bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic simulation of microstructure and rheology of fiber suspensions
Authors: Yamamoto Satoru , Matsuoka Takaaki 
Published: April 2004

AbstractA numerical simulation method has been developed to predict the motion of fiber suspensions in various flows by using the particle simulation method (PSM), in which a fiber is modeled by an array of spheres. The hydrodynamic interaction among fibers is considered by decomposing into intra‐fiber and inter‐fiber interactions. For the intra‐fiber case, the many‐body problem is solved by calculating the mobility matrix for each fiber to obtain the hydrodynamic force and torque exerted on each sphere. For the inter‐fiber case, only the near‐field lubrication force is considered between spheres belonging to different fibers. The methodology was applied to predicting the microstructure and rheological properties of rigid fiber suspensions in simple shear flow and fiber orientation in two‐dimensional diverging flow by combining this method with the finite element method (FEM). In the former, the overshoot of suspension viscosity, due to the transient change of the microstructure, was observed in semi‐dilute to concentrated systems. In the latter, the calculated fiber orientations agreed with expectations of theory.
Generation of microcellular polyurethane foams via polymerization in carbon dioxide. I: Phase behavior of polyurethane precursors
Authors: Parks Kristen L. , Beckman Eric J. 
Published: April 2004

AbstractOn investigating the generation of microcellular polyurethane foam via reaction in carbon dioxide, we have observed that common polyurethane precursors are CO2 miscible, whereas typically fluorinated compounds or specially designed surfactants are needed to solubilize polymers in CO2. Both isocyanates and polyols are CO2‐miscible at workable pressures and temperatures and in useful concentrations to allow generation of polyurethane foams in CO2. By characterizing the phase behavior of several series of propylene oxide and ethylene oxide polyols, we have observed that the combined effects of molecular weight and hydroxyl number fix the location of the phase separation pressures. In general, lower molecular weights and lower hydroxyl mole fractions produce phase boundaries at relatively lower pressures in carbon dioxide. It also has been shown that CO2‐soluble compounds may have a com̀patibilizing effect on less CO2‐soluble materials.
Generation of microcellular polyurethane foams via polymerization in carbon dioxide. II: Foam formation and characterization
Authors: Parks Kristen L. , Beckman Eric J. 
Published: April 2004

AbstractMicrocellular polyurethane foams are generated through phase separation, which is induced by reaction‐induced crosslinking or by a pressure quench. The phase separation conditions are shown to impact the microstructure of the foams. Pore growth will occur through two mechanisms: diffusion of CO2 from polymerrich regions into the pores and also through CO2 gas expansion (boiling of liquid CO2 at reduced pressure). Higher CO2 pressures for polymerization (hence, higher fluid density) provide more CO2 molecules for foaming, generate lower interfacial tension and viscosity in the polymer matrix, and thus produce higher cell densities. Increasing the functionality of the polyurethane precursors increases the Tg of the polymer network and leads to smaller cell diameters by raising the vitrification pressure and allowing less time for CO2 gas expansion to play a role in cell growth. Higher reaction temperatures result in an increase in bulk density as the cell density remains invariant and the cell size drops. The use of the more polar fluoroform as a foaming agent results in larger cells, as it is able to plasticize the polymer network and allow for gas expansion during depressurization. A constant composition method of pressure quench results in smaller cell diameters.
The effect of composition on morphological, thermal, and mechanical properties of polypropylene/nylon‐6/polypropylene‐g‐butyl acrylate blends
Authors: Sathe Sachin N. , Srinivasa Rao G. S. , Rao K. V. , Devi Surekha 
Published: April 2004

AbstractThe effect of concentration of polypropylene grafted with butyl acrylate (PP‐g‐BA) compatibilizer on thermal, morphological, and mechanical properties of polypropylene/nylon‐6 blends has been studied. It was observed that blends with 4.8 wt% concentration of PP‐g‐BA exhibited superior mechanical and morphological properties at all the compositions of PP/Ny‐6. Attempts were made to correlate the experimental data for tensile modulus and strength with existing mathematical models.
Thermodynamics of polymer solutions and blends
Authors: Hoch Michael 
Published: April 2004

