Entrance Length of Polymer Flow Through a Contraction Die: Comparison of Calculation from an Equation and Flow Induced Birefringence Measurements

When a polymeric melt flows through a contraction die, it experiences a certain distance in the slit before a fully developed flow is achieved, which is defined as the entrance length. Here, an equation for calculation of the entrance length was proposed based on an assumption that the pressure drops in an exponential function way along the flow direction in the contraction die from the entrance to the fully developed flow. The entrance length could be calculated from the flow parameters, such as volumetric flow rate, the pressures at the entrance and at the defined point in the fully developed flow. The entrance lengths of a low-density polyethylene (LDPE) and a high-density polyethylene (HDPE) melt were calculated from this equation with the measured flow parameters at various flow rates. The results are quite close to those measured from flow induced birefringence and similar to that reported in a published study by Martyn et al., which suggested that the equation could be used to describe the relation between the entrance length and the flow parameters.     

Improving Melt Flow Behavior via Melt Vibration

A self‐made melt vibration extrusion device was used to study the melt flow behavior in a vibration field. A pulse pressure was superimposed on the flowing melt during extrusion, called vibration assisted extrusion (VAE); conventional extrusion (CE) was studied for comparison. A die (L/D=17.5) was attached to the device to study melt flow behavior of an amorphous polymer (polystyrene) and semi‐crystalline polymers (high density and linear low polyethylene). Results show that the melt vibration technique is an effective processing tool to improve polymer melt flow behavior for both crystalline and amorphous polymers. Increasing with vibration frequency for extrusion at constant vibration pressure amplitude, the viscosity decreases sharply, and also with increasing vibration pressure amplitude at a constant vibration frequency. The effect of vibration field on melt flow behavior depends greatly on the melt temperature, with the largest change in viscosity obtained at low temperature. Increasing with vibration frequency at constant pressure vibration amplitude, the maximum decrease percentages of viscosities are 82.9, 66.7, and 48.9%, for HDPE, LLDPE, and PS, respectively; increasing with pressure vibration amplitude at a constant vibration frequency, the maximum decrease percentage of viscosities are 99.0, 94.3, and 99.0%, for HDPE, LLDPE, and PS, respectively.     

Flow Characteristics of Partially Hydrolyzed Polyacrylamides during Converging into a Capillary

Partially hydrolyzed polyacrylamides (HPAMs) are the most widely used polymers in enhanced oil recovery (EOR). This study presents capillary flow measurements of three different molecular weight HPAMs in synthetic brine. Polymer solutions having similar viscoelasticity were forced to flow through a 0.23 mm (radius) stainless steel capillary to investigate their flow characteristics including mobility reduction (apparent viscosity) and mechanical stability, represented by the extent of mechanical degradation (DR). The results indicated that the apparent viscosity of the polymer solutions markedly dropped with increasing flow rate until 5 mL/min, corresponding to the shear rate of 8,730s^?1; after that a slight viscosity decrease was observed. The high-molecular-weight HPAMs (6.5 and 8.0 × 10⁶ g/mol) began to have slightly greater apparent viscosity than the low-molecular-weight HPAM (1.0×10⁶ g/mol) above the shear rate of 26,180 s^?1; this might result from the occurrence of the coil-stretch transition. All the HPAMs experienced very similar percentages of mechanical degradation (10%) at shear rates between 1750 and 8730 s^?1; however, above 8730s^?1 the high-molecular-weight HPAMs exhibited a steep increase in mechanical degradation (DR). On the other hand, in the case of the low-molecular-weight HPAM, the DR curve almost leveled off at 12%. Therefore, low-molecular-weight HPAMs are generally suggested for EOR applications. These results, we suggested, should be useful to improve the efficiency of polymer EOR by minimizing mechanical degradation.     

Rheological Behavior of Blends of Poly(Phenylene Sulfide) with a Thermotropic Liquid Crystalline Aromatic Poly(Ether Ester)

A new type of thermotropic liquid crystalline aromatic poly(ether ester) (PEE) was prepared from 1,3-bis(4′-carboxyphenoxy)benzene, 1,4-diacetoxybenzene, and p-acetoxybenzoic acid through a melt transesterification process. The rheological behavior of blends of poly(phenylene sulfide) (PPS) with PEE was studied using a high-pressure capillary rheometer with the shear rate range of 50 s^?1 to 3000 s^?1. The results show that according to the range of shear rate, the flow curves of PEE/PPS blends can be divided into three zones: a first shear-thinning zone (n < 1, “n” represents non-Newtonian indexes), a shear-thickening zone (n > 1), and a second shear-thinning zone (n < 1), and the former two zones are more obvious with the increase of PEE content or elevated temperature. In the second shear-thinning zone, the PPS melt is close to a Newtonian fluid at high temperature and high shear rate; meanwhile the non-Newtonian behavior of the PPS melt at high temperature is enhanced with the addition of PEE. The apparent viscosity of PPS melts sharply dropped after adding PEE, especially at relatively low temperature and low shear rate. The curve of apparent viscosity vs. shear rate starts to flatten out after adding PEE, suggesting that the addition of PEE lowers the sensitivity of PPS to shear rate. As the content of PEE increases, the activation energy of the viscous flow, ΔE_η, of PPS decreases, which means that adding PEE weakens the temperature sensitivity of the apparent viscosity of the PPS melt. It can clearly be seen that the addition of PEE is beneficial to the processing of PPS.     

