bluuebunny/crossref_metadata_2025_split huggingface dataset:
Release of norethindrone from poly(ortho esters)
Authors: Heller J. , Penhale D. W. H. , Helwing R. F. , Fritzinger B. K. 
Published: December 2004

AbstractThe release of norethindrone from a poly(ortho ester) derived from 3,9‐bis(methylene)2,4,8,10‐tetraoxaspiro[5,5] undecane and 1,6‐hexanediol was studied. Thin circular devices containing incorporated drug and a water soluble salt, such as sodium carbonate, sodium sulfate, or sodium chloride, were placed in water buffered at pH 7.4 at 37°C, and release of drug was followed spectrophotometrically. It was found that rate of drug release was close to zero order for long periods of time and that release of the drug from the hydrophobic matrix occurred as a consequence of osmotic imbibing of water driven by the water soluble salt. Thus, a swelling front moves at a slow and constant rate through the solid device and drug release takes place by rapid diffusion of the drug from the swelling front. Polymer erosion lags behind drug release, and no erosion takes place with basic salts such as sodium carbonate when mechanical properties of the matrix are adequate to accommodate osmotic swelling.
Specification of biaxial orientation in amorphous and crystalline polymers
Authors: White James L. , Spruiell Joseph E. 
Published: December 2004

AbstractThe fundamental concepts for specifying orientation in amorphous and crystalline polymers are reviewed. A new set of orientation factors is proposed to represent the second moments of biaxial orientation. The factors are defined both for the chain axis and for three crystallographic axes of an orthorhombic (or pseudo‐orthorhombic) crystal structure. The orientation factors are defined in terms of the angles between the crystallographic axes and Cartesian coordinate reference axes defining the machine, transverse and thickness directions of films. This makes the orientation factors symmetric with respect to the machine and transverse directions unlike the Stein‐Nomura‐Kawai orientation factors which are defined in terms of Euler's angles. A graphical procedure for representing the state of orientation as a point inside an isoceles triangle is described. Methods of measuring the orientation factors are also reviewed. The paper concludes with examples of the application of these concepts to orientation in amorphous polystyrene films fabricated in our laboratories and to crystalline polyethylene samples discussed in the literature.
Free volume, excess entropy and mechanical behavior of polymeric glasses
Authors: Matsuoka S. 
Published: December 2004

AbstractFree volume fraction of the Williams‐Landel‐Ferry(WLF)‐Doolittle type has been applied to the analysis of the nonequilibrium state for the glassy polymers. The free volume fraction is a two parameter variable since it depends on the free volume and the occupied volume. The excess entropy is derived from the mixing of vacant and occupied sites, and for polymers a factor is added which corresponds to disordering the molecular segments. A relationship between the excess entropy and enthalpy is derived. For a given level of fractional free volume, there is a unique rate constant associated with changing that level of the fractional free volume. The reciprocal of this rate constant, which depends on the exponential order of the fractional free volume, can be considered as a time constant for changing the molecular conformational probability, and its value is in the order of the average dielectric relaxation time in the corresponding state. When mechanical deformation is. imposed with a rate which is too fast as compared to this time constant, the deformation without a change in the conformational probability, i.e., the reversible elastic deformation, will ensue. In contrast, a sufficiently slow deformation will be accompanied by a change in fractional free volume and the excess entropy, and the above‐mentioned time constant will change with deformation. Since dilation will tend to shorten this time constant, tensile deformation will result in reducing the modulus accompanied by the increase in entropy. Shear deformation is considered as a mixture of compression and tension, where only tension contributes to a change in entropy, and the net result is the strain softening which can be predicted from the tensile behavior. Uniaxial compression is controlled by the shear behavior, and the excess entropy and the fractional free volume increase, while the occupied volume decreases with strain. A constitutive relationship has been proposed which accounts for the effects of temperature, pressure, strain rates and thermal history on nonlinear viscoelastic behavior of polymeric glass.
The glass transition temperature of partially cured polymers as a non‐equilibrium parameter and its effect on observed dynamic mechanical behavior
Authors: Lee C. Y‐C. , Goldfarb I. J. 
Published: December 2004