AbstractTo describe the thermodynamic behavior of binary and larger polymer blends, the Hoch‐Arpshofen model is used to describe highly asymmetric phase diagrams, and asymmetric enthalpies of mixing, where the miscibility gap and the extremum of the enthalpy of mixing leans toward one of the components. The Gibbs energy of mixing of polymer blends is described as

where z can be mole fraction, volume fraction, or weight fraction. The Hoch‐Arpshofen model contains an interaction parameter W = A + B*T independent of composition and an integer number n (2, 3, 4, …), which defines the asymmetricity of the binary phase diagram and of the Gibbs energy of mixing curve. In a binary system n defines the composition where the Gibbs energy of mixing is maximum or minimum or the composition is where the temperature of a miscibility gap is maximum or minimum. In a binary system A‐B the maximum effect occurs at An–1B. The disorder reaction in polymers is treated as a transformation temperature, and defines T0, the temperature where the ordered and disordered material is equal.
Interfacial property determination for immiscible polymer blends: A model system of polycarbonate/poly(ethylene terephthalate)
Authors: Pham Hoang T. , Sehanobish Kalyan , Rightor Edward G. 
Published: April 2004

AbstractA model system, a tri‐layer of polycarbonate/poly(ethylene terephthalate)/polycarbonate, was used in this study to investigate the interfacial properties of an immiscible polymer blend system. The model system was compression molded and quenched in three different media: ice, water, and hot water. The interfacial properties of interest were the through‐thickness residual stress profiles and the interfacial strength. A method of estimating the interfacial strength of an immiscible polymer blend was also proposed, enabling the prediction of failure. The method was based on a single‐notch 4‐point bending test. The load at which failure occurred was then analyzed using finite element stress analysis to resolve the interfacial stress, i.e., the strength of the interface.
Effects of amorphous nylon on the properties of poly(butylene terephthalate) and 70/30 poly(butylene terephthalate)/nylon 6 blends
Authors: Kang Tae‐Kyu , Kim Yang , Cho Won‐Jei , Ha Chang‐Sik 
Published: April 2004

AbstractIn this work, the effects of adding small amounts of amorphous nylon (a‐nylon) on the properties of poly(butylene terephthalate)(PBT) have been studied. Miscibility and properties of PBT/a‐nylon blends were compared with those of PBT/nylon 6 blends. Blends were prepared in a twin‐screw extruder. The compositions of a‐nylon or nylon 6 were varied from 0 to 20 phr. Rheological, thermal, mechanical, and dynamic mechanical properties of the blends were examined using a capillary rheometer, a differential scanning calorimeter (DSC), a universal testing machine (UTM), and a Rheometrics Mechanical Spectrometer(RMS), respectively. The PBT showed a single endotherm around 225.4°C on the DSC thermogram at the first heating scan but exhibited a second endotherm at a temperature below that of the original endotherm at the second heating scan. When a‐nylon was added, the original endotherm was remarkably affected, but the second endotherm was not appreciably changed; i.e., the heat of fusion at the original endotherm decreased linearly with increasing a‐nylon content, meaning that the addition of a‐nylon affects significantly only the higher‐melting crystals of PBT. The impact strength of PBT was decreased with nylon 6 content but was increased with increasing content of a‐nylon. With an increase in the a‐nylon content, the tensile modulus and the flexural modulus of PBT were decreased. Of interest is, however, that the tensile strength was significantly increased with a‐nylon up to 15 phr. The melt viscosity of PBT was decreased with increasing a‐nylon content, whereas it was not significantly changed with nylon 6 addition; i.e. the addition of a‐nylon acted as a lubricant or a processing aid for PBT. The dynamic mechanical and the morphological studies showed that PBT was more miscible with a‐nylon than with nylon 6. It was also found that a‐nylon exhibited a compatibilizing effect for the PBT/nylon 6 blend of 70/30 wt% composition.
Hexafluoropropylene plasmas: Polymerization rate–reaction parameter relationships
Authors: Silverstein M. S. , Chen R. , Kesler O. 
Published: April 2004

