bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical analysis of residence time distribution functions and strain distribution functions in plasticating screw extruders
Authors: Lidor G. , Tadmor Z. 
Published: December 2004

AbstractThe residence time distribution (RTD) function in a single screw plasticating extruder was theoretically calculated. The calculation is based on the solids conveying, melting, and melt conveying models in extruders. The screw channel is divided into small axial increments and the path of each exiting fluid particle is followed from hopper to die. In addition to the residence times the total shear deformation or strain imposed on the fluid particles was also calculated. This together with the RTD function has led to the definition and calculation of the strain distribution function (SDF). This function is proposed for quantitative characterization of the mixing performance of screw extruders as well as other laminar mixers. Some simple idealized batch and continuous laminar mixers are analyzed in terms of the SDF. Finally, the effect of extruder operating conditions and screw design on the RTD and SDF were investigated by computer simulations.
An approach to thermodynamics of polymer flow based on internal state variables
Authors: Astarita G. , Sarti G. S. 
Published: December 2004

AbstractTwo kinds of thermodynamic theories, which seem to be applicable to polymer deformation and flow, have been developed in the recent literature. One of these approaches utilizes entropy far from equilibrium as a primitive undefined concept. The alternate kind of theory involves the idea of a quasi‐static process as a primitive concept. In this work, an approach based on internal state variables (specifically, the micro structure of the polymeric material) is used to argue that both primitive concepts are in some sense legitimate on physical grounds. In particular, the legitimacy of the quasi‐static process concept is related to the smoothness of the function delivering the rate of change of the microstructure.
Flow‐induced crystallization of linear polyethylene above its normal melting point
Authors: Tan Victor , Gogos Costas G. 
Published: December 2004

AbstractThe phenomenon of flow‐induced crystallization was investigated using a linear polyethylene above its normal melting point flowing continuously in a Biconical Rheometer. It was found that the resin crystallized in the superheated state at rates which increased with increasing shear rate and decreasing temperature. A method of analysis of the temperature dependence of the various stages of flow induced crystallization is proposed. It deals with and attempts to explain the experimental fact that a higher viscosity enhances the rate of flow‐induced crystallization in contrast to the effect of viscosity on the rate of quiescent crystallization. Some of the flow‐induced crystallization samples were transparent and exhibited a high DSC thermogram “tail”.
Cold compaction molding and sintering of polystyrene
Authors: Jayaraman G. S. , Wallace J. F. , Geil P. H. , Baer E. 
Published: December 2004

AbstractIt is the objective of this paper to demonstrate the applicability of cold compaction molding followed by a sintering treatment to the processing of polystyrene powders. The influence of pressure, compaction speed, and peak pressure dwell time on the green (as compacted) density and the green tensile strength, as well as the effect of sintering on the tensile strength and dimensional change, were evaluated. The resulting data indicate that room temperature compaction alone is insufficient to provide adequate tensile strength for the compacts. Sintering the green compacts at temperatures of 150 to 173°C markedly improves the tensile strength while simultaneously causing a thickness change in the compacts. This thickness change results from gas evolution, pore shrinkage, and viscoelastic recovery of the residual stresses induced by pressure. For compacts of 0.225 in. thickness, an optimum sintering treatment of 173°C for 30 mins is recommended to provide a tensile strength of 4,000 psi and a thickness change of less than + 7 percent. Coining (repressing) the green compacts does not appreciably affect the sintered strength. However, a finer particle size improves the sintered properties. A review of the literature on the flow behavior of polystyrene suggests that a non‐Newtonian viscous flow mechanism is followed by a Newtonian one as sintering progresses.
Transition behavior of poly(vinylidene fluoride)/poly(ethyl methacrylate) blends
Authors: Imken R. L. , Paul D. R. , Barlow J. W. 
Published: December 2004

