bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transverse orientation dies for solid‐state extrusion of polymers. Part II: Orientation and properties of extrudates
Authors: Mascia L. , Zhao J. 
Published: May 2005

AbstractBiaxial orientation in polymer products is normally brought about by the application of planar tensile stresses to sheets or films in either the “plastic” or “rubbery” state. More recently, other techniques have been explored as, for instance, the superimposition of rotational components in planes perpendicular to compressive forces. The present work is concerned with the solid‐state extrusion of very high molecular mass crystalline polymers, such as poly(tetra)fluoroethylene (PTFE) and ultrahigh‐molecular‐weight polyethylene (UHMWPE), using dies featuring converging and diverging walls perpendicular, to each other and with a cross‐section area at the entry being the same as at the exit. Measurements of birefringence and tensile strength on solid section extrudates have shown that dies with small converging angles, known as fish tail dies, produce a uniaxial type of orientation along the transverse direction, while dies with large converging angles at the entry region give rise to an unbalanced biaxial orientation.
Electronic structure of poly(p‐phenylene sulfide)
Authors: Tanabe Yoshikazu , Shimizu Hiroshi 
Published: May 2005

AbstractThe electronic structure of poly(p‐phenylene sulfide) (PPS) was studied through steady state photocurrent spectra and temperature dependence of dark conductivity for undoped film, by changes in the in situ optical absorption and ESR spectra under photoirradiation, and optical absorption spectra for doped film. The charge carriers in the undoped state are electronic since the photoconductivity is large and the kink point in the temperature dependence of dark conductivity is higher than the glass transition temperature. A sharp peak near the absorption edge in the photocurrent spectrum of undoped PPS is caused by the diffusion of photocarriers in a sheet with high surface recombination under conditions of low applied field. The in situ optical absorption and ESR spectra of SO3‐doped PPS were similar to those of di‐p‐tolyl sulfide (a monomer unit of PPS) and the formation of sulfur‐centered radical cations was suggested rather than bipolaron states. The stable conduction of SO3‐doped PPS after exposure to atmosphere was analyzed by the classical Lorentz model and the existence of nearly free carriers within subchains was suggested. Their conductivity and mobility were estimated to be 2 S/cm and 3.6 cm2/Vs, respectively. Inter‐chain conduction appears to be very low.
Aging mechanism of phenolic resin–nitrile butadiene composites
Authors: Cooper Anthony R. 
Published: May 2005

AbstractThe aging mechanism of phenolic resin‐nitrile butadiene composites has been investigated. Using solvent extraction and chromatographic analysis of the extract using dual detectors it was shown that the rubber component was well crosslinked. The phenolic component however was not fully crosslinked, although it would have been expected from the cure conditions employed. With increased time, at temperatures near ambient, the phenolic resin continued to react and caused increased brittleness of the composite.
Preparation and properties of a liquid crystalline segmented block copolyester
Authors: Wang Jing , Lenz Robert W. 
Published: May 2005

AbstractA segmented block copolyester with a liquid crystalline (LC) “hard block” and poly(tetramethylene glycol) (PTMG) “soft block” was prepared and characterized by intrinsic viscosity [η], by gel permeation chromatography (GPC) for number average molecular weight and molecular weight distribution, by differential scanning calorimetry (DSC), and by dynamic mechanical thermal analysis (DMTA). The “soft block” had a melting transition at about −30°C and the hard block had a glass transition at about 70°C and a nematic‐to‐isotropic transition at 260°C. Mechanical testing, which included tensile testing, hysteresis analysis and stress relaxation at small strains, revealed that the block copolyester was a flexible rubbery material with an elongation at break of about 1000% and showed reversible extension below 50% strain.
Processing‐Property interactions in vinylidene fluoride/trifluoroethylene random copolymers
Authors: Khomami B. , Langton C. A. 
Published: May 2005

