bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Analyses in a Spiral Mandrel Die Assuming Wall Slip
Authors: Higuchi H. , Koyama K.
Published: December 2013

It is often observed in industrial practice that the thickness uniformity of blown film obtained with a given die varies with the type of polymer. We have shown in previous works the importance of the wall slip of polymer melt in the film uniformity. Currently available models of polymer melt flow through spiral mandrel dies neglect the wall slip. The present work considers the slip in flow analyses and predicts the effects of rheological properties on the uniformity; the decreases in melt viscosity and wall slip and the increases in shear thinning and the stress dependence of wall slip reduce the uniformity. The predictions agree well with the experimental results obtained in our previous studies.
Optimization of Sweet Bread Dough Processing Conditions by Twin Screw Extrusion
Authors: Wu J.-Y. , Tzeng L.-S. , Wang I.-C. , Chang C.-H. , Huang P.-H.
Published: December 2013

Effects of material feed rate, water addition amount, screw speed and sets of kneading elements on sweet bread dough handling properties and bread qualities were studied by Response Surface Methodology in twin screw extrusion. Results showed that dough stickiness was significantly affected by water addition amount and screw speed (p < 0.001, R2 = 0.9227). Firmness of bread crumb and spread ratio, which is an index for bread appearance, were both significantly affected by water addition amount, screw speed, and sets of kneading elements (p < 0.001, R2 = 0.8940; p < 0.001, R2 = 0.8884). The optimal conditions for sweet bread dough processing are water addition amount ranging from 45 to 50 %, screw speed ranging from 180 to 280 min−1, with material feed rate and kneading element set fixed at 40 min−1 and ten, respectively.
The Flow Behavior of Core Material and Breakthrough Phenomenon in Sandwich Injection Molding
Authors: Watanabe D. , Ishiaku U. S. , Nagaoka T. , Tomari K. , Hamada H.
Published: December 2013

The processing conditions that exert influence on the occurrence of breakthrough during sandwich injection molding were investigated. A spiral flow mold mounted on a twin-barrel injection machine fitted with a single nozzle was used. The effect of mold cavity thickness and the effects of skin material cylinder temperature on skin material viscosity, melt strength, and drawing ratio were considered. Scanning electron microscopy was used to study the morphology of the skin material at the flow front. It was found that the flow length at core expansion region increased and breakthrough phenomenon was delayed as the thickness of the mold cavity increased. When cylinder temperature is increased, the viscosity is lowered and the flow front of the skin material extends with greater ease when pushed by the core material, thus, a greater core volume can be accommodated. As the flow front progresses, the tendency is that the skin material becomes thinner. Polishing and etching followed by SEM examination of the skin material at the flow front revealed that the skin material is oriented perpendicular to the flow direction and the extent of orientation increases with increasing cylinder temperature. This further supported the observation that the deformation ratio and drawing ratio increased with increasing cylinder temperature.
Bowing Phenomenon in Double Bubble Tubular Film Processing for PA 6
Authors: Takashige M. , Kanai T. , Yamada T.
Published: December 2013

This report is to discuss the bowing phenomenon and the sag elimination tension for biaxial oriented PA 6 film process, which consists of double bubble tubular film process and the thermosetting tentering.

The bowing phenomenon does not occur in the heat set of the triple bubble tubular process. However, there is a serious problem of the bubble stability when the sufficient thermosetting by the tubular process is carried out, so the heat set by the tenter process is required. The bowing phenomenon arises when the annealing is carried out by the tenter method. The bowing distortion becomes large when the annealing temperature is high and film relaxation ratio is large.

It is possible to reduce the bowing distortion when thermosetting is carried out in a two-step tenter process. The shrinkage stress of the stretched film was relaxed in the heat treatment during the second step whose temperature is higher than the first one. A two-step heat treatment was able to decrease the bowing distortion compared with the one-step heat treatment.

When the bowing phenomenon occurred, shrinkage percentage in hot water changes along the cross-direction of a film. The humidity expansion coefficient in the film which increases as the increasing shrinkage percentage in hot water is related to the molecular orientation. The sag also increased with increasing the bowing distortion. The bowing distortion and the sag elimination of tension have proportional connection.
Three Dimensional Analysis of Shape Deformation in Injection Molded Optical Lens
Authors: Young W.-B.
Published: December 2013

The shape deformation of optical pickup lens in injection molding was investigated in this study. It was realized that residual stresses and warpage deformation in injection molding parts were affected by different process conditions such as melt temperature, mold temperature, packing pressure and time. A two dimensional analysis in injection molding only provides information on the thickness shrinkage for optical lens. In order to simulate the surface contour variations, a three-dimensional warpage analysis was conducted in this study using the finite element method. Moldings under different packing pressures and mold temperatures were numerically investigated to study the effects on the residual stresses and deformation of a molded pickup lens. The packing pressure and mold temperature were found to be the dominant factors that affect the shrinkage of lens in the thickness direction, resulting in surface contour deviation.
Thickness Uniformity of Double Bubble Tubular Film Process for Producing Biaxially Oriented PA 6 Film
Authors: Takashige M. , Kanai T. , Yamada T.
Published: December 2013

It is known that while the double bubble tubular film process gives better impact strength and more uniform shrinkage balance than the tenter process, yet it is relatively poor in film thickness uniformity. The film thickness uniformity of the PA 6 produced by the double bubble tubular film process was investigated.

