bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure Development in Injection Molding of Isotactic Polypropylene, its Blends, Compounds and Dynamic Vulcanizates
Authors: Yu Y. , White J. L.
Published: December 2013

We make a comparative study of structure development in injection molding of isotactic polypropylene, polypropylene blends/compounds and dynamically vulcanized polypropylene thermoplastic elastomers (TPVs) WAXS 2θ scans were used to determine crystalline forms and the distribution of relative amounts of crystalline forms through the cross-section of injection molded parts. WAXS film patterns, polarized optical light micrographs and birefringence were used to qualitatively indicate polymer chain orientation variation through the cross-section. We also used WAXS pole figures to investigate polymer crystalline orientation and filler orientation in different layers of the injection molded parts.

It was found that a low or modest orientation layer exists on the part surface. There is an intermediate highly oriented layer in the parts of isotactic polypropylene and most polypropylene blends/compounds. The interior of the parts was spherulitic and increasingly isotropic as one moved to the center. The thickness of the surface layer increases as the injection pressure decreases. The layer was not observed in parts of dynamically vulcanized polypropylene thermoplastic elastomers. This would seem to be associated with the TPVs possessing a yield stress and not exhibiting substantial fountain flow in mold filling.
Impact Strength of β-Nucleated Polypropylene
Authors: Obadal M. , Čermák R. , Baran N. , Stoklasa K. , Šimoník J.
Published: December 2013

Structural transformations of semicrystalline polymers form an important field of current scientific research. The preparation of controlled supermolecular structure may lead to significant improvements in mechanical, thermal and optical properties. As for isotactic polypropylene (iPP), its properties essentially depend on its crystalline phase composition, which is due to polymorphism of iPP. Thus, the aim of this work is to analyze the influence of the β-phase content in polypropylene and of its spatial arrangement on mechanical properties, in particular on its impact strength. Commercially available isotactic polypropylene (iPP) was modified by various amounts of a specific β-nucleating agent (N, N'-dicyclohexylnaphtalene-2,6-dicarboxamide). From the prepared mixtures standard impact testing bars were injection molded. The structure of the specimens was studied by X-ray diffractometry, and impact properties were determined using Charpy impact tester. It was found that addition of the nucleator led to β-phase content increase, especially in the core region of the injection molded samples. The skin (surface layer of the samples) contained lower amount of β-phase. Furthermore, notch impact strength dramatically increased with increasing concentrations of the β-nucleating agent. The concentration of 0.03 wt.% of the nucleator can be considered a “boundary value” due to the fact that the maximum notch impact strength value was reached. With further addition of the nucleating agent the impact strength slowly decreased. Therefore it should be noted that the improvement of impact properties is not only due to the presence of β-phase, but also there are some synergy-applied factors – such as the structural heterogeneity and spatial arrangement of the β-phase in injection molded samples.
Microinjection Molding with LIGA-Like Process
Authors: Yang S.-P. , Young W.-B.
Published: December 2013

Injection molding process is used to mold component with microstructures in this study. The mold insert with microstructures having an aspect ratio around one is fabricated by the LIGA-Like process. This LIGA-Like process combines the UV-Lithography and electroplating to define the microstructure on a steel substrate. The method provides a cost effective way for molding a microstructure without the X-ray lithography. In fabrication of the mold insert, well-defined draft angle of the sidewall at the structure is a crucial factor for successful molding. The molded component has a good replication of the microstructures in the mold insert.
Numerical and Physical Modeling of Polymer Crystallization
Authors: Monasse B. , Smirnova J. , Haudin J.-M. , Chenot J.-L.
Published: December 2013

Crystallization of thin polypropylene films was performed in isothermal, constant cooling-rate and mixed conditions. The experiments were first analyzed using the classical procedures based on simplified forms (Avrami, Ozawa) of the general Kolmogoroff-Avrami-Evans (KAE) theory. These analyses, which can be applied over an unusually wide transformation range, show that the crystallizations are actually 2 D. Then, a procedure has been established for the determination of the nucleation and growth parameters involved in the theoretical model presented in the first paper of this series. These parameters have been introduced into the model in order to predict the crystallization behavior in isothermal, constant-cooling-rate and mixed-conditions: transformed fraction, number of activated nuclei, final size distribution of semi-crystalline entities. A very good agreement is generally found between predictions and experimental results.
Modelling of Cyclic 3-Dimensional Heat Transfer in Injection Moulding
Authors: Polynkin A. , Pittman J. F. T. , Sienz J.
Published: December 2013