Studies on Rheological Behavior and Structure Development of High‐Density Polyethylene in the Presence of Ultrasonic Oscillations During Extrusion

The effects of ultrasonic oscillations on properties and structure of extruded high‐density polyethylene (HDPE) were studied. The experimental results show that ultrasonic oscillations can improve the surface appearance of the HDPE extrudates; increase the productivity of the HDPE extrudates; and decrease the die pressure, melt viscosity, and flow activation energy of the HDPE. The processing properties of the HDPE improve greatly in the presence of ultrasonic oscillations. Linear viscoelastic properties tests show that dynamic shear viscosity and zero shear viscosity decrease in the presence of ultrasonic oscillations. Ultrasonic oscillations can improve crystal perfection and thermal stability of HDPE. At appropriate ultrasound intensity, ultrasonic oscillations could also increase the mechanical strength of extruded HDPE. The gel permeation chromatography (GPC) results show that at high ultrasound intensity and low rotation speed of extrusion, ultrasonic oscillations causes chain scission of HDPE, which result in a decrease of molecular weight and an increase of melt flow index.     

High Pressure High Temperature Dynamic Rheometry of Sulfonated Polyacrylamide Solutions in Electrolyte Media as Used for Oil Recovery Applications

Sulfonated polyacrylamide (SPAA) solutions were prepared and the effects of pressure, polymer concentration, and water temperature, pH and salinity on their rheological behavior were investigated using a concentric cylinder dynamic rheometer equipped with a high pressure cell. According to the rheological flow curves the shear stress of SPAA solutions increased less than in proportion to their shear rates; that is, a shear thinning effect occurred. For polymer solutions containing 15,000 ppm of SPAA, shear viscosity, and stress were nearly insensitive to pressure. However, the shear viscosity and stress of SPAA solutions were affected by temperature and this effect was more evident at lower pressure. The flow curves indicated the shear viscosity and stress of the samples increased with increasing SPAA concentration and pH of the water, but were decreased with increasing water salinity and temperature.     

Viscosity of aluminum under shock-loading conditions

A reliable data treatment method is critical for viscosity measurements using the disturbance amplitude damping method of shock waves. In this paper the finite difference method is used to obtain the numerical solutions for the disturbance amplitude damping behaviour of the sinusoidal shock front in a flyer-impact experiment. The disturbance amplitude damping curves are used to depict the numerical solutions of viscous flow. By fitting the experimental data to the numerical solutions of different viscosities, we find that the effective shear viscosity coefficients of shocked aluminum at pressures of 42, 78 and 101 GPa are (1500±100) Pa · s, (2800±100) Pa · s and (3500±100) Pa · s respectively. It is clear that the shear viscosity of aluminum increases with an increase in shock pressure, so aluminum does not melt below a shock pressure of 101 GPa. This conclusion is consistent with the sound velocity measurement.     

Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.     

Preparation and Characterization of Linear Low Density Polyethylene/Carbon Nanotube Nanocomposites

Linear low‐density polyethylene (LLDPE)/multiwalled carbon nanotube (MWNT) nanocomposites were prepared via melt blending. The morphology and degree of dispersion of nanotubes in the polyethylene matrix were investigated using scanning electron microscopy (SEM). Both individual and agglomerates of MWNTs were evident. The rheological behavior and mechanical and electrical properties of the nanocomposites were studied using a capillary rheometer, tensile tester, and Tera ohm‐meter, respectively. Both polyethylene and its nanocomposites showed non‐Newtonian behavior in almost the whole range of shear rate. Addition of carbon nanotubes increased shear stress and shear viscosity. It was also found that the materials experience a fluid‐solid transition below 1 wt% MWNT. Flow activation energy for the nanocomposites was calculated using an Arrhenius type equation. With increasing nanotube content, the activation energy of flow increases. A decrease of about 7 orders of magnitude was obtained in surface and volume resistivity upon addition of 5 wt% MWNT. In addition, a difference between electrical and rheological percolation thresholds was observed. The results confirm the expected nucleant effect of nanotubes on the crystallization process of polyethylene. A slight increase in Young's modulus was also observed with increasing MWNT content.     

