bluuebunny/crossref_metadata_2025_split huggingface dataset:
Instabilities of the deformation process in cold drawing of poly(ethylene terephthalate) and other polymers
Authors: Pakula T. , Fischer E. W. 
Published: April 2003

AbstractThe relationship between drawing rate and drawing stress was studied for amorphous poly(ethylene terephthalate) (PET) under various experimental conditions. Three types of expriments were performed: simple drawing with necking at constant rate, drawing through a conical die, and drawing at constant stress. Under constant stress conditions a transition between two stable regimes of drawing can be observed. The transition occurs at a critical stress σc at which the rate of neck propagation changes by some orders of magnitude. Such a transition was found both below and above the glass transition of PET. With constant drawing rates instabilities of neck propagation were observed under certain experimental conditions. Such self‐oscillations, described by other authors, are not due to heat effects as has been proposed, but are related to the existence of the critical stres σc.Stress‐induced transitions in deformation behavior as in PET were observed for polypropylene and nylon 6 but not for polycarbonate. The results obtained by various methods including morphological studies do not support the assumption that the instabilities are caused by thermal effects due to the dissipation of deformation energy. Rather, a model is proposed which is based on the existence of a “spinodal transition” from the isotropic into the highly oriented state.
Accordion‐type laser‐Raman scattering by drawn linear polyethylene
Authors: Peterlin Anton , Snyder Robert G. 
Published: April 2003

AbstractOne can reproduce the observed accordion‐type laser‐Raman (ALR) scattering of highly drawn linear polyethylene if one assums that any gauche defect in the crystal lattice which interrupts the all‐trans conformation sequence of the molecular chain completely decouples the accordion‐type longitudinal oscillations of the two sections on both sides of the defect. Each oscillates independently of the rest. The length of the section, smaller than the full length of the straight chain between the crystal surfaces, determines the frequency of the ALR absorption. One such defect per five chain stems of the ideal crystal yields a straight‐length distribution which agrees sufficiently well with that derived from the ALR spectrum. Small‐angle x‐ray scattering very generally registers the resulting decrease of the electron density of the crystalline component without yielding more detailed information about the location and frequency of such gauche defects.
Stress relaxation and dynamic viscoelastic properties of end‐linked poly(dimethyl siloxane) networks containing unattached poly(dimethyl siloxane)
Authors: Granick Steve , Pedersen Sven , Nelb Gary W. , Ferry John D. , Macosko Christopher W. 
Published: April 2003

AbstractStress relaxation in uniaxial extension and dynamic shear moduli G′ and G″ have been studied in networks of vinyl‐terminated poly(dimethyl siloxane) (PDMS) of five different molecular weights (Mn from 1800 to 29,200) crosslinked with cis‐dichlorobis (diethyl sulfide) platinum (II) and containing 10 and 15 wt % of two samples of high‐molecular‐weight unattached linear hydroxyl‐terminated PDMS (Mw 700,000 and 950,000). The Mw/Mn ratio of both the network prepolymers and the unattached linear species was approximately 2. In stress relaxation the stretch ratio was 1.25 or less and the shear relaxation modulus was calculated from the neo‐Hookean stress‐strain relation. In the dynamic measurements, the strain amplitude was 15% or less; after conversion to the timedependent shear relaxation modulus G(t) the two sets of measurements were combined and the contribution of the unattached species G1(t) was calculated by difference. After multiplication by (1 − v)−1G/Ge, where v2 is the volume fraction of network, G is the plateau modulus of the uncrosslinked polymer, and Ge is the equilibrium modulus of the network containing unattached molecules, G1(t) was compared with G11(t), the relaxation modulus was essentially the same in both environments. The relaxation was slower in the networks than in the uncrosslinked polymer by 1 to 2 orders of magnitude, and it increased gradually with increasing Ge, which is a measure of total to pological obstacles represented by crosslinks plus trapped entanglements. A similar but less striking difference between relaxation in a network and in the homologous environment of a linear polymer was previously observed in end‐linked polybutadiene networks and the butadiene phase of a styrene‐butadiene‐styrene block copolymer. It appears that, in these systems where the topology of the obstacles is fixed, the reptation is severely restricted or else alternative modes of configurational rearrangement which contribute to relaxation in the uncrosslinked polymer are suppressed.
Hypersonic relaxation in polybutadiene and polyisoprene
Authors: Jarry J.‐P. , Patterson G. D. 
Published: April 2003

