bluuebunny/crossref_metadata_2025_split huggingface dataset:
The synthesis and characterization of novel thermotropic liquid crystalline poly(aryl ether ketone)s
Authors: Bennett Greggory S. , Farris Richard J. 
Published: May 2005

AbstractThe synthesis and characterization of novel thermotropic liquid crystalline poly(aryl ether ketone)s based on the reaction of a liquid crystalline mesogen containing monomer, biphenol, and a crystal‐disrupting substituted monomer, t‐butyl‐ or phenyl‐, hydroquinone with 4,4′‐difluorobenzophenone are described. Two families of copolymers—a biphenol/t‐butylhydroquinone series of 90,75,50, 25, and 0% biphenol, and a biphenol/phenylhydroquinone series of 75, 50, 25, and 0%—are evaluated. Thermotropic liquid crystalline behavior was observed in the copolymers containing 50 and 75% biphenol. The first order and second order transitions associated with melting, crystallization, thermotropic liquid crystalline mesophases, and glass transition temperatures (Tgs) of each copolymer are investigated. The thermal transitions are correlated with optical microscopy and X‐ray and/or electron diffraction characteristics. It was observed that the Tg increases and end group concentration decreased after isothermal heat treatment indicative of further polymerization. These materials are believed to be the first known thermotropic liquid crystalline poly(aryl ether ketone)s.
The effect of preloading on the mechanical properties of polymeric foams
Authors: Ozkul M. H. , Mark J. E. 
Published: May 2005

AbstractThe polymeric foams investigated with regard to their mechanical properties were the rigid foams polystyrene, polyurethane, and phenolic, and the semirigid foam polyethylene. Preloading of the rigid foams was found to decrease the modulus by an amount that increased as the extent of preloading increased, and to decrease both the modulus and collapse stress in the case of the semirigid ones. The shape of the stress‐strain curves of the foams was also significantly changed by the preloading, and a reduction in cushioning properties in static compression was observed.
High pressure polymerization of ethylene and rheological behavior of polyethylene product
Authors: Kalyon Dilhan M. , Chiou Yeong‐Ning , Kovenklioglu Suphan , Bouaffar Ali 
Published: May 2005

AbstractA mathematical model of the high pressure polymerization of ethylene in tubular reactors was tested with experimental data obtained from an industrial size tubular reactor. Series of experiments involving changes in operating conditions were carried out, and process data and polyethylene samples were collected. The collected samples were characterized for their molecular weight distributions and various rheological material functions involving shear and extensional flows. The findings of the model were compared against the generated process data and the molecular weight distributions of the samples. The determined rheological behavior exhibited strong dependence on the primary characteristics of the resins. Overall, this study should introduce a better understanding of the interactions between high pressure reaction conditions and the primary properties of polyethylene, including moments of molecular weight distribution and extent of branching on one hand and the interrelationships between primary properties and the rheological behavior of the high pressure polyethylene product on the other hand.
Spinnability of ultrasonically synthesized poly(vinyl alcohol‐b‐acrylonitrile) emulsions
Authors: Xiao Weiwei , Xu Xi , Chen Keqiang 
Published: May 2005

AbstractThe relationship between spinnability and composition of poly(vinyl alcohol)/polyacrylonitrile block copolymer emulsions prepared by an ultrasonic technique is presented. Theoretical analysis and experimental investigation by multiple techniques show that the micellar structure characteristics of the block copolymer emulsions and the behavior of emulsion in shear flowing and coagulating in spinning process are the key factors affecting the spinnability. The mechanical properties of the final fibers are related to the composition, molecular weight, spinnability of the copolymers, and the processability of the as‐spun fibers.
Some effects of irradiation on properties of filled PVC compounds
Authors: Bataille P. , Mahlous M. , Schreiber H. P. 
Published: May 2005

