bluuebunny/crossref_metadata_2025_split huggingface dataset:
Residual stresses in polymers I: The effect of thermal history
Authors: Siegmann A. , Buchman A. , Kenig S. 
Published: December 2004

AbstractThe distribution of residual stresses in quenched modified poly(phenylene oxide) (PPO) specimens was investigated. Quenching was carried out from temperature level above Tg to various temperatures below Tg. As expected, compressive stresses were measured at the surface layers while tensile stresses were in the inner layers. The ratio between the tensile and compressive stresses varied, depending on the thermal history. The level of residual surface stresses was found to depend on both the total temperature difference during cooling and the initial specimen temperature. At constant initial temperature the surface stresses are proportional to the total temperature difference, whereas, at constant final temperature the surface stresses are inversely proportional to the total temperature difference. An empirical correlation describing the surface stresses as a function of thermal history has been suggested. The differences between present theories and experimental data are discussed. emphasizing the apparent discrepancy regarding the influence of initial temperature above Tg on the level of residual stresses.
Miscibility phenomena in polyester/chlorinated polymer blends
Authors: Prud'homme Robert E. 
Published: December 2004

AbstractPoly(caprolactone) (PCL)/poly(vinyl chloride) (PVC) blends are known to be miscible in the solid state. Recents measurements however indicate that a large number of polyesters are also miscible with PVC if the ratio CH2/CO of the polyester is between 4 and 10. At low CH2/CO ratios, polyesters are too rigid to interact specifically with PVC. At high CH2/CO ratios, the number of interacting groups becomes too small to give miscibility. Similarly, a large number of chlorinated polymers are shown to be miscible with PCL if their chlorine content is high enough. Surprisingly, polyesters are not in general miscible with chlorinated polymers if the mixture does not contain either PCL or PVC. The results presented in this paper suggest that a dipole‐dipole interaction, between the carbonyl groups and the C‐Cl groups, is responsible for the miscibility phenomena observed in polyester/chlorinated polymer blends.
Melt rheology of polymer blends
Authors: Utracki L. A. , Kanial M. R. 
Published: December 2004

AbstractThe rheological behavior of polymer blends is compared with that reported for emulsions, block polymers and homologous polymer blends. It has been shown that the properties of polymer alloys frequently differ from those of these “model” systems—the principal difference being the lowering of at least one rheological function below the value predicted In the log‐additivity rule. Primarily, the most recent (post 1977) results are reviewed. The data obtained by the authors on the flow of poly(ethylene terephthalate)/Polyamide‐6,6 are discussed in detail.
Model of steady‐state melt spinning at intermediate take‐up speeds
Authors: George Henry H. 
Published: December 2004

AbstractA model of melt spinning has been developed for speeds above which the effects of gravity, inertia, and aerodynamic drag become significant. The model has as an upper bound the speed at which stress crystallization begins to occur on the spin line. For poly(ethylene terephthalate), these velocities are approximately 750 and 3500 meters/minute. The calculated temperature and velocity profiles are shown to agree with measured values. The stress at the freeze point is calculated and found to correlate well with the spun yarn birefringence which, in turn, is shown to predict uniquely the spun yarn physical properties on a “simple” spin line. The stress‐optical coefficient derived from the calculated stress at the freeze point and measured birefringence agrees well with the literature.
Large deformation behavior of some thermoplastics
Authors: Mittal R. K. , Singh I. P. 
Published: December 2004

AbstractIn this experimental study the deformation behavior of two thermoplastics under uniaxial and biaxial loadings has been investigated. The experiments were conducted on thin walled tubular specimens of nylon‐6, a semicrystalline polymer, and polymethyimethacrylate (PMMA),:an amorphous polymer. These specimens were subjected to tension, torsion and combined tension‐torsion loadings until very large deformations were produced or specimen failure took place. The results are presented in the form of generalized stress‐generalized strain curves which are applicable to all types of loadings, provided the generalized stress is monotonically increasing. In addition, the results show that the generalized stress‐generalized strain relationship for nylon‐6 is parabolic in nature, whereas that for PMM A can be represented by a bilinear curve. This characterization of the response of the thermoplastics under a biaxial stress field can be used to obtain a more realistic stress interaction between fiber and matrix in composite materials, since until now all theoretical studies on this aspect have assumed an elastic or elastic‐perfectly plastic behavior of the matrix.
Melt rheology of high impact polystyrenes at high shear stresses
Authors: Santamaría Antón , Guzmán Gonzalo M. 
Published: December 2004

