bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adhesive properties of star‐shaped block copolymers
Authors: Meyer G. C. , Widmaier J. M. 
Published: December 2004

AbstractStar‐shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene‐b‐isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copolymers.
Thermal load in the processing of thermoplastics
Authors: Ingen Housz Jan F. 
Published: December 2004

AbstractBy manipulation of residence time and temperature distributions along a streamline, a reduced residence time may be formed which is a quantitative measure of the thermal load to which the material being processed is subjected in any part of the process. This method is applied in two examples. In the metering zone of a single screw extruder the highest thermal load is found at 2/3 of the channel height. For a case of pipe cool ing it is shown that a much higher extrusion temperature is possible without increasing the danger of degradation by the addition of an internal cooling system to the conventional sizing method.
Degradation and enhancement of the fatigue behavior of glass/graphite/epoxy hybrid composites after accelerated aging
Authors: Hofer K. E. , Stander M. , Bennett L. C. 
Published: December 2004

AbstractThe tensile fatigue characteristics of graphite/glass/epoxy hybrid composites were investigated before and after exposure to various high humidity environments. Accelerated aging treatments of 98 percent RH and 120°F were applied both continuously for 500 and 1000 h and coupled with a 350°F thermal shock after −67°F low temperature exposure. This latter thermohumidity cycle was applied for 500 h total exposure time. Cyclic loading tests showed that degradation due to the moisture and thermohumidity conditioning treatments was in‐most cases small. Some bereficial behavior of the humidity exposure was also noted. The hybrid fatigue characteristics both before and after exposure were a blend of the nearly flat advanced fiber composite S‐N behavior and the highly curved glass fiber composite S‐N behavior. This was attributed to a mixture of failure modes for the hybrid system.
Morphological and physical property effects for solvent cast films of poly‐2, 5(6) benzimidazole
Authors: Wereta Anthony , Gehatia Matatjahu T. , Wiff Donald R. 
Published: December 2004

AbstractA polybenzimidazole having the structural repeat unit magnified image and designated AB‐PBI was formed into films by casting or precipitating from dilute solutions. Selected films were swollen in a plasticizing medium arid drawn about 2X. All films were dried in a vacuum oven to aid in the removal of residual solvent and moisture. Wide angle X‐ray scattering (WAXS) was used to show the type of ordering found in this material and to indicate the extent of molecular orientation. Neither a glass transition nor a crystalline melting point has been observed for this polymer, A Perkin‐Elmer DSC was used to scan the temperature range from −150 to H‐400°C in search of secondary transitions. The rheovibron proved more sensitive and a transition was located in the vicinity of −60°C. An activation energy‐was determined. The morphology of this polymer is subject to speculation. The ability of the chain to adopt a linear conformation leads to the possibility of a liquid‐crystalline nature in solution. A model based on the data in hand is suggested. Stress‐strain data was used to compare the mechanical properties of films prepared by several methods as well as to demonstrate the effect of orientation on strength.
A study of viscous dissipation in the calendering of power‐law fluids
Authors: Kiparissides C. , Vlachopoulos J. 
Published: December 2004

AbstractA finite difference procedure was used to solve the equation of conservation of energy with the lubrication approximation. The temperature profiles due to viscous dissipation in the gap formed by a pair of equal sized rolls rotating at the same speed exhibit two maxima in the vicinity of the roll surfaces. The maximum temperatures also exhibit two local maxima and a minimum in the direction of flow. The calculated temperature distributions across and along the flow field reveal the possibility of excessive local heating which might be detrimental for certain temperature sensitive materials such as poly(vinyl chloride) and rubbers.
Orientation development and relaxation in injection molding of amorphous polymers
Authors: Dietz Wolfgang , White James L. , Clark Edward S. 
Published: December 2004