The optimum stretching stress during the double bubble tubular film process exists. The bubble breaks over stress 130 MPa and bubble is unstable below stress 60 MPa. In the optimum condition, which is process temperature 310 °C and stretching ratio 3.2, stretched film uniformity was twice worse than non-stretched film one. The thickness uniformity of the film stretched in the optimum condition was better than that of the film stretched at higher process temperature and at lower stretching ratio. In the observations of the bubble sample through the polarizing plates, deformation pattern showed the equality of deformation. Thickness uniformity of non-stretched film significantly affects the thickness uniformity of biaxially oriented film.

Local stretching ratio, which varies along the film width, influences tensile modulus and tensile strength at break. In order to obtain the uniform physical properties of film, it is important to produce the film with uniform thickness. Film thickness uniformity can be improved when stretching stress is high and bubble stability is good. These factors are influenced by stretching temperature, stretching ratio and air velocity from air ring.
Effects of Sparse Long Chain Branching on the Spinning Stability of LLDPEs
Authors: Bortner M. J. , Doerpinghaus P. J. , Baird D. G.
Published: December 2013

The influence of sparse long chain branching on the onset and propagation of isothermal draw resonance in fiber spinning of polyethylene melts was investigated. Six polyethylene melts were used in this study: three sparsely branched metallocene polyethylenes, a linear low-density metallocene polyethylene, a conventional linear low-density polyethylene, and a conventional low-density polyethylene (LDPE). The sparsely branched metallocene polyethylenes have almost identical shear rheology and molecular weight distributions, but strain harden to different extents under extensional deformation because of slight differences in the amount of sparse long chain branching. Critical draw ratios and the ratios of minimum to maximum diameter were found to be different for each of these polyethylenes. The two linear low-density polyethylenes, which have no long chain branching, had critical draw ratios similar to those of the sparsely branched polyethylenes, but failed (necked to the point of filament breakage) during monofilament extrusion at draw ratios significantly lower than those measured for the sparsely branched polyethylenes. In contrast, the LDPE, which has the highest degree of branching and largest molecular weight distribution, had a much higher critical draw ratio than that obtained for the other five polyethylenes. These results suggest that the degree of extensional strain hardening, arising from differences in long chain branching, has a significant effect on the onset and propagation of draw resonance in isothermal fiber spinning. In the case of LLDPE, broadening the MWD seemed to affect the drawability of LLDPE, but had no effect on the critical draw ratio.
Predicting the Long-term Creep Behavior of Plastics Using the Short-term Creep Test
Authors: Lim S. D. , Rhee J. M. , Nah C. , Lee S.-H. , Lyu M.-Y.
Published: December 2013

The creep performance of plastics is one of the main criteria for a variety of applications which requires a strict dimensional stability, including electrical/electronic parts and various automotive applications. However, obtaining or generating accurate creep data is very difficult for both resin suppliers and product designers because the creep property is time dependent, which means it takes over several weeks or even a year of time span. Hence a faster and more reliable method predicting creep behavior of plastics is needed when designing plastic products that will encounter long-term loading. This work presents an easy method for predicting the long-term creep behavior of plastics using the short-term creep experimental data. The flexural creep experiments of three plastics, ABS (Acrylonitrile butadiene styrene), PC/ABS (PC and ABS alloy) and LFT (Long fiber reinforced thermoplastics), are performed. For a quick and reliable prediction of long-term creep behavior of plastics, time regional power-law model and time-stress modulus are introduced. To analyze the reliability and validity of the proposed method, the creep analyses based on the proposed method are performed. The comparison between the FEA results and the creep tests has shown that the new method can track both primary and secondary creep behavior over a long time. The creep analyses have been carried out by commercial FE Code.
On-line Visualization of PS/PP Melting Mechanisms in a Co-rotating Twin Screw Extruder
Authors: Chen H. , Sundararaj U. , Nandakumar K. , Wetzel M. D.
Published: December 2013

The melting and deformation mechanisms of polystyrene (PS) and polypropylene (PP) blends were investigated through on-line visualization of the co-rotating twin-screw extrusion process. Two compositions, PP/PS (80:20) and PS/PP (80: 20) were chosen as the model systems for this study. A sliding barrel technique was used to realize the on-line visualization using a glass window in the barrel. The axial temperature and pressure profiles along the screw channel were measured using the same sliding technique. It was found that in the PP/PS (80:20) blend, in which PP was the major phase, there was a combined melting of PS and PP, whereas in the PS/PP (80:20) blend, in which PS was the major phase, there was initial melting of PS alone and then combined melting of PS and PP. In the partially filled region, heat conduction from the hot barrel was the major source for heating polymer pellets under the conditions studied here; while in the fully filled region, viscous energy dissipation (VED) generated most of the heat for melting of polymer pellets. The pressure profiles along the extrusion channel gave us insight into the melting process for the two blends. It was found that if there was some molten polymer in the fully filled region, the overall melting process was accelerated due to heating from viscous dissipation.
Influence of Filler Particle Geometry on Die Swell
Authors: Stabik J.
Published: December 2013

