A flow visualization technique for the determination of velocity profiles in dies with circular cross sections

A unique retainer/transparent quartz die assembly was designed and fabricated to fit on a melt extruder. It permitted visualization of polymer flow behavior during melt spinning. Tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system and used to illuminate the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. Streak photography was used to determine the cross-sectional velocity distribution of the melt as it passed through the die.     

A visualization study of polyethylene terephthalate flow using a pseudohyperbolic die geometry

Flow visualization studies were made during extrusion by using a hyperbolic die, streak photography, and flow birefringence techniques. Velocity was found to be a linear function of position along the die axis. This is equivalent to a constant elongational strain rate. Considering that the hyperbolic die maintains the stretching rate achieved in the upstream over an extended time period, this profile seems to be the optimum die design for maximum chain-ordering potential. A unique analysis of the birefringence and velocity distribution data allowed determination of characteristic relaxation time for the PET melt of 5.5 × 10^?3 at 285°C.     

A visualization study of poly(ethylene terephthalate) flow using potential chain-ordering die geometries

Streak-photographic and stress birefringence techniques were used to analyze the flow of poly(ethylene terephthalate) through potential chain-ordering die geometries. The streak photographs were used to determine velocity distributions and streamlines in various convergent dies. The different contours were seen to have a significant effect on the polymer streamlines and velocity distributions. The measured velocities were used to develop empirical equations, specific for each geometry, which relate velocity to position within the die and to throughput rate. Flow birefringence was used to determine the extent of molecular ordering. The optimum chain-ordering die geometry was determined to be one which included a rapid initial decrease in cross-sectional area. Birefringence was also used to monitor polymer flow instability. An unusual mechanism for instability was observed at intermediate throughput rates.     

Melt‐compounded nanocomposites of titanium dioxide atomic‐layer‐deposition‐coated polyamide and polystyrene powders

Polyamide and polystyrene particles were coated with titanium dioxide films by atomic layer deposition (ALD) and then melt‐compounded to form polymer nanocomposites. The rheological properties of the ALD‐created nanocomposite materials were characterized with a melt flow indexer, a melt flow spiral mould, and a rotational rheometer. The results suggest that the melt flow properties of polyamide nanocomposites were markedly better than those of pure polyamide and polystyrene nanocomposites. Such behavior was shown to originate in an uncontrollable decrease in the polyamide molecular weight, likely affected by a high thin‐film impurity content, as shown in gel permeation chromatography (GPC) and scanning electron microscope (SEM) equipped with an energy‐dispersive spectrometer. Transmission electron microscope image showed that a thin film grew on both studied polymer particles, and that subsequent melt‐compounding was successful, producing well dispersed ribbon‐like titanium dioxide with the titanium dioxide filler content ranging from 0.06 to 1.12 wt%. Even though we used nanofillers with a high aspect ratio, they had only a minor effect on the tensile and flexural properties of the polystyrene nanocomposites. The mechanical behavior of polyamide nanocomposites was more complex because of the molecular weight degradation. Our approach here to form polymeric nanocomposites is one way to tailor ceramic nanofillers and form homogenous polymer nanocomposites with minimal work‐related risks in handling powder form nanofillers. However, further research is needed to gauge the commercial potential of ALD‐created nanocomposite materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental Observations and Quantitative Predictions of Rheological Properties of Organoclay/Poly(propylene) Nanocomposites at the Startup of Shear Flows

We study the rheological characteristics of nanocomposites containing nano-sized plate like particles in a viscoelastic fluid at the startup of steady state in the simple shear flow mode. The nanocomposites of organoclay-polypropylene with different nanoclay contents were prepared by melt mixing. A rheological equation of state, originally formulated to predict the orientation state and viscoelastic behavior of suspensions of ellipsoidal particles in polymer melts, has been modified to describe the observed phenomena for the nanoclay/poly(propylene) composites. The rotational particle motion and alignment for a group of symmetric ellipsoids with the applied flow field are investigated. Additionally, model calculations of the macroscopic rheological properties for a simple flow case suggest the presence of nano-particles significantly modify the suspended fluid at volume concentrations as low as 0.5%. The model calculations for the startup viscosity are reasonably in agreement with the experimental results at the experimental range covered in this study. At the shear rate of , we observe pronounced stress overshoots at the three nanoclay loadings level tested which are found to be related to the fast alignment of the silicate layers with the shear direction in the polymer melt.     

