bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methanol‐Induced crack healing in poly(methyl methacrylate)
Authors: Lin C. B. , Lee Sanboh , Liu K. S. 
Published: May 2005

AbstractCrack healing in poly(methyl methacrylate) (PMMA) by methanol treatment at 40°C–60°C has been investigated. It is found that the methanol treatment reduces the glass transition temperature in PMMA. Crack healing only occurs at an operating temperature higher than the effective glass transition temperature. There are two distinctive stages for crack healing based on the recovery of mechanical strength. The first stage corresponds to the progressive healing due to wetting, which has a constant crack closure rate at a given temperature. Immediately following the first stage, the second stage corresponding to diffusion enhances the quality of healing behavior. The surface morphologies obtained during healing and after fracture tests confirm these two stages. By comparing the fracture stress with the fractography, the fracture surface for stage I of crack healing is coplanar to the original crack surface. On the other hand, the original crack surface is destroyed in stage II of crack healing. It occurs in the region incorporating the original healed surface and appears to be like the Virgin fracture surface. It is also found that the tensile fracture stress of PMMA treated by methanol can recover to that of the virgin material. In addition, it is interesting to find that after sustained methanol treatment, the “snake bone” phenomenon on the fracture surface emerges.
Strength development at incompatible semicrystalline polymer interfaces
Authors: Yuan B.‐L. , Wool Richard P. 
Published: May 2005

AbstractThe structure of an interface that develops from laminating polypropylene/polyethylene (PP/PE) by hot compression‐molding was analyzed by optical and electron microscopy. The interface strength was measured by means of a butt‐joint specimen. For the laminate formed by isothermal crystallization above the PE melting temperature, it was found that the interface strength increased with time due to the formation of PE influxes between the PP spherulites. The inter‐spherulitic influxes broke up the sharp PP/PE interface plane and provided considerable strength by mechanical interlocking. Intra‐spherulitic entanglements were also noted for PP spherulites nucleated near the interface. Fast crystallization prevents the formal/on of influxes and results in a weak interface. For the hon‐iscthennal crystallization case during cooling at 10°C/min, the interface morphology of PP/HDPE was found to be different from that of PP/LLDPE. The difference in crystallization temperatures and growth rates between PP and HDPE during rapid cooling permitted the HDPE to crystallize first which prevented the formation of influxes. With PP/LLDPE, the PP crystallized first allowing some influxes to develop. Normally the interface between PE and PP is very weak. However, to obtain good mechanical properties for a given PP/PE couple, one can control the processing thermal history to optimize the development of influxes and mechanical strength at the interface.
Phase morphology coarsening and quantitative morphological characterization of a 60/40 blend of polycarbonate of bisphenol a (pc) and poly(styrene‐bco‐acrylonitrile) (san)
Authors: Quintens D. , Groeninckx G. , Guest M. , Aerts L. 
Published: May 2005

AbstractA 60/40 polymer blend of polycarbonate of bisphenol A (PC) with a styrene‐co‐acrylonitrile (SAN) copolymer was prepared by melt compounding. Injection molded sheets of this, blend were annealed at 200°C as a function of time. The phase morphology of these sheets, studied using transmission and scanning electron microscopy, was found to coarsen as a function of the annealing time. Using the Chalkey procedure, the microstructure of the annealed blends was quantified. Initial tensile stress‐strain data highlight the influence of microstructure on ductility for these co‐continuous blends.
Morphology of unsaturated polyester resin‐additive blends
Authors: Suspene Laurent , Gerard Jean‐François , Pascault Jean‐Pierre 
Published: May 2005

