bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interpretation of the tensile creep response of an ABS polymer
Authors: Moore R. S. , Gieniewski C. 
Published: December 2004

AbstractTensile creep measurements were carried out on a commercial ABS polymer over a temperature range from 40 to 100°C at stress levels from 0.6 to 1.8 × 108 dynes/cm2. Experiments were conducted in a prototype of an apparatus designed to be compatible with digital acquisition systems. Analysis of the data indicated that application of the time‐temperature super‐position principle was of limited value due to the use of test temperatures near and below the effective glass transition temperature of the acrylonitrile‐styrene component of the polymer. A strong stress dependence of the compliance was observed, even at relatively short times after loading. This was analyzed in terms of a model in which the height of the potential energy barrier to motion of the molecular flow unit is lowered by the application of stress. Analysis of the temperature dependence of the compliance at low stress levels indicated that the effective Tg of the acrylonitrile‐styrene phase is about 85°C. The temperature dependence of the magnitude of the activation energy is considered as is the stress dependence of the glass transition temperature. Implications of short‐time response in creep with regard to response under impact loading are pointed out. Practical application of results to the prediction of dimensional stability of molded parts is discussed as well as the limitations involved in extrapolation of experimental data to long times and high stress levels.
Strength ‐Composition relationships of random short glass fiber ‐thermoplastics composites
Authors: Lee Lieng ‐Huang 
Published: December 2004

AbstractTwelve polymers and copolymers reinforced with random short glass fibers are used for the study of the strength ‐composition relationship. Six of these reinforced systems are new and have not been reported elsewhere. The effect of fiber volume fraction on tensile and flexural strengths is related to the Kelly and Tyson equation. For each composition the strengthening factor, F, is calculated and discussed with respect to the structure of the polymer. One factor pertaining to the actual performance of fiber glass, fiber efficiency, K, has been extrapolated for the fiber glass used for this study. The effects of fibers on toughness and the Izod notched impact strength are discussed. It is the impact strength ratio and not the toughness which is used to describe the net result of reinforcement.The deviations between the wet and the dry strengths are used to illustrate the effect of the fiber ‐matrix interfacial bond. A new parameter, Δθ, is introduced to describe the effect of structure on the fiber ‐matrix interface. The effect of water at the fiber ‐matrix interface is further demonstrated through the determination of dielectric constant and dissipation factor of the composite before and after water immersion. The rule of mixtures was found to apply to dry electrical properties of composites.
Thermodynamic and physical properties of crystals formed from dilute solutions
Authors: Mandelkern L. 
Published: December 2004

AbstractSome of the thermodynamic and physical properties of crystals of linear polyethylene, formed from dilute solution are discussed. These properties include density, enthalpy of fusion, infrared absorption spectrum, selective oxidation and dynamic mechanical measurements. Despite the fact that electron microscopic examination reveals an apparent geometric regularity to these crystals, all these physical measurements yield a consistent interpretation in that they require about 15–20% of the chain units to be in a non‐random conformation, and to form a disordered amorphous overlayer.Detailed studies of the experimentally observed relations between the crystallite thickness, crystallization temperature, and dissolution temperature (melting temperature in a dilute solution) are also presented. A thermodynamic analysis of the dissolution temperature‐size relations, based on independently determined equilibrium solubility temperatures, indicates that the interfacial free‐energy characteristic of the mature crystallites is significantly different from that involved in nucleation. The interfacial structures of the nucleus and the crystallites must, therefore, also be different. Size control by a nucleation process can be demonstrated from very general theoretical considerations. However, the detailed molecular structure characteristic of the nucleus cannot be specified solely from the fact that this process is size controlling.
Flexural fatigue of glass‐reinforced thermoplastics
Authors: Cessna L. C. , Levens J. A. , Thomson J. B. 
Published: December 2004

AbstractThe fatigue failure of thermoplastics and glass‐reinforced thermoplastics is a function of cyclic stress or deflection level, test frequency, viscoelastic polymer parameters and matrix‐to‐fiber stress transfer. This paper reports an investigation of the modes of high frequency fatigue failure in glass‐reinforced and unreinforced thermoplastics. In particular the effects and control of dissipative heating of a working specimen and the role of efficient matrix‐to‐fiber stress transfer are considered. A test procedure with which the severity of dissipative heating can be continuously followed and controlled during an accelerated fatigue test is described.
Brabender viscometry: I. Conversion of brabender curves to instron flow curves
Authors: Lee G. C. N. , Purdon J. R. 
Published: December 2004

