Rheological behavior of SAN/PC blends under extremely high shear rate

Extremely high shear rate processing was applied to the compound system of acrylonitrilestyrene copolymer/polycarbonate (SAN/PC). The viscosity was measured against the shear rate up to 10⁷ s^?1. The first non-Newtonian region, the second Newtonian region and second non-Newtonian region were observed in the compound system. The occurrence of these regions are very similar to those in the parent polymers, SAN and PC. For the calculation of the viscosity-shear rate curve, a concentric multilayer model was proposed. It gives good agreement between the calculated value and the measured one. A new mechanism for the occurrence of the non-Newtonian, second Newtonian, and second non-Newtonian regions was proposed. Nuclear spin–spin relaxation time measured on SAN, T₂, seems to be consistent with the consideration that the occurrence of non-Newtonian region, second Newtonian region, and second non-Newtonian region are caused, respectively, by the disentanglement, near saturation of disentanglement associated with snapping of macromolecules, and reentanglement through recoiling of snapped macromolecules, and further snapping of the macromolecules, which is inconsistent with the proposed explanation.     

High shear strain rate rheometry of polymer melts

The rheology of a range of polymer melts has been measured at strain rates above those attained during conventional rheometry using an instrumented injection molding machine. Deviations from shear thinning behavior were observed at high rates, and previously unreported shear thickening behavior occurred for some of the polymers examined. Measured pressure and volumetric throughputs were used to calculate shear and extensional viscosity at wall shear strain rates up to 10⁷ s^?1. Parallel plate rheometry and twin bore capillary rheometry were used to provide comparative rheological data at low and medium shear strain rates, respectively. Commercial grades of polyethylene, polypropylene, polystyrene, and PMMA were studied. Measured shear viscosity was found to follow Newtonian behavior at low rates and shear thinning power law behavior at intermediate strain rates. At shear strain rates approaching or above 10⁶ s^?1, shear viscosity reached a rate‐independent plateau, and in some cases shear thickened with further increase in strain rate. A relationship between the measured high strain rate rheological behavior and molecular structure was noted, with polymers containing larger side groups reaching the rate‐independent plateau at lower strain rates than those with simpler structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A study of low shear viscosity of polymer melts

An inexpensive, accurate falling coaxial cylinder viscometer is described. Viscosities can be measured at shear stresses at least as low as 10³ dynes per cm² and flow curves can be obtained with shear thinning fluids. Data for a polystyrene and a polyethylene polymer coincide with those from other techniques and with corresponding literature values. The lower Newtonian viscosities pf both polymers were experimentally accessible, and it is shown that estimation of η_o by extrapolation from viscosities in the non-Newtonian region may be subject to errors of uncertain magnitude. Shear history of the sample affects the Newtonian and low shear viscosities of high molecular weight polymer melts.     

Viscosity of polydimethylsiloxane gum: Shear and temperature dependence from dynamic and capillary rheometry

The rheology of Dow Corning polydimethylsiloxane gum (PDMS/silicone gum) was studied over a time range of 10^?2 to 10⁵ s^?1 and a temperature range of 23–150°C using both capillary and dynamic rheometry. A low shear Newtonian region is observed at room temperature below 0.01 rad/s (increasing to 0.1 rad/s at 150°C) for which an Arrhenius activation energy for a viscous flow of 13.3 kJ/mol was determined. The Cox–Merz rule for merging of shear and complex viscosities is found to be valid up to 10 s^?1. Viscosity is found to be independent of temperature above 100 s^?1, where terminal power‐law flow is encountered. This is exhibited in the dynamic data as equal plateau moduli for the various temperature curves. Gross wall slippage is seen in capillary flows above approximately 100 s^?1, corresponding to a stress value of 70–100 kPa. Slip‐stick (spurt) flow is not observed. The viscosity data are best fitted by the Carreau–Yasuda model with a fitting parameter a of 0.7, a power‐law index n of 0.05 (low because of slip effect), and a zero shear viscosity of 32 kPa s at 23°C. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2533–2540, 2002     

Rheological properties of new polymer compositions for sand consolidation and water shutoff in oil wells

