bluuebunny/crossref_metadata_2025 huggingface dataset:
Elongational behavior of short glass fiber reinforced polypropylene melts
Authors: Kamal M. R. , Mutel A. T. , Utracki L. A.
Published: December 2004

The Rheometrics Elongational Rheometer was employed to study the uniaxial extensional flow of glass fiber filled polypropylene melts, in which the fiber concentration, c, varied between zero and 40 weight percent. The constant strain rate mode was used for strain rates, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^. $\end{document}, between 0.003 and 0.6 s−1. Steady state elongational viscosities were observed in most cases for fiber filled polypropylene melts, even at rates at which the stress continued to increase for unfilled polypropylene. The rate of relative stress growth increased with \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^. $\end{document} and was affected by the addition of fibers. The steady elongational viscosity of the fiber reinforced melts was found to decrease with increasing \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^. $\end{document} and to increase with increasing c. Yield stresses were observed in elongational flow at high concentrations, although there was no clear evidence of yield in steady shear.
Evidence of interaction of fillers with matrix polymers via transition maps
Authors: Beatty Charles L.
Published: December 2004

Surface modifications of fillers can be detected via dielectric relaxation spectroscopy with surface coatings that interact with the matrix polymer resulting in higher glass transition temperatures of the matrix polymer. Increasing the surface area of filler present by increasing the amount of filler systematically shifts the glass transition temperature of the matrix polymer to higher values. Increasing the surface area of the filler by making the surface microporous improves many mechanical properties but may not immobilize as many matrix polymer molecules if a weak boundary layer is present.
Structural changes of chlorinated paraffins at processing conditions of particulate filled polypropylene
Authors: Ishida Hatsuo , Huang Zhen‐Hua
Published: December 2004

Structural changes of chlorinated paraffin (CP) have been studied using UV‐visible absorption spectroscopy in the 180 to 220°C temperature range. Formation and further reaction of conjugated polyene sequence with and without MgO is of major concern. It was found that CP dehydrochlorinated at normal processing temperatures of polypropylene in the absence of MgO. A mixture of various polyene sequences was formed. Unlike a stabilizing effect on poly(vinyl chloride), MgO showed a catalytic effect for dehydrochlorination of CP. As a result, longer conjugation was formed with MgO at the same conditions except for the absence of MgO. The longer polyenes were selectively reacted at the conditions studied. A possible chemical bond formation at the particulate filler/polypropylene matrix interface was suggested as one of the reinforcement mechanisms of the composite.
Thermally conductive polymer compositions
Authors: Bigg D. M.
Published: December 2004

While polymers are widely used for their excellent insulating properties, there is a growing need for thermally conductive polymer compounds. The thermal conductivity of metal particle, mineral particle, and carbon fiber filled compounds are examined at volume concentrations up to the maximum packing fraction of each filler. From these data the coefficients in Nielsen's model were determined for each type of filler. Gaps in available thermal conductivity data were then predicted using these coefficients, the properties of the polymer and filler, and the volume concentration of the filler. Gaps were found to exist mostly for compounds containing short fiber reinforced compounds. A comparison of predicted values of thermal conductivity for such systems with the sparse data available shows that Nielsen's model cannot be applied to highly filled fiber reinforced composites because it cannot account for the anisotropy of such compositions.
Tensile behavior of clay‐filled polyester composites
Authors: Newaz Golam M.
Published: December 2004

In this study, the tensile behavior of clay‐filled unsaturated orthophthalic polyester composites was evaluated. Specifically, ultimate strength, yield strength, fracture strain, and Young's modulus of two composites with small but varying fractions of clay particulates were determined. Several predictive approaches were considered for correlation with experimental values. Only the Young's modulus of the composites could be predicted satisfactorily. The irregular shape and size distribution of clay particulates seriously complicate attempts to analytically model the mechanical behavior of filled composites. Microcracking response of the composites was evaluated using an acoustic emission (AE) technique. The addition of clay is shown to embrittle the composites and is confirmed by the AE count rate and amplitude distribution data. Scanning electron microscopy of the fracture surface shows evidence of flaw initiated fracture. This study provides an insight into the influence of clay particulates in altering the properties of a polyester matrix.
Mechanical properties of polyethylene/ethylene vinyl acetate filled with calcium carbonate
Authors: Mitsuishi K. , Kodama S. , Kawasaki H.
Published: December 2004

The tensile behavior of polyethylene/ethylene vinyl acetate (PE/EVA) polymer blends filled with calcium carbonate (CaCO3) was studied using tensile and viscoelastic tests. The relations between tensile properties (modulus, strength, etc) of oriented and unoriented PE/EVA‐CaCO3, and void volume of polymer/CaCO3 interface, PE/EVA blend ratio, and CaCO3 content were investigated. The results indicated that the tensile strength and elongation of PE/EVA‐CaCO3 decreased with CaCO3 content and PE blend ratio for unoriented PE/EVA‐CaCO3 systems. In the case of oriented samples, the relative modulus (E/E, where E and E are the modulus of oriented composites and the modulus of oriented matrix, respectively) of PE/EVA‐CaCO3 is larger than that of PE/CaCO3 by increasing the EVA content relative to PE and CaCO3. The value of E/E can be simply expressed as the function of void volume and CaCO3 modulus to polymer matrix modulus.
Experimental determination of the evolution of internal stresses in a composite material: Case of a circular bilayered laminate glass‐resin
Authors: Wippler C. , Aboulfaraj M. , Schirrer R. , Pixa R.
Published: December 2004