AbstractCompounds based on poly(vinyl chloride) (PVC), and containing CaCO3 filler and trifunctional acrylic crosslinking agent have been crosslinked by exposure to γ‐rays at dosages to 70 kGy. The crosslinking agent was found to be essential for crosslinking to proceed, only minor sensitivity to the irradiation having been found in compounds omitting the chemical. The presence of filler somewhat inhibits crosslink effectiveness, as measured by solvent uptake data. Elastic moduli and elongations at rupture respond to crosslinking processes, the latter being particularly sensitive to the effects of irradiation. The presence of filler was found to raise modulus, while ductilities of compounds were greater than expected, owing to adhesion at polymer/filler interfaces. Favorable acid/base interaction forces appear responsible for the effect. The reduced sensitivity of filled PVC compounds to γ‐ray exposure is attributed to polymer immobilization, the consequence of strong interfacial bonding with the filler.
Non‐Newtonian and isothermal analysis of flow of poly(methyl methacrylate) in a model twin screw extruder. Part I
Authors: Chu Lih‐Long , Min Kyonsuku 
Published: May 2005

AbstractThe flow analysis network (FAN) method was modified to analyze the flow of poly(methyl methacrylate) (PMMA) in a model counter‐rotating nonintermeshing screw extruder. The numerical prediction of the pressure profiles was compared with the experimental results. Flow patterns in the screw elements of the model counter‐rotating nonintermeshing twin screw extruder were also predicted. A new flow path method was developed to calculate the residence time distribution. This result will be applied to analyze the flow during the reaction in the model twin screw extruder.
Non‐Newtonian and non‐isothermal analysis of flow during polymerization of methyl methacrylate in a model twin screw extruder. Part II
Authors: Chu Lih‐Long , Min Kyonsuku 
Published: May 2005

AbstractThe flow analysis network (FAN) method was modified to analyze the flow during polymerization of methyl methacrylate (MMA) in a model counter‐rotating nonintermeshing screw extruder. The shear viscosity of the reactive mixture in the twin screw extruder was considered as a mixture of polymer and monomer. Thus, the reaction viscosity of the mixture of polymer and monomer was taken to be an explicit function dependent on the shear rate, temperature, conversion, and molecular weight. A new flow path method was developed to calculate the residence time distribution, which related to the degree of conversion. The numerical prediction of the velocity, temperature, viscosity, and pressure profiles during reaction in the model twin screw extruder is described.
Experimental and theoretical investigation of the inflation of variable thickness parisons
Authors: Diraddo R. W. , Garcia‐Rejon A. 
Published: May 2005

AbstractIn today's blow molding of complex parts, an optimal resin distribution is critical to a successful operation. These goals are mostly attained through a technique known as parison programming. The process involves varying the die gap during extrusion and therefore results in a parison having a variable thickness along its length. The subsequent inflation of a variable thickness parison is a complex phenomenon involving the interaction of many process variables. The final thickness distribution and inflation patterns were obtained for various programmed parisons. Constant, one step, two step, and sinusoidal thickness parisons were studied. The inflation patterns were monitored by employing a transparent mold in conjunction with a video camera. The experimental data indicated the presence of an oscillatory inflation pattern for some of the variable thickness parisons. The experimental final part thickness distribution for these cases was highly nonlinear. Theoretical predictions of the final thickness distribution were also obtained for some of the cases. The simulation is based on the inflation of a Mooney‐Rivlin hyperelastic material. A wide range of deformation is accounted for by introducing an evolutionary Mooney constant, dependent on the level of deformation.
Computer‐aided geometric design of the preform dies for flat film extrusion through 3‐D finite element flow analysis
Authors: Wang Yeh , Tsay Hoh‐Yih 
Published: May 2005

