bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical fiber coatings: High modulus coatings for fibers with a low microbending sensitivity
Authors: Bouten P. C. P. , Broer D. J. , Jochem C. M. G. , Meeuwsen T. P. M. 
Published: December 2004

AbstractAn important function of an optical fiber coating is to prevent optical losses due to microbending induced by lateral forces on the fiber. To protect the fiber over a wide temperature range the modulus of the primary and the secondary coating should be low and high, respectively, and temperature independent. However, selecting the most appropriate organic coating materials introduces a new source of optical losses. Since the linear thermal expansion coefficients of silica and the organic coatings differ by about two orders of magnitude, thermal, fluctuations will cause axial stresses. Cooling may then induce bending or buckling of the glass fiber in the soft primary coating, resulting in increased transmission losses. This effect is especially pronounced when a high‐modulus secondary coating is selected with a glass transition temperature above 80°C. For this type of coating the difference in radial shrinkage between the buffer and the top coating during cooling from the curing temperature becomes important. The influence of primary coating thickness is discussed.
A novel process for the formation of poly(p‐phenylene terephthalamide) film from liquid crystalline solutions
Authors: Fujita Tadahiro , Fujiwara Takashi , Sato Eiji , Nagasawa Keisaku , Amano Toshihiko 
Published: December 2004

AbstractA novel process for the formation of biaxially balanced films of poly(p‐phenylene terephthalamide) was developed. The liquid crystalline sulphuric acid solution is extruded through a slit die on a flat plate. The optically anisotropic to isotropic transition is generated by controlling the temperature and/or the water content in sulphuric acid before coagulation. The wet gel films are dried while holding their width and length constant. The films thus produced are transparent and biaxially oriented. Young's modulus of 12 GPa, tensile strength of 450 MPa, and elongation at break of 25% were obtained in the plane of the film. Such films which possess high dimensional and thermal stabilities are expected to be useful for new practical uses under severe conditions.
The importance of axial misalignment on the long term strength of polyethylene pipe butt fusion joints
Authors: Bowman Jeremy , Parmar Ravindra 
Published: December 2004

AbstractThe importance of axial misalignment at polyethylene pipe butt fusion joints has been assessed by undertaking elevated temperature lifetime tests. Both medium and high density polyethylene pipes were fusion joined to give aligned and controlled misaligned butt joints. These were tested under either a constant or fluctuating internal pressure loading using conditions that induced failure by slow, stable crck growth. It was observed that the lifetime of a butt joined system depends upon both the internal pressure or pressure range applied and the level of misalignment at the butt fusion joint. Increasing either the internal pressure (range) or the misalignment reduced system performance. These two variables of misalignment and internal pressure (range) may be incorporated into a single parameter, the amplified axial stress (or stress range) at the butt joint. This amplified or butt joint axial stress (or stress range) may be derived by considering the additional bending stresses introduced at the butt joint by virtue of misalignment combined with the axial stress loading.
The effects of flow on miscibility in a blend of polystyrene and poly(vinyl methyl ether)
Authors: Katsaros J. D. , Malone M. F. , Winter H. H. 
Published: December 2004

AbstractShear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow‐induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow‐induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow‐induced phase separation.
Monitoring the cure of an epoxy‐anhydride resin
Authors: Zukas Walter X. 
Published: December 2004

AbstractThe cure of an epoxy‐anhydride resin system used in pultrusion was characterized to develop an understanding of the cure behavior and to determine potential process controls parameters. Isothermal cures of neat resin formulations were monitored by differential scanning calorimetry (DSC), torsional braid analysis (TBA), and microdielectrometry (MDE). The processing conditions define a time/ temperature region in which monitoring would be applicable. Both DSC and MDE were found to yield useful information in this region, however, the events typically monitored by TBA either did not occur or occurred too quickly to be monitored. Significant ionic conductivity was observed in the fully cured resins at temperatures above the glass transition temperature and could possibly be used as a control parameter. This study revealed an apparent change in reaction mechanism with increasing cure temperature. DSC showed a change in activation energy with extent of reaction and a decrease in heat of reaction at the higher isothermal cure temperatures. The formation of a different network structure was indicated by a decreasing glass transition temperature of the cured resin with increasing cure temperature by both DSC and TBA.
The optical properties of a polyetherimide
Authors: Philipp H. R. , Le Grand D. G. , Cole H. S. , Liu Y. S. 
Published: December 2004