The rheological properties of some newly developed polymer compositions have been investigated with and without crosslinking. These polymer compositions were developed as a water shutoff and sand consolidation treatment agents for producing oil and gas wells. The effects of several variables on the rheology of the compositions were evaluated over a wide range of temperatures (25–110°C), shear rates (0–500 s^?1), brine percentages (0–15%), crosslinker types and concentrations (0–3%), and polymer concentrations (6–50%). It was found that increasing the shear rate from 0 s^?1 to 100 s^?1 caused shear thinning and reduction of the viscosity of the dilute solutions (6–13%) from 25 cP to ～ 3 cP at 80°C. In contrast, for the concentrated solutions (20–50%), the viscosity dropped slightly in the shear rate range 0–10 s^?1, and subsequently decreased more slowly up to shear rates of 500 s^?1. The viscosities of all polymer solutions dropped by a factor of 2 as the brine concentration increased from 0% to 15%. Finally, aging time coupled with shear rates and higher percentages of crosslinkers accelerate the buildup of viscosity and gelation time of the polymer compositions. For concentrated solutions, shear rates ranging within 0–200 s^?1 accelerated gelation time from 9.75 h to 2–3 h, when they were sheared at 80°C. The polymeric solutions exhibited Newtonian, shear‐thinning (pseudo‐plastic), and shear‐thickening (dilatant) behavior, depending on the concentration, shear rate, and other constituents. In most cases, the rheological behavior could be described by the power law. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Lower Newtonian viscosities of polystyrene

A falling coaxial cylinder viscometer was used to measure the melt flow behaviour of a commercial polystyrene with Mw 260,000. The shear stress region extended down to 0.6 × 10⁴ dynes/cm² and shear rates were as low as 3 × 10^?2 sec^?1 at 186°C. The shear rate-shear stress plots were linear at low shear stresses with slopes (differential viscosities) of 3.3 × 10⁵ poises at total shear less than 120 units and decreasing differential viscosity with higher total shear. The flow curves at relatively low total shear were initially dilatant and became pseudoplastic with increasing shear stress. The inflection point represents a Newtonian apparent viscosity, which agrees fairly well with literature values for polystyrenes of the same Mw. Newtonian apparent viscosity is characteristic of a point value of shear stress and shear rate and is not necessarily a plateau region. Observation of a Newtonian region with decreasing shear stress or shear rate does not prove that this flow regime persists unchanged to zero values of the experimental parameter. The existence and magnitude of the Newtonian apparent viscosity reflects shear history of the polymer as well as its constitution and molecular weight distribution.     

Superimposed effects in high‐shear‐rate capillary rheology of polystyrene melt

During micro‐injection molding, the polymer melt may undergo a shear rate up to 10⁶ s^?1, at which the rheological behaviors are obviously different from those in conventional molding process. Using both online and commercial rheometers, high‐shear‐rate capillary rheology of polystyrene (PS) melt is analyzed systematically in this work. The accurate end pressure drop and pressure coefficient of viscosity are determined via the enhanced exit pressure technique. Experimental and theoretical investigations are conducted on four significant effects, that is, the dissipative heating, end pressure loss, pressure dependence, and melt compressibility in capillary flow. For the PS melt, which exhibits distinct temperature and pressure dependence of viscosity, both dissipation and end effects become pronounced as the shear rate exceeds 2 × 10⁵ s^?1. From lower to higher shear rates (10³–10⁶ s^?1), the competition between dissipation and pressure effects results in the overestimation to underestimation of Bagley‐corrected pressure drop, and finally the comprehensively corrected viscosity becomes about half of the uncorrected one owing to the enhanced superimposed effects. Moreover, the compressibility shows a minor influence on the shear viscosity. Under the shear rate range investigated, the power‐law relationship is sufficient for describing the corrected viscosity curve of PS melt used. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Comparison of superimposed effects in high‐shear‐rate capillary rheology of polystyrene,polypropylene, and linear low‐density polyethylene melts

Polymer melts exhibit unique rheological behaviors at high shear rate up to 10⁶ s^?1, which is a common phenomenon in micro‐injection molding. Both online and commercial capillary rheometers, which were modified to allow regulation of back pressure, were used for measuring the melt shear viscosities of polystyrene (PS), polypropylene (PP), and linear low‐density polyethylene (LLDPE) under high shear rates. The rheological characteristics of the three melts were compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6 × 10⁵, 8.0 × 10⁵, and 2.8 × 10⁶ s^?1 for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS > PP > LLDPE. It seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 10⁵ s^?1 for the PS melt among the three melts. POLYM. ENG. SCI., 55:506–512, 2015. © 2014 Society of Plastics Engineers     

Slit die flow measurements of a liquid crystalline polyesteramide and its blends with polyarylate

A commercial thermotropic polyesteramide and its blends with polyarylate are the object of a slit die flow rheological study. The measurements are carried out at 280°C, a temperature slightly above the melting temperature of the thermotropic, covering a shear rate range 10^?1 s^?1 to 10²s^?1. Except in the case of the thermotropic polymer, the pressure profiles are upward parabolic which is attributed to the dependence of the viscosity on pressure. The most striking result is the observed downward curvature in pressure profiles obtained for the liquid crystalline polyesteramide: no explanation is given for this phenomenon, for the present. The elasticity of the polymer melts is expressed in terms of the exit pressure and the extrudate swell. The thermotropic polyesteramide presents negative values of both parameters (e.g. samples shrink instead of swell). Viscosity and elasticity present negative deviation from linearity when plotted against composition; this reduction in the rheological functions, caused by the addition of liquid crystal, is more pronounced at high shear rates.     

