bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual Stresses and Birefringence in Injection Molding of Semicrystalline Polymer
Authors: Guo X. , Isayev A.I.
Published: December 2013

A composite model for the buildup and the relaxation of residual stresses and birefringence during the injection molding of semicrystalline polymer is proposed. This model takes into account the flow-induced crystallization occurring under nonisothermal conditions. The effects of crystallization on the variations of mechanical and physical properties are considered. The viscoelastic constitutive equation due to Giesekus and Leonov is employed for the calculation of the buildup and relaxation of flow stresses, whereas the Morland-Lee constitutive equation of linear viscoelasticity is utilized for the calculation of the buildup and relaxation of thermal stresses during the molding. The overall residual stresses in the molding are determined based upon the addition of residual flow and thermal stresses. The multilayered micro-structure in the moldings arising due to the flow-induced crystallization is determined. Flow birefringence is related to flow stresses according to the stress-optical rule. An expression is proposed to evaluate the overall residual birefringence based upon the resultant microstructure pattern and residual low birefringence in the moldings. As a result, numerical simulations for idealized injection molding process are formulated to calculate the residual stresses and birefringence in molded semicrystalline polymers. Based upon the above theoretical approach, the numerical simulation schemes are formulated, and a computer program is developed. Based upon the simulations, the effects of molding conditions and molecular weights on the overall residual stresses and birefringence are further evaluated.
Evaluation of the Thermal Behaviour of Injection Moulds
Authors: Barros I. , Teixeira S. F. C. F. , Teixeira J. C. , Cunha A. M.
Published: December 2013

It is well known that the thermal behaviour of moulds used for thermoplastics processing has an important effect on both the part quality and the process productivity. The present work reports a study on the evaluation of the relative effect of different geometric and operational parameters on the thermal behaviour of injection moulds. It uses a mathematical model developed to simulate the thermal transient exchanged during the entire moulding cycle. The model is based on a 2D Fourier equation, uses an adaptive grid and describes the thermal contact resistance at mould/polymer interface. The cooling time and the interface temperature distribution are calculated from the computed temperature field in the domain under study. Experimental data, obtained with an instrumented tool during typical production conditions, is used to validate the developed model. The evaluation analysis is based on the Taguchi methodology used to rank the relative effect of the parameters on the selected variables (cooling time, temperature distribution and number of cycles to reach the thermal steady state).
Rheological and Morphological Properties of Immiscible Blends and Microfiber Preparation from the Blends
Authors: Lyoo W.S. , Choi Y.G. , Choi J.H. , Ha W.S. , Kim B.C.
Published: December 2013

One modified poly(ethylene terephthalate) (m-PET) containing 16 mol% of isophthalic acid content and three kinds of isotactic polypropylene (i-PP) with different molecular weights were melt blended in various volume ratios by a twin screw extruder. The dynamic viscosity of the i-PP/m-PET blend showed positive deviation at lower volume content of i-PP and negative deviation at higher volume content of i-PP. The size of dispersed phase increased with an increase of the minor component. Also, the less difference between the viscosities of two polymers caused the smaller particle size in the blend and the smaller critical Weber number. After melt spinning of these binary polymer blends, m-PET and i-PP micro staple fiber, whose diameter was about 0.13 to 2.75 μm, could be obtained by extracting the continuous phase with a proper solvent. The less the minor component in the blend, the better the spinnability of the blended polymers and the physical properties of the fiber. Also, when i-PP was the continuous phase, the spinnability and the physical properties of the fibers were better than the opposite case. Molecular weight of i-PP and the blend ratio had a marked influence on the diameter of microfibers. The micro fiber obtained from i-PP which has similar viscosity with m-PET showed the smallest diameter than those obtained from other two i-PPs.
Filling and Postfilling Analysis of Injection/Compression Molding
Authors: Young W.-B.
Published: December 2013

Injection compression molding is a process that modifies the original injection molding process to have a compression stage after the injection. This process is suitable for precision injection molding parts. The success of an injection compression molding process relies on proper design of the mold and selection of process conditions. The main scope of this study is to develop a process simulation tool for the injection compression molding process. The simulation tool is used to predict the state variations of the material during the molding, including molding flow, distributions of temperature and pressure, and the material shrinkage. The effect of the compression action on the molding part as investigated by this study. The compression action can provide more uniform packing on the mold cavity. But, with the non uniform cooling, material can have different fluidity in the cavity, which induces pressure gradients during the compression action. From the simulation results, it is demonstrated that a two stage compression action in the injection compression molding process can reduce the pressure gradient in the cavity and still have lo shrinkage. By using this method, products ith higher precision and lower warpage can be molded.
A Transient Melting Model of Polymer Balls Sliding Against the Barrel
Authors: Yung K. L. , Xu Y. , Lau K. H.
Published: December 2013

In the study of solid conveying process in plastics screw extrusion, a particle element numerical method enables us to simulate behavior of each solid particle during the process and takes into consideration the parameters of individual particle in the calculation.

