bluuebunny/crossref_metadata_2025_split huggingface dataset:
The phase behavior and mechanical properties of polyarylate and polycarbonate blends
Authors: Golovoy A. , Cheung M. F. , Van Oene H. 
Published: December 2004

AbstractThe phase behavior and mechanical properties of a series of polyarylate/polycarbonate blends were studied. The polymers are known to transesterify, the extent of which depends upon the thermal and shear history and affects phase behavior and properties. Single screw extrusion, twin screw extrusion, and solution casting were employed for blend preparation. Two transition temperatures, corresponding to a polycarbonate‐rich phase and to a polyarylate‐rich phase, were seen in blends that were solution cast or compounded in a single screw extruder at 285°C. But after injection molding a single Tg was observed, When annealed at 180°C for several hours the molded blend was found to phase separate. Blends that were compounded in a twin screw extruder exhibited a single Tg and could not be phase separated. The flexural and tensile properties of blends that were prepared in a twin screw extruder show a small positive synergism. But the impact properties were substantially below the rule of mixtures values, probably the result of advanced exchange reaction and thermal degradation.
Structure formation during polymer blend flows
Authors: Sakellarides S. L. , McHugh A. J. 
Published: December 2004

AbstractThe structure formation processes that occur during the flow of dilute blends of high density polyethylene (HDPE) or polypropylene (PP) In a linear low density polyethylene (LLDPE) carrier phase have been studied. Due to low surface tensions, high deformations of the dispersed minor phase can be induced under slow flow conditions leading to the formation of slender filaments. Measurements on a slit die, having a large, converging flow entrance region, demonstrate that the mechanism for filament formation is droplet bursting, yielding growing tails during shear flow, or, unsteady drop elongation during extensional flow. Tail growth can be modeled as the flow of a slightly tapering cylinder in a fluid of different viscosity, For dispersed to carrier phase viscosity ratios greater than unity, extensional flow occurs in the tail phase, which can induce oriented crystallization. For ratios less than unity, the flow is compressive, which. Inhibits crystallization. Drop deformation and crystallization in the converging flow entrance region is greatly enhanced by the extensional flow, and droplet growth can be described by a model assuming a time‐dependent, planar, extensional flow field. Data for birefringence and melting points of as‐crystallized fibers are also presented and discussed.
Can the gel point of a cross‐linking polymer be detected by the G′ – G″ crossover?
Authors: Winter H. H. 
Published: December 2004

AbstractDynamic mechanical measurements allow direct determination of the instant at which a network polymer gels. In such an experiment, the evolution of G′(t,ω0) and G″ (t,ω0) is measured in small amplitude oscillatory shear as a function of cross‐linking time t. The frequency ω0 is kept constant throughout. At the beginning of the experiment, G″ is orders of magnitude larger than G′, and at completion of reaction, this order is reversed. It recently has been suggested by Tung and Dynes that the gel point (GP) might occur at the time at which G′ and G″ cross each other. However, there is much dispute whether GP occurs exactly at the crossover or just somewhere in its vicinity. This study resolves the dispute by modeling the rheological behavior at GP: There is only one class of network polymers for which GP coincides with the crossover. This class of polymers exhibits, when reaching GP, power law relaxation G(t) ∼ t−n with a specific exponent value n = 1/2. Examples are stoichiometrically balanced network polymers and networks with excess cross‐linker, however, only at temperatures much above the glass transition. Otherwise, the power law behavior would be masked by vitrification. Power law relaxation seems to be property of polymers at GP in general. However, some polymers have a different exponent value, n ≠ 1/2, in which case the crossover occurs before GP (for n < 1/2) or after GP (for n > 1/2); i.e. the crossover cannot be used for detecting GP. While there are no networks known to us with n < 1/2, recent experiments showed that network polymers that are lean on cross‐linker exhibit power law relaxation with n > 1/2. A new method is suggested for measuring GP of these imbalanced networks.
An investigation of instability of phase morphology of blends of nylons with polyethylenes and polystyrenes and effects of compatibilizing agents
Authors: Chen Cheng Chung , Fontan Eusebio , Min Kyonsuku , White James L. 
Published: December 2004

