bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Hybrid Solid-Microcellular Co-injection Molding Process
Authors: Turng L.-S. , Kharbas H.
Published: December 2013

This paper presents the development of a hybrid solid-microcellular co-injection molding process that combines aesthetic and processing advantages of injection molding with benefits and property attributes of microcellular plastics (MCPs). A two-color injection molding machine has been modified and equipped with an interfacial platen and a supercritical fluid (SCF) unit for co-injection molding with regular resins and MCPs. Co-injection molded polystyrene (PS) parts with a microcellular core encapsulated by the solid skin layer have been successfully produced. Systematic experiments were carried out with solid-microcellular co-injection molding, conventional solid-solid co-injection molding, and regular microcellular injection molding processes to study the effects of process conditions and core/skin volume ratios on the penetration and morphology of the microcellular core. Light microscopy and scanning electron microscopy (SEM) of the solid-microcellular co-injection molded specimens reveal a microcellular core with fairly fine and uniform cell size of 8 to 12 microns and a cell density of up to 3 × 10 cells/cm. Under similar process conditions, microcellular cores were found to penetrate longer and generate a more uniform and thicker skin layer than do solid cores. While improving the surface finish with solid skin layers, this process is capable of producing parts with reduced sink marks, lighter part weights, and shorter cycle times.
Novel Extrusion Dies with Rotating Rollers for CO2-Plastic Foam Production
Authors: Benkreira H. , Gale M. , Patel R. , Cox M. , Paragreen J.
Published: December 2013

This paper describes a new roller die design capable of generating high pressures to allow the direct injection of liquid carbon dioxide into polymer melts and produce low density foams. The novelty of the design lies in the counter-flow action of a pair of rotating rollers separated by a gap to build up pressure. A mathematical model of the flow in the extrusion-roller die system is described and tested against experimental data with PS, LDPE and PP under a wide range of roller speeds and gaps. The study shows that this new design is feasible but more comprehensive CFD simulations and experiments are required to optimise design and operation to obtain the low-density polymer foams sought.
On the Use of the Heating Stage to Control the Thickness Distribution in Thermoformed Parts
Authors: Duarte F. M. , Covas J. A.
Published: December 2013

This work investigates the influence of the heating stage of roll-fed and sheet-to-sheet thermoforming on the thickness uniformity of the final parts produced. Modeling of the heat transfer process involved in each case is carried out. An inverse methodology capable of setting the temperature of the heaters that produce a prescribed sheet temperature at the end of the heating stage is presented. The sensitivity of this differential heating technique to moderate perturbations of the individual set values is analyzed.
Effect of Mold Temperature on Structure and Property Variations of PBT Injection Moldings in the Thickness Direction
Authors: Shibaya M. , Ishihara H. , Yamashita K. , Yoshihara N. , Nonomura C.
Published: December 2013

During injection molding process, the surface of flowing resin in contact with the mold surface is cooled first followed by the cooling of inner part. This results in the variation of microstructure in moldings through the thickness direction. It has been reported that these phenomena result in the layered structure of injection moldings. Particularly, because of the rapid rate of crystallization, PBT injection moldings have well-defined skin and core layers. The purpose of this study is to investigate the effect of mold temperature on the development of structure and property variations of PBT injection moldings in the thickness direction. Tensile tests were performed using dumbbell specimens that were stamped out from the sliced specimens of moldings. Neck phenomenon occurred irrespective of mold temperature and distance from the surface of moldings. The start point of neck propagation shifted to higher strain with increasing distance from the surface. Tensile modulus increased with increasing distance from the surface. In order to discuss these results from a structural viewpoint, the microstructure of each layer was evaluated by density, wide-angle X-ray diffraction and Fourier transform infrared absorption measurements. The delay in necking start points with increasing distance from the surface is due to the higher crystallinity of the inner layer compared to that of the layer near the surface. Two crystal forms of PBT (α- and β-forms) were developed in injection moldings. The region near the surface, where content of α-form is larger than that of β-form, becomes thinner with increasing mold temperature. It is known that the crystal modulus of α-form is lower than that of β-form. Therefore the portion of moldings with lower tensile modulus and yield strength becomes smaller. It is suggested that the border between the skin and core layers, where tensile property changes, shifts to the surface of PBT injection moldings as mold temperature increases.
Study on Viscoelastic Behavior and Extrusion Blow Molding Processability of PP/PE Blends
Authors: Shiromoto S. , Koyama K.
Published: December 2013

