bluuebunny/crossref_metadata_2025_split huggingface dataset:
A coordinate frame for helical flows
Authors: Tung T. T. , Laurence R. L. 
Published: December 2004

AbstractThis note presents a coordinate frame representation for the conservation laws governing fluid motion in a helical configuration as suggested by a single‐screw extruder with deep flights and by the Kenics Static Mixer. This example demonstrates the care necessary in dealing with nonorthogonal coordinate systems. The conservation equations are also presented in terms of the proper physical components, as well as the physical components of the rate of deformation tensor. The paper closes with a brief statement of the boundary conditions for flow in a static mixer.
Approximate calculation and measurement of the pressure distribution in radial flow of molten polymers between parallel discs
Authors: Winter Horst H. 
Published: December 2004

AbstractThe known generalized Newtonian fluid “power law” solution of the radial flow between parallel discus has been used to estimate the normal stress, the magnitude of inertia, and the temperature changes due to viscous dissipation. The flow near the wall has been found to be “nearly steady shear flow;” thus the three viscometric functions can be expected to describe the stress at the wall. Further away from the walls, however, the flow is very different from “steady shear flow.”The temperature field in the radial flow section depends on the dimensionless parameters Nahme number, Graetz number, and ratio of inner to outer radius, as well as on the thermal initial and boundary conditions.Experimentally the radial pressure profiles for flow of three different polyethylenes and of one polystyrene have been studied. The measured pressure profiles are about 20 percent lower than the calculated ones from the “power law” solution. This discrepancy cannot yet be explained; the effects of normal stresses, of inertia, or of viscous heating in these experiments are too small to give a measurable effect.
Fatigue crack growth in polymers. II. The interaction of mean stress, frequency, and temperature
Authors: Radon J. C. , Culver L. E. 
Published: December 2004

AbstractFatigue crack propagation was studied in large centernotched plate specimens of two polymers, poly(methyl methacrylate) and polycarbonate, under tensile cycling conditions. Tests were performed at frequencies of 0.1, 5.0, and 20 Hz, and at two temperatures, −60 and +21°C. The interaction of mean stress intensity, frequency and temperature was investigated. It was found that in tests performed at constant frequency or temperature, the fatigue crack propagation rates were dependent on both the range of the applied stress intensity factor and its mean value, Km. All propagation rates increased with increasing Km. Also, the threshold stress intensities decreased with increasing Km, suggesting very low levels of ΔK for non‐propagating cracks, certainly below the 0.4 Kc, the minimum level investigated here. In PMMA, decreasing crack growth rates with increasing frequency were established for a wide range of Km. However, in PC crack growth rates increased substantially with increasing frequency. Finally, “upper and lower transition points” were noted on crack growth curves of both materials.
Estimation of mechanical properties for rigid polyurethane foams
Authors: Menges G. , Knipschild F. 
Published: December 2004

AbstractRigid plastic foams find application in construction mainly as core materials for loaded sandwich structures—in buildings, ground vehicles, and airplanes. This work provides an equation for the mechanical behavior of polyurethane foams as a function of foam density. Starting from a model conception and the qualitative microscopic consideration of the deformation and failure mechanism, simple relations are found for the tensile, compressive and shear strength and the elastic modulus, which sufficiently express the measured results.
Elongational viscosity of microbead suspensions
Authors: Nicodemo L. , De Cindio B. , Nicolais L. 
Published: December 2004

AbstractA ‘tubeless syphon’ was used as an elongational viscometer for the purpose of measuring elongational viscosities of glass bead suspensions in dilute polymer solutions. It was found that while the shear viscosities increased, the elongational viscosities decreased very sharply with increasing bead concentration. The conclusions from the present data are then compared with the observed changes in the elastic properties of two phase molten polymer systems. A double shift procedure has been successfully adopted to correlate the experimental data.
Phosphites in polyolefin process stabilization
Authors: Ray Wesley C. , Isenhart Kyle 
Published: December 2004

