bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bioabsorbable composites. II: Nontoxic, L‐lysine‐based poly(ester‐urethane) matrix composites
Authors: Storey Robson F. , Wiggins Jeffrey S. , Mauritz Kenneth A. , Puckett Aaron D. 
Published: May 2005

AbstractBioabsorbable composites were fabricated from poly(D, L‐lactide‐urethane) matrix reinforced with poly(glycolic acid) (DEXON) surgical mesh. The crosslinked polyurethane matrix was formed from the reaction of ethy1–2, 6‐diisocyanatohexanoate and poly (D, L‐lactide) triol, initiated from glycerol; the ultimate degradation products of this matrix, L‐lysine, lactic acid, glycerol, and CO2, are all nontoxic, naturally occurring metabolites. The composites were fabricated by two processing methods, with the final composite structures displaying very different physical properties. Composites fabricated by vacuum bag molding displayed tensile strength and modulus of 66 MPa and 468 MPa, respectively, with total elongation of 39%. Composites fabricated by the same method, but whose final cure included 24 h at 5000 psi, displayed tensile strength and modulus of 86 MPa and 3.4 Gpa, respectively, with total elongation of 18%, suggesting a more fully developed matrix/fiber interphase and a reduction in microvoids, which lead to lower force failures. As poly(D, L‐lactide) prepolymer molecular weights decreased, tensile strengths and glass transition temperatures of the polyurethane networks increased. These trends were attributed to increased hydrogen bonding with an increased crosslink density. The composites were sensitive to cyclic loading, regardless of the processing technique, suggesting an inefficient transfer of energy from the matrix into the load‐bearing fibers. This weakness was confirmed by SEM microscopy, which revelaed a gap at the fiber/matridx interface of an unfatigued composite sample, poly(D, L‐lactide‐urethane) matrix composites were found to be unique since they can be custom shaped when heated above the glass transition of the matrix. DSC revelaed the glass transitions for the matrices of around 60°C. The composites were easily shaped above this temperature, yet remained rigid at biological temperature.
A modeling approach to thermoplastic pultrusion. I: Formulation of models
Authors: Åström B. Tomas , Pipes R. Byron 
Published: May 2005

AbstractA fundamental understanding of the effects of processing parameters and die geometry in a pultrusion process requires a mathematical model in order to minimize the number of necessary experiments. Previous investigators have suggested a variety of models for thermoset pultrusion, while comparatively little effort has been spent modeling its less well understood thermoplastic counterpart. Herein, models to describe temperature and pressure distributions within a thermoplastic composite as it travels through the pultrusion line are presented. The temperature model considers heat transfer in an infinite slab with either prescribed boundary temperature, or prescribed heat flux from the surfaces. The pressure model is based upon matrix flow relative to the fibers and incorporates a non‐Newtonian matrix viscous, compaction, and friction resistance, is also presented. The models are evaluated studying and ideal pultrusion process for manufacturing of unidirectional carbon‐fiber‐reinforced polyether ehterketone composites.
The effects of thermal history on the structure/property relationship in polyphenylenesulfide/carbon fiber composites
Authors: Deporter Joellen , Baird Donald G. 
Published: May 2005

AbstractThe purpose of this investigation was to examine the effects of thermal history during cooling from the melt on the degree of crystallinity, morphology, and mechanical properties of polyphenylenesulfide (PPS)/carbon fiber composites. Three thermal treatments were employed in this tudy: isothermal crystallization from the melt at 140, 160, 180, 200, and 22O°C; quenching from 315°C and then annealing at 160 and 200°C; and nonisothermal crystallization from the melt at rates varying from 0.4°C/min to 38°C/s. The effect of varying the thermal history of the sample on the degree of crystallinity developed in the matrix polymer was determined using differential scanning calorimetry (DSC). The effect of thermal history on and the resulting matrix morphology was examined by scanning electron microscopy (SEM). The subsequent effects of the degree of crystallinity and the morphology on the mechanical behavior of the samples were monitored by transverse tensile tests and flexural tests. In all cases, the transverse tensile and flexural moduli increased as the amount of crystallinity in the samples increased. However, samples with greater amounts of crystallinity did not always yield higher transverse tensile or flexural strengths. Upon examination of the composite samples by electron miscroscopy, it was observed that large increases in the values of the transverse tensile and flexural strengths could be correlated with structural changes in the matrix.
Mechanical properties of in situ composites based on partially miscible blends of polyetherimide and liquid crystalline polymers
Authors: Baird D. G. , Bafna S. S. , De Souza J. P. , Sun T. 
Published: May 2005