AbstractA study of the theological properties of commercial polystyrenes, (PS), and high impact polystyrenes (HIPS), is made in the range of shear stresses of practical interest in industrial polymer processing.A general viscosity‐shear rate‐temperature relationship is defined for these products, with a power law exponent of n = 0.3 and an activation energy of 27 Kcal/mol.The fluid elasticity is studied in terms of steady state shear compliance. An expression relating shear compliance, viscosity and molecular weight distribution is obtained for HIPS. As in other two‐phase systems, a decrease in elasticity with viscosity is observed.
Rheology of polymer blends: Simultaneous slippage and entrance pressure loss in the ethylene‐propylene‐diene (EPDM)/viton system
Authors: Kanu R. C. , Shaw M. T. 
Published: December 2004

AbstractBecause the exact nature of the mechanism governing the marked viscosity reduction in the highly incompatible EPDM/“Viton” fluoroelastomer system is not fully understood, a study was undertaken to shed more light on the phenomenon. Interracial. Slippage in the blend has been suggested as the mechanism by which a substantial reduction in the melt viscosities of either component takes place upon addition of a small amount of the other, In the present investigation, a Mooney slip analysis demonstrated wall slippage in the EPDM/Viton system over the shear stress range of 40 kPa to 160 kPa. The capillary surface was examined for evidence of coating by the minor component of the blend (Viton), and 9‐fold enrichment was found by elemental analysis. However, on no occasion was pure Viton found. In other experiments, the dynamic linear viscoelastic properties and the transient squeezing flow response of the blend were found to be no different from those of the neat elastomer. In addition, the slip velocity in a capillary (and consequently, the viscosity‐lowering effect) was reduced by a factor of 2 to 3 in capillaries with a 90° included entrance angle. It is postulated that the reduction in the flow resistance for the blend is unique to the sharp‐entry capillary geometry and results from removal of Viton from the melt in the recirculating flow at the entrance. This material then feeds along the capillary wall, disrupting the already tenuous adhesion of the elastomer to the metal surface.
Analytical melting model for extrusion: Melting rate of fully compacted solid polymers
Authors: Mount E. M. , Watson J. G. , Chung C. I. 
Published: December 2004

AbstractThe melting mechanism inside screw extruders is presently analyzed using numerical, iterative methods that are too complex to be used widely by practicing engineers. Our theoretical and experimental investigations of the melting mechanism have produced simple, analytical equations for predicting the melting rate of fully compacted solid polymers without iterative calculations. The accuracy of these equations was found to be satisfactory. Consideration of the temperature and shear dependencies of the melt viscosity was found to be essential for the accurate prediction of the melting rate.
Estimation of the effective permeability of thin surface layers created by exposure of polyethylene to fluorine
Authors: Koros W. J. , Stannett V. T. , Hopfenberg H. B. 
Published: December 2004

AbstractThe significantly improved barrier properties of polyethylene, that, result from surface treatment with small amounts of fluorine are explained in terms of the reduced permeability of a thin layer produced by such treatments. Several approaches for correlating the permeabilities of the treated and untreated polymer layers to various penetrants are discussed. An analysis is also presented that permits estimation of the treatment depth corresponding to a given loss rate is related explicitly to the relative permeabilities of the penetrant in the treated and untreated polymer regions.
Carbon fiber‐reinforced composites: Effect of fiber surface on polymer properties
Authors: Ko Yoon Suk , Forsman William C. , Dziemianowicz Theodore S. 
Published: December 2004

