bluuebunny/crossref_metadata_2025 huggingface dataset:
The Pressure-Volume-Temperature Behavior Polyethylene Melts
Authors: Capt L. , Kamal M. R.
Published: December 2013

The pressure-volume-temperature (PVT) melt behavior of 12 polyethylene resins was evaluated at pressures up to 200 MPa, using both isothermal and isobaric measurements in a GNOMIX high pressure dilatometer. The resins included high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). They were produced using a variety of catalysts, including Ziegler-Natta (ZN) and metallocene catalysts. The PVT data were used to evaluate two empirical equations of state (the Tate and Inverse Volume equations) in predicting PVT behavior of the melt, the isothermal compressibility, and the thermal expansion coefficient. The dependence of the melting and crystallization temperatures on pressure was also evaluated, and compared to existing equations. It was not possible to identify structural effects on the PVT melt behavior, as well as the isothermal compressibility and thermal expansion coefficient. However, some slight dependence on density was observed for the parameters of the equations of state. The isobaric experiments revealed that the pressure effect on the melting and crystallization temperatures was similar for all resins. While the melting and crystallization temperatures varied widely for the various resins, the pressure coefficients of the melting and crystallization temperatures were approximately equal (0.25°C/MPa.) The main differences in the behavior of the resins were in the transitional region during melting and crystallization.
Assessment of LDPE Melt Strength by Use of Rheotens Mastercurves
Authors: Bernnat A. , Wagner M. H. , Chai C. K.
Published: December 2013

In a Rheotens test, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio. In this way, the melt strength can be assessed, which is an important property in many polymer processes like fibre spinning, film blowing, and blow moulding. Several LDPE grades with different melt index and polymerised by both tubular and autoclave reactor technology were investigated. It is demonstrated that to assess melt strength, Rheotens tests have to be compared at constant extrusion pressure, while comparison at constant mass flow rate can be highly misleading. At constant extrusion pressure, Rheotens curves are invariant not only with respect to temperature but also with respect to average molar mass, and polymer grades with similar branching structure and molar mass distribution fall onto a common mastercurve. Two distinct and different Rheotens mastercurves were found for grades produced by tubular versus autoclave reactor technology, indicating distinct differences in the branching structure. Irrespective of the processing conditions, all LDPE melts investigated fail by brittle fracture, and a true rupture stress in the range of 1 to 2 MPa was found.
Transient Polymer Flow Rate in Injection Mold Filling
Authors: Chan W. L. , Daver F. , Friedl C.
Published: December 2013

An analytical and experimental study of the transient flow behavior of polymer melt in injection molding is presented. The polymer volume flow rate into a rectangular mold cavity during the filling stage was determined using the Reynold's transport theory. The analysis, which neglects melt elasticity, shows that the flow rate is transient during the initial filling of the cavity. Moreover, the cavity flow rate was found to depend on material compressibility and expansivity, total volume upstream of the gate as well as time rate of change of melt pressure and temperature. Experimental results obtained through direct flow visualization are in good agreement with the theory. The effect of gate size on the cavity flow rate was also examined. A small gate gives rise to a greater degree of melt compressibility in the runner system. The prediction of actual flow rates into the cavity not only enhances determination of the interrelationship of flow rate, morphology, and properties in injection molding but also aids in the avoidance of molding defects. The results of this study can be used to improve the accuracy of CAE analysis.
Numerical Simulations and Experiments in a Double-Couette Flow Geometry
Authors: Teverovskiy M. , Manas-Zloczower I. , Elemans P. , Rekers G.
Published: December 2013

Modeling of batch and continuous twin rotor mixers, widely used in polymer processing, is a challenging computational problem. One approach to understand the mechanics of flow in twin rotor mixers is to simplify the geometry of the rotors by using cylindrical rotors. This geometry is referred to as the double-Couette geometry. Advantages of the double-Couette geometry are a simple symmetrical mesh design and no time-dependent flow boundaries. In this work, we used the double-Couette geometry to study the mechanics of flow and mixing efficiency in laminar and turbulent flow regimes. Flow visualization experiments utilizing a fluorescent dye were carried out in a transparent flow cell. A fluid dynamics analysis package—FIDAP, based on the finite element method, was used for the flow simulations in laminar and turbulent flow regimes. Numerical results showed good agreement with the experimental data. We attempted a qualitative comparison for distributive mixing efficiency in laminar and turbulent flow regimes in light of the spreading of a tracer line (dye) in the matrix. The analysis pointed out to differences in the mixing mechanisms encountered in different flow regimes.
Structure Development in Melt Spinning Syndiotactic Polypropylene and Comparison to Isotactic Polypropylene
Authors: Choi D. , White J. L.
Published: December 2013