A nondestructive method is proposed to analyze the internal stresses of a circular bilayered laminate glassresin. It is based on the measurement by optical interferometry of small deformations of the laminate under the influence of temperature, time, or applied mechanical stresses of known value. For example, the stress induced by the curing of the thermosetting resin layer is determined and the postcuring relaxation of the stress is measured. Other possibilities or improvements of the method are indicated: The determination of the Young's modulus of the thermosetting resin as a function of time, the determination of the work‐hardening rate, and the determination of the ultimate properties of the laminate are just a few of them.
Elastic moduli and failure mechanism of composites made of spherical glass beads, of polyethylene using poly (4‐vinylpyridine graft butylacrylate) as an interface agent
Authors: Pegoraro M. , Severini F. , Di Landro L.
Published: December 2004

Graft polymers were prepared by copolymerization of double bond terminated long chain poly(vinylpyridine), endowed with polar units interacting with glass, and butylacrylate (BA) having short groups interactive with polyethylene. These polymers were used to coat A glass beads which were mixed with polyethylene (PE) to obtain glass‐PE‐composites. Good adhesion due to the presence of the adhesive polymer, and to a glass hydrolyzing pretreatment, permits higher elastic moduli and higher tensile strengths than in their absence. The adhesive composition has some influence especially on the yield stress which is higher when using the g‐polymer endowed with longer BA branches. Theoretical predictions of the moduli are discussed and do not give satisfactory results when compared with the experimental values, except at low concentrations. Failure is observed to begin in the polar zone and its mechanism appears to be dependent on the presence or absence of adhesive.

The experimental stress and strain at the beginning of failure are lower for untreated fillers. The specific volume variation \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\Delta V}}{{V_O }} $\end{document} during the tensile test appears to be an important index of adhesion. Both the critical strain at which detachment begins and the slope of the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{\Delta V}}{{V_O }} $\end{document} curve can be assumed as effective adhesion indexes.
Adhesion between polybutylene terephthalate and E‐glass. Measured with a microdebond technique
Authors: McAlea Kevin P. , Besio Gregory J.
Published: December 2004

Single‐fiber pullout tests are frequently used to characterize the interfacial adhesion between resin and fiber in reinforced composites. In this report, a fiber pullout experiment in which a drop of thermoplastic resin is sheared from a single fiber is described. Specialized apparatus, developed and constructed in our laboratory, as well as the techniques for sample preparation are discussed in detail. The interfacial shear strength of polybutylene terephthalate (PBT) in contact with silane‐treated E‐glass fibers is measured quantitatively.
Melt rheological properties of nickel powder filled polypropylene composites
Authors: Maiti S. N. , Mahapatro P. K.
Published: December 2004

The melt rheological properties of nickel powder filled polypropylene composites were investigated. The effect of filler concentration on shear stress‐shear rate data, melt viscosity and melt elasticity parameters were determined by using a capillary rheometer. The study shows that the materials follow a power law in viscous behavior over the entire range of shear rates investigated and that the viscosity increases and elasticity decreases as filler concentration is increased up to a critical value. However, beyond the critical filler content melt viscosity decreases while melt elasticity increases. The effect of temperature on the viscoelastic properties of filled polypropylene was also investigated.
Applications of diffuse reflectance fourier transform infrared spectroscopy to fiber‐reinforced composites
Authors: Cole K. C. , Noël D. , Hechler J.‐J.
Published: December 2004

Diffuse reflectance Fourier transform infrared (FT‐IR) spectroscopy can be used to obtain infrared spectra directly from the surface of composite materials with little or no sample preparation. It is thus of interest as a nondestructive method for industrial inspection. In many cases, the IR spectra provide detailed information concerning the chemical composition and molecular structure of the material. The technique works particularly well for carbon‐fiber composites. This paper describes the principles involved, some factors which influence the quality of the spectra, and a number of examples of applications. These include the characterization of epoxy matrices (composition, curing, degradation), the detection of surface contamination, and the determination of the degree of crystallinity in poly(phenylene sulfide)‐based composites.
Mechanical and rheological properties of carbon black filled polyethylene
Authors: Malik Tariq M. , Carreau Pierre J. , Grmela Miroslav , Dufresne Alain
Published: December 2004

