bluuebunny/crossref_metadata_2025_split huggingface dataset:
The flow of thermoplastic melts: Experimental and predicted
Authors: Cox Howard W. , Mentzer Charles C. , Custer Russell C. 
Published: December 2004

AbstractThe flow of polypropylene, nylon 6,6, and 33‐percent glass‐fiber‐filled nylon 6,6 into a tensile bar mold was investigated. Pressures needed to fill the cavity and runner system were measured as a function of fill time and melt temperature. The experimental results were compared to pressures predicted using the Moldflow flow‐analysis programs. Correlation between experimental and predicted pressures was good provided that accurate input data to the computer programs were used. The choice of runner diameter in the approximation of the irregular shaped runner of this tensile bar mold was found to be important, since the runner length was approximately 40 percent of the total flow length. Material properties of particular importance were thermal conductivity, viscosity, and no‐flow temperature (the temperature at which the resin will no longer flow). Viscosity/shear rate/temperature data are needed for the computer programs and two methods of obtaining the data were examined: an Instron capillary rheometer and a capillary nozzle on an injection‐molding machine. Good agreement between the two methods was found for polypropylene over a shear rate range of 100 to 10,000 s−1. Only the injection‐molding capillary nozzle could be used for the nylon‐ and glass‐filled nylon due to the thermal degradation that occurred in the Instron rheometer.
Residence time distribution in a twin screw extruder
Authors: Kao S. V. , Allison G. R. 
Published: December 2004

AbstractThe residence time distribution (RTD) in a fully intermeshing, corotating twin screw extruder was determined with a stimulus‐response technique. In addition to varying three process parameters (i.e. throughput, screw rotational speed, and barrel temperature), two screw configurations were also studied: one containing four kneading block mixing sections, and the other consisting only of regular screw bushings. Although screw configuration was an important variable, it was found that for both configurations the throughput had the largest effect on RTD. The screw rotational speed was second in importance, and the barrel temperature change produced no effect.A fluid mechanical model based on the fluid flow in a partially‐filled rectangular channel was used to explain the experimentally observed dependence of RTD on the process parameters. Reaction engineering approaches were adopted to compare the RTD results of two screw configurations with two idealized flows.
Mathematical modeling of squashing flows of heated polymer particles
Authors: Kuo Youti 
Published: December 2004

AbstractA combination of shear and extension is encountered in the squashing flows of heated polymer particles. Extensional rate affects the non‐Newtonian viscosity in determining the flow field in the squashing of cylindrical particles, but both the extensional and shear rates are equally important for disc‐like particles.A viscous‐type constitutive equation is used for simplicity. The solution of the momentum equations satisfying no‐slip boundary conditions leads to a particle flattening equation that can predict flattening ratios of nonisothermal particles in terms of rheological parameters and dimensionless groups of process variables. Application of this analysis to roll fusing of toner particles in copiers is described in a companion article in this issue.
Rheological and heat‐transfer considerations for the processing of reactive systems
Authors: Ryan M. E. 
Published: December 2004

AbstractThermosetting materials have found widespread use over a broad spectrum of engineering applications due to their intrinsic mechanical strength, thermal and dimensional stability, and other unique properties. Consideration is given to those aspects of reaction kinetics, rheology, fluid mechanics, and heat transfer which are of relevance for the mathematical modeling of reactive polymer processing. Particular emphasis is given to the characterization of reaction kinetics under non‐isothermal conditions, the effect of fillers or reinforcing agents on the heat transfer and kinetic behavior, and the complex nature of the interactions brought about by the reactivity of these systems. In addition, the current status of the mathematical simulation of reactive polymer processing is briefly reviewed.
Numerical simulation of entry and exit flows in slit dies
Authors: Mitsoulis E. , Vlachopoulos J. , Mirza F. A. 
Published: December 2004