AbstractThe use of stabilizer systems containing phosphites in polyolefins is well‐established in the technical and patent literature. In addition to the known effects of improved heat and color stability for polyolfins, we have recently found that phosphite‐containing stabilizer systems impart a process stabilizing effect as evidenced by melt flow analysis. By monitoring the poly‐olefin melt flow after multiple extrusions with increasing temperature, it was found that the combination of phenolics and phosphites has a marked influence on the control of melt flow of polyolefins and the effect appears to be synergistic in operation.
Mathematical modelling and the systems approach in plastics processing: The blown film process
Authors: Petrie Christopher J. S. 
Published: December 2004

AbstractAs an example of a complex process, the production of blown film is analyzed. Systems descriptions are used to emphasize the importance of stating objectives clearly before process modelling. The mathematical treatment of confined and free flows is outlined, together with an account of the factors which are important in polymer melt flow. The uses and limitations of mathematical modelling are discussed briefly.
Non‐linear creep of polymers under superimposed static and dynamic stress
Authors: Akay G. 
Published: December 2004

AbstractThe non‐linear creep of polymeric materials under super‐imposed static and dynamic stress is considered theoretically. The equation of state due to Green, Rivlin, and Spencer to‐gether with the power law of time dependence for the kernel functions as suggested by Nakada is assumed to characterize the non‐linear materials. Expressions for creep strain under constant static, oscillatory dynamic and superimposed static and dynamic stress are obtained in terms of the material constants and time dependent functions, called dynamic creep functions. It is shown that the creep strain due to dynamic stressing is damped as the number of stress cycles is increased. Damping is faster if the power law of time dependence is high. Expressions for the cumulative creep strain after multiple stress cycles are also obtained in terms of cumulative strain functions. All these functions are evaluated numerically at one thousand stress cycles. Finally, a special case of stress history is considered where the stress periodically reaches zero. It is shown that the ratio of the strains due to dynamic and static stressing can be characterized by the power law parameter when the mean stress is either very high or very low. Due to the slow damping when the power law parameter is small, the decrease of the strain ratio with number of cycles is slow compared to higher power law parameters.
Morphology of random and non‐random olefin copolymers of ethylene
Authors: Bailey F. E. , Walter E. R. 
Published: December 2004

AbstractStudies have been published relating the mechanical properties of ethylene copolymers with short chain branching structures. Other work has emphasized that crystallites in these copolymer systems participate in superstructures and that stress distribution during mechanical testing depends on the arrangement of these structures, the morphology. While developing structure‐property correlations, morphologies of some random and non‐random olefin copolymers have been examined. Surprising morphological differences were found depending on the length, concentration and degree of randomness of the n‐alkyl branch and on vicinal substitution with norbornene derivatives as comonomers. X‐ray diffraction yielded unexpected results which can be explained by a change in the direction of chain folding. Linear side chains randomly introduced into an otherwise high density polyethylene result in a two to three fold increase in the 110:200 x‐ray intensity ratios, a slight reduction in the 110:020 intensity and a 5 to 10 fold decrease in the 200:02 intensities. These results cannot be explained by orientations introduced in sample preparation. There are associated morphological changes. Vincinal substitution with norbornene comonomers has little effect on crystal habit but does change the morphology, tending to shift superstructures from lamellar to fibrillar in nature.
The injection molding behavior of thermoplastics in thin rectangular cavities
Authors: Kamal Musa R. , Kuo Youti , Doan P. H. 
Published: December 2004

AbstractTwo models are presented for simulating the injection molding of thermoplastics in thin, rectangular cavities. One is a much simplified bounded‐radial‐flow model that utilizes an existing numerical model for semi‐circular cavities to adjust for the non‐radial flow region bounded by the lateral walls. The other is a two‐dimensional analysis which assumes that both viscosity and temperature change strongly across the narrow gap but vary weakly in the directions of flow. The latter analysis allows application of the potential theory and the determination of streamlines and progressing front shapes. Both models deal with a non‐Newtonian viscosity with temperature variation. Comparisons between experimental and computational results are shown.
Characterization and piezoelectric activity, of stretched and poled poly(vinylidene fluoride). Part I: Effect of draw ratio and poling conditions
Authors: Shuford Richard J. , Wilde Anthony F. , Ricca John J. , Thomas George R. 
Published: December 2004