The mechanical and rheological properties of high density polyethylene filled with carbon black have been examined. Two sources of carbon black (one commercial and other obtained from a pyrolysis process) and various treatments have been studied. The rheological measurements in the melt state has been performed on a Rheometrics stress rheometer and a capillary rheometer. These materials possess outstanding hardness and toughness showing great potential for structural application. Comparison of carbon black from two sources showed that the carbon from the pyrolysis process has a good potential as a reinforcing agent. It was found that surface treatment reduces the particle‐particle interactions and improves the filler dispersion. The relationship between the yield stresses, filler percentage, surface modification by the coupling agents and mechanical properties is discussed.
Rheological study of mica‐filled polypropylene as influenced by a coupling agent
Authors: Rochette A. , Choplin L. , Tanguy P. A.
Published: December 2004

The rheological behavior of mica‐filled polypropylene (PP) composites was investigated within the domain of linear viscoelasticity. The effect of mica concentration and of a silane coupling agent on material functions such as the complex viscosity (η*), the storage modulus (G') and the loss modulus (G") was examined. The dimensions of mica flakes were measured before and after coating with silane. The affinity of PP for the treated and non‐treated mica was characterized. It was found that, for low mica concentration (<30% by weight) the composite exhibits the classical viscoelastic behavior of a homogeneous material. For higher mica concentration, the material shows a strong heterogeneity as evidenced by an important drift at low frequencies in a Cole‐Cole representation. It was also found that the presence of a silane coupling agent moves this critical concentration value up to 40% by weight.
High temperature polyimides, chemistry and properties
Authors: Scola Daniel A. , Vontell John H.
Published: December 2004

Selected polyimide resins are capable of long term use at 316°C for over thousands of hours in an inert atmosphere, and approximately 2000 hours in air. This attractive feature of polyimides has provided an avenue for applications at elevated temperature (316°C) as adhesives, coatings, and secondary structures in the form of fiber reinforced polyimide composites. The chemistry and properties of thermoplastic and crosslinked polyimides, including addition‐type polyimides, will be discussed. The chemical considerations of both commercial and experimental polymer materials, Avimid N, PMR‐15, LARC TPI, IP‐600, L‐20, and L‐30 as they affect processing are reviewed. General physical, thermal, mechanical, and thermo‐oxidative stability properties of polyimides are presented Room temperature and 316°C mechanical properties of unaged and 1000 hr 316°C aged high temperature polymer composites will also be discussed.
Viscosity and die swell of acrylonitrile‐butadiene‐styrene filled with glass beads and glass fibers
Authors: Yilmazer Ulku
Published: December 2004

Shear viscosity and die swell ratio of acrylonitrile‐butadiene‐styrene filled with glass beads and glass fibers were measured. The relative viscosity of the composites increased with filler content, but decreased with shear rate. At low shear rates, fiber filled systems had higher relative viscosities than bead filled systems. At high shear rates, the opposite was observed. The die swell ratio of the unfilled material increased linearly with the logarithm of the shear rate. Systems highly filled with glass beads or fibers showed a maximum in the die swell ratio at medium shear rates. The magnitude of the maximum in the die swell ratio increased with the filler content and the die length, up to a certain length, in a series of dies that had the same radius. The presence of a maximum in the die swell ratio of the filled melts is explained by an order‐disorder phenomenon observed earlier by Wu.
Weld line studies on transfer‐molded thermosetting composite materials
Authors: Eduljee R. F. , Gillespie J. W.
Published: December 2004

Multiple gating and the presence of inserts make weld lines (also known as knit lines) almost unavoidable in commercially produced moldings. These weld regions may be significantly weaker in strength than the bulk material away from the weld line. Hence, a molded section containing a weld line will only be as strong as the weld line, no matter how strong the surrounding bulk material. The influence of processing history on weld line performance is essential to optimally designed transfer‐molded composite products with discontinuous‐fiber‐reinforced molding materials. This study has therefore been directed toward experimentally characterizing the weld line strength of a bulk molding compund (BMC) and a thick molding compound (TMC) as a function of the mold temperature, fill time/fill rate, and the postbake operation.
Elastomeric matrix‐short fibers adhesion
Authors: Ibarra L. , Chamorro C.
Published: December 2004

This paper analyzes the effects of the addition of a three‐component dry type adhesive system on the properties of composite SBR (styrene‐butadiene rubber) material containing 20 percent short polyamide (5 mm length and 60 μm diameter). The curing times are extended and green strength is doubled. The replacement of the silica component in the system by a natural silicate is not only feasible, but proves to be favorable for certain properties, such as the storage modulus E′, which becomes less sensitive towards temperature changes. Dynamic property measurements provide evidence of an additional dispersion corresponding to the matrix‐fiber interface located around 40 to 50°C, which does not occur in the composites without adhesive. The activation energies of the main relaxation process of these materials are determined, amounting to 175 KJ/mol for the matrix and 250 KJ/mol for adhesive‐containing composites, as a consequence of the formation of strong bonds between both phases.
Parameters affecting interlaminar stresses in tapered laminates under static loading conditions
Authors: Daoust J. , Hoa S. V.
Published: December 2004