A basic investigation of the development of crystallization and orientation during the melt spinning of syndiotactic and isotactic polypropylene is described. Both polymers were melt spun through ambient air or into ice water at various draw-down ratios and melt temperatures. The melt spun filaments were characterized by wide angle x-ray diffraction (WAXD), birefringence and differential scanning calorimetry (DSC). The polymorphic behavior of isotactic polypropylene during melt spinning is well known. The filaments melt spun through ambient air exhibit the monoclinic α-form while the filaments melt spun into ice water form a smectic structure at low draw-down ratios. Syndiotactic polypropylene also exhibited polymorphic behavior during melt spinning. Disordered Form I with (t2g2)2 helices was found at low spinline stresses and Form III with all trans chain conformation was found at high spinline stresses. The criterion of the spinline stress for this transition was found to be about 6–9 MPa for all samples of various molecular weights, melt temperatures and cooling rates. Syndiotactic polypropylene crystallized much more slowly than isotactic polypropylene and did not exhibit a smectic mesomorphism under ice-water quenched conditions. The melt spun filaments of syndiotactic polypropylene exhibited lower birefringences and amorphous orientations but higher crystalline orientations than those of isotactic polypropylene, compared at the same spinline stresses.
In-Process R eometry Studies of LDPE Compounds
Authors: Woodhead M. , Coates P.D. , Barnwell D. , Martin K.
Published: December 2013

The second part of a comprehensive study into the investigation and validation of in-process measurements on a low density polyethylene compound during extrusion is reported. A commercial grade of branched low density polyethylene was used in the study, compounded with various levels of magnesium hydroxide ame retardant filler, up to 0 by weight. In-line and on-line rheometry were used to monitor melt ow behaviour during single screw and twin screw extrusion; off-line capillary rheometry was performed on the compound before and after extrusion, to examine any change in rheology. Morphological observations were made using scanning electron microscopy, and molecular characterisations carried out using gel permeation chromatography. In-process rheometry was found to be able to detect the presence of filler at low and high loadings, but was unable to discriminate between intermediate levels. Off-line rheometry indicated that twin screw extrusion altered the rheology of the compound, and capillary wall slip was found to increase after extrusion. Morphological observation indicated that filler in the compound was better dispersed after extrusion, especially at high volume fractions. Molecular weight and polydispersity of the LDPE were shown to increase after extrusion, more so in the case of low filler loadings. Overall, in-process measurements provided useful rheological data, and the compound was found to exhibit complex, process-dependent rheology.
Relevance of Crystallisation Kinetics in the Simulation of the Injection Molding Process
Authors: Pantani R. , Speranza V. , Titomanlio G.
Published: December 2013

Modelling of the injection moulding process is carried out in this work on the basis of Williams and Lord model and its recent extensions to post filling stages. The emphasis is devoted to identifying the role of crystallisation kinetics in the process simulation. Data of pressure histories during injection moulding of an iPP are taken as reference to the analysis. Crystallisation kinetics of the material was described by means of a non-isothermal formulation of Avrami model whose parameters where determined either by accounting for only of calorimetric results or by describing also final density data of thin samples subjected to characterised quenching histories. Predictions of pressure histories are analysed in relation to the crystallisation kinetics adopted. The effect of pressure on crystallisation is also discussed.
Modeling Heat Transfer with Crystallization in Rods and Filaments
Authors: White J. L. , Choi C.-H.
Published: December 2013

A study of modeling heat transfer with crystallization in thick rods is described. We apply a formulation due to Nakamura et al. and Berger and Schneider to determine the temperature profiles through a thick rod. This involves a non-homogeneous cylindrical coordinate heat conduction equation with a heat of crystallization source term. The partial differential equation describing the temperature profile is represented in terms of dimensionless groups characterizing the ratios of heat of crystallization, surface heat transfer, and thermal inertia to heat conduction. These dimensionless groups are used to characterize the solutions of this equation. Different solution regimes are predicted. The application to radial temperature profiles during melt spinning of polymer filaments is described.
Crystallization Studies of LLDPE during Tubular Blown Film Processing
Authors: Bullwinkel M. D. , Campbell G. A. , Rasmussen D. H. , Krexa J. , Brancewitz C. J.
Published: December 2013

The final physical properties of semi-crystalline blown films are highly dependent on the crystalline morphology and orientation of polymer chains within the film. Simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements were successfully used to study crystallization during tubular blown film extrusion of LLDPE. SALS patterns were recorded at various vertical positions along the bubble. For LLDPE, an undeformed spherelulitic structure is formed if the stress level during processing is not too high. The change in average scattered intensity with axial position can be described using multiple step Avrami kinetic processes in parallel. The first step accounts for crystal growth and corresponds to the well-known temperature plateau. The later processes start with the impingement of the growing spherulites and may reflect secondary crystallization and orientation processes. Because the magnitude of the average intensity is responsive to changes in process conditions, the on-line SALS system is potentially a useful tool for monitoring process-property interactions.
Twin Screw Compounding of PE-HD Wood Flour Composites
Authors: Wang Y. , Chan H.-C. , Lai S.-M. , Shen H.-F.
Published: December 2013

