bluuebunny/crossref_metadata_2025_split huggingface dataset:
Processing properties of high‐ and low‐density polyethylenes and their blends
Authors: Maxwell Bryce , Dormier E. J. , Smith F. P. , Tong P. P. 
Published: December 2004

AbstractBlends of two characterized linear polyethylenes with a branched polyethylene have been prepared by melt extrusion. It has been found that the linear polyethylenes can be shear modified in a reversible manner similar to branched polymers and that this shear modification and its reversal by re‐heating does not change the molecular weight distribution, thereby indicating that the shear modification is a physical rather than chemical change in structure. Because both the high‐ and low‐density polyethylene components of the blends are capable of undergoing reversible shear modification, it is possible to produce blends with either greater or less melt elasticity than the individual components by adjusting the conditions of blending. This demonstrates that the correlation of the properties of blends with the properties of their components should not be attempted without consideration of the effect of the blending process on the properties of the individual components.
Capillary and slit flow behavior of concentrated solutions of a rod‐like polymer
Authors: Kao C. H. , Baird D. G. 
Published: December 2004

AbstractThis paper is concerned with the flow behavior of isotropic solutions of the rod‐like polymer, poly(p‐phenyleneterephthalamide) (PPT), in 100 percent sulfuric acid. Studies include entry flow visualization in a slit die and solution fracture, and die swell in capillaries and a slit die. It was observed that solutions of PPT exhibit nearly negligible die swell, a slip‐stick type of fracture that disappears at high shear rates, and radial entry flow patterns similar to Newtonian fluids. Fracture was associated with the plateau in the shear stress vs shear rate curve. Because values of the wall shear stress (τw.) obtained from capillary measurements were in good agreement with those obtained from a cone‐and‐plate rheometer and values of the loss modulus (G″) obtained from small‐strain dynamic oscillatory measurements, it is believed that the rheological properties lead to the flow instability. These results are in agreement with the predictions of a recent theory by Doi and Edwards for concentrated solutions of rod‐like molecules. Data are also presented for a flexible chain polyamide, nylon 6,6, in 100 percent H2SO4 for the purpose of comparing the flow characteristics of rigid and flexible chain polymers.
Effect of composition and processing on rheological properties of multicomponent polymer melts
Authors: Ahuja S. , Chang H. , Schreiber R. 
Published: December 2004

AbstractPolyamide and polyether maleic anhydride were blended with carbon black at various compositions and processing conditions. The compositions were varied from 0/92/8 percent, 23/69/8 percent, 46/46/8 percent, 69/23/8 percent to 92/0/8 percent of polyamide/polyether maleic anhydride/carbon black. The polymer blends were processed by a Banbury roll mill and an extruder under various conditions and were spray dried. The effects of composition and processing conditions on steady state and dynamic viscoelastilc properties were determined. These effects were compared with the thermal and morphological properties of the blends.
Positional small‐angle X‐ray scattering
Authors: Legrand D. G. , Tryson G. R. , Olszewski W. V. , Forth M. 
Published: December 2004

AbstractPositional small‐angle X‐ray scattering has been implemented and developed as a new nondestructive technique to study the formation and growth of flaws in polymers. The technique consists of measuring the intensity of scattering at a constant scattering angle while the sample is moved through the incident x‐ray beam. Examples of applications of the technique from several different materials are presented.
Use of dielectric relaxation spectroscopy to monitor deformation of polycarbonate
Authors: Venkataswamy K. , Ard K. , Beatty C. L. 
Published: December 2004

AbstractA study has been carried out to determine the effect of deformation on the dielectric properties perpendicular to the deformation direction of amorphous polycarbonate. The dielectric tan δ shows a decreasing trend during mechanical creep and increases during recovery. The reverse trend was observed for the dielectric constant, ϵ′. The experiments at different stress levels indicated that the changes in tan δ closely follow mechanical creep and recovery. Under stress, the β‐relaxation appears to shift to a higher temperature as a function of frequency.
Equilibrium solubility and permeability of sulfur dioxide in epoxy resin of aliphatic diglycidyl ether
Authors: Ranade G. R. , Nadgir V. M. , Plank C. A. , Laukhuf W. L. S. 
Published: December 2004