AbstractThe morphologies and impact behavior of blends based on an unsaturated polyester matrix and different added rubbers were studied by scanning electron microscopy (SEM). These rubbers were prepared from a carboxy‐terminated acrylonitrile‐butadiene copolymer (CTBN). The introduction of an epoxy‐terminated triblock copolymer (ETON) by exchanging 10% by weight of the CTBN rubber compatibilizes the initial blend by reducing the interfacial tension between the components. Consequently, the morphology of dispersed phase was modified: decreasing of the particle size and reducing the number of large particles. For a blend with 5 phr of rubber, Charpy impact behavior was enhanced and the number of catastrophic failures was reduced. This study displays the existence of relationships between the interfacial tension between components and the morphology of the resulting materials.
Adaptation of photoacoustic fourier transform infrared spectroscopy for studying the thermal oxidation of nylon 66 at 150°c correlated to mechanical properties
Authors: Murty E. M. , Yehl T. W. 
Published: May 2005

AbstractOven aged tensile bars of heat stabilized, glass reinforced nylon 66 material were studied by Fourier transform infrared (FTIR) spectroscopy using a photoacoustic detector. Flat weighed scrapings were removed from tensile bars whose tensile strength, elongation, impact, molecular weight, and thermal properties had previously been measured. Using the amide I band of nylon 66 as an internal standard, the thermal oxidation of nylon was followed using a commercially available photoacoustic detector. The infrared absorbance spectra demonstrate the formation of carbonyl stretching vibrations due to the thermal oxidation of nylon with a band center at 1713 cm−1 whose width at half height is 40 cm−1. The difference infrared spectra support reaction mechanisms dealing with an Initial increase in the degree of polymerization followed by transamidation reactions with subsequent formation of an α, β unsaturated carbonyl species and chain scissioning. By using data related to the percent retention of certain physical properties which had also been measured on these tensile bars, subtractive infrared spectroscopy yielded additional fundamental information regarding nylon 66 degradation. Consequently, nylon products being used in underhood automotive applications are currently being investigated for thermal oxidative degradation using this rapid and relatively non‐destructive photoacoustic FTIR technique for durability considerations.
In‐situ monitoring of the resin transfer molding impregnation and cure process
Authors: Kranbuehl D. , Eichinger D. , Hamilton T. , Clark R. 
Published: May 2005

AbstractResin transfer molding (RTM) of advanced fiber architecture materials promises to be a cost effective process for obtaining composite parts with exceptional strength. However there are a larger number of material processing parameters that must be observed, known, and/or controlled during the resin transfer molding process. These include the viscosity both during impregnation and cure. In‐situ sensors which can observe these processing properties within the RTM tool during the fabrication process are essential. This paper will discuss recent work on the use of frequency dependent electromagnetic sensing (FDMS) techniques to monitor these properties in the RTM tool. Our objective is to use these sensing techniques to address problems of RTM scaleup for large complex parts and to develop a closed loop, intelligent, sensor controlled RTM fabrication process.
Dynamic mechanical response of a thermoplastic sheet molding compound‐glass fiber composite
Authors: Otaigbe J. U. 
Published: May 2005

AbstractThe dynamic mechanical properties of nylon 6/continuous glass fiber composites at four levels of fiber volume content were studied between ‐180 and 130°C using a free resonance torsion pendulum. The composites were produced by anionically polymerizing caprolactam monomer within a swirl type glass fiber mat using a vacuum injection technique. In addition to the expected strong dependence of shear storage modulus on fiber volume content, the glass transition temperature of the nylon 6 was observed to increase slightly and the mechanical damping decrease with fiber volume fraction. Introduction of about 7 weight percent water (i.e., equilibrium hygroscopic state) into the composite led to a considerable broadening of the transition peaks and a much lower plasticizing action of water in the composite relative to the pure nylon 6 matrix.
A unified simulation of the filling and postfilling stages in injection molding. Part II: Experimental verification
Authors: Chiang H. H. , Hieber C. A. , Wang K. K. 
Published: May 2005