The melting of pellets in the solid conveying section is caused predominantly by heat from both friction and conduction through close contact. Experiments showed, melting happened before the solid plug was formed. Hence, when a particle element numerical method is used to simulate the conveying and melting process in the injection bellow, the analysis of melting process caused by solid particles sliding against wall of bellow should be included. Searching through the recent literature, no valid analysis of the transient close-contact melting process caused by viscous dissipation was found. This paper attempts to present an analysis of the melting process and derive an expression for describing the transient melting caused by both friction and close-contact heating. The melting model of polymer pellets sliding against the barrel was achieved by assuming the friction against the barrel as friction against an isothermal wall given the high heat conductivity of the barrel. To keep the expression simple, a constant temperature boundary condition is utilized for the wall which concurs with reality.
The Mapping Method for Mixing Optimization
Authors: Kruijt P. G. M. , Galaktionov O. S. , Peters G. W. M. , Meijer H. E. H.
Published: December 2013

The application of the mapping method [1, 2] on fully three dimensional flows with dynamic boundaries is presented. The computational domain is a (three dimensional) section of a particular type of screw element in a closely intermeshing corotating twin screw extruder. Screw elements include transport, different kneading, and counterconveying zones, for each of which a mapping matrix has to be constructed.

In the future, different screw assemblies could be studied by combining distinct mapping matrices, much like an actual screw is assembled from distinct modules. In this paper, the principle and applicability of the mapping method is demonstrated by the analysis of a fully filled transporting section of the corotating twin screw extruder. Concentration and residence time distributions can be computed straightforwardly and the volume average intensity of segregation is chosen as a characteristic mixing measure to quantitatively describe distributive mixing.
Impregnation Behaviors in Composite Processing
Authors: Matsuo T. , Yuba T. , Kawabe K.
Published: December 2013

In the first part of this paper, impregnation was positioned in terms of consolidation in composite processing and theoretical model for impregnation behaviors was presented. Impregnation behaviors were classified using the parameters contained in the model. Calculation for some simple cases was conducted. In the second part, impregnation behaviors of two material groups were experimentally estimated by on-line measurement of tool gap displacement during compression molding for making UD composites. First material group is composed of 4 kinds of thermoplastic composite materials. The other is thermoplastic film stacking with opened and unopened reinforcing fiber tows. Microscopic observation on the cross-section of parts fabricated at various molding time and measurement of transverse bending strength of these parts were also conducted. Based on the theoretical model proposed in the first part and these experimental data, impregnation behaviors of these materials were systematically discussed. The results suggest basic technological ways for attaining good impregnation in thermoplastic composites.
Polymer Pellet Flow out of the Hopper into the First Section of a Single Screw
Authors: Potente H. , Pohl T. C.
Published: December 2013

The flow of plastic pellets into the first section of a single screw is frequently neglected when analyzing the solids conveying process in single screw machines. In order to get a better insight into the complex correlations that exist between pellet properties, barrel and screw geomtry a physical-mathematical model is presented. As a result the pellet inflow behavior and the degree of filling in the first channel of the screw can be determined.
Modification of Polyolefin with Maleic Anhydride/Styrene and Methyl Methacrylate/Styrene
Authors: Cha J. , White J.L.
Published: December 2013

There has been little effort to quantitatively understand the simultaneous graft copolymerization of two monomers in batch and continuous mixers. In this study maleic anhydride/styrene and methyl methacrylate/styrene monomer pairs were grafted onto polypropylene in both an internal mixer and a twin screw extruder. There is little information on the evolution of grafting reactions of dual monomers with respect to time in an internal mixer and along the screw axis in a twin screw extruder. The influence of reaction time in an internal mixer and residence time in a twin screw extruder on degree of grafting was measured. The dependence of the degree of grafting with respect to ratio of comonomer concentration was determined. A kinetic scheme was proposed and experimentally tested.
Resonant and Invariant Advection in Single-Screw Extrusion
Authors: Hwang W. R. , Kwon T. H.
Published: December 2013

In this paper, we discussed how unmixed and well-mixed zones are determined by the practical design parameters of the Chaos Screw (CS) system for the single-screw extruder, e. g. the helix angle, the magnitude of adverse pressure gradient, and the fraction of no-barrier zone. The key concept is the frequency ratio distribution of the unperturbed system. Through the extensive three-dimensional numerical simulations with finite element methods and particle tracing techniques, successive creation and breakup of resonant orbits and KAM tori in terms of design parameters are presented. The results show that one can predict the spatial configuration of well-mixed and unmixed zones from the frequency ratio distribution and the amount of the perturbation strength. Finally, the exit time distributions caused by dynamical structures are discussed.
Modelling of the Flow in the Distribution Plate of a Spin Pack
Authors: Béreaux Y.
Published: December 2013