AbstractObservations of time dependent behaviors of polymeric systems are often made with the assumption that the glass transition temperature will remain constant during the course of the experiment. This assumption may not be valid for partially cured thermosetting system, where additional cure can increase the glass transition temperature. The observed behavior can be expressed as a time derivative function of two independent variables, the experimental temperature and the state of the system. With proper assumptions, these two variables can be reduced to a single parameter (T − Tg), whose time derivative will give terms representing the temperature and curing effect separately. Dynamic mechanical measurements have been made on partially cured systems, and the effects of the additional cure on the observed properties are observed. The seemingly complex experimental observations can be qualitatively interpreted with the change of the parameter (T − Tg).
Laser light scattering studies of bulk polymers in the glass transition regime
Authors: Jamieson A. M. , Simha R. , Lee H. , Tribone J. 
Published: December 2004

AbstractThe application of laser light scattering techniques to characterize the structural and dynamical properties of bulk polymers near the glass transition temperature is reviewed. Preliminary results of a study of poly(n‐butyl methacrylate) are presented. As in an earlier study of atactic polystyrene, the results suggest the coexistence of two relaxation mechanisms near Tg: a fast, single exponential decay; a slow process characterized by a wide distribution of relaxation times. The slow relaxation mechanism is evidently the main‐chain glass transition process; it appears possible that the fast decay is a manifestation of side‐chain motion. However, in contrast to the polystyrene system where the fast mechanism is always of small amplitude in the temperature range amenable to study (Tg < T < Tg + 40°), the fast mechanism in the poly(n‐butyl methacrylate) system exhibits a sudden transition to high amplitude (∼50 percent of the total observable relaxation amplitude) at T ∼ Tg + 30°. At this point therefore, we suggest that a strong resonant coupling of the fast process with the slow relaxation is occurring.
Analysis and experimental evaluation of twin screw extruders
Authors: Rauwendaal Chris J. 
Published: December 2004

AbstractTwin screw extruders can he classified according to their geometrical configuration. The main distinction is made between intermeshing and nonintermeshing extruders. Another distinguishing characteristic is the sense of rotation. The most important characteristics of the various twin screw extruders are examined, with particular emphasis on the effect of screw geometry on the conveying characteristics. A brief review is given of the state of the art in theoretical analysis of twin screw extruders. Experiments with two lab scale, intermeshing twin screw extruders are described, one co‐ and one counterrotating. Results are presented on power consumption, residence time distribution, and mixing characteristics of the two extruders. The counterrotating extruder exhibits a narrower residence time distribution and better dispersive mixing capability. The corotating extruder showed a better distributive mixing capability. These results can be explained in terms of the conveying and mixing mechanisms in both extruders. The overall extruder performance seems to be dominated by the effect of the intenneshing region. Any realistic, theoretical analysis of twin screw extruders should be centered around the flow behavior and mixing characteristics of the intermeshing region. The corotating extruder appears to be best suited for melt blending operations, while the counterrotating extruder seems to be preferred in operations where solid fillers have to be dispersed in a polymer matrix.
The melting performance of single screw extruders. II
Authors: Housz J. F. Ingen , Meijer H. E. H. 
Published: December 2004

AbstractIn the previous paper (1) the melting performance of a number of recent screw designs was analyzed, using a rather simple theory. A new screw design was proposed. Here the results of more elaborate calculations, are given in which the influence of the flight clearance and of a shear‐thinning temperature dependent viscosity are investigated. The former conclusions are not altered in essence by these effects. Experimental results with a prototype screw are presented, showing that melting capacity is increased. Up to 100 percent increase in throughput is possible in the high RPM range (in comparison with a much longer traditional compression screw), provided that the feed capacity is sufficient. This usually requires the use of a grooved, well‐cooled, feed section; the capacity of such a feed section depends, for a given screw geometry, on channel depth and granule dimensions. The melt leaves the melting section at a relatively low temperature. The melting section only melts the material and does not raise, its temperature unnecessarily. A further step towards separating distinct tasks of the extruder by functional screw design has been made.
A Note on the prediction of polyethylene melt rheological properties from molecular weight distribution data obtained by gel permeation chromatography
Authors: Shah B. H. , Darby Ron 
Published: December 2004