Die swell reduction is observed as a result of filler incorporation into polymer matrix. The degree of die swell decrease depends among others on filler particles geometry. In the paper results of experimental investigations concerning relations between particle geometry and die swell are presented for polyethylene and polystyrene filled with a number of commercial fillers. Approximation functions describing these relations were developed. This enabled simultaneous analysis of the influence of different particle geometry properties on die swell. Good fitting of approximation models to experimental results was achieved. Similar behavior of polyethylene and polystyrene compounds was observed. Shape ratio exhibited the most pronounced influence on die swell. The higher is the shape ratio of filler particles the smaller is die swell. Much less significant influence showed specific surface and mean particle diameter.
Determination of the Residence Time Distribution in Twin Screw Extruders via Free Radical Modification of PE
Authors: RazaviAghjeh M. K. , Nazockdast H. , Assempour H.
Published: December 2013

The main objective of the present work was to introduce an inline method for measuring the residence time distribution (RTD) of twin screw extruders on the basis of information obtained from the melt free radical modification of polyethylene in a modular intermeshing co-rotating twin screw extruder. The trend of increasing rate of the extruder total torque resulted from replacing the neat polyethylene feed by a mixture of polyethylene and reactants which are chemically capable of creating chainbranching and/or crosslinking reactions was considered as the main information source for evaluating the RTD of the extruder. The RTD results were compared with those obtained from the tracer pulse input method, and good agreement was found. It was also demonstrated that, the present in-line RTD measuring technique has reliability of following the effect of feeding rate, screw speed and reactant concentration on the RTD of the twin screw extruders. It was found that, increasing the feeding rate results in decreasing the minimum residence time, and results in a narrower RTD. At constant feeding rate increasing the screw speed decreased the minimum residence time and broadened the RTD. The results also showed that, reactant concentration and variation of the viscosity along the screw have not appreciable effect on the twin screw extruders RTD.
Reactive Batch Mixing for Improved Silica-Silane Coupling
Authors: Kim K.-J. , Vanderkooi J.
Published: December 2013

Moisture (55 wt%) treated silica compounds, bis(triethoxysilylpropyl)disulfide(TESPD)/silica/carbon black/S-SBR was processed in a batch mixer and they were investigated with respect to the alcohol residue level in silane, the processability, the vulcanization characteristics, and the mechanical properties.

Treatment of moisture on the TESPD/silica/carbon black/S-SBR compound showed a lower alcohol level than untreated material. The alcohol level was low at high drop temperatures. The probe temperatures of the moisture treated compound were lower than the drop temperature, while that of the untreated compound was higher than the drop one. The vulcanization properties of the compounds were changed by treatment of moisture and this improved the mechanical properties of the compounds.

The treatment of moisture on silica surface increased the hydrolysis reaction of the alkoxy silane and the hydrolyzed silane improved the coupling reaction with the hydroxyl group on silica surface during reactive batch processing. It also reduced the rate of temperature rise during batch processing due to the latent heat of the moisture and the endothermic reaction between silica and silane. At the vulcanization stage, it seemed to further increase the coupling reaction between silica and silane.

The steric hindrance theory of an alkoxy silane has to be reconsidered with a large amount of moisture treated silica/TESPD/CB/S-SBR compound system.
Laser Sintering of High Temperature Resistant Polymers with Carbon Black Additives
Authors: Wagner T. , Höfer T. , Knies S. , Eyerer P.
Published: December 2013

Selective laser sintering (SLS) experiments with polyetherketone (PEK) and polyetheretherketone (PEEK) powders are described. The absorption behaviour of the polymer powders has been investigated with respect to the content of carbon black as an IR-absorber in the range from 0.03 to 0.1 wt.%. Laser sintering process studies have been carried out at room temperature using a Q-switched Nd:YAG laser system. The sintering depths of single layer substrates have been determined according to the process parameters, such as laser power, scanning speed and hatch distance. These process parameters have been optimised with the goal of achieving good structural integrity of the substrate. The influence of melt viscosity has been determined by comparing PEEK powders of low and standard melt viscosity. Scanning electron micrographs show the morphology of the original polymer powders and the laser sintered specimens. On the basis of the experimental results a qualitative SLS mechanism is proposed to describe the energy transfer from the carbon black particles to the surrounding polymer powder.
Non-linear Viscoelastic Behavior of PVC Plastisol
Authors: Nakajima N. , Harrell E. R.
Published: December 2013

