bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of impingement mixing on striation thickness distribution and properties in fast polyurethane polymerization
Authors: Kolodziej Paul , Macosko Christopher W. , Ranz William E. 
Published: December 2004

AbstractImpingement mixing in a polyether polyol/butanediol/MDI, thermoplastic urethane system was evaluated using measurements of striation thickness distribution, adiabatic temperature rise, and molecular weight. Adiabatic temperature rise was less sensitive to mixing quality for this system than for the crosslinking ones previously studied. The average of the distribution of striation thickness as measured by optical microscopy on the resultant polymer decreased with increasing nozzle Reynolds numbers, Re. Molecular weight increased and its polydispersity decreased with increasing Re. Morphological data indicate better phase separation in the poorly mixed samples. These results are consistent with relatively slow diffusion for the polyol and thus the preferential formation of unattached hard segments at lower Re.
Failure modes in piezoelectric poly(vinylidene fluoride)
Authors: Kolbeck A. G. 
Published: December 2004

AbstractThis article describes a number of potential failure mechanisms for piezoelectric poly(vinylidene fluoride) (PVDF), including decay of piezoelectric properties, film shrinkage at elevated temperatures, electrode erosion due to water, curling and fibrillation of the highly oriented PVDF films, and abrasion or impact damage. Piezoelectric aging and shrinkage are found to be strongly correlated; neither process occurs below 60°C, and both show logarithmic time dependences above that temperature. Thus, shrinkage and piezoelectric aging likely both result from similar mechanisms associated with micro‐structural annealing effects at elevated temperatures. The degradation of piezoelectric response observed when PVDF films are exposed to moisture is found to be due primarily to water‐induced erosion of the vapor‐deposited aluminum electrodes rather than to enhanced piezoelectric decay. Observations of mechanical damage suggest that the susceptibility of PVDF films may be partially due to imperfections introduced during the manufacturing process. One conclusion of this study is that biaxial PVDF offers advantages over uniaxial film, including reduced shrinkage and piezoelectric decay, superior resistance to curling and fibrillation, and lower susceptibility to formation of pinholes and other localized defects.
Modeling of poly(ethylene terephthalate) reactors: 6. A continuous process for final stages of polycondensation
Authors: Ravindranath K. , Mashelkar R. A. 
Published: December 2004

AbstractA mathematical model of a continuous polycondensation reactor used in the finishing stages is developed. This axial dispersion model predicts the directions in which mixing, and other process and operational variables, will influence the progress of polycondensation. The available pilot plant data have been compared with the model predictions. In view of the neglect of the side reactions in our model, the comparison is only approximate but appears reasonable. The analysis developed is used to highlight certain critical design considerations.
Mechanistic studies of adhesion promotion by γ‐aminopropyl triethoxy silane in α‐Al2O3/polyethylene joint
Authors: Sung N. H. , Kaul A. , Chin I. , Sung C. S. P. 
Published: December 2004

AbstractIn order to understand the mechanism of adhesion promotion by organo silane in joints where its chemical reaction with a polymer matrix may be negligible, we studied the role of γ‐aminopropyl triethoxy silane (γ‐APS) in α‐Al2O3/ polyethylene joints. When adsorbed or deposited on α‐A12O3/ and moderately dried, γ‐APS forms a multimolecular film that is not fully cured. Drying at elevated temperatures for an extended time leads to further curing, resulting in a glassy silane film with a Tg around 108°C, while prolonged dry may cause some degradation. Joint strength is markedly improved by the application of a γ‐APS film with a maximum peel strength of 2.3 kg/cm when the silane is applied from a 2 percent aqueous solution. Drying the silane at an elevated temperature prior to joint formation reduces joint strength and also changes the failure mode from cohesive failure through the polyethylene to a mixed mode. Evidence of interdiffusion between γ‐APS film and polyethylene at a temperature (149°C) that is above the melting point of polyethylene and the Tg of the silane film was obtained by measuring the Si concentration profile across the interface of the laminate of polyethylene/γ‐APS/polyethylene. Diffusion constants in the order of 10−12 cm2/s were obtained, with a teridency toward reduced diffusion as a consequence of extensive drying. DSC results indicate at least partial miscibility of the silane polymer in the amorphous region of polyethylene. It is proposed that the interdiffusion between γ‐APS silane film and polyethylene is an important mechanism for adhesion promotion of the joints investigated in this study.
A criterion for craze formation
Authors: Juska T. , Harrison I. R. 
Published: December 2004

