bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of melt viscoelastic properties of polyethylenes and their blends—a comparison of experimental techniques
Authors: Xanthos M. , Tan V. , Ponnusamy A. 
Published: April 2004

AbstractTwo polyethylene resins (LDPE and HDPE) and their blends were characterized for dynamic shear rheology, extrudate swell in a capillary rheometer, and recoverable strain as measured by the Melt Elasticity Indexer in attempts to compare parameters related to the so‐called “melt elasticity” as obtained by different experimental techniques. Such parameters may be useful in screening materials for their melt processability. Data were obtained at equivalent shear rates/frequencies and different temperatures. With respect to the individual blend components, the LDPE resin with the lower Melt Index (MI) had higher storage modulus and Weissenberg number than the HDPE resin. However, by using criteria based on “recoil” and strain recovery, ranking was different with the LDPE resin shown to exhibit lower “melt elasticity.” In this case, extrudate swell data were found to correlate reasonably well with equilibrium recoverable strain data. With respect to blends, complex viscosity and storage modulus versus composition curves showed positive deviations from linearity, similar to those observed in melt heterogeneous blends. Similarities between the short time recoverable strain vs. composition and the storage modulus vs. composition curves suggest that similar morphological states may exist in the melt over the experimental times and conditions applicable to these different experimental techniques.
Electrical properties of polymer composites prepared by sintering a mixture of carbon black and ultra‐high molecular weight polyethylene powder
Authors: Chan Chi‐Ming , Cheng Chi‐Leung , Yuen Matthew M. F. 
Published: April 2004

AbstractConductive polymer composites were prepared by sintering a mixture of ultrahigh molecular weight polyethylene (UHMWPE) powder and carbon black. Two processing parameters—time and temperature—were shown to have a notable effect on the resistivity of the composites. The relationships between the processing parameters and morphology were studied using optical microscopy and transmission electron microscopy (TEM). The results of the optical microscopy studies indicate that the carbon black is distributed in the interfacial regions between the UHMWPE particles. The dimension of the carbon black channels increases with the carbon black concentration. TEM micrographs show that a high degree of intermixing between the carbon black and the polymer occurs at higher temperatures and longer processing times, resulting in higher resistivities. A positive temperature coefficient (PTC) effect was observed for these materials. A mechanism for the PTC effect in this system is proposed. The magnitude of the PTC effect is found to be inversely proportional to the dimension of the carbon black channels in the composites. The dimension is directly related to the carbon black concentration. The PTC effect is a result of the polymer volume expansion caused by melting of the crystallites. A large PTC effect is observed for the composites with a low carbon black concentration and vice versa. No negative temperature effect (NTC) is observed at temperatures substantially above the melting point of the polymer.
New model of flow in a Farrel Continuous Mixer
Authors: Bang Dae‐Suk , White James L. 
Published: April 2004

AbstractA model for flow in a Farrel Continuous Mixer based upon cylindrical coordinate hydrodynamic lubrication theory is presented. Pressure and flux fields over the rotor surface are calculated. The pumping characteristics of the various sections of the machine rotors were calculated. Generally Farrel Continuous Mixers are operated under starved conditions. Calculations are presented for continuous mixers operating under starved conditions. Pressure and fill factor profiles are determined. Fill factors are predicted to be increased by increasing throughput, increasing exit gate pressure and reducing screw speed.
Evaluation of the weld‐line strength of thermoplastics by compact tension test
Authors: Cho Kilwon , Ahn Sunghee , Park Jinbae , Park Chan Eon , An Jeong Ho 
Published: April 2004

