bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn, ultrahigh‐molecular‐weight polyethylene cast from solution. II. Drawability and mechanical properties
Authors: Bao Liu Liang , Murakami Noriko , Sumita Masao , Miyasaka Keizo 
Published: April 2003

AbstractThe effect of molecular weight distribution (MWD) on the ultradrawability and mechanical properties of solution‐cast films of ultrahigh‐molecular‐weight polyethylene (UHMW‐PE) has been investigated using tensile and dynamic mechanical measurements. The MWD has a marked effect on ultradrawability and thus on the ultimate mechanical properties such as the tensile modulus. It is proposed that UHMW‐PE with a narrow MWD(N‐PE) attains the ultimate structure at a lower draw ratio than UHMW‐PE with a broad MWD(B‐PE) because of the existence in the latter of less fully extended intercrystalline tie chains. It is found that, at the same drawing temperature (100°C), N‐PE shows a higher modulus than B‐PE at draw ratios up to 150 x, which is assumed to be the ultimate value for N‐PE.
Role of orientation in kinetics of nucleation and growth of crystals in polymers
Authors: Desai Prashant , Abhiraman A. S. 
Published: April 2003

AbstractA theoretical framework is provided for generalizing the inferences drawn from the results of earlier experimental studies of kinetics of crystallization in oriented poly(ethylene terephthalate). The framework is obtained by combining extensions of classical nucleation theories in polymers3,4 and a theory of crystal growth with anisotropic incorporation of segments into growing crystals.15 It is shown that, while a very strong dependence of rate of primary nucleation on orientation does exist, there is a only a much weaker dependence of rate of crystal growth on the orientation of the crystallizing polymer. The theoretical formulation provided here would allow qualitative estimates for comparison with experiments.
Coagulation studies for cellulose in the ammonia/ammonium thiocyanate (NH3/NH4SCN) direct solvent system
Authors: Liu Cheng‐kung , Cuculo John A. , Smith Brent 
Published: April 2003

AbstractAn extensive study of the coagulation of cellulose from cellulose/ammonia/ammonium thiocyanate solutions is presented. The effect of major variables upon the coagulation process for cellulose solutions is reported. Microscopic observations of the moving boundary associated with the coagulation were performed on gelled cellulose solutions to determine the coagulation rate as a function of molecular volumes of coagulant, bath temperatures, bath compositions, and cellulose concentrations. The data were analyzed by means of a one‐dimensional linear diffusion model based on Fick's law, thereby depicting the mechanism of the coagulation process, and obtaining the diffusion coefficients of mobile components involved in the coagulation.
The hard‐sphere model for linear and regular star polybutadienes
Authors: Roovers J. , Martin J. E. 
Published: April 2003

AbstractThe dilute solution properties of linear, 18‐arm, and 270‐arm star polybutadienes have been studied in a theta solvent and in a good solvent. Values of the radius of gyration RG, the second virial coefficient A2, the intrinsic viscosity [η], and the diffusion coefficient D0 have been measured for each polymer. The ratios RT/RG, RV/RG, and RH/RG for each type of polymer are used to compare the four dilute solution properties. RT is termed the “thermodynamic radius.” It is the radius of the hard sphere with the same excluded volume as the polymer coil. RT is calculated from A2 by RT = (3A2M2/16ηNA)1/3. RV and RH are equivalent hard spheres defined for the intrinsic viscosity and translational diffusion coefficient, respectively. RT/RG, RV/RG, and RH/RG increase from about 0.7 for linear polymer coils as the number of arms in the star increases. Values of the ratios for the 18‐arm stars are less than the value for the hard‐sphere, but the values of the ratios of the 270‐arm stars are equal to the hard‐sphere limit within experimental error.
Adhesion through molecular entanglements in polymer interfaces
Authors: Raghava Ram S. , Smith Ronald W. 
Published: April 2003

