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.     

Molecular dynamics study on the viscosity of glass-forming systems near and below the glass transition temperature

Temperature-dependent viscosity is critical to decipher two profound questions in condensed matter physics, namely the glass transition and the relaxation of amorphous solids. However, direct measurement of viscosity over a large temperature range is extremely difficult. Here, using classical molecular dynamics (MD) simulations, we report a novel method to calculate the equilibrium viscosity of supercooled liquid both above and below the glass transition temperature (T_g) and to estimate the nonequilibrium viscosity of glass down to room temperature. Based on the shoving model, we derived an analytical formula showing that the shear viscosity in logarithmic scale changes linearly with the shear-induced variation in shear modulus or potential energy of the glass-forming system. The shear viscosity as a function of steady-state potential energy of liquid under different shear strain rates can be directly calculated in MD simulations; together with its equilibrium potential energy, one can extrapolate the zero-strain-rate equilibrium viscosity. We verified the proposed model by reliably calculating equilibrium viscosity near T_g of four glass-forming systems (Kob–Andersen system, silica, Cu_45.5Zr_45.5Al₉, and silicon) with different fragilities. Furthermore, our model can estimate the nonequilibrium viscosity of glass below T_g; the upper-bound nonequilibrium viscosity of amorphous silica and silicon at room temperature are calculated to be ~10³² and 10²⁵ Pa·s, respectively.     

Rheological properties of poly(trimethylene terephthalate) in capillary flow

The shear viscosity, extensional viscosity, and die swell of the PTT melt were investigated using a capillary rheometer. The results showed that the PTT melt was a typical pseudoplastic fluid exhibiting shear thinning and extensional thinning phenomena in capillary flow. There existed no melt fracture phenomenon in the PTT melt through a capillary die even though the shear rate was 20,000 s^?1. Increasing the shear rate would decrease the flow activation energy and decline the sensitivity of the shear viscosity to the melt temperature. The molecular weight had a significant influence on the flow curve. The flow behavior of the PTT melt approached that of Newtonian fluid even though the weight‐molecular weight was below 43,000 s^?1 at 260°C. The extensional viscosity decreased with the increase of the extensional stress, which became more obvious with increasing the molecular weight. The sensitiveness of the extensional viscosity to the melt temperature decreased promptly along with increasing the extensional strain rate. The die swell ratio and end effect would increase along with increasing the shear rate and with decreasing the temperature, which represented that the increase of the shear rate and the decrease of temperature would increase the extruding elasticity of the PTT melt in the capillary die. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 705–709, 2005     

Viscosity of polystyrene near the glass transition

A quantitative explanation is given for the apparent viscosity increase with increasing capillary shear rate for polystyrene at temperatures approaching the glass transition, T_g. Possible shifts in T_g as a function of the parameters shear rate, frequency, and pressure are interrelated to viscosity changes. Experimentally, the Instron capillary rheometer and the Weissenberg rheogoniometer provided a means for uncoupling the variables for individual consideration. Calculated and experimental data for the apparent viscosity as a function of the given parameters are presented and discussed. The explanation of the apparent viscosity increase in capillary flow can be quantitatively explained through the pressure dependence of T_g. Brief mention is made of the pressure effects on the Bagley and Rabinowitsch corrections normally made in capillary measurements.     

Effects of ultrasonic oscillations on rheological behavior and mechanical properties of novel propylene‐based plastomers

The effects of ultrasonic oscillations on the die pressure, productivity of extrusion, melt apparent viscosity, melt surface appearance, and die swell of novel propylene‐based plastomers were studied in a specially designed ultrasonic oscillations extrusion system developed in our laboratory. The effects of ultrasonic oscillations on molecular weights, tensile strength, and dynamic mechanical properties of extrudates were also studied. The experimental results showed that the presence of ultrasonic oscillations during extrusion could significantly increase the productivity of plastomers at the same die pressure, and reduce die swell and melt fracture such as sharkskin at a given screw rotation speed. The die pressure and apparent viscosity of plastomers remarkably decreased with increasing ultrasonic intensity. Introduction of ultrasonic oscillations into plastomer melts can improve their processibility. The possible mechanism for ultrasonic improvement of rheological behavior was also proposed in this article. Under certain conditions, ultrasound‐assisted extrusion could slightly decrease the glass transition temperature (T_g) and storage modulus of plastomers due to the minor reduction in molecular weights, but showed no significant impact on yield strength and strength at break. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Studies on the polyblends of poly(vinyl chloride) with various methacrylate copolymers,melt rheological properties. II

