bluuebunny/crossref_metadata_2025_split huggingface dataset:
Highly oriented polyacetylene: Structures and electrical conductivity of the compounds doped with alkali metals and selected oxidants
Authors: Billaud D. , Begin D. , Ghanbaja J. , Lelaurain M. , Saldi F. 
Published: May 2005

AbstractFilms of polyacetylene synthesized according to Akagi method present a high degree of crystallinity. A 6‐7 times stretching of these films results in the orientation of the polymer fibers: The mosaic was ± 5 degrees. Such highly oriented polyacetylene (HOPA) films were chemically doped by heavy alkali metals in the vapor state and electrochemically with GaCl anion in nitromethane medium. The evolution of the structures and the variation of the electrical conductivity upon doping were examined in both cases.Doping with alkali metal leads to the appearance of different intercalated phases: The commensurability of these phases is discussed as a function of the nature and the concentration of the intercalated alkaline ion. The electrical maximum room temperature conductivity, which depends on the nature of the alkali metal, is maximum for K‐doped materials. In the case of GaCl doping, the unique intercalated phase observed is poorly organized except in the chain direction where a GaCl ion is found every 4.5 (CH) units. The room temperature electrical conductivity measured along the chain axis is equal to 15 000 S/cm, one order of magnitude higher than the value observed in Shirakawa unoriented polyacetylene.
Synthesis and characterization of polyamide‐imides
Authors: Dezern James F. , Gautreaux Carol R. 
Published: May 2005

AbstractA series of thermally stable, tough, linear polyimides containing amide linkages was prepared. The new polyamide‐imides were synthesized by reacting a group of isomers of diaminobenzanilide (DABA) with various dianhydrides, such as 4,4′‐oxydiphthalic anhydride (ODPA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The resulting polyamide‐acids were thermally or chemically converted to the polyamide‐imide (PAI). Twelve polyimides were synthesized from unsubstituted and N‐methyl substituted amide diamines and their properties were compared with previously made polyamide‐imides and the polyimide LARC‐TPI. These polyimides exhibited high inherent viscosities and glass transition temperatures. They were made into tough, flexible films of which some showed good thermal stability and resistance to organic solvents. Overall, the mechanical properties of the PAI films were comparable to those of LARC‐TPI with the 4,4′‐systems exhibiting exceptional properties and crystallinity. These materials have potential as high temperature films, coatings and fibers, as well as molding and laminating resins.
Catalyst fragmentation during propylene polymerization. III: Bulk polymerization process simulation
Authors: Ferrero Monica A. , Chiovetta Mario G. 
Published: May 2005

AbstractFragmentation of support/catalyst particles during propylene bulk polymerization is analyzed by means of a mathematical model including energy and mass balances, with chemical reaction. The rupture phenomenon is specifically considered by the model and analyzed as it proceeds along time. Model predictions concerning the effects of fragmentation on polymerization are discussed. The influence of mass‐transfer resistances at the macroparticle and microparticle level, as well as the microparticle nucleus‐size effects over the polymerization process, are analyzed. Macroparticle mass‐transfer resistance affects both the rate of fragmentation and temperature excursions. Microparticle nucleus‐size exerts a strong influence over the whole polymerization process. A small micronucleus‐size produces both a delay in the fragmentation process and a greater value of she final catalyst yield. The effects of major critical parameters are evaluated via model simulation, and the results are discussed. The analysis shows that fragmentation depends on the combined effect of the parameters studied. Modeling of the process considering all parameters simultaneously is the proper way of predicting the fragmentation sequence for a given support/catalyst particle. Crystallinity of the produced polymer affects the rate of fragmentation, either increasing or decreasing the rupture rate depending on macroparticle porosity and compactness. Heat transfer conditions in the liquid‐phase system make the temperature runaway problem easy to predict and control, in spite of high polymer yields. The design of “tailor‐made” support/catalyst macroparticles in accordance with catalytic activity is necessary in order to obtain high yields and controlled process temperatures.
Ultralow density polyethylene blends with polypropylene
Authors: Lee Young Keon , Jeong Young Tae , Kim Kook Choong , Jeong Han Mo , Kim Byung Kyu 
Published: May 2005