AbstractResults related to the mechanical properties of in situ composites based on partially miscible blends of polyetherimide (Ultem) and liquid crystalline polymers (HX1000 and HX4000) are discussed. It is observed that, at least in terms of the tensile and flexural modulus, there is a positive deviation from the law of mixtures. These results are analyzed and an attempt is made to explain the origin of this synergistic behavior based upon morphological data. The behavior of these partially miscible systems is compared to that of an immiscible system (Ultem/Vectra) and also that of glass‐reinforced Ultem. Using blends subjected to two passes through a single screw extruder, and thereby increasing the mixing history of the Ultem/HX4000 blend, led to improved dispersion but did not lead to any measurable improvement, within experimental error, in the tensile modulus or ultimate strength (though the toughness was enhanced). The dynamic creep compliance was measured and the creep behavior with composition and temperature is discussed. The data seem to suggest that a number of factors (including partial miscibility, the properties of the specific LCP chosen as the reinforcement and the final blend morphology) all interact in a complex and as yet undetermined manner to produce the enhanced mechanical properties.
Thermo‐stimulated creep study of the α retardation mode in epoxy‐glass beads composites
Authors: Dufresne A. , Lacabanne C. 
Published: May 2005

AbstractThermo‐stimulated creep (TSCr) analysis was performed to characterize the anelastic properties around the glass transition of the model system: expoxy resin‐glass beads. Different interphase regions have been deliberately formed by means of a silane coupling agent and an elastomeric adduct coating. In all samples the primary retardation mode, labeled α, has been found around 140°C. this retardation mode has been associated with the anelastic manifestation of the mode in filled epoxy has been used to estimate the interphase thickness. By applying “fractional stresses” the complex α peak has been experimentally resolved and local changes of morphology in the interphase zone are evidenced in terms of mobility and kinetic of motion. This last technique has also allowed us to compare the length of the mobile units liberated at the glass transition as a function of the filler‐matrix interphase.
Tow impregnation during resin transfer molding of bi‐directional nonwoven fabrics
Authors: Chan Albert W. , Morgan Roger J. 
Published: May 2005

AbstractA model has been developed for analyzing resin impregnation of fiber tows during resin transfer molding of bi‐directional nonwoven fiber performs. The model is based on the existence of two main regions of resin flow: the macropore space formed among fiber tows and the micropore space formed among individual fiber filaments within a tow. The large difference in permeability between these two regions of flow leads to the potential for void formation during resin transfer molding. The model was formulated for both constant flow rate and constant pressure mold filling. For ambient pressure mold filling, the model predicts a difference in the size of the voids and distribution between axial tows (oriented along the flow direction) and transverse tows (oriented in the transverse direction). When vacuum is imposed on the mold, the model predicts the same resin impregnation behavior for both axial and transverse tows. Furthermore, given sufficient time, voids generated under vacuum mold filling will eventually collapse because of the absence of an opposing internal void pressure. In addition to insights on void formation, the model also provides a basis for the study of the relationship between resin transfer molding parameters and the resin impregnation process.
Numerical simulation of non‐isothermal SMC (sheet molding compound) molding
Authors: Twu J.‐T. , Hill R. R. , Wang T. J. , Lee L. James 
Published: May 2005

