Viscosity Of Polystyrene Research Articles

Mechanical and viscoelastic properties of confined amorphous polymers

ABSTRACTConfinement of polymers to nanoscale dimensions can dramatically impact their physical properties. Substantial efforts have focused on the glass transition temperature (Tg) of polymers confined to thin films, but their mechanical properties are less studied despite their technological importance. In this review, challenges with mechanical measurements of polymer thin films are discussed along with novel metrologies that provide insight into their mechanical properties. A comparison of experimental measurements, simulations and theory provide several general conclusions about the mechanical properties under confinement. Confinement impacts the elastic modulus, rubbery compliance and viscosity of polystyrene, the archetypal polymer for confinement, but the confinement effect appears to depend on the measurement technique. This effect may be due to the details of averaging of gradients in properties that are dependent on the measurement details. Routes to minimize confinement effects are addressed. Despite progress in the measurements of mechanical properties of polymer thin films, there remain unresolved questions about the impact of confinement, which we highlight at the end of this review. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 9–30

Effect of Gamma-Ray and Temperature on the Viscosity of Polystyrene

Effect of Gamma-Ray and Temperature on the Viscosity of Polystyrene

Study on viscosity of polymer melt flowing through microchannels considering the wall‐slip effect

AbstractFor polymers with long, complicated, branched chains, it is difficult to measure the real shear viscosity and slip velocity, using the capillary rheometer based on the adsorption–desorption mechanism. In this study, a double‐barrel capillary rheometer was used to investigate the viscosities of four polymers including polypropylene, high‐density polyethylene, polystyrene, and polymethylmethacrylate in a microchannel. A general model of polymer viscosity based on the entanglement–disentanglement was presented. The proposed model is important in understanding the mechanism of wall slip. This general model can be transferred to the other different models when changing the parameters. Actually, the entanglement–disentanglement model can also be transformed to the adsorption–desorption model. Using the model, it was found that the viscosities of polystyrene and polymethylmethacrylate were reduced with decreasing die diameter, and the slip velocities were increased with the increase of shear stress which agrees well with polymer microrheology based on the microscale effect. For polymers with long, complicated, branched chains, the proposed model improves the accuracy of the calculated viscosity and gains the real slip velocity when polymer melt flows through a microchannel. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Temperature dependence of the viscosity through the glass transition in metaphosphate glasses and polystyrene

We measured the temperature dependence of the viscosity of metaphosphate glasses and polystyrene in the liquid and glass states using a method developed by authors. The results show the Vogel–Tammann–Fulcher equation on the viscosity–temperature relation above the glass transition temperature T g and the Arrhenius one below T g. In order to explain this viscosity change, the intermediate range order (IRO) is introduced. The effect of composition on the viscosity of metaphosphate glass and that of thermal and mechanical treatments on the viscosity of polystyrene were measured. The kinetic (viscous) transition was discovered at a temperature lower by 20 K than T g determined by differential scanning calorimetry. We propose that the glass transition is a self-organization of the IRO of nanometer orders in size.

Rheological Properties of Polystyrene/Supercritical CO2 Solutions from an Extrusion Slit Die

Recent advances in the use of supercritical CO 2 (scCO 2 ) in polymer processing (i.e. injection molding and extrusion) have increased the need for rheological data of polymer/scCO 2 solutions at high pressures. In this study, a slit die with a sudden contraction was used to investigate the entrance pressure drop as well as the shear and extensional viscosities of a polystyrene (PS) melt and of a PS/scCO 2 solution. Dissolution of CO 2 into the PS melt was shown to reduce its entrance pressure drop as well as its shear and extensional viscosities. The entrance pressure drop of PS and PS/CO 2 was found to be a strong (exponential) function of pressure. The entrance pressure drop as a function of wall shear stress could be fitted with a master curve for all experiments at different temperature, pressure and CO 2 concentrations. Shear viscosities of PS as well as PS/CO 2 were described using the generalized Cross-Carreau model and the Doolittle equation and different free volume models were compared.

Study of the solution properties of tactic polystyrenes

Viscosity measurements are reported for syndiotactic polystyrenes in a molar mass range from 35,000 to 400,000 g/mol and standard fractions of narrowly distributed atactic polystyrenes in a molar mass range from 50,000 to 600,000 g/mol in trichlorobenzene at 135 °C. The correlation between molar mass and intrinsic viscosity of different polystyrene samples was investigated as well as their solution properties. The results demonstrate that the intrinsic viscosity of polystyrene in thermodynamically good solvents is independent of the type of tacticity of the polystyrenes investigated here. The dilute solution properties were compared with those for isotactic and atactic polystyrenes. The small differences in their solution viscosities may occur due to the different molar mass distributions of differently synthesized samples.