Tapered laminates by internal ply drop‐offs have been studied. An extensive finite element program has been developed for microcomputers using displacement formulation. A 20 node, three dimensional element was used. Parameters which can influence the strength of the laminate were studied. These parameters include the location of the drop‐off in the thickness direction, the degree of resin filling inside the drop‐off, the shape of the drop‐off, the effect of width of laminate, and the orientation of the lamina where the drop‐off was made. Locations of failure based on maximum stress criterion were btained. Crack growth stimulation was also performed by consecutive removal of failed elements. Results show that crack growth is not continuous.
Permeability characteristics of multilayer fiber reinforcements. Part II: Theoretical model
Authors: Adams Kurt L. , Rebenfeld Ludwig
Published: December 2004

The permeability characteristics of multilayer fiber networks generally differ from those of the constituent layers. In heterogeneous assemblies, the effective in‐plane permeabilities and flow anisotropies are governed by the high permeability layers or directions. Based on the observation that a transverse flow mechanism contributes to filling the low permeability layers, a semipermeable wall model has been constructed to analyze encroaching flows into multilayer systems. The model identifies three flow regimes: a region in which the layers act independently and are governed by single layer solutions, a region in which the layers act as a unified homogeneous system governed by the single layer solution with weighted average properties, and a region intermediate to these extremes. A comparison of model simulations and experimental data demonstrates that the model has good predictive capabilities.
Electrochemical polymerization of xylene derivatives on carbon fiber
Authors: Li Hong , Moshonov Aharon , Muzzy John D.
Published: December 2004

Electrochemically initiated polymerization on carbon fibers is an attractive process for combining fibers with a polymer matrix. An aromatic monomer, α,α′‐para‐xylene, was successfully polymerized on carbon fibers in a three‐compartment electrolysis cell. A composite topreg with 40 volume percent of polymer was obtained. The polymer coating has a porous texture. The polymerization is rapid and efficient. Polymerization conditions and composite thermal properties are described.
Effects of reactive and non‐reactive fiber coatings upon performance of graphite/epoxy composites
Authors: Rhee H. W. , Bell J. P.
Published: December 2004

Interlayers of controlled composition and thickness were applied to commercial graphite fiber bundles by electrochemical copolymerization, and the impact and interlaminar shear strength of composites from these coated fibers were examined. Glycidyl acrylate/methyl acrylate copolymers represented coatings that were reactive to the epoxy matrix during curing; acrylonitrile/methyl acrylate copolymers represented non‐reactive systems. The reactive systems showed 10 to 30 percent simultaneous improvement in impact and interlaminar shear strengths, while the non‐reactive system failed at the interlayer‐epoxy interface and showed no improvement. There is an optimum interlayer thickness of 0.1 to 0.15 micron; the possible reasons are discussed. A detailed scanning electron microscope study illustrates how the structure of the composite fracture surface varies with the systematic changes in interlayer reactivity, composition, and thickness. Determination of the locus of failure is discussed. The observations are consistent with the mechanical property measurements.
The significance of microcomposites as experimental models
Authors: Wagner H. D. , Rubins M. , Marom G.
Published: December 2004

This paper demonstrates the usefulness of careful experimental work with model composite materials, such as thin polymeric films in which single fibers are accurately positioned, in at least two respects: to assess the validity of a theory for a given physical property, and to accurately probe the effects of various parameters on the behavior of composites. Working with such model composites has obvious advantages, such as the full control of experimental parameters, the possibility of introducing perturbative effects in a controlled way, and the possibility of verifying theoretical models in the range of low fiber content. Indeed, macroscopic composite materials contain various types of defects and perturbative effects, such as fiber misalignment or slack, fiber‐poor regions, voids, etc., which bias any quantitative assessment of mechanical and physical properties, and preclude the accurate verification of theoretical schemes. One difficulty in working with microcomposite models, also recalled here, is the need for an appropriate “scaling‐up” procedure to the level of macroscopic composites.
Determination of matrix‐dominated mechanical properties of fiber composite lamina
Authors: Lyon R. E. , Schumann D. L.
Published: December 2004

A test methodology that utilizes unidirectional, hoop‐wound tubes to determine matrix‐dominated mechanical properties of unidirectional fiber composite lamina is described. Longitudinal shear modulus and strength as well as transverse Young's modulus, transverse tensile strength, and transverse compressive strength are obtained from a single thin‐walled tube specimen and fixturing design. Data presented for two carbon‐fiber‐reinforced epoxy composite materials illustrate the simplicity and precision of the described procedure.
Processing effects and damage tolerance in poly(etheretherketone) composites
Authors: Uralil F. S. , Newaz G. M. , Lustiger A.
Published: December 2004

Thermoplastic composites in general have been found to display improved resistance to impact damage over their thermosetting counterparts. However, in earlier work, we presented data that suggested that in poly(etheretherketone) (PEEK) based composites, damage tolerance may be adversely affected if cooling rates are too slow in the processing of these parts. In this work, ultrasonic C‐scan and compression‐after‐impact testing were implemented on PEEK APC‐2 plaques cooled at three different cooling rates, in addition to toughened epoxy and bismaleimide plaques processed conventionally as a comparison. It was found that the damaged areas as measured ultrasonically varied significantly between the PEEK samples cooled at different rates, and that under the slowest cooling conditions, the damaged areas approached those of the thermosetting systems tested. However, because compressive strengths before impact were found to be greater on slow cooling, the differences in compression‐after‐impact were less dramatic than one would have expected from the C‐scan results alone. Variations in crystallinity as well as spherulite size were the source for the differences in damaged areas as well as in compressive strength.
Effect of surface treatment of pitch‐based carbon fiber on mechanical properties of polyethernitrile composites
Authors: Itoi Masaaki , Yamada Yukiharu , Pipes R. Byron
Published: December 2004

