bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of tubular low‐density polyethylene
Authors: Gupta Santosh K. , Kumar Anil , Krishnamurthy M. V. G.
Published: December 2004

The simulation of tubular, high‐pressure low‐density polyethylene reactors is performed using a comprehensive kinetic scheme which includes branching reactions as well as reactions leading to vinyl and vinylidene group formation. The variation of the physical properties of the reaction mass with position has been accounted for. In addition to predicting the conversions of the monomer and initiator, the temperature, and the number‐average molecular weight, this study enables the computation of the polydispersity index and the concentration of vinyl, vinylidene, and methyl groups as a function of position. These have important implications in terms of product properties. Detailed simulations have shown that the steady‐state approximation can be used for obtaining the concentrations of the initiator and the polymer radicals. In addition, some simple closure conditions have been established. The effect of multiple intermediate feeds is also investigated and it is found that under certain operating conditions the reactor performance becomes inherently unstable.
Recovery (spring‐back) of polyethylene from an imposed bend
Authors: Charrier J.‐M. , Gent A. N.
Published: December 2004

Measurements have been made of the recovery of polyethylene samples from bending deformations of varying severity. The amount of spring‐back from a severe bend is quite different for different densities (degrees of crystallinity), especially at short times after release, being much greater for lower‐density polyethylenes. Short‐term spring‐back measurements thus afford a simple and rapid means of determining the approximate density. Immediate recovery is small, 5 to 15 percent, and is in rough accord with expectations for elastic‐plastic solids. A major protracted recovery process follows. It is accelerated by raising the temperature, in reasonable agreement with the WLF relation for segmental mobility. It is therefore attributed to retarded molecular motions in the amorphous fraction. Final recovery is greater for lower‐density materials, but it is incomplete even after very long times or for mild degrees of bending. Thus, some irreversible processes appear to take place, even when bending strains as low as 3 percent are imposed.
Simulation of particle size distribution in continuous emulsion polymerization styrene monomer
Authors: Lu Ying‐Yuh , Lin Chen‐Chong
Published: December 2004

A detailed mathematical model for absolute particle‐size distribution in continuous emulsion polymerization of styrene monomer is proposed on the basis of the modified population‐balance theory. The computer simulation is then performed for styrene polymerization as an example of a nondesorption system. The effects of emulsifier and initiator concentrations as well as mean residence time on the absolute particle‐size‐distribution function, total concentration of polymer particles, conversion, average number and weight radii, average number of radicals per polymer particle, and polydispersity of radius are simulated by the model proposed.
Comment on the Berkeley kinetic network model
Authors: Doeksen D. K. , Jongschaap R. J. J. , Kamphuis H.
Published: December 2004

A kinetic model for the rheological behavior of polymeric systems, i.e. the Berkeley kinetic network model, is compared with a generalized transient‐network model. It turns out that the Berkeley kinetic network model fits quite well in the framework of the transient‐network model. From the point of view of the latter model, however, a number of parameters introduced in the kinetic‐network model are not independent constants as was supposed. Since the generalized transientnetwork model is totally based on microscopic assumptions, the parameters in this theory reveal information about the structure, whereas the physical interpretation of the parameters in the kinetic model is vague. Stress predictions of the generalized transient‐network model agree with experimental data from a 4 percent solution of polystyrene in arochlor, obtained from literature.
The influence of polymolecularity on thermodynamic properties of macromolecular systems
Authors: Koningsveld R.
Published: December 2004

A brief overview of the effects of chain length distribution, branching, chemical distribution, and deuterium labeling on phase equilibria is presented.
Strength degradation in γ‐aminopropyl triethoxy silane primed α‐Al2O3/nylon 6 peel joints in a wet environment
Authors: Kaul A. , Sung N. H.
Published: December 2004

Unprimed sapphire/nylon 6 peel joints (2.13 ± 0.27 Kg/cm) are found to be stronger than sapphire/polyethylene joints (0.06 ± 0.02 Kg/cm). Priming the sapphire with γ‐aminopropyl triethoxy silane (γ‐APS) improves the strength significantly resulting in adherend failure in the nylon. The rate and extent of degradation is lower with priming. The optimal silane thickness is about 1900 Å, obtained with a 0.3 percent γ‐APS solution, for a five day exposure to water at 25°C. Peel joints made with 0.3 percent γ‐APS film, both dried at 25°C (standard conditions) and dehydrated at 110°C under vacuum, fail cohesively when exposed at 25°C. Increasing the exposure to 55°C in a second step results in strength degradation only with dehydrated films. Lower joint strengths are obtained with five days exposure as compared to one day exposure. However, if the temperature is raised to 65°C the joints primed with standard dried films now begin to degrade and lose 90 percent of their strength in five days. Further, the nylon 6 peel joints made with a 0.3 percent γ‐APS film, dehydrated for three days prior to lamination, show 10 times greater wet strengths than the corresponding PE joints. Failure surface analyses by ESCA and SEM suggest that failure locus due to water degradation is within the γ‐APS layer and the failure mode is cohesive. Failure mechanics during testing the wet peel joints may also cause a partial interfacial failure mode. The effects of the silane film thickness, dehydration condition, time, and temperature dependence of the peel strength degradation indicates that the structure of the γ‐APS layer plays an important role in the promotion and retention of adhesion with a thermoplastic polymer system capable of limited primary interactions through possible interdiffusion with the silane layer.
Process control of polymer extrusion. Part I: Feedback control
Authors: Yang Bing , Lee L. James
Published: December 2004

