bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of stress birefringence and flow patterns during mold fillin and cooling
Authors: Han C. D. , Villamizar C. A. 
Published: December 2004

AbstractAn experimental study was carried out to investigate the development of stress birefringence patterns of molten polymer during the mold filling and cooling operation. For this study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the changes in stress birefringence patterns in the mold cavity during the molding operation, using a circular polariscope. The mold was equipped with an automatic relay system which closes the shut‐off valve when the pressure in the mold cavity reaches a predetermined value. The mold was also equipped with both heating and cooling devices, so that either isothermal or non‐isothermal injection molding could be carried out. The mold temperature was controlled by thermistor regulated controllers. During the entire cycle of the molding operation, the mold cavity pressure was continuously recorded on a chart recorder, using a melt pressure transducer. The present study shows how molding conditions (namely, injection pressure, melt temperature, mold temperature) influence the distribution of stress birefringence patterns in a molten polymer while it is being injected into, and cooled in, a rectangular mold cavity.
Polymer flows dominated by high heat generation and low heat transfer
Authors: Pearson J. R. A. 
Published: December 2004

AbstractThis paper aims to review recent studies of the flow of non Newtonian (temperature and shear rate dependent) viscous fluids and to relate them to commonly encountered difficulties in polymer processing. The flows considered take place in narrow channels or pipes, and are dominated by viscous forces. Heat generation and temperature variations are taken to be the most significant aspects. A dimensionless formulation of the energy and stress equations is employed, thus bringing out the role of Graetz, Nahme‐Griffith and Brinkman numbers. These latter are introduced as ratios of temperature differences. Special consideration is given to the question of the stability of such flows.
Temperature effect on the electrical resistivity of metal/polymer composites
Authors: Nicodemo L. , Nicolais L. , Romeo G. , Scafora E. 
Published: December 2004

AbstractIn this paper the effect of temperature and filler content ϕ on electrical resistivity of styrene‐acrylonitrile polymer filled with iron or aluminium powders has been investigated. The resistivity of such composites decreases suddenly by several orders of magnitude at a critical volume concentration ϕc, which depends on the size distribution of particles and on thermal history. For filler content lower than ϕc, the resistivity decreases with increasing temperature, whereas for ϕ > ϕc there is a sudden increase in resistivity at temperatures near the glass transition temperature of the polymeric matrix. This effect is more pronounced than the previously reported data on other composite systems.
The distribution of lamellar lengths within a spherulite
Authors: Phillips P. J. , Sien Herbert P. 
Published: December 2004

AbstractOne of the problems to be considered in the application of the Halpin‐Kardos theory to crystalline polymers is the relation of the crystal length to the only related and measurable parameter, spherulite size. The number average crystal length has been computed for various two and three dimensional models for the crystallization process assuming heterogeneous nucleation. It was found that high values of crystallinity are consistent only with lamellae that are stacked in a parallel fashion. For these systems the number average lamellar length is 0.55 of the spherulite radius. Lower crystallinity polymers have an average lamellar length 0.3 to 0.5 of the spherulite radius, the actual value being determined by the radius. For spherulites of radius 1μm or greater, the size of the primary nucleus has no noticeable influence on the average lamellar length.
Mathematical and experimental determination of temperature, velocity, and pressure fields in flat molds during the filling process in injection molding of thermoplastics
Authors: Thienel P. , Menges G. 
Published: December 2004

AbstractWhen injection molding thermoplastics, temperature, velocity and pressure distribution not only vary markedly over the mold cross‐section, but also along the flow path. Moreover, these parameters also vary with time. Using the example of a typical injection‐molding material‐high impact polystyrene—the distributions in the flat mold are calculated and discussed. It was possible to test calculations by means of comparative experimental tests in an injection molding unit with variable wall thicknesses and long flow paths. The purpose of these investigations is to give a better physical understanding of these complicated flow processes and to provide indications for optimum process control.
The rheology of polysulfone
Authors: Shaw M. T. , Miller J. C. 
Published: December 2004

