bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relation between thickness and warpage in a disk injection molded from fiber reinforced PA66
Authors: Kikuchi Hiroyuki , Koyama Kiyohito 
Published: April 2004

AbstractThe relation between warpage and part thickness was investigated for a disk injection molded from PA66 compounded with 33 wt% glass fiber. A thin disk (1.5 mm thick) showed significant warpage, of magnitude 6.5 mm, while a thick disk (5.0 mm thick) did not warp. Finite element analyses were conducted, and the experimental results were numerically reproduced with 21% accuracy. It has been found that the thickness dependence of the disk warpage originates from the thickness dependence of the buckling temperature of the disk, and that quantitative disk warpage depends on the temperature of warpage measurement. Thickness change affects the amount of warpage but does not change essential warpage characteristics of the disk, characteristics such as inherent warpage deformation geometry and qualitative fiber orientation.
The effect of heat treatment on the microfibrillar network of poly(p‐phenylene benzobisthiazole)
Authors: Cohen Yachin , Gartstein Efim , Arndt Karl‐Friedrich , Ruland Wilhelm 
Published: April 2004

AbstractMaterials exhibiting exceptional mechanical properties can be fabricated from rigid polymers. In a spinning process, an oriented solution is solidified by the action of a nonsolvent, which induces crystallization of an oriented rigid polymer. Drying and heat treatment result in the final material having the desired properties. The effect of heat treatment on the morphology of poly(p‐phenylene benzobisthiazole) (PBZT) films was studied by measurements of small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD). Films were formed by coagulation in water. The wet films were dried with supercritical CO2 to maintain an open network structure. Coagulation in water resulted in formation of microfibrils having diameter of ∼9 nm. Heat‐treatment at 600°C caused significant coalescence of microfibrils. The crystallite size was increased by heat treatment from a value that is smaller than the microfibrillar diameter indicating defects in chain packing, to a value comparable to the microfibrillar diameter.
Analysis of the thermal expansion behavior of oriented polyoxymethylene sheets
Authors: Zahran R. R. , Shenouda S. S. , El‐Tawil Y. A. , El‐Kayar A. 
Published: April 2004

AbstractThe applicability of the molecular composite model is extended to include the analysis of the thermal expansion behavior of oriented (anisotropic) polyoxymethylene. The model accounts for changes in the morphological and structural aspects of polyoxymethylene during solid state‐induced orientation. The results are reported and analyzed in terms of three‐dimensional surfaces. Apart from the effect of temperature, it has been found that the crystalline phase orientation distribution, λ, is the most crucial parameter affecting the thermal expansion behavior of anisotropic polyoxymethylene followed by the volume fraction crystallinity. The size and the geometry of the crystalline phase have negligible effects on the thermal expansion behavior of oriented polyoxymethylene. Above the glass‐transition temperature, a minimum in the transverse thermal expansion coefficient is exhibited in the vicinity of λ = 2 for volume fraction crystallinities ≤0.75. It is sufficient to align 75% of the crystallites with their c‐axis at ±10° to the draw direction, to attain the ultimate degree of anisotropy in the thermal expansion behavior of oriented polyoxymethylene sheets.
Mechanics of steady flow in coextrusion fiber spinning
Authors: Ji Ching‐China , Yang Jyh‐Chau , Lee Woei‐Shyong 
Published: April 2004

AbstractThe steady flow of isothermal bicomponent coextrusion fiber spinning has been investigated. A model has been chosen in which a Newtonian fluid and a Phan‐Thien/Tanner (PTT) fluid were considered to be the core and the skin layer, respectively. This model was adopted to study the effect on spinline velocity of an interaction between two fluids with quite different extensional rheology. The effects of the hoop stress, gravity, inertia, and surface and interfacial tensions were disregarded. Only viscous and viscoelastic forces were considered. A uniaxial extension was also assumed as the radius variation in the axial direction is small. The Newtonian fluid has been considered prone to fluctuate during melt processing while the viscoelastic skin layer has a stabilizing effect. The velocity profile was affected by the choice of two characteristic parameters: extensional and shear‐thinning parameters, as well as the viscoelastic skin flow rate ratio. Both shear‐thinning and extensional parameters play important roles in melt flow. The results show that as the draw ratio increases, the system is dominated by the extensional parameters, whereas slow drawing is dominated by shearing, in spite of the thin viscoelastic skin.
Homogeneous alkylation of poly(m‐phenylene isophthalamide)
Authors: Suzuki Kimihiro , Ikeda Isao , Yamamoto Ikuya , Okubo Mitsugu 
Published: April 2004

