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     

On the non‐newtonian viscous behavior of polymer melts in terms of temperature and pressure‐dependent hole fraction

A new theoretical non‐Newtonian viscosity model is developed by taking the fractional series expansion of Eyring's shearing strain rate. A broad range of experimental rheological data of various polymer melts including polyethylenes, polypropylene, polystyrene, poly (methyl methacrylate), and polycarbonate are fitted well using the proposed model. From the model; zero shear, constant shear‐stress and constant shear‐rate viscosities are derived as a linear function of viscosity related quantity, Y_h, called “thermo‐occupancy function” and their coefficients are discussed in detail. The thermo‐occupancy function is expressed in terms of temperature and structural vacancies such as hole fraction computed from the Simha‐Somcynsky Hole Theory (SS). In addition, the derivative of the logarithm of viscosities with respect to the hole fraction, named as viscoholibility, is observed decreases with the increasing hole fraction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40540.     

Rheology of concentrated sulfonated poly(ether ether ketone) solutions

Sulfonated polyether ether ketone (SPEEK), an ionic polymer, has been shown to be a potential candidate for fuel cell electrolyte as a proton exchange membrane. Rheological behavior of SPEEK solutions is of great interest to understand the molecular associations as well as due to implications in membrane processing. In this work, SPEEK of various degrees of sulfonation (58–80) was prepared and rheology of concentrated solutions of SPEEK was studied. The rheological properties were evaluated using steady and oscillatory shear. It was found that steady shear viscosity and storage modulus at any given concentration, is the highest for the lowest degree of sulfonation SPEEK solutions in N‐methyl‐2‐pyrrolidone. The low frequency plateau in storage modulus was observed at some combinations of degrees of sulfonation and concentrations, indicating gel‐like behavior in these SPEEK solutions. No significant change in rheological behavior was observed with different polar solvents. Increase of several orders of magnitude in viscosity, storage and loss moduli were observed with increasing concentrations. The role of hydrophobic aggregation and inter‐chain associations in determining rheology of SPEEK solutions is argued based on comparisons with other material systems. The rheological behavior of SPEEK solutions with 70 as the degree of sulfonation, suggests crossover from hydrophobic‐hydrophilic balance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40044.     

Preparation of hydrophilic polysulfone porous membrane by use of amphiphilic cellulose

A cellulose‐based amphiphilic co‐polymer with grafted myristyl groups was synthesized and used as an additive to modify polysulfone (PSf) membranes. Fourier transform infrared (FTIR) spectroscopy and Solid‐state cross polarization magic angle spinning carbon‐13 nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy were used to characterize the structure of the synthesized amphiphilic cellulose. The good compatibility between amphiphilic co‐polymer and PSf was confirmed by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) was conducted to inspect morphology of the membrane. Furthermore, Thermal performance was indicated by thermogravimetric analysis (TGA). Contact angle, flux and retention behavior were also measured in this work. The structural similarity enhanced compatibility among components by introducing flexible alkyl groups. According to the findings obtained from characterization, better compatibility of cellulose with PSf was achieved after amphiphilic treatment. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41664.     

Operating window of solution casting. II. Non‐Newtonian fluids

The operating windows of the solution casting of two polymeric liquids were evaluated experimentally. The experimental setup and procedure were the same as used previously for the casting of Newtonian fluids (Journal of Applied Polymer Science 2013, 129, 507–516). Aqueous carboxymethylcellulose/glycerol solutions exhibited pure shear‐thinning behavior at low polymer concentrations but became viscoelastic at high polymer concentrations, whereas polyacrylamide/glycerol solutions showed viscoelastic behavior over a wide range of concentrations. The shear‐thinning behavior, in conjunction with a low level of elasticity, of the casting solution was found to be useful in expanding the stable operating windows. However, an opposite effect on the operating windows was found for highly elastic solutions. The non‐Newtonian effect on the maximum stable casting speed was prominent only when the capillary number exceeded unity. Defects outside of the operating window were mostly similar to those observed in Newtonian solution casting. For highly concentrated solutions, a new rough surface defect was observed. This defect could be attributed to polymer chain entanglement, alignment, or breakup. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41411.     