AbstractTwo types of ultralow density polyethylene (ULDPE) of different melt viscosities were blended with a polypropylene (PP) in a twin screw extruder. Morphology, thermal, rheological, and mechanical properties of the blends were determined. Morphological observation from SEM showed a clean phase separation of PP/ULDPE blends. However, depending on the viscosity ratio, a significant difference in the extent of phase separation, as well as in the phase inversion composition, was demonstrated. The melting temperature of PP and ULDPE were respectively increased and decreased in the blend. Crystallization rate and the, crystallinity of PP and ULDPE were first increased and then decreased as the other component was increased. Yield at low frequencies was observed with 30 wt% ULDPE in PP. In ULDPE‐rich compositions, complex viscosities of the blends gave negative deviation from the additive rule of mixing. Mechanical properties such as flexural modulus, elongation at break and Vicat softening point were closely relatable to the morphology. The impact strength of PP is significantly improved by ULDPE addition.
The dynamic properties, temperature transitions, and thermal stability of poly (etherether ketone)‐thermotropic liquid crystalline polymer blends
Authors: Mehta Atul , Isayev A. I. 
Published: May 2005

AbstractDifferential scanning calorimetry, dynamic mechanical measurements, and thermal gravimetric analysis techniques have been used to thermally characterize blends of poly(etherether ketone)‐thermotropic liquid crystalline polymer (LCP) based on hydroxybenzoic and hydroxynaphthoic acid (HBA/HNA). Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentration. For these blends the glass transition temperature of both components does not change much with composition. Dynamic mechanical measurements performed under torsional and flexural modes of testing and different samples geometries indicate that the dynamic properties depend a lot on the above two factors. Anisotropy in these blends was studied by performing dynamic measurements in flow and transverse directions. The effect of orientation is found to be predominant. Dynamic mechanical properties tend to improve in the flow direction, whereas in the transverse direction they are found to decrease with increasing LCP concentration.
The effect of free radical initiators and fillers on the cure of unsaturated polyester resins
Authors: Rodriguez Ernesto L. 
Published: May 2005

AbstractThe heats of polymerization for two unsaturated polyester resins are presented using two free radical initiator systems. The first was 1% methyl ethyl ketone peroxide/0.2% cobalt octoate (12%) and the second was 2% benzoyl peroxide/0.2% dimethylanyline. The heats of reaction were measured using a differential scanning calorimeter under dynamic and isothermal modes. Infrared spectroscopy and exotherm peak temperature test were employed to further establish the differences between the initiators and to determine the influence of three fillers (sand, clay, and fly‐ash) on the cure reaction.
Rubber‐toughening of glass fiber‐epoxy filament wound composites
Authors: Zhang H. , Berglund L. A. , Ericson M. 
Published: May 2005

AbstractAn attempt was made to improve the properties of filament wound glass fiber‐epoxy composites by addition of carboxyl‐terminated‐butadiene‐acrylonitrile (CTBN)‐rubber to the matrix. The interlaminarGIcof unidirectional glass fiber‐epoxy increased significantly with CTBN addition whereas the flexural strength decreased. The weepage stress in hoop loading of ±50 degree angle‐ply pipes was higher for unmodified as compared with 10 phr CTBN‐modified epoxy matrix pipes. However, the strain at weepage and the stress and strain at nonlinearity were higher for the pipes based on toughened epoxy. The reason for the lower weepage stress is that, although the toughened matrix pipes show higher resistance to cracking, their stiffness is lower. The addition of small amounts of CTBN‐rubber (about 5 percent by weight is suggested) to the present epoxy matrix for filament winding can be done with only a minor increase in viscosity. This is a way of toughness enhancement for applications where the matrix stiffness reduction and increased moisture absorption are of minor importance.
Adaptive model following control of the mold filling process in an injection molding machine
Authors: Chu Cheng‐Ping , Wei Jong‐Hwei , Shih Ming‐Chang 
Published: May 2005