AbstractPlasma polymerization generates thin, pinhole‐free, and highly adhering films and is often described by the ratio of power to mass flow rate (energy per mass). This research explores the relationships between plasma reactor parameters such as monomer flow rate, plasma power, and reactor pressure and the rates of polymerization, etching, and deposition. The chemical structure of the amorphous, crosslinked plasma polymerized hexafluoropropylene consists largely of similar amounts of C*‐CF, CF, CF2, and CF3 groups and some C‐C groups. A dimensionless plasma parameter (E) proportional to power and inversely proportional to flow rate cubed was derived. E, reflecting both plasma energy and residence time, was used to describe various aspects of the plasma reactions. A dimensionless exponential expression successfully described the dependence of pressure on E with a master curve. An expression for polymerization efficiency (polymer conversion) derived in part through a mass balance was also successfully related to E using an exponential master curve. The rate of deposition was described as the difference between the rates of polymerization and etching. The deposition efficiency maximum and plateau were successfully described by the difference between polymerization and etching efficiencies, each related exponentially to E. The technique used to derive parameters to describe the dependence of plasma reactions on plasma operating conditions can be applied to any monomer/reactor system.
Effect of isothermal aging on the imidization of PMR‐15
Authors: Jordan Kelvin , Iroh Jude O. 
Published: April 2004

AbstractThe imidization of polymerizable reactive mixtures, PMR‐15 has been performed in a vacuum oven at isothermal aging temperatures ranging from 65 to 200°C for aging periods of 0.5 to 2.5 h. The weight loss of the resin and chemical changes that occurred as a result of aging were monitored gravimetrically and by FT‐IR spectroscopy. Differential scanning calorimetry was used to determine the temperature at which imidization took place. Imidization was observed to commence at 65°C after long aging times, t ≥ 2.5 h and at ∼95°C at a shorter time, t ∼0.5 h. At higher aging temperatures of 135 to 165°C, extensive imidization occurred. This was shown by the dramatic increase in imide absorption bands at 1780 and 1380 cm−1. Beyond 165°C, there were no significant changes in the imide absorption bands, suggesting that imidization was nearly complete. The activation energy for isothermal aging was determined from the slope of the log of the rate of weight loss vs 1/T curve to be ∼4.5 kJ/mol and is lower than the average activation energy for imidization ∼43 kJ/mol obtained from the plot of the log of the rate of increase of the imide carbonyl peak absorption at 1780 cm−1 vs 1/T.
Use of a fluoroelastomer processing aid with non‐olefin polymers
Authors: Xing K. C. , Wang W. , Schreiber H. P. 
Published: April 2004

AbstractA die coated with fluoroelastomer (FE) has been used in the extrusion of thermoplastics other than conventional polyolefins, and including chlorinated polyethylene, polystyrene, polycarbonate, and an ionomer. Inverse gas chromatography was the source of acid/base interactions between FE and each of these matrix polymers. FE was found to be effective in reducing the apparent melt viscosity when the host polymer was acidic, or non‐interactive. With strongly interactive, basic polymers the effectiveness of FE flow modifier was anulled. These polymers may be considered as effective purging agents for extrusion equipment containing FE residues.
Mechanism of degradation of poly(vinyl butyral) using thermogravimetry/fourier transform infrared spectrometry
Authors: Liau Leo C. K. , Yang Thomas C. K. , Viswanath Dabir S. 
Published: April 2004

AbstractA TG/FTIR system was used to identify the products of thermal oxidative degradation of PVB, and also to elucidate the mechanism of degradation. This technique is useful in the kinetic analysis of fast reactions such as polymer degradation, unlike the use of a TG/GC/FTIR system, in which long retention times are needed to separate the products. A computer resolution method based on a pattern recognition technique is proposed to resolve the dynamic mixture IR spectra of the degradation products. A four‐component synthetic mixture was used to evaluate the performance of the resolution algorithm and was found to be accurate within ±5%. The method was then applied to PVB degradation. The dynamic information of PVB thermal oxidative degradation obtained by resolving the mixture IR spectra was used to elucidate the reaction mechanism and to determine the kinetic parameters. Results showed that PVB degradation in air took place at a temperature 50K lower and the overall activation energy dropped from 338 kJ/mole (in nitrogen) to 200 kJ/mole (in air) compared with the degradation in a nitrogen atmosphere.
Study of the stability of the film casting process
Authors: Silagy D. , Demay Y. , Agassant J‐F. 
Published: April 2004