AbstractInvestigations of instability of phase morphology of blends of nylons with polyethylenes and polystyrenes and the effects of “compatibilizing” additives or “agents” are described. Annealing coarsens the phase morphology of blends of nylons with polyethylenes and polystyrenes. Phase growth is observed for various periods of annealing time. The addition of compatibilizing agents, specifically maleic anhydride grafted polyolefins to polyethylene‐nylon blends and syrene‐maleic anhydride copolymers to polystyrene‐nylon blends, stabilize the phase dimensions. Styene‐maleic anhydride copolymer is found more effective than styrene acrylonitrile copolymer as a compatibilizing agent. The mechanisms of this behavior are critically discussed.
Estimation and control in polymerization reactors. A review
Authors: Eliçabe G. E. , Meira G. R. 
Published: December 2004

AbstractThe control of polymerization reactors is particularly arduous for several reasons; (a) difficulty in specification of the control objectives; (b) high exothermicities and viscosities involved: (c) complicated process dynamics: and (d) problems with measurement of the polymer structure. Computer control has now simplified many tasks such as sequential operations of batch reactors; but no less important, it has made feasible the implementation of elaborate state estimation and control algorithms. The tendency in the polymerization industry and in current research centers is centered on producing ‘tailor‐made’ polymers from the view of its microscopic and/or macroscopic structures. To this end, several solutions have been proposed. For example, in the ‘chemical approach’, open loop methods have been developed based on the detailed dynamic models of the processes. Any control technique requires a knowledge of the process to be controlled through mathematical models. These models may be developed either from detailed mass and energy balances, or through empirical input‐output or “black‐box” techniques. The most promising control techniques are probably optimal control, adaptive control, and their combinations. Optimal control is powerful because it utilizes directly the detailed non‐linear plant model. Adaptive control developed for linear plants has already proven satisfactory, in spite of the highly nonlinear nature of the polymerizations. Undoubtedly, improved solutions will be obtained when this technique is extended to non‐linear systems.
Effect of crosslink density on the molecular relaxations in diepoxide‐diamine network polymers. Part 1. The glassy region
Authors: Charlesworth John M. 
Published: December 2004

AbstractThe effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide‐diamine polymers are reported. Activation enthalpies and intensities for the β relaxation have been measured using a torsion pendulum at 1 Hz. The glyceryl groups, which are thought to be responsible for this process, are divided into a number of categories defined by the structure of the surrounding matrix. Concentrations of these units are calculated using probability theory, and a correlation is obtained with three measures of the relaxation Intensity, In the case of non‐stoichiometric networks, variations in the intensity of the β relaxation are interpreted in terms of the simultaneous motion of each class of glyceryl group. The manner in which these processes combine to produce a composite peak appears to be unimportant. For the γ relaxation (−140°C), it is shown that at least four methylene units are needed in the diamine component before the process is observable, whereas only two consecutive methylene units in the center of the diepoxide molecule produce the relaxation.
The modeling of batch and continuous emulsion polymerization reactors. Part II: Comparison with experimental data from continuous stirred tank reactors
Authors: Rawlings J. B. , Ray W. H. 
Published: December 2004

AbstractA detailed model for emulsion polymerization is compared with extensive data from continuous stirred tank reactors. Model predictions are compared with both steady‐state and dynamic data, for polymerization of styrene, methyl methacrylate, and vinyl acetate. Good agreement between model and experiment is achieved with one set of parameters and without any data fitting. The results show that the model is capable of predicting all of the experimentally observed phenomena including steady‐state multiplicity, sustained oscillations, ignition and extinction dynamics, and overshoot during start‐up.
The modeling of continuous mixers. Part I: The corotating twin‐screw extruder
Authors: Meijer H. E. H. , Elemans P. H. M. 
Published: December 2004