Melt stabilisation of Phillips type polyethylene, Part III: Correlation of film strength with the rheological characteristics of the polymer

Different aspects of the melt stabilising effect of various antioxidant packages were studied in a Phillips type polyethylene in the work described in this series of papers. The polymer was stabilised with various combinations of a phenolic antioxidant with phosphite, phosphonite, and phosphine type secondary antioxidants and processed by multiple extrusions followed by film blowing. After determining the role of the antioxidants in the melt stabilisation process and the effect of antioxidant consumption on polymer properties the correlation of the rheological characteristics of polymer with the tear and impact strengths of films is discussed in this paper. The Elmendorf tear strength of films measured in transverse direction, which is sensitive to long chain branching, correlates closely with viscous compliance determined by creep recovery experiments and the ratio of melt flow indices measured at high and low loads. The relationships are independent of the type and amount of antioxidant added. This makes possible the prediction of the effect of various antioxidant packages on film properties on the basis of rheological measurements. The correlation between the dart drop impact strength of the films and the rheological characteristics of the polymer is less reliable.     

Investigation of the Wall Slip Effect in Highly Concentrated Disperse Systems by Means of Non-Invasive UVP-PD Method in the Pressure Driven Shear Flow1

A novel in-line UVP-PD non-invasive rheological measuring technique was introduced for rheological analysis of highly concentrated disperse systems. The method is based on a combination of the Ultrasonic Pulsed Echo Doppler technique (UVP, Ultrasound Velocity Profiler) and the pressure difference (PD) method. The rheological properties were derived from simultaneous recording and on-line analysis of the velocity and related radial shear stress profiles across a circular channel. Wall slip velocity was extrapolated from the on-line fit and monitored on-line simultaneously with the flow index. Two effects were found and preliminarily analyzed. The first effect refers to a transition from strongly non-Newtonian to Newtonian flow velocity profile while increasing in the absolute flow velocity. The second flow effect refers to an abrupt reduction of the wall slip velocity while increasing the absolute flow velocity. Considerable discrepancy was found between the results of the in-line UVP-PD measurement in pressure driven shear flow and the results of the conventional rheometry.     

A method for simultaneously determining the zeta potentials of the channel surface and the tracer particles using microparticle image velocimetry technique

The zeta potentials of channel surfaces and tracer particles are of importance to the design of electrokinetic microfluidic devices, the characterization of channel materials, and the quantification of the microparticle image velocimetry (microPIV) measurement of EOFs. A method is proposed to simultaneously measure the zeta potentials of the channel surface and the tracer particles in aqueous solutions using the microPIV technique. Through the measurement of the steady velocity distributions of the tracer particles in both open- and closed-end rectangular microchannels under the same water chemistry condition, the electrophoretic velocity of the tracer particles and the EOF field of the microchannel are determined using the expressions derived in this study for the velocity distributions of charged tracer particles in the open- and closed-end rectangular microchannels. Thus, the zeta potentials of the tracer particles and the channel surfaces are simultaneously obtained using the least-square method to fit the microPIV measured velocity distribution of the tracer particles. Measurements were carried out with a microPIV system to determine the zeta potentials of the channel wall and the fluorescent tracer particles in deionized water and sodium chloride and boric acid solutions of various concentrations.     

Effect of elongational flow on morphology and properties of polymer/CNTs nanocomposite fibers

Carbon nanotubes (CNTs) have been attracting increasing interest for the fabrication of polymer‐based nanocomposites because of their excellent properties. Traditional methods for the preparation of polymer/CNTs nanocomposites are in situ polymerization, solution blending, and melt mixing. The achievement of a good CNT dispersion and a percolation network is important in order to obtain better mechanical and electrical properties. However, the rheological behavior of polymer/CNTs systems, in particular regarding the extensional flow, has not been much investigated so far. In this work we present, for the first time, rheological data in non‐isothermal extensional flow and an investigation on the effect of the extensional flow upon the final properties of several polymer/CNTs systems was carried out as well. Extensional flow led to higher mechanical properties and higher melt strength, but only a slightly reduced breaking stretching ratio. This result could be particularly interesting in the view of potential industrial applications such as film blowing and spinning. Morphological analyses also showed higher degrees of dispersion and variation in the CNTs final dimensions. Copyright © 2010 John Wiley & Sons, Ltd.     