AbstractA general criterion for craze formation is presented. Crazes are deformation zones that are common to both glassy and semicrystalline polymers. Crazes are composed primarily of fibrils. This paper attempts to describe the process that transforms unoriented glassy and semicrystalline polymeric solids into a fibrous state. The criterion for crazing discussed is a local phase transition. The transition occurs at the draw temperature. Unoriented solid‐phase macromolecules, at local high‐stress regions, undergo a transition to the elastomeric phase. Rapid extension and accompanying resolidification produce the fibrous morphology of craze fibrils. Cavitation of the deforming rubber phase ocurs because the local length increase is riot compensated for by an overall area decrease. Craze formation in glassy polymers has long been suspected to involve a local solid‐to‐rubber phase change. To relate crazes in glassy and semicrystalline polymers, one can assume that a solid‐to‐rubber phase change is required to produce craze fibrils in semicrystalline polymers. The transient melt phase would undergo rapid elongation, causing the formation of extended chain crystallites. These subsequently nucleate the remaining melt, which then crystallizes epitaxially as lamellae. Crystallization during flow would, therefore, be the mechanism of fiber formation.
Characterization of plastics in fire
Authors: Paul K. T. 
Published: December 2004

AbstractFire is a complex process in which temperature and oxygen concentration vary considerably. The methods of characterizing the flammability of plastics materials advocated in this paper use simple test procedures in a series of different fire environments; i.e., at different temperatures and oxygen concentrations. The limits of both flaming and smouldering combustion, flame spread, and burning define the burning behavior of materials as dynamic multivariable parameters and not as single‐point data characteristics of the majority of current fire tests. The feasibility studies were based on modified oxygen index (ASTM D2863, NES 715) and Setchkin furnaces (ASTM D1929). The burning behavior of plastics may also be directly affected by their softening and viscosity characteristics, and this has been explored with relation to suspended ceilings and stacking chairs. The techniques used showed major differences between materials that may not always be seen in standard single‐point tests but which have been correlated with full‐scale ad hoc tests; e.g., room and corner tests, and actual product tests.
Quantitative determination of the vinylacetate content in ethylene vinyl‐acetate copolymers—a critical review
Authors: Koopmans R. J. , van der Linden R. , Vansant E. F. 
Published: December 2004

AbstractThe various methods for the determination of the vinylacetate (VA) content in any ethylene vinylacetate copolymer are examined critically. Each available method is described briefly, together with its relative accuracy. All methods give comparable results and are equally valid, but IR spectrometry can be considered the most flexible and accurate VA content measuring technique.
Flow, pressure distributions, and internal forces in stacked‐disc filters
Authors: Body Max L. 
Published: December 2004

AbstractA mathematical model is described for isothermal flow of Newtonian liquids through stacked‐disc filters. Dimension‐less flow rates, velocities through filter media, pressure distributions, and internal forces are shown as functions of resistance ratios and reduced dimensions. The distribution of velocities through the media is a strong function of the ratios of the resistances to flow through the gaps between discs and through the spaces inside the discs to the resistance to flow through the filter media. Internal forces compress the discs and can, in exceptional cases, impair the media and open up leakage passages.
Mathematical modeling of the blow‐molding process
Authors: Ryan M. E. , Dutta A. 
Published: December 2004