AbstractThis paper examines the role of polymer interdiffusion or interpenetration along and across a boundary of two compatible but dissimilar polymers in controlling interfacial adhesion in the interface region (interphase). The effect of interphase adhesion on the mechanical properties as well as the deformation and fracture behavior of sandwich laminates of poly(methylmethacrylate) (PMMA) and poly(vinylidene) fluoride (PVF2) have been studied. The interphase has been characterized using microscopy (optical, transmission, and scanning electron), dynamic mechanical spectroscopy, and x‐ray microanalysis. Conditions of multiple crazing/fracture in the brittle phase (PMMA) and shear yielding in the ductile phase (PVF2) are discussed. Scanning electron micrographs confirm these deformation modes in PMMA‐PVF2 sandwich composite laminates.
Miscibility of poly(ethylene oxide) with poly(N‐vinyl pyrrolidone): DMTA and DTA studies
Authors: Cesteros Luis C. , Quintana JosÉ R. , Fernández JosÉ A. , Katime Issa A. 
Published: April 2003

AbstractDynamic mechanical thermal analysis and calorimetric studies are reported on blends of poly(ethylene oxide) (PEO) with poly(N‐vinyl pyrrolidone) (PVP) between 80% and 40% PEO. DMTA curves show a peak corresponding to a phase of pure PEO and another peak which can be attributed to blended material. The calorimetric analysis shows an appreciable melting point depression and a marked decrease in the crystallization rate as the PVP content increases. The melting point depression follows the Nishi‐Wang equation, giving an interaction parameter of −0.50. These studies suggest the existence of microphases in the blend.
Cold crystallization and thermal shrinkage of uniaxially drawn poly(ethylene 2,6‐naphthalate) by solid‐state coextrusion
Authors: Ghanem Antoine Michel , Porter Roger S. 
Published: April 2003

AbstractSolid‐state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6‐naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature Tg. The onset of cold crystallization (Tc) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that Tc decreases markedly on draw, as much as 95°C, and, at constant draw ratio Tc goes through a minimum in the Tg region. For undrawn PEN, annealing below 153°C has no significant effect on Tc. To evaluate the crystallization rate constant (k) and the activation energy (Ea) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and Ea goes down over threefold compared with the undrawn polymer. At high ET, strain‐induced crystallization has also been shown to play an important role in lowering Ea for cold crystallization. Thermal shrinkage above Tm indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid‐state coextrusion.
Effects of fiber orientation on the stress distribution in model composites
Authors: Fan Cun F. , Hsu Shaw L. 
Published: April 2003

AbstractA Raman‐mechanical technique was used to study the relationship between stress distribution and fiber orientation in model composites. Our experimental data generally were consistent with most simplistic mechanical models. A more complete analysis, using the Eshelby equivalent inclusion method, fitted our experimental data exceptionally well. For large applied strains, compressive failure occurred for fibers which were oriented at high angles relative to the draw direction. This occurred because of the lateral shrinkage associated with the matrix when the sample was stretched. The effect of fiber end geometry on the stress distribution for these misaligned fibers was the same as observed earlier. Tapered‐end fibers generally carried loads more efficiently in composites than blunt‐end fibers.
Dielectric properties of complex zn(II) salts of ethylene‐methacrylic acid copolymer with n‐hexylamine
Authors: Yano Shinichi , Yamamoto Hitoshi , Tadano Kenji , Hirasawa Eisaku 
Published: April 2003

AbstractThis article describes dielectric properties of complex Zn(II) salts of ethylene‐methacrylic acid copolymer (5.4 mol% methacrylic acid) with n‐hexylamine. In all samples, the β′ relaxation near 340 K and γ relaxation near 170 K are observed. These are assigned, respectively, to micro‐Brownian molecular motion of long segments above Tg and to local molecular motion of short segments below Tg. The dielectric results indicate that ionic clusters are not formed in these systems.
Tracing the spontaneous mixing and mobility of miscible polymer blends using differential scanning calorimetry [Cellulose acetate‐poly(styrenephosphonate ester)]
Authors: Sun J. , Frisch H. L. , Cabasso I. 
Published: April 2003