AbstractIn order to understand the relationship between processing conditions and the properties of weld‐lines on a molecular level, it is necessary to evaluate the true strength of the weld‐line that is not affected by the V‐shape notch on the surface of the weld‐line zone. In this experiment, the weld‐line strength of several brittle, ductile, or phase‐separated polymers was evaluated using the compact tension test by measuring the critical stress intensity factor, KIC, or the critical J‐value, JIC, and the results were compared with those obtained by tensile testing. For brittle polymers such as poly(methyl methacrylate) (PMMA) or styrene acrylonitrile copolymer (SAN), the value of the weld‐line factor, i.e., the strength ratio between the welded and the non‐welded specimen, is higher than that measured by tensile testing, because of the notch sensitivity of brittle thermoplastics and the notch dependence of tensile strength. On the other hand, in the case of ductile polymers such as polycarbonate (PC), the weld‐line factor is similar for both the tensile and compact tension tests. However, the dependency of the weld‐line factor on melt temperature is more obvious in the compact tension test. From these results, it seems that the compact tension test is more appropriate for measuring the interfacial adhesion strength across the weld‐line, which excludes the notch effect.
Influence of miscibility on the morphology and properties of polycarbonate/(maleic anhydride)‐grafted‐polypropylene blend
Authors: Ning Ping , Ko Tze‐Man 
Published: April 2004

AbstractMaleic‐anhydride‐grafted polypropylene (MAH‐g‐PP) was added to polycarbonate (PC) as a processing agent. Its influence on the morphological, thermal, rheological, and mechanical properties of PC/MAH‐g‐PP blends was investigated by differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), dynamic contact angle goniometry, and tensile and impact strength experiments. The results indicated that the processability and miscibility of the blends were improved significantly by addition of 5–20 wt% MAH‐g‐PP to PC. The melting temperature of MAH‐g‐PP increased as the relative composition of MAH‐g‐PP in the blends increased mainly because of enlargement of the crystallite size. The DSC, FTIR as well as SEM results strongly suggested that a chemical reaction might have taken place between the PC and MAH‐g‐PP. This chemical reaction could have contributed to the improvement of the mechanical properties of the blends and the miscibility between the PC and MAH‐g‐PP components.
Heat transfer and solidification of polymer melt flow in a channel
Authors: Lin P. , Jaluria Y. 
Published: April 2004

AbstractA numerical study is carried out on the conjugate thermal transport and solidification in polymer melts flowing through channels. A continuum model with the enthalpy formulation is used for a laminar, two‐dimensional, axisymmetric, incompressible, and steady flow. The influences of axial diffusion, viscous dissipation, and temperature‐dependent viscosity are included. A fully elliptic, control volume, finite difference method is employed to solve the governing equations. Numerical results are analyzed by examining the effects of outer wall temperature, Biot number, and mass flow rate. Isotherms and other results are also presented.
Disordering of crystalline PEEK upon mechanical treatment
Authors: Papkov V. S. , Gerasimov M. V. , Dubovik I. I. 
Published: April 2004

AbstractIt has been established that crystalline PEEK can become completely amorphous upon rolling at room temperature. This effect was verified by data of differential scanning calorimetry. X‐ray diffraction and density measurements. In contrast to quenched amorphous PEEK samples, cold crystallization in rolled amorphous samples is shifted to lower temperatures and starts just with the onset of the glass transition. This shift, along with the decrease in the heat of cold crystallization from 21 J/g (for quenched amorphous sample) to 11 J/g, suggest some retention of paracrystalline structure in rolled amorphous samples.
Powder extrusion: Fundamentals and different applications
Authors: Wolfson S. A. , Nikolskii V. G. 
Published: April 2004

AbstractWe propose a novel polymer extrusion process, known as the solid state shear extrusion pulverization and modification (SSSE process), based on the simultaneous action of shear deformation and pressure at selected temperatures. This process can be used for continuous pulverization and copulverization of various polymers. Including different blends, filled materials, thermoplastics, vulcanized rubbers, crosslinked polymers, polymer composites, and natural polymers. Various aspects of this process are considered, including unusual microstructure and properties of powders, low energy consumption, and mechanochemical effects. Possible applications of SSSE to polymer/rubber recycling and to obtaining advanced polymer powders and modified powders are considered, together with scaling‐up problems of equipment suitable for industrial application.
Debonding and fracture of particulate‐filled isotactic polypropylene
Authors: Dubnikova I. L. , Muravin D. K. , Oshmyan V. G. 
Published: April 2004

