bluuebunny/crossref_metadata_2025_split huggingface dataset:
Creep rate variability in gel‐spun polyethylene fibers
Authors: Yakushev P. N. , Peschanskaya N. N. , Marikhin V. A. , Myasnikova L. P. , Jacobs M. J. N. 
Published: April 2004

AbstractThe phenomenon of stepwise creep has been discovered and studied earlier for unoriented polymers by a new laser interferometer method. This same technique has been used for studying long‐term menhanical properties of UHMWPE gel‐spun fibers of various draw ratios. A variability of creep rate has been observed. The creep rate variability has been characterized by two parameters: the typical period of deformation increment, with enhanced deformation rate (step), and the variability (inhomogeneity) of the deformation rate over a deformation interval. Despite a large scatter of data, at least three levels of deformation steps could be derived: (i) microns, (ii) tens of microns, (iii) hundred and more microns. The larger levels of deformation steps decrease with increasing draw ratio. Their dependence on strain is not observed. The creep rate variability significantly depends on the creep strain. First, it increases with strain and then decreases just prior to rupture. The effect of draw ratio on creep rate variability is not significant. It is assumed that the creep rate variability is a cooperative deformation. It is suggested that interfibrillar slip and slip between fibrillar layers occurs via a slip‐stick motion making a significant contribution to total deformation. The mechanism does not change with draw ratio.
Rheological, mechanical, and adhesive properties of thermoplastic‐LCP blends filled by glass fibers
Authors: Kulichikhin V. G. , Parsamyan I. L. , Lipatov Yu. S. , Shumskii V. F. , Getmanchuk I. P. , Babich V. F. , Postema A. R. 
Published: April 2004

AbstractRheological, mechanical, and adhesive properties have been studied of two‐phase polymer blends containing a liquid crystal copolyester of poly(ethylelene terephthalate) and p‐hydroxybenzoic acid plus isotactic polypropylene (PP) with varying compositions and concentrations of glass fibers. Perfect fibrillation of the disperse LC‐phase into the PP‐matrix in capillary flow was observed at LCP concentrations >20 wt% and temperatures >488 K. This effect leads to a decrease of blend viscosity and a reinforcing of the extrudate's mechanical characteristics. At the same time, more essential reinforcement is achieved by the simultaneous addition of the reinforcing agents both of the LCP and glass fibers. Processing of PP is not impaired. It was found that the adhesive strength increases substantially when the amount of LCP in the blend exceeds a definite level, corresponding to a phase inversion. The results are explained by the formation near the interface of two adhesion layers: the first is composed of pure LCP having a higher surface tension, whereas the second layer represents the blend of various compositions. At small amounts of LCP, the adhesion failure proceeds in the interphase between the LCP and the blend. After the phase inversion, where adhesion strongly increases, the failure of adhesion joints proceeds near the interface between LCP and the glass.
Rheokinetics of curing of epoxy resins near the glass transition
Authors: Malkin A. Ya. , Kulichikhin S. G. , Kerber M. L. , Gorbunova I. Yu. , Murashova E. A. 
Published: April 2004

AbstractThe cure of four epoxy‐amine systems was studied by viscometry, dynamic mechanical analysis, and DSC. The investigation was carried on at temperatures below and above the glass transition temperature (Tg) of completely cured products. Viscosity growth in the initial stage of cure is described by an exponential‐type equation, and on approach to the gel‐point by a power law, but the exponent did not coincide with the universal theoretical scaling‐law value. A universal viscosity master curve can be constructed if one reduces viscosity and time by their characteristic values. Gel‐times and activation energies of curing were found by different methods. It was established that the product of the initial rate of a reaction and the gel‐time is constant at various conditions of cure. Time dependences of the degree of conversion (calculated from calorimetric and dynamic mechanical data) in the full range of conversions are described by first‐ and second‐order kinetics, corrected by the factor reflecting self‐accelerating character of the reaction. Kinetic constants found from both methods are the same. If a reaction leads to a transition to the glassy state over the course of curing, a self‐acceleration equation is valid in the initial stage of the process only. The complete kinetic curve can be described by the DiBenedetto method relating shift of the Tg with the degree of conversion. The rate constant for vitrificating systems is presented as a sum of reciprocal values of chemical and diffusion constants. Time and temperature dependences of kinetic and diffusion constants were calculated.
Models for formation of supermolecular oligomeric liquid structures: Theory and experiment
Authors: Arinstein A. E. , Mezhikovskii S. M. 
Published: April 2004

