bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of crosslinked membranes with controlled pore size distribution
Authors: Fujita Sharon M. , Soane David S. 
Published: December 2004

AbstractA technique has been developed to prepare crosslinked, porous/asymmetric membranes from poly(styrene‐co‐divinylbenzene). Mixtures of styrene monomer, divinylbenzene, benzoin (a photo‐initiator), and some dead polystyrene are dissolved in a cosolvent and cast on a flat, transparent substrate. The coating is then irradiated with a UV lamp and subsequently phase separated by exposure to a nonsolvent bath. Pores are generated by phase separation induced by nonsolvent ingression. Crosslinking is achieved via the photo‐initiated incorporation of divinylbenzene with styrene, while the membrane morphology evolves. A mechanism for the formation of crosslinked membranes prepared by this technique has been proposed. Experimental results systematically examine the effects of crosslinking and nonsolvent/solvent combinations on pore size and overall membrane structure. Temperature and solvent treatments on the finished membrane structure are also studied.
Effect of heat aging on the properties of a nylon 6,6/poly(phenylene oxide) blend
Authors: Laverty J. J. 
Published: December 2004

AbstractAccelerated aging of an Initial formulation of a nylon 6,6/poly(phenylene oxide) (PA/PPO) blend resulted in a significant loss in impact strength after a relatively short aging period. Fourier transform infrared (FTIR) spectroscopy showed considerable surface oxidation in air‐aged samples. Scanning electron micrographs (SEM) of fracture surfaces showed evidence of embrittlement (glassy skin formation). This brittle skin apparently influenced crack propagation throughout the entire cross section of the test specimens. It was determined by nuclear magnetic resonance (NMR) analysis that the PPO phase of the blend contained a poly(styrene‐butadiene) copolymer, probably added as an impact modifier. The susceptibility of the polybutadiene to oxidation, especially at elevated temperature, is believed to have caused the oxidation and surface embrittlement. However, the surface oxidation also resulted in a large loss in molecular weight of the nylon phase (m‐cresol‐soluble portion) and considerable cross‐linking of the PPO phase (chloroform‐soluble portion). Samples aged in inert atmosphere showed no skin formation nor loss in impact properties, thus confirming that oxidative degradation caused the embrittlement.
Computer aided applications to injection molding: Transfinite/finite element thermal/stress response formulations
Authors: Tamma K. K. , Dowler B. L. , Railkar S. B. 
Published: December 2004

AbstractThe paper describes two different computational approaches for simulating the effects due to temperature variations and therein the associated thermally induced stresses and warpage with emphasis on computer aided engineering applications to ‘plastic’ components. One approach is the conventional finite element approach, and the other is termed as the transfinite element approach. The development of unified thermal/stress formulations for each of the aforementioned approaches is described for applications to injection molded plastic parts. Results of both computational formulations are in excellent agreement for predicting the thermal response and unified thermal/stress response and agree qualitatively with previous studies. For this study, it is found that the transfinite element formulations are computationally more efficient although the conventional formulations can still be effectively used. Both formulations are capable of serving as powerful computational tools to help part designers to predict the thermal/stress responses accurately and effectively. The unified concepts and approaches offer potential for extension to more complex geometries and for combined heat transfer and stress problems.
Experimental and theoretical study of the injection molding of thermoplastic materials
Authors: Agassant J. F. , Alles H. , Philipon S. , Vincent M. 
Published: December 2004

AbstractMost of the commercially available computation programs for injection molding use restrictive assumptions which lead to simple mechanical and thermal equations. These computations are generally sufficient to predict the flow distribution in the mold but the pressure and temperature distributions are not precise. Our aim was first to model very accurately the filling stage of several molds of elementary geometries. For this purpose, a two‐dimensional model has been built which solves at each time step the finite difference forms of the continuity, momentum, and energy equations. A refined grid is used near the mold walls to take into account the great temperature gradients. These models have been validated by comparing the pressure field with experimental measurements. The precision of the model is better than 15 percent for several mold geometries and several injection conditions. In a second step, molds of complex geometries have been analyzed by assembling elementary geometries. The flow distribution at the branching between several geometries has been studied with special attention. These computations have been compared with short shots and pressure measurements in a four rectangular cavities tool and in a box shaped cavity tool. Experimental and theoretical results are in good agreement.
Creep induced buckling of plastic materials
Authors: Cohen A. , Arends C. B. 
Published: December 2004