AbstractA general‐purpose finite element program has been used to simulate the flow of Newtonian, power‐law, and viscoelastic fluids in the entry and exit regions of a slit die. It was found that shear‐thinning increases the entrance correction while it decreases the exit correction. Shear‐thinning reduces the size of the small corner vortex that forms in the entry flow of a Newtonian fluid. The swelling ratio had a value of 1.196 for Newtonian fluids and decreased as the value of the power‐law index decreased. Viscoelastic calculations were performed using the Criminale‐Ericksen‐Filbey (CEF) constitutive equation. Convergence of the iterative scheme was unattainable for Deborah numbers above 1.0. The results showed a decrease of the entrance correction and an increase of the exit correction with elasticity. Extrudate swell first decreased slightly and further increased with the Deborah number.
Processing of composites with titanate coupling agents—a review
Authors: Monte Salvatore J. , Sugerman Gerald 
Published: December 2004

AbstractIt is proposed that titanium‐derived coupling agents react with free protons at the inorganic interface to form organic monomolecular layers on the inorganic surface, which causes inorganic/organic phase compatibilization resulting in new composite property, catalysis, adhesion, and rheology performance standards. Processing techniques and rheology effects using titanates are discussed. The injection pressures of CaCO3, carbon black filled polystyrene, and glass‐fiber, talc‐filled poly(phenylene sulfide) are shown to be reduced 50 percent by use of cumyl phenyl type titanate. Adhesion effects are discussed in many composites such as epoxy/aluminum, acrylic/slate, carbon fiber/polyester, etc., followed by data showing significant property improvements in 1/16 inch milled glass fiber and Wollastonite RRIM urethane, printed circuit boards and amide and anhydride cured aramid fiber‐reinforced epoxy.
Nonlinear viscoelastic response in two dimensions—numerical modeling and experimental verification
Authors: Keren B. , Partom Y. , Rosenberg Z. 
Published: December 2004

AbstractRecently we developed a nonlinear viscoelastic constitutive model which called the Phases Model (PHM) [10]. The main advantages of the PHM over existing nonlinear viscoelastic models are that it lends itself to simple, straightforward calibration of the material functions, and that it is naturally suitable to step‐by‐step computer simulation. In this paper we apply the PHM to two dimensional (2‐D) situations. To this end, we've developed a 2‐D finite difference code in cylindrical geometry which is based on the PHM. We demonstrate the validity of our modeling by applying the code to a 2‐D set‐up developed for this purpose. The 2‐D specimen is in the form of a disc of the test material compressed between two rigid metal anvils by a velocity‐controlled Instron machine. We monitor the response of the viscoelastic disc in terms of the overall axial force history, and the axial stress component at the disc center. We get good agreement between theory and experiment.
Calendering analysis without the lubrication approximation
Authors: Mitsoulis E. , Vlachopoulos J. , Mirza F. A. 
Published: December 2004

AbstractA general‐purpose finite‐element program has been used to simulate the flow of Newtonian, power‐law, and viscoelastic fluids in calendering. The analysis is fully two‐dimensional and does not make use of the lubrication approximation. Isothermal and nonisothermal calendering is studied and the results are compared with predictions from the lubrication approximation. The free surface is determined and circulatory flow patterns are predicted in the melt bank. Detailed calculations have been performed for a rigid poly(vinyl chloride) (PVC) resin that exhibits slip at the wall using rheological data for the melt and machine parameters. The results include determination of the shape and location of the free surface, vortex patterns, temperature and pressure distributions, and predictions of roll‐separating force, torque, and power consumption. Comparisons are made with experimental data available in the literature.
A method of computation of the pressure effect on melt viscosity
Authors: Utracki L. A. 
Published: December 2004