AbstractA mathematical simulation of the blow‐molding cycle has been developed by combining general conservation principles along with appropriate constitutive relations for the material. A model of the parison formation stage has been devised by considering the competing effects due to swell and drawdown. A more rigorous numerical analysis of parison formation is also discussed. A theoretical treatment of parison inflation is described for both inelastic and viscoelastic materials by assuming uniform radial growth, Comparisons are made with experimental data for all phases of the molding cycle. The mathematical model is in reasonable quantitative agreement with experimental results and is capable of elucidating the influence of material properties and process conditions on the dynamics and performance of the blow‐molding process.
13C NMR characterization of intermolecular interactions for polymers. Part 3. Solvent effect on the blend compatibility of poly(vinyl methyl ether) and polystyrene
Authors: Djordjevic M. B. , Porter Roger S. 
Published: December 2004

AbstractThe solvent has an influence on the homogeneity of the poly(vinyl methyl ether)‐polystyrene, PVME‐PS blends Prepared by drying cosolutions. This influence has been analyzed in terms of the competition among polymer‐polymer and polymer‐solvent interactions. Model solutions have been prepared in which intermoleeular interactions correspond to the interactions in this blend and in some of the cosolutions. These interactions in the model solutions have been detected and identified by applying Rummens' method. The 13C NMR spectra have been determined for PVME and for styrene oligomer dissolved in n‐alkanes, cyclohexane, diethyl ether, isopropyl methyl ether, diisopropyl ether, and chloroform, and for PVME dissolved in benzene, toluene, and cumene. The chemical shifts have been plotted against the parameter g2 = [(n22 − 1)/(n22 + 1)]2, where n2 is the refractive index of the solvent. If the structural segment represented by certain carbon and some solvent has an interaction that is stronger than dispersive, the chemical shift for this carbon will deviate from the line formed by its shifts in n‐alkane solutions, these deviations indicate characters and intensities of the intermoleeular interactions. Results indicate that cyclohexane exhibits weak interactions with both of the polymers and does not interfere with their mutual interaction, leading to a compatible blend. Results also suggest that benzene and toluene interact in the PVME in the same manner as PS. This leads to a gradual increase of the number of polymer‐polymer interactions as the concentration of the polymers is increased by solvent removal, resulting in a compatible blend. Chloroform apparently interacts more strongly with PVME than with PS but interacts strongly enough with both to restrict interaction among the two polymers. As the concentration of polymers in the cosolution is increased, PS forms a separate phase. This leads to an inhomogeneous blend when the solvent is evaporated.
Compatibilization of the polystyrene/poly(ethyl acrylate) and polystyrene/polysoprene systems through ionic interactions
Authors: Eisenberg A. , Smith P. , Zhou Z.‐L. 
Published: December 2004

AbstractInteractions between anions on one polymer chain with cations on another can lead to compatibilization of otherwise incompatible materials. Thus, if 5 mol% of ∼SO3H groups are attached to polystyrene, and 5 mol% of vinyl pyridine is copolymerized with ethyl acrylate, proton transfer occurs upon mixing, and the pairwise attractive interactions between the resultant ions compatibilize the blend. The same has been observed for the styrene‐vinyl pyridine and sulfonated polyisoprene polymer pair. Dynamic mechanical and optical properties are used as a measure of compatibilization.
Computer simulation of injection mold filling for viscoelastic melts with fountain flow
Authors: Kamal M. R. , Chu E. , Lafleur P. G. , Ryan M. E. 
Published: December 2004

AbstractThe ultimate properties of a molded article arc directly related In the microstructure of the article and are consequently influenced by the thermomechanical history experienced by the melt during processing. The mold filling behavior of thermopalastic polymer melts has been analyzed quantitatively by means of a computer simulation. The mathematical model is based on the equations of continuity, motion, and energy, along with appropriate constitutive relations and relevant initial and boundary conditions. The governing system of equations is solved numerically by means of a Marker‐and‐Cell computational scheme. One to the significant implications for microstructure development, the fountain effect at the advancing free surface is explicitly taken into consideration in the simulation. The model yields data on filling time and melt front position as well as velocity, temperature, pressure, and shear stress distributions within the mold cavity. The rearrangement of the velocity and temperature profiles in the vicinity of the melt front are considered in detail. Experimental studies have also been undertaken in order to verify the predictions of the computer Simulation.
Effects of stoichiometric mixing ratio on epoxy cure—a dielectric analysis
Authors: Day David R. 
Published: December 2004