A detailed 3-dimensional analysis of cyclic heat transfer in a complex injection moulding mould tool has been carried out, using a general-purpose commercial heat transfer code (FIDAP). A novel, generally applicable technique for modelling of heat loss to ambient from the tool parting surfaces is introduced, to facilitate inclusion of the mould-open period in the modelling. Simulations are continued through 30 cycles of moulding, to attainment of steady periodic conditions. During this period temperatures at the polymer-steel interface rose by between 10 °C and 40°C above the coolant temperature. At the start of cooling, values of cavity surface heat transfer coefficients referred to the coolant temperature ranged from approximately 4000 W/m2K to 400 W/m2K, with the highest values occurring directly below the cooling channels and the lowest near a heated sprue bush. At the end of the cooling period, values at each location had dropped by approximately an order of magnitude. These results illustrate the limitations of plastics cooling analyses that use constant values of temperature or heat transfer coefficients as boundary conditions on the cavity surface. Comparison with results obtained omitting the modelling of the mould-open period shows how, in the latter case, higher tool temperatures are attained in the steady periodic conditions, and a larger number of cycles are required to reach steady periodic conditions.
Melt Fracture of Linear PE
Authors: Muliawan E. B. , Hatzikiriakos S. G. , Sentmanat M.
Published: December 2013

In this paper we studied the melt fracture behaviour in capillary flow of a number of polyethylenes produced by various technologies. The critical shear rates for the onset of both sharkskin and gross melt fractures were found to correlate with the high-rate extensional flow behaviour of the polymers. These findings were found to mechanistically support the generally accepted observations of melt fracture occurring at the exit (sharkskin) and entrance (gross) regions of the capillary die. In addition, it was found that boron nitride (BN) behaves as an energy dissipater that suppresses the rapid increase of extensional stress associated with gross melt fracture. This enables BN to act as an effective processing aid in postponing gross melt fracture in the extrusion of polyethylenes.
Design Sensitivity Analysis for the Optimization of the Injection Molding Process
Authors: Ilinca F. , Hétu J.-F. , Pelletier D.
Published: December 2013

This paper presents an application of the Continuous Sensitivity Equation Method (CSEM) for the optimization of the injection molding process and its three-dimensional (3D) simulation by the finite element method. Finding the proper combination of process parameters such as injection speed, and melt and mold temperatures is critical to achieving a part that minimizes warpage and has the desired mechanical properties. Very often a successful design in injection molding comes at the end of a long trial and error process. Design Sensitivity Analysis (DSA) can help manufacturers improve their designs and can produce substantial savings in terms of both time and money. This work explores the ability of sensitivity analysis to predict the effects of design parameters on the performance of an injection molding process. The paper presents results of a 3D finite element solution of the filling stage of the injection molding process. Sensitivities of the solution with respect to different process parameters are computed using the continuous sensitivity equation method. Solutions are shown for the non-isothermal filling of a rectangular plate with a polymer melt behaving as a non-Newtonian fluid. The paper presents the equations for the sensitivity of the velocity, pressure and temperature and their solution by a finite element method. Sensitivities of the solution with respect to the injection speed, the melt and mold temperatures and to the heat transfer coefficient at the cavity/mold interface are shown.
Using Multi-Objective Evolutionary Algorithms to Optimize Mechanical Properties of Injection Molded Parts
Authors: Gaspar-Cunha A. , Viana J. C.
Published: December 2013

An automatic optimization methodology based on Multi-Objective Evolutionary Algorithms (MOEA) is proposed to optimize the mechanical properties of injection molded products. For that purpose an MOEA is linked to a commercially available mould filling computer simulator code, CMOLD. The developed optimization methodology was applied to a practical case study where the processing conditions are optimized as a function of a desired morphological state (skin thickness, degree of crystallinity and/or level of molecular orientation; these latter are interpreted in terms of thermomechanical indices) and envisaged mechanical performance at two strain rates levels (of the order of 10–4 and 102 s1). Generally, the optimization methodology proposed is able to take into account the influence of the process parameters and produce solutions that are physically consistent. The processing conditions maximizing the morphological state of the moldings and their mechanical performance are identified. This latter is firstly maximized individually for distinct strain-rates and then a simultaneous optimization for both low and high strain-rate response is performed. The optimized sets of processing conditions leading to the maximization of the mechanical performance are analyzed by the computation of two thermomechanical indices aiming at interpreted the resultant morphological state of the moldings.
Modelling Flow in an Intermeshing Co-rotating Twin Screw Extruder: Flow in Kneading Discs
Authors: Szydlowski W. , Brzoskowski R. , White J. L.
Published: December 2013

A model for simulation of flow in an intermeshing kneading disc region of corotating twin screw extruder is presented. This is based on hydrodynamic lubrication theory for a Newtonian fluid. Numerical procedures are used to compute the pressure distribution and flow field in the kneading disc region. The influence of staggering angle, nip clearance, screw speed and throughput rate are investigated.
The Fibrillar Structure of Melt Spun and Drawn PP Filaments
Authors: Bodaghi H. , Spruiell J. E. , White J. L.
Published: December 2013

