bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual stresses in injection molded polycarbonate rectangular bars
Authors: Pham H. T. , Bosnyak C. P. , Sehanobish K.
Published: May 2005

This study deals with the quantification of the residual stress profiles of injection molded rectangular bars with polycarbonate of various molecular weights. Determinations via the layer removal technique indicated that these bars can possess compressive stress of up to 10 MPa at the surface and up to 9 MPa in tension in the interior. The residual stress profile showed a shape similar to that observed in thermal quenching experiments, i.e., parabolic, for locations far away from the gate of the cavity. At locations near the gate of the cavity and for injection molding at high speed, the residual stress profile changed sign, going from compressive to tension at the surface and vice versa in the interior. These residual stress profiles were very dependent on gating geometry and location.
Thermoplastic starch blends with a poly(ethylene‐co‐vinyl alcohol): Processability and physical properties
Authors: George E. R. , Sullivan T. M. , Park E. H.
Published: May 2005

We investigated the effect of poly(ethylene‐co‐vinyl alcohol) (EVOH) concentration on the processability and physical properties of thermoplastic starch plasticized with glycerine and water. Waxy maize starch (Amioca), native corn starch (Melogel), and a treated high amylose corn starch (Hylon VII) were employed to explore the effect of starch type on blend properties. All the starches exhibited similar changes in properties with increasing EVOH content. The minimum injection pressure required for filling a standard test specimen (a measure of processability) decreased with increasing EVOH concentration and provided an indication of improved processability. Blends with high amylose corn exhibited higher injection pressures than the corresponding waxy maize or native corn starch blends. The ductility of all the thermoplastic starches was significantly increased upon the addition of EVOH. The waxy maize blends were stiffer and the high amylose corn blends exhibited higher elongation at low EVOH concentrations, but all the starch/EVOH blends exhibited similar physical properties when the EVOH concentration was ≥ 50 wt%. An investigation of physical properties of this blend series after long term aging from 10% to 90% relative humidity is in progress. Future studies include rheology, electron microscopy, and thermal analysis to more fully elucidate phase behavior in these binary blends.
The fracture probability of high impact polystyrene
Authors: Sjoerdsma S. D. , Boyens J. P. H.
Published: May 2005

A theory is developed to describe the fracture probability of high impact polystyrene. By assuming that fracture initiation is a consequence of the impingement of crazes due to the craze thickening process, an equation for the fracture probability as a function of the strain is derived. Experiments support the validity of this equation qualitatively while the stress and temperature dependence of the fracture probabilty correlate in the expected manner with the strain rate. An approximation allows the calculation of the fracture probability as a function of time.
Experimental study on the dynamics of thermoforming of polystyrene
Authors: Parisi M. J. , Ryan M. E. , Charrier J.‐M.
Published: May 2005

An experimental study of the dynamics of thermoforming a high‐impact polystyrene sheet was undertaken to evaluate the effect of evacuation rate and temperature on the rate of sheet deformation and the wall thickness distribution of the molded part. The studies were conducted using an instrumented cylindrical mold having an adjustable bottom insert to vary the depth of draw. The evaculation rate was varied by introducing a flow restriction in the form of an orifice plate in the base of the mold. The deformation rate of the sheet was determined by means of fiber‐optic infrared detectors located at various depths within the mold. Mold contact sensors also provided information with regard to the deformation process after contact with the mold surface had been achieved. The evaluation characteristics were monitored by a pressure transducer. A three‐level, two‐variable factorial design was conducted to provide information of the influence of the principal operating conditions and their interactions on the measured response variables. Reliable predictive expressions were derived for the minimum pressure, time to reach minimum pressure, overall forming time, and wall thickness near the lip of the mold. The wall thickness at other locations around the periphery of the mold contour was found to be relatively insensitive to the rate of evacuation and material temperature.
Radiation pyrometry on semitransparent sheets. II: Media with wavelength dependent absorption coefficient
Authors: Hajji N. , Spruiell J. E.
Published: May 2005

The apparent temperature of nonisothermal sheets with a wavelength dependent absorption coefficient was investigated. A polypropylene sheet with a parabolic temperature distribution across its thickness was used as an illustration of apparent temperature calculations. It was found that the variation of the apparent temperature of polypropylene with thickness was different from that of gray media (with absorption coefficient independent of wave length). This difference was attributed to the effect of thickness on the spectral distribution of the radiation emitted by the sheet.
Structure‐thermal expansivity relation for isotropic polyoxymethylene sheets
Authors: Zahran R. R. , Abolmagd A. A.
Published: May 2005

