bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of structure and properties of poly(ethylene terephthalate) fibers
Authors: Fu Yigang , Annis Brian , Boller Andreas , Jin Yimin , Wunderlich Bernhard 
Published: April 2003

AbstractThe structure of four semicrystalline poly(ethylene terephthalate) fibers were analyzed with full‐pattern (two‐dimensional Rietveld) x‐ray diffraction refinement, small‐angle x‐ray scattering, and thermal mechanical analysis, and compared to some of their known mechanical properties. The classical two‐phase model of crystal and amorphous phases were unable to correlate structure and properties. We found that there must be a third phase, an oriented, intermediate phase, located mainly between the fibrils. About 1/3 of the intensity of fiber diffraction of the analyzed samples was contributed from such intermediate phase. For some fiber properties the intermediate phase plays a similar role as proposed for “taut tie molecules.” A simple model for the description of structure‐insensitive properties of PET fibers was developed, based on this quantitaitve separation into three phases. The oriented intermediate phase changes the definition and calculation of the basic parameters of the fiber structure, such as crystallinity and orientation. Based on small‐angle x‐ray evidence, the crystallites are assumed to be separated by layers of largely amorphous material, both surrounded by the intermediate phase. The initial modulus of the fiber is determined mainly by the amount and orientation of the intermediate phase which has a maximum modulus of about 500 g/d on full orientation instead of the earlier predicted 150 g/d for fully oriented semicrystalline fibers. Based on the relationship between tenactity and average orientation function, the maximum tenacity for PET fibers of a structure like the ones analyzed may reach 20–45 g/d instead of earlier predictions of 10 g/d. The additional information needed to understand the structure‐sensitive property of shrinkage is discussed. Presently easily accessible parameters have no quantitative predictive capabilities. © 1994 John Wiley & Sons, Inc.
In situ thermoset molecular composites
Authors: Wiff D. R. , Lenke G. M. , Fleming P. D. 
Published: April 2003

AbstractThe polymerization of rigid rod polymer precursors in a reactive matrix precursor, which is later cured in the mold, constitutes the in situ process. A poly‐azomethine (PAM) was used as the rigid rod molecule. The resin used was an epoxy. We discuss the prediction of mechanical properties using micromechanics equations for chopped fiber composites. The chemistry used to synthesize the rigid rod polymer PAM in the epoxy precursor is reviewed. Approaches to better control the cure of these epoxy systems through cure kinetics and cure rheology studies completes the thermoset in situ molecular composite process. There was a 71% increase in tensile modulus in comparison to that of the neat epoxy resin. Molecular modeling simulations and continuum mechanics are used to help understand these findings. PAM/epoxy systems were used as a matrix material in the fabrication of unidirectional glass fiber/(PAM/epoxy) structural composites. © 1994 John Wiley & Sons, Inc.
Ion irradiation of poly(methyl methacrylate) for precise control of electrical and optical properties
Authors: Congedo T. V. , Schoch, Jr. K. F. 
Published: April 2003

AbstractIon irradiation with Xe+ has been utilized to produce electrical conductivity in PMMA, as measured using a four‐point in‐line probe. Incident ion beam energy and current density have been varied to investigate their effect on electrical conductivity and optical absorbance of the samples after irradiation. Results support the premise that selection of beam parameters that maximize the ratio of energy transfer‐producing displacements to energy transfer‐producing ionization maximizes the ratio of induced conductivity to induced absorbance in the irradiated samples. Conductivity versus ion dose has also been shown to be well estimated using a damage trial model. © 1994 John Wiley & Sons, Inc.
Rapid mechanical deformation of poly(ethylene terephthalate) fibers at temperatures above the glass transition
Authors: Hristov H. A. , Hearle J. W. S. , Schultz J. M. , Kennedy A. D. 
Published: April 2003