The compounding of wood flour filled polyethylene is discussed with reference to co-rotating twin-screw extruders from two manufacturers. An acrylic acid-grafted polyethylene (PE-HD-AA) copolymer was used as the compatibilizer in high density polyethylene wood flour (PE-HD/WF) composite system. Special consideration was given to the compounding of the heat- and shear-sensitive wood flour. The relevant screw configuration was found to consist of short mixing length with low intensity of shearing. A suitable combination of processing variables was necessary for limiting the thermal degradation of the wood filler, however, tensile properties of the composites were not affected much. Furthermore, the allowable range of processing temperature was limited, and there was an upper bound of rotating speed and a lower bound of throughput rate within which the darkening of wood filler in the composites was acceptable. The processing window was also experimentally constructed in terms of the degree of darkening of wood composites.
Causes of Cracks in Petaloid Bottom of Carbonated PET Bottle
Authors: Lyu M.-Y. , Kim H. C. , Lee J. S. , Shin H. C. , Pae Y.
Published: December 2013

Petaloid design in bottom for carbonated PET bottles is wide spread. Crack problems exist in the bottom of the bottles. Through this paper we investigated the causes of bottom crack. We examined the physical properties of material and tensile yield stress variations according to the stretch ratio of PET. Then we analyzed stretch ratio and strength in the bottom of blown bottles. We also performed crack tests to observe crack phenomena. The distributions of effective stress and maximum principal stress were examined by computer simulation to seek the influence of bottom design on crack. We concluded that the bottom crack occurs because of not only insufficient strength of material due to the insufficient stretch of PET but also coarse design of petaloid bottom. The stretch ratio at bottom in bottle blowing should be higher than strain hardening point of PET to have enhanced mechanical strength. The crack in the bottom of PET bottles occurred through crazing. The maximum principal stress at valleys in the petaloid bottom of bottles was higher than the other area in the bottom and this maximum principal stress strongly affected the crack in the bottom of bottles.
Melting of Polymer Blends in Co-rotating Twin Screw Extruders
Authors: Potente H. , Bastian M. , Flecke J. , Schramm D.
Published: December 2013

Part II of the publication describes a model for calculating the melting of polymer blends which has been implemented in the SIGMA simulation software for the design of co-rotating twin screw extruders. The model is based on the findings discussed in Part I and makes it possible to calculate the temperature progression in the solids conveying section and during the subsequent melting process for binary incompatible polymer combinations. The two material components are observed in parallel during the melting process, and the respective degrees of melting over the length of the screw are calculated. The properties of the melt phase, which forms from both components, are calculated with mixing rules implemented in the program. The calculations supply the melting profiles for both components, thereby permitting a comprehensive analysis of the melting of binary polymer combinations. The results additionally form the basis of a calculation to estimate the morphology development of polymer blends in the melting section of the extruder.

Part III of the report looks into a means of investigating the melting of binary polymer combinations, and the results of experimental investigations into polypropylene/polyamide blends are discussed. The simulation calculations are compared with the results of experimental studies in order to verify the model presented in this part of the publication.
Convective Instabilities in the Coextrusion Process
Authors: Valette R. , Laure P. , Demay Y. , Fortin A.
Published: December 2013

This paper is devoted to the numerical study of the stability of the plane flow for two immiscible fluids obeying Maxwell constitutive equation in a channel of aspect ratio 8. For fixed viscosity and flow rate ratios, the shape and non-linear behavior of interfacial waves induced by small perturbations of the input flow rate are studied using finite element simulations for various elasticity stratifications. The stationary flow, close to a Poiseuille flow and presenting a flat interface is first computed. Then the interfacial wave generated by a pulse-like disturbance on entry flow rates is computed by using time dependent computations. It takes the shape of a wave packet which is amplified or damped while moving towards the die exit. In unstable cases, the maximum deviation increases with elasticity (the Weissenberg number). Interestingly, the elastic stratification between the two layers can counteract unstable waves due to viscous stratification.
Melting of Polymer Blends in Co-rotating Twin Screw Extruders
Authors: Potente H. , Bastian M. , Bergemann K. , Senge M. , Scheel G. , Winkelmann Th.
Published: December 2013

Experimental studies of the melting process in extruders generally involve a high outlay and can only be performed with certain restrictions, both in respect of the method employed and with regard to the evaluation of the results. This part of the work describes one possible way of studying the melting of binary incompatible polymer combinations. The method described makes it possible to estimate the degree of melting of the two components over the length of the screws of the twin screw extruder. Experimental studies were performed of polypropylene/polyamide 6 (PP/PA6) blends containing low weight contents of the disperse PA 6 phase.

In order to verify the theoretical models set out in Part I, page 124 of this issue, not only were the process conditions of screw speed and throughput varied but also the viscosity ratio. This was achieved by using two different PP grades. In addition, comparable tests were performed on two different sizes of extruders.

