bluuebunny/crossref_metadata_2025_split huggingface dataset:
Orientational crystallization and orientational drawing as strengthening methods for polyethylene
Authors: Elyashevich G. K. , Karpov E. A. , Rosova E. Yu. , Streltses B. V. , Marikhin V. A. , Myasnikova L. P. 
Published: May 2005

AbstractThis paper reports on the theoretical and experimental studies of structure formation and strengthening (stiffening) of flexible‐chain polymers. Two techniques of strengthening relying on the melt extrusion, i.e., orientational crystallization (crystallization initiated by melt extension) and drawing (uniaxial stretching of a crystallized polymer) are analysed by theory. The experiments involved preparation and study of melt extruded films and film fibers of linear polyethylene formed by the two techniques mentioned above. The effect of the degree of orientation and other parameters of the formation processes on the mechanical characteristics and the factors limiting the ultimate values of these characteristics are discussed. It is shown that multistage drawing succeeds in achieving a higher tensile strength and elastic modulus (1.2 and 35 GPa, respectively) than the orientational crystallization, which gives 0.8 and 15 GPa. The strengthening by drawing is accompanied by microcrack formation. In contrast, no discontinuities are observed in orientationally crystallized samples up to their ultimate extension.
Creep/recovery behavior of toughened and untoughened graphite/epoxy systems
Authors: Tsotsis Thomas K. 
Published: May 2005

AbstractA test program was developed to compare the viscoelastic behavior of an untoughened epoxy (R922) with a toughened epoxy (R6376). Creep/recovery tests were performed on neat resin as well as [ ± 40° ]2s composites using T500 or IM7 graphite fibers. The composite specimens were subjected to at least five cycles of load/unload at each stress level. The goal was to study the viscoelastic response of a flexibilized and unflexibilized epoxy and to try and observe any microstructural changes that might occur. Neat resin tests did not show a significant difference in behavior between the two systems. Single cycle behavior was found to differ significantly from multiple cycle behavior. Recovery strains were observed to be much higher than predicted from linear theory. Linear parameters were also seen to vary with stress level; however, when a plasticity‐based approach was used to model the creep behavior, the same parameters could then be used at all load levels. Creep and recovery behavior were seen to differ significantly. This observation leads to support for the theory of Schapery (1) that creep and recovery should be considered as different behavior in contrast to the assumptions of linear and nonlinear theory. In addition, the large difference between neat resin and composite data suggests that micromechanics models, which rely on constituent properties, will lead to large errors if neat resin properties are used to characterize composite viscoelastic behavior. Different fibers showed no influence on results. Scanning electron microscopy failed to reveal any microstructural changes.
Evaluating the fatigue resistance of notched specimens of polyethylene
Authors: Zhou Y. , Brown N. 
Published: May 2005

AbstractThe fatigue life of a linear low density polyethylene was measured as a function of stress, notch depth., and temperature under plane strain conditions. The fatigue life was precisely related to the stress intensity. The temperature dependence of the fatigue life corresponded to an activation energy of 72.5 KJ which was independent of stress level. A general equation for the fatigue lifetime was proposed for polyethylenes in terms of the material parameters, the mechanical parameters such as stress intensity, stress amplitude, frequency, and waveform.
Melting and solidification behavior of blends of high density polyethylene with poly(butylene terephthalate)
Authors: Yang L. Y. , Smith T. G. 
Published: May 2005

AbstractThis study focuses on the effect of various processing and cooling conditions upon the subsequent melting and solidification behavior of blends of poly(butylene terephthalate) (PBT) and high density polyethylene (HDPE). Differential scanning calorimetry (DSC) measurements have shown that the crystallization of reprocessed PBT is different from the crystallization behavior of virgin samples. Two melting endotherms for PBT were observed for reprocessed PBT and for PBT‐PE blends. The nature of each PBT peak is discussed in relation to processing history, solidification conditions, and composition. The presence of two crystallization peaks for the PE component in blends of PE and PBT are thought to be associated with the restriction of molecular motion of PE in the presence of the second component. The relative magnitudes of the two exotherms of PE vary with composition and cooling rate during solidification.
An assessment of crazing criteria for polyetherimide in three‐dimensional stress space
Authors: Woods J. T. , Delorenzi H. G. 
Published: May 2005

