bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisotropy of electrical conductivity and structure in polymer‐carbon fiber composite materials
Authors: Nascimento J. Fernandes , Ezquerra T. A. , Baltà‐Calleja F. J. , Seferis J. C. 
Published: December 2004

AbstractElectrical conductivity for polyether and polyimide‐carbon fiber composites was measured using different fiber types. The microstructure was characterized by X‐ray diffraction methods. D.C. conductivity measurements were carried out in directions perpendicular, parallel, and at varying angles to the fiber axis. The influence of the distance between electrodes on the conductivity was examined. The dependence of the frequency and the temperature upon conductivity has been, likewise, investigated. Experimental results support the concept of a conduction mechanism in the composites occurring in the carbon fibers, which built up a highly interconnected conducting network. It is also shown that the high degree of fiber orientation is consistent with the conspicuous anisotropic behavior of the electrical conductivity.
An approximate method for the determination of poisson's complex ratio in harmonic viscoelastic behavior
Authors: Agbossou Amen 
Published: December 2004

AbstractTo improve the simulation of viscoelastic behavior of composites, an approximate and incremental method for the determination of Poisson's complex ratio of the polymer matrix is proposed. This method is based on the fact that many polymers exhibit a slight variation of their bulk modulus throughout, at their main relaxation temperature. We examine different parameters that affect the proposed method. It is shown that (i) the Poisson's complex ratio of the matrix and the complex modulus of the composite depend significantly on the initial values of the incremental method and (ii) the Poisson's complex ratio of the matrix allows for the effects of filler content on the magnitude of the mechanical relaxation.
Modification of pitch‐based carbon fibers using a nickel‐catalyzed oxidation treatment: Effect of treatment on fiber‐matrix interfacial shear strength
Authors: Rearick B. K. , Harrison I. R. 
Published: December 2004

AbstractPitch‐based carbon fiber surfaces were modified using a nickel‐catalyzed, dry oxygen etch (NCDO) and a dry oxygen etch (DO), both of which were applied using a continuous process. The treatments differed in that DCDO produced preferential pitting on fiber surfaces at nickel particle sites. Tensile strengths of all etched fibers were slightly lower than values for untreated, or “as received” (AR), fibers. Reductions in tensile strength were independent of the type of treatment administered, indicating that most degradation resulted from damage produced by the mechanics of the continuous process, not the etching treatments. Fiber‐matrix interfacial shear strengths (IFSS) of AR and etched fibers were evaluated using the Microbond test. At first glance, Microbond test data indicated that NCDO produced large increases in IFSS. However, inconsistencies in the data raised questions regarding the validity and usefulness of the Microbond test when applied to this system. Only after detailed analysis of the data for this series of fibers was it concluded that NCDO did indeed produce an increase in IFSS over AR fibers and DO fibers.
The influence of pre‐carbonization on the properties of PAN‐based carbon fibers developed by two‐stage continuous carbonization and air oxidation
Authors: Ko Tse‐Hao , Li Chien‐Hung 
Published: December 2004

AbstractThe Properties of three kinds of carbon fibers, which were pre‐carbonized at 500, 550, and 600°C during two‐stage continuous carbonization, were measured after being air oxidized for periods of 1 to 6 min at 550°C. The effects of precarbonization temperatures on mechanical properties, density, morphology, elemental compositions, and microstructure of the carbon fibers are discussed. The pre‐carbonization process affected strongly the surface properties and mechanical properties of the final carbon fibers, as measured after air oxidation. Carbon fibers measured one to six min after air oxidation showed a different oxidation behavior in the surface morphology for each pre‐carbonization temperature. Optimum conditions not only improved the tensile strength and modulus by over 50%, but also increased the density and oxygen content.
Resin flow analysis in the consolidation of multi‐directional laminated composites
Authors: Young Wen‐Bin 
Published: December 2004