The tests show that the melting of polymer blends, and particularly the melting of the second component, which melts at a higher temperature, is determined to a significant extent by the screw rotational speed, the throughput, the ratio of the extruder channel depth to granule diameter and also the material combination (viscosity ratio).

Comparisons of calculations and experiments show that the melting profiles calculated for different material combinations and process conditions tally well with the experimental studies in overall terms.
Numerical Simulation of Polymer Coextrusion Flows
Authors: Zatloukal M. , Tzoganakis C. , Vlček J. , Sáha P.
Published: December 2013

Non-isothermal calculation of flow history dependent visco-elastic stresses in a coextrusion die is performed using the 8-mode modified Leonov constitutive equation and the deformation rate field from finite element simulations. It is shown that a heuristic criterion based on the difference of normal stress differences across the layer interfaces in the merging area may be used to potentially detect the onset of interfacial instabilities. The developed technique can be a useful tool for coextrusion die design as well as for proper selection of materials and process conditions for coextrusion.
Three-dimensional Filling and Post-filling Simulation of Polymer Injection Molding
Authors: Ilinca F. , Hétu J.-F
Published: December 2013

This paper presents a finite element solution algorithm to solve polymer injection molding problems. The methodology solves the momentum, mass and energy conservation equations in three-dimensions. Packing and cooling stages of the injection molding process are modeled by considering compressibility effects. The procedure is aimed at processes in which three-dimensional effects are important. The method is also shown to be effective for thin parts. The performance of the proposed approach is measured on the injection of a plate for which experimental data are available. The procedure is also applied to a thick 3D part. The method results in accurate solutions and it is a useful tool to quantify the material behavior on cases otherwise difficult to investigate.
Generalized Flow of Ellis Fluid in the Screw Channel
Authors: Steller R. T. , Iwko J.
Published: December 2013

Analytical expressions for the isothermal, two-dimensional flow of an Ellis fluid in rectangular channel have been derived. The obtained solution describes also the flow of Newtonian and power law fluids as the specific cases. This solution was further adapted for the theoretical analysis of the temperature and pressure effects during the non-isothermal flow of Ellis fluid. The results obtained both for isothermal and non-isothermal flow conditions have been verified numerically.
Generalized Flow of Ellis Fluid in the Screw Channel
Authors: Steller R. T. , Iwko J.
Published: December 2013

Analytical model for the isothermal and non-isothermal, two-dimensional flow of an Ellis fluid in curved channel has been proposed. It describes also the flow of Newtonian and power law fluids as the specific cases. The solution basing on cylindrical coordinates can be treated as a generalization of a model in rectangular coordinates to account the effect of channel curvature on the flow. The results obtained for isothermal and non-isothermal flow conditions have been verified numerically.
Birefringence and Mechanical Property Development in Melt Spinning Cyclopolyolefin Filaments
Authors: Hong M.-H. , White J. L.
Published: December 2013

An experimental study of the characterization melt spinning cyclopolyolefins is presented. The shear and complex viscosities were measured and the data was found to fit the Cox-Merz relation. The birefringence of the melt-spun filaments was determined and correlated with spinline stress. These were found to be much lower than polycarbonate and polystyrene filaments melt spun under the same conditions. The birefringence was represented in terms of polymer chain orientation. The uniaxial mechanical behavior was also measured. The Young's modulus and tensile strength generally increased with spinline stress and orientation for most cyclopolyolefins. The elongation to break decreased with measured polymer chain orientation for most cyclopolyolefins. For others it was enhanced.
The Matching of Experimental Polymer Processing Flows to Viscoelastic Numerical Simulation
Authors: Agassant J. F. , Baaijens F. , Bastian H. , Bernnat A. , Bogaerds A. C. B. , Coupez T. , Debbaut B. , Gavrus A. L. , Goublomme A. , van Gurp M. , Koopmans R. J. , Laun H. M. , Lee K. , Nouatin O. H. , Mackley M. R. , Peters G. W. M. , Rekers G. , Verbeeten W. M. H. , Vergnes B. , Wagner M. H. , Wassner E. , Zoetelief W. F.
Published: December 2013

This paper describes work carried out in order to match experimental processing flows to numerical simulation. The work has brought together a consortium that has developed reliable experimental methods by which processing flows can be achieved in the laboratory and then ranked against numerical simulation.

A full rheological characterisation of a selected range of polymers was made and the results compared from different laboratories. The data was fitted to a number of rheological models. Multi-mode parameter fitting was universal for the linear viscoelastic response. Particular attention was paid to the non linear response of the material. Prototype industrial flow experiments were carried out for a number of geometries in different laboratories and the flow birefringence technique was used to map out the experimentally observed stress fields for different polymers in a range of complex flows that contained both extensional and shear flow components. Numerical simulation was carried out using a number of algorithms and a range of constitutive equations.

