bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model for polymer fatigue
Authors: Opp D. A. , Skinner D. W. , Wiktorek R. J. 
Published: December 2004

AbstractAttempts to use low‐cycle fatigue techniques derived from the work of Coffin and Manson to predict the fatigue performance of six diverse structural plastics are discussed. Through an analysis of dynamic property and thermal behavior studies of polymer samples in reversed‐tension fatigue, an improved model for the polymer fatigue process has been proposed. Laboratory test data are presented illustrating the relationship between the various models.
The influence of molecular weight distribution on melt viscosity, melt elasticity, processing behavior and properties of polystyrene
Authors: Thomas D. P. , Hagan R. S. 
Published: December 2004

AbstractThe influence of molecular weight and molecular weight distribution on the melt rheological behavior of two polystrenes of approximately the same weight average molecular weight, but of widely different molecular weight distribution, was determined. Then, using a series of capillaries with different length‐to‐diameter ratios in an Instron Capillary Rheometer, the entrance correction methods of E. B. Bagley and the relationships of W. Philippoff and F. H. Gaskins, the recoverable shear strain (SR) in the melt at the capillary wall for these mono‐ and polydisperse polystyrenes was determined. Shear modulus (G) and normal stress (PN) were calculated using the relationships: G = τRC/SR and PN = 2τRC SR, where τRC is the corrected shear stress at the capillary wall. These are compared to values obtained using a Weissenberg Rheogonimeter. These two polystyrenes were also injection molded into an ASTM specimen mold over a wide range of stock temperature, using a 12 OZ. in‐line reciprocating screw injection press, and evaluated for mechanical property values. The effects of the elasticity parameters (SR G & PN) and their magnitude on the rheology, processability and mechanical properties of these polystyrenes are discussed.
Fine structures and fracture processes in plastic/rubber two ‐phase polymer systems. II. Observation of crazing behaviors under the electron microscope
Authors: Matsuo M. 
Published: December 2004

AbstractDetailed crazing behavior in several plastic/rubber twophase polymer systems was studied by means of direct observation of ultrathin sections under the electron microscope by employing osmium tetroxide staining and hardening procedure. Samples used are ABS polymer, high ‐impact polystyrene and several PVC/rubber blends. All of the systems investigated showed evidence of stress ‐crazing when under flexural stress. Relationships between the dispersed rubber particles and the crazing behaviors were studied, and the role of rubber particles in the toughening mechanism of plastics was discussed based on these observations.
Natural and artificial weathering of polyethylene plastics
Authors: Howard J. B. , Gilroy H. M. 
Published: December 2004

AbstractEmpirical test data on low‐density polyethylenes exposed to the elements for very long times are compared with results on samples of the same materials subjected to artificial “weathering” in a modified carbon arc machine.The test results conform to the expression

where ta is hours of accelerated weathering, tn years of natural exposure, and the constants B and k have values of 150 and 2.4, respectively, for the materials and test conditions involved.Earlier results are confirmed in that optimum weather resistance is found to depend on good dispersion of a fine‐particle black. Protection improves with concentration up to the limit of about 5% by weight imposed by degenerative effects on mechanical properties from higher loadings of the fine channel blacks. Dependence of weatherability on molecular weight (melt index) is noted.
Meaning and measurement of crystallinity in polymers: A Review
Authors: Kavesh S. , Schultz J. M. 
Published: December 2004

AbstractA useful concept in polymer science is the degree of crystallinity—the fraction of the polymer that exists in a relatively ordered state. Methods of determination of the degree of crystallinity using density, infrared, thermal, N.M.R. and X‐ray measurements are examined in light of modern notions of the structure of semi‐crystalline polymers.
Measurement of water vapor transmission through polyethylene electrical insulation
Authors: Eichhorn R. M. 
Published: December 2004