Vitrification phenomena in polysulfone/NMP/water system

The vitrification line for the ternary system of polysulfone (PSf)/N‐methyl‐2‐pyrrolidinone (NMP)/water was determined by differential scanning calorimeter (DSC) measurements with varying compositions. Pure PSf showed both α‐ and β‐transition temperatures (T_g,α = 187.5°C, T_g,β = −21.4°C). The T_g,α of PSf decreased with increasing solvent concentration. The T_g,α of PSf decreased linearly with the addition of NMP in the concentration range of 70–90 wt % polymer. The vitrification line was indicated in the phase diagram for the ternary system of PSf/NMP/water at 15 and 60°C. As the temperature is increased, a high polymer concentration was needed to reach the vitrification condition. The vitrification composition of the polymer in the binary system of PSf and NMP was 72.0 wt % at 15°C and 79.8 wt % at 60°C. We also found that the slope of the vitrification line changed with the temperature and that a small amount of water (10–20 wt %) can induce the vitrification of the polymer solution in the PSf/NMP/water system at 15°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 431–438, 1999     

Rheological effects of polyethylenes in film blowing

The aim of this work is to correlate the rheological properties and processability of various polyethylenes during the film‐blowing process. The effect of rheology on the kinematics and dynamics of film blowing for five different polyethylene resins has been extensively studied using a fully instrumented laboratory unit. The complex viscosity, shear viscosity, uniaxial elongational viscosity, and non‐uniform biaxial elongational viscosity, as well as the strain rates and stresses during film blowing, have been determined and correlated to the bubble stability. G′ versus G″ plots were found to be virtually independent of temperature for all polymers investigated. The more elastic polymers (larger G′ values) were found to be more stable in film blowing. Also, the more stable polymer melts were found to be those possessing larger elongational properties.     

Macromolecular motions and hydrodynamic radius variation in dilute solutions under shear action

Understanding the dynamics of single polymer chains and rheological mechanism in dilute polymer solutions under shear stress is essential for fields such as the petroleum and food industries, biomedical materials and drug delivery. Here we present an experimental method for measuring the viscosity of polymer solutions and studying the variation of single polymer chain conformation and the mechanism of molecular motions according to the relationship between the intrinsic viscosity, [η], and the shear rate. Of striking interest is that we find that [η] changing with the shear rate presents three stages which may explain the nature of the viscoelastic performance of polymer solutions and the isolated molecular motions. The significance of these results is the finding of the polymer chain deformation to match the pore throat which has enormous potential implications in drug delivery, genetics and biomedicine © 2014 Society of Chemical Industry.     

Dispersive mixing efficiency of an elongational flow mixer on PP/EPDM blends: Morphological analysis and correlation with viscoelastic properties

Polypropylene and ethylene‐propylene‐diene terpolymer (PP/EPDM) blends were melt compounded in a new mixing device, designed in our laboratory under the trademark of RMX®, which predominantly generates elongational flows. Dispersion of the EPDM minor phase in PP was carried out in both RMX® and in an internal mixer (Haake Rheomix 600) at equivalent specific mixing energies and the resultant morphologies obtained by SEM were analyzed and compared. A better dispersive mixing efficiency of the RMX® mixer, i.e., lower D_n and D_v of the dispersed EPDM phase was observed. The impact of elongational flow was more pronounced for blends having a high viscosity ratio p, indicating an enhanced droplet break‐up mechanism, which was attributed to the combination of high shear rates inside the mixing element and important elongational flows in the convergent/divergent zones. The morphology of the blends was correlated with their linear viscoelastic properties by using the Palierne model. Very good agreement was found for the PP/EPDM 80/20 blends but for higher EPDM content, the Palierne model failed to describe the rheological behavior, which was attributed to percolation of the minor phase with increasing the concentration. Higher elasticity at low frequencies was observed for blends processed in the RMX®, which was attributed to a higher generated interfacial area. POLYM. ENG. SCI., 54:1444–1457, 2014. © 2013 Society of Plastics Engineers     