AbstractIn the present study, a modification of the method previously presented by the authors for predicting rheological properties of linear polyethylene melts from gel permeation chromatography (GPC) data is presented. The modification involves independent values of the zero shear viscosities for melts rather than generating these values internally. The comparison between the experimental zero shear viscosity values and those calculated from GPC data is shown to be very good.
Polymer compatibility with and without a solvent
Authors: Patterson Donald 
Published: December 2004

AbstractA qualitative review of the thermodynamics of polymer systems will be given in terms of three contributions: positional (or combinatorial) entropy, an “international” term and a free volume term. From this one finds that a simple polymer‐solvent system phase separates on lowering T to an Upper Critical Solution Temperature (UCST) or raising it to Lower Critical Solution Temperature (LCST), To achieve miscibility of two polymers of high molecular weight, one requires a “specific” interaction, usually a weak charge‐transfer complex or a hydrogen bond. Phase separation takes place on raising the temperature to an LCST. These various UCST and LCST are predicted semi‐quantitative by the Prigogine‐Flory theory. When a solvent is added to two miscible polymers, a new type of phase separation appears since there is an effect of any difference in the strengths of the two polymer‐solvent interactions. Phase separation may easily occur in the ternary system where there is none in the three binary systems, and examples will be given. In the case of two highly‐attractive polymers in a solvent, a quite different phase separation occurs, sometimes called complex coacervation. A simple Flory‐Huggins type theory predicts these phenomena in ternary systems.
Modeling of polymeric film‐blowing processes
Authors: Gupta R. K. , Metzner A. B. , Wissbrun K. F. 
Published: December 2004

AbstractIndustrial film‐blowing processes are characterized by large deformation rates, rapid changes of temperature and high stress levels. A pilot scale process was set up to simulate these variables. The pivotal element in modeling the process is a rheological constitutive equation which describes the fluid properties accurately over the entire range of conditions encountered; it was found that contributions to the stress in the material which arise out of the changing thermal history of a fluid element were a significant fraction of the total. When the deforming film is subjected to stretching but to little or no blowing, the axial stresses in the film are predicted excellently by the model under both isothermal and non‐isothermal processing conditions. With rapid blowing and major deviations from uniaxial extension, the axial stresses are predicted less well, but still satisfactorily, under the conditions used. In no case are the circumferential stresses predicted accurately: i.e. unequal biaxial extensional deformations represent complications which have not been resolved.
Poly(n‐butyl acrylate)/polystyrene interpenetrating polymer networks and related materials I. Dynamic mechanical spectroscopy and morphology
Authors: Yeo J. K. , Sperling L. H. , Thomas D. A. 
Published: December 2004

AbstractA series of interpenetrating polymer networks, IPN's, and semi‐1 IPN's of poly(n‐butyl acrylate) and polystyrene were prepared. The glass transition behavior via dynamic mechanical spectroscopy (DMS) and the morphology via transmission electron microscopy (TEM) were studied as a function of composition ratio and crosslink density. Transition‐broadening was observed at low crosslink concentrations, while a single broad glass transition peak at an intermediate position was attained at high crosslink density levels. A cellular domain structure was the morphological characteristic of those IPN's and semi‐1 IPN's possessing a low cross‐link density and mid‐range composition ratio. At higher levels of crosslink density, irregular shapes of the domain morphology prevailed. Phase connectivity was also observed at high polymer II compositions. Theoretical phase domain sizes of polymer II were calculated using both the theories developed by the present authors and that published earlier by Donatelli, et al., and were found to agree with the experimental domain sizes. While the theory was developed for uniform spheres, some of the domain structures observed experimentally for high polymer II contents had connectivity and/or a cylindrical shape.
Methods for study of thermal aging and stabilization of grafted acrylonitrile‐butadiene‐styrene (ABS) terpolymers
Authors: Chang D. M. 
Published: December 2004