Flow pattern maps for particle-fluid mixture transport in a horizontal pipe - application of a three-layer model

A modified three-layer model was applied to model particle-fluid mixture flow in a horizontal pipe, the viscoelastic properties of carrier polymer solution were taken into consideration, and the Deborah number was used to calculate solid-fluid friction factor. An energy equation was applied to determine temperature distribution of carrier fluid along a horizontal pipe to accurately represent the rheological properties of carrier fluid. During the transport process, particles quickly settle out of carrier fluid and accumulate on pipe bottom forming a particle bed, so a particle bed load flow is observed. The transport mechanisms of particles in moving particle bed are govern by fluidization, which causes the height of this layer to be small and equal to 2～5 times of particle diameter. In addition, the pressure drop is composed of solid-fluid and solid-solid friction loss, which dominate the hydrodynamic performance at different stages.     

Rheological behavior of POM polymer melt flowing through micro-channels

Determination of the rheological behavior of the polymer melt within micro-structured geometry is vital for accurate simulation modeling of micro-molding. The lack of commercial equipment is one of main hurdles in the investigation of micro-melt rheology. In this study, a melt viscosity measurement system for POM melt flowing through micro-channels was established. For measured pressure drop and volumetric flow rate, both capillary and slit flow models were used for the calculation of viscosity. The calculated results were also compared with those of PS resin to discuss the effect of morphology structure on the viscosity characteristics of polymer within micro-channels. It was found that the measured POM viscosity values in the test ranges are significantly lower (about 29-35% for a channel size of 150 μm) than those obtained with a traditional capillary rheometer. Meanwhile, the percentage reduction in the viscosity value and the ratio of slip velocity relative to mean velocity all increase with decreasing micro-channel size, but less significantly when compared with PS resin. In the present study we emphasize that the rheological behavior of the POM resin in microscopic scale is also different from that of macroscopic scale as PS resin but displays a less significant lower. It also revealed that the wall slip occurs more easily for the PS resin within micro-channels than POM resin due to enlarge the effect of molecular weight.     

Nanostructural modifications of polyamide/MMT hybrids under isothermal and nonisothermal elongational flow

The aim of this work is to investigate the effects of elongational flow on the nanoscale arrangement of the silicate inside polyamide‐based nanocomposites. Hybrids, at different loadings of a commercial organoclay, were produced by melt compounding using two polyamide matrices, a nylon‐6, and a copolyamide with similar molecular weight and rheological properties. The elongational flow characterization was performed under both isothermal and nonisothermal conditions by using, respectively, an elongational rheometer (SER) and a fiber‐spinning technique. The extensional rheological response of melt‐compounded nanocomposites, correlated to TEM and X‐ray analyses, was used to probe the nanostructural modifications developed during the uniaxial stretching. The results demonstrated that isothermal and nonisothermal elongational flow can modify the nanomorphology of the nanocomposite hybrids affecting the degree of silicate exfoliation as well as the extent of silicate orientation upon the stretching direction. The entity of structural modifications induced by the stretching were highly dependent on the initial nanomorphological state and on the polymer‐clay affinity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 981–993, 2009     

Clay network in ABS-graft-MAH nanocomposites: Rheology and flammability

A melt blending method was used to prepare ABS/clay and ABS-g-MAH/clay nanocomposites. Cone calorimeter and advanced rheological extension system (ARES^©) were employed to measure flammability and dynamic rheological properties. The main aim is to establish a relationship between the clay network structure and flammability properties of polymer nanocomposites. From the results of dynamic rheological measurements, it was found that the clay network structure was formed in ABS-g-MAH/clay nanocomposites, which strongly affected the flammability properties of the nanocomposites. The clay network improves the melt viscosity and results in restraint on the mobility of the polymer chains during combustion, which leads to significant improvement of flame retardancy for the nanocomposites.     

