bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on wire coating extrusion. I. The rheology of wire coating extrusion
Authors: Han Chang Dae , Rao D. 
Published: December 2004

AbstractWire coating extrusion was studied, both experimentally and theoretically, using a pressure‐type die. For the experimental study, a wire coating apparatus of laboratory scale was constructed, consisting of a pay‐off device, extruder, cross‐head and pressure‐type die, cooling trough, and take‐up device. The materials used were low‐ and high‐density polyethylenes and thermoplastic rubber. The following measurements were taken during the experiments: (1) the axial pressure profiles in the die, (2) melt flow rate, and (3) take‐up speed. The measurements were then used to determine the effect of the rheological properties of the polymers on the performance of the wire coating operation. It was found that a reduction in axial pressure gradient and a reduction in the recoverable elastic strain of a molten polymer at the die exit can be realized as the speed of the wire is increased. For the theoretical study, using a power‐law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymer being extruded. Solution of the system equations permitted us to predict the velocity profile and shear stress distributions of a molten polymer inside a pressure‐type wire coating die.
Penetration mechanics of textile structures: Influence of non‐linear viscoelastic relaxation
Authors: Roylance David , Wang Su Su 
Published: December 2004

AbstractA numerical simulation of ballistic impact and penetration on woven textile panels is described which can easily incorporate a wide variety of realistic constitutive and fracture models. The use of this model in assessing Viscoelastic relaxation effects is illustrated, and is further extended to include non‐linear Viscoelastic effects. Since a variety of non‐linear models is presently available and there is insufficient evidence to indicate the superiority of any single one in this instance, the Eyring non‐linear model was chosen arbitrarily to indicate the ease with which these models may be implemented into the numerical treatment. The results obtained using the non‐linear model are compared with comparable computer experiments using linear elastic and linear Viscoelastic models.
Analysis of non‐linear stress relaxation in polymeric glasses
Authors: Matsuoka S. , Bair H. E. , Bearder S. S. , Kern H. E. , Ryan J. T. 
Published: December 2004

AbstractNon‐linear stress relaxation data were obtained for polycarbonate and polystyrene as a function of temperature, strain magnitude and thermal history. Data were analyzed according to the previously proposed free volume model to account for the shift of relaxation times with strain and thermal history. The result of the analysis is shown to be in close agreement with the tensile stress‐strain data. The yield phenomenon is analyzed as a rate dependent strain‐induced glass to rubber transition.
Linear and non‐linear viscoelastic behavior of poly(methyl methacrylate) in the hard region
Authors: Koppelman J. , Hirnböck R. 
Published: December 2004

AbstractThe relaxation behavior of poly(methyl methacrylate) in the hard region is caused by hindered rotations of the methoxycarbonyl side groups of the molecules. Measurements of the Young's modulus and the shear modulus at different frequencies, temperatures and strains lead to the following conclusions: each moving side group is surrounded by the elastic matrix of mean chains, The elasticity of this matrix depends on volume and temperature. Also the activation energy of the moving side group depends on volume and temperature, because the activation energy is the sum of an intramolecular and an intermolecular component. Due to the statistical entanglement of the molecules, the intermolecular contribution to the activation energy has a statistical distribution depending on volume. The reaction rate theory is of value for interpreting the viscoelastic behavior in the linear and non‐linear range if several considerations are followed.
Structural heterogeneity of suspension poly(vinyl chloride) resins
Authors: Krzewki Rudolf J , Sieglaff Charles L. 
Published: December 2004

AbstractMorphology of poly(vinyl chloride) resin particles formed by suspension polymerization was investigated by a combination of several techniques. Significant differences were found in the internal structure of resins obtained under different polymerization conditions. Five main types of resin particles with different porosity and absorptivity were identified by scanning electron microscopy. Three methods were employed to characterize porosity and structural heterogeneity of resin particles: density fractionation of resin particles in mixtures of methanol and carbon tetrachloride; absorption of silicone oil and dioctyl phthalate by resin particles; and examination of fractured particles embedded in epoxy resins. All three methods gave consistent results and can be used for semiquantitative characterization of resin structural heterogeneity. Different particle structure and degree of resin heterogeneity: can profoundly affect compounding and processing operations.
Relationship of poly(vinyl chloride) stability to flow
Authors: Collins Edward A. 
Published: December 2004