AbstractEquilibrium sorption isotherms were obtained for the sulfur dioxide‐epoxy resin of aliphatic diglycidyl ether system over a temperature range of 1° to 45°C. The sorption isotherms indicated the presence of Langmuir sorption due to specific interaction. This is uncommon for rubbery polymers, though similar behavior was also observed previously. Zimm‐Lundberg's clustering analysis indicated a slight tendency for clustering of the penetrant molecules at low temperatures and higher activities. The number of Langmuir sites for sorption was found to be independent of temperature. The mobilities of the molecules sorbed in Henry's law mode and the Langmuir mode were found to be approximately equal. Predictions of the permeability values for this system are presented and compared with other data from the literature. The temperature dependence of different sorption parameters is presented and discussed in detail.
Isothermal and nonisothermal crystallization of polyethylene
Authors: Kamal Musa R. , Chu Edward 
Published: December 2004

AbstractDifferential scanning calorimetry is employed to study the crystallization kinetics of two commercial injection‐molding high‐density polyethylene resins. Also, polarized light microscopy has been used to elucidate the morphological structures formed at various crystallization conditions. Corrections and operating procedures are recommended in order to correct for temperature lag in scanning, transient response during isothermal crystallization and for thermal gradients within the polymer sample. As a result of these studies, a modified Avrami equation has been proposed in order to obtain a more extensive and reliable characterization of isothermal crystallization kinetics. Moreover, a procedure is recommended and employed to predict nonisothermal crystallization behavior on the basis of isothermal crystallization kinetics.
Newtonian sintering simulator of two spherical particles
Authors: Rosenzweig N. , Narkis M. 
Published: December 2004

AbstractSintering of amorphous polymer particles above their glasstransition temperature is a slow coalescence process in which surface tension is the main driving force, tending to decrease the total surface area, resisted by the polymer viscosity. The shape, and therefore the boundaries of the coalescing particles, change with time. A numerical finite‐element method (FEM) was used to solve the momentum and continuity equations for a coalescing spherical‐particles pair. The solution obtained describes a limited sintering time interval with reasonable agreement. Future modifications of the solution technique are suggested in order to extend its validity to longer sintering periods.
Shear stress at polymer/metal interface during melting in extrusion
Authors: McClelland D. E. , Chung C. I. 
Published: December 2004

AbstractPrediction of the screw horsepower requirement involves, among many others, the calculation of the shear stress (τs) between the solid polymer and the barrel surface during melting. Prediction of the solid bed down‐channel velocity also requires the calculation of τs. However, the pseudoplastic nature and strong temperature dependence of melt viscosity make the mathematics of calculating τs extremely difficult.As a first step of developing a reasonable mathematical model for calculating τs, experimental measurements of τs were made over a wide range of metal temperature and sliding speed for five commercial polymers using molded, block samples. Although dependences of τs on metal temperature and sliding speed were found to have similar functionality to those of the dependences of melt viscosity on melt temperature and shear rate, this study showed that τs could not be expressed as a sole function of the melt rheological properties. Our subsequent study, to be reported in a follow up paper, will show that τs must be expressed as a function of the thermodynamic properties and melt density of the polymer as well as the melt rheological properties and the melting conditions.
The rate of crystallization of poly(ethylene terephthalate) by differential scanning calorimetry
Authors: Lin C. C. 
Published: December 2004