Rheological behavior of PET/HDPE in situ microfibrillar blends: Influence of microfibrils' flexibility

Poly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) in situ microfibrillar reinforced blends were prepared via a slit die extrusion‐hot stretch‐quenching process. The in situ PET microfibrils contain various contents of a segmented thermoplastic elastomer, Hytrel 5526 (HT), hence having different flexibility as demonstrated by dynamic mechanical analysis. It is interesting that the simple mixing leads to nanoscale particles of the HT phase in PET phase, and the size of the HT particles is almost independent of the HT concentration, as observed from the scanning electron microscope micrographs which show that the microfibrils with different HT concentrations have almost the same diameter and smooth surfaces. The static rheological results by an advanced capillary rheometer show that the entrance pressure drop and the viscosity of the microfibrillar blends both reduced with increasing the microfibrils' flexibility. Furthermore, the data obtained by the temperature scan of the PET/HT/HDPE microfibrillar blends through a dynamic rheometer indicates that the more flexible microfibril leads to lower melt elasticity and slightly decreases the viscosities of blends, presenting a consistent conclusion about influences of the microfibrils' flexibility on the rheological behavior from the static rheometer measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1205–1216, 2007     

Die swell ratio of polystyrene melt from an electro‐magnetized capillary die in an extrusion rheometer: effects of barrel diameter,shear rate and die temperature

A constant shear‐rate extrusion rheometer with an electro‐magnetized capillary die was utilized to investigate die swell behavior and flow properties of a polystyrene melt as the application of an electro‐magnetic field to the capillary die was relatively novel in polymer processing. The test conditions such as magnetic flux density, barrel diameter, extrusion rate and die temperature were studied. The results suggest that the maximum swelling of the polystyrene melt with application of the electro‐magnetic field could be enhanced up to 2.6 times (260%) whereas that without the electro‐magnetic field was 1.9 times (190%). The barrel diameter of 30 mm was found to be a critical value in the case of the die swell ratio and flow properties of the polystyrene melt were significantly affected by the magnetic flux density. This involved the number and angle of magnetic flux lines around the barrel part. Under the electro‐magnetic field, there were two mechanical forces influencing the die swell ratio and the flow properties; magnetic torque and shearing force. The die swell at wall shear rates less than 11.2 sec^?1 was caused by the magnetic torque, whereas at higher wall shear rates it was dependent on the shearing force. For a given magnetic flux density, the maximum increase in the die swell ratio as a result of the magnetic torque was calculated to be approximately 20%. Increasing the die temperature from 180 to 200°C reduced the overall die swell ratio and suppressed the effect of the magnetic flux density. Copyright © 2004 John Wiley & Sons, Ltd.     

Influence of silica nanoparticles combined with zinc phosphinate on flame retardant properties of PET

Zinc phosphinate (Exolit OP950), nanosilica particles and polyethylene terephthalate (PET) have been blended and thereafter melt‐spinned to develop a new flame retardant (FR) system for PET textiles. The effects of the two types of nanosilica fillers on the wettability, dispersibility and thermal properties were studied to determine how the degree of hydrophilicity affects the PET matrix. The influence of the blends on thermal transitions has been investigated by differential scanning calorimetry (DSC), the thermal stability of the polymer/FR blend composites has been assessed by thermogravimetric analysis (TGA) and cone calorimetry has been used to study the fire reaction. It was noticed that the nanoparticles have a limited influence on the thermal transitions of the PET matrix, but zinc phosphinate acted as a plasticizer and a compatibilizer for the more hydrophobic particles. Thermogravimetric analysis results showed that the addition of silica particles and FR compound improves slightly the thermal stability of the PET systems under nitrogen and air atmospheres. Furthermore, it was noticed that the incorporation of nanoparticles gives almost no improvement in the PET fire reaction from cone calorimeter experiments. However, in the presence of Exolit OP950, the systems acted as FR in PET films and knitted structures. The heat release rate during the combustion decreased, and the thermal behaviors of these structures were closed to those with 10% wt of Exolit OP950. Copyright © 2017 John Wiley & Sons, Ltd.     