AbstractThe effect of flow history, processing temperature, and exit draw ratio have been studied for copolymers of vinylidene fluoride/trifluoroethylene of molar compositions 66/34 and 75/25%. The copolymers were extruded through an impinging channels film die which produces a mixed extension and shearing flow as well as a slit die. Stress fields during flow were measured using flow birefringence. Differential Scanning Calorimetry (DSC) analyses were used to characterize the thermal behavior; and flat film and Wide Angle X‐ray Scattering (WAXS) were used to evaluate the crystal structure and morphology of the extrudates. Extensional melt stresses on the order of 6.35 × 105 Pa were necessary to induce sufficient orientation for crystallization of water‐cooled 66/34 mol % copolymers into the all‐trans configuration. Preorientation of the melt by extensional stresses enhanced the transformation of the 3/1 helical to an all‐trans structure in the 66/34 copolymer as well as producing a more compact unit cell in the 75/25 mol % copolymer leading to as much as a 7°C higher Curie transition temperature.
Surface analysis of plasma‐treated poly(ethylene terephthalate) film
Authors: Nakayama Y. , Soeda F. , Ishitani A. , Ikegami T. 
Published: May 2005

AbstractSurface structures of poly(ethylene terephthalate) films produced by stretching after Ar plasma‐treatment were analyzed by X‐ray photoelectron spectroscopy, combined with a gas chemical modification technique, secondary ion mass spectrometry, and transmission electron microscopy. The formation of ultra‐fine protrusions that produce good slip and a smooth film surface after the stretching procedure was confirmed. The height of the protrusions was almost the same as the thickness of the osmic acid‐dyeable layer. The thickness of the modified layer was found to change according to the Ar pressure of the plasmatreatment. Carboxylic and hydroxyl groups produced by the plasma‐treatment were quantified. The formation of these functional groups can explain good adhesion of the film.
Numerical simulation of mold filling in reaction injection molding
Authors: Hayes R. E. , Dannelongue H. H. , Tanguy P. A. 
Published: May 2005

AbstractA two dimensional finite element model for the simulation of the advancing front in reaction injection molding (RIM) is presented. The model is based on the solution of the full Navier‐Stokes equation for the computation of the velocity and pressure. The arbitrary Lagrange‐Euler method is used for the moving front. The method of characteristics is used for the solution of the mass‐and energy equations. An automatic remeshing algorithm is used to prevent element distortion and to optimize element size and number. Numerical results are presented for flow into a complex domain in order to illustrate the versatility of the method.
Analysis of polymer membrane formation through spinodal decomposition
Authors: Caneba Gerard T. 
Published: May 2005

AbstractA phenomenological model used in a previous work for spinodal decomposition of polymer‐solvent systems is further analyzed. From the dimensionless form of the nonlinear Cahn‐Hilliard equation, the dimensionless induction time is found to be a constant number for suddenly quenched systems. Computer simulation is carried out for prediction of early stage behavior with thermal history corresponding to a linear temperature drop followed by a constant temperature vs. time. In the areas of polymer membrane formation and phase separation studies, the universality of the constant dimensionless Induction time for suddenly quenched systems allows the determination of the minimum time needed for phase separation via spinodal decomposition. Also, simulation results for the double linear temperature history allows the convenient prediction of early stage spinodal decomposition behavior at every point of a membrane cross section undergoing thermal inversion phase separation.
Rheology, morphology, and mechanical characteristics of poly(etherether ketone)‐liquid crystal polymer blends
Authors: Mehta Atul , Isayev A. I. 
Published: May 2005

AbstractThis paper is in continuation of our previous paper on Poly(etherether ketone)‐liquid crystal polymer (PEEK‐LCP) composites. Rheological, morphological, and mechanical properties of polyetherether ketone and a thermotropic liquid crystalline polymer based on hydroxybenzoic acid/hydroxynaphthoic acid have been reported. Addition of LCP resulted in a marked reduction of viscosity and improved processability. Tensile properties improved with increase in LCP concentration. Synergistic effects have been observed at certain LCP concentrations. The elongation at break was found to reduce drastically above 10% of LCP content. This is a characteristic typical of chopped‐fiber‐filled composites. Morphology of injection molded and capillary extruded samples of the blends showed that the in‐situ formed fibrous LCP phase was preserved in a solidified form. The improvement in tensile properties is likely due to the reinforcement of the PEEK matrix by the fibrous LCP phase as observed by scanning electron microscopy. A distinct skin‐core morphology was found to develop in the injection molded samples of these blends. Mechanical properties measured in the flow and transverse direction indicated an increase in the degree of anisotropy with an increase in LCP content.
Thermal properties and morphology of hydrostatically extruded polypropylene
Authors: Ariyama Takashi , Takenaga Mitsuru 
Published: May 2005

