bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid‐phase backward extrusion of thermoplastics
Authors: Okine Richard Kafue , Suh Nam P. 
Published: December 2004

AbstractThe backward extrusion process was studied as a means of forming projections and ribs on flat sections of thermoplastic parts. The simplified, open‐die axisymmetric and plane‐strain extrusion cases were mainly considered. The results were applied to the development of a continuous solid‐phase‐forming process. Commercial‐grade polycarbonate (PC), polypropylene (PP), and polystyrene (PS) were used in the investigation. The projection height and extrusion loads in the unconstrained extrusion were measured as a function of the initial temperature of the material, the load hold time, and geometric variables. Cold dies were used in the experiments, and the samples were kept below their melt temperatures. The dimensional recovery of the flange section of the formed samples was also measured as a function of the hold time for given initial temperature and geometric variables. The slab and the upper‐bound methods‐in plasticity analysis were used to theoretically derive the projection heights and forming loads. The degree of correlation between the predictions and the experimental results depended on the estimates used for the frictional factors at the interfaces between the deforming material and the dies.
Molecular weight distribution of polyethylene terephthalate in homogeneous, continuous‐flow‐stirred tank reactors
Authors: Kumar Anil , Gupta Santosh K. , Somu N. 
Published: December 2004

AbstractPoly(ethylene terephthalate) (PET) formation in homogeneous, continuous‐flow‐stirred tank reactors (HCSTRs) operating at steady state has been simulated. The feed to the reactor is assumed to consist of the monomer bis‐(hydroxyethyl) terephthalate and monofunctional compound (MF1) cetyl alcohol. The overall polymerization is assumed to consist of the polycondensation, reaction with monofunctional compounds, redistribution, and cyclization reactions. At a given time, the reaction mass consists of polyester molecules (Pn), polyester molecules with an ending of molecules of monofunctional compound (MFn), and cyclic polymers (Cn). A mass balance for each of these species in the reactor gives rise to a set of algebraic equations to be solved simultaneously. The MWD calculations show that the redistribution reaction plays a major role and cannot be ignored, This result is in contrast lo the observation for semi‐batch reactors, for which redistribution becomes important when the cyclization reaction is included. For the same residence times of semi‐batch and HCSTRs, the latter gives considerably lower‐number average molecular weight, Nav, and polydispersity index, ρ. However, for the same conversions, the ρ for CSTR is higher. The concentration of the monofurctional compound, [MF1]0, in the feed and the reactor temperature both influence ρ, but the effect is small within the range studied.
An improved lattice‐fluid equation of state for pure component polymeric fluids
Authors: Panayiotou C. , Vera J. H. 
Published: December 2004

AbstractThe Fluid‐Lattice Theory (Ising Fluid), recently tested by Lacombe and Sanchez, has been modified by introducing the typical Flory's surface‐to‐volume ratio of the characteristic‐segment of a polymeric liquid. This surface‐to‐volume ratio is not an adjustable parameter. It is obtained from Bondi's tabulations. The resulting new equation of state has three adjustable parameters per component and it represents a definite improvement for the fitting of P‐V‐T data for polymeric liquids. Extension to mixtures is not tested in this work but, in principle, it can be done by well‐established methods.
Effect of the addition of ethylene‐propylene random copolymers on the properties of high‐density polyethylene/isotactic polypropylene blends: Part 1—morphology and impact behavior of molded samples
Authors: D'Orazio L. , Greco R. , Mancarella C. , Martuscelli E. , Ragosta G. , Silvesrte C. 
Published: December 2004

AbstractTwo random commercial ethylene‐propylene copolymers (EPM) with different ethylene content have been added to binary isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends by melt mixing in a Brabender‐like apparatus. Impact Izod tests and a morphological analysis on the fractured surfaces of broken specimens have been performed and discussed, in order to improve the deficiency in toughness of the binary HDPE/iPP mixtures. The results show that the impact performance of both homopolymers and HDPE/iPP binary blends is strongly improved by the addition of the EPM copolymers. Such an effect is related to the fact that the overall morphology, as well as the mechanism and mode of fracture, are greatly modified by the presence of such additives. The extent is dependent on factors such as the nature of the matrix (HDPE or iPP), the composition, and the chemical structure and/or the molecular mass of the added copolymer.
A plasticating model for single‐screw extruders
Authors: Fukase Hisahiko , Kunio Takeshi , Shinya Sadahiko , Nomura Akihiro 
Published: December 2004