Rheology of PVC plastisol is usually conducted with steady state flow. It is inadequate, because plastisol is viscoelastic, so that deformational experiment is also required. In the viscoelastic measurements, when either frequency or amplitude is increased, dynamic viscosity decreases first (pseudo-plastic), reaching a minimum and then, increases (dilatant). It is because the shear rate during the oscillation is a product of frequency and amplitude. The pseudo-plastic behavior is explained with stress-induced phase separation into an immobilized layer of packed particles and mobile phase of reduced particle concentration. The viscosity minimum corresponds to the yield point of the immobilized layer. The yielding obeys Coulomb's criterion. After yielding the immobilized layer dilates with the further increase of shear rate. Two different modes of fracture are observed; one without yielding occurs at rather low shear stress, slightly higher than the cohesive strength of the immobilized layer. After yielding and dilation, the fracture occurs when shear stress becomes higher than normal stress. Before yielding the deformation of the immobilized layer is very small and accompanied with small fraction of particles moving over the neighboring particles. After yielding, deformation involves entire particles of the immobilized layer.
Simultaneous Biaxial Stretching of PP Resins of Varying Tacticity
Authors: Capt L. , Rettenberger S. , Münstedt H. , Kamal M. R.
Published: December 2013

The melting and simultaneous biaxial stretching behavior of three Ziegler-Natta isotactic polypropylene resins of varying isotacticity was studied. DSC melting experiments showed that the crystallinity and melt stability of the crystalline phase depend strongly on tacticity and on the degree of undermelting, ΔT = Tm – T, where Tm is the melting temperature. The level of biaxial yield stress depends on the fraction of residual “unmolten” crystallinity and the crystallite size. For specimens with same thermal history, the post-yield deformation shows strong dependence on the degree of undermelting, ΔT. The deformation homogeneity and the resulting film thickness may be related to the thermal mobility of the chains and the tie chain and entanglement densities.
Easy Tear Multilayer Film of Biaxially Oriented PA6/MXD6 by Double Bubble Tubular Film Process
Authors: Takashige M. , Kanai T.
Published: December 2013

In the market, a film which is adapted to environmental and barrier problems and easy tear property is desired. A previous report discussed easy tear PA6 film. This report discusses the film having not only easy tear, but also high barrier properties.

A biaxially oriented PA6/MXD6 blend film produced by double bubble tubular film process does possess gas barrier. So a multilayer film having high gas barrier layer and keeping easy tear cut has been studied. High gas barrier layer of high content MXD 6 in the center layer is added to PA6/MXD6 blend film in the outer layers.

When MXD6 blending ratio of PA6/MXD6 blending film layer is 30 %, the property of easy straight line cut is obtained. It is found that the plate-like cylinder structure was formed in the observation of TEM for PA6/MXD6 blend film.

The multilayer biaxially oriented film composed of PA6/MXD6 blend layer and MXD6 high content layer keeps high strength, easy tear property and high gas barrier. Namely, the material and production technology of a PA6 film could solve environmental and barrier problems.
Rotational Moulding of PVC Plastisol
Authors: Marcilla A. , García J. C. , Ruiz R. , Sánchez S. , Vargas C. , Pita L. , Beltrán M. I.
Published: December 2013

The viscosity during the earlier stages of the gelation process of plastisols formulated with 15 different commercial plasticizers has been obtained. Plastisols prepared were rotomoulded and mouldings obtained were characterized according to their wall thickness distribution. This parameter strongly depends on the minimum viscosity and on the rate of viscosity change during gelation (slope of the curves during the viscosity increase), and also on the temperature where no more flow of the plastisol is observed (gelation temperature). These variables are conditioned by the characteristics of the plasticizer and PVC employed, among other variables.

The effect of plate and arm velocity and rotation rate on the wall thickness distribution was also studied.

A simple model has been proposed to correlate the initial stage of the gelation of PVC plastisols formulated with the phthalate plasticizers. The suggested model assumes that the plastisol is a suspension constituted by a continuous phase (initially pure plasticizer) and a discontinuous phase constituted by PVC particles. It has been considered that the viscosity of the plastisol is influenced by the average mass molecular weight of the continuous phase and the temperature. The quantity of PVC dissolved in the continuous phase has been calculated by using a generic n-order kinetic equation for PVC dissolution rate. Additionally, a swelling process of the PVC particle by the plasticizer has also been considered and its effect on the viscosity of the suspension has also been accounted for. The model proposed provides a very good fitting of the sharp viscosity increase observed and is useful to predict the evolution of the viscosity of the parts in a rotomoulding process.
A Dilatometer to Measure the Influence of Cooling Rate and Melt Shearing on Specific Volume
Authors: van der Beek M. H. E. , Peters G. W. M. , Meijer H. E. H.
Published: December 2013