AbstractThe melting point, specific heat, and morphology and hydrostatically extruded polypropylene (PP) were studied to clarify the plastic deformation of three different parts of the extrudates (periphery, intermediate, and core) parallel to the direction of hydrostatic extrusion. Differential scanning calorimeter (DSC) measurements showed that, for all the parts studied, the peak and the end‐of‐transition, temperatures had a minimum value at a percentage reduction in area, R, of 50% Similar behavior was observed for the specific heat evaluated at several temperatures below the melting point. The morphological structure observed by use of a polarizing microscope indicated that the shape‐ of spherulites above R = 50% changed from spherulitic to elliptic. It is suggested that the pronounced changes taking place around R = 50% are closely related to the marked bend in the extrusion pressure versus extrusion ratio curve which takes place at the same R value. The molecular chains in the coarse spherulites appear to be deformed below R = 50% in such a way that finer spherulites are formed; but at R values above 50% the presence of elliptic spherulites implies that non‐uniform deformation is present under higher hydrostatic pressure of extrusion.
Adaptive pressure control for melt spinning processes
Authors: Jang Yu‐Jen , Wu Wen‐Tend , Bai Chi‐Chung , Liu Shang‐Ren , Chuang Yun‐Yih 
Published: May 2005

AbstractIndirect adaptive control of the pressure of an extruder for melt spinning processes was investigated. The controller was a proportional‐integral‐derivative. (PID) one. An identified model for the pressure system was determined by using weighted least‐squares estimation with an adjustable Identification interval. On‐line tuning of the PID controller based on the identified model was then carried out. Difficulties in determining the proper model and controller tuning were avoided. The experiment, carried out with a pilot‐type melt spinning machine, resulted in higher quality fiber production.
A 2‐d numerical study of intermeshing self‐wiping screws in biopolymer extrusion
Authors: Lai‐Fook R. A. , Li Y. , Smith A. C. 
Published: May 2005

AbstractA knowledge of flow behavior is important in the study of laminar flow in twin‐screw extrusion processes to predict the velocity distribution and to understand the mixing process. The flow of a power law fluid in self‐wiping twin‐screw extruders is examined using a two‐dimensional finite element analysis of a mid‐channel section of intermeshing screws. Theory is compared with experiment using food biopolymer and plastic materials. Comparisons showing overprediction of throughputs, but similarities in behavior, suggest that this model could provide an upper limit for melt conveying. For most of the throughput range examined, pumping of intermeshing self‐wiping screws appears to be almost independent of the power law flow index of the melt extruded, but the value of the flow index determines the degree of influence intermeshing has on the overall pressure gradient generated in the extruder.
The effects of varied reactant ratios on the polymeric structures of stannous dicarboxylates
Authors: Ibidapo T. A. , McIntyre J. E. , East G. C. 
Published: May 2005

AbstractSome polymeric Sn(II) dicarboxylates have been produced with good yields from aqueous solution via a double decomposition reaction using varied nonstoichiometric molar proportions of the reactants. They were obtained as highly viscous pale yellow liquids formed into separate denser phases in the precipitation bath. The highly viscous precipitates were drawn directly into fibers. Meltspun polymeric stannous dicarboxylates produced fibers which were only flexible above the glass transition temperature, Tg.When the aliphatic dicarboxylic acids were replaced with their aromatic counterparts similar highly viscous liquids were obtained, but they solidified almost at the instant of formation.
Dielectric properties of a curing epoxy/amine system at microwave frequencies
Authors: Finzel Mark C. , Hawley Martin C. , Jow Jinder 
Published: May 2005