In order to make a quantitative comparison between experiment and simulation, an Advanced Rheological Tool (ART) module was developed that was able in some cases to quantify the level of fit between the numerically predicted and the experimentally observed stress patterns. In addition the ART module was able to optimise certain non-linear parameters in order to improve the quality of fit between experiment and simulation.
Flow Characteristics of Screws and Special Mixing Enhancers in a Co-rotating Twin Screw Extruder
Authors: Brouwer T. , Todd D. B. , Janssen L. P. B. M.
Published: December 2013

The flow behavior of a Newtonian fluid through special mixing enhancers in a modular intermeshing co-rotating twin screw extruder has been examined. The mixing enhancers are slotted screws and gear mixing elements. Particular attention has been directed to drag and pressure flow characteristics and residence time distribution in such devices. The data obtained are useful for guidance in the selection of appropriate mixing elements and validation of flow simulation models for twin screw extruders.
Pressure/Throughput Behavior of a Single-screw Plasticising Unit in Consideration of Wall Slippage
Authors: Potente H. , Ridder H.
Published: December 2013

The mathematical models so far available for describing the throughput behavior of plasticising extruders were developed with the assumption of a wall-adhering melt. There are, however, a series of plastic melts, and also elastomers, polymer suspensions, ceramic materials and food products that display wall slippage during processing. A mathematical model has been developed for this material behavior, which describes the flow behavior for the unidimensional, Newtonian, isothermal case.

Apart from the development of the analytical model, the flow behavior of wall-slipping polymer melts was also analysed with the aid of finite element calculations (FEM). A comparison of the results for the pressure/throughput behavior shows that the calculation results tally very well for the two methods. It is thus possible to develop a procedure which makes it possible to describe the phenomenon of wall-slippage for the non-Newtonian, multi-dimensional, non-isothermal case.
The Prediction of Sharkskin Instability Observed during Film Blowing
Authors: Rutgers R. P. G. , Clemeur N. , Husny J.
Published: December 2013

The characteristics of sharkskin surface instability for linear low density polyethylene are studied as a function of film blowing processing conditions. By means of scanning electron microscopy and surface profilometry, is it found that for the standard industrial die geometry studied, sharkskin only occurs on the inside of the film bubble.

Previous work suggests that this instability may be due to critical extensional stress levels at the exit of the die. Isothermal integral viscoelastic simulations of the annular extrusion process are reported, and confirm that the extensional stress at the die exit is large enough to cause local melt rupture. However, the extensional stress level at the outer die wall predicts melt rupture of the outside bubble surface also, which contradicts the experimental findings.

A significant temperature gradient is expected to exist across the die gap at the exit of the die, due to the external heating of the die and the low conductivity of the polymer melt. It is shown that a gradient of 20°C is required to cause sharkskin to only appear on the inner bubble surface.
Investigation of Design Parameters and Novel Design of Petaloid PET Bottles
Authors: Lyu M.-Y. , Kim Y. H.
Published: December 2013

Carbonated soft drink (CSD) Poly(ethylene terephthalate) (PET) bottle contains pressurized liquid and its bottom design is petaloid in shape for self-standing. The trouble in this bottle is bottom cracking. In this study the design parameters of the petaloid bottom of the PET bottle have been investigated. Cracking test has been performed for different shapes of petaloid bottles and for several sizes of bottles, too. Through the cracking test, it has been concluded that the design parameters that affect the crack generation are clearance, foot length and valley width in the petaloid bottom. Computer simulation has been performed to seek for the optimum values of the design parameters that can reduce maximum principal stress concentration. Consequently the novel design of the petaloid bottom has been completed.
Residence Time Distribution Curves of Screw Elements in Twin-Srew Extruder
Authors: Calumby R. B. R. , Canevarolo S. V.
Published: December 2013

The additiveness of equivalent residence times method of deconvolution/convolution was used to determine the RTD curves of individual screw elements in the melt region of a twin-screw extruder. Initially RTD curves were obtained injecting a tracer (TiO2) at two different ports in the extruder barrel, using several screw configurations and operation conditions. Both ports are downstream, after the melt seal, well inside the molten polymer screw section. Then using the deconvolution method the RTD curve referent to the portion between the two ports was calculated. Finally, using again the deconvolution method and the data from several screw configurations the RTD of each individual screw element was obtained. The independence of screw element positions was also evaluated, where specially designed screws (e. g. changing the position and type of screw elements) were tested, showing no significant effect in the RTD curves. Kneading elements of 45 degrees (KB45) showed an important contribution of conveying, while kneading elements of 90 degrees (KB90) practically do not show any conveying, being characterized mainly by a pressure flow. With RTD curves of individual elements is possible, using the convolution method, predict the RTD curve of any screw configuration. Experimental measurements using screw configurations specially designed were used to check this analytical method. Finally it was applied to data published in the literature, obtained using other deconvolution methods and the results compared and discussed.
Three-dimensional Numerical Modeling of Co-injection Molding
Authors: Ilinca F. , Hétu J.-F.
Published: December 2013