AbstractAcrylonitrile‐butadiene‐styrene (ABS) grafted terpolymers are apt to oxidize at an elevated temperature and its stabilization by an antioxidant is critical to processing and performance. The differential thermal analysis was used to study the effect of the AgeRite® Geltrol, a modified high molecular weight hindered phenol antioxidant, on the ABS thermal oxidation. The Kissinger equation was found to be accurate enough to determine the activation energy of oxidation. The induction time was also measured and these results were compared with the activation energies. The polybutadiene component of ABS was oxidized rapidly around 200°C under an oxygen atmosphere while the styrene‐acrylonitrile (SAN) component was oxidized at a higher temperature. Air oven aging at 130°C affected the Izod impact (notched), ultimate elongation, but not the ultimate tensile, melt index and morphology. It further confirmed that the polybutadiene component was oxidized and the SAN component was fairly stable at 130°C in air.
Low temperature thermal aging of ethylene vinyl alcohol copolymers
Authors: Apicella A. , Hopfenberg H. B. , Piccarolo S. 
Published: December 2004

AbstractThe crystallites of semicrystalline polymers formed at low temperatures are subject to partial partial melting and recrystallization resulting in a systematic increase in the size and perfection of the nascent crystallites. Differential scanning calorimetry (DSC) and x‐ray studies suggest that ethylene‐vinyl alcohol copolymers (EVOH), in particular, may undergo these secondary crystallization processes upon storage at temperatures far below Tm. DSC scans have been run on “as received” and quenched samples; the mole percent of vinyl alcohol in the copolymers studied was 0, 62, 70, 72, 82 and 100 percent. Tests on secondary crystallization kinetics, performed at different temperatures, further confirm the hypothesis of an increased degree of perfection (lamellar thickening) of the bulk crystallites achieved upon long term storage at temperature between Tg and Tm.
Tensile failure of weathered polycarbonate
Authors: Sherman E. S. , Ram A. , Kenig S. 
Published: December 2004

AbstractWeatherability of several UV stabilized and unstabilized grades of LEXAN® polycarbonate (PC) was studied by exposure in a xenon arc lamp weather‐o‐meter. The tensile properties of thin (0.2 to 0.3 mm) compression molded and thick (3.4 mm) injection molded samples were investigated as a function of exposure time and correlated with the changes in fracture morphology and molecular weight by scanning electron microscopy (SEM) and gel permeation chromatography (GPC). The elongation at failure was the essential mechanical property influenced by exposure. An initial decrease in elongation at failure, followed by a slight increase before the materials turned completely brittle (i.e.; failure without yielding), was correlated with a change in the fracture mechanism starting from the exposed surface of the samples. The initial decrease was caused by penetrating surface cracks, while the later increase in ultimate elongation resulted from the flaking off of the brittle surface layer. The UV stabilized grade remained more ductile, since its molecular weight remains fairly constant up to 1500 h of exposure, while the unstabilized grades decrease in molecular weight continuously from the start of exposure. The useful lifetime of the samples, defined by the complete loss of ductility, is approximately 1500‐2000 h of accelerated exposure, which corresponds approximately to 1 year outdoor exposure under Israeli conditions.
Effects of high oxygen pressure and temperature on the aging of polypropylene
Authors: Faulkner Douglas L. 
Published: December 2004