A basic study of fibrillation and void development during drawing of melt spun polypropylene filaments is presented. The filaments are characterized by small angle x-ray scattering (SAXS), density, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), wide angle x-ray diffraction (WAXS), and birefringence. The latter two methods were used to characterize the molecular orientation produced by processing while SEM studies of peeled filaments revealed, qualitatively, the development of the fibrillated internal superstructure. The volume fraction of microvoids was computed from the intensity of SAXS and from a combination of DSC and density measurements. The microvoid fractions determined by these two techniques were in good agreement. The volume per cent of microvoids varied from 0.04 to 2.8%. It was found that the fibrillation observed qualitatively by SEM and the measured volume fraction and number density of microvoids increased with (i) increase in draw ratio, (ii) decrease in draw temperature, (iii) increased orientation of melt spun filaments, and (iv) increased molecular weight of the polypropylene. Using Guinier analysis of the SAXS data it was found that the voids had dimensions of 25–40 nm, parallel to the fiber axis and of order 15 to 30 nm perpendicular to the fiber axis. As the drawing temperature increased the SAXS void size increased and void number density decreased. The longitudinal mechanical properties of the fibers were found to be mainly a function of the orientation and were not very much affected by changes in fibrillation or void structure per se.
Modelling the Packing Cooling Stage in Injection Molding of Amorphous Polymers
Authors: Huilier D. , Terrisse J. , de la Lande M.-E. , Latrobe A.
Published: December 2013

The interaction between flow, heat transfer and thermodynamic behavior of amorphous polymers during packing-cooling stages in injection molding of thermoplastics has been studied numerically. A finite-volume method with staggered meshes has been used to solve simultaneously the continuity, momentum and energy equations coupled to an equation of state. The Generalized Newtonian (GN) fluid model has been chosen, including pressure effects during packing. The simulation, applied to a polystyrene melt injected into a rectangular shaped cavity, allows the calculation of the pressure, velocity and temperature distributions during the packing and cooling phases. The final shrinkage of the resulting molded part is also calculated.
Dynamic Simulation of Suspensions of Non-Spherical Particles by Boundary Element Techniques
Authors: Boyington D. R. , Soane D. S.
Published: December 2013

A method is developed for the simulation of the transient structure and rheology of concentrated suspensions of generally-shaped particles. This procedure is a modification of the Stokesian dynamics method using boundary element to evaluate the multiple interactions of an arbitrary number of particles. The effect of commonly-used pairwise additivity assumptions on the particle velocities and suspension stress is shown for several three-spheroid structures. In general, superposition of forces gives better results than additivity of disturbance velocities. Methods for improving the simulation and an experimental program to measure the transient particle orientations and viscosity of concentrated suspensions are discussed.
Flow of Rubber Compound in a Pin Barrel Screw Extruder
Authors: Yabushita Y. , Brzoskowski R. , White J. L. , Najakima N.
Published: December 2013

A cold feed rubber extruder has been rebuilt into a pin barrel extruder with two rows of pins. A comparative experimental study has been made of the initial cold feed extruder, the extruder with a screw with slices in two flights, and the extruder with pins as well as Slight slices. An experimental study of pumping characteristics (Q – Δp screw curves) and of flow patterns obtained from feeding black and white compound with curatives to the extruder with subsequent vulcanization after steady state is achieved. Longitudinal and transverse sections of the rubber compound cured in the flights are studied. It is shown that introducing slices into screw flights reduces pumping capability. The subsequent introduction of pins has little effect on pumping. The flow marker studies show that introduction of slices into screw flights significantly enhances mixing. Both the improved mixing and poorer pumping is due to backflow through the slices. The introduction of pins is shown to again greatly increase mixing. The results of this study are used to discuss the performance and design of commercial pin barrel extruders for the rubber industry.
Mixing, Devolatilization, and Reactive Processing in the a Farrel Continuous Mixer**
Authors: Valsamis L. N. , Canedo E. L.
Published: December 2013

The Farrel Continuous Mixer, developed in the late 50s and introduced to the market in the early 60s, has been extensively used in plastics and rubber mixing and compounding for several decades, and has undergone several design changes and refinements. This paper reviews and discusses in detail the unique mixing characteristics of the FCM. Recent developments in rotor design for controlled residence time and processing temperatures, sequential incorporation of additives, post-reactor reactive processing, and improved energy efficiency by means of total process control are presented. Flow patterns inside the mixer are established using freezing and tracer techniques. Mathematical models for mixing and devolatilization are developed and verified with pilot plant data. As an example of reactive processing, data on the vis breaking of polypropylene with organic peroxides are presented. Controlled rheology of the polymer is achieved and undesirable volatile by-products, tert-butyl alcohol in the present case, are effectively vented. Experimental residence time distribution, and calculated passage and maximum shear rate distribution functions are also presented and discussed.
Investigations of the Residence Time and the Longitudinal Mixing Behavior in Counter-rotating Twin Screw Extruders
Authors: Potente H. , Schultheis S. M.
Published: December 2013