AbstractThe viscosity‐shear rate functions for polysulfone (PSF) condensates ranging from 0.4RV to 0.95RV were determined using capillary rheometry, The most probable distribution of molecular weights of these resins allowed facile comparison with the polydisperse Bueche theory for viscosity, The agreement in shape of the viscosity function with theory was good but the data were displaced by a factor of 3 to 4 to higher reduced shear rate, a fairly common occurrence for melts. The high absolute value of PSF viscosity was explained with existing empirical correlations as a combination of low critical molecular weight and strong intermolecular interactions. The temperature dependence of viscosity was found to be close to that for polystyrene in the temperature range, Tg + 90 to Tg + 190°C. The die swell, end corrections, and melt fracture characteristics were also determined. The latter was found to occur at a constant wall shear stress of about 6 × 106 dynes/cm2 while the die swell and end corrections were found to be small.
The kinetics of fiber growth from flowing solutions
Authors: McHugh A. J. , Vaughn P. , Ejike E. 
Published: December 2004

AbstractData are presented for the longitudinal and radial growth rates of polyethylene fibers grown from high molecular weight solutions using a seeding method in Poiseuille tube flow. Results indicate growth is a two‐step process with the first step the formation of very thin untapered filaments ∼25 μm in diameter which grow very rapidly the full length of the capillary tube. The second step involves radial thickening of the filament into a tapered shape, the kinetics of which have been measured. The discussion includes an analysis of the rapid longitudinal growth and a critical comparison to earlier experiments in both Poiseuille and Couette flow. A possible growth mechanism is suggested to explain the high growth rates found in these experiments as well as the unusual growth observed earlier for Couette rotor growth. A discussion of some kinetic data for the radial growth process is also given along with preliminary results which indicate thickening may only occur in flow of extensional kinematics.
Effect of molecular weight on high pressure crystallization of linear polyethylene. I. Kinetics and gross morphology
Authors: Hoehn Harvey H. , Ferguson Raymond C. , Hebert Richard R. 
Published: December 2004

AbstractTen linear polyethylenes ranging from Mw = 4.9 × 104 to 4.6 × 106 were crystallized in a dilatometer at 0.51 GPa and 242°C and then cooled slowly. Volume vs time data were used to follow the kinetics of the crystallization. The dilatometer data for the isothermal part of the crystallization were fitted to the Avrami equation. The time exponent was independent of molecular weight and the average was n = 2.2. Electron microscopy of fracture surfaces showed that all of the polyethylenes crystallized in extended chain morphology. The crystalline order and maximum extended chain crystallite thickness decreased with increasing molecular weight. The dominant morphological feature of the crystallized high molecular weight samples was a strand‐like network superstructure. Attempts to stabilize the hexagonal structure formed in the isothermal part of the crystallization failed, and all specimens had only the usual orthorhombic crystal structure.
An electron microscopy study of the microfibrillar structure of deformed polyethylene spherulites
Authors: Tarín P. M. , Thomas E. L. 
Published: December 2004

AbstractA quantitative analysis of the deformation of thin spherulitic polyethylene films was undertaken at the microscopic level with the aid of a gold marking technique. The deformation microstructure which developed was further characterized through the use of a gold decoration technique. The microfibrillar morphology was found to agree quite well with Peterlin's model of the microfibril. Changes in the sample morphology as delineated by the gold decoration, support the proposed mechanisms of the transformation of the folded chain spherulitic morphology into the microfibriliar morphology and the subsequent deformation of the microfibrillai structure.
Diffusion of vinyl chloride from PVC packaging material into food simulating solvents
Authors: Chan R. K. S. , Anselmo K. J. , Reynolds C. E. , Worman C. H. 
Published: December 2004