AbstractA rational computer‐aided design procedure is presented for determining the optimum flow channel geometry of a flat film die, which yields a minimum pressure drop and produces a uniform transverse flow rate distribution. The three‐dimensional die surface is generated by analytic expressions that represent a dumbbell‐like contour. The die surface may be specified by several geometric parameters. The length of the transition zone turns out to be the controlling parameter. Because of the complicated geometric boundary, it is not possible to optimize the flow channel geometry explicitly; instead, a computer trial procedure is employed. The numerical computation is based on an isothermal three‐dimensional flow model, which assumes power law behavior for the polymer melts. The calculated results indicate that for a particular polymer and a particular aspect ratio of slit, there may exist an optimum transition length from which the flow channel geometry of a flat film die may be uniquely defined.
A study of the effect of the extrusion variables and screw design on the thermal and rheological characteristics of acetal and nylon 66
Authors: Shah Pravin L. , Steward Edward , Yazbak Gene 
Published: May 2005

AbstractA detailed study of the effect of several extrusion variables was made on the rheological and thermal properties of Delrin II acetal homopolymer and Zytel 42 polyamide 66 materials. A 63.5 mm Davis Standard extruder was used to measure the effect of screw design, screw rpm, die and head pressure, and melt temperature on the rheology of acetal and nylon 66 resins. A single stage metering screw was used to determine the effect of screw geometry and viscous heating on the melt viscosity breakdown and the rate of degradation of each polymer. The melt temperature was measured in the melt stream in the channel and correlations are shown between ideal melt temperature predicted from the rheology data and the actual loss of properties of each polymer due to viscous heating. The paper also discusses how to measure the melt temperature accurately in extrusion, and to use it as a key indicator to optimize the extrusion process, and to control the rheology, thermal stability, and the molecular weight of a polymer during processing.
Surface energy changes produced by ultraviolet‐ozone irradiation of poly(methyl methacrylate), polycarbonate, and polytetrafluoroethylene
Authors: Ponter A. B. , Jones W. R. , Jansen R. H. 
Published: May 2005

AbstractContact angles of water and methylene iodide were measured as a function of UV/O3 treatment time for three polymers: poly(methyl methacrylate) (PMMA), polycarbonate, and polytetrafluoroethylene (PTFE). Surface roughnesses were also measured. Surface free energies were then calculated using relationships developed by Kaelble and Neumann. The surface energy of polycarbonate was found to increase (∼ 60%) during UV/O3 treatment. However, calculations on PMMA were hampered by the formation of a water soluble surface product. On PTFE surfaces, the UV/O3 treatment etched the surface, causing large increases in surface roughness, rendering contact angle measurements impossible. It is concluded that care must be taken in interpreting contact angle measurements and surface energy calculations on UV/O3 treated polymer surfaces.
Characterization of epoxy resins by photochemical hole burning (PHB) spectroscopy
Authors: Du Yingjun , Horie Kazuyuki , Ikemoto Makoto 
Published: May 2005

AbstractThe phonon frequencies, Es, measured as the energy differences between zerophonon hole peak and pseudophonon side hole peak in photochemical hole burning (PHB) spectra, were studied for tetraphenylporphin (TPP) in epoxy resin films under various conditions of sample preparation and annealing. The values of phonon frequency, Es, reflecting low energy excitation modes of the matrix epoxy resins were about 13 to 16 cm−1. They decreased when the epoxy resin was cured at relatively low temperatures and vice versa. At the same cure temperatures the sample quenched to liquid nitrogen showed a lower value than that of the annealed sample. These results are in agreement with the results of qualitative free volume measurements. The thermal stability of holes burned at 20 K was also tested, and the results were compared with the extent of cure and glass transition temperature of the resins.
Three‐dimensional modeling of reaction injection molding. II: Application
Authors: Lo Yu‐Wen , Reible Danny D. , Collier John R. , Chen Cheng‐Ho 
Published: May 2005

AbstractThe objective of this research is to demonstrate the application of a general model of reaction injection molding (RIM) to a complex shaped mold part. Using the fundamental physical and chemical properties of the RIM system, prediction of RIM moldability can be made. The numerical techniques used in this research are presented in a previous paper (1). The rigorous modeling of the transport processes and the dynamics of the filling front for a particular application are described in this work.
Material anisotropy and warpage of nylon 66 composites
Authors: Kikuchi Hiroyuki , Koyama Kiyohito 
Published: May 2005