This paper presents a distribution function which allows to calculate the residence time distribution in a counter rotating twin screw extruder. Only the minimum and mean residence time appear in this function. The agreement between calculated and experimentally determined residence times is satisfactory. Longitudinal mixing capacity is discribed with the aid of the residence time variance.
Single and Double Bubble Tubular Film Extrusion of Polyethylene Terephthalate
Authors: Kang H. J. , White J. L. , Cakmak M.
Published: December 2013

An experimental study of double bubble tubular film extrusion of polyethylene terephthalate is presented. In the second bubble, the film is passed through a hot air where it undergoes a significant increase in inflation level. The mechanical stability of both bubbles is investigated as a function of process conditions. The film produced by the first bubble is largely amorphous/glassy (5 to 7%, crystallinity), while that produced in the second bubble can have significant levels of crystallinity (7 to 45 %) dependent upon process conditions. Crystallinity notably increases with machine direction draw down ratio. The crystallinity levels are similar to those of biaxially stretched films. Subsequent annealing increases and perfects crystallinity. The surface roughness of double bubble tubular films is similar to that of glassy polymers produced from single bubble operations and is much less than for polyolefins. The orientation in the films has been determined by (i) wide angle x-ray diffraction applying both pole figure analysis and biaxial orientation factors (ii) measurement of in-plane and out-of-plane birefringence. Biaxiality of orientation increases with the second blowup ratio. The mechanical properties of the film were determined as a function of angle in the plane of the film.
Dynamics of a High Speed Melter/Mixer
Authors: Lyons D. , Baker W. E.
Published: December 2013

A first attempt at studying the internal dynamics of the Gelimat high shear polymer melter/mixer has been made, using slow motion photography of the inside of the fluxing chamber of the device during operation. Based upon these observations, a satisfactory mathematical model has been developed for the melting process which incorporates an energy balance and energy dissipation resulting from drag flow through a fluid bed. This model is a first step towards a more complete and rigorous theoretical treatment of the device, and allows for the prediciton of the time to melt a powdered polymer based on angular velocity of the mixing paddles, mixer geometry, polymer charge size, desired discharge temperature and the thermal properties of the polymer.
Further Considerations of Simulation of Flow in Pin Barrel Extruders and in Screw Extruders with Sliced Flights
Authors: Brzoskowski R. , White J. L.
Published: December 2013

The flow and pumping capability of extruder screws with slices in their flights and pin barrel extruders have been modelled with special consideration on its single or multi-flighted character and the periodicity of the positions of the slices and rows of pins. This is done using an analytical method developed by the authors. The method of analysis is extended to non-Newtonian fluids.
Comparison of Mechanical Properties of Rubber Products Molded by Transfer and Compression Methods**
Authors: Dinzburg B. N. , Bond R.
Published: December 2013

This paper compares the differences developed in rubber properties between compression and transfer molding methods for various types of polymers. It has been shown that the two molding methods produce distinctly different rubber properties for the same elastomer. Acrylonitrile butadiene rubber (NBR) shows little difference in durability between molding methods. Transfer molding (TM) reduces modulus and hardness of NBR, but improves compression set. The crosslink density of rubbers made with TM is higher than those made with compression molding (CM). Highly saturated acrylonitrile butadiene rubber (HNBR) properties are significantly different between the two molding methods. As for NBR rubbers, the TM method reduces modulus and hardness, but improves compression set. The crosslink density of rubbers made by TM is higher that those made with CM. Silicone rubber (VMQ) that does not require post cure shows the same rubber properties change as NBR. Transfer molding yields low tensile and modulus but better compression set. Polyacrylic rubber (ACM) molded with the TM method shows reduced tensile, elongation, modulus and hardness; but after post cure, modulus and hardness did not show substantial differences. The compression set was lower with TM both before and after post cure. Crosslink density is significantly higher with TM, but the difference diminishes after post cure. Ethylene acrylic rubber (EAM) and fluoroelastomer rubber (FKM) exhibit property changes similar to acrylic rubber when molded either with compression or transfer molding methods. Rubbers molded with TM methods showed a higher degree of anisotropy in rubber properties than with CM. With enlarged extension ratio, the coefficient of anisotropy increased, with the exception of ACM.
Numerical Simulation of the Advancing Front in Injection Molding
Authors: Fauchon D. , Dannelongue H. H. , Tanguy P. A.
Published: December 2013

A 2D finite element model is presented for the prediction of the advancing front in the thickness of a part during mold filling in the polymer injection molding process. The full Navier-Stokes equations are considered for the determination of the velocity and the pressure. The computation of the flow front uses the Arbitrary Lagrangian-Eulerian approach and is coupled with an automatic remeshing technique triggered only when the mesh becomes distorted. Three series of numerical tests with a Newtonian fluid are presented. The first one deals with the fountain-flow in a flat gap and a tube and allows for validation of the code. The second example in a 90° bend illustrates the capability of the proposed method to deal with multiple fronts, and the third one deals with jetting.
Material and Numerical Aspects of Mathematical Modeling of Blow Molding**
Authors: Cohen A. , Seitz J. T.
Published: December 2013