AbstractA theoretical study of the film casting process has been carried out. In this industrial process, a molten polymer is extruded through a flat die, then stretched in air and cooled on a chill roll. This involves mainly an extensional flow. Between the die and the chill roll, thick edges are formed and a neck‐in phenomenon is observed. Above a critical take‐up speed, a drawing instability, known as draw resonance, may occur. In this paper, a one‐dimensional model adapted from the classical model of the fiber spinning is developed (for a Newtonian or a Maxwell fluid). The influence of the processing parameters (draw ratio, Deborah number, and aspect ratio) on geometry of the lateral free surface (the so‐called neck‐in phenomenon) is studied. An unattainable zone very similar to the one encountered in fiber spinning is predicted, which only slightly depends on the stretching geometry (initial film width and stretching distance). The onset of draw resonance is studied through the linear stability method. A stability zone, depending on the geometry of the process, the elasticity of the polymer, and the draw ratio, has been obtained. This instability is observed with simultaneous width and thickness film variations. It is proved that the aspect ratio (stretching distance divided by die width) has a strong influence on the onset of the draw resonance instability.
Fracture toughening behavior and mechanical properties of polyphenylene oxide/high‐impact polystyrene blends
Authors: Tjong S. C. , Ke Y. C. 
Published: April 2004

AbstractBlends of a poly(phenylene oxide) (PPO) with high‐impact polystyrene (HIPS) were injection molded. The static mechanical properties and fracture toughness of the blends were determined by means of the uniaxial tension, Brinell hardness and three‐point‐bending measurements. From the static mechanical test results, it was shown that the yield strength, Young's modulus and hardness values of the PPO/HIPS blends were considerably higher than those of their PPO and HIPS component polymers. Dynamic mechanical measurements indicated that the PPO/HIPS blends appear to be miscible as shown by the existence of a single glass transition temperature. Furthermore, theJintegral method based on ASTM E813‐89 procedure was used to characterize the fracture toughness of PPO/HIPS blends. TheJintegral analysis indicated that the PPO specimen exhibited the lowest fracture toughness (Jc). The PPO containing 50 wt% HIPS blend had the highestJc. SEM observations revealed that the crack growth zone of the pure PPO is relatively smooth. However, cavitation of the elastomeric particles and shear band formation were observed in the deformed zones ahead of the crack tip of the PPO with 50 wt% HIPS blend. The cavitation and shear band formation would dissipate bulk strain energy and their formation was responsible for the highestJcvalue observed in this blend.
Finite element analysis of 2‐D thermoviscoelastic responses based on the free volume theory and a recursive formulation
Authors: Lee H. H. , Chen R. S. , Cheng T. R. 
Published: April 2004

AbstractA two‐dimensional thermoviscoelastic problem is analyzed by the finite element method based on free volume theory and thermoviscoelasticity. The stresses are computed according to a shift factor; the shift factor is in turn calculated from the free volume ratio, defined as the free volume divided by the total volume. The free volume ratio depends on normal stress as well as hydrostatic pressure, in addition to temperature. The effect of hydrostatic pressure on the free volume ratio can be approached by an equivalent temperature effect. A finite element analysis is developed, in which the constitutive equations are formulated in recursive form. As a nonlinear analysis, the procedure finds the solution iteratively, using a shift factor as the convergence parameter. For poly(vinyl acetate) stress‐strain curves under several loading conditions are discussed with respect to temperature and pressure.
Effect of the crystallinity and morphology on the microcellular foam structure of semicrystalline polymers
Authors: Doroudiani Saeed , Park Chul B. , Kortschot Mark T. 
Published: April 2004

AbstractMicrocellular foam processing of polymers requires a nucleated cell density greater than 109 cells/cm3 so that the fully grown cells are smaller than 10 μm. A microcellular foam can be developed by first saturating a polymer sample with a volatile blowing agent, followed by rapidly decreasing its solubility in the polymer. In general, the cellular structure of semicrystalline polymer foams is difficult to control, compared to that of amorphous polymer foams. Since the gas does not dissolve in the crystallites (1), the polymer/gas solution formed during the microcellular processing is nonuniform. Moreover, the bubble nucleation is nonhomogeneous because of the heterogeneous nature of the semicrystalline polymer. In this paper, the effects of the crystallinity and morphology of semicrystalline polymers on the microcellular foam processing and on the cellular structure of products are investigated. First, polymer specimens with various crystallinities and morphologies were prepared by varying the cooling rate of the polymer melt. Then, the solubility and diffusivity of the blowing agent in and through specimens were studied. The specimens with differing crystallinities and morphologies were foamed and their cellular structures were compared. The experimental results agree with theoretical predictions, indicating that the crystallinity and morphology of semicrystalline polymers exert a strong influence on the foam processing and the structure of the product.
Experimental observation on entrance flow inside extrusion dies
Authors: Chang Yun‐Han , Wen Shu‐Heng , Liu Ta‐Jo 
Published: April 2004