We developed a dilatometer to investigate the specific volume of polymers as a function of pressure (to 100 MPa), temperature (to 260 oC), cooling rate (to 100 oC/s), and shear rate (to 80 1/s). The dilatometer is based on the principle of confined compression and comprises of a pressure cell used in combination with a tensile testing machine with rotation capability. The design of the pressure cell is a mixture of a traditional ‘pistondie type’ dilatometer and a Couette rheometer, i. e. piston and die make up an annular shaped sample spacing. Typical dimensions of annular samples are: inner radius ri = 10.5 mm, outer radius ro = 11.0 mm, height h = 2.5 mm, and a typical mass of about 60 to 70 mg. Silicon grease is used to reduce loss of hydrostatic pressure in the sample due to friction occurring between the solidifying sample and the dilatometer wall. Specific volume measurements at low cooling rate using an isotactic polypropylene (i-PP) are compared with measurements performed using a commercial bellows type dilatometer, showing relative differences in the range of 0.1 to 0.4%. Finally, results for an isotactic polypropylene are presented showing a profound influence of cooling rate and melt shearing on the evolution of specific volume.
Nozzle Injection of Physical Blowing Agents in the Injection Molding of Microcellular Foams
Authors: Bravo V. L. , Hrymak A. N.
Published: December 2013

Results obtained from the implementation of a physical foaming system for injection molding are presented. The implemented design involves the injection of gas in the upstream side of a special nozzle composed by a static mixing element (SMX type) and a shut-off valve. In order to avoid the formation of large pockets of gas in the injection point, a porous metal plug is used to create a multiple point injection area with 20 lm size pores. Gas injection simultaneously with polymer melt injection gave a consistent foamed material. However, given the total pressure drop in the system of static mixers, runners and mold, there is an inherent operational pressure limitation. The polymer injection pressure needs to be kept at a pressure below the gas injection pressure, therefore limiting the speed at which the polymer can be injected in the mold.
Experimental Study on the Filling of a Micro Injection Molding with Cylindrical Dot Patterns
Authors: Chang H.-C. , Young W.-B.
Published: December 2013

This study is to investigate the fabrication of a mold insert with negative cylindrical dot micro features using the LIGA-Like process and molding of the component. The effects of molding conditions on the filling of the polymer melt into the negative features were experimentally studied. A parametric study of the effect of the molding conditions on the filling of microstructure in micro molding was conducted. Increase of the mold temperature or injection rate is an effective method to ensure the complete filling of the microstructure. The application of packing pressure was shown to improve the filling in the microstructure also. With the low aspect ratio used in this study (about 0.2), the microdot array can be completely filled with the right selections of injection rate and mold temperature without vacuum.
Two Dimensional Description of Pressure-Throughput Behaviour of Newtonian Materials Considering Wall Slippage Effects
Authors: Potente H. , Kurte–Jardin M. , Klus S. , Timmermann K.
Published: December 2013

The description of pressure-throughput behaviour of wall adhering melts in plastifying machines has been issued in a number of publications, e. g. [1 to 4] in details. Nevertheless there are a variety of polymer melts as well as elastomers, polymer suspensions, ceramic materials and food stuff, which do not behave wall adhering in the course of manufacturing. The theoretical discussion of the pressure-throughput behaviour has not sufficiently been described up to now. Worth's [5] case studies include the isothermal one-dimensional flow of a Newtonian medium in an unwinded screw channel. He assumed that after exceeding a critical shear rate the slipping process starts on the barrel wall only – but not on channel wall and screw root surface. Mennig, [6 to 9] took up this statement again and assuming a shear rate on the barrel wall as well as on the screw root surface he derived simple relations for the radial velocity profile from it. Lawal and Kalyon [10 to 12] have developed an analytical model that describes the behaviour of visco-plastic liquids in flat channels for different quotients of wall slippage, which are derived from the wall slippage quotients on screw root surface and on barrel wall.

A mathematical model describing the flow behaviour for the two-dimensional Newtonian, isothermal case has been developed for wall slipping materials in order to describe the pressure-throughput behaviour multi-dimensionally.

In addition to the development of the analytical calculating model the flow behaviour of wall slipping polymer melts has been analysed by using the finite-element-calculation (FEM). Comparison of the pressure-throughput behaviour results show a high degree of conformity in the calculation results.
State of the Art: Recycling of EPDM Rubber Vulcanizates
Authors: Sutanto P. , Picchioni F. , Janssen L. P. B. M. , Dijkhuis K. A. J. , Dierkes W. K. , Noordermeer J. W. M.
Published: December 2013

Since the past few decades, environmental issues have become a serious concern in society. It is a requisite for the industry to minimize waste, in order to protect the environment from being polluted. The term waste here comprises processing waste and post-consumer waste. The amount of processing waste should not be underestimated since it might consist of approximately 10% of the total production. The recycling of EPDM rubber is an interesting topic, especially if considered in connection with the continuous market growth of EPDM. This paper is a summary of efforts that have been taken so far on this subject. Studies done on EPDM recycling include reusing EPDM as filler in new rubber products and chemical, thermal, and mechanical devulcanization of EPDM in order to achieve a material that resembles the virgin one and could be revulcanized. Such studies on EPDM recycling are discussed extensively and in the conceptual frame of more general rubber recycling processes.
Thermal Flow Instability in Metal Injection Molding: Experiment and Simulation
Authors: Stevenson J. F. , Ilinca F.
Published: December 2013