AbstractExperimental data on particulate‐filled polypropylene rupture are presented, with discussion and explanation of the regularities found. The systems studied are characterized by ductile properties of a semi‐crystalline matrix and a low level of interfacial interaction. Polypropylene as a host and aluminum hydroxide particles, without or with anti‐adhesive treatment, were used. Two concentration regions of different debonding micromechanisms were found. At low filler fraction (< 15–20 vol. %) particles debond independently and completely at the initial stages of drawing, and a microhomogeneous flow mechanism takes place. Above a critical filler content, debonding proceeds in a correlated way with the formation of narrow craze‐like deformation zones transverse to the stretching axes. These zones screen new debondings in their neighborhoods, more or less efficiently, dependent upon filler fraction and, hence, the porosity inside crazes and the level of interfacial interaction. Whether microhomogeneous or craze‐like mechanisms occur essentially determines the regularities of further deformation and fracture: localized or macrohomogeneous flow, ductile or quasi‐brittle fracture, the drop or the rise of ultimate strains with increase of particle diameters. A theoretical description of the transition between microhomogeneous and craze‐like mechanisms is proposed.
Rheokinetics of free‐radical polymerization of acrylamide in an aqueous solution
Authors: Kulichikhin S. G. , Malkin A. Ya. , Polushkina O. M. , Kulichikhin V. G. 
Published: April 2004

AbstractA method of rheokinetic analysis is applied to free‐radical polymerization of acrylamide in a water solution initiated by an oxidizing reducing system. The special feature of this system is the second‐order kinetics of the initiation stage. Theoretical analysis predicts the main effects, such as the time dependence of viscosity and the degree of polymerization, concentration influence of a monomer and an initiator, and the temperature dependence of the viscosity profile at different experimental conditions. Experimental data confirmed the idea about the second‐order reaction of initiation. Observed dependencies were close to theoretical predictions. Rate constants of different individual stages of a reaction and “apparent” values of activation energy were found and compared with published values. The possibility of solving an inverse rheokinetic problem from viscometric data was confirmed.
Crystallization and stress‐strain properties of ultra‐high‐molecular‐weight‐polyethylene gels filled with iron particles
Authors: Kerber M. L. , Ponomarev I. N. , Lapshova O. A. , Grinenko E. S. 
Published: April 2004

AbstractCrystallization of ultra‐high‐molecular‐weight‐polyethylene (UHMW‐PE) filled solutions and gels was studied by differential scanning calorimetry. It has been found that the structure and properties of the gelating systems depend on solvent type, polymer concentration, and filler. Crystallization rate decreases as the polymer content is increased. The crystallization rate dependence on filler concentration passes through a maximum. The influence of a disperse filler on the structure, the stress‐strain and relaxation properties of UHMW‐PE gels has been studied. The results demonstrate the advantage of using less thermodynamically active solvents (thermodynamic activity means polymer‐solvent interaction). This gel‐technology enables us to obtain UHMW‐PE based materials with a 90‐vol% content of iron particles. Highly loaded fibers based on UHMW‐PE were obtained with a tensile strength of 40–50 MPa and an elastic modulus of 350–400 MPa.
Porous materials from crystallizable polyolefins produced by gel technology
Authors: Andrianova G. P. , Pakhomov S. I. 
Published: April 2004

