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International Polymer Processing

International Polymer Processing

Volume 10 Issue 3

  • Contents
  • Journal Overview

Contents

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Contents

May 28, 2013 Page range: 193-193
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Editorial

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Fifteenth in a Series: Ikegai Corporation: From Engine Lathes to Twin Screw Extruders

James L. White May 28, 2013 Page range: 194-194
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Die Extrusion

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Analysis of Polymer Flow through Coathanger Melt Distributors

D. Schläfli May 28, 2013 Page range: 195-199
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Abstract

Coathanger melt distributors are generally designed on the basis of one-dimensional flow models. These do not always have the desired performance, wherefore a 2-D flow analysis tool was developed based on lubrication approximation theory. This tool uses a contour adapted calculation grid and accounts for manifold side walls. Good agreement is observed for a variety of distributor designs. The integration of this tool into the design process permits to evaluate distributor geometries at design stage, reducing empirical corrections and adjustments.
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Viscosity and the Formation of Die Drool at the Polymer-Metal Interfaces

Chi-Ming Chan May 28, 2013 Page range: 200-203
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Abstract

The effects of the die-wall material on the apparent viscosity of a blend of Hytrel and Viton and on the formation of a particle-like material, which is commonly referred to as die drool, at the polymer-metal interface were studied. The blend, which consisted of approximately 15 % Viton and 85 % Hytrel, was prepared by using a twin-co-rotating-screw extruder. During extrusion of this blend, small particles appeared on the surface of the extrudates; these particles were determined by XPS to be a material which consisted largely of Viton. The apparent viscosity of the blend and the amount of die drool were found to decrease as the surface energy of the material used for the construction of the die decreased. The reduction in the production rate of die drool is attributed to reduction of adhesion at the interface.
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Flow Implications in the Processing of Tetrafluoroethylene/Hexafluoropropylene Copolymers

E. E. Rosenbaum, S. G. Hatzikiriakos, C. W. Stewart May 28, 2013 Page range: 204-212
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Abstract

The melt fracture behavior of two Teflon® resins was studied in capillary extrusion in order to identify the critical conditions for the onset of melt fracture and wall slip. These resins were copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) and TFE/HFP/PAVE (perfluoro (alkyl vinyl ether)) (PAVE) respectively. The incorporation of the third monomer in the molecules of the resin was found to improve the processability of polymer without substantially changing its rheology. Surface melt fracture (sharkskin) appeared at wall shear stresses greater than about 0.18 MPa, practically independent of temperature in the range of 300 to 350°C. At higher apparent shear rates oscillating melt fracture was observed due to the presence of wall slip and compressibility of the melt. Furthermore, a superextrusion region was identified at apparent rates greater than about 700 s −1 , beyond those where oscillating melt fracture was obtained. In this region, the extrudate appears again smooth. Finally, it was found that the addition of 0.1 % of polyethylene in the resins, reduces dramatically the pressure drop along the capillary die and eliminates extrudate distortion over the whole range of apparent shear rates up to the superextrusion region.

Reactive Processing

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Thermal/Peroxide Induced Degradation and Maleation of Polypropylene by Reactive Extrusion

B. J. Kim, J. L. White May 28, 2013 Page range: 213-220
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Abstract

Experimental studies of three types of reactive extrusion are reported: thermal degradation, peroxide induced degradation and maleation of polypropylene for intermeshing modular co-rotating and counter-rotating twin screw extruder. The studies were carried out in a modular intermeshing twin screw extruder which can be co-rotating or counter-rotating and possesses different screw configurations. Generally thermal degradation was found to be more effective in intermeshing counter-rotating twin screw extruders when similar screw configurations and operating conditions are used. For peroxide induced degradation both counter-rotating and co-rotating machines performed about the same. For the maleation reaction the co-rotating twin screw extruder achieves higher conversions than the counter-rotating machine with all screw configurations and conditions studied. It would appear that the intermeshing counter-rotating twin screw extruder operates at a higher temperature and has poorer mixing characteristics than the co-rotating machine. Differences between the co-rotating and counter-rotating machines decrease with introduction of kneading disc blocks.