AbstractEquations have been derived to convert Brabender flow curves to Instron flow curves for practical application purposes. The technique involved is simple and has been described and discussed in detail. Nine pairs of Brabender and Instron flow curves of three different high polymers, each at three operating temperatures, have been found to fit each other quite well. The converted Brabender flow curves overlap a part of the Instron curves and extend the shear range toward the Newtonian flow region. An important consequence of this work is that the Brabender Plastograph can now be regarded as a formal viscometer while still functioning as a miniature of the Banbury mixers used in industry. More work is being done to take advantage of this consequence.
Post extrusion heat and solvent transfer from polymeric film
Authors: Shih N. C. , Middleman S. 
Published: December 2004

AbstractThe problem of heat and solvent transfer from plasticized film is considered. The transport equations are solved by a numerical method. The formulation of the model includes the temperature dependence of diffusivity, the dependence of diffusivity on decreasing solvent concentration, as solvent leaves the film, and the latent heat of vaporization of the solvent. The Flory‐Huggins theory is used as a model for vaporliquid equilibrium. Heat and mass transfer coefficients are taken either as constants (to simulate extrusion with blowing at the film surface) or from analytical solutions to the appropriate boundary layer equations (to simulate extrusion into a stationary medium.) The boundary layer theory takes into account the effect of rapid vaporization on heat and mass transfer coefficients. Several numerical solutions were obtained for cases corresponding to extrusion of polyvinylacetate, plasticized with acetone, extruded into air.
Rates of molecular vaporization of organic plasticizers
Authors: Wall L. A. , Flynn J. H. , Straus S. 
Published: December 2004

AbstractThe kinetics of the molecular vaporization process of 21 plasticizers were investigated in detail. By both isothermal and nonisothermal kinetic methods, it was evident that 11 were quite pure single compounds, while 10 were clearly mixtures of compounds. For the single component species internal energies for vaporization and rates of volatilization are listed. The internal energies of vaporization are about one‐half or less of values one can estimate from the additive factor method of Small. Thus, solubility parameters based on our experimental values are low by about 30 percent. From this and previous work on linear alkanes, it is concluded that in the molecular vaporization process, the large organic molecules studied evaporate approximately as spheres and hence low values for the energy of vaporization are obtained. Consequently, the difference between our experimental energy and that estimated from solubility parameters is the energy for extending the molecule in a vacuum environment.
Compression, bending, and shear of bonded rubber blocks
Authors: Gent A. N. , Meinecke E. A. 
Published: December 2004

AbstractAn approximate theoretical treatment is given for small compressions of bonded rubber blocks. The component of the compressive force arising from the bonded condition at the loaded surfaces is obtained from a pressure distribution within the block, given by the solution of the corresponding torsion problem. The bending of blocks is treated in a similar way, the pressure distribution in this case being derived from the corresponding bending stress function. The apparent shear of relatively thick blocks is then treated as a combination of shear and bending displacements. The location of an internal rupture and the deformation at which it occurs are also derived from a critical (negative) value of the pressure developed within the block, at which a small cavity increases indefinitely in size. The corresponding critical deformations are calculated for extension and bending displacements. The shear stresses developed at the bonded surfaces under extension, compression or bending displacements are also evaluated.
Flow behavior of concentrated solutions of an SBS block copolymer
Authors: Paul D. R. , St. Lawrence J. E. , Troell J. H. 
Published: December 2004

AbstractThe non‐Newtonian viscosity of concentrated solutions of a styrene‐butadiene‐styrene, SBS, block copolymer was measured with a novel capillary viscometer. Polymer concentrations ranged from 0.165 to 0.306 g/cc. Apparent shear rates ranged from 1 to 105 sec−1. Five different solvents were employed. All of the flow curves can be reduced to a single master curve with the same shape exhibited by monodisperse polystyrenes and the Graessley theory. The shift factor for the shear rate axis, τ0, approximately parallels the Rouse relaxation time, τR, but shows a residual concentration and solvent dependence not predicted by the Rouse form. For different solvents at the same concentration, better solvents show a minimum relative zero shear viscosity, η0/ηs, and a maximum ratio τR/τ0. It is concluded that all solvent effects are not adequately incorporated into the zero shear viscosity for the purposes of constructing master plots; however, the shape of the master plot is not affected by the solvent or the polymer block structure.
Effect of processing history on melt flow defects
Authors: Rudin A. 
Published: December 2004

AbstractThe two main flow defects which appear to originate in the processing machine or die are melt fracture and sharkskin. Both are associated with the elastic nature of the polymer melt. Processing variations that decrease the elastic nature of the melt diminish the severity of the effects of melt fracture. These include increased die length and temperature and shear at temperatures at which polymer segmental mobility is not too high. The sheared, less elastic melt structure may sometimes be stabilized by polymeric additives. A simple model is presented to account for this behavior, which is illustrated with examples of polyethylene and plasticized PVC.
Cause and effect in the weathering of plastics
Authors: Kamal M. R. 
Published: December 2004

