bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improving the crack resistance of bulk molding compounds and sheet molding compounds
Authors: McGarry E. J. , Rowe E. H. , Riew C. K. 
Published: December 2004

AbstractFiber‐reinforced plastics exhibit two types of mechanical failure: gross fracture and microcracking. Gross fracture involves both matrix and fiber failures. Principal resistance to crack propagation derives from partial decoupling of fibers and then stressing, remove finite volumes of them to fracture. Classical concepts of fracture mechanics can be applied to such composites, though modifications of methodology to treat anisotropy and other special effects are required. Microcracking occurs principally in the matrix phase and usually accompanies cyclic fatigue, drop impact, bending, or rapid cooling from molding temperatures. It lowers composite stiffness, environmental resistance and may reduce strength. Matrix resins require high fracture toughness to minimize or eliminate microcracking. This paper discusses cracking in bulk molding compounds and sheet molding compounds, complex materials containing high percentages of glass fibers and calcium carbonate filler. Microcracking can be greatly reduced by tire addition of small amounts of a rubber to the polyester matrix. Various tests such as impact, bending, acoustic emission and crack propagation demonstrate the improved toughness properties which result. No sacrifice of original strength characteristics occurs, and markedly improved resistance to damage has been noted with rubber modified epoxy and polyester matrix resins.
The use of coupling agents to enhance the performance of aramid reinforced composites
Authors: Vaughan D. J. 
Published: December 2004

AbstractIn view of the organic nature of aramid fiber and its ability to be combined with a number of polymer systems, fabric woven from that fiber has previously been used in an unfinished or scoured stale. However, this has resulted in a marked lack of adherence at the fiber‐resin interface that has considerably reduced compressive values in the composite; this is particularly evident when the composite is exposed to adverse aqueous environments. In order to overcome what appears to be the major deficiency in this fiber, a series of coupling agents has been developed which, when used in conjunction with a number of commercial resin systems, shows a marked improvement in interlaminar adhesion. The paper outlines the problem of using untreated fiber and establishes the area of responsibility for initial failure. It then shows how the correct use of coupling agents has overcome the interfacial adhesion problem and has enhanced the performance of aramid fiber reinforced composites.
Studies on multilayer film coextrusion II. Interfacial instability in flat film coextrusion
Authors: Han Chang Dae , Shetty R. 
Published: December 2004

AbstractAn experimental study was carried out to investigate the phenomenon of interfacial instability in multilayer flat‐film coextrusion. For the study, a sheet‐forming die with a feed block was used to coextrude three‐and five‐layer flat films. Polymers coextruded were: (a) low‐density polyethylene with polystyrene, and (b) high‐density polyethylene with polystyrene. It was observed that, for a given polymer system, there is a critical value of wall shear stress at which an irregular (i.e., unstable) interface between the layers sets in, giving rise to a pattern similar to that usually found in a wood panel. Once the instability sets in, the severity of interfacial instability is found to depend on both the total volumetric flow rate (hence wall shear stress) of the combined streams and the ratio of the individual layer thicknesses. An attempt is made to correlate the critical conditions for the onset of interfacial instability in terms of the layer thickness ratio, and the viscosity and elasticity ratios of the two polymers being coextruded.
Studies on multilayer film coextrusion III. The rheology of blown film coextrusion
Authors: Han Chang Dae , Shetty R. 
Published: December 2004