Melt Elongation Properties of Linear Low-Density Polyethylene

The melt extensional properties of a linear low-density polyethylene (LLDPE) were measured using melt spinning techniques in a range of temperature varying from 150 to 200°C, and the entry flow method in the capillary extrusion at 170°C was used to investigate the effects of elongation strain rate, temperature, and extrusion velocity in the capillary on the melt elongation stress and viscosity. The melt stretching force at break decreased nonlinearly with a rise of temperature. A low melt elongation viscosity might be beneficial to improve the melt drawability. With the increase of elongation strain rate, the melt elongation stress increased while the melt elongation viscosity decreased nonlinearly. Both melt elongation stress and viscosity decreased with a rise of temperature. Under the experimental conditions, the melt elongation stress and viscosity decreased with an increase of extrusion velocity in the capillary. Moreover, the relationship between the elongation viscosity determined from the entry flow and strain rate was similar to that from the melt spinning flow.     

Direct Observation of Crystallization of Polybutene-1 Under Low Shear Rate Flow

The isothermal crystallization process of polybutene-1 melt under shear flow was investigated with an optical microscope and a device (shear flow direct observation system, SF-DOS) newly developed by our group. The nucleation rate and growth rate of polybutene-1 were studied under slow shear rates (0–0.1 s^?1) at high crystallization temperature (102–108°C) with the SF-DOS. The nucleation remains heterogeneous. The number of nuclei after long times increased and induction time decreased by increasing the shear rate. Anisotropic and distorted spherulites were observed under shear flow, while the spherulites in the static condition were isotropic. It was clearly observed that the spherulites were rotating under shear. The average growth rates were enhanced by increasing shear rates, which acts as the main factor affecting the overall crystallization kinetics. Finally, the crystallization kinetics were analyzed on the basis of the secondary nucleation theory of Hoffman and Lauritzen. Even under very low shear rates, the product of lateral‐surface free energy σ _s and fold-surface free energy σ _e was found to be reduced as shear rate increased.     

Structural Evolution During and After Cessation of the Shear Flow for a Side-Chain-Type Liquid Crystalline Polysiloxane Above the Isotropic-Liquid Crystalline Phase Transition Temperature

Evolution of the anisotropic texture during and after cessation of shear flow for a side-chain-type liquid crystalline polysiloxane (LCS) was studied by shearing microscopy at temperatures above the isotropic to liquid crystalline phase transition temperature ( T_c=309.2 K if LCS is cooled from the isotropic phase in the quiescent state). The anisotropic texture of LCS during the shear flow was found at a temperature of 313 K and a shear rate of 50 s^?1. After cessation of the shear flow, the anisotropic texture disappeared. At a temperature of 311 K and a shear rate of 50 s^?1, LCS under shear flow also showed the anisotropic texture. It is noteworthy that the anisotropic texture was stable at this temperature, even after cessation of the shear flow. Furthermore, the evolution of the anisotropic texture was described quantitatively from the behavior of the birefringence as a function of time after cessation of the shear flow.     

The Effect of Melt Vibration on Polystyrene Melt Flowing Behavior During Extrusion

Vibration extrusion (VE) is achieved by superimposing a mechanical vibration on the flowing melt during extrusion. The effect of melt vibration on the melt flow behavior of polystyrene (PS) was studied. The melt flow behavior during conventional extrusion (CE) was studied for comparison. With the application of the melt vibration technology, the melt flow behavior of PS was greatly improved. The melt viscosity during the VE strongly depends on the vibration frequency and vibration amplitude. Extruded at constant vibration amplitude, the melt viscosity decreases sharply with increasing vibration frequency and also does so for increasing vibration amplitude when extruded at a constant vibration frequency. The improved melt flow property is explained in terms of shear-thinning criteria. The effect of melt vibration on the melt flow behavior is also related to the melt temperature and extrusion pressure; the greatest decease in viscosity is obtained at low temperature and low extrusion pressure.     