Fibers and Films

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Biaxially Oriented Polyethylene Films by Compression of Injection Moldings

R. K. Bayer, F. Ania, F. J. Baltá Calleja May 28, 2013 Page range: 221-225
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Abstract

The tensile strength, σ, of biaxially oriented polyethylene (PE) films with various degrees of biaxial stretching has been measured. The dependence of σ in the two principal directions x and y is investigated as a function of two parameters: the biaxial draw ratio (average draw ratio of the film) and the degree of biaxiality (strain distribution along the principal directions). Both parameters are related to the final applied pressure P F . The influence of initial orientation and anisometry of the injection molded precursors on the final σ x and σ y values along the principal directions is studied. Results are discussed in the light of the deformation mechanism which transforms the original uniaxial fiber structure of the moldings into the biaxial fibrillar structure of the final films. Direct evidence of this transformation is provided by small angle X-ray scattering (SAXS).
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Tubular Film Blowing

C.-C. Liu, D. C. Bogue, J. E. Spruiell May 28, 2013 Page range: 226-229
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Abstract

The literature on tubular film blowing is contradictory, even on such basic matters as to whether increasing inflation pressure increases or decreases the bubble radius. To provide a solid experimental base for physical understanding and theoretical modelling, detailed on-line measurements were made using three polyethylenes (a low density, a linear low density and a high density material, all of melt index 1.0). The measurements included blow-up ratio as a function of inflation pressure and take-up ratio; the melt temperature and the air flow rate were also varied. On-line radius, velocity and temperature measurements along the film were made in some runs. For the most part the data showed an “intuitive” effect of inflation pressure on blow-up ratio; that is, increasing the pressure caused the final radius (the blow-up ratio) to increase. However, at high blow-up ratios (typically values of 2 to 3, depending on the material and processing conditions), regimes having a “counterintuitive” relationship were observed in some cases. There were not substantial differences among the three materials except that the low density material was less prone to instabilities at high blow-up ratios.
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Tubular Film Blowing

C.-C. Liu, D. C. Bogue, J. E. Spruiell May 28, 2013 Page range: 230-236
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Abstract

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

Molding

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Elastic Calculation of Residual Stresses in Injection Molding

F. Boitout, J. F. Agassant, M. Vincent May 28, 2013 Page range: 237-242
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Abstract

A calculation of residual stresses in injection molding using a 2-D description of the geometry is presented. The polymer follows an elastic behavior law. The thermal shrinkage and the frozen-in pressure when a layer solidifies are taken into account. A calculation of the pressure in the liquid areas after the gate is frozen is presented. A simplified mold deformation model is introduced and its influence on residual stresses is shown. Results are presented for a polystyrene injected in a square plaque.
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On the Limitations of Shear Induced Crystallization in Polypropylene Melts

S. Liedauer, G. Eder, H. Janeschitz-Kriegl May 28, 2013 Page range: 243-250
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Abstract

Recently, the mechanism of shear induced crystallization in melts of isotactic industrial polypropylene has been unravelled for sufficiently high rates of shear [1]. This was achieved with the aid of, what we called, short term shearing. This shearing was applied in a rectangular duct of large aspect ratio. The development of crystallization subsequent to this short term shearing was monitored with the aid of the growing optical retardation. Other traits of this process could be deduced from the cross-sections of the samples extracted from the duct after complete solidification. Mainly one of these traits is the subject of the present paper. As with injection molding, highly oriented areas are found in the cross-sections. The laws governing the limitations of these areas are discussed. In other words, the dependence of the thickness of the layers on the previous shear rate and shearing time is described with the aid of a model containing the relaxation times of threadlike (liquid) precursors. These relaxation times are assumed to depend on the size of the precursors: The larger these precursors have grown the more stable they are assumed. Nucleation and growth are considered as statistical processes.
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Structure and Properties of Injection Moldings of β-Crystal Nucleator-Added Polypropylene