AbstractA number of investigators have reported on the high degree of piezoelectricity manifested by oriented films of poly(vinylidene fluoride) (PVF2). To develop applications for this piezoelectric effect, our laboratory is involved in a systematic investigation of the factors responsible for this remarkable behavior of PVF2. In a unique high‐speed process, commercial PVF2 film was uniaxially stretched to a series of draw ratios ranging up to 7/1. The resulting films were characterized by techniques involving infrared spectroscopy, density, birefringence, sonic modulus, X‐ray diffraction, and dynamic mechanical response. The films were then poled at various electric field strengths, temperatures, and times. Correlations have been made between draw ratio, physical properties, poling conditions, and piezoelectric activity of the films. It was found that the piezoelectric activity increased to limiting values with draw ratio, poling voltage, poling temperature, and poling time. It was evident that for PVF2film a significant amount of oriented phase I crystalline material is required for high degrees of piezoelectric activity. The Appendix gives the apparent rate dependence observed for the piezoelectric effect when signal is measured with a voltage sensor of relatively low input impedance.
Strain‐induced crystallization I. Limiting extents of strain‐induced nuclei
Authors: Yeh G. S. Y. 
Published: December 2004

AbstractThis paper points out that interpretations from stress changes alone during oriented crystallization have led to widely different proposed chain conformations and consequently very different crystallization mechanisms for strain‐induced crystallization (SIC). Many of the proposals, including the one by Keller and Machin which takes into account some electron microscopy and X‐ray observations, show varying degrees of incompatibility with existing stress relaxation, kinetic or morphological data on SIC. Another problem lies in the difficulty with proper interpretation of observed morphology on samples which have been Subjected to additional thermally‐induced crystallization (TIC) after SIC, especially, in the absence of prior characterization of SIC crystallites, the finding of a fibrillar‐to‐lamellar transformation in stretched polymers upon additional TIC (Part H) also indicates that the generally‐observed oriented lamellar morphology has a much more subtle origin than‐that depicted by most crystallization models. Part I discusses our previously published morphological data on the characteristics of SIC crystallites from the melt, which includes: (a) their melting point elevation, (Tm » T°m), (b) their nearly perfect crystalline orientation function (fc ∼ 1), (c) their fast rates of crystallization (t1/2 < 1 sec), and (d) their fibrillar morphology and limited dimensions along the fibrillar stretch axis (∼100Å). Examples of morphology of SIC from the glass and from stirred solution are also included to show the overall similarity of fibrillar morphology brought about by stretching.
Optical studies of the stress‐induced crystallization of polymers
Authors: Stein Richard S. 
Published: December 2004

AbstractStress‐induced crystallization may be studied by the birefringence technique and by low‐angle light scattering. From measurements of the change in birefringence and stress during the crystallization of a polymer above its Tg and from a calculation of the intrinsic birefringence of a polymer crystal, the change in volume fraction crystallinity may be calculated. The technique is illustrated for several polymers and found to give values in reasonable agreement with other methods for the study of crystallinity. Crystallization is also accompanied by the development of a low‐angle light scattering pattern, the size and shape of which is indicative of the amount, size and morphology of the crystalline superstructure.
The interaction of fluid mechanics and crystal growth in the formation of shish kebabs from solution
Authors: McHugh A. J. , Silebi C. 
Published: December 2004