AbstractA method is described for measuring the rate of water vapor transmission through thick sections of polyethylene used as insulation on electrical conductors of pure sodium metal. The technique could be generally useful for materials which do not react with sodium, and for cylindrical samples which can be filled with molten sodium in a dry box. For samples with uniform dimensions the results are extremely precise because sensitive electrical measurements are used. Specimens of products in final form can be employed to determine the effects of variations in processing.
Polyvinylchloride melt rheology II—the influence of molecular weight on flow activation energy
Authors: Collins E. A. , Metzger A. P. 
Published: December 2004

AbstractThe flow behaviors of a series of polyvinylchloride (PVC) resins covering a broad range of molecular weight have been examined at several temperatures. It has been shown that the influence of temperature on viscosity depends on the temperature range. That is, the flow activation energy is not constant but can be approximated by two values, one applicable to low temperatures, the other to high temperatures.The flow activation energy based on viscosities at constant shear rate decreases as the molecular weight increases. In contrast, the flow activation energy from viscosities at constant shear stress increases with molecular weight.The fact that the activation energy is dual valued does not seem to be associated with the polymer type. Both emulsion and suspension resins exhibit this behavior. Addition of certain modifiers appears to alter the activation energy at lower temperatures. These observations indicate that the shift in the activation energy in the low temperature range is due to a change in the flow mechanism.
Cold forming of plastics part II. Draw forming of laminates containing crosslinkable core
Authors: Prevorsek D. C. , Koch P. J. , Oswald H. J. , Li H. L. 
Published: December 2004

AbstractThe problems encountered with cold formed thermoplastic material, namely, low heat distortion temperature and stress and solvent crazing, can be overcome by using a laminate consisting of a reinforced thermosetting core sandwiched between two drawable face sheets. This process imposes a restriction on the material by the need for a curing cycle to transform the core into a hard, three dimensional network. To take full advantage of the very fast metal forming technique, the curing should be accomplished outside of the forming apparatus and without external restraint. In order to impart a practical shelf life to the laminate at room temperature, the chemical requirements of the core can only be met with an elevated temperature cure. This in turn places an additional restriction on the face sheets, as they will have to withstand the curing conditions without external constraint and without dimensional changes of the formed part. Finally, the face sheets then have to become an integral part of the formed laminate upon curing of the latter, involving a high adhesive strength between the cured core and the face sheets. The criteria for the selection of the materials for various layers are presented as well as the limitations on the construction of the entire laminate.
Kinetics of thermal oxidation of polyolefins—A review
Authors: Reich L. , Jadrnicek B. R. , Stivala S. S. 
Published: December 2004

AbstractThe kinetics of uncatalyzed autoxidations for polyolefin films, such as atactic and isotactic polypropylene and poly‐(butene‐1) are reviewed in light of recent work. Reaction temperatures generally varied from 100 to 150°C and oxygen concentrations from 5 to 100% by volume. A general reaction scheme is suggested and kinetic expressions subsequently derived therefrom have been satisfactorily applied to account for experimental results. Linear relationships between a maximum rate and concentration of oxygen for both low and high concentrations were obtained.In the case of the catalyzed autoxidations [Co(III) acetylacetonate] the general reaction scheme was modified to take into account the presence of the catalyst. From this modified scheme, various kinetic expressions relating maximum rate and concentrations of oxygen, polymer and the catalyst were derived. First‐order reaction with respect to the concentration of the catalyst was found at low concentrations of the catalyst, and near zero‐order at relatively high catalyst concentrations. A correlation between catalytic activities of metal acetylacetonates [Co(III), Mn(III), Cr(III), Fe(III) and Cu(II)] and the oxidation‐reduction potentials has been established.Experimental dependencies of maximum carbonyl formation rates as a function of polymer concentration were found to agree well with the theoretical both for catalyzed and uncatalyzed oxidations.
Gas separation with porous anisotropic polymer films
Authors: Bradley D. F. , Baker R. W. 
Published: December 2004