AbstractA method in which the dissolution of a miscible polymer pair is traced in a differential scanning calorimetry cell is described. The polymer blend is initially prepared as an heterogeneous system with microdomains of one component embedded in the continuous matrix of the second polymer. Annealing the system in the DSC cell above the glass‐transition temperature causes a spontaneous mixing of the polymer pair which can be observed by the progressive shift of the Tgs of both components until they merge. The time scale for dissolution and aspects of mass‐transport phenomenon are thus determined for the specific blend, cellulose acetate‐poly(styronephosphonate ester). Rather sharp progressive shifts of the Tgs are shown to prevail without significant broadening of the transition curve (ΔTg). Mass‐transport analyses supported by electron microscopy observation of the blend, before and after annealing, suggest that the domain sizes remain nearly unchanged and the physicochemical makeup of the phase boundary interfaces determines the time scale of dissolution in the system. A model from which mean‐value diffusion coefficients are calculated for both components at different annealing temperatures is reported.
Halato‐telechelic polymers. XIV. Solution behavior of α, ω‐divalent transition metal dicarboxylato polybutadiene
Authors: Horrion J. , Jérôme R. , Teyssié Ph. 
Published: April 2003

AbstractA procedure is described which allows α,ω‐dicarboxylic acid polybutadiene to be end‐neutralized using a stoichiometric amount of a transition metal acetate. In a nonpolar solvent, the solution viscosity of this new class of carboxylato telechelic polymers depends on the neutralization degree of the acid end groups in such a way that the progress of the neutralization may be compared with that of a polycondensation reaction. In contrast to Cu(II), the Zn, Ni, Co, and Mn carboxylate endgroups promote very early gelation of toluene solutions when the polymer concentration increases. The particular behavior of Cu(II) can only be explained by a difference in the coordination number compared with the other elements of the first transition series. The dependence of the solution viscosity on the atomic number of the element cannot be completely accounted for so far. Nevertheless, an electrostatic association of the cupric carboxylate end groups can be disregarded, since the solution viscosity is independent of the polarity of the solvent in the range of 2.28–7.28 D.
Kinetically stable structures in the nonlinear theory of spinodal decomposition
Authors: Mitlin V. S. , Manevich L. I. 
Published: April 2003

AbstractA nonlinear diffusion equation is used to study the spinodal decomposition of binary polymer mixtures. The structure of steady‐state solutions is analyzed. The free energy of the system for the solutions is shown to be a nonincreasing time function. The solution with the minimum free energy is the only stable solution and corresponds to complete phase separation in the system. A numerical analysis shows that transition to complete equilibrium takes place through a succession of fast concentration structure changes interspersed by periods in which the process is abruptly showed down. The free energy of the system is almost constant in the kinetically stable periods. All these facts indicate a relaxation process of an absolutely new type. Slow variables are introduced to describe the spinodal decomposition in macroscopic regions. These variables govern the spatial transformation of the forms and sizes of microphases. The perturbation theory is used to derive the equations for slow variables. The final relations of the simplest type give an exponential time dependence of the average size of a microphase. The problem of a contact of two pure components that are not compatible in the entire composition range is set.
Raman longitudinal acoustic mode (LAM) studies of folded‐chain morphology in poly(ethylene oxide) (PEO). I. Normal mode analysis of LAM of a helical‐chain oligomer of PEO
Authors: Song Kigook , Krimm Samuel 
Published: April 2003

AbstractNormal mode analyses were done for the exact structures of model oligomers of PEO to investigate the longitudinal acoustic mode (LAM) in this helical polymer. It quickly became apparent that it is impossible to reproduce observed LAM frequencies without incorporating explicit interchain interactions. We have developed a force field that includes interchain interactions through an atom‐atom potential and have shown that this force field reproduces very well the observed LAM frequencies of helical‐chain oligomers of PEO. This result indicates that the LAM of helical chains is much more sensitive to intermolecular interactions than that of planar zigzag chains.
Raman longitudinal acoustic mode (LAM) studies of folded‐chain morphology in poly(ethylene oxide) (PEO). II. Normal mode analysis of folded‐chain structures of PEO
Authors: Song Kigook , Krimm Samuel 
Published: April 2003

AbstractNormal mode calculations were carried out on model folded‐chain molecules to determine the effect of a fold on the LAM of PEO. The presence of a chain fold results in a decrease in the LAM frequency and intensity, the change in frequency being very much smaller than the change in intensity. End interactions do not seem to have much effect on the LAM when a fold is present at the chain ends. The effective chain length for determining the LAM frequency was found to be that part of the chain experiencing interchain interactions.
Relaxations of thermosets. III. Sub‐Tg dielectric relaxations of bisphenol‐A–based epoxide cured with different cross‐linking agents
Authors: Mangion M. B. M. , Johari G. P. 
Published: April 2003

