bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of microdielectrometry in monitoring the cure of resins and composites
Authors: Sanjana Z. N. 
Published: December 2004

AbstractAs thermosetting resins and composites made from them begin to be used in critical applications, it becomes necessary to monitor and analyze the cure of the resin within the confines of the processing equipment. Such measurements have been carried out using a dielectric technique called dielectrometry or dielectric analysis. Conventional dielectrometry has certain limitations associated with the use of parallel plate geometry for electrodes. For in situ measurement of cure, intrusiveness of electrodes is a problem which may require placement of electrodes in non‐strategic areas. Since electrode spacing changes during cure, it is difficult to deduce permittivity and loss factor from the data. At lower frequencies the capacitive currents are small and signal‐to‐noise ratios are small, therefore, measurement at low frequencies (>100 Hz) typically require large electrode sizes. One approach to overcome the problems described above is the development of microdielectrometry. A solid state integrated circuit chip, 2 by 4 mm in size, is used as the sensor. The miniature sensor can measure the properties of a dielectric on its surface, therefore it need not intrude into the composite part. Transistors which are built into the integrated circuit are used to amplify the signal to make low frequency (>1 Hz) measurements feasible. The electrode geometry does not change, therefore loss factor and permittivity data can be deduced in real‐time. During cure of the resin or composite material, permittivity and loss factor are measured continuously at a series of preselected frequencies. Real‐time‐data is plotted on a strip chart and is also stored in a cassette for later analysis. Temperature of the curing material is measured either by a diode on the sensor or by externally placed thermocouples. Results on an aromatic amine cured epoxy resin and a dicyandiamide cured epoxy resin prepreg are presented in this report. The data obtained by microdielectrometry is compared and correlated to results obtained using differential scanning calorimetry, infrared analysis, and dynamic mechanical analysis. Results show that microdielectrometry can be used to follow the cure of epoxy resins and absolute measurements of permittivity and loss factor can be made to provide information on the mechanisms that produce the observed changes. Data at 1 Hz can be obtained but for certain lossy systems at typical cure temperatures, the data is often out of range of the instrument, thus restricting use to 10 Hz and higher frequencies. At very high loss factors (>100) a “blocking” phenomenon is observed due to charge pile up at electrode surfaces which results in erroneously high permittivity values.
Development of a mathematical model for the pultrusion process
Authors: Han Chang Dae , Lee Dai Soo , Chin Hong Bai 
Published: December 2004

AbstractA mathematical model has been developed to simulate the pultrusion process, namely the profiles of temperature and the degree of cure in both the axial and radial directions in a pultrusion die of cylindrical shape. For the study, the equations of continuity and energy transport, coupled with a kinetic expression for the curing reaction, were solved numerically, using a finite difference method. For the kinetic expression, we used an empirical expression of the form dα/dt = (k1 + k2αm)(1 − α)n to describe the curing behavior of both unsaturated polyester and epoxy resins. Differential scanning calorimetry (DSC) was used to investigate the curing behavior of the following systems: unsaturated polyester resin/glass fiber, epoxy resin/glass fiber, and epoxy resin/carbon fiber. The results of DSC runs were used to determine the kinetic parameters, which enabled us to predict the effects on the pultrusion characteristics of the following variables: (1) the type of initiator; (2) the type of fiber reinforcement; (3) the type of resin; and (4) the pulling speed and hence the residence time.
Effect of water absorption on physical properties of high nitrile barrier polymers
Authors: Jabarin S. A. , Lofgren E. A. 
Published: December 2004

AbstractWater absorption studies were made on a series of high nitrile barrier polymers, as a function of polymer composition, rubber content, temperature, orientation and relative humidity. Results indicate that absorbed water has a great influence on both mechanical and thermal properties of the polymer. Absorbed water in high nitrile polymers causes a large decrease in the glass transition temperature and yield stress. These effects are found to depend on polymer composition, amount of absorbed water, and degree of orientation. The significance of these results is discussed in relation to end‐use properties of the polymer.
Viscoelastic properties of highly loaded ferrite‐filled polymeric systems
Authors: Saini D. R. , Shenoy A. V. 
Published: December 2004

