bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of structural reaction injection molding process. I. Mathematical model
Authors: Malkin Alexander Ya. , Kuznetsov Victor V. , Kleba Ingo , Michaeli Walter 
Published: April 2004

AbstractA mathematical model of the infusion process in producing reinforced articles is proposed. The model is based on the analysis of flow of a Newtonian liquid inside a rectangular multilayer channel. According to the model, a liquid enters the central (feeding) layer, moves through this layer, and simultaneously impregnates peripheral layers. So, the flow is two‐dimensional. Flow inside the porous layers is treated in terms of the Darcy equation with different permeability coefficients in two directions. Principal solutions for the flow front development and pressure evolution were obtained and analyzed. Then the initial model, developed for a Newtonian liquid, is generalized for the so‐called “rheokinetic” liquid, which changes its rheological properties in time as a result of temperature variation and/or any possible chemical process, in particular, the reaction of curing of a binder. It was proven that in this case the solution is automodel. This means that the solutions obtained for a Newtonian liquid in the dimensionless form are valid for an arbitrary rheokinetic liquid.
Numerical simulation of moving free surface problems in polymer processing using volume‐of‐fluid method
Authors: Kim Ju Min , Ahn Kyung Hyun , Lee Seong Jae , Lee Seung Jong 
Published: April 2004

AbstractWe have developed a numerical algorithm based on 2D/3D finite element method for solving non‐Newtonian fluid flow with the moving free surface encountered in polymer processing. The power law model is considered as a rheological constitutive equation. The standard Galerkin finite element formulation/penalty formulation are applied to discrctize the governing equations, the volume‐of‐fluid (VOF) scheme is used to track the moving free surface, and the donor‐acceptor model introduced by Hirt and Nichols is modified and implemented on FEM. We applied the numerical scheme to simulate fountain flow and viscous buckling problems. For fountain flow, the numerical prediction of this study is in good agreement with the experimental results of other investigators. For viscous buckling, both 2D and 3D numerical simulations show that the shear thinning effect retards buckling. As this algorithm is very effective in treating moving free surface problems and requires less memory than previous algorithms, it may help solve challenging problems in polymer processing such as transient visroelastic flow simulations with moving free surfaces.
A theoretical and experimental heat of mixing study for polymer‐polymer mixtures
Authors: Taimoori M. , Modarress H. , Saboury A. A. , Moosavi‐movahedi A. A. 
Published: April 2004

AbstractHeat of mixing is introduced as a guide for phase stability predictions of polymer mixtures, and an appropriate equation is presented for it. The form of this equation is a combined function of temperature and mixture composition. The capability of the presented equation has been treated qualitatively and it has been shown that all types of exothermic, endothermic, and s‐shaped or sigmoidal heat of mixing curves can be produced. Utilizing the low molecular weight analogue calorimetry method, heat of mixing was measured at two temperatures, 27°C and 37°C for three polymer mixtures—poly(styrene)/poly(vinylchloride) (PS/PVC), poly(styrene)/ poly(methylmethacrylate) (PS/PMMA), and poly(styrene)/poly(vinylacetate) (PS/ PVAc) at an entire composition range. It has been shown that excellent agreement between the results of the calculations and the experimental heat of mixing data was achieved. Using the results of analogue calorimetric measurements for phase stability studies of polymer mixtures, it was found that often, acceptable predictions can be made by this method, but they are not always completely true.
Creep and stress relaxation in methacrylate polymers: Two mechanisms of relaxation behavior across the glass transition region
Authors: Higgenbotham‐bertolucci P. R. , Gao H. , Harmon J. P. 
Published: April 2004