Synthesis and characterizations of hydrophobically associating water‐soluble polymer with nonionic surfmer

In this article, a hydrophobically associating copolymer (2‐acrylamido)‐2‐methylpropanesulfonic acid (AMPS)/AA‐EO₂₅C₁₂ was synthesized by AMPS and nonionic surfmer AA‐EO₂₅C₁₂ through free radical copolymerization. The structure of copolymer was characterized by FT‐IR and ¹H‐NMR. The properties of copolymer were studied and the results indicated that the copolymer exhibits good thickening ability due to intermolecular hydrophobic associations as the apparent viscosity of the copolymer solution increases sharply with increasing polymer concentration. Compared with homopolymer PAMPS, the rheological test indicates that the copolymer solution shows shear thickening behavior at low shear rate region. Besides, the copolymer exhibits interfacial activity as it can reduce the interfacial tension to 10° level, and ability to form emulsion with good stability, which is due to successfully introducing the structure of nonionic surfmer AA‐EO₂₅C₁₂ to the polymer chain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43195.     

Rheological behaviour of some amphiphilic β‐cyclodextrin‐based azo aromatic polyurethanes in N,N‐dimethylformamide solutions

Amphiphilic β‐cyclodextrin‐based azo aromatic poly(ether urethane)s with different soft segment lengths have been synthesized and characterized. Hydrogen bonding in these systems was demonstrated by Fourier transform infrared spectroscopy analysis (carbonyl stretching region). A rheological study was performed on solutions of the synthesized poly(ether urethane)s in N,N‐dimethylformamide at various concentrations and temperatures by employing parallel plate geometry, and a comparative evaluation of the influence of the structural components on the viscometric responses was performed. The rheological behaviour was found to be strongly dependent on the chemical composition of the synthesized polyurethanes which promotes self‐assembly and structuring in solution. Hard segment content and polymer concentration influence pseudoplastic shear‐thinning flow behaviour. The rheology can be interpreted in terms of hydrophobic associations and chain entanglements and a hydrogen bonding network occurring in solution. The start‐up flow of the polymer solutions is determined by the lifetime of the associative polymer segments. Shear stress plateaux indicative of ‘shear banding’ behaviour explained by the structuring of the polymer solutions at increased temperatures were obtained. The studied amphiphilic polyurethane solutions are thermoresponsive systems exhibiting viscosity increase with increasing temperature contrary to the usual Arrhenius thermo‐thinning behaviour. At constant shear rate viscosity was found to increase with increasing temperature due to thermo‐association. © 2014 Society of Chemical Industry     

Viscosity behavior and surface and interfacial activities of hydrophobically modified water‐soluble acrylamide/N‐phenyl acrylamide block copolymers

In this study, the viscosity behavior and surface and interfacial activities of associative water‐soluble polymers, which were prepared by an aqueous micellar copolymerization technique from acrylamide and small amounts of N‐phenyl acrylamide (1.5 and 5 mol %), were investigated under various conditions, including the polymer concentration, shear rate, temperature, and salinity. The copolymer solutions exhibited increased viscosity due to intermolecular hydrophobic associations, as the solution viscosity of the copolymers increased sharply with increasing polymer concentration, especially above a critical overlap concentration. An almost shear‐rate‐independent viscosity (Newtonian plateau) was also displayed at high shear rates, and typical non‐Newtonian shear‐thinning behavior was exhibited at low shear rates and high temperatures. Furthermore, the copolymers exhibited high air–water and oil–water interfacial activities, as the surface and interfacial tensions decreased with increasing polymer concentration and salinity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2290–2300, 2003     