Miscibility, density and viscosity of polystyrene in n-hexane at high pressures

The demixing pressures, densities and viscosities of solutions of nearly monodisperse polystyrene samples ( M w/ M n < 1.1) in n-hexane have been determined. Measurements were conducted with samples of different molecular weights ( M w = 4000–50 000) at concentrations up to 8 mass% over a pressure range from 5 to 70 MPa and a temperature range from 323 to 423 K. The demixing pressures were observed to increase with molecular weight (from about 10 MPa for M w = 4000 to 50 MPa for M w = 50 000) and show high sensitivity to temperature (Δ P/Δ T being about −1 MPa°C −1) in the range investigated. Density and viscosity data were collected in the one-phase homogeneous regions, and viscosity was correlated with an equation of the form η = Aexp{ B/(1 − V 0 ρ ), which is based on the free-volume considerations. For a given system, the viscosities increase with solution density (or pressure). At a fixed solution density, viscosity increases with polymer concentration or molecular weight. Depending upon the system, viscosities have ranged from 0.15 to 0.45 mPa s. Flow activation volumes and flow activation energies were about 40 cm 3 mol −1 and 6 kJ mol −1, respectively. The demixing and viscosity data have been also compared with the results obtained in n-butane and n-pentane for one sample ( M w = 9000). In going from n-butane to n-hexane, the demixing pressures decrease while the viscosities become higher.

Analysis of Low Molecular Weight Polymers with Gel Permeation Chromatography

Abstract Intrinsic viscosities and gel permeation chromatography (GPC) elution times were determined in toluene on commercially available standards of polystyrene (PSTY) and polymethyl methacrylate (PMMA) having Mn in the range of 103 to 105 and 104 to 106, respectively. In addition, elution times were determined on the discrete GPC peaks of dimer, trimer, tetramer, etc. as seen in lower molecular weight PSTY and PMMA. Intrinsic viscosities of oligomers were estimated by extrapolation of the Mark-Houwind-Sakurada equations determined from our data, and the results were used to establish a universal calibration curve over a wide range of molecular weights. A similar approach was taken by using literature data for the intrinsic viscosities of PSTY and PMMA in tetra-hydrofuran. It was verified by proton NMR that the universal calibration curve so constructed is useful at Mn, values as low as 300. No correction was necessary for chain length dependence of the detector response.

Effects of plasticizer on shear modification of polystyrene

AbstractThe elastic and viscous properties of polymer melts may be affected by the shear history of the polymer. The extrudate swell of a polymer melt is primarily a manifestation of the elasticity of the polymer melt. In this study, a single screw extruder was used to impose different shear histories on a polystyrene polymer which was processed with and without added plasticizer. The extrudate swell and apparent viscosity of these melts were measured with a capillary rheometer. These characteristics of unplasticized polystyrene are almost not affected by the various preshearing processes. However, the extrudate swell and viscosity of polystyrene containing plasticizer are affected by plasticizer level, shear history and thermal history. After most of the plasticizer in the presheared plasticized polystyrene was extracted, the extrudate swell was still lower than that of the parent sheared polystyrene with the same shear history and the same plasticizer content. These results were obtained without significant changes in molecular weight.Shear modification by conventional process equipment may become impractical if the shear field intensity or dwell time of the material in the apparatus is limited. In such cases, shear refinability by standard process equipment may be observed if the coupling density in the polymer is reduced by some additional means, such as blending with a plasticizer.

Rheological properties of mixtures of molten polymer and fluorocarbon blowing agent. II. Mixtures of polystyrene and fluorocarbon blowing agent

AbstractThe viscosities of mixtures of polystyrene and fluorocarbon blowing agent were determined, using the experimental technique described in Paper I of this series. For the study, three commercial grades of polystyrene were used, together with the following fluorocarbon blowing agents, trichlorofluoromethane (FC‐11), dichlorodifluoromethane (FC‐12), and blends of FC‐11 and FC‐12. For each combination of polystyrene and blowing agent, blowing agent concentration and melt temperature were varied. We have found that, for all three polystyrenes used, a single correlation exists between the viscosity reduction factor (VRF) and the blowing agent concentration, in which VRF is defined as the ratio of the viscosity of polystyrene‐blowing agent mixture to that of polystyrene homopolymer. The correlation was found to be independent of shear rate and temperature, and dependent upon only the type of fluorocarbon blowing agent. It was suggested that such a correlation be used in predicting the bulk viscosity of mixtures of polystyrene and fluorocarbon blowing agent, using information on the viscosity of polystyrene alone.