AbstractOrientation development in amorphous polymer melts being vitrified in an injection molding process is described. Predictions of orientation development are based on the argument that the stress‐optical laws are valid in the molten stare and birefringence values appropriate to the stress levels at the time of vitrification remain. This theory is compared to birefringence distributions determined in injection molded parts.
Viscosity, modulus, and die swell of glass bead filled polystyrene‐acrylonitrile copolymer
Authors: Agarwal Pawan K. , Bagley Edward B. , Hill Christopher T. 
Published: December 2004

AbstractFlow curves were obtained at 190°C over the shear rate range 0.1 to 100 sec−1 for polystyrene‐acrylonitrile copolymer containing up to 36 percent by volume glass beads, using a capillary extrusion rheometer. The addition of glass beads always increased shear stress and viscosity at a given shear rate, with the increase being more pronounced at low shear rates. The addition of glass beads decreased die swell, which also depended on shear‐stress and capillary length‐to‐radius ratio. At low shear rates a lower limiting value of die swell ratio of about 1.1 was achieved. Values of recoverable shear derived from end correction data by the technique of Philippoff and Gaskins and from die‐swell data by the method of Bagley and Duffey are compared. A fairly good agreement was found for low concentration blends at low shear, However, the values differed by a factor of up to 3 at higher shear stresses. In all cases, recoverable shear was found to increase with shear stress at a fixed filler loading and to decrease with increased filler loading at a fixed shear stress. Values of shear modulus calculated from the recoverable shear measurements decreased rapidly with increasing shear stress.
A study on the dissolution rate of irradiated poly(methyl methacrylate)
Authors: Ouano A. C. 
Published: December 2004

AbstractA detailed study of the factors affecting the dissolution rate of poly(methyl methacrylate), PMMA, showed that the magnitude of the increase in the dissolution rate of irradiated PMMA could not be entirely attributed to the reduction in the molecular weight, MW. The formation of non‐polymeric volatile fragments by radiation exposure, i.e., CO, CO2H2, CH3OH and CH4 causes a large increase in the solvent flux into the polymer matrix, thereby causing a large increase in the dissolution rate of exposed PMMA. The volatilization of these low molecular weight fragments cause an increase in the “excess free volume” (microporosity) of the glassy PMMA. The relative magnitudes of the contribution of the MW reduction and the formation of volatile matter on the increase in the solubility rate of the irradiated polymer were found to depend on the molecular size of the solvent, and also on the enthalpy of mixing.
Effect of long‐term water exposure on properties of carbon and graphite fiber reinforced epoxies
Authors: Mazor Avraham , Broutman Lawrence J. , Eckstein Bernard H. 
Published: December 2004

AbstractThe effects of long term exposure to dry and humid environments on carbon‐epoxy and graphite‐epoxy composites have been studied. Filament wound Naval Ordnance Laboratory rings were fabricated in 1965 and were placed in dry, distilled water and sea water for 11 years. Moisture desorption tests were conducted in order to determine the water content of specimens exposed to the water environments, The effect of the history on moisture absorption characteristics was investigated by re‐exposure of partially and completely dried specimens to two different environments: distilled water at 60°C and 98% relative humidity at 60°C. The weight gain was measured and diffusion coefficients were calculated. Horizontal shear tests and flexural tests were performed on “wet” specimens (current properties) and on partially and completely dried specimens (residual properties). The shear strength of the carbon‐epoxy composites is degraded by the exposure while that of the graphite‐epoxy composite is slightly increased. The composite flexural strengths are not degraded by the exposure. These results are discussed in terms of failure modes.
Block copolymer deformation
Authors: Gaylord Richard J. , Lohse David J. 
Published: December 2004

AbstractThe deformation behavior of block copolymers is examined. Interdomain bridges, loops, cilia and floating chains in spherical, cylindrical and lamellar domain morphologies are considered. In the theoretical model, which is analogous to the “three‐chain” model in classical rubber elasticity theory, interdomain chains are confined between pairs of infinite, parallel impenetrable walls constructed at the surfaces of nearest neighbor domains. The domains are taken as undeformable. The quantities which are calculated are: the Young's modulus; the partial molar elastic free energy of swelling; and the stress‐strain relation for simple extension.
Rheoiogical studies of compaction for polystyrene powder
Authors: Umeya Kaoru , Kara Ryuichi 
Published: December 2004