AbstractMultilayer blown film coextrusion was studied, both experimentally and theoretically. For the experimental study, an annular die with a feed‐port system was designed and multilayer blown films were produced by rotating the inner mandrel with a one horsepower variable‐speed drive at speeds from nearly 2 to 6 rpm, and by inflating the tubular molten film with air. The die has 16 feed slots and melt pressure transducers are mounted along the axial direction of the outer wall of the annular flow channel. The transducers were used to determine the pressure gradient in the annular flow channel, which then permitted determination of the reduction in pressure drop when different combinations of two polymer systems were coextruded. Polymers used for b own film coextrusion were: (1) low‐density polyethylene with ethylene‐vinyl acetate; (2) low‐density polyethylene with high‐density polyethylene; (3) low‐density polyethylene with polypropylene; (4) high‐density polyethylene with ethylene‐vinyl acetate. For the theoretical study, stratified helical flow was analyzed using a power‐law non‐Newtonian model. A computational procedure was developed to predict the number of layers, layer thickness, and the volumetric flow rate as functions of certain processing variables (namely, the pressure drop in the die, and the angular speed of rotation of the inner mandrel of the die) and the rheological parameters of the individual polymers concerned. Comparison was made of the theoretical prediction of volumetric flow rate with experimental ones. Some representative results are presented of the theoretically predicted axial and angular velocity distributions, shear stress profiles, and shear rate profiles.
Simultaneous interpenetrating networks based on castor oil polyesters and polystyrene
Authors: Devia‐Manjarres N. , Manson J. A. , Sperling L. H. , Conde A. 
Published: December 2004

AbstractSimultaneous interpenetrating networks (SIN's) have been synthesized by simultaneous polymerization of a rubbery polymer based on castor oil and a second plastic forming monomer plus initiator and crosslinking agent. According to the overall composition and synthetic details, SIN's of elastomeric, leathery, or plastic behavior have been obtained. Polymers employed were the crosslinked polyester from castor oil and sebacyl chloride (a castor oil derivative) and polystyrene crosslinked with 1 percent divinyl benzene, simultaneously polymerized. Electron microscopy revealed a complex two phase morphology strongly depending on the relative gelation times of the two polymers, the polymer gelling first becoming the more continuous phase. Stress‐strain curves show a SIN plastic with a well developed yield point, as well us highly toughened elastomers. Both the plastic and the elastomeric SIN's are tougher than the corresponding homopolymers. Modulus‐temperature curves show a glass transition temperature around −60°C for the elastomer component, and +100°C for the polystyrene in the SIN's.
Weathering of fiber‐reinforced epoxy composites
Authors: Roylance David , Roylance Margaret 
Published: December 2004

AbstractUnless suitably stabilized and coated, fiber‐reinforced composites are subject to photoinitiated oxidation which results in a degradation of the resin surface and an eventual reduction in the composite's mechanical properties. The photo‐oxidation, which is initiated by UV‐absorbing oxidation products created during cure, is relatively amenable to detection by techniques of analytical chemistry. Mechanical test results, which reflect a wide range of material properties, are more subject to variability and misinterpretation.
Twin screw reinforced plastics compounding
Authors: Todd D. B. , Baumann D. K. 
Published: December 2004

AbstractCo‐rotating, self‐wiping twin‐screw equipment has been developed which incorporates fiber glass or fillers into various plastics to form compounds with superior mechanical properties. Fiber glass bundles are folded into the plastic melt in such a fashion that each glass strand is wetted out with minimum breakage of the strand. The intensity of compounding is controlled externally to condition the basic polymer for optimum filler incorporation. The external control permits compounding a wide variety of plastics over a range of throughputs. The degree of mixing can be varied while the machine is in operation. The fiber resin blend passes through an independently controlled extruder for pelletizing with a hot die face cutter. Either air or water quench systems can be used for cooling the pellets. The gentle handling of the fiber resin blend through compounding and extrusion not only minimizes glass breakage, but also minimizes wear on the equipment. Retention of glass fiber length and good strand bonding impart superior properties to the fiber resin product.
Curing and heat transfer in polyurethane reaction molding
Authors: Broyer Ephraim , Macosko Christopher W. , Critchfield Frank E. , Lawler Lee F. 
Published: December 2004