AbstractSeveral observations are made regarding the role of the fluid mechanics involved in the process of flow‐induced, fibrillar crystallization from solution. Computational evaluation and discussion of various flow effects in the nucleation step, including combined shear and extensional flows, are presented in terms of the elastic dumbbell model. These results indicate the important role extensional kinematics in the growth process. A qualitative evaluation of concentration effects is also given. The evaluation of facts concerning the growth morphology is presented in terms of a model for the growth process along with data concerning rinsing and quench rate effects on the morphology and inciting behavior of shish kebab crystals.
An experimental study of the kinetics of polymer crystallization during shear flow
Authors: Lagasse R. R. , Maxwell B. 
Published: December 2004

AbstractSome principles of rheology are applied to the study of the shear‐induced crystallization of molten polymers. A new technique is described for measuring crystallization kinetics during isothermal flow at constant shear rate in a parallel plate rheometer. The crystallization rate is characterized by the time elapsed from the start of shearing until the rise in melt viscosity due to crystallization. The measured‐viscosity and induction time for crystallization are shown to be independent of sample geometry. Kinetic data are presented for crystallization of three linear polyethylenes at shear rates of 0.03 – 30 sec−1. It is shown that shear flow has a strong accelerating effect on crystallization when the deformation rate exceeds a critical value. Comparison of results for the different polyethylenes reveals that higher molecular weight materials crystallize faster at a given shear rate and temperature. Finally, shear‐induced crystallization of propylene polymers is shown to be unaffected by the presence of either a carbon black additive or a heterogeneous nucleating agent. It is concluded that the hydrodynamic origin of the shear‐induced crystallization is elastic chain extension due to entanglement couplings between molecules. Furthermore, it is suggested that transient orientation effects during the startup of shear flow may have a dominant influence on the observed phenomena.
A dynamic melting model for a single‐screw extruder
Authors: Lindt J. T. 
Published: December 2004

AbstractA new theoretical concept is given which provides an efficient and consistent method for predicting flow and heat transfer characteristics of the melting zone for a large single‐screw extruder. In contradistinction to previous, theories, significant melt accumulation in the molten films as observed experimentally is considered, instead of postulating the melt accumulation in the “melt pool”. The mathematical model has been obtained by the simultaneous solution of the momentum and energy equation of the melt flow and. solid bed, allowing for the existence of the pressure gradient: The theory is supplemented by a numerical example which shows good agreement with experimental data obtained on a 90 mm extruder with polypropylene, where the down‐channel pressure profile and me profile of the solid bed Were taken as yardsticks for the melting process. For exact determination of the area for applicability of this theory, more experimental information is required.
High performance fibers from aromatic polymers
Authors: Preston J. 
Published: December 2004

AbstractExamples are given to show how molecular structures may be synthesized to prepare polymers useful for the formation of fibers intended for specific end uses, particularly for high performance applications. Current trends and developments taken from the literature are reviewed and some new work from the laboratories of Monsanto Company is presented concerning the use of aromatic polymers for heat and flame resistant fibers. Some new polymers and new routes of synthesis are described. Correlations are made between flame resistance as measured by oxygen index (O.I.) values and the structure of a large number of aromatic polymers.
Polyphenylquinoxalines—high performance thermoplastics
Authors: Hergenrother P. M. 
Published: December 2004

AbstractThe synthesis, processing characteristics, thermal propers, and adhesive and composite properties of polyphenvlqmnoxahnes are briefly reviewed. In addition, new high molecular weight soluble carbonate/phenylquinoxaline copolymers from the cyclopolycondensation of aromatic bis(o‐diamines) with a bis(benzilyl) carbonate are reported.
Effects of multifunctional crosslinking agents on the thermomechanical properties of polyimide Films
Authors: Delvigs Peter 
Published: December 2004

AbstractFour new poly functional amines were synthesized. Polyimide films containing varying amounts of the amine crosslinking agents were prepared. Their thermomechanical properties were compared with those of control film samples prepared from difunctional amines. The effect of crosslink density on isothermal weight loss, polymer softening, and glass transition temperature is discussed.
Poly‐para‐xylelene: Its chemistry and application in coating technology
Authors: Szwarc Michael 
Published: December 2004