AbstractThe utility of anisotropic ultrafiltration membranes in gas separation has been examined. These membranes consist of a thin (0.2‐2μ) barrier layer supported upon a more porous supporting substructure. Gases permeate these membranes by a Knudsen diffusion mechanism. Permeabilities from 0.1 to 0.4 cm sec−1 cm Hg−1 were obtained. These values are 104 to 105 higher than most conventional gas separation membranes. These membranes may be useful in several gas separation processes.
The influence of molecular weight on the melt rheology of polypropylene
Authors: Thomas Douglas P. 
Published: December 2004

AbstractMelt viscosity and melt elasticity data were obtained over a broad range of temperatures and shear rates on a series of four polypropylenes of different molecular weight but approximately the same molecular weight distribution. The superposition technique was used with both temperature and molecular weight to shift flow curves for all four materials at three temperatures each along the shear rate axis to generate a master flow curve at a given temperature and molecular weight. For polypropylenes of this type, and molecular weight distribution shift, factors which can be used to extend the useful range of experimentally obtained flow data were determined. The dependency of apparent viscosity on weight average molecular weight at shear stresses as high as 106 dynes/cm2 is shown. The dependency of melt elasticity on molecular weight and temperature is discussed.
Internal pressure behavior of polymers above and below the glass temperature
Authors: Bagley E. B. , Scigliano J. M. 
Published: December 2004

AbstractIt has been well established in the literature that the internal pressure, Pi = (∂E/∂V)T, of a polymer in the glassy state is about half the value expected from the behavior of the polymer just above the glass temperature, Tg. Consideration of this behavior in terms of a recent analysis of factors affecting internal pressures leads to the conclusion that the expression for the total energy of a glass must include a volume‐dependent stored energy term, a term not present above Tg. This stored energy could be associated with actual bond and segment deformations in the glassy state. Brittleness and solvent cracking behavior of glasses will be strongly dependent on this stored elastic energy which can be modified by altering the molding conditions under which the glass is formed.
Weatheirng study of glass‐fiber reinforced polyester sheets by scanning electron microscopy
Authors: Blaga A. 
Published: December 2004

AbstractEvidence is presented of the main steps in the physical breakdown of glass‐fiber reinforced polyester (GRP) composites on outdoor weathering. The chronological sequence is fiber ridging, rupture of the resin layer covering ridging fibers or fibers running close to the surface, spalling of the resin at the site of failure and subsequent erosion, fiber prominence and formation of a network of microcracks. Breakdown is believed to be caused by a type of stress fatigue imposed on the composite by cyclic variation of humidity and temperature in conjunction with solar radiation, and by the action of water and oxygen. The under side of the exposed GRP sheeting shows only incipient breakdown, indicating that solar radiation is an important factor. Countermeasures suggested to reduce breakdown include techniques to keep fibers away from the surface, use of resins with better thermal and moisture characteristics, and use of resin formulations with the best light stability.
Converging flow of polymer melts in extrusion dies
Authors: Cogswell F. N. 
Published: December 2004

AbstractPractical extrusion processes often involve geometrically complex dies. Such dies are usually tapered, or streamlined, to achieve maximum output rate under conditions of laminar flow. These converging flows may be analysed in terms of their extensional and simple shear components to calculate the relationships between volume flow rate, pressure drop, and post extrusion swelling. The analysis can also be extended to cover the free convergence as fluid flows from a reservior into a die. Comparisons between predicted and observed data for a series of coni‐cylindrical dies suggest that using this approach the pressure drop/flow rate relationship can be predicted within ±20% and the swell ratio/flow rate relationship within ±10%. Similar treatments have been in use for the last three years in solving such complex flow problems as radial flow in injection moulding and two‐dimensional annular convergence in blow moulding dies.
Acrylic resin reinforcement of reconstituted collagen films
Authors: Chapman E. W. , Rodriguez F. 
Published: December 2004

