bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computer simulation and molecular theory of self‐organization and mechanical properties of polymers
Authors: Melker A. I. , Vorobyeva T. V. 
Published: April 2004

AbstractIn this contribution, we report on a study of the self‐organization of extended linear polymer chains into condensed globules using molecular dynamics methods. We have found that condensed chains (globules) are amorphous or crystalline depending on the interaction potential between constituents. Any structure is formed in several stages. The structures obtained were used in further computer simulations to investigate such processes as compression, decompression, fracture, and flow. We have found that there are different types of fracture and plastic behavior with their own energy, fluctuation, and defect characteristics. On the basis of the computer simulation results obtained, the equation of motion is derived for the system of chain macromolecules slipping relative to each other. The equation takes into account the relaxation and friction in the system. The solution obtained gives the general law that connects stress, strain rate, molecular mass, potential relief, and temperature. It also gives sound physical grounds for some empirical relations that are used in polymer technology.
Synthesis and characterization of glycoside non‐ionic surfactants
Authors: Ricardo Nágila M. P. S. , Glendinning Andrew , Price Colin 
Published: April 2004

AbstractWe report on the synthesis of non‐ionic surfactants via the Koenigs‐Knorr reaction with chemical structures GOR and GOPOG, where GO(H) is glucose, R is n‐decyl or n‐dodecyl, and P is polyoxypropylene or polycaprolactone. Surface properties were studied using a Cenco‐du‐Nouy tensiometer. Light and transmission electron microscopy were used to investigate the phase behavior of the surfactants over a range of concentrations. AOR surfactants, where A is the product of amylose degradation and R is decyl, were synthesized by an alcohol exchange procedure.
Synthesis and characterization of bulky side chain methacrylate polymers
Authors: Radić Deodato , Martínez Francisco , Gargallo Ligia , Hamidi Nasrollah 
Published: April 2004

AbstractThe synthesis, and dilute solution behavior of poly(2,4‐dimethylphenyl methacrylate) (2,4DMP), poly(2,5‐dimethylphenyl methacrylate) (2,5DMP), and poly(3,5‐dimethylphenyl methacrylate) (3,5DMP) is described. Comparison is made with results reported for other bulky side chain polymers. The Kuhn‐Mark‐Houwink‐Sakurada (KMHS) relationships were established. The unperturbed dimensions 〈r2〉, the rigidity factor σ, the characteristic ratio C∞, and the thermodynamic parameters were determined, using the Stockmayer‐Fixman equation, from viscometric data in good solvents. The high rigidity observed for these polymers is explained assuming that these polymers behave as kinked‐chains.
Mechanics of failure of plastics by thermal imaging examination of a thermoplastic polypropylene + EPDM blend
Authors: Anne D'Souza Nandika , Brostow Witold , Ramamurthy A. C. , Wang Yingxia , Thomas Robert L. , Favro Lawrence D. 
Published: April 2004

AbstractThermal wave imaging combined with stress pattern analysis by measurement of thermal emission (SPATE) is used to study the failure behavior of a polypropylene (PP) + ethylene propylene diene (EPDM) polymer blend. Images corresponding to a propagating crack in a single edge‐notched specimen were measured at three rates of testing: 4 mm/min, 8 mm/min, and 20 mm/min. Conversion to stress values is made through use of a thermoelastic function. It is found that in a 4 mm/min test the crack tip radii blunt rather than propagate with little initiation. Large‐scale necking precedes fracture. At 8 mm/min, some blunting occurs, followed by fast crack propagation. At 20 mm/min, fast crack propagation occurs. The images are digitized to obtain the values of the temperatures at every point in the sample. Data corresponding to the plane of the propagating crack over the span of the test are presented.
Dynamic mechanical behavior of poly(aryl ether ether ketone) in the −150°C to +100°C temperature range: Influence of the nature of sorbed solvents
Authors: Bas C. , Alberola N. D. 
Published: April 2004