AbstractBy measuring the solid‐bed transfer velocity, width and thickness under various conditions, die following results are obtained. As the result of melting, the solid bed decreases in width and thickness almost with the same rate, and the solid‐bed transfer velocity is constant, while a melt layer exists between the solid bed and the screw root; also, when the phenomenon of dam‐up occurs, caused by the combined effect of decreasing depth of the screw channel with tin insufficient decrease of solid‐bed thickness, the transfer velocity increases proportional to the rate of decrease of channel depth. Consequently, the solid bed is considered to behave us loosely packed particles. A new plasticating model is developed by making the above results an assumption and adopting finite differential calculus with the Newton‐Raphson method to obtain accurately the melting velocity, melt profile, and solid‐bed temperature. Calculated values are in remarkably good agreement with the experimental values Solid‐bed softening point, pressure, and screw torque are also successfully estimated.
Mechanical criteria for polymer compatibility: Poly(vinylchloride)/post‐chlorinated poly(vinylchloride) blends
Authors: Clark Debra D. , Collins Edward A. , Kleiner Lothar W. 
Published: December 2004

AbstractThe compatibility of poly(vinylchloride PVC) with post‐chlorinated PVC (CPVC) is investigated with the purpose of relating the mechanical properties of such blends with their compatibility. The effects on compatibility of varying mixing methods, blend composition, molecular weights of components, and chlorine content of CPVC are studied. Experimental methods include comparison of the glass transition temperatures (Tgs) of blends and homopolymers using dynamic mechanical analysis, Differential Scanning Calorimetry (DSC), and comparison of the mechanical properties of blends and homopolymers. Experimental results indicate marginal compatibility between PVC and CPVC. Blends in which CPVC is the main component are indicated to be less compatible than other compositions.
Fracture toughness and fatigue of polystyrene, polyphenylene oxide and their blends
Authors: Serrano A. M. , Welsch G. E. , Gibala R. 
Published: December 2004

AbstractBlends of atactic polystyrene (PS) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) represent a compatible system that exhibits a transition from a crazing to a shear bending mode of deformation as a function of composition. PS (Mw = 30,000; Mw/Mn = 1.06) exhibited a value of \documentclass{article}\pagestyle{empty}\begin{document}$ K_{IC} = 1.00 \pm 0.20{\rm }MPa\sqrt m $\end{document}. Blends of up to 60 wt.% PPO exhibited \documentclass{article}\pagestyle{empty}\begin{document}$ K_{IC} \sim 1.00{\rm }MPa\sqrt m $\end{document}. However, there is a very rapid increase in KIC with increasing PPO content in the vicinity of 75 percent PPO. Fatigue behavior of the blends parallels that under static loading.
Dynamic mechanical behavior of filled polyethylenes and model composites
Authors: Chacko V. P. , Karasz F. E. , Farris R. J. 
Published: December 2004

AbstractThe effect of CaCO3 filler presence and CaCO3‐polymer interface character on the dynamic mechanical spectra of three polyethylenes with different molecular weights was investigated. Differences in storage modulus and loss tangent were observed for different polymer‐filler coupling and polyethylene molecular weight. The dynamic behavior of model composites was estimated using the, etastic‐viscoelastic correspondence principle, and these predictions were compared to the behavior of real materials.
Effect of short glass fibers and particulate fillers on fatigue crack propagation in polyamides
Authors: Lang R. W. , Manson J. A. , Hertzberg R. W. 
Published: December 2004