AbstractThe mechanical properties of poly(ethylene terephthalate) (PET) fibers at temperatures above the glass transition are investigated by means of a specially constructed device. Measurements of the deformation rate and of the “dynamic” stress‐strain curves of the fibers are performed in nearly isothermal regime (after initial rapid heating) in a temperature interval 100–200°C. The results reported in the present work demonstrate that the high‐temperature mechanical characteristics of rapidly crystallizing polymers can be deduced to a satisfactory precision, while keeping the crystallinity development at low level. Our investigations indicate that if the high‐temperature deformation is sufficiently fast, the polymer behavior is similar to the deformation at sub‐Tg temperatures. Based on this similarity, a qualitative model of the deformation in the high‐temperature region is proposed. The proposed model is fundamentally equivalent to the models describing mechanical deformation of glassy polymers at temperatures below the glass transition. ©1995 John Wiley & Sons, Inc.
Molecular interpretation of miscibility in polyamide‐6 blends with alkali ionomers of sulfonated polystyrene
Authors: Rajagopalan Padmavathy , Kim Joon‐Seop , Brack Hans Peter , Lu Xinya , Eisenberg Adi , Weiss R. A. , Risen William M. 
Published: April 2003

AbstractBlends of polyamide‐6 with lithium ionomers of 9.8 and 5.4 mole percent sulfonated polystyrene, formed by combining solutions of these polymers, are miscible over a wide compositional range, but those with the equivalent sodium ionomers are not. The molecular origin of this difference is addressed by studying the far infared and infrared spectra of the blends and pure materials to follow changes in the interactions between the cations and their surroundings, and changes in the interactions between functional groups. Based on analysis of these spectra, a molecular level interpretation of the blending is proposed. The initial step involves both the interaction of one amide carbonyl with an Li+ ion and simultaneous hydrogen bonding between an amide NH and a sulfonate group. This eventually leads to formation of an Li(>CO)+n(n ∼ 4) entity while the sulfonates are converted to the acid form through hydrogen bonding to the amide NH groups. The Na+ ion does not interact strongly enough with the amide groups to leave its sulfonate environment to a significant extent. © 1995 John Wiley & Sons, Inc.
Solvent‐induced crystallization of nylon‐6I
Authors: Liu Wu , Breault Brigitte , Brisson Josee 
Published: April 2003

AbstractThe ability of various hydrogen bond‐forming solvents to induce crystallinity in nylon‐6I was studied using DSC, FTIR spectroscopy, and x‐ray diffraction. Comparison was made with predictions using the solubility parameter, which is related to possibilities of interaction formation. General predicted tendencies agreed with experimental results, in agreement with proposed influence of solvent‐polymer interactions in the solvent‐induced crystallization process. FTIR investigation of polymers treated with methanol and methanol‐d shows that polymer segments forming hydrogen bonds with solvent molecules crystallize preferentially. It is therefore concluded that hydrogen bond exchanges with the solvent favor chain rearrangements leading to crystallization. © 1995 John Wiley & Sons, Inc.
A detailed study of the viscoelastic nature of vapor sorption and transport in a cellulosic polymer. I. Origin and physical implications of deviations from Fickian sorption kinetics
Authors: Sanopoulou M. , Roussis P. P. , Petropoulos J. H. 
Published: April 2003

AbstractVarious aspects of the kinetics of sorption of acetone vapor by cellulose acetate films at 30°C have been studied in detail, the principal aim being to understand more thoroughly the physical nature and causes of non‐Fickian behavior in this and other similar polymer‐micromolecular penetrant systems. Particular attention was given to the changes in sorption (including absorption, desorption, and resorption) kinetics caused by (a) systematic variation of the vapor pressure of acetone in different ways and (b) changes in membrane thickness. It has been shown that both viscous volume swelling relaxation and longitudinal differential swelling stress effects must be invoked, in order to explain fully the observed behavior. Detailed analysis of two‐stage sorption kinetics indicated (1) reasonable agreement between estimates of the diffusion coefficient reported by different authors, as long as a consistent analysis of the first stage is used, although the significance of the values given is open to some doubt, because the said first stage is found not to be free of non‐Fickian features; and (2) reasonable conformity of the second stage to a first‐order volume relaxation process (except a long times), with a relaxation frequency strongly dependent on the width of the concentration interval covered by the sorption experiment (and hence on the applied “osmotic stress”). The close similarity of second‐stage sorption to nonlinear viscoelastic creep behavior, previously found in the cellulose‐water system was confirmed and is taken further here, by demonstrating semiquantitative agreement between the corresponding “elastic swelling” and mechanical bulk moduli. ©1995 John Wiley & Sons, Inc.
Molecular structure refinement of a segmented thermotropic polyester containing an aromatic triad mesogen
Authors: Carotenuto Maurizio , Guadagno Liberata , Iannelli Pio , Chiellini Emo , Farah Abdiaziz Ali , Galli Giancarlo 
Published: April 2003