AbstractThin films of polypropylene were aged in air and in pure oxygen at pressures ranging from 0.051 to 4.24 MPa (7.4 to 614 psi) and temperatures from 60 to 90°C. Carbonyl formation resulting from polypropylene oxidation was monitored using infrared spectroscopy. The induction time for spectroseopically detectable oxidation coincided with a drastic reduction in tensile elongation for similarly aged tensile specimens. The induction time decreased monotonically with increasing oxygen pressures, while the maximum rate of carbonyl formation increased rapidly at lower oxygen pressures and increased slightly thereafter. The maximum rate of carbonyl formation as a function of oxygen pressure was shown to be consistent with a kinetic rate equation proposed by Stivala, et al. Nearly identical activation energies for the initiation of polypropylene oxidation were determined from reciprocal induction times for samples aged in air and in 4.24 MPa of oxygen (23.9 and 23.8 kcal/g‐mole, respectively). The similarity of activation energies suggests that the same mechanism is involved in the initiation step. Samples aged 3.6 times faster in 4.24 MPa of oxygen than in air at the same aging temperature.
Crosslinking of fluorocarbon elastomers: Characterization of crosslinking system to obtain transparent, tough materials
Authors: Miller G. A. , Sperling L. H. 
Published: December 2004

AbstractViton® GLT is a new low‐temperature fluoroelastomer with a Tg near −40°C. A study was made on methods of Crosslinking this material while retaining its transparency. Combinations of trimethylolpropane trimethacrylate, TMPTM, and triallyl isocyanurate, Diak® #7, were milled into Viton GLT. After molding, the materials were exposed to electron‐irradiation, cross‐linking the material. Transparent, tough materials were obtained for compositions containing about 3 percent TMPTM/3 percent Diak #7/3 Mrads, which had an extension of over 100 percent, a tensile strength of over 1000 PSI, excellent clarity, and low surface tack.
Curing characteristics of particulate‐filled thermosets
Authors: McGee Stuart H. 
Published: December 2004

AbstractA model to describe the effect of participate fillers on the heat transfer and curing characteristics of a thermosetting polymer is presented. It is assumed that the reaction kinetics are not altered by the addition of the filler and that the thermal characteristics of the composite are adequately described by the “spherical inclusion model.” The model is used to examine the effect of fillers on several important molding characteristics: time‐temperature profiles, peak temperatures, extent of reaction, and gel time. Results are presented for the curing of a typical polyester resin with varying filler content and filler type (glass, calcium carbonate, and aluminum). These results indicate that:

mold cycle time can be reduced at higher filler content by increasing the mold temperature without inducing thermal degradation, and
the progression of cure fronts through the thickness of the mold is significantly altered with increasing filler content; at low filler content the cure front progresses from the centerline toward the wall; at higher filler content, the cure front progresses from the wall toward the centerline.
Blends of EPDM and sulfonated ethylene‐propylene‐diene (EPDM) rubber with polypropylene: Structure, physical, and rheological properties
Authors: Duvdevani I. , Agarwal P. K. , Lundberg R. D. 
Published: December 2004

AbstractBlends of ethylene‐propylene‐diene (EPDM) and of metal‐neutralized, Sulfonated EPDM elastomers with polypropylene were prepared, and their structure‐property relationships were investigated. Extensive rheological measurements, including linear viscoelastic dynamic mechanical studies, were conducted on the blends. As might have been expected, the properties were a strong function of the blend compositions. Both blend systems exhibited multiple transitions indicative of molecular incompatibility of the blend components. These observations are consistent with the morphologies that were observed by scanning electron microscopy using selective extraction techniques. Both blend systems revealed two continuous interwoven phases consisting of elastomer and polypropylene. However, on a relative basis, the moduli and flow of the two blend systems differed significantly; blends of sulfonated EPDM possess higher moduli and lower flow values. The physical and flow property differences between the two systems are directly attributed to the difference in the structure of the elastomer components.
Stress‐induced diffusion and chemical reaction in nonhomogeneous velocity gradient fields
Authors: Akay G. 
Published: December 2004

AbstractThe theoretical analysis of dispersion with or without stress‐induced diffusion and stress‐induced chemical reaction during laminar flow of viscoelastic fluids in capillaries is given. The results are applied to diffusion and degradation in polymers under nonhomogeneous velocity gradient fields. It is shown that the concentration profiles during dispersion are strongly dependent on axial and radial positions in the presence of stress‐induced diffusion. Stress‐induced degradation rate of macromolecules during capillary flow decreases if the macromolecules are subject to stress‐induced diffusion.