AbstractDynamic mechanical measurements in a torsional (shear) mode have been used to characterize an unfilled epoxy (Epon 828/m‐phenylene diamine) and A series of uniaxial graphite fiber (Hercules types A and HM) composites. In unfilled resins containing an excess of the epoxy component, Mc—the average molecular weight between crosslinks—decreases with increasing temperature and duration of cure, suggesting a temperature‐dependent side reaction. In fiber‐reinforced composites, the dynamic mechanical response is sensitive to fiber type and curing schedule; elevation of Tg by as much as 45°C has been observed. Comparison of the dynamic data with properties predicted by micromechanical models shows only a fair agreement at room temperature, which rapidly worsens at higher temperatures. Surface treatment of type A fibers gives enhanced interlaminar shear strength (ILSS), both at ambient conditions and after hydrothermal aging. Dynamic data for surface‐treated systems during hydrothermal aging show a sharper drop in G′ and increase in tan δ. The dynamic data and ILSS results are interpreted in terms of a balance of polymer‐fiber interactions, a weak but widespread preferential adsorption of epoxy oligomers on the graphite basal planes at the fiber surface, and a low concentration of covalent bonds between polymer and fiber‐surface‐functional groups.
Computational scheme for the calculation of molecular weight distributions for nylon 6 polymerization in homogeneous, continuous‐flow stirred‐tank reactors with continuous removal of water
Authors: Ramagopal A. , Kumar Anil , Gupta Santosh K. 
Published: December 2004

AbstractAn efficient computational scheme has been established for obtaining the molecular‐weight distributions (MWDs) for Nylon 6 polymerization in homogeneous, continuous‐flow stirred‐tank reactors (HCSTRs) with water vaporization. A three‐step procedure is used: the moment equations are solved by a sequential application of Brown's algorithm, the moments so calculated are used to give an empirical Flory‐Schultz distribution and, finally, this empirical distribution is used as a starting guess in Brown's algorithm applied to species mass‐balance equations to give the exact MWD. The moment‐closure approximations normally used for hutch reactors have been found to work equally well with HCSTRs for residence times of industrial significance.
Effect of sub‐Tg relaxations on the gas transport properties of polyesters
Authors: Light R. R. , Seymour R. W. 
Published: December 2004

AbstractThe relationship was determined between sub‐Tg molecular motions and the transport of O2 and CO2 in amorphous polyesters and copolyesters based on poly(ethylene terephthalate) [PET] and poly(1,4‐cyclohexylenedimethylene terephthalate) [PCDT], Modifications of the polyester with certain acid co‐monomers restricted the molecular motions that occurred in the β‐relaxation region and in turn decreased the O2 diffusion coefficient. The solubility coefficient was unchanged by those modifications. Modification of PET with 1,4‐cyclohex‐anedimethanol increased the magnitude of the β‐relaxation and both the diffusion and solubility coefficients of O2. Similar relationships between the β‐relaxation magnitude and CO2 permeability were also found. The temperature dependence of O2 permeability followed an Arrhenius relationship, with different activation energies (Ep) above and below the β‐relaxation. The activation energy was smaller below the β‐relaxation. Values of Ep above and below the β‐relaxation did not depend on the chemical structure of the polymer.
The effect of temperature and humidity on the long‐term performance of poly(butylene terephthalate) compounds
Authors: Borman W. F. H. 
Published: December 2004

AbstractA model was developed that closely fits new and previously published test data for the aging of poly(1,4‐butylene terephthalate) (PBT) compounds under conditions of elevated temperature and high relative humidity. The model equation, stated in terms of absolute temperature and water vapor partial pressure, allows extrapolation of accelerated aging data to ambient conditions that prevail in realistic applications of the materials. For practical reasons, the water vapor partial pressure is preferred as a model variable over relative humidity, although it is shown that both variables are equivalent in a formal sense.
Observation of molecular chain scission during crazing of polystyrene
Authors: Popli R. , Roylance D. 
Published: December 2004