AbstractViscoelastic properties in terms of complex viscosity |η*| and storage modulus G' have been studied for highly filled polymer composites. The viscous response and elastic response to changes in the frequency of dynamic oscillations have been fitted through an appropriate Theological model. A relationship between |η*| and G' is shown to exist, and the model parameters determined through the correlation have been shown to be useful in estimating the viscoelastic properties of commercially important ferrite‐filled polymeric systems with loading in the range of 87–94 weight‐percent.
Finite element simulation of fountain flow in injection molding
Authors: Mavridis H. , Hrymak A. N. , Vlachopoulos J. 
Published: December 2004

AbstractFountain flow is the phenomenon of deceleration and outward motion of fluid particles as they approach a slower moving interface. The use of a general purpose finite element program for the appropriate boundary conditions made possible the detailed flow description behind an advancing liquid front moving at constant speed inside two‐dimensional channels and tubes. The results were qualitatively the same for both Newtonian and shear‐thinning fluids.
Injection molding: The effect of fill time on properties
Authors: Cox Howard W. , Mentzer Charles C. 
Published: December 2004

AbstractThe effect of fill time on the mechanical properties, surface appearance, and part dimensions of several polymers was determined. Two crystalline materials, polypropylene and nylon 6,6, and an amorphous material, acrylonitrile‐butadiene‐styrene (ABS), were used. In addition, the effect of the presence of glass fibers was examined using glass fiber reinforced nylon 6,6. The fill time was varied from 0.8 to 20 sec which included both the viscous flow controlled region (short fill times) where laboratory samples are ordinarily molded and the heat transfer controlled region (long fill times) where production parts arc commonly molded. No large variations in tensile properties were observed for polypropylene or nylon, but a 10 percent increase in peak tensile stress and strain for ABS did indicate that molecular orientation increased with increasing fill time. However, significant differences did occur in the properties of glass reinforced nylon. Peak tensile stress increased 15 percent and flexural strength decreased 10 percent as the fill time was increased. Although no change in the flexural modulus was observed, the scatter in the modulus decreased with increasing fill time. These property variations can be attributed to differences in the glass fiber orientation of the skin and core regions of the part. The measurement of molded tensile bar dimensions indicated there was little effect of fill time on the shrinkage of the various polymers except for shrinkage in the length direction for polypropylene. The shrinkage increased from 13 to 15.4 mm/m over the fill time range, a great enough difference to affect the fit of large parts. The most dramatic change with fill time was the surface appearance of the glass reinforced nylon. The surface of samples molded at short fill times had a dark uniform color and smooth appearance while samples molded at long fill times had a lighter color and a porous surface. This surface porosity is due to crystallization prior to complete pressurization of the mold. Therefore, in addition to affecting surface appearance, other surface related properties such as aging and the ability to plate plastic parts could also be affected.
An experimental investigation of capillary extrudate swell in relation to parison swell behavior in blow molding
Authors: Kalyon Dilhan M. , Kamal Musa R. 
Published: December 2004

AbstractAn experimental study was carried out to study and characterize the capillary extrudate swell and parison swell behavior in extrusion blow molding of two commercial blow molding grade high density polyethylene resins. The capillary extrudate swell behavior of these resins were determined employing a capillary rheometer and a special thermostatting chamber. Parison swell behavior was determined using an Impco A13‐R12 reciprocating screw blow molding machine in conjunction with cinematography and pinch‐off. The experimental conditions under which capillary extrudate and parison swell data can be related are elucidated. Excellent agreement is found between the area swell values determined on the basis of capillary and parison swell experiments.
Microstructural influences on volumetric properties of styrene‐butadiene‐styrene block copolymers
Authors: Diamant Joram , Williams Michael C. 
Published: December 2004