AbstractThe polymorphic behavior of a polyester consisting of an aromatic triad mesogen and a flexible spacer has been investigated. The effect of thermal and mechanical treatment on the appearance of two crystalline phases stable at room temperature is discussed. The molecular packing (triclinic cell, space group P1) and the morphological parameters of the crystalline phase stabilized by drawing process are evaluated and refined. The whole‐pattern method, based on the analysis of the whole x‐ray diffraction pattern from fiber samples of polymer, has been employed. The molecular packing resembles very much that of polyethylene terephthalate. ©1995 John Wiley & Sons, Inc.
Dilute solution properties of poly(dimethyldiallylammonium chloride) in aqueous sodium chloride solutions
Authors: Xia Jiulin , Dubin Paul L. , Edwards Shun , Havel Henry 
Published: April 2003

AbstractMW fractions of poly(dimethyldiallylammonium chloride) (PDMDAAC) were prepared by preparative size‐exclusion chromatography and characterized by static and dynamic light scattering, viscometry, size‐exclusion chromatography, and electrophoretic light scattering, in 0.50M NaCl solution. The behavior of fractions with MW < 2 × 105 was as expected for a strong polyelectrolyte in a good solvent, with a Mark‐Houwink exponent of ca. 0.8, and MW‐dependencies of the hydrodynamic radius and the radius of gyration of corresponding magnitude. At higher MW, curvature appears in the MW‐dependencies, which can be best explained by the presence of branching. While this notably lowers the intrinsic viscosity at high MW, the electrophoretic mobility is unchanged regardless of molar mass. Thus, the branched polymers display the electrophoretic free‐draining behavior characteristic of linear polyelectrolytes. ©1995 John Wiley & Sons, Inc.
The application of a Gauss‐Eyring model to predict the behavior of thermoplastics in tensile experiments
Authors: Haward R. N. 
Published: April 2003

AbstractThe Gaussian expression for the isothermal tensile deformation of thermoplastics including the proposed strain hardening constant Gp, has been combined with the Eyring flow equation to provide a new relation describing the rate of strain of a thermoplastic in terms of the true stress and the extension ratio under isothermal conditions. In conventional mechanical tests this model can be used to quantify the tendency to strain localization, to predict the natural draw ratio and the inversion point where the true engineering stress passes through a minimum. The latter is expected to correlate with the value of the extension ratio where crazes do not propagate under tension. The equation is most easily demonstrated in constant load experiments where they agree well with published work. However, for a more precise evaluation of the theory the constant Gp should be measured separately and the calculated results compared with other tests on the same material. Where necking occurs it is possible to use a simplified plug flow model to calculate neck profiles. These show that no special assumptions are required to account for necking which results directly from the interaction of geometric thinning and strain hardening, even where true strain softening is absent. The procedure makes it possible to illustrate the way in which the form of the neck can be affected by the rate of extension or in a constant load experiment by the applied load. ©1995 John Wiley & Sons, Inc.
NMR relaxation study of thermal degradation in cured PMR polyimides
Authors: Bradley D. S. , Von Meerwall E. D. , Roberts G. D. , Kamvouris J. 
Published: April 2003

AbstractWe have studied cross‐linking and thermal degradation of high‐performance first‐and second‐generation PMR‐15 polyimides, both thermoset and thermoplastic versions, by performing nonspectroscopic NMR solid echo T*2 relaxation measurements at temperatures up to 430°C using probes built for this purpose. We employ signal averaging and automated decomposition of the relaxation decays into two Gaussian components, the slower of which gradually appears above 300°C. Tracking the molecular mobility spectrum in terms of the relative intensity of the components and their relaxation times as temperature is cycled, we detect essentially no irreversible effects below the glass transition, measure permanent mobility reductions attributable to completion of cure, and find that exposure to temperatures above 380°C on the order of 1 h is required for substantial thermal degradation to occur. These results are closely supported by thermal and mechanical measurements on parallel specimens. Second‐generation PMR resins appear to have higher microscopic rigidity and reduced viscous fraction at high temperatures. ©1995 John Wiley & Sons, Inc.
Determination of optimized blending fractions for particle size distributions or molecular weight distributions involving various physical properties
Authors: Sudduth Richard D. 
Published: April 2003