AbstractThis study explores the long‐term behavior of poly(methyl methacrylate), poly(ethyl methacrylate), and poly(2, 2, 2‐trifluoroethyl methacrylate) by creep and stress relaxation (SR) experiments. Dielectric analysis (DEA) and dynamic mechanical analysis (DMA) are used to measure and compare the structural relaxations associated with side group motion and with the glass transition, Tg, region. An analysis of shift factor data for creep and SR experiments reveals two modes of molecular motion in the glass‐rubber relaxation region, but the modes are less discernible than those reported previously for a series of styrene polymers. The high temperature side exhibits WLF behavior while the low temperature side exhibits Arrhenius behavior. The extent of definition of the two modes of deformation is related to the effect of cooperative α dynamics on the β relaxation process. Some discussion is presented concerning the magnitude of the activation energy for both processes and the sharpness of the transition betwen the two modes.
Pre‐melting temperature effect on the isothermal melt crystallization and multiple melting behavior of syndiotactic polystyrene
Authors: Chiu Fang‐chyou , Shen Kuan‐yeu , Tsai Stanley H. Y. , Chen Chien‐ming 
Published: April 2004

AbstractThis work examined how pre‐melting temperature (Tmax) affects the isothermal melt crystallization kinetics, the resulting melting behavior and crystal structure of syndiotactic polystyrene (sPS) by using differential scanning calorimetry (DSC), polarized light microscopy (PLM) and the wide angle X‐ray diffraction (WAXD) technique. Experimental results indicated that raising Tmax decreased the nucleation rate and the crystal growth rate of sPS. The Avrami equation was also used to analyze the overall crystallization kinetics. The Avrami exponent n and rate constant K were determined for different Tmax specimens at various crystallization temperatures (Tc's). Our results indicated that the nucleation type of sPS is Tmax and Tc dependent as well. Evaluation of the activation energy for the isothermal crystallization processes revealed that it increases from 375 kJmol−1 to 485 kjmol −1 with an increase of Tmax. From the melting behavior study, we believe that the Tmax and Tc‐dependent multiple melting peaks are associated with different polymorphs as well as recrystallized crystals formed during heating scans. Moreover, the percentage content of α form in the crystals formed under different crystallization conditions was estimated through WAXD experiments.
Fusion bonding of polyamide 12
Authors: Zanetto J.‐E. , Plummer C. J. G. , Bourban P.‐E. , Månson J.‐A. E. 
Published: April 2004

AbstractThe strength of fusion bonds between polyamide 12 plaques has been investigated as a function of processing conditions, using the double cantilever beam geometry to measure the mode I critical strain energy release rate, Gc. Bonding was carried out using an instrumented press, which allowed systematic variation of the bonding time, the holding pressure, the interface temperature and the initial difference in temperature between the plaques. Gc was generally found to increase with hold time and interface temperature. However, for a given hold time, hold pressure and estimated interface temperature, the highest Gc were obtained under nonisothermal conditions, that is, when the initial temperatures of the plaques were different. Based on fractographic analysis and observations of the effect of the hold pressure, it is concluded that enhanced wetting is an important factor in the improved efficiency of non‐isothermal bonding.
Copolymerization of ethylene and 1‐decene by metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2
Authors: Kim Il , Kim Ki Tae , Lee Min Hyung , Do Youngkyu , Chung Hoeil 
Published: April 2004

AbstractCopolymerizations of ethylene with 1‐decene have been carried out by using two syndiospecific metallocenes synthesized by modifying the bridge: highly syndiospecific isopropylidene(1‐η5‐cyclopentadienyl)(1‐η5‐fluorenyl)‐dimethylzirconium (Me2C(Cp)(Flu)ZrMe2, 1) and less syndiospecific (1‐fluorenyl‐2‐cyclopentadienylethane)‐dimethylzirconium (Et(Cp)(Flu)ZrMe2, 2), in the presence of [Ph3C][B(C6F5)4] as a cocatalyst. The ethano bridged 2 compound of smaller dihedral angle showed much higher activity than 1 compound. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1‐decene comonomer is present in the feed. The compound 1 showed better comonomer reactivity than 2. The properties (Tm, density, and crystallinity) of copolymers seem not to be affected by the type of bridge of the metallocenes, and mainly depend on 1‐decene content in the copolymer.
On helical flows of polymer fluids
Authors: Jeong Jae‐Hyeuk , Leonov Arkady I. 
Published: April 2004