On‐line computer control of extrudate thickness was carried out using a 2–1/2 Inch single screw plasticating extruder. Predried poly(methyl methacrylate) (PMMA) was extruded through a slit die. Two feedback control methods, a conventional PI controller and a Smith predictor dead time compensation, were tried for both set point changes (i. e., extrudate thickness changes) and load changes (i. e., screw speed changes). Results showed that both the PI feedback control and the Smith predictor were satisfactory for long term set point changes but not for load changes. Since the Smith predictor may compensate the process dead time, it would be useful for regulating short term set point changes such as barrel temperature settings.
Plastic deformation of crystalline polymers
Authors: Gent A. N. , Jeong Jongkoo
Published: December 2004

Draw ratios have been measured for samples of polyethylene and trons‐polyisoprene, crystallized at various temperatures and at various degrees of orientation. The values obtained range from unity, i. e., no drawing is observed, up to values of about 15X for materials crystallized in the oriented state and then drawn in a perpendicular direction. The results are in rough accord with a simple molecular network model in which network strands are incorporated into crystallites with a number of reversals of direction (folds), and the remainder of a strand between network junctions is randomly arranged. The reduction in draw ratio with increasing temperature of crystallization and with increasing orientation at the time of crystallization is then accounted for in terms of a reduction in the number of reversals (folds) per molecular strand. Differences in natural draw ratio for different polymers are attributed to variations in characteristic sequence length within a crystallite and in the number of folds per network strand.
Design of dies for the extrusion of sheets and annular parisons: The distribution problem
Authors: Winter H. H. , Fritz H. G.
Published: December 2004

A systematic design of the classical “coat hanger” die is proposed and tested experimentally. The objectives of the design are 1. distribution of the polymer over the width of the die before it reaches the final lip section for thickness adjustment, 2. invariance of distribution to flow rate, 3. invariance to changes in polymer viscosity, and 4. uniform average residence time. The die design is based on a flow model which assumes power‐law viscosity, steady shear flow In each cross‐section, uniform temperature, and separation of the flows into a manifold component and a component in a slit section of uniform height. The design corrects for an oversimplification of the pressure gradient that was applied in previous studies; and it differs from previous designs by suggesting a rectangular cross‐section for the manifold. Applications to side‐fed dies for extrusion blow molding and to a sheet extrusion die achieved uniform distribution and did not require any additional flow corrections (such as choker bars or flexible lips). With the new design, the lip region of the die can freely be used for thickness control, fine tuning, or further shaping of the extrudate.
Characterization of uniaxially oriented isotactic polypropylene films using sonic velocity measurements
Authors: Ibrahim A. Mahammad , Wedgewood Alan R. , Seferis James C.
Published: December 2004

A simple and useful experimental method has been developed for obtaining shear compliance properties for film samples using sonic velocity measurements at room temperature. In this method, the transmit and receive transducers were aligned in such a way that a shear wave was generated and transmitted through the sample. The method was used to determine the in‐plane shear compliance properties of three well characterized uniaxially oriented isotactic polypropylene films with draw ratios of 1.2, 4, and 6 respectively. It was observed that shear velocities at angles 0 through 45° were symmetrical to those from 90 through 45°. Further, as the draw ratio of these film samples increases, the determined sonic shear compliance in the draw direction decreased linearly. In addition to he shear data, the in‐plane tensile compliance data were also determined for these three films for comparison. Collectively, these sonic tensile and shear data were analyzed to evaluate the four in‐plane material compliance constants, S33, S22, S44, and S23, required to characterize a film in plane stress. Finally, a previously developed two parameter model was used to predict both the shear and tensile sonic modulus properties based on orientation parameters and intrinsic properties of isotactic polypropylene. The predicted properties agreed reasonably well to the experimental data generated for these film samples in spite of the fact that the two parameter model assumes the in‐plane shear compliance to be a constant independent of the test angle.
Processing of polyurethane/polyester interpenetrating polymer networks by reaction injection molding. Part III: Flow reorientation through multiple impingement
Authors: Nguyen Luu T. , Suh Nam P.
Published: December 2004

This is the third of a three‐part paper investigating the feasibility of processing polyurethane/polyester Interpenetrating Polymer Networks (IPN) by Reaction Injection Molding (RIM).