A detailed parametric mapping analysis of the thermal expansion coefficient for isotropic polyoxymethylene is presented. The molecular composite model has been computerized to investigate the variation of the thermal expansivity of isotropic polyoxymethylene sheets with some typical morphological and structural parameters. The results are reported and analyzed in terms of three‐dimensional structure‐property maps. The thermal expansion coefficient is found to be significantly dependent on the crystallite content, in the first place, followed by the transverse aspect ratio of the crystallites and the amorphous phase stiffness. It is only at relatively low levels of crystallinity that the thermal expansivity is sensitive to the variation of the amorphous phase tensile modulus. The longitudinal aspect ratio is slightly effective in altering the expansion coefficient as long as it is kept below 25; otherwise it is ineffective.
Entrance effects for power‐law fluid
Authors: Gupta Mahesh , Hieber C. A. , Wang K. K.
Published: May 2005

Entrance pressure losses for the creeping flow of a power‐law fluid are calculated for an abrupt contraction of ratio 2, 4, 8 and ∞ for both the axisymmetric and planar cases using P2P1 and PP1 finite elements. Contrary to some earlier findings in the literature, the entrance pressure loss obtained by using the two different types of finite elements, both of which satisfy the Babus̆ka‐Brezzi condition, are found to converge to the same results. The present results also confirm that the variational method of Duda and Vrentas gives excellent upper bounds for both the axisymmetric and planar cases with infinite contraction ratio.
Simulation of non‐isothermal flow in modular co‐rotating twin screw extrusion
Authors: White James L. , Chen Ziyun
Published: May 2005

Non‐isothermal flow is simulated in the screw and kneading disc elements in a modular co‐rotating twin screw extruder. Methods of calculating mean temperature rises for individual elements are discussed and results are presented. The implications of non‐isothermal operation for scale‐up is discussed. A method is then described for making calculations in a modular co‐rotating machine, that contains many different elements. Example calculations are given showing the tendency of larger machines to buildup greater temperatures when viscous heating is included.
A computer‐aided analysis of automatic degating molds for injection molding of plastic balls
Authors: Tseng Ampere A. , Kaplan Jeffrey D.
Published: May 2005

A computer software has been developed to speed up the design process of automatic degating molds used for injection molding of plastic balls. Following an introduction to the ball making process and the associated mold design consideration, the algorithm and formulation of the software are presented. To demonstrate its versatility, the software developed is adopted to design both testing and production molds that best meet the design and production requirements. Two testing molds were built. While one was used to verify the gate size predicted, the other was built to confirm the workability of the automatic degating design. The results of testing runs have also been used to finalize the details for designing the production mold. The software developed is compact enough to be run on an IBM/PC compatible and has the capability to communicate with commercial CAD/CAM systems to provide necessary drawings or CNC files for mold fabrication.
Double coated optical fibers undergoing temperature variations: The influence of the mechanical behavior on the added transmission losses
Authors: Cocchini Franco
Published: May 2005

A model to predict the temperature‐induced added loss in dual‐coated optical fibers is presented. Longitudinal and lateral temperature‐induced forces, originating from fiber irregularities and from the mismatch among the expansion coefficients of the glass fiber and of the coatings, are consistently included in the model. Both the bendings of the glass fiber and of the coating are considered. Transmission losses are explicity computed according to Petermann's theory on the microbending of single‐mode fibers.
Quiescent polymer crystallization: Modelling and measurements
Authors: Chan T. W. , Isayev A. I.
Published: May 2005

The problem of predicting nonisothermal crystallization kinetics based on isothermal data is considered, with reference to the difficulties involved, both experimental and theoretical. The kinetic model used is the differential form of the Nakamura equation which is an extension of the Avrami equation so as to apply to nonisothermal crystallization. Nonisothermal induction times are obtained from isothermal induction times according to the concept of induction time index. The theory of Hoffman Lauritzen is used to extrapolate the limited isothermal crystallization rate data. Good agreement between DSC (differential scanning calorimetry) nonisothermal crystallinity results and model predictions is obtained for our own data on poly(ethylene terephthalate) (PET) and some literature data on nylon‐6, if the temperature lag between the sample and the DSC furnace is taken into account. The advantages of the present approach in process modeling are pointed out. Quenching experiments have also been performed in which PET slabs are allowed to cool and crystallize from the melt under quiescent conditions. The resulting crystallinity distributions in the thickness direction are measured and predicted by using kinetic parameter values obtained from isothermal DSC measurements alone.
Polypropylene composites. III: Chemical modification of the interphase and its influence on the properties of PP/mica composites
Authors: Chiang Wen‐Yen , Yang Wen‐Der , Pukánszky Béla
Published: May 2005