AbstractThe unified numerical simulation of the filling/postfilling stages of the injection‐molding process described in Part I is compared in the present paper with experimental results obtained with instrumented test molds. Flush‐mounted pressure traces in the delivery system as well as in the cavity are favorably compared with corresponding predictions for both an amorphous and a semicrystalline polymer. It is demonstrated that the present unified formulation is well suited to handle complicated molds where compressibility effects can become important even during the filling stage, as portions of the cavity fill and undergo a packing behavior even when other regions of the cavity are still only partially filled.
Microwave joining and repair of composite materials
Authors: Varadan Vijay K. , Varadan Vasundara V. 
Published: May 2005

AbstractA novel technique that uses microwave power for joining and repair of thermoplastic and thermoset composites and ceramics is discussed. Enhanced microwave heating resulting from the use of conducting polymers and chiral microinclusions shows considerable promise for joining and repair of composites. The method is attractive because it produces clean and reliable interfacial joints, it is fast, it does not entail alteration of the bulk materials, and it does not result in volumetric heating. System details, including magnetron, waveguides, circulators, coupling iris, and the applicator for delivering microwave power, are described. Material requirements for the efficient absorption of microwave power are discussed. Microwave heating can be increased by doping the components to be joined or by the use of microwave adhesive films. Recent developments in electromagnetic chirality for microwave absorption are introduced and the design of composite materials for enhanced absorptivity is discussed. Results are presented for the welding and repair of thermoplastic, thermoset, and ceramic components.
Effect of physical aging on the fracture behavior of crosslinked epoxies
Authors: Truong V.‐T. , Ennis B. C. 
Published: May 2005

AbstractThe effect of physical aging on the fracture behavior, crack opening displacement, and plastic deformation zone of unmodified and rubber‐modified epoxies was determined at two aging temperatures and different displacement rates. The strain energy release rate decreases to between 40 and 50% (for rubber modified and unmodified samples, respectively) of the unaged values after 35 days aging. Systematic dependence of the decrease in fracture toughness by aging on the rubber content is not apparent. The increased yield stress after physical aging is the main factor contributing to the reduction in fracture toughness, crack opening displacement, and plastic deformation zone. Physical aging suppresses the crack blunting mechanisms in epoxies.
The application of size‐exclusion chromatography to study molecular‐weight changes of flame‐retardant fiber‐reinforced polyesters
Authors: Miller R. L. , Seymour R. W. , Branscome L. W. 
Published: May 2005

AbstractReinforced plastics based on poly(cyclohexanedimethylene terephthalate) (PCT) are excellent for electrical and electronic applications, particularly in the manufacture of electrical connectors. PCT offers a high heat deflection temperature, low cost, and relative ease of processing. For the injection molding process, stability of the melt is an important consideration, especially for materials with high melting points such as PCT. The combination of the polyester resin with flame retardant additives, processing aids, and thermal stabilizers results in a number of competing reactions which can change the molecular weight and molecular‐weight distribution (MWD) of the base polymer in the composite. Typical analytical techniques such as melt or dilute solution viscosity do not give adequate means of monitoring these changes so as to allow the polymer chemist to determine the effects of various additives on MWD. Size‐exclusion chromatography (SEC), by virtue of providing information on the entire MWD, was found suitable to study molecular‐weight changes in the melt due to both branching and chain cleavage, even when both phenomena occur simultaneously. Changes in the MWD over time at processing temperatures can be used to determine kinetic parameters and have been used to optimize PCT additive formulations for best processability and mechanical property retention.
Optimization of a tubular nylon 6 reactor with radial gradients
Authors: Srivastava D. , Gupta Santosh K. 
Published: May 2005

AbstractOptimal jacket‐fluid temperature profiles for tubular Nylon 6 reactors (in the presence of radial gradients of temperature and concentration) have been obtained using an algorithm based on the continuous minimum principle developed for a distributed parameter system. A gradient search technique has been devised and implemented for obtaining these optimal profiles. The optimal temperature profiles are found to be at the maximum permissible temperature, Tmax, at the beginning of the reactor and then slowly decrease to the minimum permissible temperature, Tmin, near the end of the reactor. The effect of varying several parameters is also studied. The desired value of the chain length and the reaction time are found to be the parameters which effect the optimal profiles most significantly.
Crystallization kinetics of poly(phenylene sulfide) (PPS) and PPS/carbon fiber composites
Authors: Kenny J. M. , Maffezzoli A. 
Published: May 2005