POLYFLOW在聚合物熔体压力流动教学中的应用

将Polyflow用于聚合物熔体流动教学,可以更好的解释聚合物熔体流动过程。实现了流动过程中的压力分布、速度分布、剪切速率分布、粘度分布、温度分布数值仿真。     

Shear Effect on Morphology of Poly(Butylene Terephthalate)/Poly(Styrene‐co‐Acrylonitrile) Blends

Abstract

The shear flow effect on the morphology of poly(butylene terephthalate)(PBT)/poly(styrene‐co‐acrylonitrile)(SAN) was studied by a parallel plate type shear apparatus. In PBT/SAN = 20/80 blend, particle size of dispersed domains was governed by both break‐up and coalescence processes, and it was much affected by shear rate. The minimum particle size was observed at a certain shear rate. This phenomenon can be explained by the shear matching effect of PBT and SAN; that is, the viscosity ratio of PBT to SAN changed with shear rate and the finest morphology was obtained at the appropriate viscosity ratio. Similar behavior was also observed for PBT/SAN = 70/30 (PBT was the matrix), even though the particle size was larger than that of PBT/SAN = 20/80. For PBT/SAN = 10/90 blend, the sample showed a complicated appearance during shearing. A translucent region correlated to the fine morphology was observed more than twice with increasing shear rate. This phenomenon could not be explained by the viscosity matching effect only. It was affected by small changes in the balance of breaking‐up and coalescence effects.     

Shear flows and shear viscosity in a two-dimensional Yukawa system (dusty plasma)

The shear viscosity of a two-dimensional liquid-state dusty plasma was measured experimentally. A monolayer of highly charged polymer microspheres, with a Yukawa interaction, was suspended in a plasma sheath. Two counterpropagating Ar+ laser beams pushed the particles, causing shear-induced melting of the monolayer and a shear flow in a planar Couette configuration. By fitting the particle velocity profiles in the shear flow to a Navier-Stokes model, the kinematic viscosity was calculated; it was of order 1 mm(2) s(-1), depending on the monolayer's parameters and shear stress applied.     

Study on Steady Shear Rheological Behavior of Concentrated Suspensions of Sulfonated Polyacrylamide/Na-Montmorillonite Nanoparticles

Concentrated suspensions of sulfonated polyacrylamide (SPA)/Na⁺-montmorillonite (Na-MMT) were prepared and their stability and steady shear rheological properties were described as a function of nanoparticle and polymer concentration and temperature. The results showed that the Na-MMT nanoparticles suspensions were stable in the absence and presence of SPA and no sedimentation was seen. The Z-average particle sizes for the SPA/Na-MMT suspensions increased in the presence of SPA. Rheological investigations showed that the SPA solutions and SPA/Na-MMT suspensions displayed non-Newtonian behavior in almost the whole range of shear rate. All the suspensions exhibited a shear-thinning flow character as shear rate increased. The flow curves indicated the shear viscosity and stress of the samples were decreased with increasing nanoparticles concentration up to 1.5 wt%, but for Na-MMT loading greater than 1.5 wt% there was an increase in shear viscosity and stress of the suspensions. Increasing of SPA concentration had more effect on increasing the rheological properties of SPA/Na-MMT suspensions than increasing of nanoclay content. Shear viscosity and stress of the suspensions increased with increasing SPA concentration and decreased with increasing temperature from 50°C to 70°C.     

Rheology and Dispersion Behavior of Ethylene‐Vinyl Acetate Copolymers/TiO2 Masterbatches Prepared by Melt‐Compounding

The rheology and dispersion behavior of ethylene‐vinyl acetate (EVA) copolymer/TiO₂ masterbatches prepared by melt‐compounding were investigated. The pure EVA exhibits obviously pseudoplastic behavior and the apparent viscosity decreases remarkably at experimental temperatures, especially in the range of 100–500 s^?1. The EVA/TiO₂ masterbatches exhibit similar shear rheology behavior with pure EVA and the apparent viscosities are obviously higher than that of pure EVA when the TiO₂ content is above 10 wt.%. Field‐emission scanning electron microscopy (FE‐SEM) and energy dispersive x‐ray spectroscopy (EDX) show that relatively low TiO₂ loading and moderate shear rate are helpful for the improvement of dispersion behavior of TiO₂ nanoparticles; moreover, the dispersion behavior of TiO₂ greatly influences the melt viscosity. The extensional rheology of pure EVA decreases with increasing extension rate, especially at low melt temperatures. EVA/TiO₂ masterbatches have similar extensional rheology behavior as pure EVA and the TiO₂ loading has almost no influence on the extensional viscosity of materbatches.     

Melt rheology of the polyether from bisphenol-a and 4,4'-dichlorodiphenylsulfone

The melt rheology of polysulfone was studied in steady shear and oscillatory shear flow. Even when melt viscosity data were corrected for the dependence of the glass transition temperature on M _n the viscosity molecular weight relation was not a simple power law over any appreciable range. The melt compliance is very low and reaches its maximum value at molecular weights > 2000. Since the molecular flexibility, measured as the size of the equivalent random segment of rubber elasticity theory, is similar to that of other common polymers, this suggests that the polar nature of polysulfone is contributing to the high “entanglement” density.