AbstractThe dynamic mechanical behavior of poly(aryl ether ether ketone) (PEEK) films submitted to various treatments, i.e. physical aging, crystallization, and immersion in various solvents (water and some alcohols), has been investigated at low temperatures in order to give new insights on the origin of the subglass transitions. Two processes, i.e., the simple thermorheological component at lower temperatures and the cooperative component at higher temperatures, are overlapped in the β relaxation of dry PEEK. Sorbtion of such solvent molecules as water, ethanol, methanol, and isopropanol gives rise to new relaxations.
Effect of added β‐cyclodextrin on the biostability of polyurethane
Authors: Sreenivasan K. 
Published: April 2004

AbstractBlending of β‐cyclodextrin (BCD) was found to accelerate the biodegradation of polyurethane under biotic environmental exposure. The enhanced degradation induced by BCD has been demonstrated by gel permeation chromatographic and scanning electron microscopic analysis.
Polyethylene exposed to liquid propane: Sorption and permeation kinetics and mechanical properties
Authors: Hedenqvist M. , Johnsson G. , Tränkner T. , Gedde U. W. 
Published: April 2004

AbstractData obtained by sorption and permeation measurements of liquid propane in medium‐density polyethylene were analyzed with an analytical diffusion model, assuming a constant diffusion coefficient, and a numerical model, based on the free volume theory of Fujita. The stress‐strain properties of propane‐swollen medium‐density polyethylene were recorded in an Instron tensile tester. The sigmoid sorption curves (modeled here for the first time) were adequately described using nonstationary boundary conditions. The numerical model was capable of representing sorption, desorption, and permeation data, whereas the analytical technique gave satisfactory results only for sorption/desorption data in the initial, transient stage. The difference between diffusion coefficients determined from sorption and desorption measurements and the time dependence of the modulus‐solute concentration relationship can be explained by assuming a relaxation of constrained amorphous chain segments. The penetrant‐induced structure rearrangement is, according to differential scanning calorimetry measurements, confined to the amorphous phase.
Effect of zinc stearate on the rheology of ionic elastomer based on carboxylated nitrile rubber
Authors: Mandal U. K. , Tripathy D. K. , De S. K. 
Published: April 2004

AbstractMonsanto rheometry, melt viscometry, differential scanning calorimetry, and dynamic mechanical spectroscopy have been used to study the effects of zinc stearate on the rheological behavior of ionomer based on carboxylated nitrile rubber (XNBR) ‐ zinc oxide (ZnO) system. At temperatures below its melting point, zinc stearate functions as a reinforcing agent for ionomer formation. Above its melting point, it acts as a plasticizer for the ionic domains, thereby facilitating easy processing of the ionomer.
Solidification of thermoviscoelastic melts. Part 3: Effects of mold surface temperature differences on warpage and residual stresses
Authors: Bushko Wit C. , Stokes Vijay K. 
Published: April 2004

AbstractThe solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part warpage in the injection‐molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification so that this model can be used to assess packing‐pressure effects in injection molding. Parametric results are presented on the effects of the mold temperatures and the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in‐plane and through‐thickness shrinkages, on warpage, and on residual stresses in plaque‐like geometries. The packing pressure is shown to have a significant effect on part warpage. While the results are presented in terms of normalized variables based on the properties of bisphenol‐A polycarbonate, they can be interpreted for other amorphous thermoplastics, such as modified polyphenylene oxide, polyetherimide, and acrylonitrile‐butadiene‐styrene.
On‐Line measurement of parison geometry during blow molding: Parison swelling for three high‐density polyethylenes with different molecular weights and molecular weight distributions
Authors: Eggen Svein , Sommerfeldt Arne 
Published: April 2004

AbstractAn image analysis technique has been developed to measure diameter and thickness distribution of a parison during the extrusion stage in blow molding. The system operates on‐line during extrusion on any commercial blow‐molding machine. The system has been developed to help development of new blow‐molding resins by increasing our understanding of the connection between polymer structure and parison shape. The system can also be used for die design during optimization of a production process. The combined use of experimental design and multivariate projection techniques makes this an efficient tool for the practical processing engineer. Experiments done on three high‐density polyethylene blow‐molding resins show the importance of measuring the time dependence of the diameter and thickness distribution under different extrusion conditions for a given polymer. Our results show that many of the swell and sag related properties we see cannot be directly inferred from standard laboratory swell‐experiments.
Effect of processing on the recyclability of nylon 66/poly(2,6 dimethyl‐1,4 phenylene oxide) (PPO) alloys
Authors: Laverty John J. , Ellis Thomas , O'Gara John , Kim Sooho 
Published: April 2004