Studies have been made on the melt rheological properties of poly(vinyl chloride) (PVC) with copolymers of methyl methacrylate (MMA) and methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), and 2-ethyl hexyl acrylate (EHA) at a blending ratio of 80:20. Effect of blend composition on shear stress–shear rate, melt viscosity, melt elasticity, and extrudate distortion have been studied. A significant decrease in the melt viscosity is observed on incorporation of low T_g, acrylate copolymers such as those with BA and EHA, thereby reducing the processing temperature. First normal stress and die swell ratio also decreases with an increase in the side chains of acrylate copolymer. PVC blended with P(MMA-co-BA) and P(MMA-co-EHA) is sensitive to both temperature and shear stress.     

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.     

Morphology,rheology, and mechanical properties of dynamically cured EPDM/PP blend: Effect of curing agent dose variation

The structure development, rheological behavior, viscoelastic, and mechanical properties of dynamically cured blend based on the ethylene–propylene–diene terpolymer (EPDM) and polypropylene (PP) with a ratio of 60/40 by weight were studied. The variation of two‐phase morphology was observed and compared as the level of curing agent was increased. Meanwhile, as the level of curing agent increased, viscosity as a function of shear stress always increased at a shear stress range of 2.2 × 10⁴ to 3.4 × 10⁵ Pa at the temperature of 200°C, yet viscosity of the blend approached each other at high shear stress. Dynamic mechanical spectra at different temperatures show that dynamic modulus (E′) of the blend exhibits two drastic transitions corresponding to glass transition temperature (T_g) of EPDM and T_g of PP, respectively. In the blends T_gs of EPDM increase and T_gs of PP almost remain unchangeable with an increase in curing agent level. Tensile strength increased, yet elongation at break decreased as the level of curing agent is increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 357–362, 2004     

Die swell in elastic and viscous fluids

Measurements of die swell have been made on an elastic liquid and a Newtonian liquid of similar viscosity (～ 10⁴ N s m^?2). The Reynolds number was about 10^?8. The Newtonian liquid has a die swell of 13.5% which was independent of shear rate. The die swell of the elastic liquid increased with shear rate and seemed to be asymptotic to the Newtonian die swell at low shear rates.     

Linear low density polyethylenes and their blends: Part 2. Shear flow of LLDPE's

The steady state and dynamic shear behavior of eleven commercial linear low density polyethylenes (LLDPE) and one low density polyethylene (LDPE) resin were measured in capillary and parallel plate geometries at T = 150 to 230°C. The extrudate swell and the Bagley correction were determined. A large pressure effect on capillary flow of narrow molecular weight distribution LLDPE was observed and a new corrective procedure was proposed. After the correction the steady state viscosity was found to be equal to the dynamic (not complex) viscosity: η(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) = η'(ω = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}). A newly proposed four parameter relation between η and the deformation rate was found to provide a simple means for computation of the zero shear viscosity, ηo, and the primary relaxation time. Both these parameters showed a high degree of correlation. The expected relation: ηo ∝? M_w^3.4 was observed for low molecular weight samples with low polydispersity. The LLDPE activation energy of flow, E_σ=29.9 ± 1.8 kJ/mole, was determined.     