AbstractThree point bend tests of notched, polyetherimide (PEI) beams are performed for varying notch radii and beam thicknesses. Finite element stress results including pressure sensitive yielding effects are correlated with experimental load‐to‐craze observations to determine the three‐dimensional stress state at craze initiation. Three crazing criteria; maximum principal stress, hydrostatic stress, and the critical strain criterion of Oxborough and Bowden are examined for consistency. Over the range of geometries studied, the critical strain criterion provides the best fit to the experimental data. This criterion could be used as a brittle failure criterion to help understand and prevent brittle failures.
A predictive model for the mechanical behavior of particulate composites. Part II: Comparison of model predictions to literature data
Authors: Vratsanos Lori Anderson , Farris Richard J. 
Published: May 2005

AbstractThe energy balance model presented in Part I is applied here to data taken from the literature. Care was taken to choose well‐characterized systems to give a true test of the model's predictive character, rather than its ability to curve‐fit the data. The effects of concentration, particle size, strain rate, and temperature on the stress‐strain and dilatation curves are examined. Good agreement is seen for each of these variables. This predictive approach will allow the design of particulate composites with given mechanical behavior, and analysis of material behavior in various geometries and conditions.
Experimental study of film thickness and free surface velocity around a rotating roll for non‐newtonian fluids
Authors: Chono S. , Iemoto Y. , Tomizawa T. 
Published: May 2005

AbstractMeasurements are performed on film thickness and free surface velocity around a rotating roll for Newtonian, non‐Newtonian inelastic, and viscoelastic fluids by using noncontact methods of a capacitance probe and a laser Doppler velocimeter probe. The film thickness decreases with increasing inspection angle for Newtonian fluids. For non‐Newtonian fluids, it retains an approximately constant value, owing to shear‐thinning of viscosity, except for a meniscus region development, which is dependent on fluid elasticity. Comparison of current results with the film thickness from a previous work is also made. With the increment of inspection angle, the free surface velocity increases rapidly in the meniscus region and maintains a constant value almost equal to a roll speed in the other region for viscoelastic fluids, while it increases linearly for Newtonian fluids. The shear rate at a roll surface is presented assuming that the velocity distribution in the liquid film is a polynomial equation. It is found that viscoelastic fluids exhibit different behavior from that of Newtonian and non‐Newtonian inelastic fluids. Evaluation of the force acting on the liquid film for Newtonian fluids implies that the velocity gradient at a roll surface in an ascending region may be steeper than the parabolic form assumed in this study.
The reactive modification of polyethylene. II: Mathematical modeling
Authors: Suwanda D. , Balke S. T. 
Published: May 2005

AbstractIn Part I of this work, experimental data showed that the effect of low concentrations of free radical initiator injected into polyethylene during extrusion depended upon the degree of unsaturation and branching in the feed as well as the molecular weight. This paper shows attempts to quantitatively explain these reactive extrusion results through development of two kinetic models based upon the rate equations for reactions considered dominant. The first model developed incorporated unsaturation via consideration of simultaneous crosslinking‐endlinking reactions. It contains two variable parameters: the overall initiator efficiency and a ratio of two rate constants reflecting the reactivity of the unsaturated bonds. The model was able to fit the changes in molecular weight distribution of both the low density and linear low density polyethylene but not the high density polyethylene samples. In addition to fitting the molecular weight distribution, this model also provided reasonable values of initiator efficiencies for crosslinking, endlinking, and chain extension reactions, as well as the number of terminal vinyls of the products. The second model is a special case of the first: it neglects the presence of unsaturation in the feed. This second model is actually the usual “crosslinking” model widely known from a derivation based upon statistical arguments. It was not able to fit most molecular weight distributions obtained. However, the model was shown to be useful for accounting for observed molecular weight distribution for a high density polyethylene sample of low initial unsaturation. Also, it was able to explain the amount of gel formed as a function of initiator concentration.
Jet impingement mixing in an L‐type mixhead: Comparison of mixing criteria
Authors: Baser S. A. , Shetty D. G. , Khakhar D. V. 
Published: May 2005