AbstractA series of gel permeation chromatographic (GPC) separations has been performed on polystyrene specimens in an attempt to discern whether or not mechanical crazing is accompanied by significant covalent bond scission. It was found that the extent of scission is not large but is indeed present in concentrations that are detectable by GPC. This suggests that molecular‐slippage‐only models of the crazing process are perhaps overly idealized and that crazing cannot take place in highly entangled polymer solids without some bond rupture.
Economics of polymer blends
Authors: Utracki L. A. 
Published: December 2004

AbstractEconomic, technological, and regulatory pressures gradually narrow the chemical variety of polymers: in 1975, the market share of polyethylene was 40 percent, poly(vinyl chloride), 23 percent, polystyrene, 12 percent, and polypropylene, 11 percent, adding up to 86 percent of all thermoplastics (1‐3). The same pressures compel the plastics processor to diversify formulations and production methods. He must resort to new materials (e.g., polymer blends, polymer alloys, and composites) and new methods of manufacture. In this work, the economics of blending will be discussed.There are five reasons to employ polymer blends:

higher performance at a reasonable price,
modification of performance as a market develops,
extending the performance of expensive resins,
re‐use of plastics scrap,
generation of a unique material as far as its processabilitv and/or performance are concerned.
In Canada, the cost of blending varies from 8 to about 20 ¢/lb, depending primarily on the volume and the kind of material. The cost effectiveness depends on the total technical and economic environment in which the manufacturer operates; it has to be computed for each case separately. In the text, guidelines and examples are provided.
Finite element analysis of wire coating
Authors: Mitsoulis E. 
Published: December 2004

AbstractA general‐purpose finite element program has been used to simulate the flow of polymers through wire‐coating dies. The analysis includes Newtonian and power‐law fluids. The effect of normal stresses was examined through a simple viscoelastic constitutive equation, Nonisothermal wire coating was studied to obtain the temperature field within the melt. The effect of a slip condition at the solid boundaries was also examined. The determination of the coating melt free surface was carried out through an iterative procedure. The finite element solution provides details about the existence and extent of recirculation regions, about hot spots due to viscous dissipation, and also captures the stress singularities present at the impact of the melt with the wire and at the exit from the die. Pressure distribution, maximum temperature rise, haul‐off wire tension, maximum wire tension, and stresses at the wire surface and die wall are also presented.
A study of the dynamics of foam growth: Simplified analysis and experimental results for bulk density in structural foam molding
Authors: Amon Moris , Denson Costel D. 
Published: December 2004

AbstractA cell model describing the diffusion‐induced growth of closely spaced single bubbles developed in an earlier publication is now used as the microscopic building block of an analysis of low‐pressure structural foam molding. Heat transfer, solidification, and bulk flow of the foam in the mold cavity are included in this macroscopic analysis. An experimental method is described whereby the bulk density of an expanding thermoplastic polymeric foam is measured as a function of time when the expanding foam is prepared by the short shot injection molding process. Instantaneous and final bulk foam density data obtained for various values of the controlling process parameters are compared with the predictions of the model. These predictions are found to be in qualitative agreement with the experimental measurements reported here. However, quantitative differences exist between the two. These differences are explained mainly by the omission of melt elasticity and bubble coalescence in the model.
Enthalpy recovery and physical aging of polymer‐diluent binary systems: A network epoxy and water
Authors: Ellis T. S. , Kahasz F. E. 
Published: December 2004

AbstractPhysical aging of a network epoxy resin in both the dry and water plasticized state has been investigated using calorimetric methods. Enthalpic retardation (recovery) towards equilibrium below the glass transition temperature (TK) has been qualitatively and quantitatively evaluated over a wide temperature range by following the enthalpy recovered (Er) on re‐heating through to and beyond the glass transition. Results indicate that water, acting as a plasticizer, accelerates aging at any given temperature. However, by using the respective Tg as a point of reference, a simple comparison of the kinetics of aging in the dry and plasticized state suggests that in the temperature range studied there are no significant differences. These observations, together with observed dilational and relaxational effects of water which appears to erase all accumulated aging effects in dry aged material, are commented upon and their importance in the' context of transport‐phenomena and moisture sorption‐desorption cycles are discussed.
A non‐destructive technique of measuring residual stresses in circular rods of transparent polymers
Authors: Mittal R. K. , Rasitmt V. 
Published: December 2004