AbstractHomogeneous alkylation of poly(m‐phenylene isophthalamide) (PMIA) was carried out in N‐methyl‐2‐pyrrolidone. Alkyl halides such as benzyl bromide and allyl bromide were reacted with sodium‐metallated PMIA. When the Taft equation was applied to this substitution reaction, the linear relationship was apparently obtained between log k/k0 and σ*. The molecular weight of alkylated PMIA decreased by sodium‐metallation and alkylation reactions. The weight loss of PMIA derivatives on heating increased with an increasing degree of substitution of the benzyl group, but it was improved by the reaction of the unsaturated alkyl group with 1,2‐ethanedithiol.
Orientation of triblock copolymers in planar extension
Authors: Lee Helen H. , Register Richard A. , Hajduk Damian A. , Gruner Sol M. 
Published: April 2004

AbstractThree commercial styrenic triblock copolymers were subjected to planar extension in a lubricated channel die, as a model for the orientation that may occur during processing operations. Materials that contain cylinders of polystyrene show a pronounced orientation of the cylinder axis in the flow direction, as revealed by small‐angle X‐ray scattering in the three orthogonal directions. This anisotropy produces small‐strain tensile moduli that differ by a factor of 10 or more in the two in‐plane directions. A material that contains lamellae of polystyrene shows pronounced orientation of the lamellae in the plane of the sample; in particular, lamellar normals are strongly forbidden from pointing along the flow direction. For similar strains, planar extension is much more effective in orienting these materials than simple shear.
Accurate determination of a deformation measure in the screw extrusion process
Authors: Kim S. J. , Kwon T. H. 
Published: April 2004

AbstractIt is important to evaluate the deformation process accurately in analyzing mixing in extrusion. This paper discusses numerical methods to determine a representative deformation measure over the entire cross‐section of the extruder channel accurately and efficiently. Two different numerical methods are introduced to determine a deformation measure over the entire cross‐section of the extruder channel efficiently: (i) the first method based on the mapping sequence of the deformation gradient tensor; and (ii) the second method which does not require the evaluation of velocity gradient fields. These two methods are applied to the extrusion process of a single‐screw extruder and are compared with respect to their numerical accuracy. It is found that trajectories of fluid particles are difficult to obtain especially near the screw flight and barrel surface, which causes numerical inaccuracies with respect to obtaining a deformation measure. In this paper an inverse mapping method is employed to overcome such a numerical problem. For computational efficiency and accuracy, the second method was found to be more powerful compared with the first one, especially when there are singular points as in an extruder channel.
Melt miscibility in blends of polypropylene, polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene, and processing oil from melting point depression
Authors: Ohlsson Bertil , Törnell Bertil 
Published: April 2004

AbstractThe miscibility of isotactic polypropylene (PP) in blends with (a) polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene (SEBS) and processing oil, (b) poly(ethylene‐co‐propylene) (EPM), and (c) EPM and processing oil, has been studied using the method of melting‐point depression. Near equilibrium melting temperatures were determined by applying the Hoffman‐Weeks method to PP melting temperatures determined by DSC on samples crystallized isothermally for 20 h at 80, 100, 120 and 140°C. A large melting point depression was observed for PP in blends with SEBS and processing oil, suggesting that PP was soluble in the molten blends. On melting, the turbidity of the PP/SEBS/Oil blends increased, suggesting that the equilibrium melt contains two liquid phases. For PP in blends with EPM or EPM and processing oil, a melting‐point depression was not observed. The results indicate why PP/SEBS/Oil blends, within a wide composition range, formed bicontinuous interpenetrating network structures on cooling from the melt, whereas all of the blends with EPM formed solid blends with one continuous phase and one dispersed phase.
Polymer and oligomer melts: Thermodynamics, correlations, and lattice‐hole theory
Authors: Simha Robert 
Published: April 2004