AbstractThis paper is concerned with the practical application of the adaptive model following control (AMFC) theory on the cavity pressure control of the mold filling process in an injection molding machine. The experimental results indicate that the AMFC technique based on the modified Popov‐Landau method is very useful for the cavity pressure control. Two kinds of control algorithms are implemented on a 16 bit microcomputer to control the cavity pressure. The results also show that the AMFC algorithm is superior to the classical PI control in this system when the acrylonitrile‐butadiene‐stryrene (ABS) is injected into a test specimen mold which is designed according to the ASTM code.
Diffusion of benzene vapor in blends of poly(vinyl acetate) and poly(methyl acrylate)
Authors: Nunez Elizabeth M. , Myerson Allan S. , Kwei T. K. 
Published: May 2005

AbstractSorption and diffusion of benzene in miscible blends of poly(vinyl‐acetate), PVAc, and poly(methyl acrylate), PMA, have been studied. The polymer‐polymer interaction parameter values calculated from equilibrium vapor sorption data were all negative, indicating favorable interaction between the two polymers. The sorption of benzene vapor into these blends was measured at a temperature above the Tg's of the pure polymers and found to obey Fickian kinetics. The mutual diffusion coefficients were estimated from the initial slopes of the sorption curves. The concentration dependent diffusion coefficients were fitted to the empirical relation D = Do exp(αC) which satisfactorily correlated the data. Values of the constant Do were found to vary continuously with blend composition, while the α values did not. These experimental data were analyzed employing Fujita's free volume theory. It was found that the data was consistent with this theory. If the fo values for the blends are assumed to be the weighted average of the component polymers, then the β parameter values for the blends also obey the additivity rule.
Electrical conductivity in heterogeneous polymer systems. V (1): Further experimental evidence for a phase transition at the critical volume concentration
Authors: Wessling Bernhard 
Published: May 2005

AbstractA new dispersion/flocculation phase transition model for the conductivity jump at the critical volume concentration of a conductive phase in an insulating matrix polymer is discussed. New experimental‐data including: SEM evaluations of the “seam” structure, excess pyrolytic residue analysis, BET measurements of dependence on conductive phase content, and temperature dependence of conductivity are presented for supporting the new model. Finally a first qualitative step towards a new non‐equilibrium thermodynamical description of these dissipative structures will be described.
On the application of micromechanics to the prediction of macroscopic thermal residual stresses in short‐fiber reinforced polyetheretherketone
Authors: Eduljee Rushad F. , Gillespie John W. , McCullough Roy L. 
Published: May 2005

AbstractA micromechanics theory is outlined for predicting the elastic and thermoelastic properties of dispersed, short fiber systems. This micromechanics theory is then applied to the prediction of macroscopic thermal residual stresses in a poly(etheretherketone). (PEEK)‐glass. Fiber system, in an effort to determine the influence of crystallinity on residual stress development.
The onset of orientational crystallization in poly(ethylene terephthalate) during low temperature drawing
Authors: Roland C. M. , Sonnenschein M. F. 
Published: May 2005

AbstractIt is well known that crystallization can be induced in amorphous poly(ethylene terephthalate) (PET) by orientation below the isotropic crystallization temperature. The magnitude of the strain necessary for crystallization varies inversely with molecular weight because of relaxation. However, lower molecular weight PET might be expected to, crystallize at a lower extent of molecular orientation, since the crystallization rate also varies inversely with molecular weight. Chain conformations were measured during low temperature drawing of PET of various molecular weights. The molecular configuration associated with strain induced crystallization was found to be independent of chain length. The onset of orientational crystallization was associated with a particular conformation, and this critical trans/gauche ratio was equivalent for PETs of various molecular weights. The drawing behavior is thus in accord with theory concerning the transition of flexible chain polymes from isotropy to an ordered state. This result is congruent with previous studies suggesting the presence of extended chain crystallinity in amorphous PET after low temperature drawing.
Energetics of stress relaxation of glassy polymers at high pressure
Authors: Goldman A. Ya. , Maksimov V. L. , Kestelman V. N. 
Published: May 2005