AbstractThe protein collagen is a major constituent of mammalian tissue. Treatment of calfskin with an enzyme under acid conditions simultaneously solubilizes much of the collagen and removes non‐helical telopeptides which are believed to contribute to immune response. Then, the solid collagen can be reconstituted by precipitating the solubilized material with weak alkali. Films from the enzyme‐treated, acid‐soluble collagen are strengthened by cross‐linking with glutaraldehyde. Composite films are made by coprecipitating collagen (from a solution) with an acrylic resin (from a latex). In one example, an acrylic resin to collagen ratio of 1:3 gives a wet‐tensile strength about 30 percent higher than that for collagen alone. The tensile strength range of these wetted films (20 to 30 megapascals) is typical of the upper range for such limp films as polyethylene. On the other hand, ‘bone‐dry’ collagen has a higher strength similar to that of glassy polymers such as polystyrene.
Vibrational analysis of functionalized polyolefins/poly(vinylchloride) blends
Authors: Benedetti Enzo , D'Alessio Aldo , Aglietto Mauro , Ruggeri Giacomo , Vergamini Piergiorgio , Ciardelli Francesco 
Published: December 2004

AbstractPolyolefins functionalized with diethylmaleate were mixed with poly(vinylchloride) (PVC) in different compositions. Intermolecular interactions involving the carbonyl groups of the side chains of the functionalized polyolefins and methine hydrogens of PVC were investigated by means of infrared spectroscopy. The major flexibility of the ester groups attached to the backbone chains, with respect to polyesters, seems to increase the capability of such groups to interact with groups of more polar polymers, thus allowing prediction of easier miscibility, which however also depends on the starting polyolefin structure and function‐alization degree.
Morphology and mechanical properties of amine‐terminated butadiene‐acrylonitrile/epoxy blends
Authors: Butta E. , Levita G. , Marchetti A. , Lazzeri A. 
Published: December 2004

AbstractMorphology and mechanical properties of (amine terminated butadiene acrylonitrile rubber/diglycidyl ether of bis‐phenol‐A epoxy resin) blends of different compositions, cured in wide range of temperatures, are described. Curing at low temperature promoted formation of homogeneous materials with poor fracture resistance. On the contrary, at high temperature tough heterogeneous blends were obtained. Such blends showed phase inversion above 20 percent of rubber. The volume fraction of precipitated phase, determined on SEM micrographs, was higher than the amount of added rubber. A fracture mechanism to account for this is proposed. Extensive voiding and interface damage were observed in the low temperature cured materials. Such phenomena did not contribute to the fracture energy.
A structure‐oriented computer simulation of the injection molding of viscoelastic crystalline polymers part I: Model with fountain flow, packing, solidification
Authors: Lafleur P. G. , Kamal M. R. 
Published: December 2004

AbstractA realistic simulation of the injection molding process should be capable of describing moldability parameters, such as pressure drop in the delivery system and cavity and melt‐front progression during cavity filling, as well as predicting the characteristics of the final product, such as residual stresses and crystallinity distributions. After a brief review of the existing models for the mathematical modeling of the injection molding process, a new model, that meets the above requirements, is proposed.
New polyisobutylene‐based model elastomeric ionomers: RheoLogical behavior
Authors: Bagrodia S. , Wilkes G. L. , Kennedy J. P. 
Published: December 2004

AbstractThe rheological behavior of sulfonated polyisobutylene based elastomeric ionomers has been studied. The effects of molecular architecture, type of cation, and addition of excess neutralization agent were investigated. The effect of temperature was studied to a limited extent. In a specific case, the influence of an ionic plasticizer, zinc stearate was also examined. It was found that in these telechelic ionomers where the ionic groups are located exclusively at the chain ends, significant Ionic interactions may persist even at 180°C. The zinc‐neutralized ionomers had the lowest viscosity as compared to the corresponding potassium‐ or calcium‐neutralized ionomers. The covalent character of zinc is believed responsible for this behavior. Other factors being constant, the triarm based ionomers are more viscous than the monofunctional ionomers. A mixture of monofunctional ionomers with the triarm, species is a model for dangling chain ends, and results in a slight lowering of the viscosity under the conditions studied. Zinc stearate acts as an ionic plasticizer. Upon the addition of 15 percent by weight of zinc‐stearate to the ionomer, the low shear rate viscosity drops by several orders of magnitude and renders the ionomer thermally processable at moderate temperatures.
Polyethylene toughened by rigid inorganic particles
Authors: Fu Qiang , Wang Guiheng 
Published: December 2004