A Computational Fluid Dynamics analysis of the flow through the distributionplate of a fibre spinning pack has been performed. The features of the flow that are relevant to polymer processing are addressed, such as the wall shear rate, residence time and dead zones. An analyticalmodel, that agrees very well with the calculations, is proposed. It also yields insight into the role played in the flow by different design parameters of the distribution plate. This model, primarily based upon a Newtonian fluid, is also extended to a shear thinning one.
A Comparison of the Axisymmetric and Planar Elongational Viscosities of PE-LD
Authors: Beaupre P. , Gupta M.
Published: December 2013

The elongational viscosities of a low density polyethylene in axisymmetric and planar flows are compared. The experimental data on entrance pressure loss is matched with the corresponding finite element predictions to estimate the parameters in the elongational viscosity model proposed by Sarkar and Gupta. The entrance losses in the capillary and slit rheometers are used to predict the elongational viscosities for axisymmetric and planar flows respectively. The power-law region of the axisymmetric as well as planar elongational viscosity is found to follow the time-temperature superposition principle. The vortices encountered in the flow near the abrupt contraction for the planar and axisymmetric cases are compared. The vortex near the abrupt contraction is found to reduce in size as the flow rate is increased for planar as well as axisymmetric entrance flow.
A New Method to Determine the Filament Force Tension within the Fibre Formation Zone
Authors: Brünig H. , Tändler B.
Published: December 2013

A non-contact method to determine the force tension of the spinning line is proposed by a non-vertical arrangement of the melt spinning equipment. The curvature of the spinline caused by gravitation was determined experimentally by measuring the spinline location. This is the key for the calculation of the filament force only by geometric measurements.
Investigation of the Interfacial Instabilities in the Coextrusion Flow of PE and PS
Authors: Valette R. , Laure P. , Demay Y. , Agassant J.-F.
Published: December 2013

The interface instability of the coextrusion flow of a polyethylene and a polystyrene is experimentally studied with industrial and laboratory equipments for various flow rates and temperature. Stable and unstable coextrusion conditions are identified as a function of flow rate ratio, shear rate and temperature. It is found that temperature and flow rate ratio are the most relevant parameters. Experimental results are then compared with stability analysis assuming White-Metzner constitutive equations. Agreement is fair at temperatures of 180°C and 200°C. However the longwave stability analysis is not sufficient to predict all experimental data.
Flow Effects on Polymer Transesterification
Authors: Yang I.-K. , Hong C. Y. , Pan P. H.
Published: December 2013

Transesterification between poly–ε–caprolactone (PCL) and polyethylene-terephthalate (PET) under shear flow was investigated. Two types of flow were imposed to the test samples; one is a simple shear and the other is an oscillatory shear. Comparing to reaction at quiescent state, flow provides better conversion to the reaction. For simple shear flow, the rate of reaction increases as the shear rate increases, while under oscillatory flow, increasing the frequency and the amplitude enhances the extent of reaction. Improvements of the transesterification rate by simple shear prevail over those by the oscillatory motion. The results imply that the transesterification is mass transfer limited. The improvement of the reaction rate and the prevalence of the simple shear flow can be interpreted by the convective effect. The small margin between the rates of reaction under flow and at rest can be attributed to the small Reynolds number of the system.
Flow Balancing in Extrusion Dies for Thermoplastic Profiles
Authors: Nóbrega J. M. , Carneiro O. S. , Oliveira P. J. , Pinho F. T.
Published: December 2013

To achieve a specified geometry for an extruded profile, together with a minimal degree of internal stresses, flow balancing of the die is required. To attain this objective, the flow along a profile die channel must be accurately described, and this demands a computational code able to predict complex 3D non-isothermal flow patterns. In this work new methodologies for flow balancing are implemented and illustrated. The design code developed to carry out the automatic search of a final geometry consists of an optimisation routine coupled with geometry and mesh generators and a 3D computational code based on the finite volume method. The issues discussed and described here encompass recent developments, namely the implementation of two alternative optimisation algorithms for the automatic search of a final solution, the enhancement of the strategies previously developed to balance the flow, some improvements in the routine used to generate the mesh and the adoption of a progressive mesh refinement technique. The examples show that the proposed methodology performs well and the solution is attained in just a few minutes of calculation without any user intervention during the calculation process.
Flow Balancing in Extrusion Dies for Thermoplastic Profiles
Authors: Carneiro O. S. , Nóbrega J. M. , Oliveira P. J. , Pinho F. T.
Published: December 2013