AbstractPrevious work has shown evidence that PMMA and PEMA are miscible with PVF2. The present paper examines in detail the behavior of PEMA/PVF2 blends by thermal analysis and dynamic mechanical testing. All transitions and relaxations are affected by blond composition but in a complex manner owing to the crystallization of PVF2 from blends rich in this component. Inadequacies of the simple two‐phase picture of semi‐crystalline polymers is believed responsible for some of the transitional behavior observed here. The melting point depression observed for PVF2 was found to be consistent with an exothermic heat of mixing for this pair comparable in value to that found for PPMA/PVF2/All evidence here are consistent with the previous conclusion of miscibility for these systems.
Prediction of the onset of extrudate distortion in polyethylenes from rheological data
Authors: Smith F. P. , Darby R. 
Published: December 2004

AbstractAn extensive set of rheological data, including steady shear, normal stress, and oscillatory response functions, have been obtained for several polyethylene melts, and a modified form of the Spriggs nonlinear co‐rotational model has been used to represent the data. The resulting model was used to predict the transient stress response of the melts in a simplified model of the extrusion process, with a resulting criterion for the onset of melt distortion in terms of readily evaluated rheological parameters. The predicted occurrence of melt distortion based on this criterion agreed well with observations for the polymers in this study as well as for a variety of other polymers reported in the literature.
The preparation of ultra‐high modulus polypropylene films and fibres
Authors: Cansfield D. L. M. , Capaccio G. , Ward I. M. 
Published: December 2004

AbstractFollowing the discovery that linear polyethylene can be drawn to very high draw ratios to produce oriented fibres and films with ultra‐high initial moduli, a similar study has been undertaken for polypropylene. In particular, the modulus/draw ratio relationship has been obtained for a range of polymers of different molecular weight and molecular weight distribution. The effects of thermal history and draw temperature were studied, and it was shown that under optimum conditions material with an initial modulus at room temperature of 1.9 × 1010 Nm−2 (205 gdtex, 3 × 106 psi) can be obtained. This value is at least 50 percent greater than those previously recorded for drawn fibres and about one half of the theoretical modulus.
A review of techniques for processing ultra‐high modulus polymers
Authors: Bigg D. M. 
Published: December 2004

AbstractLinear crystalline polymers can be processed to high degrees of orientation sufficient to produce dramatic increases in tensile strength and modulus. Three processes have been identified for inducing such orientation: cold drawing, hydrostatic extrusion, and solution spinning. All three processes utilize a high elongational velocity gradient in a critical temperature range to produce a high strength crystalline morphology. Although the molecular superstructure may differ in each case, the mechanical properties are similar, An increase in strength is achieved either through the creation of new tie molecules between crystal lamellae or through the creation of an extended chain crystal substructure. Temperature and molecular weight are the prime variables in determining which morphology will develop. The optimum processing temperature for many of the specific techniques is the crystalline dispersion temperature. At this temperature, the crystal structure is particularly adaptable to forming a new crystal morphology. Ul‐tradrawn polymers are more Hookean in behavior than isotropic polymers and have properties similar to steel and glass. Polyoxymethylene has been processed most closely to its theoretical strength. Polyethylene, which is the most difficult to process, has achieved the highest modulus of any common polyolefin polymer, about 7 × 1010 Pa.
Residual stresses in polymers and their effect on mechanical behavior
Authors: So Paul , Broutman Lawrence J. 
Published: December 2004

AbstractPlates of bisphenol‐A polycarbonate and poly(methyl methacrylate) have been quenched in ice water from temperatures slightly above their glass transition temperatures. Residual stresses are thus created, Measurement of these residual stresses has been accomplished by the “layer removal” method and the stress distributions through the thickness are presented. Compressive stresses, approximately 3000 psi, exist at the surface while tensile stresses‐of at least 1000 psi exist in the interior. It is shown that these residual stresses can influence the notched Izod impact strengths for polycarbonates. The mechanism is thought to be suppression of craze initiation in advance of the notch due to the presence of residual compressive stresses for specimens notched prior to quenching. In the case of poly(methyl methacrylate), it is shown that compressive residual stresses at the surface can cause plastic yielding to occur in bending experiments resulting in permanent deformation and greater energy absorption.
Inhibitor selection for vinyl monomers by differential scanning calorimetry
Authors: Riga Alan T. 
Published: December 2004