AbstractIn this work, creep induced buckling was studied for a number of thermoplastic materials. The effect was observed by monitoring top displacements of thermoplastic bars as a function of time under static loading conditions. The recorded times to failure were averaged and correlated with the applied loads. The experiments, conducted for different materials, established an exponential dependence between the critical time and the load. The evolution of the buckling eigenvalues was modeled numerically. The simulations of eccentric columns behavior under compressive loads were coupled with the eigenvalue analyses. The correlation of the time‐load predictions obtained from the numerical simulations followed the experimental results within acceptable limits. The observed phenomenon of creep induced buckling was explained by damage accumulation leading to an effective reduction of the load carrying capability.
Cost effective, high‐technology civil transports
Authors: Swihart John M. 
Published: December 2004

AbstractThis paper discusses the cost of high technology and its benefits to commercial air transportation. The manufacturer's dilemma today is that, while one could pay a 16 percent price premium to obtain a 10 percent reduction in fuel cost in the late 1970s, in 1985 that price premium has diminished to only 2‐1/2 percent to achieve a 10 percent fuel saving. Consequently, we must obtain the benefits of high technology at an extremely low cost. Four areas are discussed in some depth: Aerodynamics, including the effects of computational fluid dynamics, wing design, and laminar flow; structures, including the effects of new materials, both metallic and nonmetallic, and the automated tools necessary to build the nonmetallic structure; avionics, including both fly‐by‐wire and fly‐by‐light, and the improvements due to high‐speed digital computers as well as flat panel flight deck displays; and propulsion systems, including the effects of high‐bypass ratio, high‐pressure ratio turbofan engines, and single and counter rotation turbopropellers. The final result is an integration of these four areas of technology into a composition transport aircraft and the resulting performance.
Characterization and role of an elastomeric interphase on carbon fibers reinforcing an epoxy matrix
Authors: Gerard Jean‐Francois 
Published: December 2004

AbstractOxidized carbon fibers were coated using an on‐line filament winding process with an elastomeric adduct crosslinkable and compatible with an epoxy matrix. The coating and modifications of the epoxy network were studied by dynamic mechanical measurements. Assuming that apparent activation energies of the secondary relaxation βe of the epoxy network and main relaxation αa of adduct are very different, it is possible at low frequencies to separate the two peaks. The composite material can be described as a three phase system: an epoxy network as matrix, carbon fibers, and a soft interlayer. The mechanical behavior of unidirectional composite materials studied by impact and bending tests is strongly dependent on the presence and the thickness of the coating at the carbon fiber surface.
Fracture behavior of coated/uncoated graphite‐epoxy composites
Authors: Joseph R. , Bell J. P. , Rhee H. 
Published: December 2004

AbstractThe static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCBUniform double cantilever beam.
specimens), and pure mode II shear loading (using ENFEnd‐notched flexural.
specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (GIC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (GIIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (KIC) of composites made with commercially treated fibers was also evaluated, using double side‐notched specimens.
Crack propagation modes in fiber and particulate composites in the microstructure
Authors: Theocaris P. S. 
Published: December 2004

AbstractThe influence of the hard or soft inclusions and the mesophase layers in either a soft‐hard‐soft or hard‐soft‐hard combination of biphase plates submitted to dynamic tensile loads on the fracture mode and bifurcation process in both phases was investigated in this paper. It was assumed that the soft or hard matrix is infolding the hard or soft inclusion of the plate, so that the plate constitutes a meridional section of the representative volume element of a unidirectional fiber composite, or a principal section of a particulate. The influence of the mechanical properties of either phase on the crack propagation velocity and the initiation of crack bifurcation was studied by using high‐speed photography and dynamic caustics. The results showed that the propagating crack tended to bifurcate either in the brittle or in the mesophase layer under certain conditions of propagation velocity. It was shown that bifurcation of a propagating crack depends on the elastic moduli and Poisson's ratios of the phases, as well as on the extent of the mesophase layer, which depended on the adhesion quality of phases.
Fluid sorption characterization of PEEK matrices and composites
Authors: Stober Eric J. , Seferis James C. 
Published: December 2004