In this study, extrusion blow molding processability of polypropylene/polyethylene (PP/PE) blends was related to their viscoelastic behavior and morphology under shear flow. The propylene block-copolymer (PP-B) and blends comprising the PP-B and the linear low-density polyethylene (PE), weight fraction of the PE (ϕPE) was up to 20 wt.%, were mainly used for this study. Viscoelastic behavior under shear flow and swelling ratio of the extruded strands were measured by using a capillary type rheometer. Morphology of the strands was observed by TEM. In case of the PP-B, swelling ratio highly depended on shear rate. Coarse aggregated droplets were observed irrespective of shear rate under the measurement. The droplets were ethylene-propylene copolymers (EP) included in the PP-B aggregated at conversing section of the capillary. However, in case of the PP-B/PE blends, swelling ratio showed lower dependence on shear rate as the ϕPE was higher. When the shear rate was low, large droplets were observed and they were highly deformed in the flow direction. On the other hand, when shear rate was high, the droplets were smaller and showed no deformation in the flow direction because the droplets were broken up due to occurrence of high shear stress. Wall thickness of blow molded bottles produced from the PP-B/PE blends was not affected by the throughput rate. It was proportional to the die-core gap. On the other hand, wall thickness of bottles of the PP-B depended on the throughput rate and it was not proportional to the die-core gap. These results suggest that extrusion blow molding processability of polymer blends is good when the dependence of swelling ratio on shear rate is low.
Experiments on Characteristic Deformation and Breakup Behaviors of an Immiscible Drop in a Screw Channel Flow
Authors: Jun H. S. , Hwang W. R. , Kwon T. H.
Published: December 2013

Deformation and breakup mechanisms of an immiscible drop were investigated experimentally in a screw channel flow, which mimics the flow in the metering section of the single screw extruder. It was observed that the deformation/breakup mechanisms are far distinct from the well-known routes for the linear flow, mainly because of the complex flow history that can be characterized by the repetition of strong/weak shear, the continuously varying shear direction and the acceleration/deceleration. The experimental observations include: comet-like thread formation with the large bulbous head and the long narrow tail; the initiation of the breakup at the entrance of the low-shear zone; breakup by asymmetric end pinching; breakup by the growth of the capillary wave, propagating from the tail toward the head; monotonically decreasing droplet size distribution from the head to tail. The mechanism for the comet-like thread formation has been investigated by using the numerically obtained flow field.
Tensile and Flexural Properties of β-Nucleated Polypropylenes
Authors: Obadal M. , Cermák R. , Habrová V. , Stoklasa K. , Šimoník J.
Published: December 2013

Resuming our previous work on β-nucleated polypropylenes, namely on their impact strength, our present work directs attention towards a flexural and tensile behavior of β-nucleated polypropylenes (β-iPP). For the purposes of this work, commercially available isotactic polypropylene was modified using various amounts of a specific nucleating agent based on N, N′-dicyclohexylnaphtalene-2,6-dicarboxamide (NU100). From the prepared blends test specimens were prepared by injection molding. Structural characterization (crystallinity and the content of β-phase) was carried out by X-ray diffractometry. A multipurpose mechanical property tester was used for determination of tensile and flexural properties. It was found that β-phase content decreased both tensile and flexural strength; on the other hand, the presence of β-phase dramatically raised cold drawability of the injection-molded specimens; addition of 0.03 wt.% of NU100 in the injection-molded parts led to a more than 800 % increase of the draw ratio of specimens tested at the testing speed of 100 mm/min. Furthermore, tensile testing carried out using various strain speeds (10 and 100 mm/min) revealed that higher ductility of the material containing β-phase is particularly pronounced by faster deformation processes, such as fast drawing or impact load.
Non-linear Crystalline Spherulitic Growth Behavior for LLDPE
Authors: Kamal M. R. , Feng L.
Published: December 2013

Nonlinear growth behavior was observed in two crystallization regimes, depending on the temperature. Non-linearity may be explained by the reduction of the concentration of crystallizable ethylene sequences (CES) in the melt phase. In the two regimes, the concentration of uncrystallizable ethylene sequences (UCES) increases, as the crystallization time increases, because UCES are continuously excluded from the crystal lattice into the melt phase. An empirical equation is proposed to describe the melting temperature of the crystal stem with the maximum possible length, T

C, n
*

m
, in nonlinear growth processes, assuming that the diffusion layer is negligible. A modified form of the Hoffman-Lauritzen equation (MHL) describes well the crystallization growth kinetics of LLDPE spherulites in the non-linear growth region.
Studies on NBR-ZDMA-OMMT Nanocomposites Prepared by Reactive Mixing Intercalation Method
Authors: Liu L. , Luo Y. , Jia D. , Guo B.
Published: December 2013

Two kinds of nanocomposites of nitrile-butadiene rubber (NBR), zinc methacrylate (ZDMA) and organomontmorillonite (OMMT), NBR-ZDMA-HMMTand NBR-ZDMA-USMMT, were prepared by the reactive mixing intercalation method with ZDMA and two kinds of organomontmorillonite, hexadecyltrimethylammonium bromide modified montmorillonite (HMMT) and unsaturated chemical modified montmorillonite (USMMT). The structure and properties of the nanocomposites were investigated by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and determination of crosslinking density and mechanical properties. The results showed that the interlayer galleries of HMMT and USMMT were enlarged as ZDMA polymerized in situ in rubber matrix and between the interlayer of the silicates. The layered silicates were dispersed disorderly in rubber matrix at a nanometer level. The crosslinking density of the NBR vulcanizates was increased by the addition of ZDMA and HMMT or USMMT. The glass transition temperatures of the NBR-ZDMA-OMMT nanocomposites were higher than that of the neat NBR. The mechanical properties of the NBR-ZDMA-HMMTand NBR-ZDMA-USMMT nanocomposites are remarkably superior to those of the neat NBR vulcanizate.
Investigation of the Cooling Jets Used in the Blown Film Process
Authors: Gao N. , Li S. , Ewing D.
Published: December 2013