AbstractTwo theoretical models are proposed to describe rearrangement mechanisms for supermolecular structures of oligomeric liquids. The first is based on the concept of associate‐size distribution, varying with the addition of molecules to the associates. These molecules are activated by external action. The other model takes into account the fact that after activation, the equilibrium size distribution function is attained by way of an activated molecule redistribution between associates, owing to “cleavage‐addition.” Within the framework of accepted restrictions, the analytical solutions were obtained adequately to describe rheological and relaxation relationships revealed for various types of oligomeric systems.
Discrete models of failure for particulate polymer composites
Authors: Moshev V. V. , Evlampieva S. E. 
Published: April 2004

AbstractA stochastic discrete model is offered that simulates the behavior of particulate composites able to generate and accumulate scattered structural microdamages to the final breakdown of the model. The model is quite transparent, which allows us to observe continuously its internal state and effective behavior. Through numerical experiments, it is established that the accumulation of the scattered damage, accompanied by the appearance of the elastic nonuniformity, ends in a loss of the elastic stability of the whole of system and macrocrack formation in the most compliant part of the body. No strength criteria are needed to describe this process. Breaking stresses and strains and their scatter in repeated experiments, as functions of the virgin system specification, can be calculated and used for safety factors or for optimization of composite properties.
Advances in maleated polyolefins for plastics applications
Authors: Roberts Darilyn H. , Constable Robert C. , Thiruvengada Seshan 
Published: April 2004

AbstractThe objective of the paper is three‐fold, covering the use of maleated polyolefins as chemical coupling agents, compatibilizers, and impact modifiers. Introduction of a new chemical coupling agent for glass reinforced polypropylene details its improved properties versus current systems. Discussion of impact modifiers includes three developmental impact modifiers that combine higher melt flow properties and good room temperature notched Izod properties. The third area details the property improvements obtained in nylon/polypropylene blends through compatibilization with a maleated polyolefin.
Fluorescence monitoring of polymer injection molding: Model development
Authors: Bur Anthony J. , Thomas Charles L. 
Published: April 2004

AbstractWe have developed models to describe the behavior of an optical fiber sensor which was used to detect fluorescence from a polymer resin during the cooling phase of injection molding. The optical fiber sensor was positioned at the wall of the mold cavity by using the ejector pin channel as access to the cavity. The sources of fluorescence were dyes, which were chosen because of their sensitivity to temperature and which were mixed with the resin at dopant concentrations (parts per million by weight). The behaviors of a molecular rotor dye, dimethylamino diphenyl hexatriene, doped into polyethylene, and an excimer producing dye, bis‐(pyrene) propane, doped into polystyrene were the subjects of the modeling calculations. The models consist of two modules: (a) a solution to the thermal diffusion equation for the resin cooling in the mold and (b) using temperature/time profiles and, in the case of polyethylene, crystallinity/time profiles obtained from the thermal diffusion equation, fluorescence intensity as a function of time was computed. Factors incorporated in the models are: adiabatic heating and cooling, light scattering due to microcrystals of polyethylene, crystallization kinetics, temperature and pressure shift factors for viscoelastic relaxation near the glass transition temperature of polystyrene, and the thermal resistance at the resin/mold interface.
Physical aging kinetics of syndiotactic polystyrene as determined from creep behavior
Authors: Beckmann Jorg , McKenna Gregory B. , Landes Brian G. , Bank David H. , Bubeck Robert A. 
Published: April 2004