AbstractSimha's equation of state provides the relation between reduced pressure, temperature, and volume (P̃, T̃, and Ṽ, respectively) and the occupied site fraction, y = y (P̃, T̃). The latter theoretical parameter combines the P and T effects on the occupied and unoccupied (“free volume”) part of the model liquid. It can be computed for each liquid once the thermodynamic reducing parameters are known. Empirical correlation between published zero shear viscosity data, η = η (P, T), and y indicates that for n‐paraffins and molten polymers η is a single parameter function: η = η (y). The mathematical form of this dependence was explicitly given for n‐paraffins. However, for polymers the correlation depends on molecular weight, molecular weight distribution, branching, composition, etc. In Practical terms, η = η (y) should be determined for each polymer by measuring the temperature dependence of η in as wide a range of T as possible. Then pressure effect on η can be determined from η = η(y) plot, knowing the y = y(P̃, T̃) relation.
A simple, accurate model for viscosities of polymer blends
Authors: Carley James F. 
Published: December 2004

AbstractThe accurate but complex McAllister model for the melt viscosities (η) of binary polymer blends has been greatly simplified by dropping the terms involving only mole fraction and molecular weight, by switching from mole fraction to mass fraction, and by making the model explicit in dynamic, rather than kinematic, viscosity. The simpler Lecyar model was tested side‐by‐side with the McAllister in five binary systems and at seven levels of shear rate from 5 to 500 s−1 in each system. For the 35 pairs of curves fitted, the rms standard error of estimate was 0.0945 (In η), for the Lecyar model versus 0.0911 for the McAllister; the difference corresponds to only 0.4 percent additional error in the blend viscosity. Comparison of results in two systems, reported by Carley and Crossan (12) with those of other workers, indicate that the differences among what appear to be comparable, self‐consistent data sets are much greater than the within‐set errors of rheometric measurement and model fitting.
Properties of elongational flow injection‐molded polyethylene. Part 1: Influence of mold geometry
Authors: Bayer R. K. , Zachmann H. G. , Calleja F. J. Baltá , Umbach H. 
Published: December 2004

AbstractInjection molding of polyethylene was carried out using molds that introduce axial elongational flow during the filling process, As compared with conventional injection‐molding methods, the present technique yields polyethylene materials having higher mechanical strengths (σ ≈ 150 MPa). The σ‐value of the moldings can be systematically monitored by adequately varying the elongational flow through modification of the mold geometry. Geometrical features of the volume containing the melt before injection as well as geometry of the die, the extruder, and the inlet influence the overall elongational flow, and thus, the mechanical strength of the moldings.
Microstructural diagnosis of block copolymer nonlinear mechanical properties. III: Cycling tensile tests
Authors: Diamant Joram , Williams Michael C. 
Published: December 2004

AbstractThe same three styrene‐butadiene‐styrene copolymers discussed in the companion paper (this issue) were tested by cycling in uniaxial tension/retraction, with large magnitude (to 600% in some cases) and different sequences and rates. The behavior of “set”, at the end of each retraction, is examined in detail and invoked to explain several other features of the stress‐strain curves. Time scales for structural recovery determined in the companion paper are found to assist this interpretation. Quantitative modeling of the isostructure retraction curves is accomplished in terms of the Mooney‐Rivlin strain function, modified to employ a strain variable amplified by the volume of broken glassy “filler”. Values of the two Mooney moduli G1 and G2 are used to infer various features of the microstructure.
Some theoretical results of swelling in fiber or particle filled polymers
Authors: Wu Wen‐Li , Prahinski John R. 
Published: December 2004

AbstractThe problem of inhomogeneous swelling of polymers around particles or fibers is treated analytically within the context of Gaussian statistics for polymer chains and the Flory‐Huggins approximation for the interaction between polymer and solvent. The resulting differential equation for the displacement field around the inclusions is quite simple; it contains a homogeneous part and a nonlinear part. The nonlinear part of the differential equation is preceded by a parameter n(1 − 2χ), where n is the molecular weight between crosslinks and χ is the Flory‐Huggins interaction parameter. Accordingly, the displacement field for the case of theta solvent, i.e. χ equals 0.5, can be solved exactly. In good solvents, the problem can be treated as a perturbation of the theta solvent condition. The amount of deviation from the theta solvent solution is obtained through a numerical technique and the results are tabulated as a function of n(1 − 2χ).
Dielectric analysis of the cure of thermosetting epoxy/amine systems
Authors: Bidstrup Sue Ann , Sheppard Norman F. , Senturia Stephen D. 
Published: December 2004