AbstractHigh velocity jet impingement mixing is a unique operation of the reaction injection molding process. The quality of mixing depends on processing parameters for a given system, and can have significant effect on the properties of the product. We have compared three methods used for characterization of mixing quality reported in the literature for a cross‐linking polyurethane system processed on an industrial scale high pressure RIM machine, with an L‐type mixhead. The methods are based on, (i) visual appearance of a molded sample, (ii) adiabatic temperature rise during reaction and, (iii) flexural modulus of elasticity of a molded sample. The visual appearance test was made quantitative by using a color matching optical system. The adiabatic temperature rise increases rapidly with nozzle Reynolds number (Renzl) for polyol, up to a critical value (Renzl = 380) beyond which there is a slow increase. The latter is attributed to the geometry of the L‐type mixhead. A simple analysis is presented to explain the limiting extent of mixing at high Renzl. The flexural modulus and the visual appearance of molded samples are found to improve until Renzl = 500, implying a greater sensitivity to mixing as compared to the adiabatic temperature rise.
Compatibilization of immiscible blends with a mutually miscible third polymer
Authors: Machado J. M. , Lee C. S. 
Published: May 2005

AbstractFour immiscible blend systems, styrene‐maleic anhydride/styrene‐acrylonitrile (SMA/SAN). styrene‐maleic anhydride/acrylonitrile‐butadiene‐styrene (SMA/ABS), poly(vinylidene fluoride)/SAN (PVF2/SAN), and PVF2/ABS, were investigated. The effect of adding up to about 10 wt% of a third polymer that is miscible with each blend component, poly(methylmethacrylate) (PMMA), was determined. In every case, the addition of PMMA led to the improvement of properties such as tensile strength, tensile elongation, and notched impact strength. Furthermore, the addition of PMMA resulted in finer, more uniform dispersions of the primary blend components. The experimental results are interpreted in terms of interfacial activity of the common phase component, PMMA.
A thermoanalytical study on solid‐state cure of poly(p‐phenylene sulfide)
Authors: Park Min , Lee Kwang Hee , Choe Chul Rim , Jo Won Ho 
Published: May 2005

AbstractDifferential scanning calorimetry (DSC) was used to investigate the solid‐state cure process of poly(phenylene sulfide)(PPS) resin. Virgin PPS resin in an open sample pan was cured in DSC cell. Either air or oxygen was used as a curing atmosphere. Cure temperatures were in the range of 200 and 250 °C, which are below the melting point of PPS resin. Cure temperature as well as atmospheric condition influenced the cure behavior of PPS in the solid state. Both the rate and the amount of cure increased with increasing cure temperature. On the other hand, the time to reach the maximum cure rate was independent of cure temperature. Changing the atmosphere from air to oxygen increased both the cure rate and the amount of cure. The size effect of PPS particles on the cure reaction was also discussed.
Oligomer distribution for interfacial step growth polycondensation
Authors: Munjal S. 
Published: May 2005

AbstractLow levels of oligomer molecules are generally desirable in polymeric materials. It is known that several reactor variables can affect the oligomer distribution, and therefore it is useful to have predictive models for molecular weight distribution. The normal approach of a differential equation–based model is very complex to set up if it is applied rigorously to include all the non‐Flory aspects of the step growth polycondensation and in particular the interfacial polycarbonate polymerization. In this paper, simple methods based on the Monte Carlo method and Stockmayer distribution are applied to simulate the effects of mass‐transfer, unequal reactivity, and the starting stoichiometry of the polycondensing functional groups on the oligomer distribution. It is shown that these parameters can have a significant effect on the oligomer weight distribution and polydispersity of the final polymer.
A novel approach to a truly dynamic thermodynamics
Authors: Lindenmeyer Paul H. , Astarita G. 
Published: May 2005