AbstractThe recyclability of two commercial nylon 66/PPO [poly(phenylene oxide)] alloys has been investigated by examining the effects of multiple and abusive melt processes upon the impact strength. The loss of performance associated with these exposures has been correlated, in one instance, with the thermal degradation of polybutadiene‐based impact modifier. The degradation of the rubber has been quantified using an indirect measurement of rubber mobility obtained from the NMR free induction decay of mobile and rigid protons in the material. Substitution of the unsaturated rubber modifier with a saturated hydrocarbon resulted in improved recyclability. Both formulations provide evidence of changes in morphology related to instability of the dispersed PPO phase. The coalescence of PPO particles, evident in later stages of prolonged thermal exposure, appears to cause further loss of impact strength. Currently the chemical and/or physical changes responsible for the increase in average PPO particle size are not known. It is probable that the thermal stability of the compatibilizer, formed during the reactive extrusion manufacturing process, may be insufficient to provide a durable morphology for repeated recycling of these alloys.
Extrusion of non‐newtonian fluids in a single‐screw extruder with pressure back flow
Authors: Chiruvella Raman V. , Jaluria Y. , Sernas V. , Esseghir M. 
Published: April 2004

AbstractThe transport phenomena underlying the extrusion of non‐Newtonian fluids in single‐screw extruders is investigated numerically and experimentally. The viscosity of the investigated fluids is a strong function of the temperature and, for the non‐Newtonian case, of the shear rate. Therefore, the governing equations of motion are coupled to the energy equation through the viscosity. The velocity in the down channel direction of the screw extruder is a result of both shear and pressure driven transport. The pressure acts in a direction opposite to that of the drag flow, and comparatively high pressures arise at the die in typical extruders. When a narrow die is used in the screw extruder, the pressure gradient in the down‐channel direction becomes so large that the down‐channel velocity near the screw root becomes negative in terms of the coordinate system fixed to the screw. The conventional marching schemes fail to simulate the fluid flow when the down‐channel velocity becomes negative, since the downstream conditions are not known. Two different numerical schemes used to simulate the fluid flow in a single‐screw extruder for this circumstance, which often arises when dies with high flow resistance are used and which is termed as pressure back flow in the literature, have been discussed. One scheme is based on including the down‐channel thermal diffusion, making the problem elliptic, and the other scheme uses a different coordinate system. Both formulations are found to yield results that are fairly close. Experiments were also carried out to measure the pressures at three different locations in a single‐screw extruder. The computed results were found to be in good agreement with the experimental results. The pressures at the die obtained numerically by treating the flow as isothermal are found to be lower than those obtained when the flow is treated as nonisothermal, indicating the strong influence of thermal transport in this problem.
Computer simulation of viscoelastic flow at the entry region
Authors: Loh K. W. L. , Teoh S. H. , Tay A. A. O. 
Published: April 2004

AbstractNon‐Newtonian flow has a nonlinear constitutive relationship with an advective nature. It was found that in highly advective (convective) problems, the Galerkin formulation “under‐diffused,” resulting in divergence at low elastic numbers. The use of the Streamline‐Upwinding (SU) method improved the solution, especially when used with the Phan‐Thien‐Tanner (PTT) model. At the boundary discontinuity, however, the stress gradient did not necessarily flow along the streamline direction, and oscillations still remained at the corner. The Discontinuity‐Capturing (DC) method resolved this problem by applying control in the direction of the stress gradient rather than the stream line direction, and a smoother solution at the corner region was achieved.
Characterization of photocurable coatings using fluorescence probes
Authors: Song J. C. , Neckers D. C. 
Published: April 2004