AbstractThe value of tmax in differential scanning calorimetry is correlated with the crystallization kinetics of poly(ethylene terephthalate) (PET). The Avrami exponent, n, obtained varies as a result of a change in slope of the curve at the point tn, a secondary crystallization transition. The plot of tn vs. tmax shows a linear relationship. The rate of crystallization depends upon both molecular weight and crystallization temperature. Under a nucleation controlling step, the plot of log tmax vs. \documentclass{article}\pagestyle{empty}\begin{document}$ t_{\max } vs.\frac{1}{{T^2 \Delta T}} $\end{document}gives a linear relationship. Theoretical concepts of the treatment are discussed.
Flow instabilities of epoxide prepolymers
Authors: Aleman J. V. 
Published: December 2004

AbstractFlow of molten epoxide prepolymer (Tg = 303 K, M̄n 889, M̄u/M̄n = 1.46) shows stress jumps. A hydrodynamic explanation is forwarded, and a check of the theoretical jump is carried out, with shear viscosites and shear moduli measured at 361 K. The increase in pressure produces a decrease in volume, which increases the rigidity of the polymer, which is then reduced by relaxation of the compressed chain segments.
A low‐energy solvent separation method
Authors: Gutowski T. G. , Suh N. P. , Cangialose C. , Berube G. M. 
Published: December 2004

AbstractThis paper presents a new low‐energy method to separate solvents from polymers. The method is based upon the lower critical solution temperature (LCST), a phenomenon exhibited by all nonpolar polymer‐solvent systems. Three key issues concerning this new separation method are discussed for the specific system of high cis polybutadiene in a commercial grade n‐hexane. The first issue, energy cost, is greatly reduced from present commercial separation processes by avoiding the liquid‐vapor phase transition for more than half of the solvent. The predicted energy cost for the new method (not including inefficiencies) is about 15 percent of the present energy cost (including inefficiencies). The second issue, recycling of the dilute phase with terminator, is shown not to be a serious problem, and a solution is suggested based upon available methods. The third issue discussed, and perhaps the most difficult, is the physical separation of the two phases. This is solved by inducing spinodal decomposition, which leads to rapid gravity separation. Several alternative separation scenarios based upon this idea are presented at the end of the article.
Studies on whitening phenomena induced by some non‐solvents on highly oriented glassy polymers
Authors: Sung N. H. , Gahan R. E. , Haven R. E. 
Published: December 2004

AbstractWhitening phenomena, characterized by optically opaque regions when a highly oriented glassy polymer is immersed in some liquids, were investigated as a function of temperature, extent of molecular orientation, different solvent and molecular weight, using oriented polymethyl methacrylate (PMMA) obtained by hot‐stretching and cold drawn polycarbonate (PC). Whitened PMMA is highly porous resembling foamed plastics and shows the same Tg as in unwhitened PMMA, while whitened PC is denser with much smaller pores and exhibits melting behavior characteristic of solvent‐induced crystallinity. Whitening progresses with a sharp boundary between whitened and unwhitened layers, which advanced at a constant velocity. This feature is similar to Case II transport. However, whitening differs from Case II sorption in that it only occurs in highly oriented polymers in contact with liquids of negligible sorption. Activation enthalpy of 44.1 and 39.7 kcal/mol has been found in a certain temperature range for PMMA/N‐methyl formamide (N‐MF) and PC/di‐isopropyl amine (DIPA) respectively. At a given temperature, a higher extent of orientation leads to faster whitening process. Entropy correlation theory, in which the decrease in the configurational entropy (ΔSc) due to orientation is assumed to approximate an inerease in the activation entropy, was employed to correlate the dependency of the whitening rate on orientation. For hotstretched PMMA, where ΔSc is proportionl to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document} since affine deformation applies, a good correlation is observed. For cold drawn PC, correlation was poor, probably because ΔSc cannot be expressed to be proportational to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document}. In PMMA, when the molecular weight is in the same order as the average molecular weight between entanglements, the orientation and the whitening rate are both lower than higher molecular weight speciments. This may be due to a smaller number of chain entanglements and consequent chain slippage. In PMMA, whitening induced liquids seem to have a solubility parameter somewhat greater (2.5 ∼ 5.0) than that of PMMA. For PC, no consistent tendency is found.
Toughened nylon resins
Authors: Hobbs S. Y. , Bopp R. C. , Watkins V. H. 
Published: December 2004