AbstractIn many operations in polymer processing, such as polymer blending, devolatilization, or incorporation of fillers in a polymeric matrix, continuous mixers are used; e.g., corotating twin‐screw extruders (ZSK), Buss Cokneaders and Farrel Continuous Mixers. Theoretical analysis of these machines tends to emphasize the flow in complex geometries rather than generate results that can be directly used (1–5). In this paper, a simple model is developed for the hot melt closely intermeshing corotating twin‐screw extruder, analogous to the analysis of the single‐screw extruder carried out in 1922 and 1928 (6, 7). With this model, and more specifically with its extension to the complete nonisothermal, non‐Newtonian situation, it is possible to understand the extrusion process and to calculate the energy, specific energy, and temperature rise during the process with respect not only to the viscosity of the melt, but also to the screw geometry (location and number of transport elements, kneading sections and blisters, pitch, positive or negative, screw clearance, and flight width) and screw speed. To support the theoretical analysis, model experiments with a Plexiglas‐walled twin‐screw extruder were performed, in addition to practical experiments with melts on small‐ and large‐scale extruders, with very reasonable results, In Part 2, the Buss Cokneader will be analyzed analogously.
Calorimetric characterization of photosensitive materials
Authors: Appelt B. K. , Abadie M. J. M. 
Published: December 2004

AbstractA negative‐acting dry‐film photoresist was examined via both photocalorimetry and conventional calorimetry. The photo reaction of the resist was investigated as a function of temperature, and two distinct regimes with different activation energies have been identified. Possible reaction mechanisms were discussed in terms of termination reactions of the polymerization as well as effects of vitrification. The thermal reactivity of this particular resist was studied as well. It was possible to use Kissinger's equations to predict thermal aging effects. Finally, the utility of photocalorimetry as a tool to examine quickly the reactivity of monomers and initiator systems was demonstrated.
Influence of added salt on dynamic viscoelasticity of carboxymethylcellulose aqueous systems
Authors: Matsumoto Takayoshi , Mashiko Kimio 
Published: December 2004

AbstractUsing three series of sodium carboxymethylcellulose (NaCMC) in the range of the degree of substitution (the average number of carboxymethyl groups/glucose unit) from 0.5 to 1.3, weight‐average molecular weight Mw was determined by light scattering in solution of triethylenediamine cadmium hydroxide (cadoxene). It was found that the relation between Mw and the limiting viscosity number [η] in 0.1 N sodium chloride (NaCl) aqueous solution can be represented by Staudinger's equation. Dynamic viscoelasticity of aqueous disperse systems of NaCMC with various added salts was measured by means of a cone‐and‐plate rheometer. If the concentration of added salt is less than the concentration at which polymer begins to salt out, frequency dependence curves of the dynamic modulus, which is measured at various salt concentrations, can be superposed into a master curve by horizontal shift only. The shift factor depends on the salt concentration and the kind of salt.
Engineering analysis of reaction injection molding process of nylon 6
Authors: Lee Kwang Hee , Kim Sung Chul 
Published: December 2004

AbstractA computer simulation model was established to analyze the reaction injection molding process of nylon 6. A numerical calculation was carried out to predict the temperature, conversion, and crystallinity profile within a disc type mold. The effects of the feed temperature, wall temperature, and overall reaction constant on the eject time were discussed for searching the optimum processing conditions.
Chemorheology of an epoxy resin for pultrusion
Authors: Tajima Yuji A. , Crozier Donald G. 
Published: December 2004

AbstractThe Williams‐Landel‐Ferry (W‐L‐F) equation was shown to describe the temperature dependence of the viscosity of a sulfonium accelerated, amine cured epoxy resin that had been formulated for pultrusion. The reference temperature and the viscosity at the reference temperature of the W‐L‐F equation were found to be simple functions of the resin advancement as determined by isothermal differential scanning calorimetry, A method is described of constructing the baseline for temperature‐programmed differential scanning calorimetry analyses in which the heat capacity is changing due to reaction.
Efficiency of polymer fractionation—A review
Authors: Mencer H. J. 
Published: December 2004