Part of this paper was presented at the Third International Conference on Reactive Processing. Bischenberg Congress Center, Alsace, France, September 4– (1984)

Two basic issues are addressed concerning the improvement of the mixing scale in impingement mixing, namely, the influence of multiple impingement on the microscale and the number of flow dividing elements needed to achieve a certain degree of mixing. It was found that the incorporation of cascading stages does improve mixing further. The extent of improvement depends on the secondary stream Reynolds number and the local impingement pressure. A transition zone generally demarcates the beginning of marginal improvement on the number of elements used. Since the cascading configuration operates in a manner analogous to “motionless mixers,” there is a practical limit to the number of stages that can be used. At a primary impingement pressure of 18,000 psi, for instance, an overall improvement of 53 percent is recorded for a flow through a total of 80 stages. A noticeable 23 percent is noted within the first ten stages while the next 70 stages enhance mixing by only 30 percent. Thermal and dynamic mechanical analysis revealed some degree of interpenetration between the two networks.
A fundamental study of polymer melt devolatilization. Part I: Some experiments on foam‐enhanced devolatilization
Authors: Biesenberger Joseph A. , Lee Shau‐Tarng
Published: December 2004

A systematic, experimental study was conducted on the elementary process of devolatilization (DV) and the various parameters affecting it, using a specially designed apparatus, which is devoid of the flow complexities present in industrial equipment and which permits independent control of all pertinent parameters. The device simulates a flow configuration present in all rotating machinery used in DV, viz. the rotating melt pool. Parameters studied include exposure time, agitation rate, surface‐to‐volume ratio, melt viscosity, vapor pressure of volatile contaminant, applied vacuum level, concentration level of contaminant, and addition of inert substances for DV enhancement. The results of most parametric studies are presented here, but some will be published in a subsequent paper. All feed and product contaminant levels were analyzed using gas chromatography.
Biaxial orientation of polypropylene by hydrostatic solid state extrusion. Part I: Orientation mechanism and structural hierarchy
Authors: Pan S. J. , Brown H. R. , Hiltner A. , Baer E.
Published: December 2004

The structure which results from solid state extrusion using biaxial orientation is analyzed for oriented polypropylene. Structural changes on the spherulitic, lamellar, and macromolecular level during orientation are investigated using optical microscopy (OM), small angle X‐ray scattering (SAXS), and wide angle X‐ray scattering (WAXS). The results show that polypropylene spherulites undergo stepwise biaxial affine deformation and deform homogeneously into a disc‐like morphology. During this spherulitic flattening process, lamellar rotation into the planar direction occurs prior to lamellar break‐up at a baxial draw ratio of about 1.5. On the macromolecular level, the crystalline c‐axis orients in the plane concurrently with the lamellar break‐up, while the crystalline b*‐axis gradually orients normal to the plane. Amorphous chains are also oriented preferentially in the plane of deformation. A hierarchical model is proposed to illustrate the nature of the orientation in the flattened spherulites.
Preparation of silicon carbide‐silicon nitride fibers by the pyrolysis of polycarbosilazane precursors: A review
Authors: Penn B. G. , Daniels J. G. , Ledbetter F. E. , Clemons J. M.
Published: December 2004

The development of silicon carbide‐silicon nitride (SiC‐Si3N4) fibers by the pyrolysis of polycarbosilazane precursors that was carried out in this laboratory is reviewed. Precursor resin, which was prepared by heating tris(N‐methylamino)methylsilane or tris(N‐methylamino)phenyl‐silane to about 520°C, was drawn into fibers from the melt and then made unmeltable by humidity conditioning at 100°C and 95 percent relative humidity. The humidity‐treated precursor fibers were pyrolyzed to ceramic fibers with good mechanical properties and electrical resistivity. For example, SiCSi3N4 fibers derived from tris(N‐methyl‐amino)‐methylsilane had a tensile rupture modulus of 29 × 106 psi and electrical resistivity of 6.9 × 108 Ω‐cm, which is 1012 times greater than a value obtained for graphite fibers.
Extruder screws with barrier sections
Authors: Rauwendaal Chris
Published: December 2004

This paper presents a functional analysis of the advantages and disadvantages of several types of barrier section extruder screws, indicating preferred geometrical configurations for certain applications. In addition, aspects of barrier mixing sections are discussed and analytical expressions for optimizing channel depth and helix angle to minimize the pressure drop over the barrier mixing section are presented.
New directions in the nuclear magnetic resonance spectroscopy of polymers
Authors: Bovey F. A.
Published: December 2004

The study of polymers by nuclear magnetic resonance spectroscopy has made tremendous advances in the last few years, not only with the development of superconducting solenoid magnets with increasing field strength, permitting the resolution of increasingly fine structural detail and greater sensitivity, but also in the development of new techniques. Among these is the use of two‐dimensional (2D) NMR, permitting easier and more rigorous assignment of resonances. Another important advance has been the development of means to observe high resolution spectra in the solid state, through high‐power dipolar decoupling, cross‐polarization, and magic angle spinning. A third significant development is that of deuterium quad‐rupole echo spectroscopy, permitting the study of chain dynamics in the solid state with unprecedented power and precision.
Polymer blends as high explosive binders
Authors: Mark Hoffman D. , Caley Leonard E.
Published: December 2004