AbstractThe impact failure of blends of nylon 6,6 and low density polyethylene grafted with maleic anhydride (PEgMA) is discussed in terms of fracture morphology, composition, and particle adhesion and dispersion. Basic criteria for effective impact modification of these materials are developed. A numerical model for estimating the extent of shear banding resulting from shear stress field overlap between neighboring impact modifier particles is presented.
Investigation of the solvent‐evaporation effect on spin coating of thin films
Authors: Chen B. T. 
Published: December 2004

AbstractA simple empirical relationship exists between the thickness and the solvent‐evaporation rate of spin‐coated thin films. The thickness of a film formed from an organic solvent solution can be approximated by the relationship\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (E\lambda /C_p)^{0.60} $\end{document}, where μ is the viscosity of the coating solution, ω is the rotation speed, E is the solvent‐evaporation rate, λ is the latent heat of evaporation, Cp is the heat capacity of the solvent, and K0 is a constant for volatile organic solvents. A similar relationship for aqueous polymer solutions is\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (1.0 - RH)^{0.60} $\end{document}, where RH is the relative humidity of air around the spin coater and Ka is a constant for aqueous solutions. These relationships are helpful in understanding the mechanism of thin‐film formation in spin coating.
Fluorescence study of polymer chain interpenetration and of the rate of phase separation in incompatible polymer blends
Authors: Morawetz H. 
Published: December 2004

AbstractThe application of fluorescence techniques has been demonstrated for the study of four polymer problems: (a) If two different polymers are labeled with donor and acceptor fluorophores, respectively, which exhibit nonradiative energy transfer, the emission spectrum of their blends will depend on whether the two polymeric species are miscible or segregated into separate phases. Thus, the emission spectrum may be used as a measure of polymer compatibility. (b) Since rapid freeze‐drying preserves the extent of chain interpenetration which existed in solution, the energy transfer between labeled polymers may be used to study the extent of such interpenetration on solution concentration. (c) Phase separation when heating blends of poly(methyl methacrylate) and poly(benzyl methacrylate) may be followed by the change in the emission spectrum of the latter. (d) The interdiffusion of separated poly(ethyl methacrylate) molecules labeled with donor and acceptor fluorophores may be monitored by the increase in the nonradiative energy transfer.
Diffusion of ethyl acetate vapor in strained low density polyethylene
Authors: Phillips J. C. , Peterlin A. 
Published: December 2004

AbstractAt a fixed vapor pressure p of the penetrant and constant temperature of the experiment, the sorption S = c/p or concentration c of the ethylacetate vapor in the uniaxially strained low density polyethylene (LDPE) increases most rapidly at low strains. If, however, on the basis of strain relaxation one separates the total strain ϵ into an elastic ϵe, and a plastic ϵpl, deformation, one obtains an almost linear increase of the concentration c or sorption S of the sorbate with elastic strain ϵe. The separation of ϵ = ϵe + ϵpl depends very much on the time th the sample is kept elongated and the vapor pressure p of the sorbate. The elastic component decreases and the complementary plastic fraction increases with th and p. An almost stationary state is reached after th of about 1/2 h. The calculation of the diffusion coefficient Ds1 from the first sorption immediately after the stretching is affected by this slow adjustment in the interval 0 ≤ th ≤ ½h and shows a pseudo maximum at a strain of ϵ∼ = 10 percent. The first desorption experiment and all the later sorptions and desorptions yield the same DD = DS < DS1 that is the correctly calculated diffusion coefficient D. The coefficient D decreases with the strain ϵ or ϵe in contrast with the expected increase of Da of the amorphous component. Such an increase of Da is expected as a consequence of the fractional free volume (FFV) increase caused by the elongation. According to the FFV concept, a decrease of the measured apparent diffusion coefficient D = ψDa requires that with increasing ϵ, the tortuosity factor ψ decreases faster than the increase in Da.
Effect of a diamine additive on the structure‐property relationships of rim polyurethane elastomers
Authors: Blackwell John , Quay Jeffrey R. , Turner Robert B. 
Published: December 2004