Effects on the melt rheology of systems of Nd‐Fe‐B particles suspended in a poly(phenylene sulfide) and liquid crystalline polymer blend

The melt rheology of blends of a liquid crystalline polymer (LCP) and poly(phenylene sulfide) (PPS) and their composites with ferromagnetic Nd‐Fe‐B particles (MQP) was studied. We investigated the effects of LCP concentration, Nd‐Fe‐B particle volume fraction and size, distribution, and shear rate on the rheological properties of these composites. Enthalpy of fusion changes that were observed resulted from the addition of the LCP and Nd‐Fe‐B particles to the polymer blends/composites. The shear rate and frequency dependencies of the materials revealed a viscosity reduction at low (1–3 wt%) and moderate (10–15 wt%) LCP concentrations, and strong effects on the shear‐thinning characteristics of the melt. The suspensions of polydispersed Nd‐Fe‐B particle configurations in PPS that were of lower size ratios gave better processability, which is contradictory to previously reported behavior of suspensions containing spherical particles. Specifically, the compositions with unimodal and a bimodal distribution of Nd‐Fe‐B particles gave the lowest viscosities. The experimental data were correlated with semi‐empirical viscosity model equations of Maron‐Pierce, Krieger‐Dougherty, Eilers, and Thomas and were found to be consistent with the data. The maximum packing fraction, ϕ_m, of the MQP particles was estimated to be within the range of 0.78 ϕ ≤_m ≤ 1.0 through graphical and parametric evaluation methods.     

Effect of oxalic acid on the rheological properties of dope solution of poly[acrylonitrile‐co‐(methyl acrylate)‐co‐(itaconic acid)]

The very high dope viscosity of concentrated dope of poly[acrylonitrile‐co‐(methyl acrylate)‐co‐(itaconic acid)] (with M?_v = 10.67 × 10⁵g mol^?1) in DMF could be diminished significantly by the addition of oxalic acid (OXA). The change in steady shear rheological behaviour caused by OXA has been analysed for the dope using a rheometer working in the viscosity mode. The temperature dependence of η₀ conformed to the Arrhenius‐Frenkel‐Eyring equation. ΔG_v decreased marginally with OXA concentration, and the least value was observed at an OXA concentration of 0.63 % by weight. Shear thinning behaviour was observed under higher shear rates for the terpolymer solutions in the presence and absence of OXA. The pseudoplasticity index (n) showed an abrupt initial increase on addition of OXA. The OXA concentration of 0.63 % by weight was advantageous for decreasing the viscosity of the polymer dope. The reduction in viscosity is attributed to the disturbed polymer‐polymer interactions by way of H‐bonding of OXA with the polymer. OXA‐containing dope at higher shear rate could achieve very low viscosities. Copyright © 2004 Society of Chemical Industry     

Modeling of nonlinear extensional and shear rheology of low-viscosity polymer melts

The hierarchical multi-mode molecular stress function (HMMSF) model developed by Narimissa and Wagner [Rheol. Acta 54, 779–791 (2015), and J. Rheol. 60, 625–636 (2016)] for linear and long-chain branched (LCB) polymer melts were used to analyze the set of transient elongational and shear viscosity data of two LCB low-density polyethylenes (1840H and 2426 k), and a linear poly-(ethylene-co-α-butene), PEB A-780090 as reported by [Li et al. J. Rheol. 64, 177 (2020)], who had developed a new horizontal extensional rheometer to extend the lower limits of elongational viscosity measurements of polymer melts. Comparison between model predictions and elongational stress growth data reveals excellent agreement within the experimental window, and good consistency with shear stress growth data, based exclusively on the linear-viscoelastic relaxation spectrum and only two nonlinear model parameters, the dilution modulus G_D for extensional flows, and in addition a constraint release parameter for shear flow.     