The work describes an approach to simulation of a blow molding process. The development originated from the need to reduce the amount of experimentation through a screening of processing conditions and preform configurations. The simulation uses a standard finite element software capable of handling large deformations and an interaction with rigid surfaces, which are encountered in blow molding. The developed constitutive equation for a general purpose polystyrene in the rubbery state was incorporated into the model. Temperature and rate dependencies, typical for plastic materials, are accounted for in this model. The application of the developed model for analysis of the preform's deformations is illustrated here on a number of examples.
Finite Element Analysis of Polymer Melt Flow in Profile Extrusion Coating Die
Authors: Matsuoka T. , Takahashi H.
Published: December 2013

Automotive side protection moldings, which consist of polymer and an inserted metal core, are produced by profile extrusion coating. The molding process is similar to wire coating process except using a cross-head profile die because the cross-sectional shape of the side protection molding is complex. The polymer is extruded from the profile die covering the metal core, which is fed to the die simultaneously. Then, there are two flow regions within the profile die. One is pressure flow region where the polymer is flowed by pressure gradient. Another is drag flow region including pressure flow. The drag flow appears in the area where the polymer contacts the moving metal core in the die. Finite element analysis was developed for simulating the combined pressure and drag flow in a complex profile die. The flow is assumed to be isothermal planner flow for a non-Newtonian fluid. Power law model is used to represent viscosity of the polymer. Distributions of pressure and velocity are simulated by the analysis. Polymer melt flow through a flow channel of a die for producing the side protection molding was analyzed to achieve uniform velocity at the outlet of the die. A suitable shape of the flow channel was designed by several iterative simulations.
Study on the Formation of β-Crystalline from Isotactic Polypropylene Fiber
Authors: Chen X. , Wang Y. , Wang X. , Wu Z.
Published: December 2013

In this paper the conditions for the manufacture of high content β-form crystal isotactic polypropylene fiber in the presence of β nucleation and the β to α form transition during processing were studied. The results showed that the melt temperature had little effect on the relative content of β-form (K value) presented in as-spun fibers within a certain temperature range (210 to 230°C) while the cooling rate and cooling medium had a significant effect on it. In the case of a constant pump deliver (Q), the K value in the as-spun fiber decreased from 0.95 to 0 as the spinning speed increased from 3.25 m/min to 70 m/min. The smaller the thermal conductivity of cooling medium, the greater was the K value. After stretching the β-form PP fiber, there were many crevices at the fiber surface. It was confirmed by the mercury porosimetry that the drawn fiber possessed microvoid structure. The size and quantity of microvoids were closely related to the K value, stretching temperature and stretching ratio. Compared with PP fiber without nucleating agent, the drawn fiber had a lower apparent density and its moisture absorption was improved.
Predicting the Skin-Core Boundary Location in Injection Moldings
Authors: Brito A. M. , Cunha A. M. , Pouzada A. S. , Crawford R. J.
Published: December 2013

Over the past few years a technique for relating the quality and properties of sub-components to those of real injection moldings has been developed. A major aspect of this is the correlation of microstructure in the two situations. This paper describes the computer prediction of structure development in injection molded polypropylene. This is done on a personal computer using a finite difference method and it is shown that accurate predictions can be made in relatively low computing time. The characteristic skin in polypropylene moldings is shown to be controlled by the filling phase and is dependent on the shear stress and temperature. The computer model is able to predict the onset of skin formation and hence the skin thickness. These predictions have been shown to agree well with experimental observations. The skin-core boundary which has been found to have a major effect on the mechanical properties of molded polypropylene has also been shown to lie between the no-flow isothermal and the maximum shear rate locus. This has important implications for computer simulations of the injection molding process.
Optical Properties and Orientation Development in Uniaxially Stretched Syndiotactic Polystyrene from Amorphous Precursors
Authors: Hsiung C. M. , Cakmak M.
Published: December 2013

On-line uniaxial deformation behavior and deformation induced crystallization characteristics of initially amorphous syndiotactic polystyrene (s-PS) sheets were studied using an Iwamoto biaxial stretcher operated in the uniaxial mode. The stress strain curves obtained under various conditions indicate that this polymer can be stretched uniformly at 110°C which is between its glass transition temperature and cold crystallization temperature. The principal refractive indices were determined as a function of deformation conditions. Because of the negative intrinsic birefringence in the s-PS polymer chains the refractive indices in stretching direction decrease and those in the transverse direction increase with deformation.
Process for Improvement in Toughness of Unsaturated Polyester with Elastomer
Authors: Sakai T. , Nakamura K. , Inoue S.
Published: December 2013

By combined usage of a high speed intermeshing twin screw extruder and an injection molding press, a direct reactive extrusion and injection molding process has been developed for improving toughness of the thermoset unsaturated polyester (UP) by blending with an elastomer.