To achieve a specified geometry for an extruded profile with minimal level of stress gradient induced by pulling, flow balancing of the die is required. To fulfil this requisite, a set of operating conditions and polymer rheological properties is considered during the design step. However, fluctuations of the operating conditions and/or slight variations of the polymer rheological properties are expected to occur during long-term production. Their effect on the performance of an extrusion die will depend, among other things, on the sensitivity of the flow distribution within the die. In this work, an extrusion die is optimised (balanced) using four different design methodologies and the final shapes of the die are compared in terms of their absolute quality (when used in the optimal conditions) and stability to the factors considered. For this purpose, a finite-volume based computational code is used to perform the required simulations of the non-isothermal three-dimensional flows, under conditions defined by a statistic Taguchi technique. The influence of some operating conditions on the flow distribution is assessed and the effect of the polymer melt rheology is also investigated. It was concluded that the use of different design methodologies lead to different results in terms of flow balancing and sensitivity to the factors considered and that the most balanced and stable extrusion die was that generated by the strategy based on the parallel zone thickness control.
Cross Channel Flow Velocity and Motion Trajectory of Polymers in a Helical Channel
Authors: Sikora R. , Sasimowski E.
Published: December 2013

In reference to the comparison of polymer flow along the helical channel in the screw-based plasticating system in dependence from a kinematical system, which was presented in the previous publication [1], further comparative studies on these models in the range of cross channel flow and resultant flow were conducted. Studies were carried out for both previously described models that is the model with a rotating barrel and the model with a rotating screw. It was stated that polymer cross channel flow velocity and its distribution is different in both models and in both coordinate systems (rectangular coordinate system and helical coordinate system). In a rectangular and helical coordinate system the highest values of the drag (redrag) cross channel flow velocity are the same, the differences occur in the distribution of these velocities. The distribution of the pressure flow velocity is different in both coordinate systems. The conducted analysis of the resultant flow lets us state the differences in the motion trajectory of the polymer particle in both compared models. The spiral lead of the motion trajectory of the polymer particle is higher when the barrel rotates than in the model with a rotating screw. The cause of it lies in different barrel and screw peripheral speeds. Different senses of rotation of the barrel and the screw cause laevorotatory helical motion trajectory when the barrel rotates, and dextrorotatory when the screw rotates, whereas the behaviour of the polymer particle in the vicinity of the screw flight - change of direction by π/2 is the same.
Experimental Development of Processing Technology for Yuba-like Films Using Twin Screw Extrusion
Authors: Hwang S.-L. , Liu S.-J. , Chen W.-L. , Wang C.-Y. , Chou S.-W.
Published: December 2013

The traditional method of making yuba has several shortcomings, including complicated processes, longer processing time, requirement of many equipments, creation of uncomfortable working environments, and production of wastes. To solve these problems, extrusion may be a promising alternative. The techniques of making yuba-like films by using a twin-screw extruder with special forming dies were investigated in this study. The effects of raw materials, plasticizers, operation parameters, and forming dies on twin-screw extrusion of yuba-like films were also analyzed. The results showed that yuba-like films could be made successfully by using a twin-screw extruder with T-die. To achieve a good performance of yuba extrusion and to get a good quality of films, the heating temperature of the raw materials should be over the denaturation temperature of soy protein, and the screw speed/feed rate ratio should be taken into account. Finally, a twin-roller system should be used to extend the films.
A New Design Method to Improve Flow Uniformity in a Reaction Injection Mold Entry
Authors: Hsieh Y. C. , Chen L. L. , Tseng S. C.
Published: December 2013

Reaction injection molding involves the injection of two or more kinds of liquid polymers into a mold at relative high speed. Such high inertia effect may result in air pocket inside the mold or non-uniform velocity distribution. How to design the mold entry geometry to provide uniform velocity distribution becomes one of the major topics in reaction injection molding process. Thus a new and simple method was developed in this work to optimize the reaction mold entry design. Several regulation islands were located in a fish tail entrance to help distribute the flow more even. Dimensions and locations of the islands will affect the flow uniformity and become the factors to be optimized. Taguchi's design of experiments coupled with computer flow simulation was used to achieve die geometry optimization. Effects of different dimensions of the islands on the flow uniformity can also be evaluated through statistical analyses in the flow simulation. Flow visualization technique was done by capturing flow images with high speed CCD. The experimental results showed very good agreements with the Fluent simulation results. The design methodology proposed here can help the molders in designing different reaction injection mold entries for better uniformity and performance.
Easy Tear Film of Biaxially Oriented PA 6/MXD 6 Blend by Double Bubble Tubular Film Process
Authors: Takashige M. , Kanai T. , Yamada T.
Published: December 2013