AbstractA water‐displacement method was used to measure the specific volume of three styrene‐butadiene‐styrene (SBS) block copolymers over the temperature range 4°C to 65°C. The polymers contained 0.268. 0.293, and 0.482 weight fraction polystyrene, varied in molecular weight, and are known to be phase‐separated at these temperatures. Coefficients of thermal expansion were also obtained and found to be constant over this temperature range. Results are compared with various models of composite behavior, the most successful of which is the linear mixing rule which gives good predictions over this composition range. Deviations for specific volume are negative, and for expansion coefficient positive, from the linear rules. More complex behavior is suggested, however, and this is interpreted in terms of microstructural characteristics. Some apparent contradictions in data reported by other workers are explained. Results are presented also for samples stretched uniaxially up to 300 percent strain; only slight evidence of dilation is seen at 22°C. but increase of the expansion coefficient is more apparent.
Residence time distribution in a commercial twin‐screw extruder
Authors: Wolf D. , Holin N. , White D. H. 
Published: December 2004

AbstractThe residence time distribution of poly(vinyl chloride) (PVC) polymers in a counterrotating twin screw commercial extruder was determined and analyzed. The experimental technique involved the use of manganese dioxide as a tracer after being neutron activated and was injected into the extruder during normal operation without interrupting the poly(vinyl chloride) compound production. The experimental results enabled us to better understand the flow and mixing conditions in the extruder.
High‐TG base‐soluble copolymers as novolac replacements for positive photoresists
Authors: Turner S. Richard , Arcus Robert A. , Houle Conrad G. , Schleigh William R. 
Published: December 2004

AbstractSeveral high‐Tg, phenolic copolymers based on N‐(p‐hy‐droxyphenyl)maleimide with various comonomers were prepared, and the properties of a number of these copolymers were studied. The copolymers were 1:1 in composition and were predominantly alternating. The thermal properties of these copolymers were investigated by differential scanning calorimetry and thermal gravimetric analyses. The chain‐stiffening effect of the maleimide group was responsible for Tg's of 200°C and above. Tg was a function of composition and molecular weight. Dissolution rates of thin films of these copolymers were investigated by laser interferometry. The dissolution rates were sensitive to copolymer molecular weight and to the functionality, i. e., the type of phenolic OH groups and the concentration of OH groups present. When these copolymers were used as binders for NDS (diazonaphthoquinone sulfonate) photochemistry, high‐resolution positive images were obtained that were resistant to thermal deformation at 200°C and above.
The fracture behavior of surface embrittled polymers
Authors: So Paul K. , Broutman L. J. 
Published: December 2004

AbstractNormally ductile polymers may exhibit unexpected brittle fractures because of a phenomenon termed surface embrittlement. The problem may arise whenever a thin brittle layer is present on the surface, which may result from the application of brittle paint or, more commonly, from surface degradation caused by exposure to elevated temperatures, ultra‐violet radiation, and stress‐cracking agents. In rubber‐modified polymers such as acrylonitrile‐butadiene‐styrene and high‐impact polystyrene, exposure to the outdoor environment inevitably results in the formation of a thin surface layer containing cross‐linked rubber particles in a matrix of reduced molecular weight. Although the depth of material adversely affected is typically small compared to the bulk, a drastic reduction in ductility nonetheless has been observed. To better understand the mechanism of embrittlement, this paper examines the criterion for embrittlement by considering the mechanism for enhanced energy absorption of rubber‐toughened plastics and elementary concepts of fracture mechanics. It has been shown that a critical coating thickness exists when multiple crazing is essentially inoperative and the deformation is localized, to the tip of a fast moving sharp crack restricting strain energy dissipation to a relatively small region.
Sorption equilibria and kinetics of ethanol in miscible poly(vinylidene fluoride)/poly(methyl methacrylate) blends
Authors: Chiou J. S. , Paul D. R. 
Published: December 2004