AbstractTemperature measurements were made on the adiabatic polymerization of three urethane systems; two casting formulations, one thermoplastic and the other thermosetting, and a commercial reaction injection molding (RIM) formulation with a 10 second gel time. The data were found to fit a simple nth order overall kinetic expression. These kinetic and heat of reaction results were used to model heat transfer in a 3.8 cm diameter cylinder with an isothermal wall. Experimental temperature profiles for the two casting urethanes were in good agreement with predictions. The kinetic data on the RIM material was used to model temperature profiles1 in 3 and 6 mm thick plaque molds. Experimental measurements of temperature near the mold center agreed with the model. Temperatures measured near the wall were higher due to failure of the isothermal wall assumption.
A method to evaluate the effect of compounding technology on the stress transfer interface in short fiber reinforced thermoplastics
Authors: McNally D. , Freed W. T. , Shaner J. R. , Sell W. 
Published: December 2004

AbstractThe strength and impact resistance of short fiber reinforced thermoplastics are greatly affected by the nature of the stress transfer interface which in turn is influenced by physico‐chemical and geometric factors. The geometric factors are controlled by the compounding technology used to manufacture the composite. This paper describes the use of several compounding technologies and a method used to infer the effectiveness of those technologies from studies of molded part mechanical properties and glass fiber length distributions. Resin systems studied were acetal copolymer, polybutylene terephalate, and nylon 6,6.
Wirecoating die design using finite element methods
Authors: Caswell Bruce , Tanner Roger I. 
Published: December 2004

AbstractThe design of wire‐coating dies is described using finite element numerical analysis as a guide. Finite elements are able to accommodate awkward geometries and non‐Newtonian fluid properties in a realistic manner, and produce streamline and stress patterns within the die. Two basic die geometries are examined and a new design which eliminates recirculation within the die is proposed.
A rigid poly(vinyl chloride) compound with improved combustion characteristics
Authors: Hartitz J. E. , Yount R. A. 
Published: December 2004

AbstractBy means of compounding, we have developed a rigid poly(vinyl chloride) (PVC) formulation with improved overall combustion properties. Newly developed analytical methods indicate a considerable reduction in the level of gases released during combustion, in addition to excellent flammability characteristics and low visible smoke emission levels. The analytical methods discussed are expected to aid in the selection of a feasible protocol for biological testing and in the interpretation of results obtained from such testing. The under‐lying compounding technology is currently restricted to normal impact rigid PVC cube compounds but expected to be expanded into high impact PVC, flexible PVC, PVC powder compounds and cellular PVC.
Draw resonance involving rheological transitions
Authors: Matsumoto Takayoshi , Bogue Donald C. 
Published: December 2004

AbstractThe periodic diameter variations in melt spinning known as draw resonance have been extensively studied, both theoretically and experimentally. The theory has evolved from analyses for isothermal, Newtonian spinning in which the critical draw ratio was found to be 20.21. Compared with this, recent theories have shown that elasticity and cooling are stabilizing (with certain qualifications on the range of variables) and that non‐linear rheological response is destabilizing. The present work presents systematic data on two polymers, one that is always amorphous (polystyrene) and one that solidifies into a semi‐crystalline state (polypropylene). Isothermal and non‐isothermal data are available for the former; non‐isothermal data, for the latter. The melt temperature, the cooling environment, the die length, the spinning length, the mass flow rate and the draw ratio were varied. Certain observations cannot be explained within the existing theoretical framework, specifically the destabilizing effect of certain cooling histories in the case of polystyrene and the destabilizing effect of short dies, presumably a die swell effect, in the case of polypropylene. Very highly oriented polystyrene can be produced under certain conditions when the fiber temperature is held above Tg.
Electropolymerization on graphite fibers
Authors: Subramanian R. V. , Jakubowski James J. 
Published: December 2004