In the market, a film which adapted to environmental and barrier problems is desired. This report discusses the stretching stability and physical properties for biaxially oriented PA 6/ MXD 6 blending film produced by double bubble tubular film process. As MXD 6 blending ratio increased, the stretching stress decreased. Hydrogen bond is due to be suppressed by the steric hindrance of the MXD 6 resin. Blending film can be stretched stably and oxygen gas permeability is more excellent than PA 6. Further the film blended between 20 % and 40 % as MXD 6 blend ratio has the property of easy straight line cut. It is found that the plate-like cylinder structure was formed in the observation of TEM. However, thickness uniformity deteriorates when MXD 6 blending ratio exceeds 40 %. To improve the thickness uniformity, the influence of the kneading conditions was studied. When the melting point of MXD 6 decreased, the stretching stability deteriorated and mechanical properties drastically lowered. The excess reaction of the blending resins is not desirable. Stretchability, easy tear property and oxygen gas barrier property are maintained by following process conditions. In case of dry blending, MXD 6 30% is proper content. And in case of premixing, MXD 6 melting point keeps over 236°C. It was confirmed that there is the condition satisfying all properties. The blending film keeps the compatible performance of strength and easy tear property. Namely, the material and production technology of a film could solve environmental and barrier free problems.
Stretchability and Properties of Various LLDPE for Biaxially Oriented Film
Authors: Uehara H. , Sakauchi K. , Kanai T. , Yamada T.
Published: December 2013

Stretchability and properties of linear low density polyethylene (LLDPE) blends for biaxially oriented film was investigated in the previous report [1]. That report focused on changing the film density by blending three different densities of LLDPE. The relationship among stretchability, film density and the composition distribution was explored. In this report, several different densities and melt flow indices (MFI) of LLDPE were examined. A film with a density of about 0.915 g/cm3 displayed the best stretchability, while films not less than 2 g/10 min MFI had poor stretchability. The most suitable composition distribution for stretching was reported. The properties of biaxially oriented films were also evaluated. Furthermore, the relationship between the laboratory tenter stretched film (LTSF) and the double bubble tubular film (DBTF) was investigated. There was a correlation between the density in film over 0.910 g/cm3 and the stretchability of the DBTF and LTSF.
Modeling the Flow in the Metering Zone of Single Screw Extruders Using a Helical Geometry Model
Authors: Ghoreishy M. H. R. , Nouri M. Razavi
Published: December 2013

This research work is devoted to the development of a finite element model for the simulation of the flow of polymer melts through the metering zone of single screw extruders. The sets of the governing equations (flow and energy) were solved using the continuous penalty scheme and a streamline upwinding Petrov-Galerkin method, respectively. The non-Newtonian rheological behavior of the fluid was also taken into account by the use of the power-law model. The novelty of this work is the application of this model on the flow of a polypropylene melt through the helical geometry of a single screw extruder. To validate this model, the results of the computer simulations were compared with experimentally measured mass flow rate and also results from a previous model, which was based on the simulation of the flow in a flat flow domain. Comparisons showed that not only there are very good agreements between the model predictions and actual data but also inclusion of the curvature of the screw flights has an important influence on the accuracy of the results.
Index for Simultaneous Dispersive and Distributive Mixing Characterization in Processing Equipment
Authors: Alemaskin K. , Manas–Zloczowe I. , Kaufman M.
Published: December 2013

Computer simulation of agglomerate dispersion and sequential distribution of all particles obtained in the system allows us to evaluate the overall mixing efficiency of processing equipment. Evaluation was based on a specific mixing index, calculated using the Shannon entropies for different size fractions. The index can be tailored to give preference to different particle size distributions, thus relating the quality of mixing to specific properties of the final product.
Viscoelastic Properties of Flexible Organic Fiber Composites
Authors: Hausnerová B. , Zdražilová N. , Kitano T. , Sáha P.
Published: December 2013

In this paper, molten high density polyethylene (HDPE) was compounded with four kinds of high performance organic fibers: two types of aramid (KF29 and KF49), liquid crystalline polymer (LCP) and poly(vinyl alcohol) (VF), differing in their chemical structure and fiber lengths. From the SEM pictures, it is observed that shape and size of these organic fibers maintained almost the same even after cutting in pellets, following the mixing process. VF/HDPE and LCP/HDPE systems show generally lower rates of increase of both storage modulus and dynamic viscosity with fiber content than KF/HDPE composites. Comparison of these functions at the fixed fiber content has shown that the most effective parameter, affecting the viscoelastic behaviour of organic fiber filled systems, seems to be their rigidity/flexibility in the molten state. The influence of fiber rigidity/flexibility becomes gradually lower with the increase of both strain amplitude and angular frequency. The parameters of the equations describing relationship between relative values of viscoelastic functions and fiber content were found to be largely dependent on fiber content. Such finding remarkably differs from behaviour of short inorganic fiber filled systems, where these variables maintained constant values.
A Constitutive Analysis of Extensional Flow of EVA Nanocomposites
Authors: Pasanovic-Zujo V. , Gupta Rahul K. , Bhattacharya S. N.
Published: December 2013