AbstractKinetic changes of relaxation of the shift stress of glassy poly(methyl methacrylate) were studied when temperatures and pressures were changed in isobaric, isothermal, and isochoric conditions. In isochoric conditions the relaxation rate depends slightly on temperature. The volume of the polymer is the main parameter for the rate of stress relaxation. Isobaric and isochoric activation energies and activation vohime of stress relaxation were determined. The results are shown to satisfy the thermodynamic relation of the activation parameters of the relaxation process. The dimensions of elementary kinetic unit of the stress relaxation process were estimated.
Determining molecular weight distributions from viscosity versus shear rate flow curves
Authors: Tuminello William H. , Cudré‐Mauroux N. 
Published: May 2005

AbstractUsing the theoretical approach of Bersted and Slee, we developed a technique of determining the molecular weight distribution (MWD) from the viscosity vs. shear rate flow curve. Each molecular weight fraction was assumed to have a characteristic deformation rate. Below this rate, the viscosity was equal to the zero shear value. Above this rate, the viscosity was reduced to the zero shear viscosity of the molecular weight characteristic of the higher rate. The relationship between the weight fraction of each component and the viscosity/rate curve was derived from these assumptions. The flow curves of very well‐characterized polystyrenes were determined. MWDs were then calculated using the BerstedSlee approach and compared with results from size exclusion chromatography. Comparisons were also made with the results of Malkin and Teishev. They used the same assumptions as Bersted and Slee but chose a different methodology for determining the MWD.
High‐modulus polyaramide and polybenzimidazole blend fibers
Authors: Chung T. S. , Herold F. K. 
Published: May 2005

AbstractPolymer blends from polybenzimidazoles (PBI) and high‐performance polyaramides were spun to give a PBI variant with better tensile properties than PBI itself. Infrared absorption spectra of a hot‐drawn fiber showed 10‐wavelength shift at the carbonyl band, CO, of high‐modulus polyaramide (HMA) due to an interaction of the CO with NH. Dynamic mechanical analysis (DMA) also confirmed the interaction is at a molecular level. The mechanical properties of hot‐drawn fibers from PBI/HMA polymer blends obey Halpin and‐Tsai's theory. Hot‐drawing “immediately after” dry‐spinning yielded fibers with impressive properties. Aging as‐spun PBI/HMA fibers was very harmful for fiber tensile properties. The effects of sulfonation and heat setting on fiber thermal and mechanical properties are also reported.
Study of the relationships between melt index, density, and blend ratio of binary polyethylene blends
Authors: Wong Anthony Chi‐Ying 
Published: May 2005

AbstractTwo relationships regarding various binary polyethylene blends were studied. The first was the relationship between melt index and blend ratio. The second was the relationship between resin density and blend ratio. The results revealed that melt indexes of the blended materials tested under standard testing conditions displayed an exponential decaying characteristic with the percentage of the base blending component. It was demonstrated that the melt indexes of the blended materials could be estimated by a modified Arrhenius Law of viscosity. The estimations showed good agreement with the experimental values. Resin density, on the other hand, exhibited a property that followed an additivity relationship. This indicated that the ability of one component to crystallize was not affected by the other component present in the same system.
Morphology of polyethylene blends. II: Formation of a range of morphologies in blends of polyethylene with increasing content of styrene‐isoprene‐styrene triblock copolymers during extrusion‐blowing
Authors: David C. , Getlichermann M. , Trojan M. , Jacobs R. 
Published: May 2005

AbstractBlends containing polyethylene (LDPE, LLDPE, or LDPE‐LLDPE) with different weight percent of styrene‐isoprene‐styrene (SIS) triblock copolymers have been obtained by extrusion‐blowing. The morphology of the blends, investigated by scanning electron microcopy (SEM), has been related to composition but also to different parameters such as viscosity, nature of the polyethylene phase, and extrusion conditions. A large range of morphologies is observed and indicates that the main factors determining the morphology of the blends are the composition, the elongational fields at the exit of the die and, in certain limits, the relative viscosities of the components of the blends.
Buildup and relaxation of molecular orientation in injection molding. Part II: Experimental verification
Authors: Flaman A. A. M. 
Published: May 2005