AbstractThe fatigue crack propagation (FCP) behavior (at 10 Hz) of several commercial short‐glass‐fiber and mineral‐reinforced nylon composites has been investigated. The FCP rates can be described in terms of the well‐known Paris relationship. Significant improvement in FCP performance was found for the glass‐fiber‐reinforced materials in comparison to that of the pure matrix materials (nylon 66 and nylon 612). Also, the FCP resistance was found to increase with increasing fiber content and interfacial adhesion for nylon 66. Despite the fact that specimens were cut from injection‐molded plaques, no or only slight effects of orientation were observed by testing specimens with cracks growing parallel and perpendicularly, respectively, to the major flow direction. Electron microscopy studies of fracture surfaces revealed a complex pattern of fiber orientation, varying over the plaque thickness and consisting of layers with fibers oriented mainly parallel, perpendicularly, or randomly to the major flow direction; nevertheless, the specimens behaved quasi‐isotropically. Significant differences in fracture mechanism were observed, depending on the matrix, the interfacial bonding, and the crack speed. In contrast to the fiber‐rein forced nylons, the mineral‐reinforced material exhibited poorer FCP resistance than neat nylon 66, even though the former is superior in tensile and impact behavior.
Studies of epoxy resin systems: Part C: Effect of sub‐Tg aging on the physical properties of a fully cured epoxy resin
Authors: Chang T.‐D. , Brittain J. O. 
Published: December 2004

AbstractThe effect of sub‐Tg aging on the properties of an epoxy resin system, diglycidyl ether of butanediol, DGEB, cured with 4‐4′ diaminodiphenyl sulfone, DDS, has been studied. Aging was found to increase the DSC (differential scanning calorimetric) endothermic peak, the density, and the upper yield point. In contrast, the lower yield point was relatively unchanged. This result, together with the observation of the elimination of the DSC endothermic peak by deformation and the absence of a yield point after deformation, suggested that the aging effect was eliminated by deformation. The thrermally stimulated depolarization (TSD) α‐peak was found to decrease in strength with aging time. All of the observations were best rationalized on the basis of the free‐volume concept.
Filling thin cavities of variable gap thickness: A numerical and experimental investigation
Authors: Hieber C. A. , Socha L. S. , Shen S. F. , Wang K. K. , Isayev A. I. 
Published: December 2004

AbstractA theoretical and experimental investigation is presented for filling thin cavities of variable gap thickness. The modeling is based upon a finite‐element/finite‐difference formulation for an inelastic power‐law fluid and includes the effects of viscous heating and conduction upon the flow dynamics. Extensive results are presented for polypropylene and polystyrene melts injected into two variable‐gap‐thickness cavities, of which one has an insert. Good agreement is found between the predictions and measurements concerning the shape of the advancing melt front, the location of weld lines, and the temporal pressure trace at various positions in the cavity.
A study of structural development in the high speed spinning of poly(ethylene terephthalate)
Authors: George H. H. , Holt A. , Buckley A. 
Published: December 2004

AbstractIn recent years the spinning speeds of poly(ethylene terephthalate) (PET) fiber have increased to the point that significant structural development is being observed in the spun yarn. At even higher speeds significant crystallization has been obtained. Data characterizing these yarns will be presented and discussed showing the development of crystals and that the onset of this phenomena is related to the stress at the “freeze point.” The “freeze point” rises from around Tg at low speeds to the order of 200°C at high speeds. The spinline itself has been characterized by velocity and orientation profiles which show the crystallization process is extremely rapid, occurring over a few centimenters of the spinline.
Predicting conversion using temperature as the measured variable in the RIM process. Part I: Simulation and measurement structure
Authors: Romagnoli J. , Castro J. 
Published: December 2004

AbstractIn general the monitoring and control of many industrial processes is so complicated by problems associated with the on‐line measurement of the desired objectives that they must be inferred from available measurements. This leads to a state estimation problem in which the selection and adaptation of the structure of the measurements plays an important role. In particular, in the reaction injection molding (RIM) process, an accurate on‐line estimate of the conversion field is highly desirable. Since conversions cannot be determined readily by direct measurements, and a thermocouple can provide reliable dynamic temperature data, we can predict the conversion field from the solution of a state estimation problem using temperature as the measured variable. In this article, we describe an algorithm for designing the optimal arrangement of measuring sensors and analyze the RIM process dynamics which influence the structure depending on the operating conditions. The search for the optimal measurement structure for the purpose of state estimation makes up the bulk of the results. No particular estimation‐control strategy is investigated in this paper. Work is underway to develop the on‐line corrective system, which will use the temperature measurements to correct model predictions. The results of that work will appear in part II of this series.
Analysis of the puncture of a bisphenol‐a polycarbonate disc
Authors: Nimmer R. P. 
Published: December 2004