AbstractAdvanced fiber reinforced polymer composites have been increasingly used in various structural components. One of the important processes to fabricate high performance laminated composites is an autoclave assisted prepreg lay‐up. Since the quality of laminated composites is largely affected by the cure cycle, selection of the cure cycle for each application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary to properly select the suitable parameters for each application. This study applied the theory of consolidation and flow in a porous medium to provide a general model for the three‐dimensional consolidation process of the laminates with fibers reinforced in multi‐directions. Based on the model analysis, one can predict the pressure, velocity, and laminate thickness during consolidation process, which, as coupled with the curing analysis, can be used to properly select the cure cycle for applications of laminated composites.
Molecular structure effect of thermotropic liquid crystalline polymers on interfacial adhesion with polycarbonate
Authors: Kwon Soon Kil , Chung In Jae 
Published: December 2004

AbstractThe effect of molecular structure of thermotropic liquid crystalline polymers (TLCP) on the interfacial adhesion with polycarbonate (PC) was investigated by varying the flexible spacer length in the main chain of the TLCP. The interfacial adhesion was estimated by two methods: (1) the debonding stress from the melt‐contacted TLCP/PC plates was measured by a modified pin‐pull test; (2) the mechanical response of the melt‐mixed blend was analyzed by the composite theory. Both methods indicated that the interfacial adhesion of the TLCPs with flexible spacer was improved over that of a rigid TLCP (i.e., Vectra A950), and that it was further enhanced by an increase in the length of a flexible unit.
Composites based on drawn strands of thermotropic liquid crystalline polymer reinforced polypropylene
Authors: Sabol E. A. , Handlos A. A. , Baird D. G. 
Published: December 2004

AbstractThis paper is concerned with the use of two thermotropic liquid crystalline polymers (TLCPs), HX1000 and Vectra B950, to reinforce a thermoplastic matrix of polypropylene (PP). The goal was to pregenerate the optimal TLCP reinforcement in PP and then process the material at a lower temperature than the melting point of the TLCP to form a composite structure. Specifically, strands of the blend were produced using a dual extrusion process, which resulted in the formation of axially continuous TLCP fibrils within the PP matrix. It was found that the mechanical properties of the strands were greatly improved by increased draw ratio and that optimal reinforcement, as predicted by the rule of mixtures, could be achieved. Initial studies indicated that injection molding and sheet extrusion of the pelletized strands caused the TLCP phase to agglomerate and deform, which resulted in a reduction of the mechanical property enhancement. However, the TLCP fibrillar morphology in the pregenerated strands was maintained during compression molding, which resulted in uniaxial composites with properties equal to or greater than properties of the strands. In addition, composites were made using compression molding in which strands were randomly oriented prior to consolidation to show the limits of properties possible in composites produced from the pregenerated strands. It was found that this process could be used to produce composites in which the mechanical properties were isotropic in the plane of the sample and approached the properly limits predicted by composite theory. Additionally, it was found that many of the mechanical properties of the VB/PP materials were greatly enhanced by the addition of a maleated PP throughout the composite forming process.
Statistical aspects of infinite network formations
Authors: Saito Osamu 
Published: December 2004

AbstractInfinite network formation is discussed using the theory of molecular size distribution functions. The necessary and sufficient conditions of infinite network formation in simultaneous crosslinking and main chain scissions are reviewed. Also, the condition of endlinking associated with main chain scissions is outlined; the condition of endlinking of special terminal groups is given. Infinite network. formation in condensation as well as addition polymerizations is studied. It is shown that the existence of branch units in condensation polymerization is only the necessary condition of infinite network formations, whereas the sufficient condition is related to the form of branch units; the necessary condition in addition polymerizations is the simultaneous occurrence of chain transfer to polymer and chain termination by recombination.
Barrier and surface properties of polyurethane‐epoxy interpenetrating polymer networks. II
Authors: Frisch H. L. , Foreman R. , Schwartz R. , Yoon H. , Klempner D. , Frisch K. C. 
Published: December 2004