AbstractPolystyrene powder was compacted in a cylindrical die at constant compaction speed. Compaction was found to be influenced by test temperature, compaction speed and void fraction of the powder bed. The stress reduction behavior of an axial stress σ1 and a radial stress σ2 was observed at constant void fraction after compaction. The stress reduction thus obtained was interpretable by adopting an octahedral normal stress σoct and an octahedral shear stress τoct which were converted from σ1 and σ2. This behavior was attributable to the deformation of polystyrene around contact points and to a sliding mechanism between particles. It was ascertained that the relation between a shear stress τ and a normal stress σ obtained on compaction differed from that obtained in shear by a mechanism involving movement between polystyrene particles.
Applications of differential scanning calorimetry to photocurable polymer systems
Authors: Wight Frederick R. , Hicks George W. 
Published: December 2004

AbstractModification of a standard differential scanning calorimeter to allow irradiation of the sample material with ultraviolet light allows one to follow the course of polymerization of photocurable polymer systems. The rate and heat of polymerization are readily determined by this technique which gives it a number of very useful applications. As a quality control tool, one can use the heat of polymerization to monitor the number of reactive sites present in the prepolymer thus achieving a degree of control on the ultimate properties of the cured film. Similarly, analysis of a cured film will indicate the presence of any uncured material, thus allowing one to adjust curing conditions accordingly. The technique has numerous other applications in the study of photocurable resins, such as evaluation of initiator efficiencies, optimization of curing parameters (initiator concentration, lamp design), and the sensitivity of prepolymers to oxygen and wavelength.
Softening rates for polystyrene under shear conditions
Authors: Sundstrom D. W. , Lo J. R. 
Published: December 2004

AbstractThe processing of thermoplastics often requires conversion of a solid to a viscous fluid under shear conditions. In this study, solid blocks of polystyrene were softened on a hot, moving surface over a range of surface temperatures and velocities. The conservation equations for mass, momentum, and energy were applied to the fluid layer and simplified by an order of magnitude analysis. An integral method of solution was developed which predicted rates of softening that agreed closely with the measured rates.
Equilibrium melting of flexible linear macromolecules
Authors: Wunderlich Bernhard 
Published: December 2004

AbstractThe extensive literature on equilibrium melting of flexible linear macromolecules has been reviewed during the last year. The discussion in this paper is based on experiments on actual, large, extended chain crystals and extrapolations on metastable crystals. A series of 32 complete sets of melting temperatures, heats of fusion, volume changes on fusion, and entropies of fusion have been collected. These data are compared to melting data on rigid macromolecules and small macromolecules. Only a relatively simple model of rotational isomerism is needed to understand the entropy of fusion of flexible linear macromolecules which is 8‐12 J/K/mole of rigid backbone units whenever there is no mobility in the crystal at the time of melting. This is much less information on detailed conformational analysis than is generally assumed to be necessary to interpret melting. Instead, it is of importance to consider for the discussion of melting also the change in packing fraction on fusion, which is high for crystals with planar zig‐zag conformation, and low for helices. Both types of crystals lead to similar packing fractions in the melt. Higher packing fractions, both in the melt and crystal, are found for polyesters, polyamides, and polyoxides. The heats of fusion which make up the third group of melting parameters considered are more connected with molecular size (surface area) and cohesive energy density than mobility, so that larger mobile backbone units and higher cohesive energy densities lead to higher melting temperatures. A further addition to the heat of fusion comes from the presence of high energy rotational isomers in the melt, which again increases the melting temperature. Further refinement of this initial discussion is possible, but all aspects of melting must be taken into account rather than concentrating on single aspects as has been done in the past.
Solidification of poly(ethylene terephthalate) with incomplete crystallization
Authors: Muzzy J. D. , Bright D. G. , Hoyos G. H. 
Published: December 2004

