bluuebunny/crossref_metadata_2025_split huggingface dataset:
A field equation for the distribution of striation thickness from impingement mixers
Authors: May H.‐O. 
Published: April 2004

AbstractThe striation thickness distribution for an impingement mixer is calculated applying the methods of computational fluid dynamics (CFD). The description is based on the three‐dimensional flow field equations together with a two‐equation turbulence model so that no assumption of the residence time distribution is necessary. A field equation is derived in order to describe the striation thickness where the stretching velocity is calculated using the statistical theory of turbulent diffusion. The distribution of striation thickness follows from the solution of this field equation.
The effect of cure cycle of unsaturated polyester resin on the temperature and conversion profiles
Authors: Alperstein D. , Narkis M. , Siegmann A. 
Published: April 2004

AbstractTemperature and conversion profiles during hot curing of an unsaturated polyester resin were studied. It was found, unexpectedly, that the reaction exotherm was largest in the outer layer close to the hot mold surface and least in the center core. The opposite was true for room temperature curing with a different initiator system. Comparison of the experimental results with heat transfer calculations has led to the conclusion that the kinetic character of cure across the polyester slab thickness was location‐dependent. The variation with location was interpreted in terms of diffusion of the initiator components from the core towards the surface owing to their faster depletion close to the hot surface and the imposition of a temperature profile. Simulation of the experimental results was possible by combining the heat transfer equation with a kinetic equation accounting for an inhibitor induction time and a modified Arrhenius equation containing a location‐dependent activation energy.
Mechanical properties of rotationally molded nyrim
Authors: Harkin‐Jones E. , Crawford R. J. 
Published: April 2004

AbstractRotational molding is used primarily for the manufacture of products from powdered plastics. However, there are many advantages to be gained from the use of a liquid plastic feedstock. This paper describes the results of an investigation to study the effect of process variables, such as mold temperature, on the morphology and mechanical properties of parts manufactured by the rotational molding of a reactive liquid nylon, caprolactam plus a diol. Initial mold temperature has a significant effect on the degree of crystallinity, levels drop off sharply at mold temperatures in excess of 140°C, while spherulite size increases after this point. Flexural properties improve with increasing degree of crystallinity while impact strength decreases. A similar trend is observed in moldings containing fillers. A brief study of water uptake and dimensional stability of molded parts is also described.
The effects of powder morphology on the processing of auxetic polypropylene (PP of negative poisson's ratio)
Authors: Pickles A. P. , Alderson K. L. , Evans K. E. 
Published: April 2004

AbstractWith the use of a three‐stage thermal processing route, similar to that used previously for the production of ultra high molecular weight polyethylene possessing a negative Poisson's ratio (i.e. displaying auxetic behavior), an auxetic form of polyethylene has been fabricated. The polypropylene is processed by the compaction, sintering, and extrusion of a powder. The importance of powder morphology on the ability of polypropylene to achieve auxetic behavior has been examined, revealing that particle shape, size, and surface roughness are critical variables for successful processing. Negative Poisson's ratios of up to −0.22 at 1.6% strain have been obtained. The data have been successfully interpreted by use of a simple geometric model based on the polymer microstructure. These suggest that, by further optimizing the processing conditions, much larger negative Poisson's ratios should be achievable.
Devolatilization: A critical sequential operation for in situ compatibilization of immiscible polymer blends by one‐step reactive extrusion
Authors: Hu Guo‐Hua , Sun Yi‐Jun , Lambla Morand 
Published: April 2004

AbstractThe main objective of this study was to show that an efficient removal of residual monomers is very important for in situ compatibilization of immiscible polymer blends by one step reactive extrusion. One‐step reactive extrusion means that when compatibilizing two immiscible polymers with one polymer containing potential functional groups and the other being chemically inert with respect to these functional groups, functionalization of the chemically inert polymer and its subsequent interfacial reaction with the functional polymer are accomplished in a single extrusion process. Two model blend systems were chosen: polypropylene/poly(butylene terephthalate) (PP/PBT) and high density polyethylene/polyamide 6 (HDPE/PA6). A co‐rotating intermeshing twin screw extruder was used to process these blends. Glycidyl methacrylate (GMA) and maleic anhydride (MA) were used to functionalize PP and HDPE, respectively. Results showed that the mechanical properties of both blends in terms of elongation at break and impact strength were improved to a much greater extent with up‐stream devolatilization compared with down‐stream devolatilization.
Competition between textural transitions and pressure effects on the viscosity of thermotropic liquid‐crystal polymers
Authors: Izu Pilar , Eugenia Muñoz M. , Peña Juan José , Santamaría Anton 
Published: April 2004