AbstractCreep experiments in uniaxial extension have been performed to explore the kinetics of the physical aging process in semicrystalline syndiotactic polystyrene (sPS) having two processing histories. Classical time‐aging time superposition behavior was found for both materials at temperatures from 70 to 95°C, with the shift rate μ decreasing as temperature was increased. Virtually no aging was seen at 95°C, the DSC determined glass transition, Tg. This behavior was atypical for a semicrystalline polymer and reminiscent of the behavior of glassy amorphous thermoplastics. Some evidence for a separate crystalline aging mechanism > Tg, which manifests itself as only vertical shifts without timescale shifts, is seen in experiments at T > 100°C. Finally, the two different materials age differently, suggesting that some control of aging can be obtained by altering processing conditions or morphology.
Large deformation response of polycarbonate: Time‐temperature, time‐aging time, and time‐strain superposition
Authors: O'Connell P. A. , McKenna G. B. 
Published: April 2004

AbstractData are presented from tests of the stress relaxation response of a polycarbonate under torsional deformations. Tests were performed on samples over a range of strains from 0.0025 to 0.08, temperatures from 30 to 135°C and aging times from 1800 to 64,800 s. Individual data sets at each strain, temperature and aging time could be described using a stretched exponential form relaxation function, and time‐aging time superposition was found to be applicable to the data under all test conditions. The double logarithmic aging time shift rate, μ was found to vary significantly with both temperature and strain. Over the range of temperatures studied the data could be superimposed using conventional time‐temperature superposition. However, the master curve was found not to be described by a stretched exponential function. For strains up to 0.07, the data at each temperature could also be superimposed to form a master curve following the principle of time‐strain superposition. Interestingly, the master curves found from time‐strain and time‐temperature superposition did not have the same form. In both the time‐aging time and time‐temperature superposition analyses it was found that the application of vertical shifts was required for superposition of data.
Synthesis and characterization of flame resistant poly(arylene ether)s
Authors: Riley D. J. , Gungor A. , Srinivasan S. A. , Sankarapandian M. , Tchatchoua C. , Muggli M. W. , Ward T. C. , McGrath J. E. , Kashiwagi T. 
Published: April 2004

AbstractHydrolytically stable phosphorus‐containing monomers, such as 4,4′‐bis(fluorophenyl)methylphosphine oxide (BFPMPO), 4,4′‐bis(hydroxyphenyl)methylphosphine oxide (BOHPMPO), and 4,4‐bis(hydroxyphenyl)phenylphosphine oxide (BOHPPO), were synthesized and used in nucleophilic aromatic substitution poly‐condensation to prepare poly(arylene ether phosphine oxide) engineering thermoplastics. The synthesis and characterization of these novel polymers are described. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone, certain properties of the resulting poly(arylene ether) were substantially improved, such as an increase in Tg, thermal stability in air, modulus, and char yield compared with control poly(arylene ether sulfone)s. The high char yields obtained for these polymers in air along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion.
Control of plastic melt temperature: A multiple input multiple output model predictive approach
Authors: Dubay Rickey , Bell Adam C. , Gupta Yash P. 
Published: April 2004

AbstractGood control of plastic melt temperature for injection molding is very important in reducing operator setup time, ensuring product quality, and preventing thermal degradation of the melt. The controllability and setpoints of other process parameters also depend on the precise monitoring and control of plastic melt temperatures. We experimentally investigated the thermal interactions between the barrel zones of an instrumented plastic injection molding machine (IMM). These interactions result from the zone temperature differences that are used in normal machine operations. From these experimental interactions, multiple‐input‐multiple‐output (MIMO) and single‐input‐single‐output (SISO) models were derived for controlling these zone temperatures using a Model Predictive Control (MPC) strategy. An experimental comparison was made between MIMO MPC and SISO MPC of plastic melt temperature, which showed that the MIMO MPC scheme is more energy efficient, having zero overshoot.
The effect of composition on thermal, mechanical, and morphological properties of thermotropic liquid crystalline polyester with alkyl side‐group and polycarbonate blends
Authors: Chang Jin‐Hae , Choi Bong‐Ku , Kim Jae‐Hoon , Lee Soo‐Min , Bang Myung‐Sik 
Published: April 2004