AbstractWe have measured the advancing contact angles of drops of methanol‐ethylene glycol mixtures on films of previously studied polyurethane‐epoxy interpenetrating polymer networks. The extrapolated critical surface tensions were in excellent agreement with those obtained from advancing contact angles of drops of water‐methanol mixtures. A sharp minimum is observed in the critical surface tension at network compositions where we have previously found maxima in ultimate mechanical properties. We advance a physical explanation based on unrelieved surface strains. We have also measured the toluene vapor transmission (permeability, diffusion and sorption coefficients) in these films. These results, together with the previously obtained water vapor permeabilities, are in complete accord with the expected morphologies of these networks.
Origin of moisture effects on crack propagation in composites
Authors: Mandell J. F. 
Published: December 2004

AbstractA study has been made of the origin of unexpected moisture effects on crack extension in fiberglass laminates. Water immersion has been found to greatly reduce the rate of crack growth under constant loading while increasing the rate under cyclic loading, the latter effect being the expected one. Observations were made of the extension of the stable damage zone at the tip of precut notches in wet and dry environments. The damage zone size is postulated as a critical element in the relaxation of high stress concentrations in composites, such as those at notch or crack tips. Under constant load, moisture is shown to greatly expand the interply delamination region in the damage zone, thus reducing the local fiber stresses and increasing crack resistance. Under cyclic loading moisture has little effect on the delamination region, which is large even for dry environments, and the only effect is weakening of the material and acceleration of cracks. Severe hygrothermal conditions can so weaken the material that the crack resistance is reduced under constant loading as well.
Strain‐induced crystallization, Part III: Theory
Authors: Yeh G. S. Y. , Hong K. Z. 
Published: December 2004

AbstractA nucleation theory for strain‐induced crystallization is formulated to explain and to predict the effects of molecular strain on crystallization kinetics and crystallite size. Unlike any current theories that have based their formulations on some assumed extended‐chain line nuclei or folded‐chain crystals, the present theory avoids all assumptions concerning the crystal morphology. It is based on experimental findings which indicate limited crystal growth in the strain direction, following a reciprocal dependence of crystal thickness on supercooling ΔT. (ΔT = T, − T, where the equilibrium melting temperature, T, is a variable dependent on degree of molecular strain prior to strain‐induced crystallization.) It is predicted that the logarithm of the nucleation rate, No, is dependent on (T)2/T(ΔT) or T/T(ΔT), and that the critical nucleus thickness l*o is shown to be proportional to T/ΔT. In addition, expressions are also presented, including examples, to show the dependence of No, l*o and Tom on degree of molecular strain, ϵ, or melt entropy reduction, Δs′. Our analysis predicts that, on comparing a polyethylene crystallized in the presence of strain to one crystallized in the absence of strain at 130°C, an increase in “coil” dimension of less than about 50 percent can bring about a 104 fold increase in heterogeneous nucleation rate, a 30–40 percent reduction in critical nucleus thickness and a 10°C increase in equilibrium melting temperature. These results will be discussed and compared with available experimental evidence.
Ultradrawing of thermoplastics by solid state coextrusion illustrated with high density polyethylene
Authors: Zachariades Anagnostis E. , Griswold Phillip D. , Porter Roger S. 
Published: December 2004

AbstractUltra‐thin films of high density polyethylene of high orientation have been produced by the recently developed technique of solid state coextrusion. The films were prepared under moderate conditions, without lubricant in continuous lengths by extruding through conical dies of extrusion draw ratio up to 36. This is a draw ratio higher than achievable by conventional solid state extrusion at comparable processing conditions through slit dies. The ultra‐thin films of high orientation were transparent and exhibited dead bend. The physical and mechanical properties were evaluated and compared with the properties of the same high density polyethylene extruded through a slit die. The increase in the melt point, crystallinity, tensile modulus, and birefringence indicates that the method is very efficient for the production of ultra‐thin and highly oriented films. An experimental technique is also presented for preparing billets of controlled and uniform initial morphology and free of voids.
Application of the ‘dual sorption’ model to drug transport through skin
Authors: Chandrasekaran S. K. , Campbell P. S. , Watanabe T. 
Published: December 2004