AbstractInhibitors to prevent vinyl polymerization were selected rapidly and effectively by differential scanning calorimetry. The autopolymerization temperature (APT) and the relative polymerization rate constants were used to define the type and amount of inhibitor necessary to prevent polymerization of acrylic esters and acrylamides. The APT was also used to determine the amount of inhibitor in a vinyl monomer. The rate of polymerization and storage stability of vinyl monomers were determined by these methods.
The effect of corona and ozone treatment on the adhesion of ink to the surface of polyethylene
Authors: Stradal M. , Goring D. A. I. 
Published: December 2004

AbstractLow density polyethylene sheet was subjected to treatment by corona discharge in oxygen, nitrogen, helium and argon; in addition some sheets were treated with ozone gas. The bond strength between two similarly treated sheets was then measured using a commercial flexographic ink as an adhesive. The results showed that although surface oxidation improved both the ink adhesion and the wetting properties of polyethylene it is not a necessary prerequisite for good bonding. When the sheet was subjected to electrical discharge in nitrogen, argon or helium, considerable enhancement of ink adhesion was obtained without any detectable change in the surface chemistry of the polymer. The results indicate that ink adhesion after treatment in various gases follows closely the trends established previously in corona‐induced autohesion of polyethylene. This suggests that the mechanism of bonding is similar in the two cases.
Techniques for compounding glass fiber‐reinforced thermoplastics
Authors: Stade K. 
Published: December 2004

AbstractThe processing characteristics of various glass fiberreinforced thermoplastics (FRTP) and the basic approaches for their production are discussed. Experimental work on twostage production‐scale continuous kneaders was conducted to define the most important process variables in compounding FRTP materials. Results demonstrate how processing conditions and screw design influence the temperature profile in the kneader and the glass‐fiber length in finished products. Feed steek appearance (i.e., pellet shape and size), melt viscosity, and volume percentage of fibers are basic material variables. High quality products can be achieved through a careful, layout of the continuous kneader in order to minimize thermal degradation of the base polymer and to effect adequate dispersion of the glass fibers in the matrix.
Molecular order and orientation in aromatic polyamide fibers by internal reflection spectroscopy and wide angle X‐ray diffraction
Authors: Druschke F. , Siesler H. W. , Spilgies G. , Tengler H. 
Published: December 2004

AbstractThe results of wide angle X‐ray diffraction and, ATR polarization measurements are reported in order to characterize the anisotropy in poly(m‐phenyleneisophthalamide) and poly(p‐phenyleneterephthalamide) (Fiber B) fibers. Additional information on the state of order of the investigated fibers is derived from ATR spectroscopic accessibility measurements by deuterium exchange.
Interfacial (polymer‐substrate) failure of ultraviolet radiation curable coatings
Authors: McGinniss Vincent D. , Kah Ann 
Published: December 2004

AbstractThe development of ultraviolet radiation technology to cure or photopolymerize acrylic unsaturated monomers, oligomers, and polymers into tight network structures introduces several adhesion problems that can be related to or associated with interfacial polymer‐substrate failure. This paper discusses network formation, polymer‐interfacial growth association and failure as a function of the following variables: light intensity (effect on sol/gel conversion), photoinitiator (structurereactivity as a function of conversion), polymer shrinkage, and substrate wetting. The results of this study show that all of the above variables interact in a composite fashion to influence the final properties of the ultraviolet cured coatings.
Effect of center block structure on the physical and rheological properties of ABA block copolymers. Part II. Rheological properties
Authors: Futamura Shingo , Meinecke Eberhard A. 
Published: December 2004