AbstractThe numerical simulation of the injection molding process described in Part I is compared in the present paper with experimental results obtained with an instrumented test mold. Pressure and birefringence profiles are compared with corresponding predictions for an amorphous polymer. The influence of the melt temperature, the flow‐rate, and the packing pressure on the pressure profiles and the frozen‐in birefringence is investigated. It is demonstrated that the prescription of a specified packing pressure profile can reduce the frozen‐in birefringence. The shape and the tendencies of the predicted birefringence profiles agree well with the experimental ones. This leads to the conclusion that the, model can be used to optimize the processing conditions to mold high‐quality products with minimum frozen‐in orientation.
Study on the microphase structure of sodium sulfonated polystyrene lonomer by nuclear magnetic relaxation measurements
Authors: Park Jung‐Ki , Lim Jong‐Chul , Kim Chul‐Hwan , Ryoo Byung‐Kyu , Yoo In Suk 
Published: May 2005

AbstractNuclear magnetic relaxation techniques have been used to study the microphase structure of sodium sulfonated polystyrene ionomers. Microphase separation in the ionomers could be evidenced by the magnetization decays, which were resolved into two components. At lower temperature, 300K, the decay function for the ionomer was found to be a combination of two Gaussian functions that are indicative of more rapid dephasing of individual spins, while the magnetization decay at higher temperature, 413K, was composed of both a Gaussian function and a Lorentzian function. The relative portion of the ionic phase in the ionomer was seen to be significantly affected by the ion concentration or the temperature. From the comparison of the relative amounts of the ionic phases obtained from both the material's composition and the nuclear magnetic relaxation experiment, it is anticipated that the ionic domains contain a substantial amount of hydrocarbon segments.
The fracture behavior of oriented poly(methyl methacrylate)
Authors: Lin C. B. , Hu C. T. , Lee Sanboh 
Published: May 2005

AbstractThe fracture behavior of oriented poly (methyl methacrylate) (PMMA) has been investigated. The stress intensity factor KIC, characteristic distance a, and angle θ of switching propagation direction decrease with increasing draw ratio in the range of 1.25 and 3.25. The microstructures such as the plastic zone and the features of morphology are in good agreement with the variations of these three variables, i.e., KIC, a, and θ.
Temperature dependent dc dark conductivity in poly(n‐vinyl carbazole): Arrhenius and density of state model
Authors: Santos‐Lémus S. , Luna M. 
Published: May 2005

AbstractDC dark conductivity (σ) has been measured in thin films of poly(N‐vinyl carbazole) (PVK). The dependence of σ on temperature (T) followed a typical Arrhenius relation but at the same time a relation σ(T)α exp(‐[T0/T]2) could be fitted to the experimental points. To reconcile this observation, it is suggested that the expression for the conductivity then is expected to contain in addition to the activation term, the factor exp[‐(T0/T)2] which is the behavior expected in a trap‐free molecular hopping system with a Gaussian distribution of sites energy, so that the DC dark conductivity would be of the functional form

.
Rubber toughened polyamide 6: The influences of compatibilizer on morphology and impact properties
Authors: Wu Chung‐Jen , Kuo Jen‐Feng , Chen Chuh‐Yung 
Published: May 2005

AbstractIn this study, styrene‐(ethylene‐co‐butylene)‐styrene (SEBS) triblock copolymer (Kraton G‐1652) was modified with maleic anhydride (MA). The maleated SEBS was used as compatibilizer for the blends of Nylon 6 (PA6) and SEBS. The morphology and impact strength of the blends were measured as functions of concentration and MA graft ratio of maleated SEBS. The compatibility and fracture mechanism of the blends were evaluated from the SEM micrographs of the xylene‐etched surfaces and of fractured surfaces. Some of the blends exhibited an impact strength up to about 30 fold greater than neat PA6. The fracture involved both both cavitation and shear yielding. The mechanism of compatibilization of maleated SEBS in the ternary components blends was proposed.