AbstractA thermotropic liquid crystalline polymer (LCP) with an alkyl side‐group was synthesized. Blends of the LCP with polycarbonate (PC) were prepared by coprecipitatton from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of PC, and significant viscosity reductions were observed in the temperature range of 200–230°C. Blends of different LCP compositions were extruded with different draw ratio from a capillary rheometer. The ultimate tensile strength showed a maximum at a 10 wt% LCP composition in the blends. It decreased for compositions greater the 10 wt% LCP, whereas the initial modulus increased with increasing LCP content. The morphology of the blends was found to be affected by their compositions. Scanning electron microscopy (SEM) studies revealed finely dispersed spherical LCP domains in the PC matrix. The SEM micrographs also showed a poor adhesion between the two phases.
Molecular mobility in polycyanurate networks investigated by viscoelastic measurements and molecular simulations
Authors: Georjon Olivier , Schwach Gregoire , Gerard Jean‐François , Galy Jocelyne , Albrand Michel , Dolmazon Rene 
Published: April 2004

AbstractThe dynamic mechanical behavior of a series of polycyanurate networks has been studied in the glassy state as a function of cyanate conversion. Two relaxations, β and γ, were defined and the Arrhenius dependence and Starkweather treatments were applied. To understand the origin of these sub‐Tg relaxations, molecular modeling (both mechanics and dynamics) was used on model molecules representative of the network structure. Two types of molecular motion were examined: rotation of the phenylene ring and crankshaft of the chain segment between crosslinks (i.e., triazine rings).
Viscoelastic relaxations in polyepoxide joints related to the strength of bonded structures at impact rate shear loading
Authors: Lataillade J. L. , Cayssials F. 
Published: April 2004

AbstractThe aim of this paper is to show the excellent impact behavior of a modified epoxy joint on consideration of the viscoelastic relaxation processes of an adhesive. The investigation of the epoxy joint properties, over a range of strain rates (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ \cdot $\end{document}= 10−2to 104S−1) and temperatures (−30, 24, 60, 80°C), shows that there is a good correlation between high impact resistance and the presence of a secondary transition. We successfully applied the Bauwens approach to explain the strain rate sensitivity of the yield stress in terms of a difference in relaxation times at low and high strain rates (α and β). Our purpose is to confirm these results by applying the Escaig model, which reviews thermoset behavior in terms of a thermally activated dislocation propagation mechanism. The Bauwens approach and the Escaig model lead to the same conclusion: They indicate that there is a critical strain rate\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ \cdot $\end{document}β(T), correlated to a critical temperatureTβ(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ \cdot $\end{document}), that corresponds to the limits between the two modes of deformation required to free the different kind of molecular motions implied in the deformation process, the α mode to the α + β mode. But at low temperature (−30°C), these models are no longer valid, which means that there is a heterogeneous deformation process, characterized by local molecular motions, which involve a decrease of the polymer entropy and a permanent evolution of molecular structure.
The three successive stages of creep of PMMA between 55°c and 90°c
Authors: Chérière J. M. , Bélec L. , Gacougnolle J. L. 
Published: April 2004