AbstractThe dual sorption theory has been extended to the transport of drug molecules through human skin in vitro. By assuming that sorption of drug molecules occurs by both dissolution and binding of drug to immobile sites in the skin, the experimental sorption isotherm can be predicted, and the disparity between steady state and time lag diffusivities can be reconciled. Furthermore, the dual sorption model has been used to develop techniques for controlling these sorption transport processes in order to rapidly achieve predictable transdermal drug delivery in vivo.
A comparative study of the tensile and charpy impact tests from a fracture mechanics viewpoint
Authors: Newmann L. V. , Williams J. G. 
Published: December 2004

AbstractCharpy and tensile impact tests have been conducted on two materials poly(methyl methaerylate) (PMMA) and polycarbonate. It is shown that by adopting a fracture mechanics approach, it is possible to measure meaningful values of material toughness, and that the results obtained in bending are consistent with those in tension. A discussion of the assessment of “kinetic energy” errors is also presented.
Sensitivity of diazoquinone resists to optical and electron‐beam exposure
Authors: Kaplan Michael , Meyerhofer Dietrich 
Published: December 2004

AbstractThis paper compares the response of resists consisting of novolak resin and diazoquinone sensitizers (inhibitors) to optical and electron‐beam radiation. In both cases, irradiation destroys the sensitizer leading to an increased rate of solubility in alkaline developer. For optical exposure in the near‐uv region, the light is absorbed only by the chromophore sites and a unique quantum efficiency of 0.30 ± 0.03 can be measured for a range of wavelengths and sensitizers (10.5 ± 1.0 eV/bleached site). In the case of electron‐beam exposure, the initial rate of bleaching in pure sensitizer implies that 7.6 ± 0.6 sites are destroyed per 100 eV absorbed (13 ± 1 eV/molecule). In mixtures of sensitizer and resin (i.e., resists), this inherent sensitivity, or G‐value, based on the calculated absorption by the sensitizer only, increases by almost a factor of 2 as the proportion of resin is increased. While the electron and optical exposure both destroy the sensitizer center, absorption spectra and solubility properties show that the end products of the chemical reactions are not the same in the two cases. In addition, high doses of electrons produce cross‐linking and insolubilization of the resin.
Effect of chemical composition upon the radiation and electron beam resist behaviors of vinyl polymers
Authors: Helbert J. N. , Iafrate G. J. , Pittman C. U. , Lai J. H. 
Published: December 2004

AbstractChemical composition effects upon polymer electron energy absorption and radiation chemistry have been identified to develop resist design criteria. By use of Bethe's theory for electron scattering in solids, chemical incorporation of higher atomic‐numbered substituents is predicted to decrease energy absorption and increase scattering. Incorporation of chlorine or fluorine into vinyl polymers at the possible substituent sites is empirically found to have a large effect upon radiation G (scission) and G (crosslink) values. G (scission) values determined for several copolymers over a large range of compositions are found to vary linearly with composition. In contrast, G (crosslink) values are found to be generally less than those predicted from a linear extrapolation between the homopolymer values. Electron beam resist behavior is found to correlate well with the Gs/Gx ratio.
Mechanism of formation of fluted void superstructures in the coagulation of wet spun fibers and application to membranes
Authors: Hancock Tony A. , White James L. , Spruiell Joseph E. 
Published: December 2004