The unsaturated polyester and elastomer were homogenously kneaded with each other and a radical initiator dissolved in a liquid monomer was added to the molten mixture. This was carried out at a relatively low temperature from the final feeding port of the twin screw extruder to allow not the curing reaction to proceed during the twin screw extrusion stage.

The molten UP-elastomer alloy was accumulated, injected into the hot mold, and cured. The products obtained from these experiments were evaluated with regards to their physical properties and their morphologies. The elastomer, NBR produced the greatest improvement in toughness. The physical properties of the UP-NBR alloy obtained by this reactive extrusion process were generally equivalent to those of polypropylene except for thermal characteristics.
Skew Stretched Polycarbonate Films
Authors: Wu J. P. , White J. L.
Published: December 2013

The formation and characterization of complex chain orientation of polycarbonate skew stretched films is described. The directions of symmetry axes of orientation are represented in the form of refractive index and infrared absorption ellipsoids. The chain orientation is evaluated in terms of White-Spruiell biaxial orientation factors based on the principal axes of orientation. The anisotropic mechanical properties of skew stretched films are correlated with their orientation states. The major symmetry axes of skew stretched polycarbonate films tend to move toward the second stretching direction as increasing second stretching ratio. The chain orientation behavior of these films exhibit increasing uniaxial orientation character at high second stretching ratio. The anisotropic characters of tensile modulus and yield stress of skew stretched films follow a linear relation with the magnitude of chain orientation within our stretching range.
In-cycle Deterministic and Stochastic Dynamics of Extrusion Blow Molding
Authors: DiRaddo R. W. , Garcia-Rejon A.
Published: December 2013

Optimization of the thickness distribution in extrusion blow molded parts is crucial to minimize cycle times and resin usage. Closed-loop parison programming can be cycle-to-cycle or in-cycle. Corrective action occurs between cycles for the case of cycle-to-cycle control. However, this control scheme does not correct for high frequency disturbances that enter the system, such as periodic flowrate changes, noise from the gap position transducer, uneven melting and compression of the polymer and uneven inflation.

Corrective action occurs during the cycle for in-cycle control. This allows for regulation of the high frequency disturbances. Deterministic in-cycle model identification was performed by obtaining the impulse responses of the bottle thickness distribution to pulses in the die gap input during the extrusion cycle. The response was found to be time variant along the individual cycle. Stochastic identification was also performed in order to ascertain a noise model for the system. A first order ARMA noise model was found to adequately describe the process.

Control simulations were performed to determine the feasibility of in-cycle control. A minimum variance controller with a constraint for minimizing of manipulated variable movement was found to adequately regulate both a deterministic and a stochastic disturbance input during the extrusion cycle.
Simulating Polymer Mixing Processes Using the Boundary Element Method
Authors: Gramann P. J. , Osswald T. A.
Published: December 2013

The mixing of plastic into filled and unfilled polymer blends has been an important issue in the polymer industry. Processing difficulties with these polymers have been encountered in the mixing quality as well as in the thermal degradation due to viscous heating. Mixing often occurs as an element of the processing step, e.g., inside single and twin screw extruders used in the fabrication of final parts or sheets, and inside internal mixers such as the Banbury type mixer. Quantifying the mixing inside an extruder or an internal mixer and predicting the thermal degradation due to viscous heating is an extremely difficult task. A better understanding of the mixing process and control of viscous heating will lead to optimal parts and may eventually allow us to increase the relative amount of fillers within the material. This paper presents a boundary element simulation of the flow of filled and unfilled polymer blends inside extruders and internal mixers. First, the general equations that govern such flows are shown. The boundary integral equation and the fundamental solutions are then formulated followed by the numerical implementation and logistics of the simulation. After the theoretical background is presented, a numerical example is given. The paper then shows how the simulation was used to analyze the flow inside a single screw extruder and internal batch mixers. Such a simulation can be used to eliminate some of the tedious trial-and-error tasks that are typically performed in the early stages of material synthesis and can also be used by manufacturers of mixing equipment when optimizing the geometries of cavities and mixing heads to achieve optimum mixing with reduced viscous heating. This research will significantly increase our knowledge of the behavior of filled and unfilled polymer blends and expand our understanding of the complex phenomena that take place during their mixing process.
Crystalline Orientation in Injection Molded Polyethylene Parts
Authors: Wu J.-P. , White J. L.
Published: December 2013