Linear and nonlinear oscillatory and extensional flow was studied for polymer layered silicate nanocomposites of organically modified bentonite in ethylene-vinyl acetate copolymer with 18 wt.% of vinyl acetate (EVA18). It was found that the rheological properties of EVA18 nanocomposites were distinctly different from the pure copolymer. The elastic response at low frequencies was significantly enhanced in comparison to that of pure EVA18. The linear to nonlinear transition for stress relaxation measurements and the damping function were examined. The relaxation spectrum was shifted toward the longer relaxation time scales for EVA18 nanocomposites, while the dependence of the damping for EVA18 nanocomposites was much stronger than that of the EVA18. In contrast, the uniaxial extensional viscosity of EVA18 nanocomposites gave weaker strain-hardening properties. The prediction of strain-hardening behaviour for EVA18 and EVA18 nanocomposites through relaxation spectrum and the damping function based on Kaye-Bernstein-Kearsley-Zapas (K-BKZ) model is discussed. A simplified estimation of the nonlinear material parameter ß in the K-BKZ model is proposed to predict more accurately the extensional viscosity for EVA18 and EVA18 nanocomposites. Experimental data and detailed predictions are also presented in this paper.
Algorithms for Two Gate Optimization in Injection Molding
Authors: Zhai M. , Lam Y. C. , Au C. K.
Published: December 2013

In injection molding, the injection pressure is often limited by the capacity of injection machines. Therefore, for large-volume part, multiple gates are needed so that the maximum flow path can be shortened, with a corresponding decrease in injection pressure. Many components produced by injection molding today require more than one gate. As multiple gates affect resin flow in a mold interactively, their locations might not be easily determined. For a mold with two gates, a pressure gradient search scheme (PGSS) is proposed to optimize their locations in this investigation. A search direction associated with pressure gradient is developed based on the physical nature of the mold-filling process. An alternative scheme based on genetic algorithm is also employed for comparison. Through minimizing the objective function of injection pressure, the optimum gates can be located to achieve balanced flow. Examples indicate that the proposed pressure gradient search scheme is more efficient than genetic algorithm for two gate location optimization.
Preparation and Characteristics of Reactive Blends of Phosphate-containing Maleimide and Epoxy
Authors: Shu W. J. , Hoang K. C. , Chiu H. J.
Published: December 2013

Three kinds of phosphate-containing maleimide(PMI) monomers, namely diethyl (4-(N-maleimido) phenyl) phosphate (4P) diphenyl (4-(N-maleimido) phenyl) phosphate (PP) and diethyl (2,6-dibromo-4-(N-maleimido)phenyl) phosphate (BrP), were synthesized and blended with a phenol-novolac type of epoxy so as to study their potential as reactive flame retardants. Thermal reaction of these blending systems had been discussed. Mechanical and thermal properties of blends had also been analysed. It was expected that with an increase in the PMI content in the blending system, the Michael-addition reaction would take place more and easily. Increasing the PMI contents reduced the storage modulus, the Tg and the tensile strength, however good thermal stability was maintained. The flame retardancy of all the phosphate-containing epoxy systems was promoted significantly by increasing the PMI content. Besides, the PMI with halogen atom may combine the flame retarding mechanism of gas-phase and solid-phase to promote their flame retardancy.
Monitoring Reactive Processes along the Extruder
Authors: Covas J. A. , Machado A. V.
Published: December 2013

This paper reports data obtained from monitoring the evolution of chemical conversion and morphology during the production of a compatibilized polymer blend of PA 6/EPM/EPM-g-MA and of modified polyolefins (grafted with MA) in a co-rotating twin screw extruder. In the first case, the MA content of the modified rubber decreases strongly to almost zero-level and the particle size reduces dramatically from mm to sub-lm level already in the melting zone. The process seems to be mainly influenced by the local flow characteristics, as they assure efficient generation and renewal of interfacial area. In the second case of MA grafting, a similar evolution is observed regardless of the polyolefin type but, for this kind of reactions, temperature and residence time play an important role.

A brief presentation of the on-line monitoring tools used in the above studies is also included.
Visualization Analysis of Asymmetric Fountain Flow Phenomenon in Injection Molding of Filler-reinforced Resins by Rotary Runner Exchange System
Authors: Yokoi H. , Kanetoh Y.
Published: December 2013