AbstractIn this paper, we describe a novel method for monitoring the degree of cure and coating thickness of photocurable resins using intramolecular charge transfer (ICT) fluorescence probes such as 5‐dimethylaminonaphthalene‐1‐sulfonyl‐n‐butylamide (DASB) and 6‐propionyl‐2‐(dimethylamino)‐naphthalene (PRODAN). As the curing reaction proceeded, the fluorescence emission spectra of the ICT probes were found to exhibit hypsochromic spectral shifts because of the increase in matrix microviscosity, which made it more difficult for the excited molecule to relax to its twisted charge transfer state. The spectral changes of the probes as a function of the degree of the cure were monitored using a fluorescence intensity ratio method, which enabled an internal calibration of fluctuations in lamp intensity and sample thickness. It was found that the ratios of the fluorescence emission intensities at two different wavelengths were correlated linearly with the degree of polymerization for different types of acrylic or unsaturated polyester resins using either UV or visible (VIS) initiators. The coating thickness of photopolymers was measured based upon the nascent fluorescence from the coating substrate by virtue of an emission (from the substrate) and adsorption (by the coating) mechanism. The thicker the coating, the less the nascent fluorescence emission that can be observed. So the intensity of the nascent fluorescence from the substrate can be correlated to the coating thickness.
Effect of casting solvents on the morphology and properties of styrene‐butadiene‐styrene triblock copolymer membranes
Authors: Yang Jen‐Ming , Hsiue Ging‐Ho , Chen Hsin‐Lung 
Published: April 2004

AbstractThe effect of the casting solvents on the morphology and properties of styrene‐butadiene‐styrene (SBS) triblock copolymer membranes has been investigated. The SBS membranes were prepared by both dry and wet processes. The stress relaxation of the membranes prepared by the dry process was studied. It was found that the stress relaxation of the membrane prepared from tetrahydrofuran (THF) proceeded faster than that of the membrane prepared from the mixed solvent of THF and heptane. This phenomenon could be ascribed to the different membrane morphologies created by the two solvent systems. Three different SBS membrane structures were obtained from three different casting solvents. The results were interpreted based on the miscibility between the solvent and the nonsolvent.
Control of a chaotic polymerization reactor: A neural network based model predictive approach
Authors: De Souza Maurício B. , Pinto José Carlos , Lima Enrique L. 
Published: April 2004

AbstractContinuous polymerization processes may be very sensitive to small changes of the operation conditions. Continuous VA (vinyl acetate) solution homopolymerization reactors may present multiple steady‐states and oscillatory behavior. A predictive control scheme that uses an internal model of the process is employed to stabilize such reactors and make them less sensitive to disturbances while subject to “hard” control action constraints. An ANN (artificial neural network) is used as the internal model, leading to fairly good predictions of the reactor behavior, including its multiplicities. The performance of the resulting control algorithm is compared to that of a “well‐tuned” conventional proportional‐integral‐derivative (PID) controller.
Degradation of polyolefin pipes in hot water applications: Simulation of the degradation process
Authors: Viebke J. , Elble E. , Gedde U. W. 
Published: April 2004

AbstractA program was developed that yields the number of chain scission and crosslinking events representing the best fit of a simulated molar mass distribution to a molar mass distribution determined by size exclusion chromatography. The program was applied to molar mass distributions of samples taken from pressure‐tested pipes of an unstabilized medium‐density polyethylene. Good fits were obtained after various exposure times at different temperatures and at different positions in the pipe wall. The ratio of the number of chain scission to crosslinking events generally decreased with increasing exposure time and with decreasing accessibility to oxygen in the pipe wall. Correction for long‐chain branching effects led to significant changes in the optimum chain scission and crosslinking values obtained. The broad and asymmetric shape of the molar mass distributions, typical of degraded material from originally stabilized medium‐density pipes, was shown to arise from a combination of a uniformly degraded and a nondegraded component. The program was also successfully applied to the molar mass distribution of a sample taken from a degraded commercial polybutylene‐1 pipe.
A novel method to prepare high‐resistivity polymer composites
Authors: Chan C.‐M. 
Published: April 2004