A surface treatment technology was developed for PP/mica composites that produces a diffuse interlayer with excellent adhesion between the components. The interlayer is created by the silane treatment of the filler and the chemical modification of the polymer components, and its polarity gradually decreases from the surface of the filler to the matrix. Properties of the composites depend on the characteristics of the interphase. With changing chemical composition, the characteristics of the interphase change from a thin, rigid layer to a more diffuse, elastic one. Properties of the composites change accordingly, optimum properties are achieved with a thick interlayer ensuring good stress transfer, strength, hardness, acceptable impact properties, and low mold shrinkage.
Residual stress development in neat poly(etheretherketone)
Authors: Eduljee Rushad F. , Gillespie John W. , McCullough Roy L.
Published: May 2005

Material property models for poly(etheretherketone) (PEEK) have been combined with a residual stress model to provide a means for investigating the effect of crystallization process on the residual stress development in semicrystalline materials. The analysis shows that crystallization causes an increase in the residual stress levels. This increase is affected through an increase in the resin modulus values and through the resin modulus build‐up at higher temperatures. The shrinkage due to crystallization was found to have no effect on the residual stress development in neat PEEK.
Flow field analysis of an intermeshing counterrotating twin screw extruder
Authors: Li Tao , Manas‐Zloczower Ica
Published: May 2005

The intermeshing counterrotating twin screw extruder is widely used for compounding, devolatilization, blending, and reactive extrusion. A fluid dynamics analysis package‐FIDAP, using the finite element method, was implemented to simulate the 3‐D flow patterns in the region of conveying elements and shearing discs of a Leistritz LSM30.34 twin screw extruder. The rheological behavior of the fluid was described by a power law model. The flow fields were characterized in terms of velocity profiles, pressure distributions, shear stresses generated, and a parameter λ quantifying the elongational flow components. The influence of screw rotational speed and axial pressure difference on the flow characteristics was also analyzed. A comparison between the flow characteristics in the shearing discs operated in a corotating or counterrotating mode was also presented.
Optimization of the structure of integral skin foams for maximal flexural properties
Authors: Khakhar D. V. , Joseph K. V.
Published: May 2005

The effective flexural properties of integral skin foams (ISF), are modeled using Euler‐Bernouli beam theory along with a power law empirical equation relating the properties of a homogeneous foam to its density. The optimal density profile that maximizes the effective flexural modulus of an ISF beam of fixed overall density, and with the density constrained to lie in a given range, is continuous when the power law exponent (n) is less than 1. For n > 1, the optimal density profile is discontinuous with a low density core and a high density skin. The effective flexural modulus of such sandwich beams is maximized for a fixed density ratio (ratio of the core density to the skin density) and fixed overall density. The maximal flexural modulus is found to increase monotonically with decreasing density ratios and increasing values of n. The flexural strength of the sandwich beam is also maximized considering failure to occur by tensile fracture or buckling of the skin. In this case an optimal skin thickness and an optimal density ratio are obtained for a fixed overall density. The results are useful for the design and evaluation of flat ISF panels.
On the rheological behavior of latex polystyrene blends
Authors: Nemirovski N. , Narkis M.
Published: May 2005

The synthesis of latex two‐phased polystyrene blends has been accomplished by three different mixing routes: (1) PS‐b‐XPS system consisting of a physical blend of polystyrene (PS) and crosslinked polystyrene (XPS) lattices, the latter being lightly crosslinked with divinylbenzene (less than 1% DVB), (2) (XPS‐s)‐PS system obtained by styrene polymerization in presence of a XPS seed latex, and (3) (PS‐s)‐XPS system, in which styrene and DVB are copolymerized in presence of a PS seed latex. Structuring of these PS/XPS systems resulted in different microstructures by each of the procedures. Different rheological behaviors have been noticed, along with a rather interesting property dependence on XPS content and DVB concentration. The polymerization method appears to be critical to the development of well‐characterized, tailor‐made latex microstructures, insofar as the order of monomers addition determines much of the polymerizations sites.
The synthesis and characterization of novel thermotropic liquid crystalline poly(aryl ether ketone)s
Authors: Bennett Greggory S. , Farris Richard J.
Published: May 2005