AbstractAfter cooling from 140°C, the physical aging of poly(methyl methacrylate), PMMA, has been studied at 55, 70, 84, and 90°C by means of temporary microcreep tests. The systematic analysis of recoveries reveals that at 90°C, creep follows successively three different stages. After stress application, creep starts by a logarithmic function of time, while recovery follows exactly the same kinetics. An Andrade creep begins after the logarithmic creep: It is in fact the beginning of the Kohlrausch‐Williams‐Watts creep with an exponent of 0.36. This creep is fully recoverable, but the duration of this recovery is ∼3 times the creep duration. The third stage of creep is superimposed on the Andrade creep and follows a power law in t0.8, but it is not recoverable in the usual duration of experiments. By comparison with the recoverable creep of PMMA studied by Plazek above Tg, which can be fitted by a KWW law with an exponent 0.8, this third creep is interpreted as the beginning of the rubbery deformation.
Polymers under mechanical stress: Deformation of the nanostructure of isotactic polypropylene revealed by scanning force microscopy
Authors: Castelein G. , Coulon G. , G'sell C. 
Published: April 2004

AbstractScanning force microscopy (SFM) was used to study the lamellar morphology of α and β spherulites in bulk intruded isotactic polypropylene (iPP) samples deformed under shear stress. The iPP specimens were sheared at a constant shear rate at room temperature. Just beyond yielding, at a shear strain level of 0.5, the lamellar structure of the α‐spherulites resembles that for unsheared iPP; few cracks are observed along the interfaces between neighboring α‐spherulites: this behavior is attributed to a “cross‐hatched” lamellar texture of the α‐spherulites. In β‐spherulites, at the same shear strain, SFM observations reveal the presence of nanocracks perpendicular to the principal tensile strain axis, going through stacks of crystalline lamellae. Profuse local lamellar kinkings occur along the principal compressive strain axis and few nanocracks parallel to the molecular axis are seen in individual lamellae that lie along the shear direction. Neither particular preferred lamellar orientation nor localization of deformation within shear bands has been detected.
Interface and mechanical coupling effects in model particulate composites
Authors: Alberola N. D. , Mele P. 
Published: April 2004

AbstractDynamic mechanical spectra of polystyrene (PS) or styrene‐co‐methacrylic acid copolymer (SAMA) filled by various amounts of raw or coated glass beads have been recorded in the glass transition (Tg) region of the polymers used as the matrix. The relative contribution of the two key features governing the magnitude of the main mechanical relaxation, i.e., (i) the mechanical coupling between phases, and (ii) the physico‐chemical interactions at the polymer/filler interface, is separated by an original mechanical modeling, which gives evidence only for the reinforcement effect of the polymer matrix. Thus, by comparing experiment and theory, it was shown that the decrease in the tanδ maximum displayed by PS reinforced by high volume fractions of raw glass beads mainly results from an improvement of the reinforcement effect, because of the presence of clusters of particles. In contrast, for SAMA copolymer used as the matrix, it was found, in addition, a decrease in the molecular mobility of chains due to interactions at the polymer/coated glass bead interface. Differential scanning calorimetry and scanning electron microscopy analysis agree with this conclusion.
Durability of sheet molding compounds: Influence of hydrothermal aging on morphology and molecular mobility at microscopic scale
Authors: Blancon R. , Martinez‐vega J. J. , Merle G. , Camino G. , Polishchuk A. Ya. , Luda M. P. , Revellino M. 
Published: April 2004

AbstractThe physicochemical aging for parts of Sheet Molding Compound should be considered for their lifetime management and reusability. This material has a complex morphology and contains porosity due to the process and to shrinkage compensation. This SMC study has two complementary approaches. One describes the morphological consequences of water uptake, showing the decrease in the total amount and the fractal dimension of micro‐voids by scanning electron microscopy and image processing. The other shows, by mechanical spectrometry, the effect of water on physical or chemical bonds. In both cases, the “low profile agent” in SMC plays an important role. The molecular mobility was taken as a sensor parameter for the structural changes at the molecular scale, highlighting and quantifying the first steps of the aging. The loss factor level increases, and the activation energies are modified, even for the first aging days. The analysis shows recovery for the material near the relaxation peak of the low profile agent, since the curve recovers its initial shape.