bluuebunny/crossref_metadata_2025_split huggingface dataset:
Engineering and molding properties of poly(vinyl chloride), acrylonitrile‐butadiene‐styrene and polyester blends
Authors: Khanna S. K. , Congdon W. I. 
Published: December 2004

AbstractPolymer blends with varying amounts of poly(vinyl chloride) (PVC), acrylonitrile‐butadiene‐styrene (ABS) and polyester have been developed to produce parts with highly flexible, good impact strength, and flame retardant hinge properties. In the present work, the rheological and dynamic mechanical properties are balanced by changing the blend formulations. It is shown that blends morphology and rheology have greater impact on the dimensional stability and delamination at the surface of the molded hinge parts.
Rheological properties of blown film low‐density polyethylene resins
Authors: Montes Sergio A. 
Published: December 2004

AbstractThree blown‐film‐grade low‐density‐polyethylene (LDPE) resins were studied using different rheological techniques. Eccentric rotating disks (ERD), cone‐plate viscometry, capillary rheometry, annular die extrusion, and non‐isothermal stretching of a filament were used. The viscoelasticity of the melts was found to play a dominant role in the observed behavior. Extrudate appearance in annular flow, melt strength, and extensibility are affected by melt elasticity. A correlation was found between the maximum draw ratio of a filament stretched under non‐isothermal conditions and minimum film thickness.
A rheo‐optical study on the reformation of structure in racemic poly(γ‐benzyl glutamate) liquid crystals
Authors: Asada Tadahiro , Onogi Shigeharu , Yanase Hiromi 
Published: December 2004

AbstractTransmitted light intensities were measured by means of the polarized light technique for the nematic liquid crystal phase of racemic poly(γ‐benzyl glutamate) (PBG) in m‐cresol at 25°C after cessation of steady flow at shear rates ranging from 0.2 to 110 s−1. Weight‐average molecular weights of PBG used were 1.5, 2.1, and 2.6 × 105, while the concentrations varied between 20, 30, and 40 wt percent. Transmitted light intensities with crossed and parallel polarizers, Ix and I|, show wavy changes with time after cessation of steady flow, indicating the retardation decreases with time. An attempt was made to explain experimental results on the basis of a simple model, in which not only relaxation of molecular orientation but also effects of the wall and disclination were taken into account.
The determination of the thermodynamic interaction parameter χ in polymer blends
Authors: Riedl Bernard , Prud'homme Robert E. 
Published: December 2004

AbstractThe miscibility of polymer blends is related to the polymer‐polymer interaction parameter χ23, Several methods can be used to evaluate this parameter and five of the most important ones are reviewed: two equilibrium methods (melting‐point depression and vapor sorption), a transport method (inverse‐phase gas chromatography) and two scattering methods (neutron scattering and small‐angle x‐ray scattering). Examples are cited where χ23 values for a given blend were determined by several of these methods. This comparison leads to the conclusion that a reasonable agreement is often reached despite conceptual differences between the methods involved.
A review of miscibility enhancement via ion‐dipole interactions
Authors: Eisenberg A. , Hara M. 
Published: December 2004

AbstractIt is shown that ion‐dipole interactions induce considerable miscibility enhancement in blends of styrene ionomers with poly(alkylene oxides). Dynamic mechanical studies, in conjunction with transparency and brittleness of the samples, are used to evaluate miscibility. The effect is clearly thermodynamics in that phase separation can be induced in miscible samples by raising the temperature, with miscibility reestablished ons cooling. The miscibility enhancement in these systems is compared with that resulting from hydrogen bonding. In addition to the styrene/alkylene oxide system, ion‐dipole interactions are found to be effective in enhancing the miscibility of many ionic polymer/polar polymer pairs. The ionomers used in this study were styrene lithium methacrylate and ethyl acrylate lithium acrylate copolymers, while polyethers, polysulfides, polyesters, polyimines, and substituted polyethylenses served as polar polymers.
Polycarbonate blends with polystyrene and polypropylene
Authors: Rudin Alfred , Brathwaite N. E. 
Published: December 2004

AbstractBlends of polycarbonate/polystyrene (PC/PS), polycarbonate/polypropylene (PC/PP) and ternary blends of the three components (PC/PS/PP) were studied. Extrudate swell of the molten blends increased with increasing concentrations of the minor components and leveled off at characteristic blend compositions. These compositions corresponded to the limits of compatibility as judged by the onset of brittleness in tensile tests. Both PS and PP appear to have some limited practical compatibility with PC. The change in extrudate swell behavior with concentration may be a rapid and convenient test for the effective concentration limits of partially miscible polymers.
Chemiluminescence apparatus and method for studying thermal oxidative stability of polymers
Authors: Zlatkevich L. 
Published: December 2004

AbstractA chemiluminescence multi‐sample apparatus and method are described for determining polymer stability by measuring the intensity of the light emitted during thermal oxidation. Depending on the nature of a material analyzed the experiments are performed either under O2 atmosphere at a constant temperature or under N2 atmosphere at a constant heating rate. In the former case applicable to polypropylene (PP) and acrylonitrile‐butadiene‐styrene copolymers (ABS), parameters such as induction time and oxidation rate can be evaluated. In the latter case applicable to nylon and polyethylene terephthalate (PET), the extent of oxidation in a certain temperature region can be evaluated by measuring the area under the intensity of light—temperature curve. Along with providing a great deal of knowledge on thermal oxidative stability, the chemiluminescence approach gives the additional information concerning polymer quality. The appearance of the low‐temperature pulses on the chemiluminescence curve observed before the onset of autocatalytic oxidation is associated with the history and processing of the sample and with the natural aging of the polymer.
Deformation recovery behavior of a solid polymer after tensile yielding
Authors: Rizzo Giovanni , Spadaro Giuseppe 
Published: December 2004

AbstractThe deformation recovery at room temperature of a polycarbonate after large tensile deformation and subsequent stress relaxation is measured as a function of time. The effect of the main parameters which affect the amount of recovered deformation is analyzed. This suggests a plot of the recovery versus time curves by means of proper coordinates which allow shifting of all curves towards a single master curve, thus indicating that most of the phenomena involved in the recovery process are taken into account.
Simulation of tubular low‐density polyethylene
Authors: Gupta Santosh K. , Kumar Anil , Krishnamurthy M. V. G. 
Published: December 2004

AbstractThe 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

AbstractMeasurements 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

AbstractA 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

AbstractA 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.
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

AbstractUnprimed 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

AbstractOn‐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

AbstractDraw 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

AbstractA 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

AbstractA 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

AbstractThis 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

AbstractA 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

AbstractThe 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

AbstractThe 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.
New directions in the nuclear magnetic resonance spectroscopy of polymers
Authors: Bovey F. A. 
Published: December 2004

AbstractThe 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.