AbstractWe discuss the position of lattice hole theories in the original Simha—Somcynsky formulation and modifications by Nies, Stroeks and Xie, as applied to a series of mixed systems, of the intermolecular as well as teh intramolecular type. The former encompass molecular mixtures of low and high molar mass constituents, and also composites. The latter include statistical copolymers as well as oligomers with their distinctive terminal and internal constituent groups. An important ingredient of these theories is the temperature and volume dependent hole fraction, obtained by the minimization of the configurational free energy. It has the character of a free volume quantity and is shown to bear a close relation to the free volume fraction extracted from positron probe spectroscopy. Its importance is implicit in the above applications. It is explicit in problems of phase relations and in correlations between surface tension and bulk properties of polymer and oligomer melts. Its significance for transport processes in the melt was pointed out by Utracki, and subsequently for viscoelastic processes in melt and glass, by several authors.
Droplet deformation in immiscible polymer blends during transient uniaxial elongational flow
Authors: Delaby I. , Ernst B. , Froelich D. , Muller R. 
Published: April 2004

AbstractThe deformation of dispersed droplets in immiscible polymer blends was studied in elongational flow by means of an original method based on quenching specimens elongated in the melt. Results for nearly Newtonian phases at high capillarity numbers were found to be in good agreement with the predictions of the small deformation Newtonian theory, up to relatively high drop deformations. The linear theory could be generalized to viscoelastic phases, using Palierne's theory of viscoelastic emulsions. The description of some experimental data could be improved in this way, but discrepancies due to nonlinear effects remained. Numerical simulations were carried out for different capillarity numbers in the Newtonian case and were in good agreement with experimental data. Preliminary results were also obtained for viscoelastic constitutive equations.
Influence of normal stress difference on polymer drop deformation
Authors: Levitt Leon , Macosko Christopher W. , Pearson Scott D. 
Published: April 2004

AbstractPolypropylene drops of varying viscosity and elasticity were sheared in a polystyrene matrix. Two transparent, counter‐rotating parallel disks provided simple shear flow. By adjusting the speed of one disk the drop center was fixed in the laboratory frame and deformation followed via high magnification video camera. It was found that with high matrix elasticity drops of the minor phase stretched perpendicular (x3) to the flow direction (x1). This is the first report of widening of drops in shear flow. An analytical relation was established between the second normal stress differences of the phases and degree of widening. The formation of sheets and the phenomena of widening results in a larger than affine area generation.
Viscosity ratio effects in the compounding of low viscosity, immiscible fluids into polymeric matrices
Authors: Scott Chris E. , Joung Sandra K. 
Published: April 2004

AbstractMany low viscosity, immiscible fluids are difficult to incorporate into polymer matrices because of thermodynamic immiscibility and a large mismatch of melt viscosities. In this investigation, a model system was used to determine the mechanisms and kinetics of mixing in such formulations. The model systems consisted of a series of different molecular weight polyethylenes in polystyrene. The viscosity ratio, η(polyethylene)/η(polystyrene), at 180°C and 100 s−1 was varied from 0.7 to 0.003. Phase inversion was observed during the compounding of these formulations. The phase inversion was associated with a transition from low to high mixing torque during compounding. This change was primarily due to an increase in the blend viscosity caused by the morphological transformation. The melting behavior during compounding depended on the melt viscosity of the polyethylene. A critical viscosity ratio of ≈ 0.1 exists below which softening of the polystyrene, and thus mixing of the two components, was greatly retarded. Even at very low concentrations, low viscosity polyethylene can have a significant effect on the processing behavior. Effects of mixer set temperature, degree of fill, and polyethylene particle size were explored. The roles of thermal conduction and mechanical energy input were evaluated in the melting regime of the process.
Polymer blend mixing and dispersion in the kneading section of a twin‐screw extruder
Authors: Huneault M. A. , Champagne M. F. , Luciani A. 
Published: April 2004