AbstractCooling is a critical step in any crystalline polymer molding or extrusion process. A simulation is proposed which will predict the transient temperature and crystallinity profiles developed when a finite polymeric slab comes in contact with a cooling fluid. A generalized, phenomenological model of the crystallization kinetics of polymers is incorporated to account for the effect of the latent heat of crystallization on the thermal history as well as on the crystalline structure at any point in the slab. The model assumes heterogeneous nucleation and temperature‐dependent radial growth of spherulites. DSC cooling thermograms for the polymer are used to verify the kinetic model for comparing experimental measurements against simulated results. Observed spherulite sizes should also be matched by the simulation. Kinetic data have been obtained for two grades of poly(ethylene terephthalate) which have the same growth rate expression but different nucleation characteristics. Crystallinity of these two polymers decreases rapidly as either quench temperatures or nucleation densities are decreased independently. Calculations have been carried out for 1/16 in. thick sheets of polymer exposed to a cooling medium with a heat transfer coefficient of 100 Btu/hr/ft2/°F. Temperature gradients are also presented. The simulation can be used for optimizing quench conditions in polyester film extrusion.
Effect of molecular weight on high pressure crystallization of linear polyethylene. II. Physical and chemical characterizations of crystallinity and morphology
Authors: Ferguson Raymond C. , Hoehn Harvey H. 
Published: December 2004

AbstractThe high pressure crystallized specimens described in the preceding paper (1) were characterized by X‐ray diffraction, density, and differential scanning calorimetry, Nitric acid etching, followed by gel permeation chromatography and DSC on the residues provided further characterization of the morphology. The crystallinity decreased from 100 to 80 percent with increasing molecular weight, over the rangeMw= 4.9 × 104to 4.6 × 106. The crystallites were predominately in extended chain morphology, but the percent in extended chain form decreased from 98 to 85 percent over the indicated molecular weight range. In all cases, there was a wide, bimodal or multi‐modal, distribution of lamellar thickness. The physical characterization results were consistent with and complementary to the results from electron microscopy. The large differences in crystallinity and gross morphology readily account for observed molecular weight dependent differences in mechanical properties.
Strength of discontinuous reinforced composites: II. Isotropic crystalline polymers
Authors: Kardos J. L. , Piccarolo S. , Halpin J. C. 
Published: December 2004

AbstractCrystalline polymers are heterogeneous materials consisting of two distinct phases. They may therefore be treated as molecular versions of engineering composite materials. This paper summarizes the physical model which, when used in conjunction with composite theory, yields a complete calculational format for stiffness, expansion strain, and yield strength. The important input parameters to the calculation are the mechanical properties of the individual constituent phases (crystalline and amorphous), the crystallite aspect ratios, the volume fraction crystallinity, allowable failure strains for a continuous crystal system, and a measure of stress concentrations and strength reduction caused by the discontinuous nature of the actual crystalline reinforcing phase. An expression for the strength reduction factor is developed and details of the stiffness and yield strength calculations are presented for high density polyethylene (HDPE). Comparison with experiment for HDPE yields excellent agreement well within the necessary design accuracy. Agreement with experiment in the case of low density polyethylene (LDPE) is not as good, but within expectations considering the degree of theory refinement and the poorer morphological data base for LDPE.
The amorphous contribution to the modulus of a semi‐crystalline polymer
Authors: Lohse David J. , Gaylord Richard J. 
Published: December 2004

AbstractThe amorphous contribution to the Young's modulus of a semi‐crystalline polymer is calculated for two morphologies: the spherulite and the stacked lamellae structure. Four types of amorphous chains are considered: bridges (or tie molecules); cilia; loops; and floating, unattached chains. The statistics of a polymer chain between two, infinite, impenetrable, parallel walls are used in the modulus calculation. It is found that for each type of amorphous chain, the Young's modulus is greater in the stacked lamellae structure than in the spherulite. The Young's modulus of a cilium, loop and floating chain all increase with increasing chain contour length while the Young's modulus of a bridge passes through a minimum value. The behavior of the Young's modulus as a function of temperature is analogous. These results are discussed in terms of the relative importance of crystalline lamellar impenetrability and the inherent elastic nature of the amorphous chains, in the Young's modulus behavior.
Preparation of ultradrawn polyethylene by a novel radial‐compression method
Authors: Griswold Phillip D. , Porter Roger S. , Desper C. Richard , Farris R. J. 
Published: December 2004