AbstractThe evolution of crystallinity of neat PPS and of the carbon fiber reinforced polymer under different processing conditions is studied. Crystallization from the amorphous state at low temperatures (cold crystallization), crystallization from the melt during cooling, and crystal melting processes are analyzed using calorimetric techniques under both isothermal and nonisothermal conditions. Cold and melt crystallization kinetics are described using an Avrami equation and an Arrhenius expression for the temperature dependence of the kinetic constant. Also, the melting kinetics of the, reinforced and of the unreinforced polymer are studied in this work. The effect of carbon fibers on the crystallization kinetics of PPS is analyzed, and a comparison of the crystallization behavior of PPS and other semicrystalline thermoplastic matrices, such as poly(etheretherketone) (PEEK), is presented.
Viscoelastic response of model epoxy networks in the glass transition region
Authors: Gerard J. F. , Galy J. , Pascault J. P. , Cukierman S. , Halary J. L. 
Published: May 2005

AbstractSix epoxy networks with various structures built up from a diepoxy prepolymer, DGEBA, and three different diamines or mixtures of a monoamine and a diamine were studied by dynamic mechanical analysis in the glass transition region. The systems were designed in order to investigate the dependence of glass transition Tg on both crosslink density and network chain flexibility. The time (frequency)—temperature superposition principle (WLF equation) was used to determine the viscoelastic coefficients Cg1 and C which are related to some free volume characteristics on the molecular scale. Cg1, related to the free volume fraction available at Tg depends mainly on crosslink density, even though the product Cg1C, related to the free volume expansion coefficient, is dependent on both chain flexibility and crosslink density. Thus, viscoelastic properties determined over large temperature and frequency ranges are shown to yield more precise information on epoxy network structure than the simple analysis of glass transition temperature.
RIM‐pultrusion of nylon‐6 and rubber‐toughened nylon‐6 composites
Authors: Ning Xin , Ishida Hatsuo 
Published: May 2005

AbstractUnidirectionally reinforced thermoplastic composites of Nylon‐6 and polypropylene oxide‐Nylon‐6 block copolymers have been prepared by the reaction injection molding (RIM)‐pultrusion process. This process takes advantage of both the RIM and the pultrusion techniques, while avoiding their inherent shortcomings. It also represents a novel way of incorporating toughening rubber domains into a thermoplastic composite. The composites produced exhibit excellent mechanical integrity with essentially zero void content. The chemical and physical states of the composites produced by the process were probed in terms of mechanical relaxation behavior using a dynamic mechanical spectrometer. Due to the simultaneous occurrence of both polymerization and crystallization processes in the reacting system, the resulting material is in a thermodynamically nonequilibrium state. An annealing effect is shown to correspond structurally to an increase in matrix crystallinity and the degree of phase separation, Izod impact tests were used to compare Nylon‐6 and rubber‐toughened Nylon‐6 RIM‐pultruded composites. The potential of secondary processing was, demonstrated by compression molding of the RIM‐pultruded composite rods.
A study on the mold filling process in resin transfer molding
Authors: Um Moon‐Kwang , Lee Woo Il 
Published: May 2005