AbstractA low molecular weight epoxy resin is cured isothermally with an aromatic amine hardener, and the dielectric properties are measured as a function of the frequency, reaction time, and cure temperature. At specific stages in the cure, small samples from the reacting mixture are quenched and subsequently analyzed for the glass transition temperature and epoxy group conversion by differential scanning calorimetry. In this manner, the change In dielectric properties can be directly correlated with the network structure. The ionic conductivity is modeled as a function of the cure temperature and the cure‐dependent glass transition temperature using a Williams‐Landel‐Ferry (WLF) relation. Combining this WLF relation with the DiBenedetto equation, a comprehensive model relating conductivity with the extent of reaction and cure temperature has been developed.
Dielectric determination of cure state during non‐isothermal cure
Authors: Day David R. 
Published: December 2004

AbstractAs a result of increased interest from industry in using dielectric cure monitoring, a need has arisen for simplifying frequency, cure, and temperature dependent data so that control decisions can be readily made. Techniques utilizing data covering several decades of frequency now exist for separating ionic conduction levels from dipole and electrode polarization responses. Ionic conduction levels are particularly useful since they can be correlated to both viscosity and extent of cure. In addition to being a function of extent of cure, dielectric properties are also influenced by temperature. This dependence often makes the dielectric response more difficult to interpret. This paper investigates two methods for overcoming the temperature dependence of the dielectric response during nonisothermal cure. The first method utilizes recent WLF modeling techniques and extends them with the end result of extracting Tg in real time during cure. The second technique involves measuring the temperature dependence of uncured and cured material. Utilizing the correlation between log ionic conductivity and extent of cure, which has been noted by previous researchers, the normalized conductivity can be converted to a cure index. Several examples including epoxy, polyurethane, and a UV cured photoresist are presented, showing data before normalization and after both Tg and cure index determination.
Model reference adaptive control of a continuous polymerization reactor under periodic operation
Authors: Eliçabe G. E. , Meira G. R. 
Published: December 2004

AbstractThis work proposes a cascade model reference adaptive algorithm to control a continuous polymerization reactor, which is operated under forced oscillations of its feeds. The objective is to produce a polymer with desired average values of the average chain length, of the average polydispersity and of the average polymer production; in spite of the fact that some of the model parameters may be unknown and/or may vary slowly with time. This objective is achieved by imposing the first two moments of the number chain length distribution (NCLD) to follow predetermined periodic trajectories. The proposed control scheme is an extension of that by Eliçabe, et al., when the number of independent controls is less than the number of system states. Computer simulations have shown the feasibility of the proposed technique, provided continuous state measurements are available.
Structure and orientation development in biaxial stretching of ultrahigh molecular weight polyethylene gel films
Authors: Kyu Thein , Fujita Kenichi , Cho Myung H. 
Published: December 2004

AbstractUltrahigh molecular weight polyethylene (UHMWPE) gel films were prepared by gelation crystallization from decalin solutions. According to wide‐ and small‐angle X‐ray scattering (WAXD and SAXS) studies, single crystal mat texture with crystal c‐axis oriented normal to film surface generally develops. However, randomly oriented structure can also develop if an external force is applied to gel films during gelation crystallization. Both textures invariably yield high drawability in uniaxial mode with outstanding modulus and strength. Biaxial films, typically 5 × 5, 6 × 6, 8 × 8, and 10 × 10 times the original dimensions, were prepared at 130°C–135°C in a biaxial stretcher. Optical microscopic Investigations reveal the development of interwoven fibrillar structure in all specimens. WAXD and SAXS studies show that lamellar structure transforms to fibrillar texture during biaxial stretching. Crystal orientation is characterized by WAXD pole figure and infrared dichroic methods. Mechanical studies suggest that tensile modulus and strength appear uniform. In comparison with uniaxial deformation, significant improvement in the lateral strength is seen in the biaxially stretched films.
Effect of molecular weight distribution on the rheological and mechanical properties of polypropylene
Authors: Tzoganakis C. , Vlachopoulos J. , Hamielec A. E. , Shinozaki D. M. 
Published: December 2004