AbstractWith respect to molecular masses, polymers are polydispersive. Since many of their properties depend on the distribution of molecular masses, to study this correlation it is necessary to have samples of narrow molecular mass distribution or samples with accurately defined distribution. In spite of the developmental progress of fast instrumental methods (analytical and preparative gel chromatography) used to determine the molecular mass distribution curve and to obtain higher amounts of fractions of narrow molecular mass distributions, there still exists an interest in classical methods of fractionation. On the basis of a survey of monographs on polymer fractionation, numerous publications and personal experience, this review describes primarily what is an efficient fractionation. Afterwards, factors that affect fractionation efficiency according to the type of effects arc given and causes of their action are described. Conditions under which efficient fractional precipitation and fractional solution methods are applied are considered separately. At the end of the review, criteria on the basis of which fractionation efficiency is evaluated are considered in detail.
Heat transfer effects on the processing‐structure relationships of polyetheretherketone (PEEK) based composites
Authors: Velisaris Chris N. , Seferis James C. 
Published: December 2004

AbstractAn analytical methodology was developed capable of describing interrelations between thermal processing and polymer structure for thermoplastic based composite laminates. Specifically, this modeling methodology was used to describe experimental results generated with a specially designed match die quench mold by processing both neat PEEK polymer and carbon fiber reinforced laminate samples at different cooling rates. The developed model accurately predicted temperature profiles for PEEK laminates of different thicknesses, under normal as well as extreme quenching conditions of 114°C/s. surface cooling rates that are possible to generate with the quench mold. In general, the modeling methodology is capable of predicting a part's thermal profile during processing in terms of the composite's microscopic intrinsic properties (fiber and matrix), composition, and lamina orientation. Furthermore, by coupling to the thermal profile description, a previously developed crystallization kinetics model for PEEK polymer and its carbon reinforced composite, a quantitative description of structural development during processing was obtained. Thus, with this analytical methodology, a skin‐core crystallinity profile, where the crystallinity varies with part‐thickness as a result of uneven cooling experienced during processing, was predicted both for the neat PEEK polymer and its carbon reinforced laminate forms. Finally, the developed methodology clearly established the interplay of both microscopic heat transfer and kinetics of crystallization/solidification of the matrix that must be accounted for in predicting the final structure of a carbon fiber reinforced laminate that will, in turn, govern microscopic and macroscopic performance.
Interlaminar fracture toughness testing of composite mode I and mode II DCB specimens
Authors: Ilcewicz L. B. , Keary P. E. , Trostle J. 
Published: December 2004

AbstractA computer controlled test procedure for evaluating mode I and mode II interlaminar fracture behavior was used in experiments with eight different resin matrix/graphite fiber composites. Four analytical methods for calculating fracture toughness were compared. These included an energy rate determination of theJ‐integral, a compliance calibration procedure, equations based on linear beam bending, and an Area method calculation. Methods that account for nonlinear material behavior, such as theJ‐integral, were needed for characterizing the systems with high fracture toughness. The ratio of mode II to mode I fracture toughness ranged from 1.5 to 8.0, depending on the material system. Finally, preliminary work with a technique for constant strain rate testing of mode I DCB specimens is presented.
Polymer fatigue fracture diagrams: BPA polycarbonate
Authors: Takemori Michael T. 
Published: December 2004