AbstractThe effect of molecular weight and polymerization temperature on thermal stability is critically examined. The concept of flow‐stability is introduced as a new method of evaluating the thermal stability of poly(vinyl chloride). In the processing temperature range 200 to 220°C, the viscosity decreases by a factor of two while the thermal stability decreases by a factor greater than three.
Composites with planar reinforcements (flakes, ribbons)—A review
Authors: Rexer J. , Anderson E. 
Published: December 2004

AbstractUnlike fibers, planar reinforcements, such as flakes and ribbons, provide reinforcement in two directions. If such reinforcements are arranged parallel to their principal plane in a composite material, they thus provide a distinctly higher performance than fiber reinforcements for two‐dimensional loading conditions. This higher performance amounts to about a factor three for the Young's modulus and a factor two for the tensile strength. However, in spite of this obvious advantage, composites with planar reinforcements are as yet relatively unknown. This is mainly due to the fact that planar reinforcements are not as readily available as fiber reinforcements and therefore not much work has been done on them. The present article gives first a short outline of the theory of the elastic and tensile properties of composites with planar reinforcements. Then, a non‐exhaustive review is presented of the work on composites with planar reinforcements, with particular attention given to recent developments. A final aim of this article is that by showing the merits of planar reinforcements as compared to presently existing fiber reinforcements, it may contribute to their use in the design of composite structures.
Application of small system thermodynamics to polymer molecules. II. Secondary nucleation
Authors: Lindenmeyer P. H. , Beumer H. , Hosemann R. 
Published: December 2004

AbstractStatistical mechanical methods can be used to relate not only structure and thermodynamics but also structure and kinetics. Methods are developed for calculating the crystal growth rate kinetic models. When the usual macroscopic thermodynamics are applied, the resulting surface energies, σ and σe extracted from the experimental growth rates are quite comparable to those obtained from kinetic models. However, when one applies small system thermodynamics, a substantially smaller σ is obtained. This latter assumption has the advantage of explaining why extended chain seed crystals do not promote crystal growth and why folded chain crystals grow on such seeds. The statistical mechanical methods in both of these cases predict the observed decrease in the rate constant, Kg with decreasing molecular length without the necessity of a separate theory for varying σe with molecular length.
Dynamic mechanical and broad line nuclear magnetic resonance behavior of some aromatic polyamides
Authors: Frosini V. , Levita G. , Butta E. 
Published: December 2004

AbstractThe results of dynamic mechanical and broad‐line proton magnetic resonance studies carried out over a broad, temperature range on a series of aromatic polyamides are presented. At temperatures lower than 300 K, the NMR data show no relaxation for the all‐meta linked benzene rings polyamide, whereas processes for the other polyamides are found, the magnitude of which is dependent on the polymer structure. Between 400 and 500 K further decreases in the second moment take place for all materials. Two secondary mechanical loss peaks are evident in these polymers, one in the 200‐380 K region (β) and one in the 380‐500 K region (β*), at about 104 cps. In particular, the relaxation strength of the β* peak depends on the conditions of isolation of the polymers from solution. The results are discussed in terms of possible motional processes of these polymers characterized by a long range intramolecular uniaxial order. An attempt is made to correlate the relaxational properties of aromatic polyamides to the existence of a phase of low regularity such as the nematic or smectic mesophases.
Geometry design of a coat‐hanger die with uniform flow rate and residence time across the die width
Authors: Matsubara Yutaka 
Published: December 2004