AbstractDielectric data collected at 2.45 × 109 Hz has been analyzed using a mean relaxation time model over the temperature range 50 to 100°C and at extents of cure from 0 to 57% for a stoichiometric DER 332 (Dow)/DDS (Aldrich) mixture. The relaxation times thus obtained obey the Arrhenius law and tend to increase with the extent of cure. This corresponds to the more rigid nature of the molecular structure as the network forms and the dipolar relaxations become more inhibited. Decreases in the activation energy of the relaxation along with a widening of the relaxation time distribution imply that the relaxations involve ever shorter chain segments as the extent of cure increases.
Microtexture and mechanical properties of carbon fibers: Relationship with the fiber‐matrix adhesion in a carbon‐epoxy composite
Authors: Guigon M. 
Published: May 2005

AbstractThe structure and the microtexture of carbon fibers are determined by transmission electron microscopy. All PAN‐based carbon fibers are made up of elemental microtextural units (EMU) whose microtexture governs their mechanical properties. EMU Carbon layers exhibit either their edge or their surface for outcropping the external surface of the fiber. Interfacial phenomena between fibers and matrix in a composite material depend on this outer microtexture.
Effects of air entrainment on the rheology of concentrated suspensions during continuous processing
Authors: Kalyon Dilhan M. , Yazici Rahmi , Jacob Cherian , Aral Birnur , Sinton Steve W. 
Published: May 2005

AbstractSamples of a concentrated suspension were systematically collected from the mixing volume of a continuous processor. The large amplitude oscillatory shear behavior of the samples was found to be significantly affected by the screw configuration employed and the location. Microstructural analyses employing nuclear magnetic resonance imaging, wide‐angle X‐ray diffraction and X‐ray radioscopy revealed substantial entrainment of air into the suspension during continuous processing. The volume fraction of the entrained air increased with geometries and operating conditions leading to partially full channels. Overall, air entrainment is identified as a dominant factor in the development of the microstructure and the rheology of concentrated suspensions and should be considered in their optimum processing.
Dynamic mechanical response of model epoxy networks in the glassy state
Authors: Cukierman Serge , Halary Jean‐Louis , Monnerie Lucien 
Published: May 2005

AbstractThe dynamic mechanical properties of model epoxy‐amine networks are investigated in the glassy state over a wide range of frequencies, at temperatures between 123 K and 350 K. The effects of crosslink density and network chain flexibility on the β relaxation are examined. Motions responsible for the β process begin to develop at the same temperature, whatever the crosslink density. However, an increase in crosslink density is accompanied by an increase in amplitude and a broadening towards high temperatures of both damping tan δ and loss modulus E″. This effect is responsible for the decrease of elastic modulus E′ at room temperature with increasing crosslink density.
Examination of dimethacrylate inhomogeneity by solvent swelling techniques
Authors: Simon George P. , Allen Peter E. M. , Williams David R. G. 
Published: May 2005

AbstractDimethacrylate monomers polymerize to form highly crosslinked networks with an inhomogeneous distribution of regions of low and high crosslink density. The systems are probed in this work by observing the effects of solvents (nitrobenzene and water) on dynamic mechanical measurements, diffusion kinetics and fracture toughness experiments. Dynamic mechanical analysis showed that the addition of nitrobenzene is found to have little effect on the position of the glass transition or secondary relaxations for solvent levels of under 3.5 mass %. It is proposed that solvents initially diffuse into low crosslink density regions, impinging little on the methacrylate mainchains which reside largely in regions of high crosslink density. Only at higher solvent concentrations do these chains become plasticized. Confirmation of heterogeneity is provided by diffusion analysis of isothermal solvent uptake. This is also interpreted interpreted in terms of a two‐stage diffusion process due to differential rates of sorption which occur in different microregions. Weighing of the water uptake of samples suspended in water indicated that some 30% of water absorbed at equilibrium exists within void regions. Addition of water causes the fracture mechanism to change from a ‘stick‐slip’ mechanism characteristic of brittle polymers to stable crack growth with a lower fracture toughness. This is also attributed to differential swelling of the material causing internal stresses which aid material failure.
Fracture studies on a polyacetal—new thermoplastic polyurethane blend
Authors: John Reji , Neelakantan N. R. , Subramanian N. , Nair E. M. S. 
Published: May 2005