AbstractThe effect of the chemical structure of the center block on the rheological properties of ABA block copolymers with polystyrene end blocks has been investigated. The chemical structure of the center blocks investigated in the present paper are polybutadiene, polyisoprene, ethylene/butene copolymer, ethylene/propylene copolymer and polydimethyl‐siloxane. The chemical structure of the center block was found to have a pronounced effect on the rheological properties of the ABA block copolymer melts. The long range relaxation times of these block copolymer melts increases with increasing incompatibility between the styrene block and the center block. However, the rheological properties of the block copolymers are not influenced significantly by the glass transition or the entanglement molecular weight of the center block.
Predicting the service life of polysulfone in steam or hot water
Authors: Dearing Rogers K. 
Published: December 2004

AbstractA quantitative definition of stress‐environmental, interactions on polymers must be made in order to designstructural parts. This definition for design urposes is best obtained by measuring creep of the plastic under constant stress and in the environment in which it is to perform. In order to measure creep in steam or hot water, a relatively simple test apparatus was devised so that clamped circular test specimens acting as a diaphragm were stressed by controlled steam pressure. Creep was measured by deflection of the diaphragm. A case history was developed with polysulfone: the allowable stress limits at various temperatures were determined; and a method developed for predicting the long time service life of the material from short time data using the Goldfein equation of state. Creep measurements over a year in steam were in excellent agreement with predicted values.
Craze and creep resistance of high‐impact polystyrene in alcohols
Authors: McCammond D. , Hoa V. S. 
Published: December 2004

AbstractIn the present state of development of the polymer industry, all of the lower cost, widely used, plastics exhibit some susceptibility to environmental stress crazing. Past developments have improved some polymers' resistance to this phenomenon (e.g., the addition of rubber to polystyrene) and this paper considers one such improved polymer, high‐impact polystyrene, and examines its craze and creep resistance in the alcohols. This family of fluids does not affect the unstressed polymer but has a marked effect when the polymer is stressed. The results of creep tests at different stresses indicate the existence of a delay time after which the creep rate accelerates rapidly. The requirement of a definitive time under stpess before this acceleration occurs is supported by the results of cyclic stress tests. Plots of delay time against stress for the different alcohols show two distinct regions: (i) at high stresses, where the delay time increases from methanol to butanol and the mechanism would appear to be one of molecular volume controlling the mobility of the fluid to “penetrate” the polymer, and (ii) at low stresses, where the delay time decreases from methanol to butanol and the criterion would appear to be that of ability to “plasticize” the polymer as evidenced by the solubility parameters.
An improved method for determining polymer melting temperatures
Authors: Predecki Paul , Karr P. H. 
Published: December 2004

AbstractA method for determining polymer melting temperatures,Tm, based on a simple modification of thermo‐optical analysis is described. The method makes use of a small, highly conducting substrate and a preselectedTm, procedure which results in rapid heating rates (∼1500°C/min) without temperature overshoot or superheating. Accuracies to within ±0.15°C are readily obtained. Application of the method to isothermally crystallized polyoxymethylene (Delrin 100 and 500) shows thatTm, increases with both time and temperature of crystallization as well as with increasing molecular weight. The potential of the method for characterizing polymer thermal history and molecular weight is discussed.
Flow visualization of fiber suspensions
Authors: Lee Wei‐Kuo , George Henry H. 
Published: December 2004

AbstractA visualization study of the flow of fiber‐filled resin through cylindrically convergent channels has been conducted. Epoxy resins filled with glass fibers were tested to simulate the flows experienced during the processing of fiber reinforced thermoplastics. Specific phenomena which have been investigated include the kinematics, orientation of the suspended fibers, formation of possible unwanted stagnant eddies at the entrance of the channel, and the fiber length degradation. It was found that the extensional flow in the convergent channel plays an important role in orienting the fibers.
Impact and yield properties of polycarbonate as a function of strain rate, molecular weight, thermal history, and temperature
Authors: Ryan James T. 
Published: December 2004