In this work, a three-dimensional finite element flow analysis code is used to solve sequential co-injection molding problems. Non-Newtonian, non-isothermal flow solutions are obtained by solving the momentum, mass and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. Solutions are shown for a center gated rectangular plate. The effect of varying the melt/mold temperature and the ratio between the skin and core materials is investigated. The solution obtained for the same skin and core materials is compared with those in which viscosities of core and skin materials are much different. Finally, the solution for the co-injection of a C-shaped plate is presented. The three-dimensional modeling of co-injection molding provides the complete shape of the core polymer as well as the skin polymer thickness at any location. This is a major improvement over the traditional mid-plane approach, which is unable to recover the material behavior in critical regions as near corners, obstacles, and changes in part thickness.
Biaxially Oriented PP Films Using the Double Bubble Process
Authors: Benkreira H. , Talford M. C.
Published: December 2013

Biaxially Oriented Polypropylene (BOPP) film has become an increasingly important commodity over the last 30 or so years, offering an alternative to more traditional cellulose films with much improved mechanical and optical properties. The process is similar to the traditional bubble process for manufacturing films from a polymer melt, and the main difference in modelling the two processes lies in the constitutive equation employed. As the manufacturing process involves large strain deformations, a convected Standard Linear Solid constitutive equation was used in conjunction with the Pearson and Petrie force balance equations and a suitable energy balance to arrive at a mathematical model of the double bubble process. The non-linear ordinary differential equations forming the model require simultaneous solution, carried out using numerical techniques. An experimental program was conducted to obtain large-scale biaxial tensile test data. This data was used to determine the necessary material properties required to allow the model to be applied to a particular commercial process. Material data not obtained thus far has been estimated using previously published data for similar materials. Operating data was obtained from a fully instrumented full-scale industrial bubble process to enable the model to be validated. Initial comparisons between the model results and process data suggest that the model developed is a good starting point for a process simulation but that more accurate material data is required.
Rheological Effect of Zinc Surfactant on the TESPT-Silica Mixture in NR and S-SBR Compounds
Authors: Kim K.-J. , VanderKooi J.
Published: December 2013

The effects of zinc surfactant (ZB) on the TESPT (bis(triethoxy-silylpropyl)tetrasulfide)-silica mixture in NR (isoprene rubber) and S-SBR (solution butadiene-co-styrene rubber) were investigated, and their processability, dynamic, mechanical, heat build-up, blowout properties, and silica dispersion characteristics were compared. In the NR composite, the addition of ZB increased the reversion resistance time, tensile modulus, and blowout time and lowered the viscosity, heat build up, and tanδ values. In the S-SBR composite, the addition of ZB increased the heat build up, and tanδ values and lowered the reversion resistance time, tensile modulus, blowout time, viscosity, and tanδ values of the compound.

Over all, in the NR compounds, addition of the ZB significantly increased the processability and mechanical property; however, in the S-SBR compounds, it increased the processability but it was not effective in improving mechanical property.
Flow Visualization of Filling Process during Micro-Injection Molding
Authors: Yang S. Y. , Nian S. C. , Sun I. C.
Published: December 2013

Micro-injection molding has been under development for the mass manufacture of micro parts. This paper presents fundamental research on the filling characteristics during micro-injection molding. Flow visualization was employed to observe the fast filling process. A lab-made impact type micro-injection machine was developed and used in this study. Filling of 4 × 4 × 0.2 mm3 and 2 × 2 × 1 mm3 cavities in quartz glass molds was recorded with a high-speed video camera. The effects of the processing conditions on the filling behaviors are systematically studied. The processing parameters include air pressure, mold temperature, and melt temperature. Based on the analysis of flow patterns, it was found that the melt fronts advanced quickly and filled the cavity in less than 0.1 seconds. The filling process can be divided into impact-filling and pressure-filling stages. Mold temperature and air pressure are found to be the dominant processing parameters.
Visualisation and Analysis of the Flow along the Kneading Block of a Twin-screw Extruder
Authors: Carneiro O. S. , Poulesquen A. , Covas J. A. , Vergnes B.
Published: December 2013

The flow of a silicone oil of high viscosity along a block of staggered kneading discs of a co-rotating twin screw extruder was investigated with the use of an acrylic transparent barrel. A digital video camera recorded the flow path of a red dye, dispersed in the silicone oil, along the screws and in the intermeshing zone. Different geometrical configurations were studied, namely various staggering angles (+30°, 90° and −30 °) and thicknesses (7.5, 15.0 and 22.5 mm) of kneading blocks. The effects of these geometrical parameters on the pressure generation and filling ratio were investigated. It was observed that, even for negative staggering, the filling ratio of the kneading block was lower than one. Based upon these experiments, analytical expressions describing the filling ratio as function of geometry (staggering angle, thickness and number of discs) and operating conditions (feed rate and screw speed) were derived.
Melt Spinning of Reactive Extruded and/or Blended Polymer Fibers by Means of an Online Coupled Twin Screw Extruder
Authors: Beyreuther R. , Tändler B. , Vogel R. , Hoffmann M.
Published: December 2013

After some general introductory remarks to the advantageous application of a twin screw extrusion to the melt spinning the lecture deals with investigations of elastomeric fibers consisting of ethylene-octene-copolymers which have been grafted by organosilanes and additionally blended with polybutylenter-ephthalates (PBT) and/or polyesterelastomers (PEE), all by means of a reactive twin screw extruder coupled with a side feeding single screw extruder in an online melt spinning process. It will be demonstrated that considerably improved mechanical properties of the elastomeric EO-fibers can be reached with this additional blend step. All spun fiber samples will be characterized regarding their structural and mechanical properties extensively.