Altering the viscosity of cationically modified cellulose polymers by the addition of salt

The concentration dependence of viscosity is examined for four cationically modified cellulose polymers (UCARE? JR400, UCARE? JR30M, UCARE? LR400, and UCARE? LR30M) in both salt‐free and 50 mM NaCl solution. Similarities in the four polymer systems include: Newtonian viscosity in the dilute regime, shear thinning at higher concentrations, four concentration regimes in salt‐free solution, and three concentration regimes in salt solution. The zero shear rate viscosity and the degree of shear thinning increase with increasing polymer concentration in both salt and salt‐free solutions. While the addition of salt to the lower molecular weight polymers JR400 and LR400 resulted in small changes in viscosity across all concentrations, JR30M and LR30M exhibited significant decreases (up to 81%) and increases (up to 57%) in viscosity upon the addition of salt in the semidilute and entangled regimes, respectively. This viscosity increase in the entangled regime (when comparing salt‐free and 50 mM NaCl solutions) is reported for the first time in cationically modified cellulose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41616.     

The viscoelastic behavior of concentrated polyacrylonitrile/1‐butyl‐3‐methylimidazolium chloride from solution to gel

The viscoelastic behavior of concentrated polyacrylonitrile (PAN) /1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) solutions at different concentrations and temperatures has been investigated by rheology. For concentrated polymer solutions at low temperature (40°C), the shear viscosity was found to show a raid decrease from the ending of Newtonian plateau. At relatively high shear rate or frequency for the concentrated PAN/[BMIM]Cl solutions, the deviation from the empirical Cox–Merz rule was quite evident, which suggested the formation of heterogeneous structures within these solutions. However, the dependence of G′ and G″ on angular frequency presented approximate linearity with similar slope at some temperatures between 100°C and 20°C. All the results lead us to the fact that the gelation has occurred within the concentrated solutions during cooling and the process was found to be thermoreversible. The gelation temperatures of the solutions have exhibited strong concentration dependence. It may be suggested that the microphase separation may be the major reason for the gelation of the concentrated PAN/[BMIM]Cl solutions during cooling process. POLYM. ENG. SCI., 54:598–606, 2014. © 2013 Society of Plastics Engineers     

Shear and elongational flow properties of peroxide‐modified wood/low‐density polyethylene composite melts

Adding fillers to a polymer melt may result in a strain softening behavior in elongational flow in long‐chain branched materials, showing strain‐hardening behavior when compared with unfilled one. To improve the strain‐hardening properties in wood/LDPE composites, the effect of peroxide concentration on both the molecular architecture and molar mass distribution, and the rheological quantities in shear and elongation is studied. Addition of wood flour increases the viscosity according to a logarithmic mixing rule, as expected from the large particle size and the filler fractions used. The peroxide has multiple effects on the molar architecture of the polymer. First, a gel fraction of cross‐linked material is formed, the concentration of gel being dependent of the amount of peroxide used. Second, a higher molar mass component is detected, leading to higher value of M_w and to a broader molar mass distribution. Finally, the degree of long‐chain branching unexpectedly decreases with increasing peroxide content. The changes in molecular architecture are hardly influenced by addition of the wood flour. The peroxide treatment leads to an improved strain‐hardening behavior, detected by elongational viscosity and melt strength measurements. However, the addition of wood flour decreases the amount of strain hardening.POLYM. COMPOS., 33:2084–2094, 2012. © 2012 Society of Plastics Engineers     

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.     

The effect of shear rate on the molecular weight determination of acrylamide polymers from intrinsic viscosity measurements

The rheological response of dilute solutions of high molecular weight polyacrylamides at low shear rates has been measured using a capillary viscometer that provided for a fivefold variation in shear rate at each concentration. The non-Newtonian effects were found to be significant for polyacrylamides with number-average molecular weights exceeding 10⁶. The molecular weight average–intrinsic viscosity relationship most widely used in the literature, [η] = 6.80 × 10^?4M , was found to be valid when [η] was measured at high shear rates where the polymer solutions approached Newtonian behavior. A new relationship was developed relating M _n to the intrinsic viscosity extrapolated to zero shear rate.