The effect of surface treatment of pitch‐based carbon fiber on a new engineering thermoplastic resin, polyethernitrile, was investigated. Pitch‐based carbon fiber (CF) was treated in two separate oxidizing solutions. In the first method, a nitric acid solution was used as an oxidizing agent. In the second method, a hydrogen peroxide solution was used. Both methods demonstrated that each of these solutions was a satisfactory oxidizing agent for the pitch‐based CF. These treated fibers were combined with polyethernitrile polymer by the powder impregnation method, and unidirectional laminates were obtained. Improvements in both interlaminar shear strength and transverse flexural strength were achieved. The laminates fabricated from the treated CF maintained the same longitudinal flexural strength as laminates from the untreated control. In addition, scanning electron micrographs of composite fracture surfaces also showed excellent bonding of the treated fiber.
Mechanical and microscopic investigation of whisker‐reinforced silicone rubber
Authors: Weber Mark E. , Kamal M. R.
Published: December 2004

Franklin Fiber whisker‐reinforced silicone rubber composites were molded using both transfer and compression molding. Processing parameters, such as sprue design, milling procedure, and mold temperature were varied. The fiber orientation in the composites is anisotropic and independent of sprue design and mold temperature, but dependent on milling procedure. Fiber attrition is significant for all samples. The Young's modulus is affected by fiber orientation. The experimental modulus values are higher than those predicted by the Halpin‐Tsai equations for short fibers.
Analysis and characterization of prepreg tack
Authors: Ahn K. J. , Seferis J. C. , Pelton T. , Wilhelm M.
Published: December 2004

As part of an engineering analysis and experimental methodology to characterize prepreg tack, a compression‐to‐tension test was optimized to enhance reproducibility and generate intrinsic property data. With the resulting stress‐strain compression and tension data, a theoretical model was developed to describe tack as a bulk viscoelastic property of a prepreg laminate stack. Using the viscoelastic analysis, four intrinsic material parameters to characterize prepreg tack could be defined. These were 1) relaxed modulus, 2) unrelaxed modulus, 3) relaxation time, and 4) initial void content of the prepreg stack. Relaxed and unrelaxed moduli of the prepreg stack were independent of temperature, while the relaxation time was highly dependent on temperature and matrix viscosity. In addition, the relaxation time was found to be influenced by resin/fiber content and prepreg surface characteristics, which also influenced the void content of the prepreg stack. Using these measured parameters, good agreement was observed between theory and experimental data for both the stress‐strain curve of the tack test and the simplified compression tack index (CTI*), defined as the ratio of output energy of the prepreg stack during tensile unloading to input energy during compressive loading.
The effects of additives on curing properties, resin contents, and mechanical properties of graphite/epoxy composites
Authors: Shu Wen‐Yung , Lin King‐Fu
Published: December 2004

The effects of additives such as boron trifluride‐monoethylene amine (BF3MEA) and fumed silica in the TGDDM/DDS epoxy formulations on the curing properties, resin contents, and mechanical properties of their graphite/epoxy (Gr/Ep) composites were investigated. The addition of BF3MEA increased the viscosity of resin as well as the resin contents of cured laminates because of its catalytic effect. Although the fumed silica was considered a thickening agent, it also acted like a co‐catalyst with BF3MEA. As the resin content of cured laminates was increased, the excess resin was likely to accumulate in the interlaminar region, which increased the interlaminar shear strength but decreased the flexure strength as well as the interlaminar fracture toughness value, GIC.
Rubber‐filler interaction effects on the solid state dynamic mechanical properties of polyethylene/EPDM/calcium carbonate composites
Authors: Scott C. , Ishida H. , Maurer F. H. J.
Published: December 2004

Composites of polyethylene, ethylene propylene diene rubber (EPDM), and calcium carbonate are milled and analyzed by solid state dynamic mechanical spectroscopy. The torsion pendulum measurements show that the multicomponent composites exhibit complex viscoelastic behavior. In composites of polyethylene and calcium carbonate, the experimentally observed modulus enhancement is greater than that expected from the properties of the constituent materials, assuming well‐dispersed inclusions. In composites of polyethylene, rubber, and calcium carbonate, interactions of the rubber with the filler surface are significant. Specifically, maleic anhydride modification of the EPDM results in rubber‐filler interactions that drastically influence the properties of the composite. The maleic anhydride modification results in a morphology with more rubber around the filler particles and thus an enhanced rubber glass transition peak. The rubber‐filler interaction has been attributed to salt formation at the filler surface. The interaction was also detected by solid state proton nuclear magnetic resonance (NMR) relaxation experiments. Treatment of the filler surface with gamma‐aminopropyltriethoxysilane (γ‐APS) or gamma‐methacryloxypropyltrimethoxysilane (γ‐MPS) has significant influence on the dynamic mechanical properties.
Melt‐spinning of in‐situ composites of a thermotropic liquid crystalline polyester in a miscible matrix of poly(ether ether ketone) and poly(ether imide)
Authors: Crevecoeur G. , Groeninckx G.
Published: December 2004