The complex crystalline orientation character of injection molded high density polyethylene was examined. The principal axes and level of orientation along these axes were evaluated using wide angle x-ray diffraction pole figure analyses for various injection molding conditions. The principal axes of each layer were determined by means of ellipsoidal representations from wide angle x-ray diffraction pole figure data. It has been found that the principal axes of crystalline orientation do not exactly coincide with the flow direction. The crystalline orientation state for each layer was evaluated in terms of biaxial orientation factors with appropriate principal axes of orientation. The general behavior of crystalline orientation indicates b-axis orientation normal to the wall and perpendicular to the flow and width directions and c, a-axes biaxial orientation in the plane of the flow and width directions. A mechanism leading to this distribution of crystalline axes is discussed.
Orientation Development of Mixed Anisotropic Particles in Compounds
Authors: Lim S. , White J. L.
Published: December 2013

An experimental study of the development of orientation of mixed fiber and flake polymer compounds in polymer processing operation including extrusion and molding is discussed. Aramid fiber and talc and mica flakes are studied. The orientation of the particles is determined using wide angle x-ray diffraction. It is found that mixed particle systems lead to lower orientation of both fibers and flakes. The fibers tend to orient in the primary machine direction, while the flakes tend to orient perpendicular to the fibers. This is distinct from fiber compounds and flake compounds where fibers orient in the plane of the machine and transverse directions and flakes orient parallel to machine surfaces.
An In-line Rheometer for Molten Plastics
Authors: Broadhead T. O. , Nelson B. I. , Dealy J. M.
Published: December 2013

A novel in-line rheometer for use with molten plastics has been developed and evaluated. It is a process sensor designed to be installed in a melt flow stream, for example at the exit of an extruder. The entire process stream flows through the rheometer, so there is no output signal delay due to the flow of melt in a sampling line and gear pump. A small fraction of the melt entering the rheometer is drawn into a small gap between a rotating drum and an outer cylindrical wall. The shear stress acting on a small area of the outer wall is monitored by a shear stress transducer. A technique for taking into account the small pressure flow that is superposed on the drag flow in the shearing gap is described. The major problems that must be addressed in designing an in-line sensor arise from the fact that the temperature, pressure and flow rate of melt entering the rheometer are subject to the fluctuations and upsets that are ubiquitous in industrial processes. The new rheometer is able to operate in this environment and yield reliable viscosity values. However, the output signal of the shear stress transducer was found to be affected by the pressure and contained a low frequency noise component that limited its accuracy. An improved version of this transducer is currently under development.
Heat Transfer in Single and Twin Screw Extruders
Authors: Domschke T. , Justus C.
Published: December 2013

The elementary processes during heat transfer in screw extruders are described by a simulation model. The balance equations are solved numerically with a personal computer. By contrast with known computational approaches, consideration is given to the non-stationary processes in the melt layer between the screw flight and the barrel wall. This is guaranteed by incorporating the “pulsating shear” in this layer into the model as a dissipative energy source. The computational results are used to demonstrate, in an exemplary fashion for one extruder series, the influence of all the relevant machine and process parameters on the internal heat transfer.
The Gas-assisted Injection Molding Process
Authors: Potente H. , Hansen M.
Published: December 2013

This paper presents an application example for the modelling of a mold used for the gas-assisted injection molding process. The simulation software used allows the computation of the distribution of the thickness-fraction of skin material all over the part depending on the process conditions. The illustrations are shown in connection with an industrial mold and the simulation results are compared with experimental data showing a reasonable agreement. The influence of variations of different operation point parameters is shown. Some effects occurring due to the gas flow into the cavity are described.
Flow Mechanisms, Material Distributions and Phase Morphology Development in a Modular Intermeshing Counter-Rotating Twin Screw Extruder of Leistritz Design
Authors: Lim S. , White J. L.
Published: December 2013

An experimental study is presented of the mixing of polyamide-6 and polyethylene in a Leistritz modular counter-rotating twin screw extruder. Seven different screw configurations were investigated and the material distributions and phase morphology developments along the axis of the screw were characterized. The behavior of different modular elements was determined including screw flights of varying thickness, Kiesskalt compression elements and shearing elements.
Flow and Fiber Orientation Calculations in Reinforced Thermoplastic Extruded Tubes
Authors: Ausias G. , Agassant J. F. , Vincent M.
Published: December 2013

A calculation of fiber orientation of reinforced thermoplastics in two tube die geometries is presented. The flow field and fiber motion are calculated using coupled anisotropic constitutive equation and equation of change for fiber orientation. A finite element method is used for the flow field computation, and a simplified characteristic method for the fiber orientation. Results show that fibers orient parallel to the tube axis in a classical die of constant radius in the final land whereas fibers have a more isotropic orientation in a die with a final divergent land. Experimental observations and quantification of fiber orientation in reinforced thermoplastic tubes extruded with the two dies are presented. Results of the calculation agree well with the experimental data for the classical die. For the diverging die, the agreement is good at the tube surface, but the calculation underestimates the degree of orientation perpendicular to the tube axis in the core of the tube.
Tubular Film Blowing
Authors: Liu C.-C. , Bogue D. C. , Spruiell J. E.
Published: December 2013