In this study, we attempted to visualize the flow patterns inside molded samples of glass-fibers or talc reinforced GPPS and PP especially in the vicinity of the flow front, using a rotary runner exchange system which instantaneously switches melt flowing into the cavity. From the visualization results, an extremely characteristic flow behavior was seen at the flow front area for resins with fillers which was not observed for those without fillers. Especially in the case of resins with 40 wt.% talc or 30 wt.% GF, a-symmetric zigzag fountain flows were generated alternately upward and downward along the cavity width direction. Moreover along the outer layer of the flow front, one observed a large amount of residual resin remaining for a long time during the cavity filling process, in the case of 40 wt.% GF, primarily due to the increase of viscosity which restricts the occurrence of diverging flow. Based on the above visualization results, we proposed a generic model of zigzag fountain flow; an a-symmetric upward flow in a certain area starts preventing the fountain flow in the upper side of the adjacent area, causing the diverging center to sink. This phenomenon subsequently causes an a-symmetric flow in the opposite direction in the next adjacent area, which continuously propagates along the cavity width direction.
The Gloss of Injection-Moulded Recovered Polypropylene
Authors: Pisciotti F. , Boldizar A. , Rigdahl M.
Published: December 2013

In our recent work, it was shown that the rate of filling during injection moulding did not significantly affect the tensile and impact properties of recovered and virgin polypropylene, whereas significant changes in the properties were observed after ageing at 100 °C. The purpose of the present work was to extend the former study to include the effects of processing and ageing on surface-appearance-related properties, in particular the gloss. In-mould rheology and gate-seal analyses were performed in order to select the filling and post-filling processing windows, respectively. The influences of filling rate, holding and cooling times on the gloss measured in the gate area and at the far end of the moulded specimens were evaluated. The mould used had an embossed surface giving test plaques with a matte appearance. The results showed that the gloss varied by about 30 to 40% within the filling window obtained by in-mould rheology. The slight gloss difference between the two PP-grades noted at the lowest injection speed vanished with increasing filling rate. Gloss differences were observed between the gate area and the far end of each processed moulding, again at the lowest injection speed. The materials processed at a high filling rate exhibited a fairly constant gloss as the holding time increased regardless of the position of the analysed region, whereas a more significant decrease was noted in the case of the mouldings processed at the low filling rate. The cooling time had a negligible effect on the gloss in comparison to the effect of filling rate. Ageing at 100 °C for 240 h increased the gloss level, especially at the far end of the moulding, but only for specimens manufactured at the lowest filling rate. Roughness measurements with a profilometer showed that the gloss development during processing and ageing was related to the topographical matching between the developing polymer surface and the mould topography.
Orientation and Residual Stress Distributions in Thick Melt Spun Polystyrene and Polycarbonate Filaments
Authors: Kang Ho Jong , White James L.
Published: December 2013

A study of orientation development and residual stresses in thick melt spun polystyrene filaments and polycarbonate filaments described. Linear relationships between spinline stress and mean birefringence under different melt spinning conditions were obtained. These results were used together with models of the dynamics of melt spinning to predict the characteristics of thick melt spun filaments. Birefringence distrbutions and residual stresses were computed. High orientations and compressive circumferential residual stresses were predicted at the larger radii and low orientation and tensile circumferential and radial residual stress in the fiber core are obtained. The distribution of birefringence across the thickness of thick melt spun filaments was measured by determining changes of retardation across a wedge. The birefringence distributions were correlated with severity of quench and model prediction. Thick melt spun fibers were peeled and found to have fibrillar cores.
Second Moment Specification of Complex States of Polymer Chain Orientation in Fabricated Plastic Parts
Authors: White J. L. , Cakmak M.
Published: December 2013

A generalized representation of second moment orientation in polymer systems is presented. Orientation is expressed through the asymmetry of the polarizability tensor. The formulation presumes that local symmetry directions differ from macroscopic machine and transverse directions. The formulation leads to a set of biaxial orientation factors (equivalent to those of White and Spruiell) defined relative to symmetry axes I, II, III and a set of angles ϑI1 ϑII2 and ϑIII3 representing the directions of the axes relative to the laboratory axes (1, 2, 3) such as the machine (1), transverse (2) and thickness (normal) directions (3). Any two of these angles eγ, ΘI1 and ΘII2 are sufficient. The formulation is applied to interpret orientation developed in simple shear.
Characterization of Crystallinity and Orientation in Poly-p-Phenylene Sulfide
Authors: Maemura E. , Cakmak M. , White J. L.
Published: December 2013

We present a basic characterization methods and parameters for poly-p-phenylene sulfide (PPS) which are necessary to interpret experimental studies on fabricated parts. In particular (i) we determined the heat of crystallization of 100% crystalline PPS from density and DSC data, this allows the use of DSC to determine the percent crystallinity (ii) devised a method of calculation of crystalline orientation factors from Wide-Angle X-ray diffraction experiments. The latter problem is non-trivial because of WAXS peak overlap. The methods and parameters developed were applied to uniaxially stretched and annealed PPS films. (iii) We theoretically computed the intrinsic birefringence Δ° from first principles, this allows interpretation of birefringence data.
Studies on High Speed Spinning of PET
Authors: Cheng J. , Guan X. , Wei R. , Ma H.
Published: December 2013