An approach to high‐density, high‐modulus binders for explosives is to blend low‐density, high‐modulus polymers with high‐density, low‐modulus polymers. Improved properties, which these pairs theoretically should have, are discussed. Two attempts to achieve miscibility between a high‐density fluoropolymer (Kel‐F 800) and high‐modulus thermoplastics (Lucite 130 and Phenoxy PKHJ) were unsuccessful. These blends are immiscible and their physical properties are additive or only slightly enhanced. Anelastic properties of the blends indicate phase separation by the presence of two glass transitions, one associated with each phase.
A methodology for describing creep‐fatigue interactions in thermoplastic components
Authors: Bowman J. , Barker M. B.
Published: December 2004

In service, some plastics components are subjected to intimate mixtures of creep and fatigue loading, such that both have the potential to cause component failure. This paper examines, for the case of a single design of an injection molded fitting that comprised part of a polyethylene pipeline system, the response of that fitting to fatigue loading patterns that included significant elements of creep loading. The performance of the fitting was monitored and the data interpreted in terms of the concepts of fractional fatigue and fractional creep damage. The approach helps in identifying the design criteria to be used for components that are to be subjected to complex fatigue loadings. For the cases where significant creep‐fatigue interactions occur, such that the additive damage was nonlinear, the method can identify critical frequencies at which maximum damage occurs. This style of analysis will be most useful for plastics components that are used in critical applications where failure has to be avoided.
Dynamic fracture instability in glassy polymers as studied by ultrasonic fractography
Authors: Takahashi K.
Published: December 2004

Ultrasonic fractography studies were performed on poly(methyl methacrylate) of high molecular weight. The transient fracture velocity change at the slow‐to‐fast transition during discontinuous propagation has been measured precisely. Fast fracture starts with a characteristic velocity which falls in a narrow range between 90 to 150 m/s, nearly independent of the loading speeds and the specimen temperature from −50 to 40°C. Parallel double‐cantilever‐beam specimens exhibited stick‐slip type propagation whose velocity change was also evaluated. In these specimens, the fast fracture abruptly slows down to speeds on the order of 10° m/s. These intermediate velocities have never been obtained in the slow‐to‐fast transition. Velocity measurements under hydrostatic pressure have shown that fracture velocities decrease significantly with increasing pressure, and that the slow‐to‐fast transition tends to disappear at a pressure between 5 and 10 MPa. Models have been presented concerning the mechanism of the slow‐to‐fast transition, crazing and cracking under superposed cyclic stress field, and the relationship between dynamic toughness and fracture velocity in this material.
Surface tension of polymer liquids
Authors: Couchman P. R. , Van Ness K. E.
Published: December 2004

A cell theory for the prediction of the surface tension of simple liquids is adapted to polymer liquids. The combinatory, free volume and potential energy zero terms of the partition function are all modified to account for the preservation of connectivity when a surface is created. Theory and experiment are in good agreement without an adjustable surface parameter.
Blends of polycarbonate and poly(hexamethylene sebacate): I. Physical properties
Authors: Shih K. S. , Beatty C. L.
Published: December 2004

The compatibility of polymer blends of high‐molecular‐weight polycarbonate (PC) and high‐molecular‐weight poly(hexamethylene sebacate) (HMS) were characterized. Samples were prepared by solution blending them In methylene chloride followed by doctor blade casting. Optical spectroscopy, tensile stress‐strain, differential scanning calorimetry, and dielectric relaxation spectroscopy were employed to determine the physical and mechanical properties of the blends. These high‐molecular‐weight blends exhibit a limited solubility of HMS In PC as evidenced by a decrease in the glass‐transition temperature of PC. In fact, HMS solubility increases PC mobility sufficiently to allow partial crystallization of PC. Over most of the composition range, HMS phase separates and crystallizes.
Melting and crystallization behavior of an unusual compatible blend based on propylene copolymers
Authors: Shih Chi‐Kai
Published: December 2004

An unusual compatibility was observed with the melt blends of propylene/α‐olefin copolymer with isotactic homopolypropylene. The simple binary blend exhibits a single glass‐transition temperature, and, by differential scanning colorimetry, a single melting and crystallization temperature over the entire blending ratios examined. Depending on the compositions, the characteristic temperatures vary between those exhibited by the component polymers. Vigorous annealings failed to phase separate the components. The melting behavior of the annealed polymer sample suggests the crystalline components of the two polymers are cocrystallized in this unique compatible system.
The computer modeling of multicomponent, semibatch emulsion copolymerization
Authors: Omi Shinzo , Kushibiki Koji , Iso Mamoru
Published: December 2004