AbstractHigh density polyethylene (HDPE) is toughened by particles of rigid inorganic filler CaCO3, which is treated with phosphate. The stress‐strain curve of the HDPE/modified‐CaCO3 (80/20) composite covers a greater area than that of HDPE, and the impact strength of HDPE is greatly improved by modified CaCO3 from 230 J/m to 580 J/m as CaCO3 content is increased to 50 wt%. Morphological observation indicates a finer dispersion of the modified‐CaCO3 particles and a large plastic deformation of HDPE. The cavitation and stress field interaction around the particles are considered to explain the toughening mechanism.
Finite element modeling of ultra fine particle filtration by a membrane filter
Authors: Seo Yongsok , Kim Kwang Ung 
Published: December 2004

AbstractTheoretical work has been carried out to investigate the filtration of ultra fine aerosol particles in a membrane filter. The analysis was done using a finite element method with a Newtonian fluid model for the carrier medium. Both inertial filtration and diffusional filtration were considered. Prior to the main analysis, our numerical scheme was tested with the analytical results for the diffusion of particles in the cylinder and showed good agreement, which confirms the importance of axial diffusion occurring in a short cylinder like a very thin membrane filter. Particle size, porosity, pressure drop, and flow velocity are found to be main variables that determine the filter efficiency. Two important mechanisms of filtration have opposite effects on the efficiency, depending on the variables. Increases in particle size, pressure drop, and flow velocity cause increases in the efficiency for intertial deposition, while decreases in those variables cause increases in the diffusional efficiency. The existence of a minimum value of total filtration efficiency (sum of inertial efficiency and diffusional efficiency) was indicated for intermediate values of the variables. Lower porosity is found to favor inertial deposition more than diffusion. Some other effects of filtration conditions on the total efficiency are also discussed.
Study of polymer gelation by fluorescence spectroscopy
Authors: Berghmans M. , Govaers S. , Berghmans H. , De Schryver F. C. 
Published: December 2004

AbstractA fluorescence technique is used to study the mechanism and dynamics of thermoreversible gel formation in concentrated polymer solutions. Two examples of these ordered structures were studied: isotactic polystyrene (iPS) in decalin and syndiotactic poly(methyl methacrylate) (sPMMA) in toluene. iPS can form two types of gels in decalin solutions. Turbid suspensions are formed between 60°C and 130°C. When the solution is quenched beneath 20°C, transparent gels are formed. In the former solution the polymer has a 31 helix structure; in the latter a 121 helix is formed. These structures formed by iPS in decalin solution have different fluorescence spectra. The ratio (Im/Ie) of the intensity of the monomer fluorescence band in the spectrum over the intensity of the excimer emission band is higher in the spectra of transparent gels. The formation of the transparent gels from a solution can be followed by plotting Im/Ie as a function of temperature. The kinetics of the gel formation are studied by following Im/Ie as a function of time at a fixed temperature. sPMMA forms gels in toluene by a mechanism called “conformational gelation.” This mechanism consists of two steps: a fast conformational change followed by a slower aggregation of polymer chains. Both steps were followed by measuring fluorescence of a pyrene label attached to the polymer. The fluorescence lifetime of this probe is sensitive to the polarity of the environment. When the polymer conformation goes from a random coil to an all trans conformation, the environment of the fluorescent label becomes increasingly richer in solvent. This change in polarity is reflected in a change in fluorescence lifetime. The change in fluorescence anisotropy of the label reflects the second step of the mechanism and correlates with the occurrence of chain aggregation.