AbstractIt has been found that the warpage mode of an injection molded disk depends on the type of reinforcement of the material. To clarify the reason for the finding, correlations among the aspect ratio (λ) of reinforcements, anisotropy in linear thermal expansion coefficient (α), and warpage have been studied for an injection‐molded disk. The λ is defined as the ratio of the length to the radius. The warpage of the disk is defined as the difference between the maximum and the minimum of the deformation at the free state, which is observed immediately after the disk is released from the mold. The study has been conducted with respect to the PA66 composites compounded with the reinforcement of λ = 1 and λ = 4. Rα≡α11/α22 has been defined to represent the anisotropy of α, where α11 is the α in the flow direction, and α22 is that in the transverse to the flow direction. The flow is defined as the flow of the melted polymer in the injection molding. It has been experimentally found that Rα = 1.0 for unreinforced PA66, Rα < 1.0 for PA66 compounded with λ = 4 reinforcement, and Rα > 1.0 for PA66 compounded with λ = 1 reinforcement. The warpage mode in the Rα < 1.0 composite resembles a coffee cup, while the warpage mode in the Rα > 1.0 composite resembles a saddle. The results indicate that Rα determines the warpage mode of the disk. To prove that Rα is the adequate condition for determining the warpage mode, finite element analysis was conducted for the material of Rα < 1.0 and for the material of Rα > 1.0. It has also been found that the amount of warpage in the case of Rα 1.0 is approximately 10 fold that in the case of Rα = 1.0. On the other hand, the warpage of a disk molded from the blend of Rα < 1.0 composite and Rα > 1.0 composite decreases to the warpage level of the disk of Rα = 1.0. It is deduced that Rα is the important parameter for controlling the warpage since Rα < 1.0 and Rα > 1.0 represent the two counteracting material properties in warpage.
Simulation of bulk free radical polymerization of styrene in tubular reactors
Authors: Soliman M. A. , Aljarboa T. , Alahmad M. 
Published: May 2005

AbstractA model that takes into consideration radial and axial changes in velocity in a tubular reactor for the thermal polymerization of styrene is used to simulate the effect of changes in inlet tube wall temperature and tube radius. The reactor performance is sensitive to the changes of these parameters. The method of orthogonal collocation is used to discretize the modeling equation in the radial direction and Gear method to solve the resulting stiff differential equations in the axial direction. It is found that reducing the wall temperature and the tube radius along the direction of the flow of the monomer reduces the variation in conversion between the tube center and tube wall and thus are advantageous.
Elongational flow properties of low‐density polyethylene and linear low‐density polyethylene from nonisothermal melt spinning experiments
Authors: Bailey L. E. , Cook D. G. , Pronovost J. , Rudin A. 
Published: May 2005

AbstractLow‐density polyethylene (LDPE) and also linear low‐density polyethylene (LLDPE) resins can be characterized by the degree of strain hardening and down‐gaging during elongation. A new method for the determination of the apparent elongational flow characteristics is presented. In a small scale apparatus, a molten monofilament is stretched under nonisothermal conditions similar to those found in tubular film extrusion. Measurement of resistance to elongational flow and apparent elongational strain rates permit the comparison of the process‐ability of different resins under specified conditions. The effect of melt temperature and extension ratio are examined. The importance of the molecular structure of both LDPE and LLDPE resins on these properties is also outlined.
Poly(ethyene terephthalate)–solvent interaction: Gelation and melting point depression
Authors: Tang Ming‐Ya , Kim Soojaa L. 
Published: May 2005