AbstractIn most instances, the study of the weatherability of plastics follows empirical schemes that show little correlation with the actual effects of outdoor exposure. A more reliable analysis must be based on a knowledge of the factors in the weather which affect plastic properties and of the modes of interaction between these factors and the plastic material. It is shown that both the factors of the weather and the kinetics of polymer degradation may be expressed in a quantitative manner suitable for analytical treatment. Furthermore, it is shown that the analytical approach yields predictions which are in qualitative agreement with the results of actual outdoor exposure. Finally, some new techniques are proposed for more reliable predictions of long‐term outdoor weatherability on the basis of laboratory studies.
Melt fracture of polystyrene
Authors: Vlachopoulos J. , Lidorikis S. 
Published: December 2004

AbstractThe results of an experimental study of melt fracture using polystyrene samples of narrow and broad molecular weight distribution are presented. The weight average molecular weight (M̄w) ranged from 9.72 × 104 to 1.80 × 106 and the distribution breadth M̄w/M̄η from 1.06 to 9.21. The critical shear stress varies linearly with 1/M̄w, increases slightly with temperature and is independent of the distribution of molecular weights. This type of behavior is satisfactorily explained in terms of Graessley's entanglement theory.
Force requirements in forging of crystalline polymers
Authors: Wissbrun K. F. 
Published: December 2004

AbstractThe forces required to compress billets of crystalline polymers below their melting points were determined and related to the initial billet dimensions and amount of deformation. The studies involved the use of three high‐density polyethylenes and an acetal copolymer. The results were found to obey an equation derived from plasticity theory using, at each temperature and for each material, a single parameter very nearly equal to the yield strength determined in ordinary tensile tests, and having the same temperature dependence. An empirical equation that describes the pressure required to form cups by backward extrusion of metal billets is also successful for the same process with polymers, using the yield parameter from the compression experiments. Cold working causes a high degree of orientation, increased clarity, and greatly increased tensile strength.
Cold forming of plastics part I. Draw forming of thermoplastic sheets
Authors: Li H. L. , Koch P. , Prevorsek D. C. , Oswald H. J. 
Published: December 2004

AbstractAn experimental procedure is outlined to examine the potential of thermoplastic sheets in draw forming. Experiments carried out on a variety of materials indicate that the following requirements must be fulfilled for a thermoplastic sheet to be cold formable: (1) The glass transition of polymer should be above ambient temperature and above the temperature of forming, (2) tensile elongation at break should equal or exceed 30%, (3) ratio of tensile to compressive yield stress should equal or exceed 1.6 and (4) sheet must not yield locally (neck) when strained in tension.An experimental method has been developed to determine the compressive, friction and bending forces which oppose the drawing force exerted by the punch. It is shown that the compressive force is, in most cases, largest. A stress analysis is carried out leading to an expression correlating the maximum depth of draw as a function of basic properties of sheets such as tensile strength (St*) and compressive yield stress (Sc). The effect of rolling on drawability is examined and interpreted in terms of the ratio St*/Sc. The cold formed items have a lower heat distortion temperature than their thermoformed counterparts.
Prediction of high density polyethylene processing behavior from rheological measurements
Authors: Shida M. , Cancio L. V. 
Published: December 2004

AbstractIn order to predict the processing behavior of a high density polyethylene resin one must know the resin flow behavior over a wide range of shear rates. Low shear properties are important in applications where melt strength, sagging, etc. are critical. On the other hand, high shear flow properties are a determining factor in applications where melt instability, melt fracture and heat generation are important. The flow behavior of a resin can be established by measuring the zero shear viscosity, η0, the maximum relaxation time, τ0, and the shape of the flow curve. We have measured these basic rheological parameters on a large number of high density polyethylene resins. A shear sensitivity parameter which is independent of molecular weight was derived from a correlation between η0 and τ0. This parameter, together with η0, provide the vital information needed in order to predict the processing behavior of the resin. This method is applicable to other polymer systems provided that the rheological parameters η0 and τ0 can be experimentally obtained.
Characterization of polyvinyl chloride part I. Molecular weight determinations by gel permeation chromatography
Authors: Chan R. K. S. 
Published: December 2004

AbstractThe universal calibration and universal correction curves for the correction of resolution dispersion and skewing are established for polyvinylchloride (PVC). The effect of solution concentration on skewing is also demonstrated. The application of these curves to the determination of number and weight average molecular weights of PVC samples is illustrated. The results obtained are consistent with those determined by membrane osmometry and light scattering.
A comparison of constant and complex creep loading programs for several thermoplastics
Authors: Benham P. P. , Hutchinson S. J. 
Published: December 2004