AbstractAt 35°C miscible blends of poly(vinylidene fluoride) (PVF2), and poly(methyl methacrylate) (PMMA), may be semicrystalline or wholly amorphous and rubbery or glassy depending on composition and prior history. Ethanol is rather soluble in PMMA and plasticizes it, while sorption into PVF2 is rather small. The equilibrium sorption of ethanol into these blends decreases in a well defined manner as the PVF2 content increases and is only slightly affected by prior history of the sample. On the other hand, the kinetics of ethanol sorption varies in a complex manner with composition, ranging from Case II kinetics for glassy blends to Fickian diffusion for rubbery ones, and is a strong function of prior history. Quantitative descriptions are given and discussed in terms of the various mechanistic processes known to occur.
Small angle x‐ray studies of siloxane‐urea segmented copolymers
Authors: Tyagi D. , McGrath J. E. , Wilkes G. L. 
Published: December 2004

AbstractNovel segmented copolymers were synthesized using aminopropyl terminated linear poly(dimethylsiloxane) oligomers as the soft component and various diisocyanates as the hard segments. As a result of the large differences in the cohesive energy density (solubility parameter) between the two components, phase separation occurs to form a microdomain structure at relatively low oligomer molecular weights. Since chain extenders were not employed during the synthesis, the “hard” segments are strictly related to the length of the diisocyanate moiety utilized in the reaction, In this paper we utilize these copolymers as reasonable models for investigating the various methods available for determining the interfacial layer thickness between the hard and soft phase. Specifically, in these systems there is no hard segment length distribution as is the usual case for segmented urethanes. Utilizing Porod's law, and appropriate analysis, both positive and negative deviations were found in the systematic series of copolymers. The degree of positive and negative character was found to be dependent upon copolymer composition. Negative deviations were accounted for in terms of a finite interfacial thickness, which turned out to be relatively small as anticipated, while the positive deviations were assigned to isolated hard segments that reside within the soft segment matrix, i.e., concentration fluctuations. In calculating the interfacial thickness, several methods were applied and in general, close agreement was obtained. Finally, correlation function analysis in conjunction with determination of the coherent Porod lengths, etc. were determined and discussed accordingly. Cautionary comments are also provided for researchers who apply less complete small angle x‐ray scattering (SAXS) analysis to related block or segmented copolymers with regard to phase separation behavior.
Forced in‐plane flow of an epoxy resin in fibrous networks
Authors: Adams Kurt L. , Miller Bernard , Rebenfeld Ludwig 
Published: December 2004

AbstractA method to study the forced in‐plane flow of an epoxy resin into fibrous networks is presented. A radial in‐plane flow apparatus has been developed which allows strict control of all important experimental variables as well as visual observation of the experiment. From the position and shape of the advancing resin front as a function of time, effective directional permeabilities are obtained and used to compare structurally different fibrous networks. Test results for an initial series of woven and nonwoven fabrics reinforce the method of data analysis and demonstrate the effects of pore structure, weave type, weave balance, fabric layering, fiber orientation, and compressibility.
The process of cavity filling including the fountain flow in injection molding
Authors: Gogos Costas G. , Huang Chieh‐Fong , Schmidt Larry R. 
Published: December 2004

AbstractThis work deals with the simulation of the filling of a cavity utilizing the Marker‐and‐Cell numerical technique in solving the transient problem involved. The cavity is confined by two parallel plates, and is “end fed.” The flow was assumed isothermal and the fluid incompressible, obeying the power law model. Special attention was given to the flow region near the advancing melt front, in order to obtain a better insight of the “fountain effect,” during which the fluid flows from the center to the walls of the cavity. The results of the simulation of the front flow region are supported by and in qualitative agreement with experimental results involving “tracer resins” during cavity filling. Although the flows considered were slow and isothermal, this study has significant practical ramifications on industrial mold filling during injection molding.
Polycarbonate/phenoxy blends: Physical behavior and development of interchange reactions in melt‐processing conditions
Authors: Mondragón I. , Gaztelumendi M. , Nazábal J. 
Published: December 2004