AbstractThe electrodic polymerization on graphite fibers of a variety of monomers having different types of functional groups has been investigated. In addition to vinyl polymerization, some novel polymerizations of cyclic functional groups have been conducted under appropriate polymerization conditions. In many instances, the grafting of the surface polymer to the fiber has been confirmed. The stereochemical configuration of poly(methyl methacrylate) resulting from electropolymerization was measured, but conclusive evidence could not be obtained for the occurrence of stereo‐regulation in electrochemical polymerization on graphite fiber surface; Composite specimens were prepared by the incorporation of the coated fibers in an epoxy matrix. It was demonstrated that the effect of electropolymerization on the interfacial properties of the resulting composite was manifested in variations of the measured interlaminar shear and impact strengths of the composite specimens. The increase or decrease in interlaminar shear was accompanied by the usually observed reverse change in impact strength. In exception to this general trend, it was also indicated that the shear and impact strengths could simultaneously be increased. Implicit in these findings is the contribution of the electrochemically formed interlayer to one or more of the toughening mechanisms that are available to fiber reinforced composites. The potential value of interphase modification by electrochemical polymerization is thus clearly indicated.
Interfacial flow instability in multilayer coextrusion
Authors: Schrenk W. J. , Bradley N. L. , Alfrey T. , Maack H. 
Published: December 2004

AbstractIn coextrusion of multilayer film and sheet, one type of flow instability which can occur is a wavelike distortion of the interface under certain coextrusion conditions. Severe instability can cause intermixing of the layers, particularly in thin skin coextrusion. Observations have shown that the onset of instability is associated with a “critical interfacial shear stress”. This paper describes a mathematical model of non‐Newtonian multilayer flow which was used to correlate experimental observations.
Relative toxicity of the pyrolysis products from some thermoplastic and thermoset polymers
Authors: Kourtides Demetrius A. , Gilwee William J. , Hilado Carlos J. 
Published: December 2004

AbstractRelative toxicity data on the pyrolysis products of a variety of thermoplastic and thermoset polymers are presented. The data are presented in terms of time to incapacitation and time to death with a fixed sample weight of 1.0 g, and in terms of the apparent lethal concentration required to produce 50 percent mortality within a fixed exposure period of 30 min.
Value recovery from polymer wastes by pyrolysis
Authors: Roy M. , Rollin A. L. , Schreiber H. P. 
Published: December 2004

AbstractPyrolysis of polymer wastes appears to be a suitable means of dealing with an increasingly important environmental problem. To provide background on the pyrolytic behavior of wastes, model mixtures of polyethylene and polystyrene have been pyrolyzed in various gas phases including nitrogen and carbon monoxide, at atmospheric and at reduced pressures and at temperatures from about 300–900°C. When the pyrolyzing temperature is attained by gradual heating, and when pyrolysis occurs at pressures in excess of about 200 torr, the process occurs as if each component were present alone—that is, no evidence for component interaction was noted. In these cases, the known mechanisms for pyrolysis of the pure polymers can be applied to the behavior of mixtures. Complicating effects due to interactions between the starting polymers, or among the pyrolysis products, were observed in low pressure pyrolysis (≲20 torr); further, it was shown that the balance of pyrolysis products depends on rates of attaining the pyrolyzing temperature, more rapid rates favoring the production of carbon‐rich solid residues of possible use as carbon blacks. More detailed understanding of pyrolytic processes in polymer mixtures is needed to permit selection of conditions producing the optimum balance of useful products.
Micromechanical analysis of a model for particulate composite materials with composite particles—survey of craze initiation
Authors: Riccò T. , Pavan A. , Danusso F. 
Published: December 2004

AbstractParticulate‐filled materials consisting of a continuous matrix phase and a discontinuous filler phase made up of discrete heterogeneous particles are simulated by an elementary model consisting of a single spherical particle embedded in an infinite matrix, the particle being constituted by a spherical core within a concentric spherical shell. The specific case studied is one in which the particle core and matrix are of the same glassy polymer, and particle shell is a rubbery material. The distributions of six suggested craze initiation factors in the region surrounding the single particle are calculated when the material is subjected to a uniform uniaxial tension at infinity. Results indicate that the critical regions for craze formation are located either at the pole or at the equator of the particle (the polar axis being parallel to the applied tension), depending on the criterion considered and on the relative size of the glassy core in the particle.
Assessment of relative flammability and thermochemical properties of some thermoplastic materials
Authors: Kourtides Demetrius A. , Parker John A. 
Published: December 2004