Polymer multilayer films for high temperature capacitor application

Advanced film capacitors require polymers with high thermal stability, high breakdown strength, and low loss for high temperature dielectric applications. To fulfill such requirements, two polymer multilayer film systems were coextruded via the forced assembly technique. High glass transition temperature (T _g) polycarbonate (HTPC, T_g = 165 °C) and polysulfone (PSF, T_g = 185 °C) were multilayered with a high dielectric constant polymer, poly(vinylidene fluoride) (PVDF), respectively. The PSF/PVDF system was more thermally stable than the HTPC/PVDF system because of the higher T_g for PSF. At temperatures lower than 170 °C, the HTPC/PVDF system exhibited comparable breakdown strength and hysteresis loss as the PSF/PVDF system. While at temperatures above 170 °C, the PSF/PVDF system exhibited a higher breakdown strength because of the higher T_g of PSF. The electric displacement-electric field (D-E) loop behavior of the PSF/PVDF system was studied as a function of temperature. Moreover, a melt-recrystallization process could further decrease the hysteresis loss for the PSF/PVDF system due to better edge-on crystal orientation. These results demonstrate that PSF/PVDF and HTPC/PVDF systems are applicable for high temperature film capacitors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47535.     

Die swell of liquid crystal-forming solutions of hydroxypropyl cellulose through a long capillary die

The die swell and shear viscosity of lyotropic liquid crystal-forming hydroxypropyl cellulose solutions in N,N-dimethylacetamide were determined over a relatively wide range of shear stress or polymer concentration at 30°C by using a long capillary die with an aspect ratio of 114. The dependence of die swell on the concentration was similar to that of shear viscosity: a maximum at a critical concentration C_a and a minimum at another critical concentration C_b (C_a < C_b). The dependence of the swell on shear stress is greatly affected by the solution phase: in an isotropic range (below C_a), the die swell increased monotonously with shear; in the vicinity of C_a, the die swell exhibited a maximum; in a biphasic range (between C_a and C_b), the die swell decreased monotonously; in a single-phase anisotropic range (above C_b), the die swell exhibited a minimum. Above C_b, extrudate distortion was observed and disappeared around the shear where the die swell exhibited a minimum.     

Flow properties of ABS (acrylonitrile–butadiene–styrene) terpolymer

ABS (acrylonitrile–butadiene–styrene) terpolymer is a two-phase thermoplastic with SAN (styrene–acrylonitrile) copolymer constituting the continuous phase (matrix). The flow properties of ABS with varying molecular parameters were studied using a capillary viscometer at the shear rate range encountered in its processing. The viscosity-average molecular weights (M_v) of matrix SAN with 26% acrylonitrile content are in the range of 90,000 to 150,000, and M_v of poly-butadiene-are in the range of 150,000 to 170,000. The weight-average molecular weight of the matrix SAN is the main controlling factor for the flow properties of ABS at low shear rate, while the molecular weight distribution of the matrix SAN becomes increasingly important with the increase of shear rate. The presence of SAN grafted polybutadiene increases the melt viscosity of ABS by 40–60% over comparable free SAN copolymer and also decreases the activation energy at constant shear stress to 24–25 kcal/mole from the 33–36 kcal/mole for free SAN. The die swell of ABS and SAN can be correlated with the dynamic shear modulus G′, and the melt fracture of ABS and SAN starts at G′ equal to 3.6 × 10⁶ dynes/cm².     

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     

Synthesis of poly(aryl ether sulfone)‐graft‐polystyrene and poly(aryl ether sulfone)‐graft‐[polystyrene‐block‐poly(methyl methacrylate)] through atom transfer radical polymerization

A new graft copolymers poly(aryl ether sulfone)‐graft‐polystyrene (PSF‐g‐PS) and poly(aryl ether sulfone)‐graft‐[polystyrene‐block‐poly(methyl methacrylate)] (PSF‐g‐(PS‐b‐PMMA)) were successfully prepared via atom transfer radical polymerisation (ATRP) catalyzed by FeCl₂/isophthalic acid in N,N‐dimethyl formamide. The products were characterized by GPC, DSC, IR, TGA and NMR. The characterization data indicated that the graft copolymerization was accomplished via conventional ATRP mechanism. The effect of chloride content of the macroinitiator on the graft copolymerization was investigated. Only one glass transition temperature (T_g) was detected by DSC for the graft copolymer PSF‐g‐PS and two glass transition temperatures were observed in the DSC curve of PSF‐g‐(PS‐b‐PMMA). The presence of PSF in PSF‐b‐PS or PSF‐g‐(PS‐b‐PMMA) was found to improve thermal stabilities. © 2002 Society of Chemical Industry     