The 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

The 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

A 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

The 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

Compounds 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

The 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

The 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

In 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

A 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

A 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

Contact 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

The 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

The 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

It 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

A 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

Low‐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

The 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

The 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

Polyethylene 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

Coefficient 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.
Isothermal gas‐assisted displacement of viscoplastic liquids in tubes
Authors: Poslinski A. J. , Oehler P. R. , Stokes V. K.
Published: May 2005

Isothermal experiments on gas‐assisted displacement of viscoplastic liquids in tubes show that a liquid coating remains on the tube wall. The thickness of this coating approaches 0.35 of the tube radius at high gas penetration rates, the asymptotic limit previously observed for Newtonian liquids. At low gas penetration rates, the viscoplastic coating is much thinner than its Newtonian counterpart. During the displacement process, the gas front moves faster than the liquid front and, prior to blowout, it rapidly accelerates as the amount of liquid downstream of the gas is depleted by the liquid coating. Based on these observations, a simple isothermal model is developed to describe the gas‐liquid dynamics. This model provides an insight into the gas‐assisted injection molding process in which the injection of molten plastic into a mold is assisted by a pressurized gas. In particular, the results show that the wall thickness around the hollow cores in gas‐assisted parts is set during processing by the solid skin and a thick molten layer. The thickness of the molten layer depends on the gas penetration rate and the viscous behavior of the molten plastic. By coupling the isothermal model with a one‐dimensional heat‐transfer analysis, the gas penetration rate is shown to be several orders of magnitude higher than the plastic freezing rate, so that most of the heat transfer between the melt and the gas occurs after the mold is filled.
Crystal orientation and twinning in cold‐rolled ultrahigh molecular weight polypropylene
Authors: Hibi Sadao , Niwa Takahiro , Mizukami Jun , Wang Chi , Kyu Thein
Published: May 2005

The mechanisms of plastic deformation in cold‐rolled ultrahigh molecular weight polypropylene (UHMWPP) have been explored by means of wide angle X‐ray (WAXD) pole figures. The melt crystallized UHMWPP slabs were rolled unidirectionally in a two‐roll mill at 408 K as well as in the cross (transverse) direction. In the unidirectional rolling, all reciprocal lattice vectors of (110), (040), and (130) were found to orient preferentially in the film normal (thickness) direction. The cross‐rolling of UHMWPP shows the preferential orientation of the above plane normals in the film thickness direction, but the distribution of poles broadens toward the transverse direction. Such orientation behavior is very different from that of conventional cold‐rolled polypropylene. Various orientation mechanisms involving the orientation of lamellae in the film plane, twinning of the (110) plane and slippage mechanisms have been taken into consideration to account for the observed pole figures. A theoretical simulation has been carried out based on an orientation distribution function approach by introducing a slippage angle along the maximum shear stress in conjunction with intralamellar slip around the transverse direction. This model simulation conforms closely with the experimental WAXD pole figures of the (110), (040), and (130) planes.
Mechanical properties of polyurethane‐unsaturated polyester interpenetrating polymer networks
Authors: Chou Y. C. , Lee L. J.
Published: May 2005

Interpenetrating polymer networks (IPNs) based on a polyurethane (PU) and two unsaturated polyester (UPE) resins (a commercially available UPE and a partially endcapped UPE) were prepared. The mechanical properties, such as tensile strength, elongation at break, impact strength, and dynamic mechnical properties of IPNs, were studied by changing reaction temperature, PU reaction rate, and UPE reaction rate. Owing to the unique microgel formaton of UPE, the first formed network tends t be the dispersed phase in the PU‐UPE IPN system. The reaction sequence was found to be an important factor in determining the phase mixing and phase morphology of the IPNs. When the PU reaction was faster, extensive phase mixing due to strong grafting or chain interpenetration was obtained. When the UPE reacted first, grafting was retarded by the microgel formation of the UPE network. It was found that simultaneous reaction of the two reacting system resulted in a co‐continuous structure that provided enhanced tensile properties and impact strength.
Water adsorption at a polyimide/silicon wafer interface
Authors: Wu Wen‐Li , Orts William J. , Hunston Donald L. , Majkrzak Charles J.
Published: May 2005