AbstractA fatigue fracture diagram for BPA polycarbonate has been created from fatigue lifetime data obtained from knit line notched samples. This fatigue fracture diagram maps out stress‐temperature zones where fatigue fracture is dominated by crack growth through leading crazes and zones where fatigue fracture occurs through shear fracture at 45 degrees to the load direction. Both craze and shear planes coexist in the fatigue crack tip plastic zone, and both compete to determine the ultimate crack growth behavior. The shear planes preferentially develop (and fracture) at higher temperatures and stresses, but this fracture process is quite slow. Consequently, an inversion in the fatigue lifetime curve is observed, with longer lifetimes at higher stresses. This inversion is easily understood as a transition between a craze branch and a shear branch on the fatigue lifetime plot. When the fatigue lifetime curve is plotted for data at different temperatures, with the stresses normalized to the yield stress at the respective test temperatures, the craze branch data from different temperatures overlap. This overlap can be explained by the N = 2 power law dependence of crack growth in the discontinuous crack growth regime.
Vibration welding of thermoplastics. Part I: Phenomenology of the welding process
Authors: Stokes V. K. 
Published: December 2004

AbstractIn vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters in vibration welding are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time. How these parameters affect weld quality, the conditions that result in the best welds, the weldability of dissimilar plastics, and the effect of fillers such as glass are of interest. To address these issues, a research vibration welding machine in which all the parameters can be independently and accurately controlled and monitored was designed and fabricated. The phenomenology of welding, as determined by experiments on the four thermoplastics polycarbonate, poly (butylene terephthalate), polyetherimide, and modified poly (phenylene oxide), is described.
Modeling of extrusion with slip boundary conditions
Authors: Meijer H. E. H. , Verbraak C. P. J. M. 
Published: December 2004

AbstractSlip at boundaries is possible in viscous flows; for instance, in the extrusion of foodstuffs, water‐containing materials, and some polymers. There are two phenomenological descriptions of slip: The first is based on the presence of a very thin, low viscosity boundary layer and has been derived for capillary flow and extrusion; the second is based on a Coulomb‐friction mechanism and has been derived for capillary flow only. After a survey of these results, the friction model is derived for the extrusion process. All calculations are as simple as possible: two‐dimensional, Newtonian, isothermal, and with constant boundary layer parameters of coefficients of friction. A strong dependence of pumping characteristics and efficiency on the slip boundary conditions, and also on the extruder length in the case of friction, was found, especially when slip is only allowed for at the screw surface. Exercises like these may help in understanding abnormal extrusion behavior of slippery materials in practice.
Transmission of mechanical energy through polymeric liquid crystals and their blends
Authors: Brostow Witold , Dziemianowicz Theodore S. , Romanski Janusz , Werber Walter 
Published: December 2004

AbstractMolecular composites, also called polymeric liquid crystals (PLC), are contrasted with the traditional composites; the name heterogeneous composites is proposed for the latter. Advantages of blending PLCs with ordinary engineering polymers are discussed. Results reported for blends of poly(ethylene terepthalate) (PET) with a PLC containing sequences of PET and p‐hydroxybenzoic acid (PHB) include thermophysical properties, melt rheology, mechanical properties of solid blends, and scanning electron microscopy of fracture surfaces. A model called the island model was developed to explain the results: One assumes that the lines of force as well as propagating cracks tend to concentrate in the phase rich in the more flexible engineering polymer, avoiding the islands rich in the liquid‐crystalline phase. This prevails until the phase inversion occurs. Predictions from the model are fully confirmed by the experimental evidence.
Preparation, structure, and properties of two‐phase co‐continuous polymer blends
Authors: Miles Isabel S. , Zurek Andrew 
Published: December 2004

AbstractPhase continuity has been explored as a function of composition for three two‐phase polymer blends produced by mixing in the melt: polystyrene/poly(methyl methacrylate), polystyrene/cis‐polybutadiene, and poly(methyl methacrylate)/ethylene‐propylene rubber. The condition for dual phase continuity Is the application of shear close to phase inversion and this can be predicted fairly accurately using the relation

where 1 and 2 are the blend components, η is viscosity, \documentclass{article}\pagestyle{empty}\begin{document}$\mathop \gamma \limits^.$\end{document} is the shear rate in the mixing device used to produce the blend and ϕ is volume fraction. The co‐continuous materials, which we call Interpenetrating polymer blends (IPBs) are non‐equilibrium structures and are subject to disruption by changes in flow regime.