Metal injection molding (MIM) is similar to plastic molding in many respects, but MIM compounds (metal powders with polymer binders) are more susceptible to thermally induced flow instability because of their higher thermal diffusivity. The flow patterns for a 17-4PH MIM compound were observed and simulated for mold filling through a diaphragm gate over a range of filling times and melt-mold interface temperatures. Simulation predicted the observed free annular jet and internal voids in the molded part and also predicted that initial contact with the outside wall of the gate would eliminate the jet, thereby reducing voids and surface defects. Parts made using a mold with a thicker gate verified these predictions. For combinations of operating conditions and mold geometry that gave large thermally induced viscosity gradients, both observation and simulation showed unstable, asymmetric flow. In these cases, flow slowed and stopped in one region of the gate and accelerated in other regions. When the flow was inherently unstable, simulations predicted an exponential growth in maximum temperature differences at symmetric locations in the mold gate. Based on 34 experimental observations and 102 simulations, a boundary was established between regions of stable and unstable flow in terms of the dimensionless Graetz number Gz (ratio of heat conduction time to fill time) and B, a dimensionless ratio indicating the sensitivity of viscosity to temperature differences in the mold. To establish a common basis for comparison of simulation and experiment, the melt-mold interface temperature was estimated using a heat transfer coefficient, which was a fixed value for experiment and a parameter for simulation.
Pressure and Temperature Dependence of LDPE Viscosity and Free Volume: The Effect of Molecular Structure
Authors: Sedlacek T. , Lengalova A. , Zatloukal M. , Cermak R. , Saha P.
Published: December 2013

Temperature and pressure dependencies of shear and elongational viscosities were examined using rotational and capillary rheometers. Two different batches of the same polymer grade have shown that the molecular structure diversion significantly influences the magnitudes of pressure coefficients, which vary more than the temperature coefficients. The pressure effect on viscosity notably depends on the amount of long-chain branching in polymer. Further, the paper shows that pVT data analysis via the Simha-Somcynsky equation of state can be employed to reveal differences in temperature and pressure viscosity dependencies through the free volume fraction.
Coating and Polymer Processing
Authors: Benkreira H.
Published: December 2013

Coating like polymer processing contributes greatly to the production of thin films using polymers in solutions or in a melt form. From a fluid mechanics perspective, coating operations share common features with polymer processing film operations and it is the purpose of this review to highlight the similarities and help foster a common approach for analysis, design and operation of these processes.
Functionalization of PP with Sulfonyl Azide through Reactive Processing
Authors: Li Q. , Tzoganakis C.
Published: December 2013

The functionalization of polypropylene (PP) by 4-carboxybenzene sulfonyl azide (CBSA) was investigated in a batch mixer and the reaction was monitored through FTIR,1H-NMR and XPS spectroscopy. The degree of grafting was found to increase initially with azide feed content and subsequently to level off at azide concentrations of 2 wt.%. Experiments performed at different reaction temperatures showed that a maximum degree of grafting was obtained around 190°C. The linear viscoelastic properties the functionalized PPs were also evaluated by oscillatory shear measurements and were found to correlate with the grafting degree results. Finally, the adhesive properties of the functionalized PPs were evaluated through peel tests on aluminum substrates. The peel strength increased with the degree of grafting and it was found to be significantly higher for purified samples than for non-purified ones. Finally, it was demonstrated that the cooling rate of the PP/aluminum laminate specimens had a major effect on the peel strength.
Development of Planar Orientation in Polymer Processing
Authors: Horio Masao
Published: December 2013

A critical discussion is presented of the development of planar orientations in various polymer processing operations. These include tubular blown film and subsequently drawn and multiply stretched blown films. The response of polyethylene, various nylons, poly(ethylene terephthalate), cellulose and poly(p-phenylene terephthalamide) are discussed.
A Dispersive Mixing Testing Apparatus
Authors: Chohan R. K. , David B. , Nir A. , Tadmor Z.
Published: December 2013

The dispersion process of agglomerated soldis, such as carbon-black, into rubbers and plastics is still not understood to a satisfactory extent. Dispersive mixing is commonly carried out in roll mills, internal mixers and continuous intensive mixers. It is accomplished by repeated passage of the mixture, through converging-tight clearance high stress regions, of the mixers. The key design and operational variables are the geometry of this region, the stress history of the fluid element, and the passage distribution function. A laboratory apparatus was designed and built to enable a systematic study of the effect of these variables on mixing. The apparatus, and experimental results are described. Results verify that the number of passages is a dominant variable in dispersive mixing, and proves the utility of the apparatus to study the dispersive mixing process.
Shear Modification of Polyolefines and its Integration in Polymer Processing
Authors: Ritzau G.
Published: December 2013

The viscous and especially the elastic properties of polymer melts can be altered by a previously imposed deformation history. This phenomenon, usually termed as shear modification, is caused by the reversible physical disentanglement of the polymer molecule chains. The shearing unit presented in this paper was used to systematically investigate the processing parameters governing shear modification.