Characterization of mechanical properties of thermoplastic films by creep measurements

Plasticized poly(methyl methacrylate) and methyl methacrylate/acrylate copolymer films were examined by isothermal creep at low loads measured at several temperatures from ～T_g to T_g + 15°C. Viscosity calculated using η = σ/3\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} was plotted vs temperature giving precise values for T_g based on a viscosity criterion of η = 10¹³ poises. Creep fracture data at various temperatures below T_g were interpreted using the maximum apparent viscosity measured at the minima of strain rate vs strain curves. Plots of η_max VS stress at several temperatures gave values of ΔT_g/Δσ of ?1° to 2°C/10⁶ N/m² in agreement with treatment of ΔT_g/Δσ based on free volume. Fracture occurred at low elongations when η_max was ≥10¹³ poises, and at higher elongations when η_max was <10¹³ poises supporting the concept that fracture is related to the lowering of T_g under stress. Plots of log σ VS log ε_b (the elongation at fracture) had the same form as that for crosslinked elastomers above T_g reported by T. L. Smith. Plots of log \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}_b VS log ε_b also had the same form supporting proposals on the rate sensitivity of fracture.     

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     

Viscoelastic behavior of AN‐g‐casein copolymer concentrated solution of sodium thiocyanate

The viscoelastic behavior of sodium thiocyanate concentrated solution of graft copolymer of acrylonitrile onto casein (AN‐g‐casein) was investigated in detail by nitrogen pressure capillary rheometer. The experimental results show that the concentrated solution of AN‐g‐casein is a non‐Newtonian fluid of shear thinning. The end correction increases with the increase of shear rate. In the course of practical spinning, the real shear stress only attributes about 35% to the apparent shear stress, which confirms the essentiality of end correction for the capillary extrusion of the concentrated solution of the graft copolymer. By using the Dewitt model, the Couette correction ξ and recoverable shear strain S_R were analyzed and separated. Quantitative function relation of ξ and S_R versus shear rate and temperature were deduced. It is a common equation within the range of experiment. In practical spinning process, the real viscoelastic parameters can be easily predicted by only a piece of flowing curve based on the common equation. Real elastic model G under any shear rate in the range of experiment was calculated. It was found that G increases with an increase of shear rate, which is opposite to the conclusion reported by Hayahara. The main reason for the error may be that Hayahara used the same Couette correction at a higher shear rate. Further, the die swell in the spinning process can be estimated efficiently. The theoretical base for the stability of AN‐g‐casein spinning technology was provided. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1721–1728, 2002; DOI 10.1002/app.10554     

Physical properties of perfluoropolyethers: Dependence on composition and molecular weight

Three copolymeric perfluoroethers with the structure CF₃[(OCF₂CF₂)_p(OCF₂)_q] OCF₃, having different p/q ratios, have been fractionated. The fractions obtained have been characterized by Gel Permeation Chromatography and ¹⁹F-NMR. The viscosity η the specific volume v and the glass transition temperature, T_g have been measured by standard techniques for all the above samples as well as for some other perfluorinated polyethers. The temperature dependence of viscosity of the unfractionated samples is described by the W.L.F. equation. The values of f_g (fractional free-volume at T_g) and of a_f (free-volume expansion coefficient) are independent of composition, for p/q ratios from 0.53 to 1.15. The critical molecular weight, M_c, is of the order of 8–9,000. From the molecular weight dependence of specific volume, the contribution to the molar volume of the in-chain CF₂ group and the excess molar free volume of the chain ends have been determined. The limiting value of T_g for an infinite molecular weight polymer was found to depend linearly on the compositional ratio O/C and the extrapolated values for polytetrafluoroethylene and for the homopolymer (CF₂O)_n were found to be respectively 200 K and 120 K.