AbstractTwo models are used to describe vinyl chloride monomer (VCM) diffusion from poly(vinyl chloride) (PVC) packages to food simulating solvents. It was found that when the initial solid concentration in a PVC package is 0,35 ppm: (a) For poor solvents such as water and oils, VCM concentration in the solvent, Cl, theoretically will not exceed 20 ppb. (b) For strong solvents, the volume ratio of package solid/solvent should not exceed 0.1 in order to keep (Cl)max below 20 ppb. (c) It was demonstrated that thickness can be adjusted to give a Cl = 20 ppb at the time equal to the shelf‐life of the package. The method can also be used to calculate the initial concentration of VCM in a package which will give a proposed level of maximum Cl when the solvent and package geometry are fixed. VCM diffusion from PVC pressure pipe to pipe fluids was similarly analyzed.
Prediction of diallyl phthalate molding performance from laboratory tests III. Correlation of data from capillary extrusion rheometer, mechanical spectrometer and differential scanning calorimeter
Authors: Slysh Roman , Guyler Karl E. 
Published: December 2004

AbstractThe purpose of this work was to determine if capillary extrusion rheometer and mechanical spectrometer data can be used to predict the molding performance of a commercially available diallyl phthalate (DAP) compound. In addition, differential scanning calorimetry (DSC) curves of “good” and “bad” batches were statistically analyzed in order to determine if the DSC peak shape is related to the molding performance. It was found that the data obtained from all three techniques correlate very well with the molding behavior of the DAP material studied. Capillary rheometer and mechanical spectrometer results show that lower melt viscosities and lower curing rates are desirable for obtaining satisfactory molding performance. The mathematical moments analysis of DSC curves indicates that DAP batches which molded well give peaks of fairly high symmetry, while all peaks of “bad” batches are skewed to the left. The center of gravity of the former is at a higher temperature and the variance is smaller than the corresponding values of “bad” compounds.
Characterizations of poly(methyl methacrylate) for optical coating or thermal forming operations
Authors: Wen Walter Y. , Hauschild Danny L. 
Published: December 2004

AbstractThe bulk surface and thermal properties and chemical conformation of several poly(methyl methacrylate) samples have been characterized. The results of the analysis have correlated well with the suitability of the thermoplastic sheets for optical coating or thermal forming operation. Techniques for inspection of the plastic sheets appropriate for such special applications have been recommended.
The fatigue behavior of graphite fiber reinforced nylon
Authors: Dibenedetto A. T. , Salee Gideon 
Published: December 2004

AbstractThe fatigue lives of graphite fiber reinforced nylon composites were related uniquely to the tensile strengths of the materials. The distributions of tensile strength and fatigue life were measured and correlated with either two‐ or three‐parameter Weibull functions. For a specific population, there existed a unique relationship between the two cumulative distributions. Thus, if the effect of an environmental variable on the distribution of strength is measured, the effect on the fatigue life can be estimated. It was also found that the mechanism of fatigue failure was influenced by the technique of fabrication. Compression molded materials failed through an isothermal, brittle mode of fracture, while injection molded materials failed in a ductile, thermal mode.
The operating characteristics of twin screw extruders
Authors: Smith John M. , Janssen Leon P. B. M. , De Koning W. L. , Abeln P. P. J. 
Published: December 2004

AbstractThe operation of a twin screw extruder processing a powder or granular solid is reviewed. The operating variables of screw speed and barrel temperature profile interact with a number of design parameters— screw design, die geometry, feed zone geometry and with the material properties, in determining machine performance. The factors that determine output and pressure development are specified in a sequence of block diagrams. The dynamic response of an operating machine to disturbances in the steady state conditions is explained in the light of the established relationships and interpreted in conventional control theory terms. Attention is drawn to the importance of mixing in the chambers formed by the screw channels and of the residence time distribution in determining the quality of the final product.
Kinetics and flow of diallyl phthalate resins
Authors: Sundstrom Donald W. , English Michael F. 
Published: December 2004