A theoretical model for tubular film blowing, based on treating the bubble as “quasi-cylindrical” at each point and incorporating a deformation-thinning viscosity equation, explained all of the essential features of the experimental data. The viscosity function required to fit the blown film data was in plausible agreement with viscosity data (complex viscosity data) measured independently. Under most conditions the model predicts an “intuitive” effect of inflation pressure on blow-up ratio; that is, increasing the pressure causes the final radius (the blow-up ratio) to increase. The predicted passage from an “intuitive” regime to a “counterintuitive” regime, which occurs at high blow-up ratios, results from the thinning behavior of the viscosity model. Comparisons with the earlier model of Pearson and Petrie are also made. This model, based on thin-shell theory, disagrees with the data in several essential ways: it predicts counterintuitive results as regards the effect of inflation pressure and melt viscosity on bubble radius. These effects come about from an axial curvature term in thin-shell theory. The differences between the two models are discussed in detail.
Melting and Blending in a Modular Co-Rotating/Counter-Rotating Twin Screw Extruder
Authors: Cho J. W. , White J. L.
Published: December 2013

A comparative experimental study of blending polyethylene and polystyrene in a modular self wiping co-rotating and intermeshing counter-rotating twin screw extruder is described with similar modular screw configurations. Comparisons are made using different screw configurations possessing different numbers and placement of kneading disc blocks. Generally the intermeshing counter-rotating mode melts and mixes more rapidly than the co-rotating mode. The phase morphology in each machine seems to similarly from mixtures of pellets to polyethylene lamellae surrounding polystyrene pellets to a co-continuous morphology. Kneading disc blocks greatly enhance the rate of melting and mixing and are most effective when placed near the feed port rather than near the die. At 160°C, where the polystyrene has a much higher viscosity a co-continuous morphology develops. At 260°C where the polystyrene has a lower viscosity first a co-continuous and then a disperse phase morphology evolves.
Frame Indifference: Fluid Flow in Single Screw Pumps and Extruders
Authors: Campbell G. A. , Sweeney P. A. , Dontula N. , Wang Ch.
Published: December 2013

In this paper we define the extruder analysis in the Eulerian frame. Then, we convert the analysis to the Lagrangian frame to avoid the difficult moving boundary problem. Finally, unlike the classical analysis we convert the solution back to the Eulerian fame before calculation of velocities and flow rates. The single screw pump or extruder has classically been evaluated by leaving the analysis in the Lagrangian reference frame and the flow in the pump is described as due only to down channel drag flow. Since velocity is not frame indifferent, we complete the analysis by transforming the Lagrangian analysis back to the Eulerian solution. The pumping mechanism is quite different when the velocities are properly converted back to the Eulerian frame of reference. This new analysis demonstrates that, if the problem is approached using superposition, the pumping mechanism in a screw pump is due to the “piston like” action of the helix x-component velocity, and that the down channel z-component velocity, drag flow, from the helix and screw core reduce the maximum pump efficiency of the helix by about 50 %.
Structures and Properties of Injection Moldings of β-Crystal Nucleator-Added Polypropylenes
Authors: Fujiyama M.
Published: December 2013

The β-crystal nucleating effect on polypropylene has been compared between γ-quinacridone and quinacridonequinone. While the β-crystal does not form at γ-quinacridone content below 1 ppm where red coloring is recognized on the molded article, much β-crystal forms even at quinacridonequinone content below 1 ppm where brown coloring is not recognized on the molded article. This means that the β-crystal nucleating ability of quinacridonequinone is superior to that of γ-quinacridone. However, both nucleators show a similar change in the physical properties of injection molded article against nucleator content.
Influence of Design on Mixing Efficiency in a Variable Intermeshing Clearance Mixer
Authors: Yao C.-H. , Manas-Zloczower I.
Published: December 2013

The Variable Intermeshing Clearance (VIC) mixer possesses the unique feature of the ability to change the inter-rotor clearance during the compounding process. To improve the mixing performance of the VIC mixer new designs are proposed. A fluid dynamics analysis package-FIDAP, using the finite element method was employed to simulate the flow behavior in the VIC mixer. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries with 20 degree increments to represent a complete mixing cycle. Dispersive mixing was evaluated in terms of both the shear stress distribution and the elongational flow components generated in the flow field. Distributive mixing was studied numerically by means of tracking the evolution of particles originally gathered as clusters. Our studies indicate that the new design of an enlarged chamber gives overall better dispersive and distributive mixing performance than the traditional VIC. The VIC mixer with both an enlarged chamber and wider rotor blades design shows poorer dispersive mixing but better distributive mixing capability. The effect of inter-rotor clearance on mixing efficiency is also discussed.