AbstractA novel approach to a truly dynamic thermodynamics is proposed in which equilibrium is defined in terms of explicit time, distance, and acceptable error scales. This approach involves reformulating the second law of thermodynamics in terms of an excess energy that vanishes at equilibrium instead of an entropy that assumes some unknown maximum value. Excess energy is defined mathematically as the total Legendre transform of energy with respect to an independent set of extensive variables. Excess energy is effectively the free energy functional of a nonequilibrium system and is a function of the time, distance, and acceptable error scales. Elimination of entropy from thermodynamics requires recognizing temperature as a thermal stress, proportional to the antimetric component of the stress tensor that is neglected when one assumes the validity of Cauchy's second law of motion. The inclusion of temperature as part of the stress‐strain couple completes the science of thermomechanics and opens the way for a practical unification of chemistry and physics in strictly mechanical terms.The last sentence of the abstract shows how high the goals that Lindem meyer set for himself were. I personally do not agree with the idea that mechanics is the queen of all sciences, and that given deep enough probing one could achieve “a practical unification of chemistxy and physics in strictly mechanical terms”; for instance, electromagnetism has full citizenship's rights in physics, and it is hard to conceive that it could be reduced to mechanics.
The oxidative degradation of imide polymers. I: Ozonolysis of a model compound, N‐phenylphthalimide
Authors: Barman S. , Newhouse E. I. , Neely W. C. 
Published: May 2005

AbstractThe reactions of N‐phenylphthalimide films with ozone have been studied under a variety of conditions: dry ozone, moist ozone, ozone plus ultraviolet light, as well as ozone plus water vapor plus ultraviolet light. This compound is a conveniently available model for imide polymers. These reaction conditions represent simulation of certain aspects of the space environment. For each set of reaction conditions the reaction products were determined by combined gas chromatography/mass spectrometry. Semiempirical molecular orbital computations were made of the relative energetics of possible reaction pathways consistent with the generation of the observed products. The reaction products found indicate fragmentation of the imidic moiety for which the energetics are favorable.
Properties of electropolymerized polycarboxyphenylmethacrylamide matrices/graphite fiber composites: Crosslinking effect
Authors: Liang Jeng‐Li , Bell James P. , Scola Daniel A. 
Published: May 2005

AbstractImide formation from ‐CONH and ‐COOH functional groups of 2‐carboxyphenylmethacrylamide (2‐CPM), 4‐carboxyphenylmethacrylamide (4‐CPM), 4‐carboxyphenyl methacrylamide/methylmethacrylate (4‐CPM/MMA) and 4‐carboxyphenylmethacrylamide/N‐phenylmalemide (4‐CPM/NPMI) electropolymerized matrices was investigated. It was found that 2‐CPM polymers undergo intramolecular imidization and anhydride formation, which result in a small amount of crosslinked network. On the other hand, the thermally cured 4‐CPM polymer demonstrates a significant increase in gel fraction. Tg and dynamic storage modulus, owing to crosslinked network formation. Tgs of 4‐CPM/MMA and 4‐CPM/NPMI composites measured by thermomechanical analysis after thermal heating were increased and were correlated very well with the preheating time. The 4‐CPM/MMA composites with a particle crosslinking (Tg increased to 245°C) maintained a higher Izod impact strength than a typical epoxy composite (200 kJ/m2 vs. 100 kJ/m2). Upon heating to promote crosslinking, a lower shear strength (65 MPa) of a 4‐CPM/MMA composite increased to a strength of 78 MPa, close to the 80 MPa of an epoxy composite at 67% fiber volume fraction. A lower water absorption of around 1% was associated with the increased crosslinking. The mechanical properties of the 4‐CPM/NPMI composites showed a similar trend upon preheating.
Orientation parameters for the specification of effective properties of heterogeneous materials
Authors: Munson‐Mcgee S. H. , McCullough R. L. 
Published: May 2005

AbstractA general formulation is presented for the orientation averaging of the properties of representative volume elements of heterogeneous materials. Approximations are introduced that result in the identification of four independent orientation parameters that are required to specify a general state of three‐dimensional orientation. The general relationships are reduced further for the special case of “planar” and “axial” distribution and applied to an aggregate averaging scheme for short‐fiber composites.
Shear test for thermoplastic polymers
Authors: Hedner Gert , Seldén Ragnar , Lagercrantz Per 
Published: May 2005