A set of rheological tests was carried out with the shear modified sample material and the expected changes in the rheological behaviour were detected. The relative change of the storage modulus G', measured using a Rheometrics On-line Rheometer system, was taken as a measure for the degree of modification and was found to correlate with the specific energy dissipated during sample preparation. The effects of shear modification on product properties were investigated for the tubular film-blowing process. Changes in the optical and mechanical properties of films which can be attributed to the previously imposed shear modification process were found.
Shear Flow Properties of Carbon Fibre-Filled Polyethylene Melts
Authors: Kitano T. , Funabashi M. , Klason C. , Kubát J.
Published: December 2013

A fundamental investigation of the influence of fibre loading, fibre length and matrix properties on shear viscosity, complex viscosity and the first normal stress coefficient of filled polyethylene melts prepared by different compounding techniques was carried out. Carbon fibre was compounded into two different types of low-density polyethylene (PEA and PEB) at concentrations up to about 20% by volume using different compounding techniques: a single screw extruder, and a twin screw extruder. The main difference in flow behaviours for the two kinds of carbon fibre-filled systems (CF/PEA and CF/PEB) is not due to differences between the matrix polymers, but due to the difference in fibre length or its distribution caused by the difference in compounding technique. Increasing fibre loading and fibre length increases the shear viscosity and the normal stress coefficient, with the highest increase observed at low shear rates. Especially for longer fibre-filled melts (CF/PEA series) one can estimate the yield stress in the very low shear rate region from the steady shear and dynamic flow data. In the moderate and high shear rate regions the viscosity and normal stress coefficient are influenced greatly by shear flow. Data on the relative viscosities ηr, the relative complex viscosities |η*|r and the relative normal stress coefficients ψr of the two filled systems in the moderate and high shear rate regions were compared with the empirical equation derived previously for ηr for short fibre filled polymer melts. It was found that a form of the expression similar to that obtained previously could describe ηr, |η*|r, and ψr for relatively long carbon fibre filled systems.
Modelling of the Peroxide Degradation of Polypropylene
Authors: Tzoganakis C. , Vlachopoulos J. , Hamielec A. E.
Published: December 2013

A fully-predictive mathematical model has been developed for the peroxide promoted degradation of polypropylene in a plasticating single-screw extruder. The model is based on a free radical kinetic mechanism for the degradation reaction and on conventional plasticating extrusion theory. Solids conveying, melting, melt pumping and reaction phenomena have been combined and the interactions between flow pattern, mass and heat transfer fields via residence time distribution and the chemorheology of the reactive melt have been considered. Given the geometrical configuration of the screw, the operating conditions and the physical properties of the starting polymer, the model can predict: flow rate, pressure, temperature and molecular weight profiles in the extruder channel and in the die, and the residence time distribution in the system. Finally, model predictions are compared with experimental data from runs on a 38mm, 24:1 L/D single-screw extruder using various peroxide concentrations and rotational screw speeds.
Simultaneous Interpenetrating Networks of Polybutadiene-based Polyurethane/Poly (Methyl Methacrylate-co-Glycol Dimethacrylate)
Authors: Jia D. M. , You C. J. , Wu B. , Wang M. Z.
Published: December 2013

Polybutadiene-based polyurethane/poly (methyl methacrylateco-glycol dimethacrylate) interpenetrating polymer networks (PU (HTPB)/P(MMA-co-EGDMA)-IPN) was synthesized by simultaneous polymerization. FTIR and dynamic mechanical spectra (DMS) show no apparent chemical bonds between the two component polymers. The results of DMS also demonstrated that the interpenetration of networks exists mainly between P(MMA-co-EGDMA) and the hard segments of PU(HTPB). The results of transmitting electron microscopy (TEM) indicate that when the amounts of P(MMA-co-EGD-MA) are from 20 to 80 wt%, the domain sizes increase from 100 to 200 Å to several microns, and the morphology features vary from the interpenetration of microphase separation structure to the boundary interpenetration of cellular structure. Besides, the IPN has dual phase continuity. With increasing amounts of P(MMA-co-EGDMA), the stress-strain curves indicate that the corresponding IPN materials transform from reinforced rubbers to toughened plastics. The mechanical properties of the full-IPN are far superior to those of the corresponding linear blends, and also higher than those of the corresponding semi-IPN.
The Processing and Properties of γ-irradiated HDPE Granules
Authors: Bowman J.
Published: December 2013