AbstractStructural and mechanical data have been compared for reaction injection molding (RIM) polyurethanes prepared from uretonimine‐modified diphenylmethane 4,4′‐diisocyanate (MDI), ethylene glycol (EG), and a polyol (a polyether; Mn ≃ 5000), in order to investigate the effect of addition of a small amount of a polyetherdiamine (PEDA; Mn ≃ 400) to the reaction mixture, A series of specimens containing 18 parts and 30 parts EG, with and without the diamine additive, were examined both as‐prepared and after thermal annealing. The specimens were compared in terms of their x‐ray crystallinity, elongation, flexural modulus, impact strength, and heat‐sag behavior. All of the specimens showed evidence for crystalline hard segments, which are more abundant in the series containing 30 parts EG. The crystallinity is lowest in the as‐prepared specimens without the PEDA additive, and is increased by annealing for 1 hour at 120°C. The as‐prepared specimen with additive has a hard segment crystallinity similar to that of the annealed specimen without additive. These results correlate with the mechanical property data, which improve as a result of annealing and/or the use of a PEDA additive. It is argued that the use of the polyetherdiamine enhances the phase separation and facilitates hard segment crystallization, leading to better heat‐sag behavior. It is significant that the unannealed/with PEDA and annealed/without PEDA specimens have similar properties. Use of PEDA additive improves the green strength and impact strength of molded parts.
Characterization of polymer conformation and morphology through small‐angle neutron scattering—A literature review
Authors: Sperling L. H. 
Published: December 2004

AbstractSmall‐angle neutron scattering, SANS, stands forth as one of the most important of the new tools for evaluating polymer chain conformation and morphology. This paper reviews the SANS literature through 1982, with a few early 1983 references added. The theory of SANS is outlined and compared to light scattering. SANS values of polymer molecular weights and radii of gyration obtained in the bulk state were found to be in agreement with values obtained from dilute solutions by light scattering. In each case, deuterated fractions of polymer were inserted into the hydrogeneous matrix, or vice versa, to provide contrast. Several new research areas are then discussed, including unidirectional stretching of elastomers, stress‐relaxation, polymer‐polymer miscibility, crystallization from the melt compared with crystallization from dilute solutions, nonclassical aggregation during bulk polymerization of thermoset systems, morphology of polymer blends, block copolymers and ionomers, the core‐shell structure of latexes and polymer blocks, and grafts as surfactants in emulsions and latexes. Much new and sometimes unexpected information is being provided by the SANS research now in progress.
Fluorescence techniques in the study of polymer colloids
Authors: Winnik Mitchell A. 
Published: December 2004

AbstractApplications of fluorescence techniques to the study of polymer colloids are reviewed, with emphasis on excimer and exciplex forming probes and fluorescence energy transfer processes. In these experiments non‐aqueous dispersions covalently labelled with naphthalene or anthracene were examined by a variety of techniques in order to elucidate aspects of core morphology with a resolution of about 10Å. The current “concentric sphere” or “core‐shell” model of colloid structure was found to be inconsistent with the results of the luminescence experiments. A new “microphase” model is proposed which overcomes these difficulties. In this model, the core structure is seen to be made up of phase‐separated microdomains of core and stabilizer chains.
A note on the numerical treatment of the thermally developing flow in screw extruders
Authors: Elbirli B. , Lindt J. T. 
Published: December 2004

AbstractThis paper proposes a new solution for the problem of thermally developing flow in a single‐screw extruder with power law fluids. It is shown that a transformation to a Lagrangean frame enables one to extend the solution to extrusion situations where appreciable “pressure back flow” exists. The utility of the model is demonstrated using a polystyrene melt as a model fluid.