AbstractIsothermal and non‐isothermal steady helical flows are theoretically investigated under the assumption that the flow is fully developed in both the thermal and hydrodynamic senses. It is well known that the basic gross characteristics of steady isothermal helical flows of non‐Newtonian liquids can be found relatively easily if the flow curve (or non‐Newtonian viscosity) in simple shearing is known. Nevertheless, evaluation of more detailed viscoelastic properties in this type of flow is also sometimes desirable. These properties are shown to be exactly determined in both the isothermal and non‐isothermal cases as soon as a nonlinear viscoelatic constitutive equation is specified. Shear thinning due to fluid rotation and strong temperature dependence of Newtonian viscosity highly increase dissipative heat. This can produce significant non‐isothermal effects in intense helical flows, even when the wall temperature is kept uniform and constant. It is shown that the energy consumption in isothermal and non‐isothermal helical flows is always higher than in respective annular flows with the same flow rate. Comparisons between our calculations and available experimental data are also discussed.
Thermally stimulated depolarization currents in poly (ethyleneterephthalate‐ran‐p‐hydroxybenzoates)
Authors: D'Souza Nandika Anne 
Published: April 2004

AbstractThermally stimulated polarization (TSPC) and depolarization currents (TSDC) are measured on polyethylene terephthalate (PET) copolymerized with p‐hydroxy benzoic acid (PHB). These systems are important since they comprise components of many commercial polymer liquid crystals (PLCs). There has been some speculation about the origins of the multiple transition peaks in TSDC of PLCs and secondary peaks have frequently been designated as resulting from Maxwell‐Wagner interphase polarization. The applicability of this designation for main chain PLCs has been investigated. TSDC as a function of field strength and window polarization has been conducted and the transitions have been identified as glass transition peaks as opposed to space charge relaxations. A comparison of the TSDC current versus the polarization current (TSPC) reveals that TSPC is not generated for transitions associated with the PHB component.
Preparation of fibers with nanoscaled morphologies: Electrospinning of polymer blends
Authors: Bognitzki Mikhail , Frese Thomas , Steinhart Martin , Greiner Andreas , Wendorff Joachim H. , Schaper Andreas , Hellwig Michael 
Published: April 2004

AbstractThe aim was to prepare fibers with diameters below the micrometer range characterized by specific bulk morphologies and surface topologies. Such materials are of interest for various applications including reinforcement, sensors or filtration as well as the formation of functional tubes by the use of fiber templates. We were able to manufacture highly structured submicrometer fibers by electrospinning from ternary solutions using polylactide (PLA) and polyvinylpyrrolidone (PVP) as polymer model components. Co‐continuous phase morphologies resulted from phase separation processes taking place during fiber formation. In a subsequent step, specific surface topologies or fine pores were generated by selective removal of one of the components.
Evolution of structure in the softening/melting regime of miscible polymer mixing
Authors: Burch Heidi E. , Scott Chris E. 
Published: April 2004

AbstractStructure development in the softening/melting processing regime is investigated using the model miscible blend poly(styrene‐co‐acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA). Feed materials of four different particle sizes are compounded to study their effects upon structure development. Fourier‐transform infrared spectroscopy is used to help determine the normalized sample variance, a quantitative measure of mixing. The normalized sample variance is determined both as a function of sample size and as a function of feed particle size in an effort to assess the characteristic size scale(s) present in the blend at short mixing times. Results of these experiments indicate that the distribution of size scales in the softening regime is at least bimodal. Optical examination of pigmented mixtures reveals that this multimodality is due to the operation of the Scott/Macosko sheeting mechanism of morphology development, which was previously shown to be active in immiscible blends. This is contrary to the currently accepted laminar mixing model, which postulates the formation of a striated mixture while ignoring the softening/melting regime.
Glass‐polymer melt hybrids. I: Viscoelastic properties of novel affordable organic‐inorganic polymer hybrids
Authors: Adalja Sunil B. , Otaigbe Joshua U. , Thalacker Jason 
Published: April 2004