AbstractThe effect of molecular weight distribution on the Theological and mechanical properties of a series of polypropylenes is evaluated. The polypropylenes tested were produced by controlled chemical degradation in a single‐screw plasticating extruder. Measured properties include shear, extensional and intrinsic viscosity, melt flow index, extrudate swell, melting and crystallization temperatures, impact strength, flexural modulus, and tensile stress.
Nonisothermal crystallization kinetics of poly(etheretherketone) (PEEK)
Authors: Choe Chul Rim , Lee Kwang Hee 
Published: December 2004

AbstractAnalysis of the crystallization kinetics of poly(etheretherketone) (PEEK) was achieved with dynamic differential scanning calorimetry results. A new kinetic model for the nonisothermal crystallization was derived and the possibility of its application was investigated. By evaluating the parameters in the model, the crystallization behavior of PEEK was analyzed. The experimental and predicted crystallinity change showed good agreement, which indicated that the model equation was appropriate to describe the nonisothermal crystallization kinetics of PEEK. As the melt temperature was increased the number of heterogeneous nuclei decreased, hence the crystallization was delayed.
Hydrolysis of 1,4‐cyclohexanedimethanol‐based copolyester
Authors: Golovoy A. 
Published: December 2004

AbstractThe solid state hydrolysis of a copolyester based on a mixture of 1,4‐cyclohexanedimethanol and ethylene glycol condensed with terephthalic acid was studied at 100°C and 57 to 96 kPa water vapor partial pressure (55% to 95% relative humidity). The equilibrium water sorption in weight percent (C∞) was found to be

where P is the water vapor partial pressure in kPa. For specimens 0.32‐cm thick, it took about 24 h to reach 0.9C∞. The intrinsic viscosity (IV) was measured and used to calculate the relative change in molecular weight (M̄w) from the relationship IV ∝︁ (M̄w)0.7. The decrease in molecular weight was linear with time, and the rate of decrease was found to be proportional to C∞; the empirical correlation is

where the rate constant, k, is in day−1. A decrease of 50% in M̄w was observed after 22 days at 95% relative humidity.
Applications of polymeric materials for condensing heat exchangers
Authors: Bigg D. M. , Stickford G. H. , Talbert S. G. 
Published: December 2004

AbstractManufacturers have begun to investigate the use of plastic materials for use in condensing heat exchangers attached to high‐efficiency gas‐fired furnaces. However, a number of technical problems have slowed the use of polymers in this application. While a low thermal conductivity relative to metals is one limitation, a more significant problem relates to the unknown performance of polymers in the harsh chemical environment of a condensing heat exchanger. Recent years have seen some major developments in the use of coatings and plastics for hightemperature service in heat exchangers. In these studies, commercially available acid‐resistant and heat‐resistant polymers were tested, primarily as protective coatings on metal heat exchanger elements, in both experimental‐ and prototypecondensing heat exchangers. These studies indicated that the effectiveness of polymers as coatings was sensitive to the presence of pinholes, and thus, the coating thicknesses had to exceed 0.25 mm to insure adequate protection. The use of a covering, rather than a coating, was found to be one method of insuring pinhole‐free coatings. In this study several all‐plastic heat exchanger elements were found to perform satisfactorily as heat exchanger elements in a gas‐fired condensing heat exchanger. This investigation identified several promising polymeric materials that survived 10,000 cycles in a highly acidic condensing heat exchanger. The polymers that successfully survived this evaluation included fluorinated ethylene propylene, poly(phenylene sulfide), polysulfone, poly(ether imide), and poly(tetrafiuoroethylene).