AbstractThe finite element technique is applied to analytically predict the response of a disc made of BPA‐polycarbonate during a displacement‐controlled puncture test with a hemispherical indenter. The analysis includes effects of contact load, large displacements and rotations, and large strains and material yielding. Two general topics are addressed with this analysis. First, it is shown that the load‐displacement behavior of impacted, BPA‐polycarbonate plates can be accurately predicted over a wide range of engineering interest (strains up to 30 percent) using a bilinear representation of the stress‐strain curve and flow theory of plasticity. For this purpose, the von Mises criterion is applied to define yielding in a generalized biaxial stress state, and strain rate effects are incorporated through the use of a yield stress consistent with the initial strain rate during the test. Second, in order to broaden the understanding of results associated with this widely used test, a number of mechanical and material effects are discussed, including large displacements, friction at the clamped support and indenter head, and clamping pressure at the support. Lack of agreement between the present analysis and experimental results with regard to ultimate load at puncture suggests that strain hardening and strain rate hardening of the material during the high‐strain portion of the test (30 percent‐60 percent) must be more accurately modeled for improved predictive capability.
Thermokinetic modeling of an epoxy resin I. Chemoviscosity
Authors: Tajima Y. A. , Crozier D. 
Published: December 2004

AbstractIt is shown that the Williams‐Landel‐Ferry equation can be taken to describe the temperature dependence of viscosity of an amine‐cured epoxy resin. Furthermore, for this resin system, the two parameters of the W‐L‐F equation can be expressed simply as functions of hardener concentration. Since the hardener concentration decreases with advancement, and since the reaction rate equation for advancement is readily determined and known, the viscosity can be calculated over any temperature (cure) cycle.
Thermal aging study of carboxyl‐terminated polybutadiene and poly(butadiene‐acrylonitrile)‐reactive liquid polymers
Authors: Okamoto Y. 
Published: December 2004

AbstractA thermal aging study of carboxyl‐terminated polybutadiene (CTB) and poly(butadiene‐acrylonitrile) (CTBN) reactive liquid polymers has been conducted at 50°, 75°, 100°, and 125°C. All CTB and CTBNs are stable at 50°C aging. On aging at higher temperatures prior to use, viscosities of CTB and CTBNs increase, and terminal carboxylic acid functional groups start disappearing. Rate of viscosity increase and rate of carboxylic acid functional group disappearance increase with higher aging temperature and also with higher cyano group concentration in the polymers. The major cause of rapid viscosity increase and disappearance of carboxylic acid functional groups seems to be crosslinking between terminal carboxylic acid groups and cyano groups, which form imide structures. Crosslinking among the unsaturation in polybutadiene segments may contribute to the slow, steady viscosity increase. No acid‐anhydride formation and decarboxylation reaction, which may also result in viscosity increase and disappearance of carboxylic acid functional groups, are observed during the thermal aging at elevated temperatures.
Orientation development in thermotropic liquid crystal polymers
Authors: Ide Yoshiaki , Ophir Zohar 
Published: December 2004

AbstractThermotropic liquid crystal polymers are a new class of polymeric materials that consist of rigid backbone molecules and thus, even in the quiescent condition, take extended chain conformation to form optically anisotropic melts. A systematic investigation was carried out on how this type of material responds to two basic flow fields: shear and elongation. Rheological properties of the polymer in these flow fields have also been measured. It was found that a high level of molecular orientation was readily obtained by elongational flow but not with shear flow. Specifically, extraordinarily high orientation was obtained when the melt was subjected to small elongational strains, whiel shear strain or shear rate had little effect. A possible mechanism to explain these behaviors is illustrated based on the existing observations or theories of rodlike molecules. This finding was used to interpret the orientation distribution in the extruded and injection‐molded articles.
Orientation development in the injection molding of amorphous polymers
Authors: Isayev A. I. 
Published: December 2004