AbstractThis paper examines the mechanisms by which a polymer is dispersed in a co‐rotating twin‐screw extruder. An experimental investigation of the morphological evolution has been carried out on a 45‐mm co‐rotating twin‐screw extruder. Polyethylene/polystyrene (PE/PS) blends in the low concentration range (i.e., 5–15 wt% of PE) were used as a model system. The following general trends were observed. First, the minor phase right after melting is predominantly in a fibrillar form. Secondly, droplet and fiber diameter at this early stage of compounding are already in the micron or sub‐micron range. Even though a wide variety of mixing section configurations were used, the fibers created in the early compounding stages were relatively stable throughout extrusion. Morphological evolution after melting must therefore be discussed in terms of variation in the fiber fraction (i.e., fiber to droplet transition) rather than in a change in particle diameter. A control volume model for the flow in kneading blocks is used to interpret the morphological results and to predict the deformation and breakup of dispersed phase fibers under shear and in absence of coalescence. Theoretical results indicate that fiber breakup under shear is not likely in the kneading block under the normal processing conditions, which is confirmed by morphological observations made at the mixing section exit. The influence of several geometrical parameters on mixing and pumping in kneading blocks is also discussed with the use of flow model results.
A new rheometer measuring infrared dichroism in molten polymers subjected to transient and steady shear flow
Authors: Skytt M.‐L. , Färnert G. , Jansson J.‐F. , Gedde U. W. 
Published: April 2004

AbstractA rotational parallel plate rheometer that enables simultaneous measurement of the transient or steady‐state rheological properties and infrared dichroism was designed and constructed to study orientation in molten polymers. Measurements can be carried out at shear rates between 0.05 and 300 s−1 and at temperatures between 20 and 300°C. Both shear stress and axial normal force together with dichroism are continuously measured during shear flow. Infrared dichroism data for polypropylene showed excellent agreement with data obtained with a FTIR‐instrument. The Hermans orientation function for molten poly(dimethyl siloxane) at steady state showed a strong shear‐rate dependence in the region 0.1−20 s−1. Rheological data for molten poly(dimethyl siloxane) agrees with data obtained from a conventional rheometer.
New developments in the melt rheology of nylons. I: Effect of moisture and molecular weight
Authors: Khanna Y. P. , Han P. K. , Day E. D. 
Published: April 2004

AbstractPeculiar observations on the melt rheology of ultra‐dry nylon resins, nylon 6 in particular, are reported. One aspect of this study deals with a sharp increase in zero shear melt viscosity (e.g. 2 to 5 times) as the nylon 6 resin moisture is taken from 0.10 down to 0.00%; the effect being reversible. Changes of such magnitude are unexpected considering that there are no detectable variations of the chemical/compositional/molecular weight type in the starting resin, when subjected to the imposed drying conditions. Another aspect of this study deals with a deviation of nylons (6, 6,6, and 12) from the Bueche (1952) relationship, well accepted for polymers to date. Under moderate drying conditions (e.g. 50°C/17 h/110 millitorr), the molecular weight exponent is found to be 3.8, which is within the range of 3.4 to 3.8 reported for nylon 6. However, under more severe drying conditions (e.g. 110°C/17 h/110 millitorr), the molecular weight exponents for nylon 6, nylon 66, and nylon 12 are 4.8, 5.4, and 4.6, respectively. We are proposing that a sharp increase in melt viscosity of ultra‐dry nylon 6 is partly due to an increase in the molecular weight of the melt (extrudate) which then, has a more pronounced impact on melt viscosity in view of the 4.8 exponent. Such unique results, in contrast to polyethylene (free radical polymer) and poly(ethylene terephthalate) (condensation polymer) are tentatively attributed to H‐bonding in nylon melts. Yet another aspect of this study deals with the rheology of supercooled molten polymers that can offer advantages for analytical characterization.
Evidence for inversion of phase continuity during morphology development in polymer blending
Authors: Sundararaj Uttandaraman , Macosko C. W. , Shih Chi‐Kai 
Published: April 2004