Measurements were performed to characterize the development of the cooling jets produced by a typical dual-lip air ring used in the blown film manufacturing process. The distribution of the pressure on the bubble surface and the velocity field in the region above the forming cone were measured for a rigid model bubble with a blow-up ratio of 2.5. The measurements indicated that the development of the flow below the top of the forming cone in the air ring could be divided into two regions separated by local maxima in the static and fluctuating pressure. These maxima seemed to be associated with the location where the lower jet attached to the bubble surface. There was a region of negative gauge pressure on the bubble surface below the forming cone that should act to stabilize the bubble against the forming cone in practical applications. Above the forming cone, the lower jet was initially decelerated and then entrained into the upper jet. The upper jet then attached to the bubble surface and finally the flow recovered to a wall jet along the bubble surface. The profiles of the static and fluctuating pressure in the first and third regions above the forming cone collapsed reasonably well when they were scaled using the velocity of the lower jet and the velocity of the upper jet, respectively. The magnitude of the local maxima in the static and fluctuating pressure where the upper jet attached to the bubble depended on the upper jet velocity and the ratio of the upper and lower jet velocities.
Processing-induced Properties in Glassy Polymers
Authors: Govaert L. E. , Engels T. A. P. , Klompen E. T. J. , Peters G. W. M. , Meijer H. E. H.
Published: December 2013

A new method is employed to directly predict the development of yield stress distributions in injection molded products of glassy polymers. The approach is based on the results of a study on the temperature dependence of the evolution of yield stress during annealing of polycarbonate below Tg. In combination with the process-related thermal history, derived from numerical simulations of the injection molding process, an estimate of the yield stress distribution throughout a product can be obtained. Computed yield stresses of injection molded plates prove to be in excellent agreement with the experimental values, including their dependence on mold temperature and plate thickness.
Cast Film Extrusion
Authors: Agassant J. F. , Demay Y. , Sollogoub C. , Silagy D.
Published: December 2013

Cast film extrusion is a widely used technique to produce polymer films for packaging or coating applications. The final width of the film may be smaller than the initial die width (necking phenomenon) and therefore is the final film thickness larger than what one could expect. Moreover it is heterogeneous (in terms of showing a larger thickness along the borders, also called dog bone defect). Above a critical draw ratio between the chill roll and the die both width and thickness fluctuations are observed (Draw Resonance Instability). All these phenomena limit the productivity of the process.

This paper provides an overview of the processing and material parameters governing the development of these geometrical defects and instabilities. Numerical models capturing the main experimental features are proposed, allowing to investigate process modifications in order to limit the development of these defects.
Numerical Analysis of Rubber Moulding Using Finite Element Modelling
Authors: Hanspal N. S. , Nassehi V. , Ghoreishy M. H. R.
Published: December 2013

Finite element technique is used to model the free surface flow regime representing injection mould filling of elastomeric material such as rubber compounds. The most distinct feature of the constitutive behaviour of elastomers, is the influence of material elasticity on the elongation and shear deformation suffered by the fluid during flow. In the present study this feature has been tackled through the use of Criminale-Erickson-Fibley (CEF) model. A scheme based on the Volume of Fluid technique is developed for free surface tracking. The results represented in this paper have also been compared against the Phan-Thien/Tanner model and are shown to be in closer agreement with the theoretical expectations than those obtained by the P-T/T equation. The results prove the applicability of the developed model to industrially relevant situations.
Assessment of the Degree of Mixedness of Filled Polymers
Authors: Erol M. , Kalyon D. M.
Published: December 2013

For a given compounding application the selection of the type of processing equipment, the geometry and the operating conditions is always an important challenge. The outcome of this selection process significantly affects the economics of the process, as well as the microstructural distributions and hence the ultimate properties of the compound. Here mixing indices, defined on the basis of the statistics of the distributions of the concentrations of a plasticized elastomeric binder and graphite filler, were used to quantitatively characterize and compare the degree of mixedness of products of batch mixing, co-rotating and counter-rotating fully-intermeshing twin screw extrusion processes. Two separate experimental methods, involving the wide-angle x-ray diffraction and thermo gravimetric analyses, were used for the characterization of the mixing indices at two different scales of examination. The mixing indices were sensitive to changes in geometry and operating conditions. The resulting electrical properties of the conductive composite samples, mixed with either the batch or continuous, i. e., using either co-rotating or counter-rotating twin screw extrusion, correlated with their degree of mixedness. The presented methodologies should facilitate more accurate comparisons of the performances of different types of processors and better tailoring of the structure and ultimate properties of filled polymers.
Microcellular Injection Molding
Authors: Gong S. , Yuan M. , Chandra A. , Kharbas H. , Osorio A. , Turng L. S.
Published: December 2013