AbstractNeat poly(ether‐ether‐ketone) (PEEK) and carbon fiber reinforced PEEK (APC‐2) specimens were prepared using a variety of cooling rates to achieve a range of crystallinities. Amorphous specimens were exposed to a variety of fluids to determine the penetrant types which are able to strongly influence the material. This allowed the estimation of the solubility parameter and hydrogen bonding index for PEEK to be 9.5 and 3.1, respectively. Methylene chloride was used to investigate the kinetics of penetrant sorption. The data demonstrated Case II behavior, with the initial crystallinity having a pronounced effect on both the kinetic and equilibrium data. Accordingly, a model was proposed capable of describing the sorption level and penetration depth as a function of time given the sample crystallinity and sorption temperature. With Case II behavior there was no difference in the sorption kinetics of neat and fiber reinforced PEEK. Finally, the dynamic mechanical properties measured during sorption were found to be dependent on the sorption process.
Morphology and rheological properties of polypropylene‐linear low density polyethylene blends
Authors: Levij M. , Maurer F. H. J. 
Published: December 2004

AbstractThe dynamic shear viscosity and the morphology of polypropylene homopolymer and copolymer blended with linear low density polyethylene are studied. A maximum in the dynamic shear viscosity vs. blend composition is reported for the polypropylene copolymer, linear low density polyethylene system. The increasing dynamic shear viscosity is in accordance with the occurrence of a morphology of polyethylene inclusions in rubber surrounded by a polypropylene matrix. Comparing calculations of the dynamic shear viscosities—based on a shell model with interlayer—and experimental results supports this view.
A tensile flow stress model for oriented polypropylene
Authors: Tate K. R. , Perrin A. R. , Woodhams R. T. 
Published: December 2004

AbstractMany solid‐phase processing and forming operations for polymers require tensile stretching forces to produce flow. To make forming operations practical, a knowledge of the flow stress of the polymer is required. This paper presents a simple formulation for predicting the flow stress of polypropylene In the oriented direction as a function of the controlling parameters, which are strain rate, temperature, and deformation ratio. It will be shown that the experimental flow stress data may be formulated in a way that is similar to the constitutive laws for metals. Equations for metals relating flow stress Lo strain rate, flow stress to strain, and flow stress to temperature are compared with an equivalent formulation for oriented polypropylene. The experimental conditions, chosen to develop the constitutive equations, reflect practical forming conditions, The deformation ratios (i.e., strains) were varied from 6 to 14. The strain rates imposed were between 10 and 1000% per min. Most of the tests were conducted in the temperature range 150 to 160°C, although a few were conducted at 130°C.
A study on the reactive extrusion process of polyurethane
Authors: Hyun M. E. , Kim S. C. 
Published: December 2004

AbstractAn engineering analysis of the reactive extrusion process of a thermoplastic polyurethane was made through numerical simulation and actual experiment. The reactants used in this system were 4,4′diphenylmethane diisocyanate, polycaprolactone diol (M.W., 824), and 1,4‐bu‐tanediol with equivalent weight ratio of 2:1:1. As a catalyst, dibutyltin dilaurate was used. The reaction kinetics and the viscosity function were obtained through experiments, and the mathematical model which includes the conservation equations of mass, momentum, energy, and chemical species was solved numerically to obtain the velocity, concentration, temperature, viscosity, and pressure profiles. The actual experiments were performed in the laboratory scale extruder to compare the experimental results with those of the numerical simulation.
Interpenetrating polymer network from blocked isocyanates. I. Structure and properties of polyurethane‐urea polyvinyl simultaneous interpenetrating networks
Authors: Michaud Philippe , Camberlin Yves , Mai Christian 
Published: December 2004