A computer modeling concept was developed to deal with multicomponent emulsion copolymerization systems. Based on the model, a simulating program called NSBEC (n‐component, semibatch emulsion copolymerization) was prepared., NSBEC is capable of carrying out a variety of operations involving any number of monomers with different modes of ingredient feed. In this paper, first the basic concept of the model is explained, then several applications to the actual experimental systems (e.g., acrylonitrile‐vinylidene chloride, vinyl acetate‐butyl acrylate, and methyl methacrylate‐butyl acrylate) are discussed. Finally, the probable control of copolymer composition by means of the semibatch operation based on NSBEC is proposed. The authors expect that use of NSBEC can substantially reduce the number of experimental runs previously required to describe the system.
A fundamental study of polymer melt devolatilization: III More experiments on foam‐enhanced DV
Authors: Biesenberger Joseph A. , Lee Shau‐Tarng
Published: December 2004

A systematic, experimental study was conducted on the elementary process of devolatilization (DV) of volatile contaminants from polymer melts. Emphasis was placed on foam‐enhanced DV from rolling melt pools, which are present in rotating machinery. All experiments were conducted in a specially designed apparatus at room temperature using poly(dimethyl siloxane) to simulate the melt, and methyl chloride together with several chlorofluorocarbons as the contaminants. The special apparatus was devoid of the flow complexities present in industrial equipment and permitted independent control of all pertinent operating parameters. Physical properties and process parameters examined include feed composition and vapor pressure of contaminant, applied vacuum level, rotational speed of the pool, viscosity of the melt, and the effect of air entrainment.
Yield stress and flow measurements in ABA block copolymer melts
Authors: Hansen Paula J. , Williams Michael C.
Published: December 2004

A parallel‐plate constant‐stress rheometer is used to measure the yield stress τy, and the post‐yield flow curveT(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}), where τ is shear stress and\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}is shear rate, for microphase‐separated triblock copolymer melts. Five polymer samples, all styrene‐butadiene‐styrene but with differing composition ratios and molecular weights, are tested at 125°C. Specimens are prepared by casting sheets from solutions made with different solvents. The τ(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) is found usually to be sigmoidal, for the range 10−5<\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}< 10−3s−1, representing different stages of microstructural degradation in flow. Measurements indicate that a true τyexists, with values in the range 100 < τy< 500 Pa for these melts. A general trend is detected for τyto decrease as the casting solvent solubility parameter increases. A scheme for correlating the dependence of τy, on composition and molecular weight is proposed for the various polymers. For selected samples, the effect of mechanical history (sequence of stress application) and a temperature variation that crossesTs(110 to 150°C) are also explored.
Optimization of the polycondensation step of polyethylene terephthalate formation in semibatch reactors
Authors: Kumar Anil , Sainath A. E.
Published: December 2004

The polycondensation stage of polyethylene terephthalate (PET) formation is assumed to include side reactions leading to the formation of diethylene glycol, vinyl end groups, and acid end groups, in addition to the usual polymerization of bis (2‐hydroxyethyl) terephthalate (BHET) in semi‐batch reactors. A, flexible objective function has been proposed with temperature and pressure as control variables. Computations from the first variation technique show that the pressure should be reduced to the lowest limit under all possible conditions. Consequently, optimal temperature profiles in batch reactors are obtained for various lower limits of reactor pressures using the combination of first and second variation techniques. For the first variation technique, the vector iteration method of computation was used, and the near optimal profile so obtained was used as the initial guess for the second variation technique. The result of optimization shows that the lower limit of pressure and weighting parameters appearing in the objective function have profound effects on the optimum profiles. For higher pressures, it is shown that a high temperature must be used initially; but must be lowered later to minimize the formation of side products. However, for lower pressures, the temperature must be increased from a low value initially; but for large polymerization times, the temperature must be further reduced to minimize the formation of side products. It is thus seen that the optimum temperature profile for low pressures exhibits a broad maximum.
Uniaxial drawing of a copolyterephthalate based on ethylene glycol and 1,4‐cyclohexane‐dimethanol
Authors: Benavente R. , Pereña J. M.
Published: December 2004

The drawing of an amorphous copolyester based on poly(ethylene terephthalate) and poly(1,4 cyclohexylene‐dimethylene terephthalate) has been studied at temperatures from 20° to 100°C and various strain rates. The tensile properties, densities, and stress whitening of the stretched samples depend on whether the drawing temperature is below or above the glass transition temperature.
On the crystallinity and some structure/property relationships of poly(ethylene terephthalate)—poly(amide‐6,6) blends
Authors: Pillon L. Z. , Lara J. , Pillon D. W.
Published: December 2004