AbstractA novel class of organic‐inorganic polymer hybrids was developed by melt‐blending up to 50 (v/v) % [about 83 (w/w) %] tin‐based polyphosphate glass (Pglass) and low‐density polyethylene (LDPE) in conventional plastics processing equipment. The liquid‐ and solid‐state rheology of the polymer hybrids was studied under oscillatory shear flow and deformation to understand the behavior of these materials and to accelerate efforts to melt process the Pglass with organic polymers. All the materials were found to be linearly viscoelastic in the range of temperature and frequencies examined and their viscoelastic functions increased with increasing Pglass concentration. The Pglass significantly enhanced the shear‐thinning characteristics of the Pglass‐LDPE hybrid, indicating the presence of nonlinear chemical and physical interactions between the hybrid components. Morphological examination of the materials by scanning electron microscopy revealed interesting evolution of microstructure of the Pglass phase from droplets (or round beads) to elongated and interpenetrating network structures as the glass concentration was increased in the Pglass‐LDPE hybrids. Melt viscosities of the materials were well described by a simple power‐law equation and a Maxwellian (Hookean) model with three relaxation times. Time‐temperature superpositioning (TTS) of the complex viscosity versus frequency data was excellent at 170°C < T < 220°C and the temperature dependencies of the shift factors conformed excellently well to predictions from an Arrhenius‐type relation, enabling calculation of the flow‐activation energies (25–285 kj/mol) for the materials. The beneficial function of the Pglass in the hybrid system was significantly enhanced by pre‐treating the glass with coupling agents prior to incorporating them into the Pglass‐LDPE hybrids.
The effect of feeding mode on dispersive mixing efficiency in single‐screw extrusion
Authors: Elemans P. H. M. , van Wunnik J. M. 
Published: April 2004

AbstractIn the case of dry color compounds, where polymer pellets are coated with a pigment powder, the latter tends to form agglomerates during extrusion, owing to the hydrostatic pressure that prevails in the screw channels. In single‐screw extruders, this pressure is due to the Coulombic fricional transport in the solids conveying zone. The formation of agglomerates can be prevented to a considerable extent by operating the extruder in an underfed mode. This result has emerged from a study of the problems encountered when dispersing pigments in poly(butylene terephthalate) (PBT), but can also be applied in the case of numerous compounds where a fine dispersion of solids in polymers is required.
Blends of two thermotropic liquid crystalline polymers: The influence of reactions during injection molding on the phase structure and the mechanical behavior
Authors: Vallejo F. J. , Eguiazábal J. I. , Nazábal J. 
Published: April 2004

AbstractBlends of two different thermotropic liquid crystalline polymers, poly(p‐hydroxy benzoic acid‐co‐2, 6‐hydroxy naphthoic acid), VA, and poly(p‐hydroxybenzoic acid‐co‐terephthalic acid‐co‐aminophenol), VB, were obtained by direct injection molding throughout the full composition range. The blends were almost fully immiscible apart from a low degree of reaction. This, as well as the nature of the blends, probably influenced their mechanical properties. Enhanced properties were obtained both in the modulus of elasticity and in the tensile strength, at all the compositions studied, with absolute maxima at VB contents between 50% and 75%. These synergisms were mainly due to a greater orientation of the components in the blends than in the pure components.
Effect of molecular weight and branch structure on the crystallization and rheological properties of poly(butylene adipate)
Authors: Chae Han Gi , Kim Byoung Chul , Im Seung Soon , Han Yang Kyoo 
Published: April 2004

AbstractHigh molecular weight linear and branched poly(butylene adipate)s (PBAs) were prepared, and crystallization behavior and rheological properties were investigated. PBAs showed multiple melting behavior. Increasing molecular weight retarded the crystallization rate and increased the induction time for crystallization. Introducing branches to the polymer led to similar results. The Avrami exponent (n) for the linear and branched PBAs were 3.79–4.39 and 2.09–3.64, respectively. The Mark‐Houwink exponent of the PBAs was 0.554. Unlike general‐purpose polyesters, high molecular weight PBAs did not exhibit a Newtonian flow region. High molecular weight PBAs exhibited gel‐like rheological properties, producing high elasticity. The slopes of a log‐log plot of storage modulus (G′) vs. loss modulus (G″) ranged from 1.75 to 1.17, and the slope decreased with increasing molecular weight. For comparable molecular weights, the branched PBAs had higher viscosity and G′ than the linear polymers.
The dependence of rapid crack propagation in polyethylene pipes on the plane stress fracture energy of the resin
Authors: Brown Norman , Lu Xici 
Published: April 2004