AbstractThe analysis of molding operations for thermosetting polymers requires knowledge of the rheology and reaction rates of the materials. The purpose of this research was to measure kinetic and rheological data on diallyl phthalate resins and to integrate these results into models describing the flow behavior. The chemical kinetics of the curing reactions were derived from calorimetric measurements taken with a differential scanning calorimeter. The rheological data were measured with a mechanical spectrometer equipped with eccentric rotating discs. A model based on the theory of ideal rubber elasticity was used to correlate the elastic storage modulus with reaction time and temperature. For the region below the gel point, the dynamic viscosity exhibited a power law dependence on angular frequency and an Arrhenius dependence on temperature.
Free coating of viscous and viscoelastic liquids onto a partially submerged rotating roll
Authors: Middleman Stanley 
Published: December 2004

AbstractExperiments are performed on the dynamics of formation of a liquid coating picked up by a cylindrical roll rotating partially submerged in a free bath. Data on coating thickness for Newtonian fluids are found to correlate according to T = H(ρg/μU)1/2 = 0.56 for fluids whose viscosities range from 0.11 to 33 poise. Data for strongly non‐Newtonian and Viscoelastic fluids (polyacrylamide solutions) can be forced to fit this correlation by defining an “equivalent coating viscosity.” It is clear that this defines a pseudo viscosity, because the “equivalent coating viscosity” is observed to increase with increasing roll speed. This suggests that strongly Viscoelastic fluids respond to the rapid deformation suddenly imposed in the dynamic meniscus near the pickup point in a distinctly elastic manner that alters the flow through the meniscus.
Determination of rheological parameters from parison extrusion experiments
Authors: Ajroldi G. 
Published: December 2004

AbstractThe parison extrusion and the effects of post‐extrusion swelling and sagging in the blow molding process have been studied by several authors and some qualitative relationships with rheological parameters have been attempted. The aim of this work is to show that, under some simplifying assumptions, the relevant rheological parameters—the swelling of the parison and its tensile compliance—can be directly determined from the viscoelastic analysis of the process. The reliability of the model has been tested by experiments carried out by the pinch‐off mold technique which provides the parison weight profile as a function of both previous extrusion history and mold closing delay. First of all it has been shown that the proposed model is suitable to represent the data. The swelling behavior shows the expected dependence on time and shear rate and the long‐time swelling data compare well with those determined by capillary extrusion experiments. It has also been found that the measured tensile compliance is of the same order of magnitude as that determined by conversion of tensile relaxation experiments; however, in the blow molding experiments the compliance of the parison decreases with increasing extrusion shear rate, i.e., by increasing the induced anisotropy of the polymer. As rheological examples, the performance displayed on both industrial and laboratory machines is discussed for three high density polyethylenes.
A simplified description of viscoelastic behavior of polymers as illustrated with biaxially‐oriented poly(ethylene terephthalate)
Authors: Titomanlio G. , Rizzo G. 
Published: December 2004

AbstractA rheological model of solid polymers is proposed. Its mechanical analog is a parallel of a linear spring and a Maxwell element with variable viscosity. The viscosity of the dashpot is allowed to change with stress both directly, by an Eyring‐type mechanism, and through free volume changes according to the Doolittle equation. Predictions of the model reproduce many of the features shown, especially after yielding, by constant velocity stress‐strain, stress‐relaxation and creep data taken at room temperature on biaxially‐oriented poly(ethylene terephthalate) over a wide range of loading rates.
The operation of the rheovibron in the shear mode
Authors: Locati G. 
Published: December 2004

AbstractThis paper describes the use of the Rheovibron visco‐elastometer in the shear mode. A new self‐centering sample holder was designed allowing the evaluation of the real and imaginary parts of the shear modulus on low modulus materials such as polymer melts, uncrosslinked and slightly crosslinked elastomers, and elastoplastics.
Orientation effects and cooling stresses in amorphous polymers
Authors: Struik L. C. E. 
Published: December 2004