Following the ester‐amide interchange reaction in the poly(ethylene terephthalate)/poly(amide‐6, 6) (PET/PA) system in the presence of p‐toluenesulfonic acid (TsOH), samples were injection molded and tested in the tensile mode. A brittle fracture was observed for these unoriented specimens. To separate the influence of the crystallinity from that of the interphases, the samples were studied using differential scanning calorimetry (DSC). The DSC results indicated an increase of crystallinity in the blends caused by enhanced nucleation of PA (which crystallizes first) and that of the copolymer resulting from the esteramide interchange reaction. It has been independently verified that neat PET samples of comparable crystallinity to that existing in the PET/PA blends show a similar behavior.
Rheology of polymers containing carbon black
Authors: Lakdawala K. , Salovey R.
Published: December 2004

In order to elucidate the flow behavior of electrophotographic toner systems, shear stress was measured as a function of shear rate in a cone and plate rheometer for polymer melts containing carbon blacks of surface area 24 and 625 m2/g at several concentrations and temperatures. Polymers included high and low molecular weight polystyrene and poly(butyl methacrylate). The addition of carbon black to the polymers caused a large increase in viscosity, especially at low shear rates and shear stresses. As the concentration of carbon black was increased, the viscosity at low shear rates became unbounded below a value of the shear stress designated the yield stress. The absolute magnitude of the yield stress depended primarily on the concentration and surface area of the carbon black and was independent of the polymer and temperature. Apparently, carbon black forms an independent network within the polymer at low shear rates which precludes flow. In some cases, the viscosity of polymers filled with carbon black was lower than that of the pure polymer. This effect was favored for polystyrene compared to poly(butyl methacrylate) and was facilitated by increasing the molecular weight of polystyrene, reducing the surface area and concentration of carbon black, and by increasing the temperature and shear rate.
Rheology of copolymers containing carbon black
Authors: Lakdawala K. , Salovey R.
Published: December 2004

The rheological response of random copolymers of styrene and butyl methacrylate containing carbon black simulates the behavior of toner in the electrophotographic process. Both the relative viscosity and the dependence of viscosity on shear rate were increased by raising the temperature and raising the concentration and surface area of carbon black. For high concentrations and surface areas of carbon black and at elevated temperatures, a well‐defined yield stress varied from 2.5 × 102 to 1.6 × 104 Pa, depending on the concentration and nature of the carbon black but independent of the type of polymer and temperature, implying the formation of a carbon black network. Plasticization by carbon black was favored at low surface area and concentration of carbon black and at elevated temperatures.
Effect of die temperature on the flow of polymer melts. Part I: Flow inside the die
Authors: Yang Bing , Lee L. James
Published: December 2004

The effect of die wall temperature on the flow of polymer melts in circular capillary dies was studied. At constant flow rates, it was found that die wall temperature had a greater effect on the pressure drop than melt temperature. A capillary die with two circular channels with different diameters was designed to simulate the profile extrusion. Changes of wall temperature varied the flow rate ratio between the two channels. An implicit finite difference method was used to simulate the velocity and temperature profiles inside the die. Values predicted by this model matched well with experimental data for both dies.
Effect of die temperature on the flow of polymer melts. Part II: Extrudate swell
Authors: Yang Bing , Lee L. James
Published: December 2004

The effect of die wall temperature on the extrudate swell of polymer melts flowing through dies with single and dual circular channels was studied. Extrudate swell was measured at constant flow rates using an Instron capillary rheometer with a modified die section. It was found that under isothermal conditions, extrudate swell plotted against the average wall shear stress gave rise to a temperature independent correlation for polystyrene. Under non‐isothermal conditions, such a correlation did not exist, which might be due to the change of wall shear stress in the axial direction. The extrudate swell in the non‐isothermal cases can be better correlated with the wall shear stress at die exit. For the two‐hole die, changes of die wall temperature varied both the flow rate ratio and the extru date swell ratio. The latter is, however, much less sensitive to the die wall temperature than the former.
Fatigue and environmental resistance of polyester and nylon fibers
Authors: Mandell J. F. , Steckel M. G. , Chung S.‐S. , Kenney M. C.
Published: December 2004

The fatigue resistance of individual synthetic fibers can govern the performance of complex fiber assemblies such as tire cord and marine rope under certain loading conditions. This paper explores the relative performance of polyester and nylon 6,6 fibers and yarns, both dry and in aqueous solutions, primarily synthetic seawater. Fiber failure over a range of loading conditions and frequencies was found to occur at a critical cumulative strain, governed by a creep rupture process; the cyclic lifetime for both fibers is predictable using a simple creep rupture based theory. Polyester is more resistant to creep rupture, and consequently outperforms nylon 6,6 in cyclic fatigue. The advantage of polyester is considerably greater in aqueous solutions, where the performance of the nylon is diminished. Other comparisons indicate that the particular polyester fibers studied have higher stiffness and strength, lower strain to failure, and much lower hysteresis energy absorption compared with the nylon. The actual fatigue performance of complex fiber assemblies such as ropes is also limited under many conditions by factors not present in single fiber or yarn fatigue, including hysteric heating and internal and external abrasion.
Effects of strain‐induced crystallization on the elastic and thermoelastic properties of some fluoroelastomers
Authors: Hsu Y.‐H. , Mark J. E.
Published: December 2004