AbstractSteady measurements in capillary and slit dies and transient experiments in a cone‐plate system are presented for two thermotropic copolyesters, X7G® and Vectra A950, and a thermotropic copolyesteramide, Vectra B950. The wide shear rate range covered, from 10−2 to 104 s−1, allows us to observe the three regions defined by Onogi and Asada (1). However, the copolyesters on one hand, and the copolyesteramide on the other, show different rheological behavior that can be summarized as follows: For X7G® and Vectra A950: i. higher viscosities in slit than in capillary die flow; ii. upward‐concave pressure profiles in slit die flow; iii. overshoot peaks in transient experiments at a shear strain γM = 2. For Vectra B950: i. lower viscosities in slit than in capillary die flows; ii. linear or slightly convex pressure profiles in slit die flow; iii. overshoot peaks in transient experiments at a shear strain of γM = 180. These seemingly contradictory results are explained by the competition between the texture changes along the flow (a transition from a worm texture to a flow‐aligned region) and the pressure effect on viscosity.
A temperature rising elution fractionation study of short chain branching behavior in ultra low density polyethylene
Authors: Karoglanian Serop A. , Harrison Ian R. 
Published: April 2004

AbstractThe properties of ultralow‐density polyethylenes (ULDPE) have been studied using temperature rising elution fractionation (TREF) as both an analytical and preparative process. TREF was employed to determine the short chain branch distribution and to fractionate the polymer into fractions that enabled further properties studies, including carbon‐13 nuclear magnetic resonance, differential scanning calorimetry, dynamic mechanical thermal analysis, density gradient studies, gel permeation chromatography, analytical TREF, and some simple tensile tests. The results of these studies are reported here.
Mechanical and morphological behavior in polystyrene based compatible polymer blends
Authors: Chun Byoung Chul , Gibala Ronald 
Published: April 2004

AbstractMechanical and morphological behavior of polystyrene (PS) based compatible polymer blend systems were studied using a tensile tester and scanning electron and optical microscopes. Four different binary compatible blend systems were employed and characterized: PS and poly (2,6‐dimethyl 1,4‐phenylene oxide) (PPO), PS and poly(vinylmethylether)(PVME), PS and poly(α‐methyl styrene)(PαMS), and PPO and PαMS. The compositional dependence of the mechanical properties showed a synergistic effect with respect to modulus, but a negative deviation from the rule of mixtures relationship for strain at break. From the scanning electron microscope (SEM) observations, a deformation mode transition from crazing to crazing and shear banding occurs at ˜25 wt% PPO in the PS/PPO blends, as indicated by the patch and river patterns above this composition. In the PS/PVME blends, a similar transition was observed at >10 wt% PVME. The PS/PαMS blends showed brittle fracture regardless of composition. The PPO/PαMS blends showed a brittle fracture for a PαMS content >25 wt%. Optical microscope (OM) observations showed that blending of PS/PPO and PS/PVME resulted in a decrease of craze density and length as the PPO and PVME content was increased. PS/PαMS and PPO/PαMS blends showed few crazes, all of which were localized near the fracture surface. The mechanical and morphological behavior can be explained using models of intermolecular interactions and entanglement density in compatible blends, respectively. Overall the mechanical property and the consequent morphological behavior were similar to the effect of antiplasticization.
Effects of particle size and rubber content on fracture toughness in rubber‐modified epoxies
Authors: Kim D. S. , Cho K. , Kim J. K. , Park C. E. 
Published: April 2004

