°C. Combining data obtained from both controlled rate and controlled stress experiments over a wide range of shear rates, we observed Newtonian flow (shear stress proportional to shear rate) at very low shear rates, a plateau “shear thinning” region at intermediate shear rates, and a second region of linear dependence of shear stress on shear rate at high shear rates. The adhesive pastes exhibited a very broad range of rheological behavior. Two flow parameters important to adhesive application technology, the plastic viscosity and the apparent yield stress, were measured for each adhesive. The plastic viscosity ranged from 11.6 to 329.5 Pa. s; the apparent yield stress ranged from 56.2 to 413 Pa. The temperature dependence of the rheological parameters of the epoxy adhesive pastes was also determined. The results are reported as the activation energies, E_η and E_σ , of plastic viscosity and apparent yield stress, respectively. The apparent yield stress of each adhesive paste was much less sensitive to changes in temperature than was the plastic viscosity. This suggests that the processing characteristics are likely to show qualitative as well as quantitative changes with temperature.     

Elastic behavior of LDPE/HEPE blend melts in capillary extrusion

The studies of the elastic behavior in the capillary flow of LDPE/HDPE blend melts were carried out at a test temperature range from 180 to 200°C and at an apparent shear rate of about 25–120 s⁻¹. The end‐pressure drop (ΔP_end) increased nonlinearly with increasing wall shear stress (τ_w) and achieved a minimum value at a weight fraction (ϕ_HD) of HDPE of 50%. The die‐swell ratio (B) increased basically linearly with increasing τ_w or ΔP_end and achieved a maximum value at ϕ_HD of 50%. With the addition of the die length–diameter ratio, the values of B were decreased linearly. At a low shear rate, the temperature sensitivity of the melt die‐swell was more significant than at a high shear rate. With increasing ϕ_HD, B increased when ϕ_HD < 50%, then decreased. B reached a maximum value at ϕ_HD of 50% and a fixed apparent shear rate. This phenomenon may be explained by using the theory of viscoelastic competition between components of polymer blend melts. Furthermore, the first normal stress difference (N₁) of the sample melts was estimated by using an equation published in a previous work. The results showed that B increased linearly with increasing N₁. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 759–765, 2000     

The yield stress of fibre suspensions

Yield stresses were determined for commercial wood pulp suspensions and synthetic fibre suspensions of low and medium mass concentration. The yield stresses measured represent interfibre failure of the network rather than failure between the suspension and a solid surface. The measurements were carried out in a rotary viscometer at low yield stresses and in a concentric rotary shear tester at yield stresses in excess of 2500 Pa. The experimental results were correlated with the volumetric concentration C_v in equations of the form τ_y = aC^b_v where a and b are constant for a given fibre type. It was found that b ? 3, in agreement with the predictions of a theoretical model of fibre network strength based upon the interlocking of elastically bent fibres. The dependence of the yield stress on the fibre properties of aspect ratio and modulus of elasticity was not adequately predicted by the model, suggesting that fibre bending alone did not account for the network strength over the concentration range studied.     

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

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.     

Flow behavior of concentrated solutions of an SBS block copolymer

The non-Newtonian viscosity of concentrated solutions of a styrene-butadiene-styrene, SBS, block copolymer was measured with a novel capillary viscometer. Polymer concentrations ranged from 0.165 to 0.306 g/cc. Apparent shear rates ranged from 1 to 10⁵ sec^?1. Five different solvents were employed. All of the flow curves can be reduced to a single master curve with the same shape exhibited by monodisperse polystyrenes and the Graessley theory. The shift factor for the shear rate axis, τ₀, approximately parallels the Rouse relaxation time, τ_R, but shows a residual concentration and solvent dependence not predicted by the Rouse form. For different solvents at the same concentration, better solvents show a minimum relative zero shear viscosity, η₀/η_s, and a maximum ratio τ_R/τ₀. It is concluded that all solvent effects are not adequately incorporated into the zero shear viscosity for the purposes of constructing master plots; however, the shape of the master plot is not affected by the solvent or the polymer block structure.     

Shear-induced phase separation and crystallization in semidilute solution of ultrahigh molecular weight polyethylene: Phase diagram in the parameter space of temperature and shear rate

In the previous papers, we elucidated enhancement of concentration fluctuations, phase separation, and crystallization induced by steady state or step-up shear flow, as observed by shear small-angle light scattering, optical microscopy, and birefringence, for a semidilute solution of ultrahigh molecular weight polyethylene in paraffin as an athermal solvent. However the studies were done only at a given temperature of 124 °C, which is higher than the nominal melting temperature of the quiescent solution T_nm (115–119 °C). It is crucial to extend the studies over a wider temperature range in order to generalize shear-induced phase behavior of the solution. Thus in this work we constructed a kind of phase diagram in the parameter space of temperature (T) and shear rate (). The temperature range covered was higher than T_nm, so that the phase diagram is strictly concerned with shear-induced phase behavior (i.e., without shear the solution is homogeneous and in a single-phase state). The diagram identified Regimes I–III in the T– space as will be detailed in the text. In constructing the phase diagram we found the following new points also. (i) The critical shear rate _cx which defines the boundary between Regimes I and II was independent of T. (ii) Regime III identified previously through the dependence of the integrated scattered intensity only at a particular temperature T = 124 °C was further separated into two regimes of III_a and III_b below and above a critical temperature (147 °C), respectively, through the observation of the dependence as a function of T: In Regime III_a, the sheared solution developed the optically anisotropic fibrous structures, indicative of the shear-induced crystallization triggered by the shear-induced concentration fluctuations in Regime II; In Regime III_b, the solution is so stable that it did not show a trend of the shear-induced crystallization even at the highest shear rates accessible in this experiment, but it only showed the shear-induced phase separation. (iii) The critical shear rates _c,streak and _cz, which define respectively the boundary between Regimes II and III_a and that between Regimes II and III_b, are sensitive to temperature.