AbstractBrillouin scattering is used to study hypersonic relaxation in 1,2‐polybutadiene and cis‐polyisoprene. The temperature of maximum loss was determined to be 125°C for a frequency of 5.0 GHz for polybutadiene and 100°C at a frequency of 5.9 GHz for polyisoprene. Hypersonic loss maxima are examined for many polymers and general conclusions are reached concerning the factors that can be used to predict the temperature of maximum loss.
Crystalline stoichiometric adducts of polyamides with phosphoric acid
Authors: Aharoni Shaul M. 
Published: April 2003

AbstractIt is shown the crystalline stoichiometric adducts of phosphoric acid with polyamides such as nylon 6 and poly‐p‐benzamide, and probably nylon 66, nylon 69, nylon 11, and nylon 12, can be prepared. These adducts are characterized by their unique wide‐angle x‐ray diffraction patterns and by rather low melting or decomposition temperatures. The thermal behavior and infrared data, indicate that interactions between the acid and the polymeric amide residues are weak.
Orientation and morphology of high‐density polyethylene film produced by the tubular blowing method and its relationship to process conditions
Authors: Choi Kyung‐Ju , Spruiell Joseph E. , White James L. 
Published: April 2003

AbstractThe orientation and crystallinity of a series of high‐density polyethylene (HDPE) tubular films is characterized using wide‐angle x‐ray scattering pole‐figure analysis and birefringence. The films ranged from uniaxial to equal biaxial. The data were used to compute biaxial orientation factors which were then plotted on an orientation‐factor triangle diagram. It was shown, within the range of conditions studied, that both the crystalline biaxial orientation factors were unique functions of the stresses exerted on the bubble at the freeze line. Both correlations are the same as those developed by Dees and Spruiell for melt‐spun HDPE fibers. SAXS measurements on the films suggest lamellar structures in both uniaxial and biaxial films.
Effect of glass filler size on the tensile properties and tear strength of polybutadiene
Authors: Eckstein Y. , Dreyfuss P. 
Published: April 2003

AbstractAn experimental study of the tensile properties, tear strength, hysteresis, and swelling ratio of model composite elastomeric compounds consisting of polybutadiene filled with glass beads has been carried out as a function of the size of the beads. The diameter of the beads ranged from 25 to 1000 μm and the volume fractions examined were 0.16, 0.092, and 0.048. Mechanical properties of the filled elastomers were functions of the loading (separation distance), the particle size (surface area/volume), and the elastomer‐filler systems studied.
Miscibility of polycaprolactone/chlorinated polyethylene blends
Authors: Bélorgey Georges , Prud'Homme Robert E. 
Published: April 2003

AbstractBlends of polycaprolactone (PCL) with chlorinated polyethylenes (PECls) having chlorine contents of 25, 30, 36, 42, and 48% by weight were prepared and studied by differential scanning calorimetry and small‐angle light scattering (SALS). It was found that blends made with PECls containing 30% or more chlorine are completely miscible with PCL (a single glass transition temperature Tg is found) while the PCL/PECl(25) blends are immiscible. PCL crystallizes in the miscible blends at any composition and it has an enthalpy of fusion which decreases only slightly with PECl content. Blends in the PECl composition interval of 0–80% are spherulitic, as shown by SALS, but a rodlike morphology is found at the 85% composition and dispersed crystals are observed at higher compositions. It is suggested that the k parameter of the Gordon‐Taylor equation can be taken as a measure of the strength of the specific interaction between PCL and PECl. Low values of k (0.26 and 0.35) are found for PCL/PECl blends but a higher value of k (0.51) has been reported for PCL/poly(vinyl chloride) (PVC) blends, indicating a stronger interaction in the latter mixtures. In agreement with these findings poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone) and poly(valerolactone) are not miscible with PECl, whereas they were previously shown to be miscible with PVC.
Dynamic bulk and shear relaxation in glassy polymers. I. Experimental techniques and results on PMMA
Authors: Yee A. F. , Takemori M. T. 
Published: April 2003