AbstractA flow visualization technique was employed to observe the flow fields at the entrance region inside extrusion dies. Four types of solutions, i.e., Newtonian, shear‐thinning, Boger, and viscoelastic fluids, were used as test fluids. Entrance flows inside center‐fed and end‐fed dies of different configurations were examined. It was found that, even though the swirling motions appear in the entrance region of center‐fed dies, no vortex develops. Shear‐thinning behavior tends to enhance swirling, but fluid elasticity suppresses the swirling. On the other hand, vortices exist at certain end‐fed die geometries, and vortices will grow if the fluid exhibits shear‐thinning, yet fluid elasticity reduces the size of vortices. Several inlet designs effective for eliminating vortices were studied.
Viscoelasticity of rubber‐toughened poly(methyl methacrylate). Part I: Deformational behavior
Authors: Mariani P. , Frassine R. , Rink M. , Pavan A. 
Published: April 2004

AbstractViscoelasticity of a rubber toughened poly(methyl methacrylate) has been investigated both in the linear and the non‐linear range by means of tensile creep and tensile constant strain rate tests. An empirical time‐temperature‐strain reduction scheme is proposed to analyze the modulus data obtained at different temperatures and strain levels: a single master curve and relevant time‐temperature and time‐strain shift factors have been obtained. Two different thermal histories were considered for testing. It has been shown that, once aging effects can be considered under conditions where aging time elapsed before testing is the same, modulus master curves obtained from linear and from non‐linear data substantially coincide. This shows that both temperature and strain level determine the modulus master curve via their influence on a single variable: the free volume of the material.
Linear low‐density polyethylene addition to polypropylene/elastomer blends: Phase structure and impact properties
Authors: Holz N. , Goizueta G. S. , Capiati N. J. 
Published: April 2004

AbstractMorphology features and effects of particle size and composition of the disperse phase on the impact properties have been studied for the blends of isotactic polypropylene (PP)/ethylene‐propylene‐diene terpolymer and (EPDM)/linear low‐density polyethylene (LLDPE). The blend components were mixed in a twin‐screw extruder, press molded, and analyzed by scanning electron microscopy, SEM (fractured and toluene etched samples), and by transmission electron microscopy, TEM (RuO4 stained samples). TEM was most effective for the identification of component distribution and particle size measurement. An increasing degree of LLDPE and EPDM interpenetration was observed with the PE content. Not one case of a neat component separation was detected. LLDPE addition improves the EPDM dispersability, affecting mainly the larger particles. The impact properties at room temperature were especially dependent on the rubber content, whereas at low temperature the particle diameter appears to be the controlling parameter. The affect of LLDPE on blend toughness is more evident in the latter case.
A compatibilizer for a blend of polysulfone with a liquid crystalline polyester
Authors: Yang Hongli , Wu Xuqin , Li Shijin 
Published: April 2004

AbstractA ternary blend of polysulfone (PSF), a thermotropic liquid crystalline polymer (TLCP), and a compatibilizer was investigated. The TLCP was composed of terephthalic acid (TPA), m‐phthalic acid (MPA), p‐acetoxybenzoic acid (Ac‐HBA), and 4,4′‐diacetoxy bisphenyl (Ac‐BP). The compatibilizer was a block copolymer of low molecular weight polysulfone and a rigid‐rod chain. Morphological investigations showed that the TLCP in the ternary system exhibited improved adhesion and dispersion in a much finer scale than in binary blends of PSF/TLCP prepared under the same processing conditions. Differential scanning calorimetry confirmed this result. Significant improvements were seen in the values of tensile modulus and strength.