AbstractFrozen‐in orientation in the injection‐molding of amorphous polymers has been considered in terms of flow‐ and cooling‐induced birefringence. In particular, measurements of the frozen‐in orientation distribution in polystyrene (PS) molded strips and circular runners have been performed. Three birefringence components, Δn, n22 − n33, and n11 − n33, have been measured for strips, and two components, Δn and nrr − nθθ, for runners. The effects of various processing conditions, of strip thickness, and of runner diameter on orientation development have been analyzed and compared with those predicted by our previously developed viscoelastic theory. In addition to injection‐molding experiments, free and constrained quenching experiments for PS and poly(methyl methacrylate) (PMMA) strips have been carried out and the gapwise distribution of cooling‐induced (thermal) birefringence has been measured. Relaxation of thermal birefringence following quenching has been observed for PMMA. The effects of flow‐ and cooling‐induced orientation on various components of birefringence in molded parts have been elucidated and limitations on the applicability of the stress‐optical law to the injection‐molding of amorphous polymers have been discussed.
Physical aging in polystyrene: Comparison of the changes in creep behavior with the enthalpy relaxation
Authors: Roe Ryong‐joon , Millman Gregg M. 
Published: December 2004

AbstractPhysical aging in polystyrene was studied by annealing samples isothermally (at 22°, 57°, and 93°C) for various lengths of time and measuring the changes in the enthalpy and the flexural creep property. The enthalpy decrease reached a constant value after about 10 hours of aging at 93°C, indicating an apparent attainment of equilibrium, whereas the creep behavior continued to change with prolonged aging even after 10 hours. At room temperature it took about a year of aging to induce a measurable change in enthalpy, while the creep behavior showed changes clearly only after hours of aging. These and other items of evidence indicate that the effect of aging on the creep behavior cannot be interpreted solely in terms of the free volume concept. Thus the hope of being able to predict the mechanical properties of aged polymers from the measurement of specific volume or enthalpy alone is not likely to be realized.
Properties of polyisobutylene‐polyurethane block copolymers: I. Macroglycols from ozonolysis of isobutylene‐isoprene copolymer
Authors: Speckhard T. A. , Strate G. Ver , Gibson P. E. , Cooper S. L. 
Published: December 2004

AbstractThe properties of a series of polyisobutylene (PIB) based polyurethanes were studied and compared to those reported in the literature for polyether, polyester, and polybutadiene‐based polyurethanes. Good phase separation was reflected in the invariance of the soft segment Tn with increasing hard segment content. Increasing hard segment content resulted in larger domains, higher modulus and lower ultimate elongation. The modulus above the soft segment Tn was higher than that previously reported for polyurethanes of similar hard segment contant; improved phase separation and short contour lengths of the PIB chains were cited as possible causes of this behavior. Stress‐strain data indicated a change from isolated to interconnected domain morphology with incerasing hard segment contant. Generally similar trends were seen for all types of urethanes. The overall properties of polybutadiene polyurethanes were closest to those of the polyisobutylene polyurethanes studied. The properties of both of these systems were suggested to suffer from significant synthesis problems in urethane formation due to the incompatibility of the nonpolar hydrocarbon soft segment and the polar diol chain extender. Preliminary environmental tests indicated that polyisobutylene based materials exhibit improved hydrolytic stability and reduced moisture permeability compared to polyether and polyester polyurethanes and greater oxidative stability compared to polybutadiene based materials.
Polyurethane‐poly(methyl methacrylate) interpenetrating polymer networks: Some mechanical properties
Authors: Morin A. , Djomo H. , Meyer G. C. 
Published: December 2004

AbstractThe mechanical behavior of polyurethane‐poly(methyl methacrylate) interpenetrating polymer networks (PUR/PAc IPN's) was investigated. Stress‐strain and impact resistance measurements were made on IPN's with a variable PUR content. The effect of the degree of crosslinking of each network on the mechanical properties was also studied. It appears that only the ultimate elongation varies largely upon changing the crosslink degree. The results are interpreted in terms of the contribution of each network to the mechanical behavior, but also by the interpenetration of both components and by the phase continuity of the PAc network.