AbstractThe effects of particle size of core‐shell rubber on the fracture toughness of rubber‐modified epoxies were investigated. Various sizes of core‐shell rubber particles, from 0.16 to 1.2 μm in diameter, were synthesized by seeded emulsion polymerization. Particle size effects were clearly seen for lower crosslinked diglycidyl ether of bisphenol A (DGEBA)/piperidine resin. Fracture toughness increased as the particle size of core‐shell rubber decreased from 1.2 to 0.4 μm. On the other hand, fracture toughness was constant in this range of particle sizes for higher crosslinked DGEBA/diaminodiphenylmethane (DDM) resin. Cavitation in the rubbery core and shear deformation in the matrix are the toughening mechanisms for DGEBA/piperidine resin, whereas cavitation is the only mechanism for DGEBA/DDM resin. Toughening effectiveness decreased with <0.2 μm core‐shell rubber particles since they are difficult to cavitate. The effects of core‐shell rubber content on fracture toughness of rubber‐modified epoxies were also examined. The optimum rubber content for maximum toughness of rubber‐modified epoxies decreased with decreased particle size of core‐shell rubber in shear deformable DGEBA/piperidine resin. But the fracture toughness of rubber‐modified DGEBA/DDM resins increased as the rubber content increased.
Phase behavior, crystallization, and morphology of poly(ether ether ketone)/polyarylate blends
Authors: Krishnaswamy Rajendra K. , Kalika Douglass S. 
Published: April 2004

AbstractThe phase behavior, crystallization, and morphology of blends based on poly (ether ether ketone) [PEEK] and bisphenol‐A polyarylate [PAr] are described. This system is partially miscible in the melt. Upon quenching to an amorphous glass the system displays two glass transitions corresponding to a nearly pure PEEK phase (Tg1) and a PAr‐rich mixed phase (Tg2). The presence of the PAr has a strong retarding influence on the rate of crystallization of PEEK in the blends. Cold crystallization from the amorphous glass occurs in two stages with increasing temperature, corresponding to the mobilization of the PEEK‐rich and PAr‐rich phases, respectively. At lower cold‐crystallization temperatures (below Tg2), the immobile PAr‐rich phase constrains crystallization of the PEEK‐rich phase, as manifested in both a decreased rate of crystallization and decreased bulk crystallinity. Dynamic relaxation studies of the crystallized blends reveal two glass‐rubber relaxations originating from interlamellar amorphous populations in the PEEK‐rich and PAr‐rich phases. In the PAr‐rich phase, there is no evidence of large‐scale PAr exclusion to interfibrillar or interspherulitic regions.
Modeling and simulation of thermally induced stress and warpage in injection molded thermoplastics
Authors: Liu Shih‐Jung 
Published: April 2004

AbstractThermally induced stress and the relevant warpage caused by inappropriate mold design and processing conditions are problems that confound the overall success of injection molding. A visco‐elastic phase transformation model, using a standard linear solid for the solidified polymer and a viscous fluid model for the polymer melt, of 2‐D finite element scheme with 8 noded overlay isoparametric elements was used to simulate and predict the residual stress and warpage within injection molded articles as induced during the cooling stage of the injection molding cycle. Computed results are in good agreement with published experimental data. The approach proposed here is to examine and simulate the injection molding solidification process with the intent of understanding and resolving more inclusive and realistic problems.
The observation and origin of micro flow marks in the precision injection molding of polycarbonate
Authors: Yoshii Masaki , Kuramoto Hiroki , Kawana Takeshi , Kato Kazunori 
Published: April 2004

AbstractMicro flow marks have been found to occur in injection molding of polycarbonate. Their minimum depth is ˜ 5 nm on the mold smooth surface. Such marks seem to be formed when the molten polymer near the mold wall at the advancing front is cooled to the no‐flow temperature of resin before it comes into contact with the mold wall, preventing the precision transcription of the mold smooth surface. We investigated the molding factors affecting their occurrence by heat transfer analysis. It was found that the size of micro flow marks is related to the melt temperature, mold temperature, no‐flow temperature, thermal diffusivity of the resin, and time pitch formation of flow mark ridges and valleys. The relationships between those factors and the sizes of micro flow marks are clarified quantitatively, and the guidelines for precision transcription in injection molding are formulated.
Prediction of linear viscoelastic response for entangled polyolefin melts from molecular weight distribution
Authors: Wasserman Scott H. , Graessley William W. 
Published: April 2004