AbstractA series of polyurethane‐urea/polyvinyl simultaneous interpenetrating polymer networks (SINs) were prepared starting from a mixture of isocyanate prepolymer blocked with N‐(1‐1′‐dimethyl‐3‐cxobutyl) acrylamide oxime, chain extender, vinyl monomers, and catalysts. Their physical properties and morphology were investigated using differential scanning calorimetry, dynamic mechanical measurements, and small‐angle X‐ray scattering. The polyurethane‐urea networks examined were two‐phase in nature. The vinyl network was formed with diacetone acrylamide oxime, trimethylolpropane trimethacrylate, and N‐vinyl‐pyrrolidone. Calorimetric analyses revealed that the polyether soft segment phase separated within the SINs. At higher temperature, dynamic mechanical measurements demonstrated the presence of only one glass transition temperature (Tg) intermediate in temperature to the Tg of the vinyl network and the Tg of the urethane hard phase. This is indicative of chain entanglement (interpenetration) between the vinyl network and the polyurethane hard segments resulting in a two‐phase morphology. Small‐angle X‐ray scattering analyses provided measurements of diffuse phase boundary thickness, phase mixing, and domain size distribution. Appreciable interfacial thickness was not observed and thus phase mixing occurred within the phases. Domain size distribution indicated that high network constraints hindered the development of domains and limited the phase segregation.
Mechanical property enhancement of semicrystalline polymers—A review
Authors: Bigg D. M. 
Published: December 2004

AbstractProcessing plastics below their melting points has been shown to be an effective way to significantly enhance the mechanical, chemical, and physical properties of semi‐crystalline thermoplastics. A number of techniques have been developed that are capable of producing highly oriented fibers, films, and shapes. In general, these techniques can be classified as drawing, extrusion, arid rolling, with some very specific modifications having been made to each, that affects the performance of the process. Of particular interest is the rate of production, the range of thicknesses achievable, the uniformity of properties in the product, and the extent, if any, of biaxiality in the product. In recent years, the productivity of such forming processes has been increased by reducing the level of molecular entanglement among neighboring molecules. As an alternate to these orientation processes, techniques have been developed which rely on strain Induced crystallization to enhance the modulus of molded parts and extrudates from a melt. This paper constitutes a review of these techniques with emphasis on the process parameters, polymers investigated, and properties of the resulting materials.
Interpenetrating polymer networks from castor oil based polyurethanes, XI
Authors: Patel Prashant , Suthar Bhikhu 
Published: December 2004

AbstractUnder different experimental conditions, various liquid polyurethanes (PU) were synthesized from castor oil and isophorone diisocyanate varying NCO/OH ratio. These polyurethanes were then subsequently interpenetrated with n‐butyl acrylate (nBA) monomer and ethylene glycol di‐methacrylate as crosslinker by radical polymerization using benzoyl peroxide as an initiator. This leads to the formation of novel PU/PnBA interpenetrating polymer networks (IPNs) by transfer molding. These IPNs were characterized by their resistance to chemical reagents, thermal behavior (TGA), mechanical properties, namely; tensile strength, Young's modulus, elongation at break (%) and hardness (Shore A). The morphology of the IPNs was studied by Scanning Electron Microscopy. The dielectric behavior was computed in terms of electrical conductivities, dielectric constant (ε′), loss tangent (tan δ) and dielectric loss (ε″).
Thermodynamic miscibility of polymer‐liquid crystal blends
Authors: Patwardhan Ashutosh A. , Belfiore Laurence A. 
Published: December 2004

