bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Pressure-Volume-Temperature Behavior Polyethylene Melts
Authors: Capt L. , Kamal M. R. 
Published: December 2013

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

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

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

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

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

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

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

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

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

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

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

Abstract
Part II of the publication describes a model for calculating the melting of polymer blends which has been implemented in the SIGMA simulation software for the design of co-rotating twin screw extruders. The model is based on the findings discussed in Part I and makes it possible to calculate the temperature progression in the solids conveying section and during the subsequent melting process for binary incompatible polymer combinations. The two material components are observed in parallel during the melting process, and the respective degrees of melting over the length of the screw are calculated. The properties of the melt phase, which forms from both components, are calculated with mixing rules implemented in the program. The calculations supply the melting profiles for both components, thereby permitting a comprehensive analysis of the melting of binary polymer combinations. The results additionally form the basis of a calculation to estimate the morphology development of polymer blends in the melting section of the extruder.
Part III of the report looks into a means of investigating the melting of binary polymer combinations, and the results of experimental investigations into polypropylene/polyamide blends are discussed. The simulation calculations are compared with the results of experimental studies in order to verify the model presented in this part of the publication.
Convective Instabilities in the Coextrusion Process
Authors: Valette R. , Laure P. , Demay Y. , Fortin A. 
Published: December 2013

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

Abstract
Experimental studies of the melting process in extruders generally involve a high outlay and can only be performed with certain restrictions, both in respect of the method employed and with regard to the evaluation of the results. This part of the work describes one possible way of studying the melting of binary incompatible polymer combinations. The method described makes it possible to estimate the degree of melting of the two components over the length of the screws of the twin screw extruder. Experimental studies were performed of polypropylene/polyamide 6 (PP/PA6) blends containing low weight contents of the disperse PA 6 phase.
In order to verify the theoretical models set out in Part I, page 124 of this issue, not only were the process conditions of screw speed and throughput varied but also the viscosity ratio. This was achieved by using two different PP grades. In addition, comparable tests were performed on two different sizes of extruders.
The tests show that the melting of polymer blends, and particularly the melting of the second component, which melts at a higher temperature, is determined to a significant extent by the screw rotational speed, the throughput, the ratio of the extruder channel depth to granule diameter and also the material combination (viscosity ratio).
Comparisons of calculations and experiments show that the melting profiles calculated for different material combinations and process conditions tally well with the experimental studies in overall terms.
Numerical Simulation of Polymer Coextrusion Flows
Authors: Zatloukal M. , Tzoganakis C. , Vlček J. , Sáha P. 
Published: December 2013

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

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

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

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

Abstract
An experimental study of the characterization melt spinning cyclopolyolefins is presented. The shear and complex viscosities were measured and the data was found to fit the Cox-Merz relation. The birefringence of the melt-spun filaments was determined and correlated with spinline stress. These were found to be much lower than polycarbonate and polystyrene filaments melt spun under the same conditions. The birefringence was represented in terms of polymer chain orientation. The uniaxial mechanical behavior was also measured. The Young's modulus and tensile strength generally increased with spinline stress and orientation for most cyclopolyolefins. The elongation to break decreased with measured polymer chain orientation for most cyclopolyolefins. For others it was enhanced.