AbstractA new method for obtaining porous and porous fiber polymers is presented. This method is based on using gel‐type technology (without previously preparing polymer solutions) for crystallizable polymers, preparing polyethylenes, and including polyethylenes of very high molecular mass and isotactic polypropylene. The method consists in swelling crystalline polymer films at elevated temperatures in a proper solvent with subsequent precipitation with a non‐solvent at different conditions. In this case, simultaneous or consecutive processes of phase separation of amorphous or/and crystalline type occurs; stretching the sample can also accompany this process. Complete phase diagrams of two‐ and three‐component systems (polymer‐solvent and polymer‐solvent precipitator) were constructed. Temperature‐concentration boundaries of amorphous separartion (binodal) and crystallization (liquidus) are reported for the system polyethyleneo‐xylenedimethyl formamide. Phase transitions of both types influence characteristics of the resultant porous structure. They were prepared by simultaneous (precipitation of a gel by dimethyl formamide at 25°C) or consecutive (precipitation with a hot non‐solvent at 138°C and following cooling) phase separation. Studied were the effect of experimental conditions (temperature, times for solvation and precipitation, polymer molecular mass, the thermodynamic quality of solvents and parameters of film stretching) on peculiarities of the structure and quantitative characteristics of final porous and fiber‐porous polyolefins. It has been demonstrated that the method proposed allows us to obtain a crystalline and highly porous polymer with open poros, a bimodal size distribution and with a highly developed inner surface. Further high strength and small shrinkage are characteristic of the fiber‐porous materials. The method under discussion appears to be universal, it does not require a preliminary preparation of polymer solutions and can be realized within a general technology of polymer films and sheet processing. Highly porous polymers obtained by this technology, primarily based on polyethylenes of very high molecular mass, can be used as neutral supports for multi‐functional membranes, polymeric covers, frame systems for implants and other applications.
Thermally stable polyimide binders from aromatic dianhydrides and acetyl derivatives of aromatic diamines: Formation mechanism
Authors: Goykhman M. Ya. , Svetlichnyi V. M. , Kudriavtsev V. V. , Antonov N. G. , Panov Yu. N. , Gribanov A. V. , Yudin V. E. 
Published: April 2004

AbstractPolyimide resins based on dianhydrides of aromatic tetracarboxylic acids and acetyl derivatives of aromatic diamines have been developed for impregnating carbon fibers and glass cloth. Binder prepolymers are soluble in amide solvents and acetone and also form melts with a viscosity of 0.1–0.3 Pa · s at 250–300°C. The melt lifetime is 20–30 min. An increase in temperature leads to the formation of a crosslinked insoluble system of high thermal stability. The formation of polyimide binders was studied with the aid of IR and NMR spectroscopy. A mechanism of the reaction of aromatic dianhydrides with acylated amines is proposed. On the basis of polyimide binders from dianhydride of 3,3′,4,4′‐benzophenonetetracarboxylic acid and bis‐[4‐acetaminophenyl]‐sulfone, bis‐[4‐acetaminophenyl]‐ether, and N,N‐diacetyl‐p‐phenylene diamine, carbon fiber composites with good physico‐mechanical properties were obtained.
Influence of hydrodynamic stirring on composition of copolymer obtained in continuous reaction systems
Authors: Kuchanov S. I. , Kholostyakov A. G. , Kozlov N. I. 
Published: April 2004

AbstractA mathematical modeling method is employed to analyze the dependence of the composition of a copolymer prepared under a continuous regime on the level of longitudinal stirring in a reactor. The extent was established to which this factor controls the limits of the alteration range of copolymer composition at various values of the reactivity ratios of monomers and their feed composition.
Mechanical and dynamic mechanical properties of zinc neutralized salts of poly(ethylene co‐acrylic acid) and its blend with epoxidized natural rubber
Authors: Mohanty S. , Vijavan K. , Neelkantan N. R. , Nando Golok B. 
Published: April 2004

AbstractMechanical and dynamic mechanical properties of the zinc neutralized salts of poly (ethylene co‐acrylic acid) (PEA) and its blends with epoxidized natural rubber (ENR) have been studied. Improvement in tensile strength, hardness (Shore‐A), and a reduction in elongation at break and tension set with the increase in degree of neutralization of the blend constituents corroborate the existence of hard and rigid domains of ionic clusuters in the non‐hydrocarbon and flexible backbone chain. The occurrence of a new relaxation peak due to ionic aggregates and the disappearance of the crystalline transition indicates the formation of a new ionic cluster phase in the matrix. A shift in the glass transition temperature towards higher temperature supports the existence of ionic crosslinks in the polymer matrix.
A new approach in modeling template polymerization
Authors: Semino Daniele , Polacco Giovanni , Ricciardi Alessandra 
Published: April 2004