A Viton copolymer containing vinylidene fluoride (VF2) and hexafluoropropylene (HFP), and a terpolymer containing VF2, HFP, and tetrafluoroethylene (TFE) were cross linked using varying amounts of Bisphenol AF to yield two series of fluoroelastomer networks, Stress‐strain isotherms in elongation were determined for these samples at several temperatures and at two degrees of swelling with phenyl acetate. Strain‐induced crystallization was observed, as evidenced by upturns in the isotherms at high elongations. It appears to be more pronounced in the terpolymer samples, presumably because the TFE units not only can crystallize themselves, but can co‐crystallize with the VF2 units. The crystallization was found to persist upon moderate increase in temperature, but was suppressed when the networks were swollen, Thermoelastic (force‐temperature) measurements were used to obtain values of the fraction fe/f of the elastic force that is due to energetic effects. Negative values were obtained for both types of samples and, in the case of two samples studied in detail, their magnitudes increased with increase in elongation. The magnitudes were larger and the increases more pronounced in the case of the terpolymer networks, as would be expected from a greater tendency for straininduced crystallization.
Analysis of reaction injection molding process of polyurethane‐unsaturated polyester blends. Part I: Computer simulation
Authors: Kim J. H. , Kim S. C.
Published: December 2004

A computer simulation model was developed to analyze the reaction injection molding (RIM) process of polyurethane and unsaturated polyester blends. The reaction kinetics and viscosity functions of each component were obtained through actual experiments, and a mathematical scheme for numerical calculation was set up in cylindrical coordinates to predict the temperature and conversion profiles within a disc‐type mold. The temperature change calculated from the simulation was compared with the temperature rise measured in actual RIM experiments. The effects of the feed temperature, wall temperature, and catalyst levels on the maximum exothermic temperature and the demolding time were evaluated in a search for the optimum processing conditions.
Injection‐molding process control—A review
Authors: Agrawal A. R. , Pandelidis I. O. , Pecht M.
Published: December 2004

This paper reviews control strategies employed in the injection‐molding process. For clarity, the controlled variables have been categorized into all‐phase control, phase‐dependent control, and cycle‐to‐cycle control. All‐phase control includes variables that must be monitored and controlled at all times; i.e., in all the phases. Control of variables that are triggered during a specific phase are discussed under phase‐dependent control. In cycle‐to‐cycle control, previous data are used to predict future trends and take appropriate corrective actions, The cyclic, dynamic, and unsteady state nature of the injection‐molding process is discussed with respect to the conventional proportional‐integral (PI) and proportional‐ integral‐derivative (PID) controllers as well as the more advanced control schemes such as self‐tuning control, optimal control, and statistical process control. Suggestions involving specific advanced control schemes and recommendations for future research in injection‐molding process control also are made.
Functional polymers LI: Characterization and property analysis of ω‐functionally substituted polyolefins; novel polyolefin ionomers
Authors: Purgett Mark D. , MacKnight William J. , Vogl Otto
Published: December 2004

Homopolymers of 2,6‐dimethylphenyl 10‐undecenoate and copolymers of 2,6‐dimethylphenyl 10‐undecenoate with α‐olefins, prepared by coordination initiators using aluminum activated titanium trichloride, and the corresponding sodium carboxylate and carboxylic acid derivatives have been characterized. IR and NMR investigations gave the normal; spectral characteristics typical for estersubstituted polyolefins and their derivatives. The thermal behavior of the polymeric esters, investigated by differential scanning calorimetry, showed glass transitions characteristic of poly(α‐olefins). Polymeric acids and salts presented quite different behavior; most notably the polymeric salt showed no glass transition, but rather an exothermic transition, resembling a broad melting peak at 250‐270°C, which is characteristic of a crystalline polymer. We interpret this behavior as the melting of carboxylate cluster domains, which according to our WAXD analysis has a domain size of about 25 Å.
The importance of enthalpic interactions in polymeric systems
Authors: Barlow J. W. , Paul D. R.
Published: December 2004

Enthalpic interactions between blend components primarily determine the state of miscibility and many of the physical properties of the blend. Recent applications of these thermodynamic considerations are reviewed for a variety of systems, including binary and ternary blends of homopolymers, binary blends of copolymers with homopolymers, and polymer‐solvent mixtures. Recent advances toward predicting polymer blend miscibility through use of a modified quasichemical thermodynamic model and heats of mixing data for liquids are also discussed.
Linear low density polyethylenes and their blends: Part 4 shear flow of LLDPE blends with LLDPE and LDPE
Authors: Utracki L. A. , Schlund B.
Published: December 2004