AbstractThe optical properties of polyetherimide resin as described by the complex index of refraction, N = n ‐ ik, are derived by Kramers‐Kronig analysis of experimental absorption and reflectance data obtained in the range 40 μm ≥ λ ≥105 nm. Potential uses of this polymer as a printed circuit board material and as a packaging medium for microelectronic circuitry and the relevance of optical data in laser‐assisted processing schemes used in these and other applications are briefly discussed.
Monitoring the quality of mix of polymer melts with particulate fillers using fluorescence spectroscopy
Authors: Bur Anthony J. , Shibata John , Trout Todd K. , Wang Francis W. , Thomas Charles L. 
Published: December 2004

AbstractFluorescence spectroscopy has been employed to monitor the mixing of polymer melts with filler material. The polymer melts were low molecular weight polybutadiene and PBAN, a terpolymer consisting of 85% butadiene, 11% acrylonitrile, 4% acrylic acid, and the filler material was aluminum oxide. To carry out the fluorescence observations, a dopant chromophore was mixed into the polymer melt at very low concentrations, 10−4 to 10−6 molar or 11 to 0.11 ppm by weight. The mixing experiments were carried out using a small laboratory mixer which had glass walls for viewing the fluorescence spectra from the dopant chromophore. Fluctuations in fluorescence intensity were observed to decrease as a function of mixing time indicating that the spatial distribution of the fluorescent chromophores was becoming more uniform. Concerning the mixing of polymer melt and filler, we hypothesize that uniform mixing of ingredients is achieved when fluorescence intensity as a function of time is constant. In order to obtain quantitative support for this hypothesis, we used a fluorescence microscope to measure fluorescence intensity and optical transmittance from microscopic regions of well‐mixed and poorly mixed specimens.
Studies on blends of polyethylene terephthalate with bisphenol‐a‐polycarbonate and polypropylene
Authors: Halder R. S. , Deopura B. L. , Misra A. 
Published: December 2004

AbstractMoldability and mechanical properties of polyethylene terephthalate (PET) under normal molding conditions were found to improve significantly when it was blended with bisphenol‐A‐polycarbonate (PC) and polypropylene (PP) to form ternary polymer blend systems. DSC results of these blends revealed that the PET and PC components formed a miscible blend while PP being incompatible with them, formed a separate phase. PP was also found to form a sleeve around the PET‐PC miscible phase and, thereby, showed a skin‐core type of morphology. Variations of mechanical properties with varying amounts of PP was measured keeping the ratio of PET and PC constant. Tensile and flexural properties of the blends decrease with the amount of PP. Notched impact strength increases up to a certain level of PP and then decreases, while the unnotched values decrease gradually. The effect of annealing on the mechanical properties of these blends have been discussed on the basis of the increased crystallinity of some of the components.
Grafting of a liquid crystal polymer on carbon fibers
Authors: Bhama Satya , Stupp Samuel I. 
Published: December 2004