AbstractStudies based on fracture mechanics have been made on polyacetal toughened with a synthesized thermoplastic polyurethane. The effects of elongation rate and defects like holes and notches on tensile properties have been investigated. Using three‐point bending specimens, fracture mechanics parameters such as strain energy release rate, G, Rice's contour integral, J, and fracture toughness, K have also been determined under plain stress conditions. The mechanical loss from the hysteresis curves, and ductile, brittle fractography using scanning electron microscopy have also been studied.
A method for predicting the useful life of moisture‐sensitive plastics
Authors: Dixon Robert R. 
Published: May 2005

AbstractArrhenius plots have long been used to allow predictions of the long‐term useful life for a variety of materials. These plots are generated by testing materials exposed to elevated temperatures for different intervals of time. Since such a technique eliminates moisture from consideration, a different technique should be employed for moisture‐sensitive materials used in humid ambients. A technique is described to allow for humidity in the prediction of useful life in moisture‐sensitive plastics. Modified Arrhenius curves are presented for a number of such plastics.
Predicting the behavior of nonlinear viscoelastic materials under spring loading
Authors: Brueller O. S. 
Published: May 2005

AbstractStructural parts made of plastics are usually tested under creep loading conditions, i.e., the stress is applied almost suddenly and then kept constant, while defomation is measured. In practice, however it happens that such a structural part is loaded by an elastic member (for example, by a spring). In this case, the acting force is no longer constant; it decreases in the course of time, while the deformation of the specimen increases (and, obviously, that of the spring decreases). The present paper describes a numerical approach for the solution of this problem, based on the assumption that the creep behavior of the material is known. An example is presented.
Dielectric monitoring of the curing process in cyanoacrylate resin
Authors: Radhakrishnan S. , Saini D. R. 
Published: May 2005

AbstractThe cure monitoring of cyanoacrylate resin using a dielectric technique shows that in addition to the usual fast anionic polymerization step, there may be a secondary process involved over longer time scales. Two peaks are distinctly observed in the isothermal curing curves, and from the position of these at various temperatures, the activation energies of 0.4 eV and 0.17 eV could be derived. In cured cyanoacrylate resin, three relaxations were observed, viz., α, β, and γ, occurring at 152°c, 87°c, and 47°c, respectively (for 1 KHz measuring frequency), with activation energies of 1.3 eV, 0.56 eV, and 0.4 eV, respectively. The various results have been explained on the basis of secondary bond formation through the nitrile group, for which some evidence could be obtained from the infrared absorption spectra.
Optimization of the vulcanization process of rubber products
Authors: Steen J. , Aben W. J. , Wapenaar K. E. D. 
Published: May 2005

AbstractSelection of the optimum conditions for the vulcanization of rubber products, particularly of bulky ones, often is quite difficult. Especially in cases of high demand, it is unavoidable to destruct expensive prototypes in order to check important properties of the rubber at various locations throughout the product. Finite element calculations can be used to predict the flow of heat during the vulcanization process. By converting the total heat input at a selected location during a certain time into a so‐called “effective vulcanization time” at a fixed reference temperature, it becomes possible to predict the properties of the rubber at that location. An example of such a procedure is given. However, to secure optimum conditions in this way would require repetitive (expensive) calculations. In this article a method is developed in which the vulcanization conditions are derived from the required properties of the rubber compound. The idea behind it is that optimal vulcanization is reached when at each location within the rubber product the effective vulcanization time at a selected reference temperature lies within predefined limits. The choice of the limits can be derived from the dependence of each of the properties chosen on the vulcanization time at the reference temperature.