AbstractHigh density polyethylene has been ultradrawn at 80°C by a novel radial–compression method which involves the gradual buildup of highly‐stretched elastic (spandex) filaments around the circumference of a solid polymer cylinder. The sheath of tightly‐wound filaments generates a high‐radial pressure which forces the polyethylene cylinder to neck down, uniaxially extend, and ultradraw. The physical and mechanical properties of radially‐compressed polyethylene of maximum draw ratio, 40‐45X, were evaluated and compared with the same polymer ultradrawn in other stress fields. In most physical property categories, the radially‐compressed samples are virtually indistinguishable from samples prepared by solid‐state extrusion at higher temperature and pressure. The transparency and the maximum tensile modulus, 62 GPa, further confirm the effectiveness of radial compression in achieving ultradraw. An experimental technique for measuring the radial pressure generated by the winding of the highly‐stretched elastic filament is presented. The upper‐bound pressure in the radial‐compression experiments was less than 100 MPa.
Metal‐containing cured resins based on divalent metal salts of ethylene glycol‐methacrylate‐maleate
Authors: Matsuda Hideaki , Okamoto Takanori 
Published: December 2004

AbstractDivalent metal salts of ethylene glycol‐methacrylate‐maleate in the amorphous state were easily soluble in styrene, methyl methacrylate and ethyl acrylate, to give homogeneous, curable mixtures with high metal content. The viscosities of the mixtures varied depending on the metal present. The mixtures were copolymerized to give metal‐containing cured resins of increased compressive strength and Rockwell hardness. Moreover, heat distortion temperature could be improved by introducing Mg or Ca. Of the cured resins studied, the Mg‐containing resin showed the best physical properties. Resistance of the metal‐containing resins to attack by organic solvents was generally high, whereas greater degradation by aqueous reagents was noted. The thermal behavior of the resins is discussed.
Electrical properties of carbon black filled polyethylene
Authors: Narkis M. , Ram A. , Flashner F. 
Published: December 2004

AbstractResistivity and dielectric constant of polyethylene/carbon black compounds were measured from room temperature to 140°C. Within the polyethylene melting region a PTC/NTC (positive followed by negative temperature coefficients) phenomenon is observed, whose intensity depends on the type of carbon black, its concentration and other parameters. Reproducibility of the PTC phenomenon in polyethylene compounds containing a single type of carbon black is rather low. However, by using mixtures of carbon blacks differing appreciably in their particle size, remarkable reproducibility improvements can be achieved. Several other aspects are also discussed in the present paper covering current‐voltage relationships in these materials, comparison of PTC curves with DSC thermograms upon heating and cooling, and dielectric constant‐temperature relations. The carbon black concentration giving the optimum PTC intensity can be predicted approximately from room temperature data.
Polymer blends containing poly(vinylidene fluoride). Part II: Poly(vinyl esters)
Authors: Bernstein R. E. , Paul D. R. , Barlow J. W. 
Published: December 2004

AbstractBlends of poly(vinylidene fluoride) PVF2, with poly(vinyl acetate), PVAc; with poly(vinyl propionate), PVPr; and with poly(vinyl butyrate), PVBu, were prepared by solution blending. Solutions containing PVF2 with either PVPr or PVBu exhibited phase separation, and it was concluded that neither of these polymers are miscible with PVF2. Phase separation did not occur with solutions containing PVF2 and PVAc. Dried samples of this blend system were subjected to differential thermal analysis, dynamical mechanical testing, and visual observations of their melts. From these results, it was concluded that PVF2 and PVAc are miscible. The detailed results and the structural implications of these observations are discussed.