AbstractCovalent grafting of mesogenic chains on carbon fiber surfaces was attempted as part of a study on composite materials containing liquid crystal polymer matrices. Grafting in these composite systems is viewed not only as a mechanism to achieve interfacial bonding but also as an approach to modify the interphase physical structure. The synthetic approach to grafting involved the in‐situ polymerization of monomers in the presence of functionalized fibers in order to grow chains covalently attached to the fibers. The chemical mechanism may be viewed as the “transesterification of car boxy lated fibers” with acetylated monomers. The monomers used were pimelic acid, p‐acetoxybenzoic acid and diacetoxy hydroquinone which are known to yield upon condensation a chemically aperiodic nematic polymer. Evidence for grafting was obtained from X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on fibers retrieved from composite samples. Interestingly, SEM micrographs of fractured composite specimens containing the mesogen‐grafted fibers reveal excellent wetting and interfacial bonding of a liquid crystalline matrix on the carbon surfaces. Based on theoretical considerations for end‐adsorbed macromolecules and the nematogenic nature of the grafted chains we infer that dense layers of adsorbed polymer may form at the interfaces studied. From a materials point of view the in situ growth of liquid crystal polymer chains on fibers may offer mechanisms to control composite properties through both bonding and molecular orientation in interfacial regions.
Crystallization of isotactic (D,L) poly(propylene oxide) in the presence of fine‐particle silica. I: Radial growth rates of spherulites
Authors: Kennedy M. A. , Brown G. R. , St‐pierre L. E. 
Published: December 2004

AbstractThe effect of added silica on the spherulite radial growth rates of isotactic poly(propylene oxide) (i‐PPrO) has been investigated by optical photomicroscopy. Two different i‐PPrO samples were used of different molecular weights and isotacticity, 87 and 100% as determined by 13C NMR. The addition of fine particle silica, an effective nucleating agent, depresses the spherulite growth rates throughout the entire temperature range, but the effect is more dramatic for the i‐PPrO of lower isotacticity. For a given sample, the retardation increases as the quantity of filler increases. The growth rate‐temperature behavior is analyzed in terms of the classical Hoffman‐Lauritzen equation, modified to take into account the polymer‐filler interaction.
Dimensional stability and property gradients in thick sheet molding compound (SMC) sections
Authors: Kau H. T. , Petrusha L. A. 
Published: December 2004

AbstractThe dimensional stability of sample cylinders cured with sheet molding compound pastes was investigated. A significant amount of dimensional change was found for these samples when they were annealed. Furthermore, the amount of change varied with location from the center to the wall along the radial direction of the sample cylinder to form a strain gradient. A series of experiments were then carried out to determine property gradients along the same direction in search of the source of the dimensional instability. It was found that the sample also had a gradient in cure and a gradient in dynamic mechanical properties. But these gradients are not in full agreement. In particular, the gradient of cure appears to be opposite to the direction of the strain gradient, while the gradient of the dynamic mechanical properties coincides with it. These results, therefore, suggest that the dimensional stability may be predominantly governed by the viscoelastic behavior of the material.
Analysis of the birefringence distributions in compact discs of polycarbonate
Authors: Wimberger‐Friedl R. 
Published: December 2004

AbstractThe birefringence distributions in injection‐molded Compact Discs (CD) are determined in radial and tangential cross‐sections and interpreted in terms of the process. The influence of processing conditions is discussed in several examples. It is shown that despite the high birefringence level the retardation of a beam of normal incidence is almost zero due to several compensation mechanisms. One optical axis is almost perpendicular to the surface. The medium, however, is biaxial with the preferential directions depending on the distance from the surface and the radial position. In contrast to a parallel beam, zero retardation cannot be achieved with a convergent beam in injection‐molded polycarbonate disks for that reason.
Crystallization and structure‐mechanical property relations in poly(aryl ether ether ketone) [PEEK]
Authors: Medellin‐Rodriguez F. J. , Phillips P. J. 
Published: December 2004

AbstractIn the development of advanced composite materials, the mechanical behavior of the matrix is of critical importance. The next generation of composite materials will be based on high modulus tough matrices, of which poly(aryl ether ether ketone) [hereinafter, referred to as PEEK] is one of the first crystalline thermoplastics to receive serious attention. As in all crystalline polymers, the matrix is itself a composite material whose properties depend significantly on the crystalline morphology developed during processing. In this contribution, the current understanding of crystallization in PEEK and its influence on mechanical properties is reviewed. Problems yet to be resolved are highlighted.
Rheological properties of multicomponent polymer systems undergoing melting or softening during compounding
Authors: Shih C.‐K. , Tynan D. G. , Denelsbeck D. A. 
Published: December 2004