Blends of a thermotropic liquid crystalline polyester (TLCP) and a thermoplastic matrix of 75 wt% poly(ether ether ketone) and 25 wt% poly(ether imide) were melt‐spun into fibers. The fibers were evaluated in terms of morphology and mechanical properties. Composite fibers containing more than 25 wt% TLCP exhibited a morphology in which the TLCP was dispersed as very long fibrils with good alignment of the molecules in the spinning direction; correspondingly the fibers followed the rule of mixtures behavior for stiffness versus composition. For fibers containing 5 and 10 wt% TLCP, both fibril aspect ratio and molecular orientation were lower, and the stiffness was below the rule of mixtures. This difference can be explained by interfacial tension effects, which are of paramount importance in the deformation of TLCP particles into fibrils.
Fatigue fracture of long fiber reinforced nylon 66
Authors: Wyzgoski M. G. , Novak G. E.
Published: December 2004

The fatigue behavior of long fiber reinforced nylon 66 has been investigated by measuring fatigue crack propagation rates of injection molded samples. Plaques varying in thickness from 3 to 10 mm were employed for nylong 66 containing either glass, carbon or aramid fibers. Both conventional chopped, short fiber reinforcements and pultruded long fiber filled nylon 66 were examined. Long fiber reinforced nylon 66 exhibits improved fatigue resistance as shown by decreases in fatigue crack propagation rates compared to short fiber filled composites. Using a fracture mechanics analysis, it is shown that the improvements are due primarily to the higher moduli of the long fiber reinforced nylon 66, with only a slight increase in the calculated strain energy release rate associated with fatigue crack growth. For short or long glass fibers, and for short carbon fibers, the effects of fiber orientation on fatigue crack growth rates can be predicted from the fracture mechanics model. More significant effects of fiber length on fatigue fracture energies are noted for long aramid and long carbon reinforced nylon 66. It is also shown that thicker plaques can exhibit poorer fatigue fracture behavior owing to their inferior core sections.
Rheology of short fiber filled thermoplastics
Authors: Ghosh Tamal , Grmela Miroslav , Carreau Pierre J.
Published: December 2004

We examine the applicability of the conformation tensor to describe the fiber orientation and rheology of moderately concentrated fiber‐filled thermoplastics subjected to large deformation flow. To retain computational simplicity, we assume a Newtonian matrix. We present a model that can account for orientation effects, Brownian motion, semiflexibility, and interactions through excluded volume effect, of the fibers. The model predicts a wide variety of rheological effects. We present predictions of steady shear viscosity, primary normal stress and the creep functions, as well as uniaxial elongational viscosity, due to the fibers. We have compared rheological data for 9.54 wt% carbon fibers in polyethylene and 30 wt% glass fibers in polypropylene, with the model predictions. By defining an “effective fiber concentration,” we have been able to correlate the model well with data. With fitting parameters from the steady state viscosity vs. shear rate data, we have been able to predict the steady state primary stress coefficient data as well as the creep data.
Application of artificial neural networks for the optimal design of sheet molding compound (SMC) compression molding
Authors: Twu Jun‐Tien , Lee L. James
Published: December 2004

A sequential design optimization scheme based on artificial neural networks (ANN) is proposed. It is a combination of an ANN model and a nonlinear programming algorithm. The proposed scheme is implemented with network training, optimization, and sheet molding compound (SMC) process simulation in a closed loop. A “cyclic coordinate search” technique is employed to initiate the optimization process, to collect training data for the neural network model, and to perform a preliminary design sensitivity analysis. Emphasis is placed on the development of an integrated, automatic optimization‐simulation design tool that does not rely on the designer's experience and interpretation. Testing results based on the design of heating channels in an SMC compression molding tool show that the optimal design can be achieved with fewer data points than other methods, such as factorial design. The efficiency of the ANN method would be greater as the number of design variables grows.
DSC and TBA studies of the curing behavior of two dicy‐containing epoxy resins
Authors: Schneider N. S. , Sprouse J. F. , Hagnauer G. L. , Gillham J. K.
Published: December 2004

The curing behavior of two commercial dicy‐containing resins (I & II), both with recommended cures of 127°C/2 h, has been studied by differential scanning calorimetry (DSC), torsional braid analysis (TBA) and Fourier Transform infrared spectroscopy. Compositional analysis reveals that the two resins differ primarily in the amine/epoxy ratio and the nature of the main epoxy components. Factors contributing to the complex curing behavior observed with II are identified. Isothermal kinetic runs by DSC and TBA lead to estimates for the conversion at the gel point, and to results which suggest that the reactions of epoxy with amine and hydroxyl occur with similar activation energies and similar heats of reaction.
The isothermal crystallization of crosslinked polyethylene under uniaxial extension
Authors: Remec Thomas M. , Gaylord Richard J.
Published: December 2004