This work is a decisive expansion of our results published during the last two years regarding to the twin screw extrusion melt spinning [1 to 4].
Influence of Non-Newtonian Behaviour on the Processing Characteristics of Wall-slipping Materials
Authors: Potente H. , Kurte M. , Ridder H.
Published: December 2013

So far it has been assumed that when describing the flow process in single-screw extruder, the melt will be wall-adhering. Using certain process conditions, however, some materials such as PVCs, high-molecular PEs, elastomers, polymer suspensions, ceramic materials and food products become wall-slipping [1 to 4].

During simulation of the flow process using the Finite Element Method (FEM), the boundary condition of “wall-adhering” was substituted for “wall-slipping”. The numeric results refer to one-dimensional, non-Newtonian, isothermal flow processes and have been evaluated accordingly.

Since the wall-slipping properties are dependent on critical shear stress, the influence of non-Newtonian behaviour on wall shear stress is illustrated by investigating the barrel and screw root surface. Conclusions with regard to wall-slipping properties may be drawn from the resulting upper and lower limits.

The effect of wall slippage on pressure/throughput behaviour is examined along with the various velocity profiles, resulting from different compression ratios, dimensionless critical shear stress, material-related constants and screw configuration.
Flow Behavior of Sandwich Injection Molding in Sequential and Simultaneous Injection
Authors: Watanabe D. , Ishiaku U. S. , Nagaoka T. , Tomari K. , Hamada H.
Published: December 2013

The flow behavior of skin and core materials in co-injection molding was investigated to understand the flow patterns that could lead to core breakthrough in sequential and simultaneous injection molding. A spiral-flow mold was used and the core material was loaded with a black master batch to facilitate the monitoring of the core material. PC/ABS blend was used as the skin material and ABS was the core material. It was revealed irrespective of simultaneous injection time, sandwich injection molding display the four flow regions identified earlier i. e. primary injection region, core advance region, core expansion region and core breakthrough region. The flow length of core expansion region lengthened with increasing simultaneous injection time of skin and core material while the overall injection time decreased. It was also observed that the core became thinner and wider with increasing simultaneous injection time.
Rotational Moulding and Powder Processing of Natural Fibre Reinforced Thermoplastics
Authors: Torres F. G. , Aguirre M.
Published: December 2013

The present paper describes the development of a new processing technology: rotational moulding of natural fibre reinforced thermoplastics. Different polymer-natural fibre and polymer-flour systems have been characterised. A rotomoulding grade of high density polyethylene has been used as the polymer matrix for the experiments. Fibres, including jute, sisal and cabuya, as well as wood, pecan and rice shell flour of different types have been used as reinforcements.

The rotomoulding process for those composite systems has been studied using an in-house built two-axis rotomoulding rig with variable speed. The final products have been characterised with special emphasis on estimating the level of dispersion of the fibres and their degree of orientation, as well as the consolidation, sintering and bubble formation processes during the different stages. Comparisons have been made with other powder processing routes, involving the sintering of fibre (or flour) reinforced polymer particles including compression moulding.

Morphological characterisation techniques have been adapted to determine the structure-property relationships in these materials at different processing stages. Important improvements in the compression strength of the natural fibre reinforced rotomoulded products compared to the unreinforced materials, accompanied of a good dispersion level of the reinforcing fibres have been reported.
Electret-thermal Analysis of Polymer Blends
Authors: Pinchuk L. S. , Goldade V. A. , Kravtsov A. G. , Zotov S. V. , Jurkowski B. , Kelar K.
Published: December 2013

Electret-thermal analysis (ETA) was used to study polymer blends and processes of their compatibilization. Potentialities of ETA method have been visualized by the analysis of thermally stimulated current (TSC) spectra of the polyamide-polyethylene blends with a maleic anhydride functionalized styrene-(ethylene-co-butylene)-styrene block copolymer as compatibilizers. Peaks on TSC spectra of blend composites are identified with the composition and distribution of the components in the blend. Based on the physical method of analysis it has been proved that the charge state and structure of the blends strongly depend upon compatibilizer content and the degree of the melt mixing. It was confirmed previous conclusion that in a studied case compounding does not result in the formation of any new chemical compounds. ETA in combination with traditional physical methods appeared to yield trustworthy estimates of components distribution in the blend, the degree of their chemical interaction and on this base to preliminary forecast mechanical properties of blends.
Influence of Low Molecular Weight Additives on Die Extrusion Rheometer Flow of Thermoplastic Melts
Authors: Ahn S. , White J. L.
Published: December 2013