AbstractThe rheological characteristics of a number of polymer blends, including amorphous and semi‐crystalline plastic matrices, during melting or softening, are analyzed with a batch mixer. The physical changes accompanying the phase transitions taking place as the slat‐and‐pepper blends are heated and mixed in the region of their component melt transition temperatures are monitored visually through a transparent window with video recordings. The torque of mixing and the mixture temperature are also recorded continuously. The strong effects of additives such as filler or lower melting resin as well as rotor speed, degree of fill, and ram pressure were observed.
Curing of unsaturated polyester resins: Effect of surface treatment of particulates
Authors: Shieh Jiunn‐Jye , Hsu Tzu‐Chien J. 
Published: December 2004

AbstractThe effect of surface treatment of particulates on the curing kinetics of unsaturated polyester resin has been investigated using a differential scanning calorimeter. Two coupling agents, γ‐methacryloxy propyltrimethoxy silane (γ‐MPS) and phenyltriethoxy silane (PTS), were employed. The former reacted with the resin; the latter did not. A kinetic model of free radical addition polymerization was used. A correction factor was used to represent the effective free radical concentration in order to account for the formation of charge transfer complex between the glass beads and the free radicals in the resin. The results indicate that (1) the resin with treated particulates showed generally faster reaction rate and conversion than the resin with untreated particulates; (2) no obvious difference on the curing kinetics was observed between these two coupling agents; the primary role of coupling agent is to inhibit the influence of particulates on the curing kinetics of the resin by effective surface coverage; and (3) a minimum aqueous concentration of 0.05 wt% was suggested for surface treatment of particulates; the reaction rate of the resin was slightly improved when the concentration of the coupling agent was 0.01 wt%; this might possibly be due to insufficient coverage of the particulate surface.
Dynamics of a continuous stirred tank reactor for styrene polymerization initiated by a binary initiator mixture. II: Effect of viscosity dependent heat transfer coefficient
Authors: Kim Kee Jeong , Choi Kyu Yong , Alexander James C. 
Published: December 2004

AbstractThe dynamic behavior of the solution polymerization of styrene in a continuous stirred tank reactor is analyzed with a mixture of tert‐butyl perbenzoate and benzoyl peroxide as an initiator system. In the modeling of the reactor, a viscosity dependent reactor wall heat transfer coefficient is used to account for the changing heat transfer efficiency as monomer conversion and polymer molecular weight increase. The steady state and bifurcation behaviors have been investigated with the reactor residence time, initiator feed composition, initiator concentration, feed solvent volume fraction, and coolant temperature as bifurcation parameters. Unlike the reactors with constant heat transfer coefficient, the present system exhibits relatively simple steady state and dynamic bifurcation behaviors. Oscillatory behavior is observed only when the solvent volume fraction in the feed exceeds 0.2. The dynamic simulation of the reactor also indicates that a feedback temperature controller may fail to maintain the reactor temperature when the heat transfer coefficient changes as a result of process disturbances.
Catalysis and kinetics of cyclotrimerization of cyanate ester resin systems
Authors: Osei‐Owusu A. , Martin G. C. , Gotro J. T. 
Published: December 2004

AbstractThe kinetics of cyclotrimerization and the thermal stability of bisphenol Abased cyanate ester resin systems were determined using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. The bisphenol A dicyanate was cured with 4 phr nonylphenol and with the octoates of zinc and manganese, and cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. An empirical rate law was used to predict the cyanate concentration profiles. The observed reaction rate showed a first‐order dependenće on the initial metal concentration and a second‐order dependence on the cyanate concentration in the kinetically controlled regime. For the uncatalyzed systems, the kinetics was described by a second‐order autocatalytic model. The thermal stability of the network was found to be dependent on the catalyst concentration for the zinc catalysts. For the samples cured with manganese, no effect of concentration on the thermal stability was observed.
Applications of flow simulation in reactive processing for cases in which the filling stage can be decoupled from heat transfer and chemical reaction
Authors: Castro J. M. 
Published: December 2004