AbstractDesign of molding tools and molding cycles for sheet molding compounds (SMC) is often expensive and time consuming. Computer simulation of the compression molding process is a desirable approach for reducing actual experimental runs. The focus of this work is to develop a computer model that can simulate the most important features of SMC compression molding, including material flow, heat transfer, and curing. A control volume/finite element approach was used to obtain the pressure and velocity fields and to compute the flow progression during compression mold filling. The energy equation and a kinetic model were solved simultaneously for the temperature and conversion profiles differential scanning calorimetry (DSC) was used to experimentally measure the polymer zation kinetics. A rheometrics dynamic analyzer (RDA) was used to measure the rheological changes of the compound. A series of molding experiments was conducted to record the flow front location and material temperature. The results were compared to simulated flow front and temperature profiles.
Quantitative image processing analysis of composite materials
Authors: Yang Heechun , Colton Jonathan S. 
Published: May 2005

AbstractQuantitative digital image processing has been used to analyze unidirectional thermoplastic composites. The fiber volume fraction is determined by the template matching method and compared with the conventional thresholding method. A combination of skeleton and edge cutting is used to obtain the centers of the fibred in the image. The Voronoi distances are calculated from the result. The Hough transform is applied to the fiber orientation in conjunction with thresholding by the line length in the image. To describe the fiber orientation, characteristic function are defined in the width and thickness directions, which allow a much more accurate and effective description of the fiber distribution and orientation than other methods. Advantages of the template method are that similar results to the threshold method can be obtained as thresholding with a lower magnifications, resulting in an improved statistical sample with a reduced number of photomicro‐graphs.
A T1 lattice relaxation study of the molecular motions of a semicrystalline polyimide matrix
Authors: Russell Vernon M. , Koenig Jack L. 
Published: May 2005

AbstractThe molecualr dynamics of a semicrystalline polyimide were studied by 13C nuclear magnetic resonance (NMR) spectroscopy. The T1 spin lattice relaxation times were observed over a temperature range of 24°C to 94°C.
Performing analysis of thermoformable glass fiber mats—deformation modes and reinforcement characterization
Authors: Fong Lihwa , Xu Jingyi , James Lee L. 
Published: May 2005

AbstractThis work is and anyalysis of the performing process of a thermoformable glass fiber mat. Important processing variables associated with the preforming operations were extracted from stamping experiments. From the study of deformation modes, we may conclude that the defects found in fiber mat preforming are closely related to these deformation modes. Stretching causes finer thinning and re‐orientation. Bending results in mat springback and thickness reduction, while in‐plane compression induces wrinkles through buckling. Each defect may be reduced by specific adjustments. These adjustments, however, tend to interact with each other, and make the preforming control a challenging task.
X‐ray diffraction analysis technique for determining the polymer crystallinity in a polyphenylene sulfide composite
Authors: Lee T. H. , Boey F. Y. C. , Khor K. A. 
Published: May 2005

AbstractThe degree of crystallinity in polymers is commonly known to significantly affect their mechanical properties. To that extent, it also affects the mechanical properties—such as compression, buckling, and creep—of thermoplastic composites that are matrix dominant. For this reason, it is important that the degree of crystallinity in a thermoplastic composite be precisely determined, which is the focus of this paper. In particular, the crystallinity for a thermoplastic poly(phenylene sulfide) composite reinforced with glass fibers is determined using an X‐ray diffraction technique (XRD). While conventional methods have been adopted for homogeneous phases, a modified method has been adopted to account for the heterogeneous nature of the composite. The results have also been compared with results obtained using DSC and DMA techniques, indicating that the XRD method yielded lower values, which are considered to be more accurate. This was attributed to the absence of a recrystallization effect in the XRD method, which was unavoidable in the other two methods.
Assessment of the dispersibility of surfactant‐treated titanium dioxide powders for compounding with polyethylene
Authors: Arellano Martin , Manas‐Zloczower Ica , Feke Donald L. 
Published: May 2005