AbstractThe linear viscoelastic properties of polymer melts depend strongly and systematically on the molecular weight distribution. A molecular theory relating dynamic modulus and molecular weight distribution for linear polymers, developed and confirmed earlier with data for three other polymer species, is applied here to commercial samples of isotactic polypropylene and high density polyethylene. Experimental master curves are compared with predictions based on only the fundamental rheological parameters of the species and molecular weight distributions as obtained by the methods of size exclusion chromatography. Agreement is fairly good for the two polypropylene samples, about the same as had been found earlier for the other species, but it is highly variable for the ten polyethylene samples. We attribute this variability to differences among high density polyethylenes in the frequency, length, and type of long‐chain branching. However, we could find surprisingly little supporting evidence for this from such supposed signatures of long branches in polyethylene as the flow activation energy Ea. Measured values of Ea agreed well with the literature results for linear polyethylene; none showed the elevation in Ea that would be expected for polyethylene with long branches.
Sorption and migration of organic liquids in poly(ethylene terephthalate)
Authors: Nir M. M. , Ram A. , Miltz J. 
Published: April 2004

AbstractSorption kinetics of organic liquids in amorphous poly(ethylene terephthalate) (APET) and biaxially oriented PET (BPET) were determined at 34°C. With heptane and 1,2 propanediol, no sorption or swelling was observed. Estimated diffusion coefficients based on analysis from pseudo‐Fickian sorption data are 3.7 ± 1.0 × 10−9 cm2/sec for toluene sorption in APET, 12.7 ± 4.1 × 10−9 cm2/sec for benzyl alcohol in APET, 0.44 ± 0.4 × 10−9 cm2/sec for toluene in BPET, and 0.33 ± 0.4 × 10−9 cm2/sec for benzyl alcohol in BPET. Weight gain of sorbed APET samples at equilibrium was 11.4 ± 0.1% in toluene and 21.7 ± 0.8% in benzyl alcohol. BPET weight gain at equilibrium was 9.5 ± 0.1% in toluene and 13.5 ± 0.2% in benzyl alcohol. Subsequent migration of sorbed toluene from APET samples into water at 34°C was measured by gas chromatography. Migration from toluene‐sorbed APET films sandwiched between virgin APET layers was two orders of magnitude less than from sorbed films placed directly in water.
Improving poly(ethylene terephthalate)/high‐density polyethylene blends by using graft copolymers
Authors: Boutevin B. , Lusinchi J. M. , Pietrasanta Y. , Robin J. J. 
Published: April 2004

AbstractThe synthesis and the application of graft copolymers prepared from ozonized polyethylene (HDPE) are described. The homopolymer was treated with ozone and then copolymerized with monomers, such as methyl methacrylate, hydroxy ethyl methacrylate, glycidyl methacrylate, maleic anhydride, and ethyl acrylate. The products were used as compatibilizers in HDPE/PET [poly(ethylene terephthate)] blends. The mechanical properties and the influence of graft comonomers are described. The copolymers were characterized by the grafting rate and FTIR spectroscopy.
Three‐dimensional flow modeling of a self‐wiping corotating twin‐screw extruder. Part I: The transporting section
Authors: Goffart D. , Van Der Wal D. J. , Klomp E. M. , Hoogstraten H. W. , Janssen L. P. B. M. , Breysse L. , Trolez Y. 
Published: April 2004

AbstractA three‐dimensional modeling of the transporting elements in a self‐wiping corotating twin‐screw extruder has been carried out by using the finite element package Sepran (1). This simulation uses the 3D geometry of the channel rolled over the twin‐screw, which consists of the intermeshing and normal areas. The flow profile, the backflow volume, the pressure buildup, the shear and elongation rates, and the adiabatic axial temperature gradient have been calculated by solving the Navier‐Stokes equations and the continuity equation for a Newtonian fluid. These results are given for different extruder parameters such as the throughput of the extruder, the rotation speed of the screws and the helix angle of the screws to better understand the influence of different extruder configurations. This study belongs to a program of research on the self‐wiping corotating twin‐screw extruder that also includes the modeling of the kneading elements (Part II) and, in the future, the study of scale‐up and heat transfer.
Two‐dimensional multilayer coextrusion flow in a flat coat‐hanger die. Part 2: Experiments and theoretical validation
Authors: Puissant S. , Vergnes B. , Agassant J. F. , Demay Y. , Labaig J. J. 
Published: April 2004