AbstractFlow simulation to predict the position of the flow front during SMC and IMC compression molding, RIM, SRIM, and RTM, is very useful in obtaining better molded parts. We have derived criteria to determine when the filling stage for these processes can be decoupled and simulated without regard to heat transfer and chemical reaction. We discuss why a Generalized Hele‐Shaw model can be used to predict the flow front. Examples are given of the use of flow simulation in designing and locating SMC charges so as to reduce or eliminate knit lines, in locating IMC injection ports so as to avoid trapping air, in locating RIM injection gates to avoid trapping air and minimize knit‐lines, and in locating vents to avoid trapping air in RTM or SRIM molding.
Morphological responses in thermally conditioned linear low density polyethylene
Authors: El‐Kindi Mohammed , Schreiber Henry P. 
Published: December 2004

AbstractAn octene‐modified linear low density polyethylene has been used to examine the mechanisms involved during thermal annealing. Annealing temperatures ranged from 60 to 100°C. Annealing results in crystallinity increments and these respond to two concurrent effects. One involves the segregation from crystalline regions of low molecular weight moieties in the polymer's molecular weight distribution; the other is lamellar thickening, leading to the formation of more highly perfected crystalline domains. In the present polymer, the two effects were found to be in balance at annealing temperatures near 80°C leading to the optimum distribution of crystalline regions in the amorphous portions of the polymer. The effect of thermal conditioning on mechanical properties of the polymer was illustrated in terms of the initial modulus and the polymer's yield strength. The twin mechanisms of molecular fractionation and lamellar thickening were found to influence both of the mechanical property parameters.
Influence of reprocessing on the mechanical properties of a commercial polysulfone/polycarbonate blend
Authors: Sánchez P. , Remiro P. M. , Nazábal J. 
Published: December 2004

AbstractCommercial polysulfone/polycarbonate (PSU/PC) polymer blends were reprocessed up to five times to determine the influence that reprocessing has on their structure and physical properties. All the high strain properties, mainly ductility, significantly decreased under harsh processing conditions, such as five cycles at 320°C. The results of reprocessing the blends at 320°C have been compared with results at a lower temperature and also with those of the separate components with the aim of clarifying the origin of the degradation. These results plus Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis, and melt flow index measurements (MFI) indicate that the presence of the two polymers together clearly decreases the resistance to degradation of each component. Moreover, degradation under the stated conditions is mainly thermal and does not change the chemical nature of the blends. However, a clear decrease in molecular weight was observed both by viscosimetry and MFI measurements as was a shift to higher temperatures of the low temperature secondary transition of both PC and PSU. Both molecular weight and secondary transition changes usually deteriorate mechanical properties but not in the degree observed here. This probably means that the fine and difficult‐to‐observe structure of the blend has also changed.
The influence of intracomplex compounds of copper and cadmium on the properties of epoxy amine systems
Authors: Kurnoskin A. V. 
Published: December 2004

AbstractThe influence of intracomplex metal compounds, namely, copper salicylate and cadmium anthranilate on the properties of diglycidyl bis‐phenol A ether (DGEBA) hardened with diethylene triamine and triethylene tetramine has been investigated. The dependence of hardenability of the amines modified with the salts on the content of the salts has been determined. The saturation of the amines with salts has been shown to result in formation of hardeners affording good stability of compositions. The above fact can be attributed to the blocking of the amino nitrogen atoms by the metals and neutralization of the hydrogen atoms with the anions. The properties of metal‐containing polymers has been studied; increases of their strength indices and heat stability in comparison with the initial aliphatic amines have been established.