AbstractThis article provides an approximate but sufficiently practical method of geometry design of a coat‐hanger die having both uniform flow rate and residence time across the full width of the die. Such a die is often needed when a heat‐sensitive resin such as poly(vinyl chloride) is sheeted, because different residence times across the die width are apt to cause a sheet defect in the transverse direction of the sheet. Although some assumptions were made facilitating mathematical analysis, an application of this method to a sheeting die 1 m wide gave good uniformity of flow rate and residence time.
A method for the determination of the internal particle structure of poly(vinyl chloride) suspension resins by analyses of vinyl chloride desorption rate data
Authors: Daniels C. A. , Longeway G. D. 
Published: December 2004

AbstractA method has been developed for analyzing the vinyl chloride desorption rate data from poly(vinyl chloride) resins. This technique, based on Fickean diffusion kinetics already demonstrated for this system, yields fundamental internal particle morphology information, which is in agreement with that determined by other methods. The approach detailed in this manuscript can be applied to other particle‐penetrant systems for which the nature of the diffusion kinetics is known.
A study of chain‐addition polymerizations with temperature variations. IV. Copolymerizations—Experiments with styrene‐acrylonitrile
Authors: Sebastian D. H. , Biesenberger J. A. 
Published: December 2004

AbstractFree‐radical copolymerizations were studied under nonisothermal conditions with emphasis on their thermal runaway and ignition behavior. Computational models are presented in generalized form and compared with experiments on the system styrene‐acrylonitrile. A new, useful method is proposed for the evaluation of runaway parameters from scant kinetic data.
Processability of raw elastomers and its relation to deformational and failure behavior
Authors: Nakajima N. 
Published: December 2004

AbstractA method was proposed for a scientific description of processability of raw elastomers involving a master curve representing deformation behavior and a failure envelope representing the ultimate properties. When a specific machine is given, the mechanical and environmental conditions may be defined from the geometry and operating condition of the machine. Matching these conditions, specific information on processability may be extracted from the master curve and failure envelope. In constructing the master curve, we have proposed to use the strain‐time correspondence principle including the behavior at both small and large deformation. The necessary measurements may be considerably simplified; for example, the Rheovibron and the Mooney rheometer provide necessary data over the entire range of the rubbery behavior. The latter instrument may be operated at a slow speed, i.e., 0.05 RPM and the torque‐rise curve is used. With the rotational viscometer, the stress often reaches a maximum before reaching steady state, particularly with rubbers. We have shown that the curve leading to the peak is the shear stress‐strain curve. The maximum was found to correspond to the failure point in the tensile deformation. The stress‐time correspondence principle is not applicable to some rubbers. In these cases, the same calculation may still be conducted to evaluate the deviation from the master curve. Then, the extent of deviation may be used to represent the degree of long chain branching.
Poly(ethylene terephthalate) nucleation as studied by shrinkage of film of low orientation level
Authors: Adams G. C. 
Published: December 2004

AbstractPoly(ethylene terephthalate)s of weight average MW 74,000 and 30,000 have been uniaxially stretched, cooled under restraint, reheated, and shrunk unrestrained. Five stretch temperatures between 80 and 120°C and elongations up to 280 percent have been employed. Density and wide‐angle X‐ray diffraction results indicate conventional crystallization to have occurred only for the highly oriented samples, e.g., stretching above 200 percent at 90°C. The majority of stretching conditions studied produced only nucleated polymer. A sensitive, qualitative measure of nucleation is the degree of stretch imposed. Sufficiently high stretch temperature and low stretch rate lead to negligible nuclei formation. Nucleation in stretched, unshrunk films correlates with relatively high shrinkage, low orientation, low density and the absence of crystallinity until after the film has been shrunk. Crystallization on the other hand correlates with relatively high density, relatively low shrinkage and high orientation.
Scaleup factors of tubular emulsion polymerization reactors
Authors: Vatanatham T. , Forsyth T. H. 
Published: December 2004