AbstractThe interactions between poly(ethylene terephthalate) (PET) and six high temperature solvents are discussed in terms of gelation and melting temperature depression. The six solvents are 1′‐acetonaphthone (AN), phenyl ether (PE), biphenyl (BP), 1‐methyl naphthalene (MN), nitrobenzene (NB), and a eutectic mixture of phenyl ether and biphenyl (EU). Although the six solvents have very similar solubility parameter values, the dissolution, gelation, and gel melting temperatures of the PET‐solvent systems are vastly different. The characteristic transition temperatures (dissolution, gelation, and gel melting temperatures) of the six solvents decrease in the following order: PE > EU > BP > MN > AN > NB, which is the reverse order of the solvent power. While the transition temperatures of the gel vary with the solvent system, the melting temperature of the dry gel formed from quiescent solution is independent of solvent system. That is, PET‐solvent interactions are only discernible in solvated state (wet gel). All the experimental results suggest crystallization is the primary cause of gelation of high temperature PET solutions, with crystals acting as junction points in the network. Based on the dissolution and gel melting temperatures, interaction parameters for the six PET‐solvent systems have been calculated.
The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass transition particles. Part II: Experimental results and discussion
Authors: Ramesh N. S. , Rasmussen Don H. , Campbell G. A. 
Published: May 2005

AbstractThe experimental data obtained for the nucleation of microcellular foams are compared with the theoretical model developed in the first part of this paper. Polystyrene (PS) with rubber particles as nucleation sites is used as an exploratory system. Nitrogen is used as a physical blowing agent to nucleate the bubbles. The influence of process variables, such as saturation pressure, foaming temperature, and concentration and size of rubber particles, is discussed. Results indicate that all these variables play important roles during the nucleation process. A nucleation mechanism based on the survival of microvoids against the resisting surface and elastic forces has been modeled to obtain the cell nucleation density. Increase in saturation pressure increase the cell density to a critical pressure. Beyond this critical pressure, there is no increase in bubble number, indicating that all microvoids are activated. The effect of temperature is more complex than the effect of pressure. Increase in concentration of the rubber particles increase the nucleation cell density. In general, the experimental data are well described by the nucleation model presented in Part I.
Effects of component addition protocol on the reactive compatibilization of HDPE/PET blends
Authors: Dagli Sanjiv S. , Kamdar Kunal M. 
Published: May 2005

AbstractPolyethylene terephtyalate (PET) and high‐density polyethylene (HDPE) constitute a major portion of the thermoplastic materials currently being used in the packaging industry. Blends of HDPE/PET can be compatibilized by utilizing ester groups or terminal carboxyl and hydroxyl groups present in PET. An ethyleneglycidyl methacrylate copolymer (EGMA) was found to be very effective in compatibilizing this blend by forming a compatibilizer in‐situ. The in‐situ formation of the compatibilizer and its distribution could be affected by different sequences and modes of component addition. To determine the best protocol of component addition for such a reactive compatibilization process, different sequences and modes of component addition were tried out in an intensive batch mixer and in a twin‐screw extruder. All these experiments resulted in blends with vastly different dispersion of the minor phase and mechanical properties. In general, sequences where the reactive polymer was grouped with the nonpolar component of the blend initially resulted in the best compatibilization.
A viscoelastic micor‐mechanical analysis for dimensional stability of a composite layer
Authors: Chiang Martin Y. M. , McKenna Gregory B. , Yuan Jih 
Published: May 2005

AbstractCoefficient of thermal expansion mismatch between the epoxy layer and composite substrate of “inner layers” can lead to large residual stresses during the manufacture of printed wiring boards (PWB). The viscoelastic nature of the polymeric resin (epoxy) leads to a relaxation of the stresses and a resulting change in dimensions of the inner layer over long periods of time. Here, we treat a micro‐mechanical model using linear viscoelasticity in a finite element thermal stress analysis to demonstrate the time dependency of the ply dimensions upon cooling from near the glass transition temperature (Tg) of the resin to room temperature. The inner layer shrinkage reaches its highest value when room temperature is reached, but the part will continue to change dimensions (shrinkage recovery) for a long time as the in‐plane residual stresses relax from their peak values. This evolution takes place over many decades of time. The results show that the long term behavior of dimensional changes is especially pronounced when the effects of time‐temperature superposition (TTS) are included below Tg.