This paper reviews some of the recent developments of microcellular injection molding, which is capable of producing parts with excellent dimensional stability using lower injection pressure, shorter cycle time, and less material. Process conditions as well as nano/micro-fillers such as nanoclay and core–shell rubber have a strong influence on cell density and cell size, hence, the final material properties of the molded parts. The addition of nano/micro-fillers at optimum loading levels can generally facilitate the formation of microcellular plastics with higher cell density and smaller cell size leading to superior mechanical properties. The novel integration of a solid plastic surface with a microcellular plastic core via the co-injection molding technique has been investigated to achieve Class “A” surfaces and improved material performance. An improved mathematical model has been developed to simulate the cell growth behavior in the microcellular injection molding process.
Injection Moulding and Mechanical Properties of Recovered Polypropylene
Authors: Pisciotti F. , Boldizar A. , Rigdahl M.
Published: December 2013

This work is a part of a study aiming at assessing the processability of recovered polypropylene in relation to the mechanical and aesthetic performance of as-manufactured and heat aged mouldings. The effects of processing and heat ageing on the mechanical properties of injection-moulded recovered polypropylene were studied here. A similar grade of virgin polypropylene was used as a reference. Multipurpose test specimens were manufactured with a two-cavity mould, according to decoupled moulding procedures. The mouldings were aged at 100°C for 170 h and 340 h. The stiffness, the strength, the elongation at break and the Charpy impact resistance of as-moulded and heat-treated materials were investigated. The results show that the recovered polypropylene could be processed as the analogous virgin grade. Insignificant changes in the measured properties due to the different filling conditions were observed for each polypropylene used. The stiffness and strength of the recycled polypropylene was systematically 20% lower than that of the analogous virgin grade, whereas the impact resistance of the recycled grade was on average 40% higher than that for the virgin grade. There was no significant difference in the elongation at break of the two materials. After the short ageing period, an increase in stiffness and strength of the materials was observed, together with a sharp decrease in the elongation at break and a modest increase in the impact resistance. This was related to re-crystallisation. The long ageing period reduced the stiffness and strength of the materials but there was no significant change in the elongation at break or in the impact resistance.
Two Component Injection Molding of Phase Separating Blends
Authors: Keestra B. J. , Anderson P. D. , Meijer H. E. H.
Published: December 2013

A partially miscible polymer PMMA/SAN blend is used in two component injection molding to produce a sandwich structure with a heterogeneous skin layer. Two different strategies are explored to obtain the desired structure either via sequential injection molding or via the use of the fountain flow. Both cases are studied with scanning electron microscopy to visualize the structure in the skin layer. In addition, numerical modelling examples are presented to improve understanding of the morphologies that have been created with injection molding.
Inkjet Printing of Conductive and Resistive Coatings
Authors: López F. Varela , Diez A. , Odriozola A.
Published: December 2013

Coating of functional materials is the basis of many electronic device manufacturing processes. Screen printing, roll coating and other methods have been used for decades, permitting low cost, high production rates of Printed Circuit Boards (PCBs), where conductive pathways are printed before components are integrated. Nowadays, the PCB industry in developed countries is suffering a revision of all manufacturing processes, to cope with severe market constraints: short runs and fast time-to-market. Inkjet technology has arrived to complement the traditional, analogical production, with new tools that makes possible to produce goods with great versatility.

In this work we will state the problem of inkjet printing functional materials in the frame of PCB manufacturing. The use of numerical methods to asset the formation of conductive pathlines using digital techniques will be presented. Also, the use of resistive and dielectric inks will be discussed.
The Characteristic Behaviour of the Stretch-Orientation Zone during High-Speed PET Spinning**
Authors: Wu Jialin , Guan Diaosheng , Quian Baojun
Published: December 2013

A theory is proposed to separate the on-line stress in the stretch-orientation zone during high speed PET spinning into two parts: the thermodynamically equilibrium or quasi-equilibrium stress associated with rubber elasticity and the non-equilibrium driving stress, which leads to coordinated orientation of the macromolecular chains. Precise and simultaneous measurements of the online spinning parameters at five spinning speeds, ranging from 2200 to 4200 m/min, were conducted. A physical model consisting of a dashpot placed in parallel with a Gaussian network was found to describe well the behaviour of the stretch-orientation zone of high speed PET spinning.
Present and Future Trends in Polymer Blends Technology**
Authors: Utracki L.A.
Published: December 2013