AbstractIn this paper the authors describe in detail the experimental techniques for the simultaneous measurement of the dynamic Young's modulus and the dynamic Poisson's ratio, from which the dynamic bulk and shear moduli can be calculated. Experimental results are presented on the effects of temperature, frequency, and tensile strain on these properties of poly(methyl methacrylate) (PMMA). The temperature and frequency effects indicate that the β relaxation in PMMA is not a purely internal motion but is coupled to the bulk.
Comparison between neutron and quasielastic light scattering by polyacrylamide gels
Authors: Geissler E. , Hecht A. M. , Duplessix R. 
Published: April 2003

AbstractThe authors describe small‐angle neutron scattering measurements of the screening length ζ in polyacrylamide‐water gels. Although these are inhomogeneous systems, the screening length is clearly observable and is in good numerical agreement with the relation E = 3kT/4πζ3, where E is the longitudinal elastic modulus of the gel obtained from measurements of the intensity of qu‐asielastically scattered light. Static light scattering observations reveal a larger‐scale (ca. 30 nm) superstructure in the gel.
Influence of the conformation of polyethylene on wide‐angle neutron scattering patterns
Authors: Stamm M. 
Published: April 2003

AbstractWide‐angle neutron scattering investigations of mixtures of deuterated and nondeuterated chains are well suited to detect sequences of regular adjacent reentry folding of a polymer chain in particular crystallographic directions. It is shown that the diffuse neutron scattering intensity is peaked at large scattering angles for (100) and (010) folding, whereas (110) folding is difficult to detect. Detailed calculations indicate that the position, intensity, and half‐width of the diffuse peak depend strongly on the mode of folding as well as on the number of adjacent stems. By a comparison with experimental data adjacent reentry folding in (100) and (010) crystallographic planes with more than five adjacent stems can be excluded. The implications for other folding models containing regular folded chain sequences are discussed.
Mechanical and transport properties of drawn crosslinked low‐density polyethylene
Authors: DeCandia F. , Russo R. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractThe values of drawing dependence of the density ρ, axial elastic modulus E, and maximum draw ratio λ of crosslinked low‐density polyethylene (CLPE) rather similar to those obtained with un‐crosslinked branched material of similarly low density. Very much the same applies to the equilibrium concentration of sorbed methylene chloride in the amorphous component and the zero‐concentration diffusion coefficient D0. The exponential concentration coefficient γD, however, even at the maximum draw ratio, shows no indication of the rapid increase so characteristic of the completed transformation from the lamellar to the fibrous structure. On the basis of this finding, one can understand the small deviations in the dependence of the mechanical properties between the crosslinked and uncrosslinked branched material. The segments between the crosslinks, much shorter than the free molecules, favor the formation of the interfibrillar tie molecules that limit the drawability of the sample. But since they cannot be extended to the same length as the free molecules, they contribute less to the total fraction of tie molecules per amorphous layer and hence yield a smaller axial elastic modulus.
Fractionation in mixtures of polyethylene oxide fractions during crystallization
Authors: Prud'Homme Robert E. 
Published: April 2003