AbstractIt has been shown in this study that the effects of particle size distribution or molecular weight distribution on selected physical properties can be related by a generalized blending approach that involves similar equations. The blending equations developed involve different z‐fractions where z = 3 for volume blending of spherical particles, or z = 2 for surface blending of spherical particles, or z = 1 for the weight blending of molecular weights. This new analysis approach addresses the magnitude of the ratios of particle size averages, Dx/Dy, or ratios of molecular weight averages, Mx/My, as well as the location of this maximum, the level of distribution information available for the starting materials, and the type of z‐fraction blending. To illustrate this approach suspension viscosity/concentration data was used to show how the Dx/Dy ratio could be introduced successfully to analyze latex volume blending where z = 3. In addition, the maximum steady‐state elastic compliance, Je, as a function of weighted blends (z = 1) of two different molecular weights of polyisobutylene was shown to fit the simple equation Je = 1.187 (M3/M2) (M4/M1) reasonably well. © 1995 John Wiley & Sons, Inc.
Effect of solution concentration on the gelation of aqueous polyvinyl alcohol solution
Authors: Liu Mingzhu , Cheng Rongshi , Qian Renyuan 
Published: April 2003

AbstractThe concentration dependence of cryogenic gelation for aqueous solution of poly(vinyl alcohol) was studied by measuring the apparent gel fraction G and the swelling ratio Q of the gel formed by freezing and thawing. It was found that for the gelation process there were three distinct regions of solution concentration bounded by two concentrations Cgel and C. The gel started to form at C = Cgel, while no visible gel could be detected even upon repeated freezing and thawing of the extremely dilute solutions of C < Cgel. The entire solution was gelatinized as a whole in the high concentration region of C > C. In the intermediate concentration region, Cgel < C < C, which covers three orders of magnitude in concentration, gel and sol phases coexist. Both concentration dependencies of G and Q show two branches jointed at a concentration very close to the overlap concentration C*. The curve of GċQ versus C shows a sharp cusp. In case the sharp cusp concentration is really the value of C*, gelation offers a precise method to determine the overlap concentration. ©1995 John Wiley & Sons, Inc.
Morphology of nylon 6/polypropylene blends compatibilized with maleated polypropylene
Authors: González‐Montiel A. , Keskkula H. , Paul D. R. 
Published: April 2003

AbstractTransmission electron microscopy (TEM) was used to examine the morphology of blends of nylon 6 and polypropylene (PP) containing various maleated polypropylenes (PP‐g‐MA). The size of the dispersed polypropylene particles decreases as the content of maleic anhydride in the PP‐g‐MA increases for binary blends of nylon 6 and the maleated polypropylenes. Ternary blends of nylon 6, PP, and PP‐g‐MA show morphologies that depend on the content of maleic anhydride of the PP‐g‐MA and on the miscibility of PP and PP‐g‐MA. Blends where PP and PP‐g‐MA are immiscible show a bimodal distribution of particle sizes. Miscibility of the PP and PP‐g‐MA was determined by TEM using a special staining technique. Experimental observations of miscibility were further corroborated by thermodynamic calculations. The morphology of the ternary blends was also found to be dependent on the ratio of PP/PP‐g‐MA. By changing this ratio it was possible to induce drastic changes of morphology, going from a continuous nylon 6 phase to a continuous PP phase at a fixed composition. The mechanical properties of these blends were found to be dependent on their morphology. ©1995 John Wiley & Sons, Inc.
Hydrodynamic properties of model 3‐miktoarm star copolymers
Authors: Iatrou Hermis , Siakali‐Kioulafa E. , Hadjichristidis Nikos , Roovers Jacques , Mays Jimmy 
Published: April 2003