The plastics industry shows the highest growth rate of all industrial materials. Within this group the engineering resins (ER) are developing fastest. The review focuses on polymer alloys and blends (FAB) of ER. After the discussion of the economic aspect of PAB the patent literature is briefly reviewed and illustrated by a summary of selected, recent patents on polyphenylene ether blends. There is little doubt that the future trend in PAB technology will require control of morphology, especially in most common multiphase systems. For this reason the last part of the article summarizes the available information of criteria for rheological and thermodynamic control of morphology. The review ends with a brief description of the methods and equipment used by industry to compound and form the PAB.
Simulation of Balancing Multi-Cavity Molds
Authors: Ghoneim H.
Published: December 2013

A finite element program is developed for simulating the non-isothermal flow of non-Newtonian liquids in a multi-cavity mold with convergent runners and gates of any arbitrary cross-sectional shape. The program is used to investigate the problem of balancing multi-cavity molds. Results of simulating an actual mold filling show that balancing can be achieved by using a straight runner together with convergent gates having successively increasing angles of convergence. In addition, a strategy for approximating those angles of convergence is suggested.
Wide Angle X-ray Line Profile Analysis of Post-neck Drawn Filaments of HDPE
Authors: Cakmak M. , Clark E. S.
Published: December 2013

Wide angle X-ray diffraction technique was used to characterize a series of post-neck drawn high density polyethylene filaments which were stretched by a two-stage drawing process. The first stage of this drawing process utilizes 100%/min draw rate until the natural draw ratio of 8–10 × ist attained. In the second stage, the fully necked filament is re-clamped and further stretched at lower stretch rate (1%/min) upto the desired stretch ratio. Wide angle X-ray diffraction data were analyzed using the Warren-Averbach fourier technique. This analysis showed that number average crystallite size increase with increasing draw ratio. In addition, the root mean square strains (∊2)½ in the crystals decreased with increasing draw ratio upto the draw ratio of 25 then showed an increase with further increase of draw ratio.
Flow of a Generalised Power-Law Fluid in Triangular Dies for Rubber Extrusion
Authors: Kakouris A. P. , Freakley P. K.
Published: December 2013

A theoretical and experimental study of the flow of a rubber compound through dies of equilateral triangular cross-section is presented. To determine the pressure drop in these sections both the variational approach and the finite difference method are used. Velocity profiles for different non-Newtonian indices have been obtained under the assumption that rubber compounds conform to the generalised power-law equation of state. Comparisons between the two methods adopted and experimental data are made. Memory effects which contribute to extrudate swelling are also considered; and a quantitative analysis is carried out in which these effects are used to calculate a minimum die land or preform length. Experimental trials were carried out with an ethylene propylene ter polymer (EPDM) compound and a fair agreement was obtained with theoretical predictions. Also the assumed isothermal conditions were found to conform well with experimental results.
Flow Visualization and Performance of a Non-Intermeshing Counter-Rotating Twin Screw Extruder
Authors: Min K. , Kim M. H. , White J. L.
Published: December 2013

A laboratory modular twin screw extruder with transverse and tangential apex windows for flow visualization is described. The machine is operated as a tengential twin screw extruder with right- and left-handed screw elements. Screw characteristic curves, Q-Δ p, were measured and compared for polyethylene in matched and staggered flight screw configurations with right-handed screw elements. Configurations with matched screw elements are better pumps. We have introduced left-handed screw elements into each screw configuration. This reduces the total pressure developed. Again matched screw element configurations are better pumps. Pressure profiles are measured along the length of the extruder. For right-handed screws, the pressure rises monotonically. Left-handed screw elements produce regions of decreasing pressure. Flow visualization investigations allow us to locate the position and follow the mechanism of the melting process. Using colored markers, we were able to see that in most (but not all cases) there was no inter-screw transfer of material.
System Analysis and Morphological Classification of Procedures and Molds for Injection Molding
Authors: Čatić I. , Raos P. , Razi N.
Published: December 2013

The theoretical foundation of system analysis is given after historical development of the problem. The key concepts and the technical systems of things are discussed. Based on investigated procedures of injection molding of polymers and other matters a general definition of injection molding is given. This enables us to work out the general model of injection molding of matter, as well as the system analysis of molds for injection molding. From this analysis, it follows that the mold has different functions: primary shaping of the product as well as structuring on the molecular and supramolecular level. The mold is at the same time a very complicated and complex technical system of things. The morphological classification of different systems gives the basis for better process control.
New Developments in Fiber- and Filmextrusion
Authors: Hensen F.
Published: December 2013

The demands of the fiber and film producers, the result of scientific polymer research studies and the ideas and work of machine manufacturers determine the trends and developments in fiber and film extrusion. The main goal is the improvement of the fiber- and filmproduct-quality and of the process efficiency. Judged by their results, we believe the most significant new developments in the fiber and filmextrusion are: Polymer cleaning by melt filtration, polymer blends by dynamic polymer mixing, coextrusion of different polymers, product specific orientation, precision in melt metering, high speed spinning resp. high speed film extrusion, inline processes with automatic process control.
Modifying Threadline Dynamics in the High-speed Melt Spinning Process
Authors: Cuculo J. A. , Tucker P. A. , Chen G.-Y. , Lin C.-Y. , Denton J.
Published: December 2013