AbstractTwo narrow‐molecular‐weight‐fraction polyethylene oxides were mixed and studied by differential scanning calorimetry (DSC), small‐angle x‐ray scattering (SAXR), microscopy, and small‐angle light scattering (SALS). DSC measurements indicate the presence of two melting points at each composition, leading to a eutectic diagram with a eutectic point located close to the axis of the constituent with the lower molecular weight. The depression in melting point of the higher‐molecular‐weight component allows the calculation of a thermodynamic interaction parameter of −0.09 between the two fractions, indicating that they are miscible in the melt despite the fractionation process occurring during crystallization. Two SAXR long periods are also observed at each composition, indicating phase separation during crystallization. These two phases are included into large spherulites, the structure of which depends mainly upon the crystallization characteristics of the higher‐molecular‐weight component. The other component must then crystallize between the spherulite lamellae. Finally, small spherulites of the order of the micron are observed from the SALS patterns inside the large spherulites (of the order of one millimeter as seen by microscopy). The two polyethylene oxide fractions give rise to different size SALS spherulites and both types of spherulites are present in the mixtures.
The energetics of the epitaxial deposition of polyethylene onto the basal plane (0001) of graphite
Authors: Baukema P. R. , Hopfinger A. J. 
Published: April 2003

AbstractPolymer‐substrate interaction energetics have been determined in order to describe the epitaxial deposition of polyethylene into graphite. The potential energy was calculated using van der Waal's interactions. A closed‐form representation of the potential was derived for a substrate which was considered infinite in planar area. Inspection of the relative polymer‐substrate energies for various positions above the substrate indicate a planar‐zigzag polyethylene chain segment deposits with its backbone parallel to the substrate. The chain axis preferentially orients in the (1120) directions of the graphite surface layer. Specifically, deposition occurs along the lines which intersect the nearest‐neighbor midpoints of the CC bonds in the surface layer.
Oscillatory shear flow of polymeric systems
Authors: Isayev A. I. , Hieber C. A. 
Published: April 2003

AbstractOn the basis of the Leonov viscoelastic constitutive equation, oscillatory shear flow of elastic fluids in the linear and nonlinear regimes has been considered. The Fourier components and associated phase angles of the shear and normal components of the elastic strain tensor have been found as functions of frequency and deformation amplitude in the range usually employed in experiment, and are presented in a form convenient for further rheological applications. In the linear case, the results correspond to many known theories. In the nonlinear case, the theoretical results have been compared with experiments, on different polymeric systems, with very good agreement being obtained for the shear stress in polymeric solutions but only qualitative agreement for the shear stress and first normal‐stress difference in polymer melts.
Structure‐property behavior of films containing disk spherulites: A model study
Authors: Mohajer Y. , Wilkes G. L. 
Published: April 2003

AbstractThin films of a polyester of lactic and glycolic acid were prepared to give controlled amounts of disk spherulites. The spherulite contents ranged from zero to 100% and were accurately measured. The stress‐strain properties of the films were then determined at 60°C, i.e., about 20°C above the glass transition temperature Tg. The mechanical behavior varied quite systematically with spherulite content and displayed little dependence on spherulite size. It was found that much of the mechanical data could be reasonably well described by a simple composite model. In addition, the yield strain as well as the strain to break could be principally coupled to the deformation of only the amorphous phase. SEM and optical microscopy studies supported the above conclusion, also demonstrating that the isolated spherulites adhered well to the amorphous matrix and behaved as stress concentrators in the system when the deformation temperature was above Tg.
Spectroscopic study of rigid‐rod polymers. II. Protonation effect
Authors: Shen D. Y. , Venkatesh G. M. , Burchell D. J. , Shu P. H. C. , Hsu S. L. 
Published: April 2003

AbstractThe protonation of a heterocyclic rigid‐rod polymer poly(p‐phenylene benzbisthiazole) and its model compound has been studied by UV‐visible and Raman spectroscopy. Because of the two nitrogens on the heterocyclic ring, spectroscopic features of unprotonated, half‐protonated, and fully protonated structures have been identified. For the fully protonated molecule, there is also an increase in conjugation between the phenyl ring and the heterocyclic ring.
Small‐angle neutron scattering from two‐phase polymeric systems
Authors: Koberstein Jeffrey T. 
Published: April 2003