A corresponding states interpretation of the temperature dependence of the intrinsic viscosity of polystyrene in isopropyl acetate

A corresponding states interpretation of the temperature dependence of the intrinsic viscosity of polystyrene in isopropyl acetate

The Effect of Pressure on the Shear Viscosity of Polymer Melts

In many polymer processing operations like injection molding, the polymer melt flows under the influence of high pressure, sometimes exceeding 20,000 psi. It has been suggested by a number of workers, on the basis of both experimental and theoretical considerations, that the effect of hydrostatic pressure on viscosity cannot be ignored in such instances. However, most of the proposed techniques to determine the effect of pressure on viscosity suffer from limitations especially at high shear rates. The present work proposes a more general and quantitative method for obtaining the effect of pressure on the viscosity of polymer melts from capillary viscometer data. In addition to its applicability over a wide range of practical shear rates, the proposed method employs less restrictive assumptions than previous techniques and contains corrections for the effect of viscous heating. The results obtained for the effect of pressure on the viscosity of polystyrene at 180°C are compared to rheological data obtained by conventional methods. Preliminary results on the pressure coefficient of viscosity appear to be in agreement with predictions based on the W-L-F equation.

The effect of pressure on the shear viscosity of polymer melts

In many polymer processing operations like injection molding, the polymer melt flows under the influence of high pressure, sometimes exceeding 20,000 psi. It has been suggested by a number of workers, on the basis of both experimental and theoretical considerations, that the effect of hydrostatic pressure on viscosity cannot be ignored in such instances. However, most of the proposed techniques to determine the effect of pressure on viscosity suffer from limitations especially at high shear rates. The present work proposes a more general and quantitative method for obtaining the effect of pressure on the viscosity of polymer melts from capillary viscometer data. In addition to its applicability over a wide range of practical shear rates, the proposed method employs less restrictive assumptions than previous techniques and contains corrections for the effect of viscous heating. The results obtained for the effect of pressure on the viscosity of polystyrene at 180°C are compared to rheological data obtained...

Comments on “viscosity of polystyrene near the glass transition”

Comments on “viscosity of polystyrene near the glass transition”

Viscosity of polystyrene near the glass transition

AbstractA quantitative explanation is given for the apparent viscosity increase with increasing capillary shear rate for polystyrene at temperatures approaching the glass transition, Tg. Possible shifts in Tg 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 Tg. Brief mention is made of the pressure effects on the Bagley and Rabinowitsch corrections normally made in capillary measurements.

Volume relaxation and bulk viscosity of polystyrene in the softening region

Volume relaxation and bulk viscosity of polystyrene in the softening region

The non‐newtonian viscosity of polymers in relation to their molecular conformation

AbstractThe non‐Newtonian viscosities of polystyrene and polyisobutylene were measured in various solvents over a wide range of shearing stress, τ (up to the order of 104 dynes/cm.2). The shear dependence of the intrinsic viscosities, [η], is closely related to the molecular extension of the polymers. The non‐Newtonian behavior of a polymer is greatest in a “good” solvent and least at Flory's Θ temperature. The maximum percentagewise drop in the intrinsic viscosities at highest attainable shearing stress was found to increase with increasing root‐mean‐square end‐to‐end distance, 〈r2〉1/2, of the polymer chains in “good” solvents. By plotting [η]τ = ∞/[η] τ = 0 against 〈r2〉1/2 / 〈rof2〉1/2(where 〈rof2〉1/2 is the theoretical 〈r2〉1/2 assuming free rotation about the chemical bonds of the polymer chains), the shear dependence of the intrinsic viscosities appeared to be absent when 〈r2〉1/2 / 〈rof2〉1/2 was extrapolated to unity. Furthermore, polymer having different degrees of chain stiffness seemed to form a composite curve in the plot, where the stiffer chains exhibited the most drastic drop in the intrinsic viscosities. Additional support was given with the experimental results of polydimethylsiloxane and cellulose triacetate solutions.

Study of the Viscoelastic Behavior and Molecular Weight Distribution of Polyisobutylene

Abstract The viscoelastic behavior of linear high polymers has commanded considerable attention in recent years. The very thorough studies by Fox and Flory of the melt viscosity of polystyrene and polyisobutylene, the stress relaxation experiments of Tobolsky and coworkers, and dynamic-mechanical studies by Ferry have contributed greatly to our knowledge of the mechanical behavior of these interesting substances. However, there are many facets of this subject which have not received thorough experimental investigation. In particular, there has been no detailed study of the effect of molecular weight and polydispersity on the elastic behavior of viscoelastic materials. It was felt, therefore, that a study of the viscoelastic behavior of a series of very carefully characterized samples of a representative linear high polymer would contribute substantially to the understanding of this subject. The polymer chosen was polyisobutylene, which displays both flow and elastic behavior at room temperatures.