AbstractThe synthesis of well‐defined, nearly monodispersed, 3‐miktoarm (from the greek word μlkτós meaning mixed) star copolymer of the A2B type is described. A and B is either polystyrene (PS), polybutadiene (PBd), or polyisoprene (PI). The sequential controlled addition of living anionic B and A chains to methyltrichlorosilane leads to narrow molecular weight distribution miktoarm star copolymers with homogeneous composition. Characterization was carried out by size exclusion chromatography, low‐angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, nuclear magnetic resonance and ultraviolet spectroscopy. Analysis of [η], RH and Rv of the A2B and one A2B2 miktoarm copolymers, suggests that a small expansion of the copolymer occurs either in a good solvent for both species or in a Θ solvent for one of them, as compared with the corresponding star homopolymers. This is in contrast to results obtained on linear block copolymers, and is due to the increased occurrence of heterocontacts in the miktoarm starshaped architecture. © 1995 John Wiley & Sons, Inc.
Scanning force microscopy and effective medium theory study of free‐standing polyaniline thin films
Authors: Porter T. L. , Minore D. , Stein R. , Myrann M. 
Published: April 2003

AbstractThe technique of scanning force microscopy was used to study the nanometer‐scale structure of NMP cast films of polyaniline. Noncontact mode images provide direct evidence that polyaniline prepared in this form is a granular conductor. The films were found to consist of micrograins whose size and density were determined by the pH of the acid solution used to protonate the films. At pH 7, the polyaniline films exhibited a mostly disordered structure, with small 2–10 nm particles visible. Protonation at pH 5 to pH 3 resulted in partial agglomeration of the primary particles into larger bundles, with sizes up to 75 nm. Treatment in solution pHs of 2 or less resulted in films consisting of close‐packed bundles of dimension 20–30 nm. The conductivity of the films exhibited a sharp rise beginning with protonation at pH 2 or less. Effective medium theory (EMT), was used to model the macroscopic conductivity of these films based on the SPM measured microscopic film structure. Using the size and size distribution of polymer micrograins or bundles in a modified EMT, we are able to obtain predicted conductivities that are close to the measured values for these films. © 1995 John Wiley & Sons, Inc.
Correlations between gas permeation and free‐volume hole properties probed by positron annihilation spectroscopy
Authors: Jean Y. C. , Yuan J.‐P. , Liu J. , Deng Q. , Yang Hsinjin 
Published: April 2003

AbstractFree‐volume hole sizes, fractions, and distributions in a series of polycarbonate‐based polymers are measured by using positron annihilation lifetime (PAL) spectroscopy. Correlations between the obtained free‐volume hole properties and gas diffusion coefficients are observed. © 1995 John Wiley & Sons, Inc.
Physical aging of a polyetherimide: Creep and DSC measurements
Authors: Echeverria Isabel , Su Ping‐Chung , Simon Sindee L. , Plazek Donald J. 
Published: April 2003

AbstractCreep and differential scanning calorimetry (DSC) measurements have been used to study the physical aging behavior of a polyetherimide. Isothermal aging temperatures ranged from 160°C to Tg with aging times ranging from 10 min to 8 days. The only measurable effect of physical aging on the short‐time creep curves is a shift of the creep compliance to longer times. Andrade plots of the compliance versus the cube root of time are linear at short times with the slope β decreasing with increasing aging time to a constant value once equilibrium is reached. Log β3 is related directly to the degree to which the creep curves shift to longer times with physical aging, and is used in this work as a measure of physical aging. A reduced curve of log β3 versus log aging time is obtained for the aging temperatures investigated by appropriate vertical and horizontal shifts. The enthalpy change during aging increases linearly with the logarithm of the aging time, ta, leveling off at equilibrium at values which increase with decreasing aging temperature. Hence, both nonequilibrium and equilibrium temperature shift factors can be calculated from the DSC data. Good agreement is observed between the equilibrium temperature shift factors obtained from the creep and DSC data. The temperature dependence of the nonequilibrium temperature shift factors is found to be an order of magnitude smaller than that of the equilibrium shift factors. The time scales to reach equilibrium for enthalpy and for mechanical measurements are found to be the same within experimental error. © 1995 John Wiley & Sons, Inc.