AbstractThis paper examines the important dimensionless numbers that control emulsion polymerization in a tubular reactor. It was found that the activation energy of polymerization was of major importance, while the role of monomer diffusion was not very significant. By selecting certain combinations of the dimensionless numbers, changes occurring during scaleup from a small tubular diameter to a larger diameter can be approximated.
Elastic moduli of the crystalline regions in the direction perpendicular to the chain axis of ethylene‐vinyl alcohol copolymers
Authors: Nakamae Katsuhiko , Kameyama Masao , Matsumoto Tsunetaka 
Published: December 2004

AbstractIn order to clarify the crystal structure and intermolecular cohesion forces of ethylene‐vinyl alcohol copolymers (EVA), the elastic modulus (Et) of EVA copolymers was measured. We proposed that EVA copolymers are crystallizable over the entire range of copolymer composition and can produce, an isomorphous crystallite. On the basis of these crystal structures, the value of Et was expected to be dependent on the copolymer composition. Et values are indeed closely dependent on composition and decrease with decreasing VA segment. From the anisotropy of Et for (100) and (002) planes, which means the anisotropy of the intermolecular interaction, the direction of hydrogen bonding seems to be in the a‐axis direction.
Order‐disorder transitions in the extrusion of fiber‐filled poly (ethylene terephthalate) and blends
Authors: Wu Souheng 
Published: December 2004

AbstractOrder‐disorder transitions occur in fiber orientation and distribution during extrusion of fiber‐filled poly (ethylene terephthalate) and its blends with other polymers. Associated with these transitions are three characteristic regimes of extrudate surface morphology, cross‐sectional structure and fiber distribution. Low wall shear rates result in a “smooth porcupine” surface, polygonal cross section, and uniform fiber distribution. Medium wall shear rates produce a “rough porcupine” surface, irregular cross section and tubular depletive fiber distribution with fibers depleting at a relative radial position r/R of 0.63 and accumulating at the surface and the axis. This is exactly opposite to the tubular pinch effect observed for neutrally buoyant rigid spheres which accumulate at r/R of 0.63 and deplete at the surface and the axis. High wall shear rates give a “shorn porcupine” surface, rounded or distorted polygonal cross section and radial migration of fibers toward the axis. The extant of disorder decreases with increasing pseudoplasticity, of the fluid, suggesting that the characteristic fiber orientation, distribution and transitions arise from normal stress effect and/or the eccentric rotation of fibers dictated by the complex velocity profile of the flowing fluid. These phenomena have not been previously reported.
Award address formation and properties of network polymeric materials
Authors: Gillham John K. 
Published: December 2004

AbstractA general model for thermosetting materials which relates polymerization to properties is discussed. In particular, a phase diagram relates the four states of matter encountered (i.e., liquid, rubber, ungelled glass and gelled glass) to gelation and vitrification phenomena. The model is extended to rubber‐modified thermosetting systems to show that, by control of the time to gelation, a given chemical formulation can provide different morphologies and hence different material behavior. The principal experimental approach uses a torsional braid analyze (TBA), an automated version of which is described. Use of the technique to measure gelation and vitrification times is discussed.
Pyrolysis‐molecular weight chromatography‐vapor phase infrared spectrophotometry: An on‐line system for analysis of polymers—a review
Authors: Kiran Erdoǧan , Gillham John K. 
Published: December 2004

AbstractAn instrumental system consisting of a combination of a programmable pyrolyzer, a thermal conductivity detector, a mass chromatograph, a gas chromatograph, a fast‐scan vaporphase infrared spectrophotometer and a computer is reviewed with examples which show the utility of the system in the analysis of decomposition phenomena in polyolefins, polyolefinsulfones, polymethacrylates, polystyrenes, and polybutadienes. The system records the thermal history before and during pyrolysis of the sample and provides chromatographic retention times, infrared spectra, mass numbers and relative amounts of the volatile products of pyrolysis. Identification of the constituents is thus facilitated and mechanisms for decomposition become easier to estimate and verify.
Viscoelastic properties of epoxy polymer concrete
Authors: Tolbert R. N. , Hackett R. M. 
Published: December 2004