The rheology and spin coating of polyimide solutions

The rheological properties of five types of concentrated polyamic acid and polyimide solutions are characterized by non-Newtonian shear viscosity η(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma} $\end{document}) and primary normal stress coefficient Ψ₁(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma} $\end{document}) measurements over a wide range of shear rates. Onset of non-Newtonian flow of the polyamic acid solutions was observed in the shear rate range 30 to 400s^?1 and of the fully imidized polyimide solution at below 3 × 10^?2s^?1. Significant viscoelastic properties exemplified by normal stresses were observed in all the solutions. The solution rheology results are discussed in the context of spin coating for the deposition of thin films. The relative magnitude of effects of non-Newtonian flow on the dynamics of spin coating is assessed with a Deborah number characteristic of the flow.     

Zum Fließverhalten von kurzglasfasergefüllten Styrol-Acrylnitril-Copolymeren

The viscosity of high polymer melts increases usually when adding fibres. Such an increase has been measured for a short fibre reinforced styrene/acrylonitrile copolymer with 25 and 35% (by weight) glasfibres on a rotational viscometer in the range of shear rates from 10^?3 to 10¹s^?1 for different temperatures and pressures. The viscosity curves show a zero shear viscosity. Its dependence on temperature, pressure and concentration of fibres can be described by straight lines. Furthermore it is possible to shift the viscosity curves in a way that they form a temperature- and pressure-independent, and even a concentration-independent master curve.     

A model viscoelastic fluid

Shear stress and first normal stress difference data are presented for materials which exhibit a constant viscosity and yet at the same time exhibit elasticity levels of the same order as polymer melts. Flow pattern observations in circular die entry flows in conjunction with independent shear and normal stress measurement strongly suggest that these fluids would make excellent model fluids for melt studies. Studies in which the influence of elasticity in the absence of shear thinning and fluid inertia can easily be made. Furthermore it is clearly shown that a realistic solution to the die entry flow problem is not obtained using second order flow theory. In the second order region the secondary cell is observed to be almost identical in size to the cell observed for an inelastic Newtonian fluid in creeping flow. Marked growth in the secondary cell as a function of elasticity is not observed until the shear rates exceed the region of second order behavior. This growth in cell size as a result of elasticity is followed at higher shear rates by a spiraling flow instability like that observed for some polymer melts.     

An experimental study of morphology and rheology of ternary Pglass‐PS‐LDPE hybrids

Ternary blends of low‐density polyethylene (LDPE), polystyrene (PS), and a low T_g tin‐based phosphate glass (Pglass) were prepared at compositions ranging from 0–50 vol% Pglass in which either LDPE or PS was the continuous matrix phase. Differential scanning calorimetry was used to investigate the phase behavior of the pure components, PS‐LDPE blends and binary Pglass‐polymer hybrids. Interesting steady‐shear and transient rheology was observed for the hybrids. In particular, the steady shear viscosity curves for the hybrids of ?_Pglass ≤ 30% exhibited unusual, four‐region flow behavior, similar to that of liquid crystalline polymers. Two Newtonian plateaus at low (${\rm \dot \gamma }$ ≤ 0.1 s^?1) and moderate (0.4 ≤ ${\rm \dot \gamma }$ ≤ s^?1) shear rates connected by two distinct shear‐thinning regimes were apparent. This observed rheology is ascribed to a unique composite morphology of these multi‐component systems. Rheological data on the binary Pglass‐polymer systems suggest that the presence of the Pglass within both PS and LDSE contributes significantly to this unusual behavior, perhaps because of the interfacial behavior between the phases. Micrographs obtained via scanning electron microscopy reveal preferential placement of the Pglass phase dispersed within the PS‐phase and surrounding the LDPE phase. Optical shearing data confirmed the evolution of this microstructure under specific shear conditions.     

Concentration,temperature and deformation effects in concentrated polymer solutions with volatile solvents

A novel high pressure polymer solution viscometer has been experimentally evaluated using the polystyrene/ethylbenzene system. The polymer solutions range in concentration from 60 weight percent polystyrene to the pure melt. The overall temperature range is 132°C to 240°C. The shear rates range from roughly 5 s^?1 to 2000 s^?1. It has been concluded that the present method is useful in determining the shear dependent behavior of these volatile solutions, The shear dependent nature of this system is consistent with accepted non-Newtonian viscosity theory.     