An experimental study of the crystallization of chemically crosslinked polyethylene at constant strain under isothermal conditions was carried out. Changes in the stress and birefringence were measured simultaneously as a function of time. Both the stress and the birefringence behavior are consistent with previous work carried out under constant rate of cooling conditions. This indicates that the cooling conditions do not affect the structural features of the crystallization process. A comparison of the stress and birefringence curves shows that there are periods off time during which both stress and birefringence increase; stress increases and birefringence decreases; stress decreases and birefringence increases; and both stress and birefringence decrease. None of the crystal morphological models proposed to date for the strain‐induced crystallization of crosslinked polyethylene appear to be able to account fully for this behavior.
The effect of strain‐induced crystallization on the ultimate properties of an elastomeric polymer network
Authors: Mark James E.
Published: December 2004

Elastomeric networks made up of chain molecules of sufficient structural regularity generally exhibit strain‐induced crystallization. Crystallites thus formed have a pronounced reinforcing effect within the network, and thus increase its ultimate properties (ultimate strength and maximum extensibility), Increase in temperature or addition of diluent (plasticizer) suppresses the strain‐induced crystallization and thus diminishes the ultimate properties. These effects are demonstrated using stress‐strain isotherms obtained in elongation for crystallizable networks of cis‐1, 4‐polybutadiene and of polyisobutylene. The magnitude of the effects of strain‐induced crystallization are determintud by comparisons of the ultimate properties of these two crystallizable networks with the corresponding ultimate properties of noncrysrallizable networks of polydimethylsiloxane.
Factors affecting the formation of hard elastic fibers
Authors: Noether H. D.
Published: December 2004

Factors affecting the formation of hard elastic polypropylene and nylon 6,6 are described. In the case of polypropylene, it is shown that the morphology of the stress spin‐oriented fibers depends on the molecular weight, the molecular weight distribution, and the cooling rate. Narrow molecular weight distribution and/or fast cooling rate can lead to a smectic, essentially fibrillar morphology in contrast to the normally observed crystalline, essentially lamellar structure. Hard elastic nylon 6,6 fibers are produced by drawing regularly spun nylon 6,6 yarn to draw ratios in the range of 1.6‐3 and annealing the resulting fibers in phenol solutions (cone. 1‐5 percent). By this method, a highly increased crystalline order is created, simultaneously transforming the original morphology to a lamellare one or superimposing a lamellar morphology on the poorly organized fibrillar base. Some tensile and elastic characteristics of polypropylene and nylon 6,6 yarns as. functions of spinning and annealing variables are presented.
Monodisperse polyethylenes: Crystallization kinetics
Authors: Hser J.‐C. , Carr S. H.
Published: December 2004

Crystallization kinetics of hydrogenated monodisperse polybutadienes have been measured using hot‐stage microscopy, and the data have been analyzed in terms of crystallization half‐time and Avrami exponent. Results obtained from hydrogenated polybutadienes having M̄w's in the range 5,100 to 340,000 were compared with what was obtained from several commercial polyethylenes. A four‐branch star hydrogenated polybutadiene was also included in this study. Crystallization half‐time at constant undercooling was found to go through a minimum when expressed as a function of M̄w; such behavior is consistent with polyethylene data already reported in the literature. It was found that crystallization half‐times for all polyethylene homopolymers studied (hydrogenated polybutadienes as well as commercial polyethylenes with their broad molecular weight distributions) exhibit similar exponential dependences on undercooling.
On the conformational behavior and solid‐state extrudability of crystalline polymers
Authors: Aharoni S. M. , Sibilia J. P.
Published: December 2004

Extrusion experiments on thirteen polymers in our laboratory and extrusion and forging studies on nine polymers in other laboratories reveal that solid‐state extrusion and malleability occur in semi‐crystalline polymers that have a crystalline relaxation, αc at the temperature Tαc, and do not occur in semicrystalline polymers devoid of αc. The solid‐state extrusion takes place in the temperature range of Tαc ≤ T < Tm with Tm being the melting point. In this temperature, range, the polymeric crystals show a measure of disorder, observed by several techniques and by small heats and entropies of fusion. A survey of the literature indicates that, in general, polymers which have a αc and are solid‐state extrudable have shallow and broad bottoms to the energy‐wells describing their most stable crystalline conformations, and polymers showing no αc have steep‐walled energy‐wells for the same conformations.
Sorption and diffusion of hydrocarbon vapors in glassy polymers
Authors: Barrie James A. , Williams M. J. L. , Munday Keith
Published: December 2004