AbstractA novel method was developed for the preparation of high‐resistivity conductive polymer composites reproducibly. The conventional method which involves the simple mixing of a conductive filler and a polymer usually produces a conductive polymer composite having a loading curve with a region in which the resistivity changes rapidly as the filler concentration changes. Hence, it is very difficult to obtain reproducible materials in that region. This newly developed method involves the preparation of a conventional conductive polymer composite, which is prepared by the simple mixing of carbon black and a polymer as the first step. The resulting compound, which is crosslinked by either electron‐beam radiation or a chemical‐crosslinking agent, is ground into a fine powder (composite filler) with the particle size less than 250 microns. The composite filler is mixed with another polymer to form a conductive particulate composite which has a loading curve showing a more gradual change of resistivity as a function of filler concentration. The modification of the loading curve is controlled by the resistivity, the shape, and the size of the composite filler.
The recycling of thermoplastics: Prediction of the properties of mixtures of virgin and reprocessed polyolefins
Authors: Bernardo C. A. , Cunha A. M. , Oliveira M. J. 
Published: April 2004

AbstractA theoretical basis for the prediction of the properties of mixtures of virgin and reprocessed polymers is presented. The concept is developed using equations that describe the loss of polymer properties as a function of processing cycles. These equations correspond to properties that are important in characterization and quality control, such as melt flow index and tensile and impact strengths. Experimental data were determined and used to test the models derived. For glass‐fiber‐reinforced thermoplastics, the data on the degradation of fiber lengths and mechanical properties can help to understand the effect of reprocessing on the fiber‐matrix interaction.
Effect of intramolecular interactions on the miscibility windows of PVC blends with modified SAN copolymers
Authors: Kim Chul‐Hwan , Park Jung‐Ki , Hwang Taek‐Sung 
Published: April 2004

AbstractWe investigated the miscibility windows in the blends of poly(vinyl chloride) (PVC) with chemically modified styrene/acrylonitrile (SAN) copolymers such as α‐methyl styrene/acrylonitrile (α SAN), α‐methyl styrene/methacrylonitrile (MSMAN). The blends of PVC with α SAN were found to have the broader miscibility window. This enhanced miscibility was interpreted in terms of intramolecular repulsion that originates from unfavorable interaction between counits of the copolymers and also intramolecular association of AN units. The intramolecular interactions were studied by using Fourier transform infrared (FT‐IR) spectroscopy. These interactions were reflected by a peak broadening in the nitrile stretching band in the acrylonitrile segments. The intermolecular interactions governing the miscibility in the blends of PVC with the series of copolymers were also discussed.
Mechanical behavior of a ductile polyamide 12 during impact
Authors: Schang O. , Billon N. , Muracciole J. M. , Fernagut F. 
Published: April 2004

AbstractThe mechanical behavior of a polyamide 12 is characterized using a viscoplastic law taking into account viscoelastic deformation. Experimental determinations are performed at constant and very low strain‐rates in isothermal conditions during tensile tests. A finite elements code, based on this behavior, enables us to reproduce tensile tests even at different strain rates (up to 0.5 s−1) provided that heat power dissipation due to deformation is taken into account. The same model partially reproduces multiaxial impact tests. Strain hardening is generally over‐estimated by the calculation. It is pointed out that mechanical behavior should be characterized in ways closer to impact loading conditions than tensile tests to be more efficient because of the difference in microstructural evolutions during drawing.
Cure monitoring of photosensitive resins by photo‐dynamic mechanical analysis
Authors: Renault Thierry , Ogale Amod A. , Drews Mike J. 
Published: April 2004

AbstractA new technique, photo‐dynamic mechanical analysis, was developed to monitor the cure of photosensitive resins. In this technique, the resin is dispensed on a low modulus substrate and the force needed to maintain a prescribed elongation on the sample is measured while the sample is exposed to an ultraviolet source. The force increases with the extent of cure and reaches a plateau when the resin is fully cured. Photo‐dynamic mechanical analysis was found to be a rapid, continuous, and reliable technique to monitor the extent of cure of photopolymerizable resins. A finite element analysis was developed to calculate the resin modulus from the experimental force data. Thus, it was possible to monitor the resin modulus from the liquid state to the solid state.