AbstractA small‐angle neutron scattering method is presented for the determination of single‐chain scattering functions in heterogeneous two‐phase polymeric materials such as incompatible polymer blends and microphase‐separated diblock copolymers. Development of the method makes use of both the discrete and continuum approaches to scattering theory. In this fashion it is shown that extraction of the single‐chain scattering function requires only two experimental observations, regardless of the compressibility of the system. These experiments consist of small‐angle neutron scattering profiles from two samples: an unlabeled two‐phase material and a similar two‐phase material in which a portion of the molecules in one phase have been replaced by molecules which are contrast labeled by isotopic deuterium substitution. Anticipated difficulties associated with actual application of the procedure and requirements of the necessary experimental samples are discussed.
Möussbauer spectroscopy of nafion polymer membranes exchanged with Fe2+, Fe3+, and Eu3+
Authors: Rodmacq B. , Pineri M. , Coey J. M. D. , Meagher A. 
Published: April 2003

AbstractMössbauer spectra of “Nafion” perfluoronated acid membranes exchanged with iron or europium have been studied as a function of ion concentration, water content, temperature, and applied magnetic field in order to characterize the ionic phase in these materials. In every sample, the recoil‐free fraction falls to zero at a temperature which decreases from 280 to 220 K with increasing water content. The sudden fall in recoil‐free fraction corresponds to a glass transition in the ionic phase rather than its melting point. In Fe2+ Nafion, the spectrum is independent of water content above 6 wt%, and is typical of fully hydrated, isolated Fe2+(H2O)6 species. The isomer shift, quadrupole splitting, and linewidth all change continuously below 6 wt % water, indicating a range of environments for the iron. For Fe3+ Nafion, ions in several distinct environments can be identified on the basis of their magnetic properties. Isolated Fe3+ species (Fe–Fe distances greater than 12 Å) showing paramagnetic hyperfine structure in their 4.2‐K spectra predominate in slightly neutralized samples, and in those with high water content. The proportion of dimers, whose quadrupole splitting is about 1.7 mm/s, increases with increasing iron content or decreasing water content. A third component of the spectra has a quadrupole splitting of 0.4 mm/s. It is associated with paramagnetic iron having other iron ions in the neighborhood, and also with iron ions located in the interior of small groups or chains formed from dimers. There is no iron belonging to magnetically ordered clusters involving hundreds of ferric ions of the type found in some other ionomers. All the exchanged ions belong to the ionic phase, and none are associated with the polymer backbone.
An analysis of the β transition of linear and branched polyethylenes by carbon‐13 NMR
Authors: Dechter J. J. , Axelson D. E. , Dekmezian A. , Glotin M. , Mandelkern L. 
Published: April 2003

AbstractCarbon‐13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of branched polyethylenes whose β transition temperatures were determined independently. Resolvable spectra could be obtained at temperatures either corresponding to or very close to the temperature of the β transition. Together with results for other systems, these observations preclude the indentification of the β transition with the glass temperature. From the measured spin relaxation times and nuclear Overhauser enhancements average correlation times were calculated as a function of temperature. The average correlation times were calculated as a function of temperature. The average correlation time is on the order of 10−8−10−9 s at the β transition. These results argue strongly against it being assigned to the glass temperature.
The use of chemical contrast in the SEM analysis of polymer blends
Authors: Hobbs S. Y. , Watkins V. H. 
Published: April 2003

AbstractA novel method for investigating the morphology of multiphase polymers is discussed. In this procedure, inherent differences in secondary and backscattered electron emission from the various components rather than topographical variations are used to produce image contrast. The combined use of various selective stains and energy‐dispersive x‐ray analysis to accentuate and positively identify individual phases is discussed. The effects of coating thickness and type and changes in accelerating voltage on image quality are also described.