AbstractThe thermochemical and flammability characteristics of some typical thermoplastic materials currently in use and others being considered for use in aircraft interiors are described. The properties studied included (a) thermal mechanical properties such as glass transition and melt temperature, (b) changes in polymer enthalpy by differential scanning calorimetry, (c) thermogravimetric analysis in an anaerobic and oxidative environment, (d) oxygen index, (e) smoke evolution, (f) relative toxicity of the volatile products of pyrolysis, and (g) selected physical properties. The generic polymers which were evaluated included: acrylonitrile‐butadiene‐styrene, bisphenol A polycarbonate, bisphenol fluorenone carbonate‐dimethylsiloxane block polymer, phenolphthalein‐bisphenol A polycarbonate, phenolphthalein polycarbonate, polyelher sulfone, polyphenylene oxide, polyphenylene sulfide, polyaryl sulfone; chlorinated poly vinyl chloride homopolymer, polyvinyl fluoride, and polyvinylidene fluoride. Processing parameters including molding characteristics of some of the advanced polymers are described. Test results and relative rankings of some of the flam inability, smoke and toxicity properties are presented. Under these test conditions, some of the advanced polymers evaluated were significantly less flammable and toxic or equivalent to polymers in current use. A relationship of the anaerobic char yield of the polymers to their relative flammability properties is shown.
Solid state coextrusion: A new technique for ultradrawing thermoplastics illustrated with high density polyethylene
Authors: Griswold Phillip D. , Zachariades Anagnostis E. , Porte Roger S. 
Published: December 2004

AbstractUltraoriented films of high density polyethylene (HDPE) have been prepared in continuous lengths by a new method, solid state coextrusion, through conical dies of extrusion draw ratios up to 36. Preformed HDPE billets ∽7 cm long and ∽1 cm in diameter of duPont Alathon 7050R, Mw = 59,000, Mn = 19,900, were split longitudinally into halves and then one or more wafers of the same polymer were inserted between the two sheath halves. Thereafter, the whole assembly was extruded through a conical die of 20° included entrance angle in the absence of lubricant and at temperatures substantially below the melting range yielding continuous and transparent films. The physical and mechanical properties of the HDPE films so produced were evaluated and compared with the properties of the same polymer extruded through a slit die. The high melt transition, tensile modulus and transparency confirm the effectiveness of the new method in continuously attaining ultradrawn films.
Heat transfer to a plastic tape traveling over heated rolls
Authors: Brazinsky I. , Davis H. L. 
Published: December 2004

AbstractTemperature was calculated as a function of lateral and axial position within a thin poly(ethylene terephthalate) (PET) tape traveling alternately over a heated roll and through air. The system consists of a pair of rolls which are internally heated and located in an oven. The centers of the rolls are ten inches apart and the tape makes eight wraps around the roll pair. Three sources of heat transfer to the tape are considered: convection and radiation from the heated rolls, convection from the air, and radiation from the hot oven walls. Calculations were carried out for oven wall temperatures of 100 and 1000°C, air temperatures of 100 and 205°C, and roll surface temperatures of 180 and 235°C. The computations generally indicate that after several wraps the temperature of the outside surface of the tape (i.e., the surface that does not contact the rolls) is essentially the same each time the tape leaves the roll. However, this temperature changes us the tape then travels through the adjacent, downstream air space. Although there is a temperature gradient across the tape, the temperature of the inside surface (i.e., the side that contacts the rolls) exhibits behavior similar to that of the outside surface.