Neutron reflectivity (NR) was applied to measure te concentration of water at the buried interfaces between an amorphous poltimide and silicon single crystal wafers. Excess water was discovered within 30 Å of the metal/polymer interface, where the water concentration reached 17% (by volume) for the samples without a coupling agent and 12% for the ones with coupling agent. Beyond the interface, the water concentration was measured at2 to 3%, which is typical of bulk polyimide. The above results demonstrate conclusively the unique power of NR in determining water concentration near a buried interface, and provide the first quantitative evidence for a water concentration profile which peaks in the interface region.
Dynamic simulation of flow‐induced fiber fracture
Authors: Yamamoto Satoru , Matsuoka Takaaki
Published: May 2005

A dynamic simulation method has been developed of the fracture process of a fiber in a flow field using the particle simulation method proposed i a previous paper. The fiber is modeled with bonded spheres as a fiber model. The flexibility of the fiber model is altered by changing three parameters of the stretching, bending, and twisting constants between adjacent spheres. The stress induced in each bond of the fiber model as a result of deformation is formulated using displacement of the bodn distanc, bond angle, and torsion angle fr each pair of spheres. After deformation, the fiber model fractures at the bond at which the stress surpasses the strength of the fiber. The motion of the fiber model in a flow field is determined by solving the translational and rotational motion equations for individual spheres under the hydrodynamic force and torque exerted on them. The correctness of the method and formulation was verified by comparing the simulated deflection curve of a cantilever beam (with a concentrated load at the end) with the theoretical curve. Good agreement was found in both the deflection and slope of the beam. The fracture process of a fiber after bending deformation in a two‐dimensional siimple shear flow was simulated under assumptions of an infinitely dilute system, no hydrodynamic interaction, and a low Reynolds number of a particle. The calculated critical conditions of the flow field for fiber fracture were compared with Forgacs and Mason's theoretical ones. Simulated values of the fracture condition of the fluid shear stress related to the Young's modulus of a fiber agree with theoretical ones over an aspect ratio of 15.
Measuring the viscoelastic properties of an ethylene4‐tetrafluoroethylene copolymer at ultrasonic frequncies
Authors: Thomas V. , Giacomin A. J. , Wolfenden A.
Published: May 2005

Since poly(tetrafluoroethylene) (PTEE) and its copolymers are soluble only at high temperatures in primarily perfluorocarbon solvents, direct measurement of their molecular weight distribution by conventional dilute solution techniques is not possible. Instead, the structure must be inferred from the linear viscoelastic properties of the melt. To make this inference, the spectrum must be determined over a wide enough range of relaxation times t include the plateau modulus, G. This is accomplished by time‐temperature superposition for most polymers. For PTFE and its copolymers, the range between the melting point and th degradation temperature is too narrow for time‐temperature superposition to be used reliably for determination of the high frequency response. Hence, as they do not exist in the melt state over a wide enough temperature range for superposition, their viscoelastic properties at high frequencies must be measured directly. A new technique employing a piezoelectric ultrasonic composite oscillator has been developed. The viscoelastic Properties, G′(ω) and G″(ω), of Tefzel 280 (a high molecular weight ethylene‐tetrafluoroethylene copolymer) have been measured at ultrasonic frequencies (40 to 200 kHz).
Morphology and mechanical properties of epoxy resins containing functionalized perfluoroether oligomers
Authors: Mascia L. , Zitouni F. , Tonelli C.
Published: May 2005

Chain extended perfluoroether oligomers were found to be miscible with bisphenol epoxy resins at all concentrations. These were evaluated as modifiers for anhydride cured resin systems, taking advantage of the carboxylic acid functionality at the chain ends. By altering the mixing and curing procedure different two‐phases morphologies could be obtained varying from fine co‐continuous networks, which produced transparent castings, to opaque systems consisting of precipitated heterogeneous particles. While the Tg and flexural modulus were found to be slightly lower than the control cure resin, the addition of the fluoroligomer modifier produced large increases in flexural strength, ductility, and fracture toughness. Samples with an IPN type morphology were found to exhibit an increase in ductility after aging at 200°C for three weeks proportionally to the concentration of fluoroligomer used.