AbstractA shear test is proposed as a complement to the tensile test in order to characterize the short time mechanical behavior of thermoplastic polymers. The proposed test geometry makes the test easy to perform and to evaluate and gives relevant information about anisotropy, plastic deformation, crack initiation, and propagation properties. Three different materials have been tested and the results are discussed.
Radical terpolymerization of zincacrylate, acrylonitrile, and styrene initiated by As2S3‐styrene complex
Authors: Agrawal B. P. , Srivastava A. K. 
Published: May 2005

AbstractTerpolymerization was investigated by dilatometry for zincacrylate (ZnA2), acrylonitrile (AN), and styrene (St), radically initiated by a As2S3‐styrene complex (I) in dimethyl sulphoxide (DMSO), at 90 ± 0.1°C for 1 h under inert atmosphere. The system follows non‐ideal kinetics, due to primary radical termination as well as a degradative chain transfer reaction. The kinetic expression for the system is Rpα(I)0.27 (St)0.31 (AN) 0.22[ZnA2]0.12. The value for the activation energy and k/kt are 55 kJ mol−1 and 1.87 × 10−7 1 mol−1 s−1 respectively. The terpolymer has been characterized by IR and NMR spectroscopy. The thermal stability and solubility of the terpolymer have also been studied.
Multilayer extrusion: Experiments and computer simulation
Authors: Mavridis H. , Shroff R. N. 
Published: May 2005

AbstractA mathematical model is presented for the computer simulation of multilayer flow of polymer melts in coexitrusion. The proposed model can handle an arbitrary number of layers. The viscosity of each layer is shear‐rate and temperature dependent. Given the material properties, die dimensions, and process conditions, the model determines the flow field throughout the die gap. Computer simulations and experimental data are presented for a three‐layer polyester/EVA/polyester film coextrusion, with emphasis on the interfacial instability and its effects on optical properties of the film. The rsults are discussed in the context of the critical interfacial shear stress criterion that has been proposed by Schrenk, et al. (1) for the onset of interfacial instability. It appears that elasticity differences between layers contribute to the interfacial instability. It is conjectured that minimizing interfacial shear stress and matching elasticities of adjacent layers is an appropriate criterion in coextrusion analysis.
A sliding plate normal thrust rheometer for molten plastics
Authors: Oakley J. G. , Giacomin A. J. 
Published: May 2005

AbstractA sliding plate rheometer has been developed to measure the normal thrust of a molten plastic in large amplitude oscillatory shear. The normal thrust of a molten plastic in large amplitude oscillatory shear is a significant nonlinear effect that has previously been unobtainable. Normal thrust measurements may now be used to help understand and characterize nonlinear viscoelastic behavior inherent in most molten plastics. The new rhemoeter incorporates a piezoelectric pressure transducer in a very stiff plate that minimizes compliance. Normal thrust measurements with cone and plate rheometers are made by measuring the total force on the plate (or cone) and are subject to error due to edge effects. The new rheometer measures the local pressure in the sample and is therefore unaffected by sample size or edge effects. Normal thrust measurements in large amplitude oscillatory shear are reported for both molten Phillips TR480 high density polyethylene pipe resin which contains 2% by weight of carbon black filler and IUPAC LDPE X. Crosstalk due to shear stress on the active face of the pressure transducer causes signal error which for oscillatory shear is filtered out using a discrete Fourier transform.
Spectra composite that withstands torch flame test
Authors: Lem K. W. , Kwon Y. D. , Chin H. B. , Li H. L. , Prevorsek D. C. 
Published: May 2005

AbstractIn recent years, the development of high performance Spectra® fibers has received increasing attention in industry. Because of the outstanding capability to absorb energy, these polyethylene fibers are frequently used in damage tolerant composite materials to protect equipment, apparatus, and/or people against blast and debris of explosion or projectiles. Since the fiber is thermally stable, it is possible to design composite structures that are suitable for use in applications where prolonged exposure to flame is anticipated. In this paper, we report the findings obtained in a recent flammability evaluation of a Spectra composite subjected to a torch flame, and to hot metal balls. The Spectra composite structures that will be discussed were found to withstand these exposures without burning and the smoke generation and toxic gas emission were far below the limits set in the standard for current aircraft interior materials.