Polyethylene terephthalate (PET) was spun into fibers in the speed range of 3000 to 5000 m/min. Threadline dynamics was modified by altering the threadline temperature profile. This was achieved using a combination of on-line zone cooling and heating(OLZCH). Experimental results showed that the structure development in the threadline was significantly influenced by the OLZCH conditions. The orientation, crystallinity and crystal dimensions of the resulting fibers were greatly increased by the introduction of OLZCH in the take-up speed range of 3000 to 5000 m/min. Various characterization techniques confirmed that the fiber structure was obviously changed with OLZCH. The fiber tensile properties were noticeably improved via this approach. It is concluded that the fiber structure development may be dominantly enhanced by modifying the threadline dynamics in the high speed melt spinning process.
Transient Compressible Flow in Injection Molding Runner**
Authors: Amon M.
Published: December 2013

The transient flow of a compressible polymer melt in an injection system consisting of a ram, a runner, and a shutoff valve is studied. Experimentally, the exit flow rate is found to have an initial value determined mainly by the precompression level and a steady state determined mainly by the ram speed. This flow rate can fall before it rises again, or it can overshoot its steady state. Such complex behavior is predicted qualitatively by a simplified mathematical model, which neglects elasticity but accounts for the finite compressibility and bulk viscosity. Four dimensionless parameters governing system dynamics are identified and their effects investigated by computation.
Optical and Mechanical Measurements to Characterize Injection Molded Polypropylene Plates
Authors: Fleischmann E.
Published: December 2013

By the determination of birefringence and elongation at break as functions of the distance from the surface detailed informations are obtained about the states of orientation of the molecules in injection molded polypropylene plates. Both, the birefringence profile and the profile of elongation at break in the cross-section of the plates, exhibit the skin/core structure typically for injection molded polypropylene articles. An analysis of the results of two polypropylene grades molded at different processing conditions shows a good agreement of both methods.
Blow Molding of Thermotropic Liquid Crystalline Polymers
Authors: Blizard K. G. , Baird D. G.
Published: December 2013

The process of extrusion blow molding was considered in an attempt to obtain biaxial orientation and properties in two thermotropic copply esters: hydroxybenzoic acid/polyethylene terephthalate (HBA/PET) and hydroxybenzoic acid/6-hydroxy-2-naphthoic acid (HBA/HNA). Some degree of biaxial properties and orientation was obtained in blow molded samples in which the die temperature was maintained below the melting temperature. However, the biaxial orientation was present as a layered structure in which the orientation and texture varied from the outside to the inside surface of the blow molded article. Tensile and flexural properties, as well as the morphology and orientation as determined by scanning electron microscopy (SEM) and x-ray diffraction (WAXS), attested to the resulting structure in the blown parison. The orientation and properties were strongly dependent on the thermal and deformation histories during the process. For liquid crystal polymers with relatively slow crystallization kinetics, blow molding in the supercooled state represents a possible processing method to obtain multidimensional properties.
Foam Processing with Rigid Polyvinylchloride
Authors: Kim K. U. , Kim B. C. , Hong S. M. , Park S. K.
Published: December 2013

Rheological and processing studies have been performed on the extrusion of neat and expandable polyvinylchloride (PVC) compounds. Processing additives greatly change both rheological and physical properties. In the normal PVC processing temperature range, the neat compound exhibits very small values of power-law index, which increase with temperature. The usual usage level of dioctylphthalate (DOP), a plasticizer, and Acryloid K-125, a processing aid based on polymethylmethacrylate, increases the power-law index, whereas BTA, an impact modifier based on terpolymer of methylmethacrylate-butadiene-styrene, decreases it. DOP normally decreases viscosity and first normal stress difference. On the other hand, Acryloid K-125 and BTA increase them. Plotting first normal stress difference against shear stress, however, eliminates the effect of DOP and BTA level. Inclusion of a blowing agent increases the powerlaw index, and produces a substantial reduction in viscosity. At high shear rates, all the viscosity data of the expandable PVC compounds fall onto the single viscosity curve of the neat PVC compound. Two blowing agents, azodicarbonamide (ADCA) and sodium bicarbonate (SBC), yield similar reduction of the torque on a screw, but ADCA brings about much larger viscosity reduction than SBC. Further, ADCA shows more rapid bubble expansion rate on leaving the die exit and produces more uniform cells. On the other hand, SBC requires induction time for bubble expansion after leaving the die exit and gives a wider cell size distribution. Particularly in the foaming process with SBC, skin formation is considerably promoted by incorporating small quantities of DOP along with BTA, suggesting a strong potential for manufacturing rigid PVC structural foams with thicker skins by a single extrusion process.
Structure Development in Melt Spinning and Drawing of Nylon-11 and Nylon-12 Fibers
Authors: Shi Y. , White J. L.
Published: December 2013