Granular high density polyethylene has been irradiated to relatively low doses prior to processing. The molecular weight was, at the lower doses, increased and the molecular weight distribution broadened with increasing dose. At the two highest doses an insoluble gel was introduced. These variously irradiated granules were processed by two routes, compression and injection molding, and selected structural features and mechanical properties ascertained. For all granule doses compression molded samples could be produced, with the plaque density decreasing with increasing granule dose. While the ductility of the moldings improved with increasing granule dose, the modulus and yield stress both declined as the density of the moldings decreased. Injection molded samples could only be prepared from granules free of gel. The density of the moldings depended on both granule dose and barrel temperature: in general, the density first increased then declined with increasing granule dose, an effect associated with preferred molecular orientation. The yield stress and modulus both appeared to correlate better with melt flow index rather than density, to infer that preferred molecular orientation is significant in injection moldings and can override the influence of density.
Dynamic Measurements on Polymer Liquid Crystals**
Authors: Horio M. , Kamei E. , Yao S. , Ishikawa S. , Matsunobu K.
Published: December 2013

The dynamic experiments were made on the solutions of poly (l,4-phenylene-2,6-benzobisthioazole) (PBT) in poly(phosphoric acid) at frequencies from 10−2 to 102 radian· sec−1. For the liquid-crystalline solutions, the logarithmic plots of G′ and G″ against frequency show abnormally small slopes and those of η′ exhibit large slopes at low frequencies in contrast to the plots for the optically isotropic solutions. However, the viscoelastic behavior of liquid-crystalline solutions is regarded as linear. The temperature of anisotropic-isotropic phase transition of solution is higher for high-molecular-weight PBT than for lowmolecular-weight PBT. The dilution of solution lowers the transition temperature. The transition goes through various stages of mixed phases. The method of reduced variables is applicable to the isotropic solutions, and the resulted composite curves were discussed. The method, however, is inapplicable to the anisotropic solutions, suggesting that the configuration, interaction and aggregation state of molecules in liquid-crystalline solutions may change sensitively by temperature. The slow relaxation mechanisms are involved in the mesophase systems, but the quick shrinkage of highly oriented nematic mesophase at the onset of relaxation produces the zigzag-fibrillar structure of fibers and films made by stretch spinning or casting.
Analysis of Agglomerate Rupture in Linear Flow Fields
Authors: Manas-Zloczower I. , Feke D. L.
Published: December 2013

A dispersive mixing model focusing on the rupture of agglomerates as the step that primarily determines the dynamics of the mixing process was developed and analyzed. Rupture is predicted to occur when hydrodynamic forces exerted on the outer surface of the agglomerate exceed cohesive forces binding the agglomerate together. Agglomerates are modeled as clusters of aggregates bound by van der Waals forces. The magnitude and orientation of the rupturing hydrondynamic force depend on the local stress field in the fluid. Cleavage of the agglomerate is predicted to occur at the mid-plane of the agglomerate where the effects of hydrodynamic tension is the largest. Under the assumption that parent agglomerates and their fragments have the same shape, the kinetics of the rupture process is found to be independent of the absolute size of the agglomerate. Following from this is the result that the dispersion process is governed by flow dynamics, i.e., a minimum value of flow strength, which depends on the geometry of the bulk flow field, is required for rupture of the agglomerate. Agglomerate rupture was investigated in four flow geometries: simple shear; pure elongation; uniaxial extension, and biaxial extension. The efficiency of each flow geometry is compared on the basis of power and time requirements to achieve a given degree of dispersion.
Flow Visualization of the Rubber Compounding Cycle in an Internal Mixer based on Elastomer Blends
Authors: Morikawa A. , Min K. , White J. L.
Published: December 2013

A flow visualization study of the blending of elastomers and the subsequent mixing of carbon black and oil in an internal mixer is described. The elastomers studied were natural rubber, cis-polybutadiene and a solution styrene-butadiene copolymer. Studies were made of addition to the mixer of mini bales of earch rubber pigmented with different colors and their subsequent homogenization. Subsequently we investigated the blending of bales of the different rubbers and determined the homogenication times. Similar investigations were made of the addition of carbon black and oil black homogenization times and oil absorption times were determine. These are correlated with the rheological properties of the elastomers.
Use of Chilled Die Lips to Improve Production Rates in Extrusion of PE
Authors: Cook D. G. , Cooke R. , Rudin A.
Published: December 2013

Extrusion rates of polyethylene are limited by the onset of surface defects in the extrudates, which are variously termed sharkskin, melt fracture and so on. Several expedients are effective in relieving this problem. We report here that extrudate surface distortion can be eliminated under some conditions by cooling the die, at normal melt extrusion temperatures. This technique appears to be generally effective for LLDPE and HDPE. The process has been patented [10] for polymers with narrow molecular weight distributions.
Characterization of the Sharkskin Defect and its Development with the Flow Conditions**
Authors: Beaufils P. , Vergnes B. , Agassant J. F.
Published: December 2013

We have studied the development of the sharkskin defect of a linear low density polyethylene, by using complementary experimental techniques. Roughness measurements have allowed to accurately characterize the surface of the extrudates. Flow birefringence observations have permitted to visualize the flow conditions inside the die. The development of the defect is strongly dependent on the temperature and quasi-independent on the geometry (die length, entry angle). Theoretical computations of the flow through the slit die have allowed the correlation of the amplitude of the defect with the stress distribution. Sharkskin defect appears as a continuous and regular phenomenon of surface degradation without intervention of wall slip.