AbstractAn experimental study is reported of the origins of fluted void structures in wet spun fibers. Optical microscopy studies of the interaction of spinning solutions and coagulating bath liquids suggest these voids originate in a fingering phenomenon occurring at the interface. Further studies show that this fingering effect is generally independent of the presence of the polymer and dependent on the two low molecular weight liquids alone. In the systems investigated it is found that the occurrence of the fingering is associated with a critical value of the heat of solution. It is argued that the fingering and associated fluted void structures in wet spun fibers are due to a “Thomson‐Marangoni” type interfacial instability. This can be justified using the theory of hydrodynamic stability. Fluted void structures produced in asymmetric membranes probably have a similar origin.
Biaxially oriented poly(ethylene terephthalate) bottles: Effects of resin molecular weight on parison stretching behavior
Authors: Bonnebat C. , Roullet G. , de Vries A. J. 
Published: December 2004

AbstractUni‐ and biaxial stretching of poly(ethylene terephthalate) (PET) specimens of appropriate geometry at temperatures near the glass‐rubber transition may lead to non‐uniform deformation unless the draw ratio exceeds a critical value, the natural draw ratio, characteristic of the onset of strain hardening due to stress‐induced crystallization. Experimental results obtained in the present investigation show that natural draw ratios in uni‐ and biaxial stretching decrease with increasing resin molecular weight and with decreasing temperature. Undesirable uneven wall thickness distribution in biaxially stretched cylindrical parisons can only be prevented if draw ratios in both orthogonal principal stretching directions exceed the corresponding natural values. The minimum thickness reduction required for uniform biaxial stretching of a cylindrical parison at 95°C may vary between 12 and 5 depending on the resin's molecular weight or viscosity and this will affect the optimum design of parison geometry. The degree of unbalanced biaxial molecular orientation in the wall of cylindrical parisons stretched up to or beyond the natural draw ratios also depends on the resin molecular weight. Unbalanced biaxial orientation has been investigated by means of wide angle X‐ray diffraction and birefringence measurements as well as its effect on various properties: rigidity, yield stress, creep compliance, and dimensional stability.
Effect of aging and moisture on the reactivity of a graphite epoxy prepreg
Authors: Sanjana Z. N. , Schaefer W. H. , Ray J. R. 
Published: December 2004

AbstractThe effect of moisture on the curing reaction of Hercules 3501‐6/AS graphite‐epoxy prepreg was investigated. Test samples of prepreg were aged under humid conditions, while control samples were aged under identical temperature conditions but with negligible humidity. Determinations of the amounts of moisture absorbed and desorbed fom the samples were accomplished gravimetrically. Dielectric analysis was used to monitor the relative reaction rates and overall activation energies of the prepreg after various aging periods. Changes taking place in monomer concentrations were observed using high performance liquid chromatography (HPLC). As aging continued, samples aged under humid conditions displayed, significant decrease in the overall activation energy accompanied by increased reaction rates. This change did not occur in the control samples. Samples aged in high humidity showed increased conversion of monomers to polymer when compared to dry aged samples. The aging time required before the above changes became apparent was temperature dependent; the higher the aging temperature, the sooner the changes in reactivity occurred.
Predicting the shock mitigating properties of thermoplastic foams
Authors: Bigg D. M. 
Published: December 2004

AbstractA procedure is presented by which the impact response of polymer foams can be predicted from basic compressive stress‐strain data. The effect of strain rate is accounted for by dividing the cushion into incremental thicknesses. The changing velocity in each increment is related to a changing strain rate by an iterative procedure incorporating experimental data taken over a wide range of strain rates. This procedure represents a considerable savings in the time required to evaluate a cushion over the currently used drop test method.
Influence of crosslinking on the moduli and impact strength of methacrylate polymers
Authors: Gomes A. S. , Timbó A. M. P. 
Published: December 2004

AbstractGlassy crosslinked networks were prepared by copolymerization of methyl methacrylate with up to 5.2 mole‐percent of ethylene and triethylene dimethacrylates. The moduli of these materials were measured by tensile and two dynamics methods: forced resonance vibration and ultrasonic. Impact strength were measured using the Izod geometry and Sharpy notched samples to induce brittle fracture. The increase in the length of the crosslinking agent caused an increse in the deformability and impact strength of these materials without any effects in the moduli.