AbstractThis work attempts to describe the peculiar kinetics that take place in template polymerization which proceeds according to the zip‐mechanism. The unique situation of the molecules adsorbed on a template chain, which, with respect to the template propagation and termination reactions, are bound to react with the molecules that are positioned on their sides, is characterized. The definition of different species according both to their nature and to the nature of their neighbors leads to the construction of a kinetic model that, despite its analytical complexity, is characterized by a quite limited number of unknown kinetic constants. The model is developed by deriving the dynamic equations that describe the conversion versus time behavior all along the course of the reaction. The model predictions are compared with experimental data referring to the radical polymerization of sodium methacrylate (MAA · Na) in the presence of poly(allylamine) hydrochloride (PAAm · HCl). The good agreement confirms the validity of the model. Moreover, the model offers a significant contribution into understanding the peculiarities of template polymerization systems.
The craze initiation response of a polystyrene and a styrene‐acrylonitrile copolymer during physical aging
Authors: Gusler Gloria M. , McKenna Gregory B. 
Published: April 2004

AbstractThe influence of structural recovery or physical aging on the craze initiation of amorphous polystyrene and a styrene‐acrylonitrile copolymer has been examined in two states of stress/deformation and at different temperatures. Studies of craze initiation in equibiaxial creep were performed using a “bubble” inflation test geometry while uniaxial elongation in stress relaxation conditions was studied by bending the specimen over a variable radius of a curvature test jig. All tests were performed by aging the specimen and testing it at the same temperature subsequent to a quench from above the glass transition to below it. The results are compared with expectations from three craze models: Sternstein and Ongchin (1), Argon (2), and Kambour (3). The results are most consistent with the model of Kambour, but discrepancies arise because, e.g., the impact of aging on the stress for crazing in the equibiaxial tests is different for the polystyrene than for the styrene‐acrylonitrile copolymer. The results also suggest that there are two regimes of behavior for craze initiation under equibiaxial stresses, a behavior not manifested in the uniaxial stress relaxation experiments.
Evolution of phase morphology in compatibilized polymer blends at constant quench depths: Complementary studies by light scattering and transmission electron microscopy
Authors: Jackson C. L. , Sung L. , Han C. C. 
Published: April 2004

AbstractThe effect of added block copolymer on the phase separation and morphology evolution in a partially miscible blend of polystyrene and polybutadiene near the critical composition is studied by temperature jump light scattering (TJLS) and transmission electron microscopy (TEM). As block copolymer is added, the phase boundary is shifted to lower temperatures and the phase separation process is slowed dramatically. Since the quench depth greatly affects the rate of phase separation in any blend system, we have used equivalent quench depths by adjusting for the shift in the phase boundary as block copolymer is added. The morphology evolution of these ternary blends was studied by preparing TEM specimens at equivalent shallow quench depths (ΔT = 1.6°C) and allowing each blend mixture to coarsen for the time required to reach a specific constant size, or q‐value, using the TJLS data on the kinetics of phase separation. The q‐range selected was q ∼ 0.003–0.005 nm−1, which corresponds to a spacing of 1–2 μm in real space. The combination of light scattering and microscopy techniques more rigorously describes the compatibilization process in these complex ternary systems.
Stress relaxation experiments in polycarbonate: A comparison of volume changes for two commercial grades
Authors: Colucci D. M. , O'Connell P. A. , McKenna G. B. 
Published: April 2004

AbstractStress relaxation experiments were performed on two grades of polycarbonate at room temperature. The tests were performed in uniaxial extension and compression at deformations from the small strain, linear viscoelastic regime to the highly nonlinear viscoelastic regime just below yield. Simultaneous to the control of axial strain, both stress and lateral strain were measured, the latter providing the volume change for the samples. The volume change measurements in tension show initial dilatation of the samples followed by a volume relaxation that at the largest strains in one grade of polycarbonate leads to densities greater than those of the undeformed sample. In the case of the compression measurements, the volume decreases upon deformation, but, rather than relaxing back towards the undeformed volume, the samples continuously densify. The differences in the tensile dilatation for the two grades of polycarbonate suggest that the volume behavior may be related to the propensity to yield vs. fracture.