AbstractThe sub‐Tg relaxations of bisphenol‐A–based thermosets cured with diaminodiphenyl methane and diaminodiphenyl sulfone have been studied by dielectric measurements over the frequency range 12 Hz to 200 kHz from their ungelled or “least” cured states to their fully cured states. Both thermosets show two relaxation processes, γ and β, as the temperature is increased toward their Tgs. In the ungelled states, the γ process is more prominent than the β process. As curing proceeds, the strength of the γ process decreases and reaches a limiting value, while that of the β process initially increases, reaches a maximum value, and then decreases. An increase in the chain iength and the number of crosslinks increases the number of ‐OH dipoles and/or degree of their motions in local regions of the network matrix. This is partly caused by the decreasing efficiency of segmental packing as the curing proceeds. The sub‐Tg relaxations become increasingly more, separated from the α relaxation during curing. Physical aging causes a decrease in the strength of the β relaxation of the thermosets as a result of the collapse of loosely packed regions of low cross‐linking density, and this decrease competes against an increase caused by further crosslinking during the “post‐cure” process.
Scaling tests of late stages of spinodal decomposition in PC/PMMA blends
Authors: Kyu Thein , Saldanha Jeanne M. 
Published: April 2003

AbstractTime‐resolved light scattering studies were undertaken to elucidate the kinetics of phase separation in polycarbonate (PC)/polymethyl methacrylate (PMMA) blends. The 40:60 PC/PMMA blend undergoes thermally induced phase separation through spinodal decomposition. Temperature jump experiments were carried out from a single‐phase to a two‐phase temperature region. The general trend of spinodal decomposition in this blend system is nonlinear in character and obeys the power laws. The time evolution of scattering curves was analyzed in accordance with dynamical scaling laws for self‐similarity and the shape of scaled structure functions.
Permeation of pure carbon dioxide and methane and binary mixtures through cellulose acetate membranes
Authors: Sada E. , Kumazawa H. , Xu P. , Wang S.‐T. 
Published: April 2003

AbstractSteady‐state permeation rates for pure CO2 and CH4 and their binary mixtures through homogeneous dense cellulose triacetate membranes have been measured at three temperatures between 20 and 40°C and pressures up to 2.8 MPa. The pressure dependence of the mean permeability coefficient for CO2 can be described by the total immobilization model in conjunction with a modified free‐volume model. No appreciable pressure dependence of the permeability coefficient for CH4 is observed, while the permeability coefficients for CH4 in binary mixture of CO2 and CH4 depend on applied gas pressure. The pressure dependences of the mean permeability coefficients for the components in the binary mixture are discussed in terms of the above mobility model. Membrane plasticization induced by CO2 affects permeation by both gases.
Thermal response and structure of PET fibers
Authors: Hristov H. A. , Schultz J. M. 
Published: April 2003

AbstractThe structure and the thermal response of polyethylene terephthalate (PET) fibers, melt‐spun at speeds of 3 to 6 km/min, are investigated in the temperature region 0–200'C. Differential scanning calorimetry thermograms, and radial distribution functions from wide‐angle x‐ray scattering are used. Interpretation of multiple glass transition and crystallization peaks and of the range of structural coherence is interpreted in terms of a nonhomogeneous molecular arrangement for fibers melt‐spun at intermediate spinning speeds. A three‐phase model of the molecular structure of these fibers is used to explain the results. An important feature of the model is the existence of a threadlike, interconnected, highly oriented noncrystalline phase, coexisting with a more unoriented amorphous phase. The model can qualitatively explain a number of experimental observations.
Phase dominance, multiple glass transitions, and apparent activation energies in some poly (styrene‐co‐alkali methacrylate) ionomers
Authors: Hird B. , Eisenberg A. 
Published: April 2003