AbstractIn a previous paper (1), a two‐dimensional computation model for multilayer flows in coat‐hanger dies was proposed. It was based on lubrication approximation theory and enabled us to obtain the pressure field, the streamlines, and the interface positions in the whole die. The present paper is aimed to present experimental results obtained on an industrial line for a three‐layer configuration and to compare the results to the theoretical computation. The order of magnitude of pressure drops, flow rates, and interface positions were correctly predicted by the model. Some remaining discrepancies may be explained by the isothermal assumption and the lack of encapsulation mechanism in the computation.
Chemorheological analysis of unsaturated polyester‐styrene copolymerization
Authors: Muzumdar Shailesh V. , James Lee L. 
Published: April 2004

AbstractAn important feature of free radical crosslinking copolymerization of unsaturated polyester resin (UP) ‐ styrene is the formation of a heterogeneous structure through intra‐molecular reactions and phase separation. Such structure formation affects not only the cure behavior, but also the rheological changes. The chemorheology and the effect of shear on the structure formation, as well as the rheological changes, were investigated using rheometry, electron spin resonance spectroscopy, and dynamic light scattering goniometry. Based on experimental results, a conceptual model and a simple mathematical formulation are proposed to explain the shear effect on resin viscosity changes. Predictions obtained from the mathematical model are compared with experimental results.
Effect of compression process on void behavior in structural resin transfer molding
Authors: Ikegawa Naoto , Hamada Hiroyuki , Maekawa Zenichiro 
Published: April 2004

AbstractTo realize low void content molded parts, we propose structural resin transfer molding (SRTM) with the compression process. Resin was injected with a gap height between the upper and lower halves of matched metal dies. Mold filling was performed by a squeezing motion of the upper mold die. The usefulness of the compression process was examined by comparison to a conventional SRTM method. Void distribution and bending properties in both processes were compared. The SRTM method with compression was better at driving out voids. The effects of the gap height between the upper and the lower halves of the molds and of the gap closure rate during mold closing after injection on the void distribution were examined. The gap height did not affect the void distribution. When the gap closure rate was high, the voids were expelled towards the end of cavity, whereas voids remained on the top surface of the molded parts using a small gap closure rate. The difference in void behavior due to the gap closure rate was determined by a balance of the permeability between the flow and the transverse directions.
The effect of processing variables on the formation and removal of bubbles in rotationally molded products
Authors: Spence A. G. , Crawford R. J. 
Published: April 2004

AbstractThe rotational molding processing method for plastics is steadily expanding its product range and market areas. However, a drawback of the process has always been the surface pin‐holes and internal bubbles that occur in the products because of the inherent nature of the process. In an attempt to alleviate this problem, a program of research has been carried out to investigate the factors that affect the formation of the bubbles and, more importantly, that influence their removal. This paper describes the results of the first stage of this work and covers variables such as the viscosity of the polymer melt, the nature of the pigmentation, the particle size, shape and distribution in the powder feedstock, the mold release agent, the metal used for the mold, the temperature distribution in the mold, etc. It is shown that the mechanisms of bubble formation and removal can be explained and having done this, steps can be taken to ensure that once formed, the bubbles will decrease in size rapidly. This provides significant advantages in terms of reduced cycle time and improved product quality.
Optical properties of extruded polyethylene thin films related to anisotropy and inhomogeneous microstructure
Authors: Bernabeu E. , Boix J. M. 
Published: April 2004

AbstractIn this paper a method has been developed to extend the use of the well‐known expression of Clausius‐Mosotti for inhomogeneous materials, considering their anisotropy through a series expansion based on the structural factor of nonsphericity. This is related to experimental results available from the ordinary and extraordinary refractive indices of a set of samples of low‐density polyethylene films, where such phenomena are observed. Here results are obtained which are valid for the microscopic optical response, as it is shown by the linear fitting of these general expressions, with excellent correlation coefficients. Furthermore, if we apply the Bergman‐Milton limits, we can theoretically confirm the existence of two neutral lines experimentally obtained.