Rheology of 1‐butyl‐3‐methylimidazolium chloride cellulose solutions. III. Elongational rheology

The elongational rheology of solutions of cellulose in the ionic liquid solvent 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl) was measured at 80, 90, and 100°C; 8, 10, and 12 wt% cellulose; Hencky strains 5, 6, 7; and strain rates from 1 to 100 s^?1. Master curves were generated by shifting the elongational viscosity curves with respect to temperature and Hencky strain. Also, general master curves were generated by simultaneously shifting with respect to both temperatures and Hencky strain. From the Arrhenius plots of the temperature shift factors, the activation energy for elongational flow was determined. The elongational rheology of these solutions was elongational strain rate thinning similar to that of their shear behavior and polymer melts and they were also strain hardening. Both effects and the viscosity increased with cellulose concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Shear dependence of thermal conductivity in polyethylene melts

Thermal conductivity measurements with a modified Couette flow cell were obtained as a function of shear rate for two linear polyethylene melts of weight-average molecular weights 27,300 and 56,700, respectively. The lower-molecular-weight polyethylene revealed a maximum decrease in thermal conductivity of 55 percent at 150 s^?1. After shearing at 400 s^?1, approximately 90 minutes was required to recover the value corresponding to the zero shear condition. This was considered consistent with molecular orientation into the flow direction during shear with a subsequent relaxation upon the removal of stress. The higher-molecular-weight polyethylene gave a similar decrease in thermal conductivity at 50 s^?1. Unlike the lower-molecular-weight melt, an increase was observed at higher shear rates. Enhancement of energy transport via cluster flow mechanism was presented as a possible interpretation of these results. A theory of molecular orientation of liquid poly(dimethylsiloxane) (PDMS) under shear flow was previously developed from thermal conductivity and birefringence data of this material. An attempt to clarify the difference in behavior between the two melts examined in this work, and between the polyethylene melts and the PDMS previously studied is presented.     

Rheo-optical investigations of highly concentrated polyurethane solutions for industrial processing into elastic fibres

On a large industrial scale, segmented polyurethanes are processed from solution in the dry spinning process to produce textile fibres. Rheo-optical investigations of the flow behaviour of polyurethane solutions enable new material functions to be determined and provide important information for processing. Proportional increases with shear rate were observed for the flow birefringence, Δn', and the orientation, ϕ. The polymer segments were more easily aligned in the direction of the shear field in more concentrated solutions than in dilute solutions. The same tendency was observed for samples with differing molar masses. An ideal standardisability for the temperature (in a window of 20 K) was found over the entire range of shear rate and, hence, the change in the Newtonian and non-Newtonian flow behaviour was also observed to be completely identical. Using the stress-optical rule, it was possible to determine the first normal stress difference. The stress-optical coefficient, C, was 2.6·10^–9 Pa^–1. The normal stress values lie in the range of accessible shear rates below the shear stress, but do, however, rapidly approach this value as the strain increases. Even at a shear rate of 100 s^–1 the viscoelasticity of a 17 wt.-% polyurethane solution is already significant. At a high shear rate the Weissenberg number, We, which is a measure of the viscoelasticity, has a constant limiting value that only depends on the power law exponent, n. Its values in the range of high shear rates mostly lie between 2 and 3 and are rarely (for the smallest n) above 3.     

The rheology of filled polymers

The flow properties of polymer melts containing fillers of various shapes and sizes have been examined. If there is no failure of either the filler or polymer in the solid state, then the modulus enhancement for randomly distributed filler is equal to the melt viscosity enhancement under medium shear stress conditions (10⁴ Nm^?2) in simple shear flow or in oscillatory shear flow. Submicron-size fillers, in particular, can form weak structures in the melt that greatly increase the low shear rate viscosity without changing the modulus of the solid proportionately. The highly pseudo-plastic nature of polymer melts at shear stresses of 10⁶ Nm^?2 means that, even without orientation of filler particles toward the flow direction, the viscosity enhancement is less than at lower shear stresses.     

Rheological behavior of molten epoxide prepolymers

Flow properties of four molten epoxide prepolymers of number average molecular weight 900(I), 1,500(II), 2,100(III) and 4,000(IV), were measured at temperatures ranging from 361 to 463K, and shear rates from 500 to 10,000 s^?1. Apparent shear viscosities showed that all prepolymers used have Newtonian behavior up to shear rates of 2,000 s^?1. Shear thinning occurs at higher shear rates. Flow activation energies at constant shear rates in the range of 500 to 7,000 s^?1 vary for prepolymer III from 5 to 24 kcal/mol, and for prepolymer IV from 9 to 25 kcal/mol. Flow indices in the same shear rate range vary for prepolymer III from 1.0 to 0.7 and for prepolymer IV from 1.0 to 0.3.