AbstractVariation of molar mix ratio of the Epon 828/Diamino‐diphenyl sulfone (DDS) system was found to have significant influences on pre‐cure and post‐cure properties. Microdielectrometry showed that dielectric constant varies from about 9 to above 30 depending on DDS content before cure. Times to the 10 kHz loss peak during cures at 177°C were found to decrease with increasing DDS content. Above a ratio of 2/1 and below 1/2, due to the low molecular weight of the reaction products, loss peaks did not occur. Ionic conduction was shown to have a strong correlation with calorimetric kinetic cure data. The influence of both excess amine and excess DDS was to produce cured material with high ionic conduction levels indicative of loose networks. Deviations from ideal stoichiometry as small as 1.1/1 produced noticable differences in the finally cured network.
The polymerization of a phenolformaldehyde resin in a porous glasswool composite
Authors: Järvelä Pentti K. , Törmälä Pertti , Purola Jaakko , Järvelä Pirkko 
Published: December 2004

AbstractThe polymerization of the phenolformaldehyde matrix material of porous glass fiber composites is of vital importance in the production of the composite; it also has an, essential effect on the strength properties of the composite, which correlate directly with the degree of polymerization. With a certain material combination, the optimal strength properties can be obtained by a suitable thermal treatment, which depends on the kinetics of the polymerization process. In this study we found that the highest strength values of the composite are obtained by making the polymerization (curing) rapid at a very high temperature using resins with a high degree of polymerization and a high dry matter content. As regards the structure of the composite, the factors that affect the polymerization process arc density, resin content, and thickness. The results obtained with this kind of a composite are valid within a density region of 600 to 1500 kg/m3. At lower densities, the polymerization process changes, since thermal convection plays a greater role, and at higher densities the insulating effect of porosity begins to decrease.
Chemorheology of an amine‐cured epoxy resin
Authors: Tajima Yuji A. , Crozier Donald G. 
Published: December 2004

AbstractThe objective of a chemoviscosity model of a thermosetting resin is to describe the change of viscosity for a temperature‐time program. A model is most advantageously developed by starting with a viscosity‐temperature relationship and then relating the parameters of this equation to the rate of polymerization. Thus, the chemoviscosity is related directly to the polymerization kinetics of the thermosetting resin and, thereby, to its chemical composition. Viscosity‐temperature relationships based on free‐volume theory such as the Williams‐Landel‐Ferry equation and the Vogel equation appear to fit the chemoviscosity of an amine‐cured epoxy resin more precisely than relation ships based on resin flow as an activated process.
Causes of edge beads in cast films
Authors: Dobroth T. , Erwin Lewis 
Published: December 2004

AbstractCast polymer films are extruded through a uniform thin slit onto a quench roll. Between the die and the quench roll, thick edges called edge beads form, which have to be trimmed from the film, and are often scrapped. The relation between edge beads and neck‐in is shown. Three causes of edge beads are discussed: surface tension, die swell, and an edge stress effect. Surface tension and die swell effects can be important in low viscosity and elastic materials respectively. The predominant cause of edge beads is an edge stress effect which occurs because the film is stretched between the die and the roll. The edge elongates in uniaxial stress while the center material elongates in plane strain.
Flow induced fiber orientation in an expanding channel tubing dies
Authors: Doshi S. R. , Dealy J. M. , Charrier J.‐M. 
Published: December 2004

AbstractIn the application of plastic pipes for fluid transport and for the protection of underground electrical cables, it is desirable to improve mechanical properties, particularly in the hoop direction. The use of orientable reinforcing particles such as chopped glass fibers could make possible such an improvement if the orientation of the fibers could be controlled. While conventional pipe extrusion dies tend to promote axial fiber orientation, the use of an expanding channel die has been proposed to produce a preferential hoop orientation of fibers. In this paper, a theoretical model of the flow of a fiber suspension through an expanding channel die that predicts the fiber orientation distribution at the die exit is described. The effects of Theological properties and die geometry on the final fiber orientation distribution are predicted. The results of an experimental study of fiber orientation in pipe extruded using an expanding channel die are shown to be in agreement with the theoretical predictions.
A mechanistic kinetic model for the initiated anionic polymerization ofϵ‐caprolactam
Authors: Cimini R. A. , Sundberg D. C. 
Published: December 2004