AbstractThe viscoelastic nature of polymer concrete was investigated utilizing an epichlorohydrin/bisphenol A‐type epoxy resinaggregate system. Compression specimens were tested for linearity of viscoelastic behavior, the effect of size of mass on creep, and for determination of the specific creep compliance and the associated elastic modulus. The creep compliance was determined by least squares curve fitting of the experimental creep data. Collocation, a numerical Laplace transform inversion routine, was used to develop the equation for the relaxation modulus.
A new technique for determining the oxidative stability of molten polymers
Authors: Trizisky J. D. 
Published: December 2004

AbstractA new method and apparatus for determining the oxidative stability of molten polymers, especially polyolefins, is described. The apparatus consists of a laboratory scale mixer modified to allow for the continuous determination of the oxygen absorbed by the polymer. The oxygen uptake curve observed for polyolefins is of the type normally associated with the autocatalytic oxidation of hydrocarbons and yields an induction period—a traditional measure of stability. Typical results from experiments concerning the antioxidant type, antioxidant level and temperature on polyethylene stabilization are presented to illustrate the usefulness of the technique in both quality control and research applications.
An approach towards the reduction of sink marks in sheet molding compound
Authors: Smith Kenneth L. , Suh Nam P. 
Published: December 2004

AbstractSink marks are shallow depressions normally observed above reinforcing ribs in molded Sheet Molding Compound (SMC) parts. In this paper, the effect of mold geometry, particularly the rib entrance shape, on the flow pattern of molding compound and the resulting sink marks in molded parts is presented. Flat plate specimens with a single reinforcing rib in the center were used in this work. Rib entrance shape was varied and its effect on both sink depth and fiber orientation measured. A reduction in sink depth from 0.0007 in. to less than 0.0001 in. was observed when comparing rounded and protruding rib entrances, respectively. The effect of inducing unequal flow rates from the two sides of the rib was also investigated and found to give a reduction in sink depth of about one‐third. A computer simulation of the flow during molding was, used to compare observed flow patterns with simple theoretical predictions. The SMC was modeled as a highly viscous Newtonian fluid and finite difference methods were used to solve the Navier‐Stokes equations. Extension of this modeling procedure to more complex geometries will aid in the design of nearly sink free molds.
Application of a chemical group contribution technique for calculating solubility parameters of polymers
Authors: Ahmad Husain , Yaseen M. 
Published: December 2004

AbstractA chemical group contribution technique, based on the principle of additivity of molar attraction constants for groups in a molecule, has been used for determining the solubility parameters for several polyesters, polyethers and a few other types of polymers. The solubility parameter for a polymer is calculated by using the contributions for chemical groups reported in the literature with the resultant values found to compare favorably. For geometrical isomers of polymers, the calculated solubility parameters are identical but differ for positional substitution.
The confined chain approach to the deformation behavior of bulk polymers
Authors: Gaylord Richard J. 
Published: December 2004

AbstractA theoretical “two wall” model of polymer chains confined between a pair of infinite parallel walls is developed to represent the amorphous regions in filled or reinforced elastomers, block copolymers and semicrystalline polymers. The free energies of the various types of confined chains are determined using statistics which incorporate nearest‐neighbor interactions. The stress‐strain, tensile ii odulus and swelling properties of the individual chains as a function of chain contour length and temperature are discussed. A mean field, free energy expression is used to account for interactions between confined chain segments: The free energy due to the direct interaction between the walls is given by a van der Waals potential. The equilibrium wall separation of the two wall model is determined as a function of the number of each type of chain, chain contour length and temperature. The two wall model is shown to display several deformation phenomena, including: yield, stress softening; draw; stress hardening; the Mullins effect; set; and crack or craze propagation.