A basic study of the development of crystallinity and polymer chain orientation in melt spinning and drawing nylon-11 and nylon-12 fibers is presented. The fibers were examined using wide angle x-ray diffraction, differential scanning calorimetry and optical retardation (birefringence) measurements. Melt spun nylon-11 fibers possesses an α-triclinic structure, while melt spun nylon-12 forms a γ-structure. Orientation factors were computed from wide angle x-ray diffraction measurements. These were correlated together with birefringence as a function of spinline stress. The influence of annealing and solid state drawing on fiber structure was investigated.
Naphthalene-ring Containing Thermotropic Copolyester and its Blends with PET
Authors: Zhou Z. , Wu X. , Yu M.
Published: December 2013

A series of thermotropic liquid crystalline copolyesters based on p-acetoxybenzoic acid, 2,7-diacetoxynaphthalene, terephthalic acid and polyethylene 2,6-naphthalate were prepared via melt transesterification. Their thermotropic liquid crystalline behavior was studied by visual observation on the hot stage of a polarized light microscope. The dependence of the crystallizability and melting temperature of the copolyesters on the 2,7-diace-toxynaphthalene content was examined by x-ray diffraction and differential scanning calorimetry. A blend sample was prepared by physically mixing 40% thermotropic copolyester and 60% polyethylene terephthalate and the phase-separated charackter of the copolyester and PET in the blend was proved by TOT and dynamic mechanical measurements. The SEM micrographs of the as-spun fibers of the blend show separation of the two phases. The highly oriented macromolecules and the fibril alignment of the mesomorphic copolyester in the blend has also been revealed after the dissolution of the PET phase in a solvent.
Rheological Properties and Morphological Structure of Blended and Filled Nylon-6
Authors: Wu D. , Tang N. , Gu D. , Wen W.
Published: December 2013

Rheological properties and morphological structure of PA 6/NBR and PA 6/EVA blends with and without CaCO3 fillers are studied. It is found that viscosities of samples investigated can be described approximately by the power law. The rheological behaviour of PA 6/NBR blends slightly deviates from the so-called logarithmic additivity law of the relation between viscosity and composition. The viscosity-composition curve of PA 6/EVA blends shows a positive deviation at the range of low shear rate and changes to the manner of negative deviation after the shear rate is greater than a certaine value. All the samples fabricated in the experiment perform very satisfactory in their processing. An unique morphological structure is found for them, which may be presented by the model of “sea and island”.
Film Blowing of Thermotropic Liquid Crystalline Polymers
Authors: Blizard K. G. , Wilson T. S. , Baird D. G.
Published: December 2013

The process of film blowing was considered in an attempt to obtain biaxial orientation and properties for two thermotropic copolyesters: p-hydroxybenzoic acid/polyethylene terephthalate (HBA/PET) and p-hydroxybenzoic acid/6-hydroxy-2-naphthoic acid (HBA/HNA). Tensile properties of the blown film were exceptional for these materials: tensile strengths of 300 to 400 MPa and moduli of13 GPa were observed in the axial direction, for example. This result if believed due to the absence of a skin-core texture in which the core often remains relatively unoriented. Despite some improvement in the transverse direction with increasing blow up ratio (B UR), properties did not exceed 20 to 25% of those in the machine direction. Wide angle x-ray scattering measurements confirmed the predominantly axial orientation in the films, which was believed to be generated in the annular die gap and not significantly disrupted during the subsequent blowing process. The properties and morphology of the blown film were compared to those ofuniaxially drawn films. It was found that in the machine direction the properties were similar, while significantly higher properties were obtained in the transverse direction for the blown film.
Structural Gradients in Injection Molded PPS
Authors: Hsiung C. M. , Cakmak M. , White J. L.
Published: December 2013

The processing-structure-property relationships in injection molded poly-p-phenylene sulfide (PPS) has been investigated. The structural gradients developed in the molded parts were characterized using optical microscopy, differential scanning calorimetry and wide angle X-ray diffraction techniques. Generally amorphous parts are produced with cold molds and crystalline parts with hot molds. At intermediate mold temperatures the parts produced exhibit a glassy surface and core and a crystalline annular ring sandwiched in between. The characteristics of this crystalline ring formation were studied as a function of processing conditions and position in the molded parts. Tensile and impact properties of the injection molded parts were correlated with the processing conditions and structure. The samples containing crystalline rings were found to exhibit greater toughness and tensile strength as compared to the samples that are uniformly amorphous or uniformly crystalline.
Flow Analysis in an Internal Mixer
Authors: Kawanishi K. , Yagii K.
Published: December 2013