It is observed that preoriented yarn (POY) begins orientating crystallization near the area of sharp structural change through the measurements of stress, optical birefringence and density at the speed of 3600 m/min. The investigated relationship between optical birefringence (Δn) and stress (σ) of spinning line proposed by Hamana is, to some extent, deviated from our observation. This paper gives an empirical formulation as Δn = 13.18 × 10−3 + 6.32 × 10−10 σ with a deviation within 4%. It also provides a predicting method for controlling the change of PET structure of spinning line. Our tests have shown that the less the denier of POY single yarn, the greater the stress and crystallinity during the fiber formation, and that stress induced effect of the crystallization kinetics of PET high speed spinning is greater than that of the cooling rate.
Speckle Photography of the Rheological Measurements of Polymer Systems
Authors: Ivanov Y. , Hadjikov L. , Kavardjikow V.
Published: December 2013

The speckle photography method is used for measurement of the viscosity changes during curing of polymer composites. Subject of considerations are the changes in the reflective ability of the composite during the hardening, in the degree of polymerization and of the properties. A new relation for a time dependence of viscosity is proposed on the basis of the obtained specklegrams.
Temperature and Velocity Profiles in Drag Flow of a Temperature Dependent Power Law Fluid
Authors: Rauwendaal C. J. , Ingen Housz J. F.
Published: December 2013

This paper analyzes non-isothermal drag flow between parallel plates. First, non-isothermal drag flow is considered of a Newtonian fluid with a non-zero pressure gradient, assuming viscous dissipation is negligible. Second, non-isothermal drag flow is considered of a power law fluid with zero pressure gradient, again assuming viscous dissipation is negligible. Finally, pure drag flow of a temperature dependent power law fluid is analyzed, including the effect of viscous dissipation. When the temperature of the stationary plate is increased, the flow rate increases. Applying this analysis to screw extrusion, this means that increasing the screw temperature relative to the barrel temperature will increase the flow rate. Also, the temperature sensitivity of the flow rate reduces with increasing screw temperature and with increasing power law index. This points to useful benefits of screw heating. With shear thinning fluids increased channel depth raises the stock temperatures, even though the shear rates in the fluid will be reduced. The increased temperatures are due to longer heat transfer distances; the viscous heat generated is less easily conducted away to the walls. At high values of the Brinkman number, the heat flux at the lower plate reduces when the upper plate temperature increases, while at low Brinkman numbers the opposite is true. This is important in the analysis of melting in extruders. It indicates that while high barrel temperatures in the melting zone may be beneficial at low screw speeds, it can be detrimental at high screw speeds. At high screw speeds, therefore, lower barrel temperatures may be more appropriate to obtain efficient melting.
Injection Molding without Packing
Authors: Friesenbichler W. , Knappe W. , Rabitsch R.
Published: December 2013

By injection molding two kinds of frozen-in orientation will arise: During the filling phase the outer layers of the molding will be sheared and simultaneously cooled. This results in highly oriented layers at the outside of the molding (orientation by filling). During the packing phase the melt, forced into the cavity, gives rise to low rates of deformation in the molding, but since the viscosity has become high by cooling, high stresses and frozen-in orientation will also result (orientation by packing). This last kind of orientation can be avoided by high pressures in the filling phase, followed by immediate mechanical sealing of the cavity (injection molding without packing), and hereby a better quality of the moldings can be achieved. Some results with moldings of PS and PP are given.
Numerical Simulation of Wire-Coating Coextrusion
Authors: Heng F. L. , Mitsoulis E.
Published: December 2013

The wire-coating coextrusion process has been simulated numerically using the Lubrication Approximation Theory (LAT) and the Finite Element Method (FEM). The analysis includes both Newtonian and shear-thinning fluids under isothermal or nonisothermal conditions. Special Streamline-Upwind/Petrov-Galerkin schemes have been used for an accurate solution of the energy equation in highly convective flows. The determination of the unknown a priori interface and free coating surface was carried out through an iterative procedure that allows for no cross-flow along these surfaces. The analysis shows how an initial die design for high-speed wire-coating coextrusion can be modified to meet several criteria deemed necessary for better operation. These involve: (a) lack of recirculation everywhere inside the die, (b) the development of smooth stresses along the die wall, especially near the contact region of the two melts, and (c) the location of an interface that runs almost parallel to the wire. The improved die design that meets these criteria consists of moving the torpedo to a position of optimum “gum space” and also reducing the taper in the die region. Subsequent non-isothermal studies of two typical polymer resins, namely HDPE and PS, show that the initial melt and boundary temperatures do not influence so much the results and especially the interface location as do the individual flowrates (hence flowrate ratios) for a given total coating thickness. The analysis also provides a wealth of information regarding pressure and shear stress distributions, stream-line patterns and temperature fields, along with such overall quantities as pressure drops, wire tension, maximum temperature rise and maximum stresses.