AbstractA study has been made on the impact and yield properties of polycarbonates from two manufacturers as a function of strain rate, melt flow rate, notch radius, thermal history, and test temperature. The yield stress increases with the strain rate and annealing time in exactly the way predicted by a recently proposed theory on nonlinear viscoelasticity of glassy polymers. The critical molecular weight for the transition from a ductile to a brittle break increased at higher rate of strain and also with the longer annealing times.
Two‐phase mixture—viscoelasticity and general equivalent mechanical model
Authors: Marinov Pencho 
Published: December 2004

AbstractQuasistatic viscoelastic behavior of a two‐phase mixture is discussed on the basis of simple mechanical models. The mixture consists of a viscoelastic matrix with Kelvin‐Voigt properties and elastic inclusions. The Gibbs' equation of a two‐phase mixture is derived. Finally a linear constitutive theory of a two‐phase mixture is obtained that takes into account the interaction between the phases.
Theory of mixing sections in single screw extruders
Authors: Erwin Lewis 
Published: December 2004

AbstractA discussion of the effect of deformation on mixing leads to reorientation of fluid interfaces as a proposed mechanism for special “mixing sections” in single screw extruders. Based on the kinematics of mixing it is shown how a mixing section can greatly decrease the amount of work necessary to accomplish extensive mixing through orienting the fluid more favorably for mixing by subsequent shear. Mathematical development quantitatively describes favored configurations of mixing sections. An upper bound for the mixing performance of a simple model of an extruder with special sections is shown to be similar to turbulent mixing. Based on this theory the key actions of the special sections are identified.
A simplified method for analyzing mold filling dynamics Part I: Theory
Authors: Stevenson James F. 
Published: December 2004

AbstractA graphical method based on dimensional analysis is presented for estimating the injection pressure and clamp force required for injection molding amorphous polymers to form disk‐shaped parts with a constant wall thickness. A procedure is suggested for estimating clamp force when the projected area of the mold cavity is smaller than the surface area of one side of the molded part. The results reported here are based on a numerical simulation of a power‐law fluid filling a cold mold at a constant injection rate. The dimensionless bulk temperature and the ratios of the nonisothermal injection pressure (clamp force) to the isothermal injection pressure (clamp force) are given as functions of the dimensionless cooling time τ, the Brinkman number Br which characterizes viscous heating, the power‐law exponent n, and a dimensionless temperature β which includes the inlet melt and mold wall temperatures and the temperature coefficient for viscosity.
The effect of molecular weight and weight distribution upon polymer melt rheology
Authors: Pearson G. H. , Garfield L. J. 
Published: December 2004

AbstractA major objective in polymer rheology is to predict a fluid's response to a general deformation from molecular information. A method has been developed which allows one to predict the viscoelastic properties of polymer melts from a limited amount of rheological and molecular data for the polymer. The input parameters are: (a) zero‐shear viscosity; (b) molecular weight distribution; (c) temperature and density; and (d) constants relating Graessley's relaxation time to the Rouse relaxation time. The technique then “simulates” a discrete relaxation spectrum using G′ and G″ data from the Rouse theory and finally requires that a continuum model of polymer viscoelasticity be fit to shear viscosity data predicted by Graessley's theory. Examples of the utility of the procedure are given to illustrate the role of molecular weight and weight distribution in determining rheological behavior.
Concentration dependence of zero‐shear viscosity for polymer solutions: A test of the lyons‐tobolsky equation
Authors: Rink M. , Pavan A. , Roccasalvo S. 
Published: December 2004

AbstractThe empirical equation proposed by Lyons and Tobolsky (1) to describe the concentration dependence of zero‐shear viscosity in polymer solutions was tested on a variety of data taken from the literature, covering different polymer‐solvent systems, molecular weight, temperature, and the whole concentration range. This equation was fitted to each set of experimental viscosity‐concentration data by a least squares method. The validity of this equation is verified. The dependence of the optimal values obtained for the three parameters intrinsic viscosity, [η], Huggins constant, k, and new empirical constant, b, on molecular weight, temperature, and solvent is also discussed.