AbstractThe thermodynamic phase behavior of two polymer‐liquid crystal blends was investigated in both the solid and molten states. One of the blends (p‐hexyloxybenzoic acid and poly[ethylene glycol]) contains a semi‐crystalline polymer. The second example (p‐pentyloxycinnamic acid and bisphenol‐A polycarbonate) contains a high‐impact‐resistant amorphous thermoplastic. Whereas, the former system is almost completely immiscible at ambient temperature, yet advantageous for applications in the microelectronics industry, the latter blend exhibits partial (concentration‐dependent) miscibility. Our multi‐technique assessment of miscibility/phase separation includes high‐resolution carbon‐13 solid state NMR spectroscopy, differential scanning calorimetry (DSC), and group‐contribution thermodynamics (Universal Quasi‐Chemical Functional‐Group Activity Coefficient formalism including a Free Volume correction for the small molecule activity, UNIFAC‐FV). Approximate temperature‐composition (equilibrium) phase diagrams are constructed for both blends in light of the results from NMR, DSC, and UNIFAC‐FV.
Molecular orientation in drawn smectic and crystalline isotactic polypropylene
Authors: De Candia F. , Russo R. , Vittoria V. , Iannelli P. 
Published: December 2004

AbstractThe drawing behavior of two polypropylene films of different structures was analyzed. The two films differ as a consequence of different quenching conditions. At low temperature, a biphasic smectic‐amorphous system was obtained, while quenching at 100°C produced a biphasic crystalline‐amorphous system. The drawing of samples was carried out at 110°C at which temperature the smectic phase is not stable and is transformed into the crystalline α‐form. The initial structure affects the drawing behavior and the properties of the drawn samples. The mechanical, optical, and X‐ray analyses clearly show that high molecular orientation is achieved at lower deformations in the initially smectic sample. In particular, the amorphous phase is highly oriented, inducing higher axial elastic modulus.
Application of a concept of distributed damage to creep induced buckling of high density polyethylene specimens
Authors: Cohen A. , Arends C. B. 
Published: December 2004

AbstractIn this work, a concept of distributed damage, including its inception and propagation, was applied to creep induced buckling of specimens prepared from high density polyethylene (HDPE). Using a kinetic relationship for damage accumulation, an integral equation for the front of the damage zone was derived. A time parameter associated with the inception of the damage front was obtained. The motion of the front was approximated for small times. Long time estimation was obtained using an assumption for a shape of the damage distribution. These results enabled us to review reported experimental results on creep induced buckling using a new insight into the relationship between applied load and time to buckle.
Thermal behavior, morphology, and some melt properties of blends of polycarbonate with poly(styrene‐co‐acrylonitrile) and poly(acrylonitrile‐butadiene‐styrene)
Authors: Kim W. N. , Burn C. M. 
Published: December 2004

AbstractBlends of bisphenol‐A polycarbonate (PC) with poly‐ (styrene‐co‐acrylonitrile) (SAN) and poly (acrylonitrile‐butadiene‐styrene) (ABS) prepared by screw extrusion and solution‐casting were investigated by differential scanning calorimetry and scanning electron microscopy. From the measured glass‐transition temperatures (Tg) and specific heat increments (ΔCp) at the Tg, SAN appears to dissolve more in the PC‐rich phase than does PC in the SAN‐rich phase. Also, the decrease of Tg (PC) in PC/ABS blends is larger than in the PC/SAN blends. From the Tg behavior and the electron microscopy study, it is suggested that the compatibility increases more in the SAN‐rich compositions than in the PC‐rich compositions of the blends. In the study of extrudate swell of the PC/SAN blends and the PC/ABS blends, the maximum level of extrudate swell is reached at 0.5 weight fraction of PC for both blend systems. The Flory‐Huggins polymer‐polymer interaction parameter (χ12) between PC and SAN was calculated and found to be 0.034 ± 0.004. A similar value of χ for PC and SAN was found with the PC/ABS blends.
A thermodynamic base for the stress activated phase transition deformation model
Authors: Liu Tuomin , Harrison I. R. 
Published: December 2004

AbstractThe three essential factors of the Juska–Harrison stress activated phase transition (SAPT) deformation model are analyzed. Based on the concept of “mechanical melting”, a formula for the theoretical melting stress is derived from thermodynamics. A comparison of experimental and calculated results for a number of polymers shows that the strain energy is high enough to induce isothermal “mechanical melting” during extension, and the observed yield stress has the same order of magnitude as the theoretical melting stress.