AbstractThe miscibility of the polycarbonate of bisphenol A with the polyhydroxyether of bisphenol A was analyzed using differential scanning calorimetry and the, results are compared with the torque data obtained using a Brabender Plasticorder. The possibility of interchange reactions was analyzed by means of the observation of the melt‐viscosity variation versus processing time in the mixer‐bowl. These reactions form graft‐copolymers that develop into crosslinked copolymers at higher residence times. It was also shown that the speed of these reactions depends on the processing temperature. The variation produced on the glass‐transition temperature because of branching was also analyzed.
The melt compatibility of blends of polypropylene and ethylene‐propylene copolymers
Authors: Lohse David J. 
Published: December 2004

AbstractBlends of polypropylene with ethylene‐propylene copolymers of various compositions have been studied by small angle neutron scattering with regard to their compatibility at room temperature and in the melt. It has long been known that such blends separate into distinct phases at lower temperatures due to the crystallinity of the isotactic polypropylene, The work described herein has shown that these blends are also immiscible in the melt, even where the ethylene content of the copolymer is as low as 8 percent. Moreover, the separated phase domains grew rapidly at melt temperatures. Blends of atactic polypropylene with isotactic polypropylene did become miscible upon melting.
Hydroxyl group determination in prepolymers by 1H NMR spectroscopy
Authors: Goldwasser J. M. , Adolph H. G. 
Published: December 2004

AbstractA fast and specific method has been developed for the determination of hydroxyl content in prepolymers that contain hydroxymethylene functional groups. This method involves reaction of the sample with either trifluoroacetic anhydride or hexafluoroacetone to separate the terminal oxymethylene signals in the 1H NMR spectrum from those of the repeating unit and integration against an internal trinitrobenzene standard. This procedure generally requires less than 50 mg of polymer and has been employed in the analysis of prepolymers with number average molecular weights ranging up to 10000. The analysis has been tested using several different prepolymers. Precision of analysis was determined to be within 2.7 percent using a Varian XL‐200 spectrometer.
Characterization of epoxy thermosetting systems by differential scanning calorimetry
Authors: Galy Jocelyne , Sabra Abed , Pascault Jean‐Pieirre 
Published: December 2004

AbstractDifferential Scanning Calorimetry (DSC) is used to study the curing behavior of epoxy systems. For non‐catalyzed diamine‐epoxy systems, the reaction enthalpy ΔH and the glass transition temperature Tg are evaluated and related to the structure of the hardener. A method is developed to determine the activation energy. The effect of variations in the amine‐to‐epoxy ratio r on Tg is also examined. A maximum value is observed for r = 1. Then, the influence of benzyldimethylamine as catalyst in an anhydride/DGEBA system and in three diamine/DGEBA systems is reported. In the cases of DDS and DDA curing agent the maximum value of Tg is shifted, to r = 0, 6. The results are explained by different reaction mechanisms.
Montmorillonite polymer concrete: Zero‐shrinkage and expanding polymer concrete with enhanced strength
Authors: Haque E. , Armeniades C. D. 
Published: December 2004

AbstractConventional polymer concrete (PC) suffers from setting stresses, generated during the cure of the resin binder, when polymerization shrinkage is hindered by the close packing of filler and aggregate particles. Setting stresses impair significantly the strength of the cured PC. Current zero‐shrinkage and expanding PC formulations achieve these properties with a sacrifice in strength. Here we present a novel method for producing zero‐shrinkage and expanding PC systems with concomitant enhancement in strength. This is achieved by dispersing small amounts of the mineral montmorillonite (MMT) into the resin. As the system cures, the resin interacts with the hydrated mineral: at temperatures above 100°C some of the hydration water is released, creating expansion forces, which counteract resin shrinkage. MMT contents of 0.2 percent or less give rise to zero‐shrinkage polyester PC systems with flexural strength 30 percent greater than the corresponding conventional PC; higher MMT contents create PC systems that expand upon curing or generate hydrostatic pressure during constant‐volume cure. We discuss the effects of MMT content and cure temperature on the volume change and strength of the resulting PC. We then propose a mechanism for the action of MMT as a highstrength expansion agent, based on differential scanning calorimetry and thermomechanical analysis of these systems.