Effects of organoclays on morphology and thermal and rheological properties of polystyrene and poly(methyl methacrylate) blends

Morphology, thermal and rheological properties of polymer‐organoclay composites prepared by melt‐blending of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PS/PMMA blends with Cloisite® organoclays were examined by transmission electron microscopy, small‐angle X‐ray scattering, secondary ion mass spectroscopy, differential scanning calorimetry, and rheological techniques. Organoclay particles were finely dispersed and predominantly delaminated in PMMA‐clay composites, whereas organoclays formed micrometer‐sized aggregates in PS‐clay composites. In PS/PMMA blends, the majority of clay particles was concentrated in the PMMA phase and in the interfacial region between PS and PMMA. Although incompatible PS/PMMA blends remained phase‐separated after being melt‐blended with organoclays, the addition of organoclays resulted in a drastic reduction in the average microdomain sizes (from 1–1.5 μm to ca. 300–500 nm), indicating that organoclays partially compatibilized the immiscible PS/PMMA blends. The effect of surfactant (di‐methyl di‐octadecyl‐ammonia chloride), used in the preparation of organoclays, on the PS/PMMA miscibility was also investigated. The free surfactant was more compatible with PMMA than with PS; the surfactant was concentrated in PMMA and in the interfacial region of the blends. The microdomain size reduction resulting from the addition of organoclays was definitely more significant than that caused by adding the same amount of free surfactant without clay. The effect of organoclays on the rheological properties was insignificant in all tested systems, suggesting weak interactions between the clay particles and the polymer matrix. In the PS system, PMMA, and organoclay the extent of clay exfoliation and the resultant properties are controlled by the compatibility between the polymer matrix and the surfactant rather than by interactions between the polymer and the clay surface. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 44–54, 2003     

Rheological Aspects of PP-TiO2 Micro and Nanocomposites: A Preliminary Investigation

The linear rheology of PP-TiO₂ composites was investigated as a function of the filler particle size. Small amounts (ϕ = 4.5%) of micron and nano-sized TiO₂ spherical particles were added to the polymer by melt compounding. In spite of the low particle volume fractions and the weak polymer-filler interactions, relevant changes have been observed in the linear viscoelastic behaviour of the nanostructured formulations. Microstructural analyses performed through electron microscopy have shown a good degree of dispersion of micron-sized particles. Conversely, the presence of a relevant number of TiO₂ nanoparticle clusters has been detected for the nanocomposite. The structure of these aggregates seems to be strongly responsible for the rheological behaviour of these last materials in comparison with microstructured ones. Relevant similarities between the viscoelastic properties of nanocomposite and the flow feature of many soft glassy materials have been noticed, and a simple physical picture has been proposed in order to interpret the rheological response of studied nanocomposites.     

RHEOLOGICAL PROPERTIES OF POLY(VINYLIDENE FLUORIDE) IN MOLTEN STATE

The theological behavior of poly(vinylidene fluoride)(PVDF)samples of different molecular weights was investigated by means of high pressure capillary rheometer and rotational rheometer.Information on the rheological properties of such materials above melt temperatures is of interest as this can lead to an improved understanding of polymer behavior in processing and fabrication technologies.Shift factors derived from time-temperature superposition showed good fit to the Arrhenius equation with a flow act...     

Mechanism for effect of ultrasound on polymer melt in extrusion

This paper explores the rheological characteristic and molecular mechanism of the polymer melts during extrusion when ultrasound is applied to them at the entrance of the die. Applying of ultrasound disturbs the convergent flow of polymer melt in the entry zone and changes the stream patterns, which leads to lesser elastic tensile strains happen. It also activates the molecular chains, so that the elastic tensile strains can be recovered very quickly. That is why the ΔP measured is reduced. These conclusions are made based not only on rheological calculations but also on looking‐inside characterizations of the molecular conformations. Ultrasound irradiation increases the free volume of PS, reduces the molecular entanglements of polymer melt. All these effects of ultrasound contribute to the productivity raising and product quality improvement of extrusion processing. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1226–1233, 2007