AbstractThe high‐temperature dispersions occurring in some poly (styrene‐co‐alkali methacrylate) ionomers are investigated by dynamic mechanical thermal analysis as a function of ion content. The heights and areas of the loss modulus peaks associated with these dispersions suggest that the ionic “cluster” phase becomes the dominant and perhaps even continuous phase above an ion concentration of ca. 6 mol %. Apparent activation energies of these high‐temperature transitions support the phase‐separated cluster model and indicate that the dispersions are true glass transitions.
An optical study of phase transitions of poly (ethylene terephthalate‐co‐p‐hydroxybenzoic acid) liquid crystal
Authors: Sun Tong , Bhattacharya Subrata K. , Lenz Robert W. , Porter Roger S. 
Published: April 2003

AbstractThe copolyester containing 40 mol % ethylene terephthalate (PET) and 60 mol % p‐hydroxybenzoate (HB) units has been reported by several investigators to be biphasic in the solid and the liquid states. The reported thermal transitions in the two phases, however, are in part contradictory, perhaps partly due to different polymerization conditions. The present work is a study of the transitions in each of the two phases of this copolyester by polarized light microscopy and by light transmission measurements. By light transmission measurements, the two phases were found to have two different glass transition temperatures for the onset of segmental motion, consistent with two assignable temperatures (T.). Cold crystallization and melting in each of the two different phases was also detected. The results help clarify the nature of transitions and agree with the results of dynamic mechanical analysis on the same thermotropic liquid crystalline copolyester.
Preparation and thermal characterization of the glass transition temperatures of sulfonated polystyrene‐metal ionomers
Authors: Yang Sen , Sun Kang , Risen William M. 
Published: April 2003

AbstractThe glass transition temperatures and heat capacity changes in the transition region are reported for six sulfonated linear polystyrenes in the hydrogen form, H‐SPS, in the 3.4–20.1 mol % sulfonation range and 76 metal SPS ionomers in the 3.4–12.8 mol % range. The metals are those which interact predominantly ionically and include +1, +2, and +3 ions of the alkali metal, alkaline earth, and rare earth (lanthanide) series. The results show the effect of H2O or coordinating ligands on glass transition temperatures (Tg) and the importance of eliminating it to obtaining reproducible values for Tg and ΔCp. The Tg values of dry M‐SPS ionomers depend only on the sulfonation level despite wide variation in metal ion charge and size. The variation of ΔCp with sulfonation level is interpreted as showing that at high levels a few unsulfonated styrene units adjacent to sulfonated ones are constrained, presumably by clustering, from participation in the polystyrene‐like cooperative rearrangements in the transition region.
Computer simulation of laser backscattering from fiber surfaces
Authors: Luo Cheng , Bresee Randall R. 
Published: April 2003

AbstractThe application of laser backscattering to fiber surface characterization was studied theoretically. Computer simulations were employed to investigate the theoretical influence of root‐mean‐square fiber surface roughness, fiber cross‐sectional shape, fiber diameter, and surface asperity shape on scattering patterns. Results from this work indicate that laser backscattering may be useful for obtaining fiber structural information in a variety of applications.
Experimental studies of fiber surface roughness characterization by laser backscattering
Authors: Luo Cheng , Bresee Randall R. 
Published: April 2003

AbstractThe application of laser backscattering to the characterization of fiber surface roughness was studied experimentally using instruments based on optical Fourier transforms. Applications included comparing surface roughness of various fibers, measuring the effect of fiber delustering with TiO2 and detecting surface crystallization. The optical transform method was found to be a simple means of providing nonintrusive, real‐time measurements of fiber surface structure.
Stress relaxation in stretched networks immersed in solvent
Authors: Ozkul M. H. , Onaran K. , Erman B. 
Published: April 2003

AbstractStress relaxation in swollen polybutadiene networks is studied. The networks, which are immersed in solvent at equilibrium, are uniaxially stretched suddenly and the relaxation of the force required to keep them at constant length is monitored. The observed relaxation is predominantly due to the diffusion of solvent into the stretched networks. Measurements are made at different extensions and temperatures. The degree of swelling of the networks is calculated as a function of the observed force by adopting the phantom network model of rubber elasticity. The relationship between the diffusion of solvent into the networks and stress relaxation is given. The variation of the degree of swelling with time is used to calculate the coefficients of diffusion for n‐hexane and dodecane in polybutadiene.