M. Fujiyama May 28, 2013 Page range: 251-254
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Abstract

Isotactic polypropylene (PP) with MFIs of 0.43 to 44.5 g/10 min were added with 0 to 10 ppm of γ-quinacridone, a β-crystal nucleator of PP. Flexural test specimens were injection-molded from the PPs at constant molding conditions and the structures and properties have been studied. 1) The crystallization temperature increases with γ-quinacridone content and MFI of the base resin. 2) The β-crystal content increases with γ-quinacridone content and MFI. 3) The thickness of the skin layer decreases with MFI and scarcely depends on γ-quinacridone content. 4) The orientation of β-crystals decreases with MFI. 5) The Izod impact strength increases with γ-quinacridone content for PP with MFI < 40 g/10 min, and decreases with MFI. However, little improving effect of γ-quinacridone is observed for MFI > 40 g/10 min. 6) The flexural modulus and strength decreased by about 10 to 20 % by the addition of γ-quinacri-done and the decrease is more significant for PP with higher MFI. 7) The heat distortion temperature increases with γ-quinacridone content and the increase becomes more prominent with increasing MFI. 8) The mold shrinkage increases with γ-quinacridone content and decreases with MFI.
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Study on the Performance of Cooling Systems in Precision Injection Molds

S. Y. Yang, H. C. Chang May 28, 2013 Page range: 255-261
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Abstract

Mold temperature is one of the most important factors regarding the quality and production rate in injection molding. Enhancing the performance of mold as heat exchanger is expecially critical to precision molding. In this study, mold temperatures measured at four selected points are used to assess the effects of cooling channel layout and core material on the cooling performance of injection molds for precision molding. Measured data indicate that mold temperature is a complex function of space and time (in-cycle and cycle-to-cycle). Three performance indices based on the measured data are first established for comparing the cooling performance between molds with various design parameters. They are the response to reach equilibrium, the thermal uniformity, and the average mold temperature. Molds implemented with three typical cooling channel configurations and inserted with three core materials are constructed. Their cooling performances during injection molding of disks with steps have been compared. Information from computer-aided simulation of the mold cooling process further facilitates the evaluation of mold cooling performance. General guidelines for planning of cooling channel layouts and selection of core materials are drawn from this study. Experimental and theoretical results suggest that high thermal conductivity of the cores enhances the thermal uniformity, while high heat capacity retards the response of the system to reach thermal equilibrium. High convective area to mold volume improves the overall performance of mold as heat exchanger.
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Measurement of Planar Orientation of Fibers for Reinforced Thermoplastics Using Image Processing

H. Yaguchi, H. Hojo, D. G. Lee, E. G. Kim May 28, 2013 Page range: 262-269
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Abstract

The characteristics of fiber-reinforced thermoplastics depend on the quantity and shape of fibers. The fiber-matrix separation and fiber orientation are caused by the flow during a molding process. Then, the product tends to be nonhomogeneous and anisotropic. Hence, it is very important to clarify the relations between separation-orientation and molding conditions. In this paper, we propose the measurement method which is called image intensity method for fiber orientation distribution by image processing. In order to examine the accuracy of intersection counting and image intensity methods, the fiber orientation of simulation figure is measured using image processing. The image intensity method is rather accurate compared with the intersection counting method.

Welding

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Dynamics and Structure Development in Spin Welding of Polyvinylidene Fluoride Cylindrical Rods

S. Schaible, M. Cakmak May 28, 2013 Page range: 270-282
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Abstract

Dynamics and structure development during the course of spin welding of polyvinylidene fluoride were studied using an instrumented spin welding machine. At least four distinct events were found to occur during the melting sequence that occurs during melting of interface. Wear of asperites, melting as a result of Coulombic friction, appearance of finger-like formations whose long axes aligned in the radial direction and final smearing of these finger-like formations transforming the topography of the interface to fibrillar appearance. In the formation of structural variations in radial and axial directions in the HAZ, the Weissenberg effect was found to play a substantial role.

About this journal

International Polymer Processing offers original research contributions, invited review papers and recent technological developments in processing thermoplastics, thermosets, elastomers and fibers as well as polymer reaction engineering. For more than 25 years International Polymer Processing, the journal of the Polymer Processing Society, provides strictly peer-reviewed, high-quality articles and rapid communications from the leading experts around the world.
All articles are subject to thorough, independent peer review.
Editor: Polymer Processing Society
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