AbstractA strategy involving the use of anionic surfactants to compatibilize titanium dioxide powders with nonpolar polymers has been applied to facilitate the dispersion of these powders into polymer composites. The methodology first involves the adsorption of surfactant onto the powder within aqueous dispersions. Surfactantcoated powders are then removed from the dispersion and dried. The cohesivity and some surface properties of the surfactant‐coated powders were measured and compared to that of the uncoated powders. Dispersion experiments of titania agglomerates in polyethylene were performed in a rotating cone‐and‐plate device set within a temperature controlled oven. The titania agglomerates dispersed by an erosion mechanism in which small fragments detached from the surface of the parent agglomerate. The erosion rate was higher for the surfactant treated powders in comparison to uncoated powders. The links between the enhanced erosion rates and the surfactant coating were investigated in terms of the cohesivity of the powders, the penetration of the polymer into the agglomerates, and the interactions between the powders and the polymer media that govern wetting and the transmission of hydrodynamic stress.
Swelling behavior in extrusion
Authors: Miller John C. 
Published: May 2005

AbstractThe diameter increase of a molten thermoplastic extrudate is discussed in terms of the viscoelasticity of the resin. A swelling index, the ratio of the extrudate diameter to the orifice diameter, is defined. It was observed that swelling data taken at different temperatures can be correlated with stress in the die. An unexpected influence on the swelling for polyethylenes is the length of the die where short dies show larger swelling than long dies. Some suggestions for reducing swelling tendencies are made based on a simple model for flow in a capillary.
Short‐ and long‐term strength characteristics of particulate‐filled cast epoxy resin
Authors: Hojo Hidemitsu , Toyoshima Wataru , Tamura Masayasu , Kawamura Noriyuki 
Published: May 2005

AbstractParticulate‐filled thermosetting composites are widely used, yet little systematic work has been done on their long‐term strength characteristics. In this study short‐term tensile, flexural, and impact tests as well as tensile creep‐rupture tests were made for unfilled and filled epoxy to clarify the effects of filler size, filler content, and temperature. Fillers used were silica, alumina particles, and glass beads. Test temperatures were varied from 25 to 110°C. As a result of short‐term testing, it was found that the Petch relation held between strength and filler size if brittle fracture occurred, while a strength and filler size if brittle fracture occurred, while a strengthening effect existed when ductile fracture occurred. On creeprupture testing, a strengthening is observed with filler size and content for silica and glass beads. The Arrhenius plot of rupture time for various filler sizes and contents converges to a characteristic point corresponding to the glass transition temperature of the material. Using this relation, a modified Larson‐Miller master rupture curve is proposed which can predict the long‐term strength of particulate‐filled thermosetting composites as functions of rupture time, temperature, filler size, and content.
Thermal, mechanical, and rheological behavior of blends of ultrahigh and normal‐molecular‐weight linear polyethylenes
Authors: Bhateja S. K. , Andrews E. H. 
Published: May 2005

AbstractPhysical Blends of ultrahigh‐molecular‐weight linear polyethylene (UHMW LPE) and normal‐molecular‐weight linear polyethylene (NMW LPE) have been evaluated in terms of melt flow rate, tensile stress‐strain behavior, heat of fusion, melting temperature, and crystallinity. The behavior of the blends is intermediate between that of the parent polymers; no synergistic effects are observed. The addition of small quantities of NMW LPE does not improve the flow behavior of UHMW LPE sufficiently to render it amenable to conventional melt processing.
X‐ray photochemistry: ω‐Chloro olefin sulfones
Authors: Kaplan Michael 
Published: May 2005