The steady state and dynamic shear behavior of linear low density polyethylenes (LLDPE) blended with low density polyethylene (LDPE) and with another LLDPE resin were measured in capillary and parallel plate geometries at T = 150, 190, and 230°C. The extrudate swell and the Bagley correction were determined. It was observed that the pressure correction plays a significant role in capillary flow of LLDPE/LDPE blends–an indication of immiscibility. Several other rheological functions also suggested a phase separation for the system. Nevertheless, the blend behaved as a “compatible” mixture of emulsion type. By contrast, blends of two LLDPE resins show expected miscibility. However, even in this case additivity was not always observed. A new simple method of calculating the relaxation spectrum was developed. The method is analytical and its accuracy depends on adequacy of the semiempirical relation (proposed previously) to describe dynamic viscosity dependence on the test frequency. For all samples the spectrum allowed computation of storage modulus in good agreement with experimental findings.
Light‐scattering characterization of polyblends in the presence of multiple‐scattering conditions
Authors: Cielo P. , Favis B. D. , Maldague X.
Published: December 2004

A novel approach is described for the noncontact evaluation of structural morphology in polyblends by light scattering. Optical methods are attractive for the on‐line characterization of translucent materials because they are noninvasive, rapid, and applicable to high temperature materials. One limitation of conventional light‐scattering techniques is their requirement for relatively thin samples in order to avoid multiple‐scattering effects that smear out the details of the light diffraction pattern. The approach described in this paper is meant to circumvent this limitation by resorting to turbidimetric measurements, which provide useful information on the average size, shape, concentration, and orientation of the dispersed phase particles even in the presence of multiple scattering. The sample thickness is no longer restricted, and methods are described by which the near‐surface volume of infinitely thick parts may be inspected with access to a single side of the material. Results are presented for polypropylene‐polycarbonate (PP/PC) samples of different thicknesses and microstructural morphology, including fibrillar‐type oriented structures.
A modeling of semibatch reactors for melt transesterification of dimethyl terephthalate with ethylene glycol
Authors: Choi K. Y.
Published: December 2004

A mathematical model of a semi batch reactor was developed to investigate the oligomerization reactions in the melt transesterification of dimethyl terephthalate with ethylene glycol catalyzed by metal acetate catalyst. The detailed kinetic scheme based on the molecular species model is used to estimate the conversion of methyl ester groups and the concentrations of various oligomeric species. The numerical simulation of the model shows that the oligomerization reactions lower the overall conversion of methyl ester end groups. Effects of ethylene glycol/dimethyl terephthalate mole ratios, reaction temperature and, catalyst concentration on the conversion, oligomer concentration, oligomer molecular weight, and molecular weight distribution were also analyzed.
Formation of diethylene glycol by dehydration of glycol in the presence of terephthalic acid
Authors: Yamada Toshiro
Published: December 2004

The amount of diethylene glycol (DEG) formed as a result of the dehydration reaction of ethylene glycol (EG) in the presence of terephthalic acid (TPA) was measured. It became clear that the amount of DEG formed at the boiling point of EG can be expressed by a regression equation. It was confirmed that by this equation, the amount of DEG formed under the carboxylic end group concentration of 0.0 to 0.6 Eq/kg and the reaction time of 0 to 20 h can be estimated with high accuracy.
Strength properties of melt blown nonwoven webs
Authors: Choi K. J. , Spruiell J. E. , Fellers J. F. , Wadsworth L. C.
Published: December 2004

A method to obtain the tenacity and Young's modulus of nonwoven webs without direct measurement of web thickness is proposed. This has been tested with several series of samples with different basis weight. It was found that these properties were nearly Independent of the sample gage length, and both tenacity and modulus generally decreased with increase in the die temperature, the air pressure at the die, or the die to collector distance [DCD]. The web stiffness as measured by bending rigidity followed similar trends. The elongation Lo break also decreased as die temperature and air pressure at The die increased, but it increased with increasing DCD. The average filament diameter in the web decreased with increasing die temperature or air pressure at the die. The single filament strength was measured and compared with strength properties of web and of high‐speed melt spun filament prepared from the same resins. The strength of single filaments in the web lie in between those of the web and high‐speed spun filaments. The mechanical properties of melt blown web were interpreted in terms of the changes in Fiber diameter, the level of interfilament bonding, the molecular orientation developed in the filament, the diameter uniformity along the individual filaments in the web, and the presence of voids in the filament.
Relation between characteristics and melting point of oligomers in poly(ethylene terephthalate) manufacturing
Authors: Yamada T. , Imamura Y.
Published: December 2004

The applicable range of the regression equation proposed by Yamada, et al. expressing oligomer melting point by oligomer characteristics and relations derivable from the equation correlating each oligomer characteristic and melting point were studied. It was confirmed that the equation is applicable not only to poly(ethylene terephthalate) (PET) oligomer but also to the extent of polymerization. As number‐average degree of polymerization (Pn) increases, the influence of end groups on melting point becomes weak, and when Pn exceeds 50, the influence of end groups becomes negligibly small. On the other hand, when Pn is below 2, It was confirmed that the influence of end groups on melting point is very strong.