AbstractA numerical simulation of the mold filling process during resin transfer molding (RTM) was performed using the boundary element method (BEM). Experimental verification was also done. Darcy's law for anisotropic porous media was employed along with mass conservation to construct the governing differential equation. The resulting potential problem was solved with the boundary element technique. As the calculation domain changed due to the proceeding resin front, boundary nodes were rearranged for each time step. The node which goes out of the calculation domain as time progresses was relocated at the intersection between the solid boundary and the line drawn between the node at previous and at current time steps. Results showed good agreement with data for a rectangular mold. To evaluate further the validity of the model, the area velocity of the resin‐impregnated region during mold filling was calculated. The area velocity thus calculated was compared with the corresponding resin inlet velocity to check the mass conservation. A close agreement was observed, which renders confidence in the resin front proceeding algorithm. Numerical calculations were also performed for complicated geometries to illustrate the effectiveness of the current method.
Experiments and modeling of flow of elastomers in an internal mixer with intermeshing rotors
Authors: Min K. , Suh K. G. 
Published: May 2005

AbstractThe direct observation of flow in the internal mixer with various rotor geometries is described. With decreasing distance between two rotors, additional transfer flow was observed in the inter‐rotor area. The FAN (Flow Analysis Network) method with assumption of fully filled, Newtonian fluid and isothermal condition was employed to simulate the flow patterns in the mixer with non‐intermeshing and intermeshing rotors. The distributive mixing capability was considered in terms of the fractional flow in the mixer calculated for various rotor geometries.
A study on the performance of the maddock mixing head in plasticating single‐screw extrusion
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C. 
Published: May 2005

AbstractAn experimental and theoretical study was conducted on the performance of the Maddock mixing head in plasticating single‐screw extrusion. For the experimental study, a low‐density polyethylene was extruded in an extruder that had nine pressure transducers mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel. Two screws with the Maddock mixing head were used, namely: one screw to measure the pressure difference between the entrance and the exit of the mixing head in the down‐channel direction, and the other screw to measure pressure variations in the cross‐channel direction in the middle of the mixing head. Our experimental results showed both pressure decrease and pressure increase in the down‐channel direction of the mixing head, depending upon the extrusion conditions employed. Using the flow analysis network (FAN) method, we predicted pressure variations in both the downchannel and cross‐channel directions of the Maddock mixing head, which agree with experimental results.
Effects of catalyst fragmentation during propylene polymerization. IV: Comparison between gas phase and bulk polymerization processes
Authors: Ferrero Monica A. , Chiovetta Mario G. 
Published: May 2005

AbstractA comparative study of the effects of catalyst fragmentation in the gas phase and bulk polymerization processes in performed. Typical operating conditions for each process are used for the comparison. The monomer concentration in the bulk process is nearly one order of magnitude larger than that in the gas phase process. The energy transfer conditions between the particle and the fluid phase are better in the liquid phase. The rate of mass transfer within the macroparticle at the initial steps of the polymerization is found to be slower in the bulk process than in the gas phase process. In the liquid phase process, fragmentation takes place more slowly. Temperature excursion values are smaller even though the dimensionless monomer concentrations are, in fact, greater because of the higher monomer concentration available in the liquid phase. The final steady rate of reaction and the ultimate catalyst yield reflect this phenomenon. Although the microparticle nucleus size affects both processes, the diffusion control that occurs when the fragments are large affects the gas phase process more intensely. In the bulk process, even at the lowest value reached by the rate of reaction, this is still sufficiently high so as to produce high yields.
Photoinduced reversible refractive index changes in doped poly(methyl methacrylate) lightguides
Authors: Lückemeyer Th. , Franke H. 
Published: May 2005

AbstractPlanar polymer lightguides of poly(methyl methacrylate)(PMMA) doped with the azo dye, N,N‐dihexyl‐4‐amino‐4′‐nitro‐azobenzene (DHANA) were fabricated on a suitable glass substrate or on one surface of a regular prism. The absorption of this azo dye is strong in the green spectral region. With the red light of a HeNe laser (633 nm) these polymer films may be used as lightguides. However, in this spectral region, the guided light influences the waveguiding properties of the polymer film, making this combination a possible candidate for an all optical device material. The observed refractive index changes are intensity dependent and the response time is of the order of 100ms.