AbstractThe preparation of Nylon‐6 via the initiated anionic polymerization of EE‐caprolactam is characterized by rapid reaction rates displaying marked auto‐acceleration. A mechanistic approach has been taken to analyze the kinetics of this system and has resulted in the postulation that the auto‐acceleration is directly linked to a polymer chain degradation reaction. This reaction is significant even in the early stages of the polymerization and in many cases becomes the dominant mechanism for the production of reactive end groups, thereby controlling the overall reaction rate. A kinetic model is presented which is capable of differentiating between polymerizations carried out with different levels and ratios of catalyst and initiator, and contains but two rate constants—one for the propagation reaction and one for the degradation reaction. Predictions of the model are compared to experimental rate data derived from using both mono‐and difunctional initiators and close agreement is found.
Effects of water absorption on physical properties and degree of molecular orientation of poly (ethylene terephthalate)
Authors: Jabarin Saleh A. , Lofgren Elizabeth A. 
Published: December 2004

AbstractPoly(ethylene terephthalate) (PET) is known to be a hygroscopic thermoplastic, which absorbs moisture from its environment at a rapid rate. The water absorption characteristics of PET as a function of relative humidity, exposure time, temperature, thickness, and molecular weight are reported here. Results indicate that absorbed moisture has significant influences on the physical properties of PET, leading to large decreases in the glass transition temperature, crystallization temperature, and degree of molecular orientation.
Mechanisms for variations in electrical properties of silicone rubber vulcanized by the condensation reaction
Authors: Yokoyama T. , Kinjo N. , Wakashima Y. 
Published: December 2004

AbstractThe electrical conductivity and the dissipation factor of silicone rubber vulcanized by the condensation reaction of α,ω‐dihydroxypolysiloxane with ethoxysilane, using dibutyltin dilaurate as a catalyst, were studied. Rubber specimens, with different amounts of catalyst, were prepared using various vulcanization times and then heat treated in dry or wet atmospheres containing oxygen and nitrogen. The electrical properties of these specimens were measured at 20 to 200°C in dry air. The amounts of residual catalysts and unreacted ethoxy groups were analyzed by colorimetric and gas chromatographic methods. Factors influencing the specimen electrical properties were discussed in terms of preparation conditions and amount of residual compounds.
Wire coating extrusion–an approximate solution
Authors: Tiu Carlos 
Published: December 2004

AbstractAn approximation method is proposed to predict the Mow rate‐pressure drop relation for isothermal laminar flow of any time‐independent fluid in wire coating extrusion. A geometric parameter method proposed earlier is used in predict the pressure‐driven flow in the annulus. The method is demonstrated for Newtonian, power law, and Ellis fluids. The accuracy of the method is shown by comparing the predictions with the theoretical and experimental results of Han and Rao. An expression for wire coating thickness is also given.
Study of polymer powder and melt rheology using a constant pressure, non‐isothermal rheometer
Authors: Lee Biing‐Lin 
Published: December 2004

AbstractA rheological analysis is proposed on a non‐conventional, constant pressure, non‐isothermal rheometer. The test usually starts with a polymer powder and ends with melt extrudate. The volume‐ (or displacement of plunger) temperature curve of the test is analyzed according to the following model: (1) at a temperature below the glass transition temperature, the test is related to the packing and/or compaction of powders, and also the compressive deformation of powders; (2) as the temperature is raised to where polymer flow begins, the test is analyzed according to melt viscous flow. The activation energy of flow of a polymer may also be estimated using this rheometer. Comparison and correlation of data using other techniques (e.g. torsional pendulum dynamic measurement, capillary rheometer, Rheometric dynamic spectrometer) will also be discussed.