AbstractPolymethyl methacrylate, polyacetal and polypropylene samples were subjected to constant‐load uniaxial creep in tension and compression up to 3% strain in times up to 105 sec. A higher creep resistance was obtained in compression compared with tension due to the influence of free volume on mobility. Square wave cyclic creep tests alternately in tension and equal compression for dwell times of 10, 100, 1000 sec were also conducted on each material up to a total time of 105 sec. Under low cyclic creep stresses tension creep cancelled out compression creep in each successive half cycle so that there was no overall increase in creep strain as cycling proceeded. The unidirectional creep data was used successfully to predict this behavior. At higher cyclic stress levels creep strain range increased steadily throughout the test indicating a softening process. A few tests were conducted in unidirectional and cyclic stress relaxation on polymethyl methacrylate.
Transverse properties of undirectional aluminum matrix fibrous composites
Authors: Lin J. M. , Chen P. E. , Dibenedetto A. T. 
Published: December 2004

AbstractThe effects of fiber volume content, fiber‐matrix bonding, heat treatment, and age hardening on the transverse mechanical properties of undirectional aluminum matrix fibrous composites have been investigated. Test results have indicated that the increase of the matrix strength is directly responsible for the increase of the transverse strength of a composite fabricated under heat‐treated conditions, as compared with the corresponding strength for the annealed condition. The composite transverse tensile strength and elastic modulus have been calculated by using the finite‐element method and the von Mises‐Hencky criterion. Both the square and hexagonal arrays have been considered for the fiber configuration in the matrix. The analytical results are compared with the experimental data obtained at room temperature and low strain rate.
A study of polymer melt flow instabilities in extrusion
Authors: Han C. D. , Lamonte R. R. 
Published: December 2004

AbstractAn experimental study is carried out to elucidate the melt fracture mechanism. For the study, the electrical outputs of the melt pressure transducers, mounted on the wall of a circular tube, are recorded on a Sanborn recording system. It has been observed from this study that the wall pressures start to fluctuate prior to the inception of visible melt fracture. The frequency and amplitude of the excursion signals are increased as the shear rate is increased up to and beyond the critical value. This behavior has been observed for three polymer samples tested: polystyrene, high density polyethylene, and low density polyethylene. The fluctuations of wall pressures are interpreted as due to an irregular flow of polymer melts at the tube wall. It is further investigated to find the effects of the die entry angle of a capillary, and capillary length‐to‐diameter ratio on the critical shear rate. A correlation between exit pressure and shear stress has been found for polystyrene and low density polyethylene. It is found that at and above the critical stress, the exist pressure increases abruptly. This is interpreted to be a sudden change in the elastic properties of the materials above melt fracture since Han et al have shown that the exist pressure is a measure of the elastic properties.
Holographic grating formation in photopolymers—Polymethylmethacrylate
Authors: Laming F. P. 
Published: December 2004

AbstractPolymethylmethacrylate has been sensitized to 4880 A light and used as a holographic recording medium. The polymer is sensitized with a material which may itsel be degraded by exposure to ultraviolet light. The new process is, therefore, both self‐developing and fixable without chemical processing. Holographic diffraction gratings written into this material have diffracting efficiencies as high as 70 percent. Various parameters such as angular selectivity, film thickness, variation of diffracting efficiency with writing angle etc., have been studied. The spontaneously produced diffracted intensity is so high that efficient interference between first and zero ordes is observed during the writing process.
Extensional flow of non‐newtonian fluids—A review
Authors: Dealy J. M. 
Published: December 2004

AbstractExtensional flows have been the object of study in several laboratories in recent years. Polymeric systems have been studied in most cases because of their interesting behaviour and also because of the importance of their rheological properties to the plastics engineer. Controlled, steady elongation is more difficult to achieve in the laboratory than the more traditional viscometric flows. Moreover, it is not in general possible to predict the response of a viscoelastic material to steady extension based on knowledge of its viscometric functions.This review begins by presenting some useful expressions describing the kinematics of extensional flows. Then some results of interest from rational mechanics are presented and the behaviour predicted by a number of constitutive equations for viscoelastic fluids are discussed. After presenting the pertinent relations of linear viscoelasticity for extensional flows, experimental methods and results for steady simple extension are reviewed and some possible implications for the processing of molten polymers are discussed.
Strength of short‐fiber reinforced composites
Authors: Lavengood R. E. 
Published: December 2004

AbstractThe structural utility of short, glass fiber‐reinforced epoxy composities is experimentally investigated for fiber volume fractions from 0.15 to 0.5. The strength and stiffness of systems with randomly oriented fibers are compared with those of similar composites with aligned fibers. The ultimate strength of both types of material increses in a reasonably linear fashion with volume fraction up to 0.5. For all volume fractions in this range, strength of the random composites is slightly higher than the longitudinal and much higher than the transverse strength of equivalent compsites with aligned fibers. The modulus of the random system is approximately two‐thirds the longitudinal and twice the transverse modulus of the unidirectional material. The structural utility of the flow molded material is greatest in uniaxial, stiffness critical situations. The greater strength and planar isotropy of the random composites make them preferable in all strength limited or multiaxial applications.