An experimental study of slippage induced in various thermoplastics in rheometers by the presence of small amount of low molecular weight additives is described. Capillary and cone-plate experiments are reported. A series of polymers of varying polarity including polyethylene, polypropylene, polystyrene, poly (methyl methacrylate) and polyamide 12 are compared. Five eighteen-carbon amphiphilic ω-compounds are used as additives including octadecanoic acid, octadecanamide, octadecanol, calcium stearate and zinc stearate. The greatest effects were found in polyethylene and polypropylene. Little or no effects are found with the other polymers. The most effective additives were octadecanoic acid and zinc stearate. Octadecanamide and octadecanol had some effectiveness. Mechanisms for this behavior are described.
Design of a Static Temperature Scanning Ultrasonic Measurement System and Application to Multi-phase Polymer Systems
Authors: Adebayo G. , Cakmak M.
Published: December 2013

A static bench ultrasonic setup was designed and implemented after due consideration for the heat transfer characteristics. The set up allows the measurement of the temperature profile of pertinent ultrasonic variables. The ultrasonic attenuation-temperature profiles in a few compositions of a partially miscible blend of Poly(α-methyl styrene acrylonitrile)/Poly(methyl methacrylate), as well as a PVC compound filled with mineral calcium carbonate fillers of three different particle sizes were followed using this set up. It was found that as the temperature was increased, the attenuation decreases with increase in the PαMSAN content of the blend, reached a peak and then decreases with further temperature increase. The peak value occurred in the 1-phase region while the peak temperature increases with PαMSAN content in the chosen blends. In the filled PVC system, the attenuation also increases with filler loading, especially within the vicinity of typical processing temperatures. The ultrasound technique, if applied to polymer processing, looks promising especially in closed regions along processing equipments.
Raman Spectroscopy as an On-line Technique to Monitor Shear Flow Effect on Partially Miscible Polymer Blends
Authors: Adebayo G. , Koombhongse P. , Cakmak M.
Published: December 2013

The phase behavior of two partially miscible polymer blends in simple shear flow was monitored on-line by Raman spectroscopy and subsequently with optical light microscopy on the resulting extrudate. Emphasis was placed on investigating the phase behavior in two polymer blend systems of high and low shear viscosity as they flow through a custom built flow cell with slit conduit. Shear flows initiated from one- and two-phase temperatures were monitored in the higher viscosity blend system of poly(α-methyl styrene–co-acrylonitrile) (PαMSAN) and poly(methyl methacrylate) (PMMA). For the second lower viscosity blend of poly(styrene–co-acrylonitrile) (PSAN) and PMMA90, shear flow was conducted at one-phase temperature and various shear stresses. These blends exhibit a lower critical solution temperature (LCST). The chosen blend composition used for PαMSAN/PMMA had the widest miscibility window in view of the high viscosity of the neat polymers, while for PSAN/PMMA90 blend, a composition very close to the LCST was investigated for the shear flow effects. We observed that for a blend composition of PαMSAN/PMMA system, at small temperature gap from the quiescent cloud point curve, the morphological effects due to shear heating overrides other effects. For a lower melt viscosity blend composition of PSAN/PMMA90, shear induced demixing initially occurs at low shear rates, shear-induced mixing regime follows with increasing shear flow prior to the onset of shear heating effects that brings the material to two phase region resulting in creation of locally optically observable demixed regions where the temperature rise due to shear heating across the extrudate are at maximum.
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 variables that control the occurrence of breakthrough phenomenon in sandwich injection molding were investigated. Particular attention was paid to the conditions that would yield an optimum sandwich molded part. The effects of variation of core volume ratio that would yield optimum core shot size, injection speed and the skin/core viscosity ratio were examined. The flow morphology at the various stages of flow was also explored. The study was conducted with a bar-flow mold mounted on a twin-barrel injection machine fitted with a common nozzle. It was noted that the core material flow distance depends on the core cylinder screw metering position (core shot size). At the stage at which the core material completely penetrated through the skin material (breakthrough), four distinct regions of flow could be identified. The flow distance of the core material is controlled by the injection speed of the core material while the injection speed of the skin material is of little significance. In order to increase the flow distance of the core material, it is effective to increase the core material injection speed albeit limited by an optimum value of screw metering position. It was found that the flow distance of the core material was longer when the core material viscosity was lower than that of the skin material but breakthrough occurred much earlier so core volume is limited. Breakthrough failed to occur when the viscosity of the core material was higher than that of the skin material. It was found that optimum core volume and core distribution occurred when skin/core viscosities were intermediate. The morphology of the skin material leading to breakthrough was also analyzed.