AbstractTo be efficacious as an x‐ray resist, a material must efficiently undergo a desirable chemical change upon being irradiated with x‐rays. The probability of such a change taking place is given by the product of the fractional x‐ray absorption and the “inherent sensitivity,” which we define as the yield per unit energy absorbed. Increasing the absorption of the polymer, as, for example, by chlorinating an olefin sulfone thereby increasing the absorption at wavelengths just below the chlorine absorption edge will result in improved usefulness if, and only if, this increased energy absorbed can be used by the polymer to enhance the desired chemical reaction. The “usefulness” of chlorinating is thus dependent on the efficiency of intramolecular energy transfer. We have studied the efficiency of this transfer by monitoring the loss of SO2 from the main‐chain backbone as a function of absorbed x‐ray energy, using x‐ray wavelengths both abov and below the chlorine absorption edge. The polymers studied were 1‐olefin sulfones, with and without the chlorine atom in the ω‐position. Through the use of this series of polymers it was hoped to observe an effect due to the changing separation of the chlorine atom from the backbone. The experiments indicate that (a) the inherent sensitivity is independent of irradiating wavelength, for both the chlorine‐containing and the non‐chlorine‐containing polymers; (b) the hexene polymers are considerably more sensitive than the lower members of the series (which exhibit a sensitivity which is approximately independent of the side chain length); and (c) the chlorine‐containing polymers are less sensitive than the non‐chlorine‐containing species. At this time the explanation for these observations is speculative.
Evaluation of poly(allyl methacrylate)‐co‐(hydroxyethyl methacrylate) as negative electron‐beam resist
Authors: Tan Zoilo C. H. , Georgia Sharon S. 
Published: May 2005

AbstractPoly(allyl methacrylate)‐co‐(hydroxyethyl methacrylate) has been evaluated as a high‐sensitivity, high‐resolution, high temperature‐resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E‐beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight‐average‐molecular‐weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster‐scan‐type or vector‐scan‐type electron‐beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma‐etch resistance was about twice that of PMMA.
Recent resist developments in Japan—a review
Authors: Nonogaki Saburo 
Published: May 2005

AbstractSeveral kinds of resist materials for microlithography have been developed in Japan. Poly(4‐vinyl phenol) sensitized with 3,3′‐diazidodiphenyl sulfone has been proved to be a high resolution negative deep UV resist with high sensitivity and good resistance to dry etching. The use of this resist enables a 1:1 projection printer to replicate fine patterns with 1 micrometer (μm) minimum feature size at the rate of 90 wafers per hour. Poly(methyl isopropenyl ketone) (PMIPK) has been investigated as a positive deep UV resist. Several resists composed of PMIPK with or without sensitizers are commercially available. Dry‐developable photo‐ and deep UV resists comprising PMIPK and aromatic bisazides have been developed. Poly(glycidyl methacrylate) having the sensitivity of 0.4 micro Coulomb (μC)/per square centimeter (cm2) is now being routinely used as a negative electron beam resist in the fabrication of chromium masks. Recently, aromatic polymers such as chloromethylated polystyrene, iodinated polystyrene, chloromethylated poly(α‐methylstyrene), poly(vinylnaphthalene) and its copolymers have been investigated as dry‐etching resistant electron beam resists.
Ketocoumarins as photosensitizers and photoinitiators
Authors: Williams J. L. R. , Specht D. P. , Farid S. 
Published: May 2005

AbstractSeveral 3‐ketocoumarins with alkoxy or dialkylamino substituents in the 7 position, which are efficient sensitizers for crosslinkable polymers, were evaluated as photoinitiators. Proper combinations of certain derivatives of these ketocoumarins with activators such as amines, acetic acid derivatives, and alkoxypyridinium salts gave quantum yields for initiated radical polymerization much higher than that obtained from the Michler's ketone/benzophenone combinations. For each class of activators the dependence of the efficiency of polymerization on the redox properties of the ketocoumarins is explained in terms of charge transfer or electron transfer from the activator to the excited ketocoumarin (acetic acid and amine activators, respectively) or electron transfer in the opposite direction (pyridinium salt activators).
Deep UV photolithographic systems and processes
Authors: Wilkins C. W. , Reichmanis E. , Chandross E. A. , Hartless R. L. 
Published: May 2005

AbstractDeep UV[200 to 300 nanometers (nm)] photolithography has received much recent attention because it promises higher resolution than conventional exposure technology. Except for the change in wavelength from the 400 nm region, the exposure technology would remain virtually unchanged. We will discuss resist materials and processes explored in the last few years for optimization of deep UV lithography. Particular emphasis is placed upon the chemistry of resist design, multilevel processing schemes, and new sources for deep UV exposure.