Sorption isotherms in the region of low relative pressures have been determined at several temperatures for methane, propane, and chlorodifluoromethane in polystyrene and for propane in bisphenol‐A polycarbonate and poly(vinylacetate). The results are well represented by the isotherm equation of Dual Sorption Theory as applied to glassy polymers. The temperature dependence of the isotherm parameters is examined and discussed; the Langmuir component to sorption decreases as the glass transition temperature is approached and measurements with poly(vinylacetate) confirm that this component is absent above the transition. Average diffusion coefficients were obtained from sorption (desorption) rate curves at constant pressure for propane in polystyrene and polycarbonate and a procedure developed for their analysis to yield the diffusion coefficients of the two sorbed species of penetrant. For the polycarbonate there is evidence of mobility in that fraction of the penetrant: population exhibiting Langmuir‐type sorption.
Solvent interactions with polysulfone
Authors: Dangayach K. C. B. , Bonner D. C.
Published: December 2004

We have used gas chromatography to study solvent interactions with polysulfone at temperatures below the glass transition. A previously published procedure has been employed to decompose the Gibbs energy of sorption of various solvents in polysulfone into its component contributions from dispersion forces, polar forces, and forces of specific interactions such as hydrogen bonding. The gas chromatographic results and the analysis of Gibbs energy of sorption has been used to establish general criteria for solubility of nonpolar, polar, and specifically interacting solvents in polysulfone.
Effect of sub‐Tg annealing on CO2 sorption in polycarbonate
Authors: Chan A. H. , Paul D. R.
Published: December 2004

High pressure CO2 sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity term C of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation of C has found support in the good correlation between C and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation of C. The experimental uncertainties in the data compromise a more critical test of the relationship between C and the density of annealed samples.
Gravimetric and volumetric study of the sorption of gases and vapors in poly(vinyl chloride) powders
Authors: Berens A. R.
Published: December 2004

The sorption of a variety of gases and organic vapors in poly(vinyl chloride) (PVC) powders has been studied gravimetrically with a recording microbalance and volumetrically with a gas pycnometer and an automatic surface area analyzer. For nitrogen, carbondioxide, vinyl chloride, methanol, acetone, n‐butane, and benzene at low penetrant activities and temperatures below Tg, sorption isotherms exhibit the downward curvature characteristic of dual‐mode sorption. The solubility of each of these penetrants is lower in heat‐treated PVC samples than in samples recovered from the polymerization without additional heating. It has been possible to estimate the parameters of the dual‐mode sorption model for carbondioxide, vinyl chloride, and methanol. The results indicate that the history‐dependence of gas or vapor solubility is associated only with the “hole‐filling” term of the dual‐mode model; the normal dissolution or Henry's Law term is essentially unaffected by the prior heat treatment of the PVC.
Experimental deep‐channel velocity profiles and operating characteristics for a single‐screw extruder
Authors: Choo K. P. , Neelakantan N. R. , Pittman J. F. T.
Published: December 2004

Data have been obtained on the operation of a deep‐channel single‐screw extruder, pumping a Newtonian liquid under isothermal, developed flow conditions. Flow rate, screw speed, and pressure gradient characteristics were measured, and a tracer particle technique was employed to determine channel velocity profiles. The data were required for the testing and development of a computer model for flow in the extruder, which takes into consideration channel curvature. Results confirm the correctness of the computer solutions previously reported.
The influence of the axial pressure gradient on flow rate for Newtonian liquids in a self wiping, co‐rotating twin screw extruder
Authors: Denson C. D. , Hwang B. K.
Published: December 2004

The isothermal flow of a Newtonian liquid in a co‐rotating twin screw extruder having screw elements with three tips has been analyzed when the effect of the intermeshing zone on flow can be neglected. It was found that values for four dimensionless parameters must be specified in order to obtain a unique relationship between the dimensionless axial pressure gradient and the dimensionless volumetric flow rate. These parameters included the number of screw tips, the helix angle, the ratio of the clearance to the screw radius, and the ratio of the distance between screw centers‐to the screw radius Values for the dimensionless throughput and pressure gradient were computed for a range of helix angles at fixed values for all other dimensionless parameters. Shape factors were also computed and it was found that the shape‐factor for pressure How is substantially less than that for drag flow. Asymptotic values for both these factors at large values of the channel width (large helix angles) were found to be less than unity.
Iodinated polystyrene: An ion‐millable negative resist
Authors: Shiraishi H. , Taniguchi Y. , Horigome S. , Nonogaki S.
Published: December 2004

Iodinated polystyrene (IPS) is obtained by direct iodination of polystyrene and its lithographic characteristics are investigated. The sensitivity of the polymer to electron beams is increased as the result of iodination by a factor of about 10 and reaches 1 μC/cm2. Coated IPS films are very stable and no changes in exposure characteristics are observed even after pre‐baking at 220°C for 10 min. It is found that crosslinking does not proceed in a vacuum after electron beam exposure. The milling rate of IPS under Ar+ bombardment is measured to be 0.25 nm/s. This is lower than that of poly(glycidyl methacrylate‐co‐ethyl acrylate) (0.67 nm/s) and that of permalloy (0.42 nm/s), both obtained under the same conditions. The mechanism of sensitization by iodination is discussed.