AbstractResidual stresses, generally present in solid polymers, arise as a result of temperature gradients during solidification. These stresses influence the mechanical behavior of polymers and therefore it is important to measure them; most conventional methods are destructive. In the present work, a non‐destructive photoelastic technique is discussed and applied to circular rods of poly(methyl methacrylate) (PMMA). This technique involves the measurement of the distribution of total birefringence across a diameter; the residual stress distribution is obtained numerically from the birefringence distribution. The influence of the birefringence caused by molecular orientation is also investigated. This technique is also applied to a glass rod, in which case the molecular birefringence is minimum. It is seen that the residual stresses obtained in this case are consistent with equilibrium considerations.
Time‐dependent behavior of nylon‐6 under uniaxial and biaxial loadings at constant rate
Authors: Mittal R. K. , Singh I. P. 
Published: December 2004

AbstractThe large deformation behavior of nylon‐6 when subjected to constant loading rate tests has been investigated experimentally. Three types of loadings—tension, torsion, and combined tension‐torsion—have been used and the strain histories for each type analyzed. It is shown that a piecewise power law in time can adequately describe the strain histories up to equivalent strains as high as 30 percent for all cases. This piecewise power law shows well‐defined transitions from one mode to the other while each mode is characterized by a power law exponent valid for all types of loading. On the basis of experimental results, it is also possible to establish the functional form of various kernels involved in the Green‐Rivlin representation of the non‐linear viscoelastic behavior of nylon‐6. This method of finding kernels is much simpler than the conventional method of carrying out a large number of multi‐step creep tests. A comparison is also made between the results of the present work and the well‐known Findley equation, particularly with respect to the instantaneous strain response of materials.
Continuous extrusion of reacting polyurethane foam
Authors: Jerard Robert B. , Ravens Thomas R. 
Published: December 2004

AbstractThis paper explores the concept of continuously extruding reacting polyurethane foams. The control of the process is hampered by the fact that the state of the conversion of the extrudate is not directly observable. We present the general concept, describe an experimental apparatus, present a mathematical model of the process, and report on some initial experimentation. In the experimental work, low density (0.5 g/cc) polyurethane foam was extruded in a cylindrical cross section at a rate of 250 g/min. Maximum run time was thirty minutes. In all cases, the experiment had to be stopped due to problems in the process. Problems requiring further investigation were identified: channelling of uncured liquid foam around the solid cured foam, poor skin quality due to adhesion of the foam to the wall, and the general lack of observability of the conversion field.
Monitoring of laminate cure with microdielectrometry
Authors: Bidstrup Wayne W. , Sheppard Norman F. , Senturia Stephen D. 
Published: December 2004

AbstractWe report the use of microdielectrometry for monitoring the cure of the matrix resins in epoxy‐glass and epoxy‐graphite composites. The multi‐ply laminates are cured in a press using ramped temperatures. The microdielectrometer sensor is embedded in a cavity made by cutting a hole in each of the inner plies. For a brominated‐epoxy glass‐reinforced prepreg ramped to final cure temperatures as high as 200°C and at pressures up to 60 psi, a reproducible pattern of cure events is observed beginning with the flow of resin onto the sensor electrodes and ending with the characteristic stabilizing of the loss factor late in cure. The apparent dielectric properties (permittivity and loss factor) show good reproducibility for identically prepared samples, but their characteristics differ from those observed in neat resin. A ten‐fold increase in resin conductivity is noted when cures of glass‐reinforced prepreg are compared to cures of neat resin flaked off the prepreg. Special techniques are required in sample preparation when monitoring the cure of prepregs containing conductive fibers such as graphite.