AbstractThis paper deals with two kinds of internal stresses in amorphous polymers. First, the internal stresses connected with molecular orientation are discussed. A framework is presented that describes the interrelations of the various orientation effects (anisotropy, birefringence, etc.) and their dependence on the thermomechanical history of the material. The second part of the paper deals with the residual thermal stresses generated by rapid inhomogeneous cooling through the glass transition range. These so‐called cooling stresses are well‐known in glass technology. The theory of the quenching of flat glass plates is described, generalized to objects of arbitrary geometry, and shown to be applicable to polymers. The practical importance of cooling stresses is discussed.
The water relaxation in polymers containing the amide group
Authors: Pezzin Giovanni 
Published: December 2004

AbstractThe low temperature water relaxation of synthetic polymers containing the amide group is usually attributed to the motion of a water‐polymer complex in the amorphous region. According to Puffr and Sebenda the complex is formed by water and amide group in the stoichiometric ratio 1.5. Elastin, an insoluble protein of vessels and ligaments, seems the ideal polymer for testing the model, being practically free of polar side groups and having a glass transition at 200°C, so that its “water peak” can be easily investigated. Calorimetric investigations show that the molar ratio for “bound water‐amide group” is indeed 1.5, as predicted by the model. The activation energy of the “water peak” is very close, for the “dry” protein, to that of nylons, but it decreases with increasing hydration to a limit of 9 kcal/mole. The results give additional support to the traditional interpretation of the polyamide beta relaxation and to the Puffr and Sabenda model for the interaction of water and amide groups in synthetic polymers.
The fracture mechanics of polymers at high rates
Authors: Casiraghi T. 
Published: December 2004

AbstractInstrumented pendula have been applied to investigate the fracture toughness of some polymeric materials—homopolymers and composites—by fracture mechanics. The method is simple, and can be easily used for routine testing or research work. The load transducer is such that it allows the achievement of very accurate stress‐time curves. Data are reported which clearly show the dependence of Kc on speed, temperature, and molecular weight. Kc is the critical stress intensity factor. It has also been found that the Kc experimental values can be correlated with a peculiar feature of the fracture surface for the determination of the intrinsic value of Kc/1 by the use of both the Dugdale model and a simple graphic correlation.
Poly (alpha‐methylstyrene) as a processing aid for rigid poly (vinyl chloride)
Authors: Wilson A. P. , Raimondi V. V. 
Published: December 2004

AbstractPoly (alpha‐methylstyrene) (PAMS) is a new approach to process improvement in rigid poly (vinyl chloride) (PVC)—the use of a low molecular weight polymer as a process aid. PAMS can reduce fusion time, melt viscosity and improve heat stability of rigid PVC compounds. The reduced melt viscosity allows the addition of fillers to PVC without adverse effect on extrusion rates. This polymer also improves the resistance to melt fracture and shear “burning” at high shear rates. When used within the optimum concentration range, physical properties such as tensile strength, Izod impact and heat distortion are maintained. In addition, PAMS gives, improved production rates in both pipe extrusion and injection molding processes without sacrifice in properties.
The appearance retention properties of poly (vinyl chloride) compounds during weathering
Authors: Isner James D. , Summers James W. 
Published: December 2004

AbstractDamage to poly (vinyl chloride) (PVC) compounds due to thermal degradation during processing has an important influence on its subsequent weatherability. High melt temperatures and/or high residence times cause white PVC to become more yellow and colored PVC to fade and bleach more upon weathering. If high melt temperatures are used, then short residence times are needed to maintain excellent weatherability. In addition to careful consideration of extrusion conditions, stream‐lined equipment is necessary to produce extrudate of uniform thermal history. Also, relatively high thermal stabilizer levels help reduce thermal damage and, therefore, improve weatherability. Impact resistance is better retained when processing occurs at higher melt temperatures. A reasonable compromise between extrusion rate and temperature must be reached to provide for adequate color and impact retention.