AbstractThe chemistry of p‐xylelene and of its analogues has been reviewed. Its modes of formation and polymerization to poly‐p‐xylelene have been described, and the initiation and hypothetical termination steps have been discussed. The reactions taking place in the gas phase and in the deposited film are contrasted with those taking place in solutions. The problems of crystallization of the polymer simultaneously proceeding with its growth have been stressed. Finally, the properties of poly‐p‐xylelenes and their application in the coating industry have been described in some detail, emphasizing the special advantages of gas‐deposition leading directly to a solid and coherent film. Some future fields of application of this technique have been outlined.
Lactone polymers VII. Activation energies for glass transitions of poly‐ϵ‐caprolactone and poly‐ϵ‐thiocaprolactone
Authors: Seefried C. G. , Kodeske J. V. 
Published: December 2004

AbstractThe activation energies for segmental motion have been determined for partially crystalline poly‐ϵ‐caprolactone and poly‐ϵ‐thiocaprolactone over a temperature range that extends from below the glass transition to near the melt region. Based on the shift factors obtained from the time‐temperature superposition of stress relaxation data, the activation energy for the glass transition of poly‐ϵ‐caprolactone is 160 kcal/mole and of poly‐ϵ‐thiocaprolactone is 200 kcal/mole. The value obtained for poly‐ϵ‐caprolactone is in excellent agreement with the reported value obtained from dielectric relaxation studies. A relatively broad secondary maximum in the activation energy spectrum was observed for each polymer in the respective temperature regions between the glass transition and the melt zone.
New techniques for mixing viscous reacting liquids. Part II. Electrical‐mechanical hybrid mixer
Authors: Rotz Christopher A. , Suh Nam P. 
Published: December 2004

AbstractBased on an understanding of the basic mechanisms and governing laws for liquid mixing, a new concept for increasing the efficiency of laminar mixing is advanced. The new concept is motivated in part by the observation that in laminar flows, the interface between two fluid components tends to line up parallel to the streamlines, leading to decreased mixing efficiency. This decrease in effectiveness can be overcome by simultaneously applying mechanically induced shear forces and electrically induced destabilizing forces (which act on the interfaces) to mix the liquids. Results show a dramatic increase in mixing efficiency with the electrical‐mechanical hybrid system. Descriptions of the analytical and experimental work done to characterize the concept and prove its efficacy are presented in detail. Scale‐up factors are discussed in terms of dimensionless groups.
Powder processing of ultra‐high molecular weight polyethylene I. Powder characterization and compaction
Authors: Halldin G. W. , Kamel I. L. 
Published: December 2004

AbstractPowders of ultra‐high molecular weight polyethylene from three suppliers were characterized for density, crystallinity, particle size, particle size distribution and particle morphology. The powders had molecular weights in the range 2‐5 million. Bulk powder behavior, compressibility, green strength and springback were evaluated and explained in terms of particle characteristics. The green densities of the powders were found to reach a plateau at pressures of about 100 MPa. These plateau density levels were found to depend upon powder, characteristics and to lie between 80 and 90 percent relative density. Green strength is shown to be a unique function of a densification parameter.
The role of polymers in optimizing therapeutic effectiveness of drugs
Authors: Leeper Harold , Benson Harriet 
Published: December 2004

AbstractA new class of pharmaceutical dosage forms—therapeutic systems—has been developed. Unlike conventional dosage forms (i.e., pills, capsules, or sustained release preparations), which are specified only by the amount of drug they contain, therapeutic systems are described both by the rate and duration of drug delivery. The first products to embody this technology are: (1) an ocular therapeutic system that delivers the anti‐glaucoma drug, pilocarpine, to the eye for one week; (2) an intrauterine contraceptive system that delivers the fertility controlling hormone, progesterone, to the uterus for one year; and (3) an oral osmotic delivery system for administration of drug to the gastrointestinal tract. Specific furictiQns of polymers as constructional elements of therapeutic systems are discussed and consideration is given to properties critical to the intended performance, test procedures, and parameters for prediction of mechanical and physico‐chemical functionality, stability, and safety.