AbstractWhen polymer blends are prepared from a mixture of pellets, the melting order of the components is important in determining the mechanism of morphology development. Here, we show that an inversion of phase continuity occurs during processing when a minor phase component has a softening or melting transition temperature which is lower than the softening temperature of the major phase component. Three 80:20 concentration systems were studied: polyarylate/rubber, polyamide 6,6/polystyrene, and polystyrene/ethylene propylene rubber. Initially, the minor phase was the continuous phase and coated the major phase in all three systems. As the major phase melted, a switching of phase continuity occurred, and in the final blend state, the major phase was the continuous phase. An increase in power input was required during the switching of the dispersed and matrix phases. The compounding process was studied through continuous video monitoring, torque‐temperature analysis, and microscopy of quenched samples. A continuity inversion mechanism is proposed. It is found that the initial morphology of the blend consists of sheets of the major phase inside the minor phase. These sheets break up into irregularly shaped particles, which then coalesce around the minor phase. The effects of compatibilization (using reactive polymers or adding a premade diblock) on the rheology and morphology of the blend are also investigated. Interfacial reaction is seen to delay and intensify the inversion of phase continuity, whereas addition of premade diblock does not have any significant effect. The torque increases due to interaction of the major phase domains and due to reactive stabilization of the interface against coalescence, and the contributions of each to the torque can be decoupled.
Three‐dimensional finite element analysis of polymer rotational extrusion
Authors: Tzoganakis Costas , Karagiannis Aristotelis 
Published: April 2004

AbstractA three‐dimensional finite element approach has been employed to model steady, creeping, isothermal helical flows and to study the effect of an imposed rotational field in a wire coating process and a tube extrusion process. It has been shown that the rotational field can affect process characteristics with an underlying viscous character, such as the velocity profile, pressure drop, viscous extrudate swelling, material pathlines, and deformation field. Significant pressure drop reduction may be achieved with implications on the process productivity, pressure drop reduction being most prevalent at low power‐law indices because of the increased nonlinearity in the shear‐thinning viscosity function. Extrudate swelling has been shown to be affected by the rotational field owing to the shear‐thinning nature of polymeric materials. Finally, it has been shown that significant material deformation may result from the imposition of the rotational field.
Three‐dimensional flow simulation of a film‐casting process
Authors: Sakaki Kazutaka , Katsumoto Ryuichi , Kajiwara Toshihisa , Funatsu Kazumori 
Published: April 2004

AbstractThree‐dimensional flow simulation of a film‐casting process was performed using a finite element method assuming an isothermal and steady Newtonian flow. The simulation was carried out under industrial operation conditions. The neck‐in and the edge bead phenomena could be simulated. The effects of draw ratio, air gap length, and die width on these phenomena are discussed. The neck‐in and the edge bead phenomena were affected by the draw ratio and air gap length and not by the die width. The neck‐in value, which was defined as the difference between the die width and film width at the chill roll, increased with the draw ratio and air gap length.
Ultrasonic wave attenuation during water sorption in poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Maffezzoli A. , Luprano V. A. , Montagna G. , Esposito F. , Nicolais L. 
Published: April 2004

AbstractA scanning laser acoustic microscope (SLAM) was used to measure the acoustic attenuation during water sorption in a film of crosslinked poly(2‐hydroxyethyl methacrylate) [poly(HEMA)] hydrogel. The contribution of reflection, scattering, and absorption of acoustic waves to the measured attenuation is evaluated. The analysis of a model accounting only for the possible reflection of the acoustic waves at the swollen/unswollen boundaries indicates that the time dependence of the attenuation during water sorption cannot be explained simply by accounting for the presence of two additional interfaces. A predominant contribution of acoustic wave absorption during the glass transition, occurring at the two swollen/unswollen interfaces, is assumed. Also, microvoids cannot be excluded as contributors to craze growth in the glassy matrix at the penetrant/polymer interface.