A modified laboratory mixer (Banbury-type; batch volume is 250 cm3) with transparent front windows was used to observe the flow of silicone rubber. A pair of specially designed rotors was used in order to estimate the influence of rotor design upon the behavior of silicone rubber. Five parameters were picked up in designing the rotors. The rotor consists of a number of thin plates of identical shape. The plates are designed so that they can construct a double-winged rotor. By assembling the plates properly, the angles of twist of longer and shorter wings and lengths of wings can be varied, i. e. the overlap ratio of longer and shorter wings can be controlled. The rotor tip clearance is also variable. Batch homogenization times were measured with torque and unit-work for all experiments, observing the flow of silicone rubber through the front window at the same time. The torque and unit-work increase as rotor tip clearance decreased and as overlap ratio of wings increased. The twist angle of wings had little influence on torque and unit-work. The batch homogenization time became shorter with increases of rotor tip clearance, overlap ratio of wings and twist angle of wings and with the decrease of rotational speed ratio.
Modelling Flow in Tangential Counter-rotating Twin Screw Extruders
Authors: Kim M. H. , White J. L.
Published: December 2013

The flow of Newtonian fluids in a (modular) tangential counter-rotating twin screw extruder is analyzed using hydrodynamic lubrication theory and a modified Flow Analysis Network Method. The flow in systems with (i) forward puming screws and (ii) backward pumping screw pairs is investigated. For forward pumping screw elements we analyze the extent of back flow between the screws for different levels of screw flight staggering. The ratio of backflow to net flow is the highest when the flight staggering angle is 180°. The computed flow fields of backward pumping screw elements shows backward helical flow along the screw channel and forward flow between the screws. Screw characteristic curves of backward pumping screw elements are shifted by a factor of 2 Δp/L Q=0 from the forward pumping screw characteristic curves. The flow and pumping characteristics of modular systems have also been considered.
Influence of Melting Zone and Melt Homogeneity on Extrusion and Injection Molding Processes
Authors: Sakai T.
Published: December 2013

In this study, the melting behavior and melt homogeneity in a single screw extruder have been investigated to obtain better products in quality and higher productivity for extrusion and injection molding. For the analysis of the melting behavior, so-called “cooling experiments” were used. For the melt homogeneity evaluation, furthermore, molten polymer temperature fluctuations at the exit of a single extruder and injection molding machine were measured. As a result of these analyses, we have concluded that the melting process in extrusion and injection molding played an important role on improving product quality and its productivity. Based on experiments and analyses on the melting mechanism, we have developed a mixing and kneading screw configuration with a new melting process, in which the compulsory circulation flow in solid bed accelerates rapid melting of raw materials and melt homogeneity.
Instability Phenomena in Film Casting Process
Authors: Barq P. , Haudin J. M. , Agassant J. F. , Roth H. , Bourgin P.
Published: December 2013

This paper deals with instability phenomena in PET film casting. An experimental investigation makes it possible to confirm the occurrence of draw-resonance above a critical draw ratio, and to show interesting coupling effects between thickness and width fluctuations. A theoretical model is developed on the basis of some important assumptions: constant width, vertical film, isothermal regime and Newtonian behavior. It allows to calculate the response to a sudden increase of the chill roll velocity and to predict the critical draw ratio (DR = 20.3). Other types of perturbations of the roll velocity (sinusoidal oscillation, random fluctuations) are also treated using this model.
Influence of Stretching and Cooling Conditions in Cast Film Extrusion of PP Films
Authors: Duffo P. , Monasse B. , Haudin J. M.
Published: December 2013

In cast film extrusion, the polymer melt is extruded through a slit die, slightly stretched in air and then cooled on a chill-roll. An important part of the present work was to study the effect of the roll temperature on the polymer crystallization in the thickness of extruded films. A thermomechanical model of the whole process taking into account the polymer crystallization was used to determine the mean stretching stress in air, local temperature, local cooling rate and local crystallization development. The morphologies in the thickness of the films were observed by optical microscopy on microtomed slices and the crystalline structures were investigated by wide-angle X-ray diffraction and DSC measurements. From DSC melting curves of thin sections it is possible to know the local crystallization temperature and to check the thermomechanical model. The model is validated and explains the influence of the roll temperature on the formation of structures and morphologies. Nevertheless neither the existence of three different zones in the thickness nor the high p phase concentration are predicted by the model, which needs new developments.
Multilayer Injection Molding
Authors: Vos E. , Meijer H. E. H. , Peters G. W. M.
Published: December 2013

Visualization of the fountain flow in a piston driven non-Newtonian flow is studied by means of experiments and numerical computation. The result will be applied to the multilayer injection molding technique, where an accumulator is used, to store the polymer melt. The discontinuity at the contactline of the piston and the wall of the cylinder appears to have considerable influence on the total deformation history.
Flow Analysis of Sheet Molding Compounds in Compression Molding
Authors: Lee L. J. , Fan J. D. , Kim J. , Im Y.-T.
Published: December 2013

A series of experiments and a numerical simulation were carried out to investigate the flow of silly putty and sheet molding compound (SMC) at various processing conditions in compression molding. The flow resistance and the interface friction of both materials were characterized by using a squeeze flow rheometer and the ring compression test, respectively. Molding experiments were carried out on an instrumented mold and the finite element code ALPID (Analysis of Large Plastic Incremental Deformation) was used for numerical simulation. The flow front shape, temperature profile, and pressure change obtained by numerical simulation compared well with experimental results.