AbstractThe critical temperature [CT] for rapid crack propagation [RCP] was measured in 11 polyethylene [PE] 200 mm diameter gas pipes each with different resins. The plane stress fracture energy [PSFE] in thin Charpy impact specimens of the resin was found to correlate with the CT. The higher the PSFE, the lower the CT. This result was related to the observation that the PSFE decreases as the temperature decreases. It was found that the impact energy of specimens from compression molded pipe that was remelted at 180°C gave a better correlation with the CT than specimens that were machined from the inner wall of the pipe. Consequently, it is now possible to predict the CT of a pipe by measuring the PSFE of the resin without making the pipe.
Effect of entanglement on brittle‐ductile transition in polyethylene
Authors: Kitao Koichi 
Published: April 2004

AbstractThe brittle ductile transition temperature (BDTT) of polyethylene with different degrees of entanglement density produced by crosslinking was evaluated using the Charpy impact test. BDTT was defined as the temperature at which the Charpy impact value Et changed abruptly from low to higher values. The increase in entanglement density brought about only a slight fall in BDTT, although that led to an increase in Et at ambient temperature corresponding to the occurrence of a dimple type fracture. A transition model between brittle fracture, patchwork type fracture (craze‐like) and yielding deformation, depending on the degree of crosslinking, was proposed to explain those experimental results.
An investigation on craze growth at a crack tip in polymers
Authors: Yang Ting‐Qing , An Qunli , Luo Wenbo 
Published: April 2004

AbstractA craze zone model with damage at the crack tip in polymers under creep is presented. By taking into account a power law material, time‐dependence of both craze advance and thickening at the tips of a center crack is investigated. Numerical results show that both length and thickness of the craze zone increase with time while the mean stress decreases. It is also shown that the calculated craze zone profile is coincident with previous experiments, and the size of the craze zone with a damage model is larger than that without considering damage at crack tip zone.
Thermophysical property modifications in functional polymers via lanthanide trichloride hydrates
Authors: Belfiore Laurence A. , Ruzmaikina Izolda Y. , Das Pronab K. 
Published: April 2004

AbstractFourteen water‐soluble trivalent metal chlorides from lanthanum to lutetium in the 1st‐row of the f‐block form complexes with poly(vinylamine) and increase the glass transition temperature from 57°C to well above 100°C at very low molar concentrations of the lanthanide. The large ionic radii of these hard‐acid cations allow several hard‐base amino sidegroups in the polymer to occupy sites in the first shell coordination sphere via ion‐dipole (i.e., electrostatic) interactions, which leads to microclustering of the ligands about a single metal center. The enhancement in the glass transition temperature is explained in terms of multi‐functional coordination crosslinklng. f‐Block salts induce larger increases in Tg, relative to transition metal‐complexes from the d‐block, however CoCl2(H2O)6 performs comparably to some of the more efficient lanthanides. Blends of poly(vinylamine) and trimethoxysilyl‐propylpoly(ethylene imine)hydrochloride form complexes with europium(III) and exhibit synergistic single Tg response. Since lanthanides form very stable complexes with chelating (i.e., bidentate) oxygen ligands, it is possible to increase the elastic modulus of commercially important copolymers of ethylene and methacrylic acid via Eu3+ complexation with the carboxylate anion. This claim is verified by infrared spectroscopy. Temperature and pH‐sensitive applications for drug delivery and removal of contaminants from wastewater streams should increase the utility of these lanthanide complexes.
Melt‐spun hollow fibers: Modeling and experiments
Authors: De Rovère Anne , Shambaugh Robert L. 
Published: April 2004

AbstractPolypropylene hollow fibers were prepared via melt spinning at speeds of 1000–2500 m/min. The outside diameters of the fibers were measured on‐line with high‐speed photography. The fiber formation process was modeled with momentum, energy, and two continuity equations (one for the polymer, and one for the lumen fluid). The equations were solved numerically, and the results were compared to the on‐line diameter data. Both Newtonian and viscoelastic constitutive equations were considered.