bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and dielectric properties of segregated carbon black–polyethylene systems
Authors: Yacubowicz J. , Narkis M. , Benguigui L.
Published: December 2004

The electrical and dielectric properties of compression‐molded segregated polyethylene‐carbon black mixtures are described in the frequency range between 10 and 8000 kHz as a function of frequency, temperature, and carbon black loading. The segregated systems investigated exhibit insulator‐conductor transitions in the range 0.25–0.65% (volume/volume) carbon black. The dielectric constant and the dissipation factor of the conductive samples are relatively very high in the frequency range studied. The dielectric constant increased sharply with the carbon black concentration, and then increased moderately beyond the insulator‐conductor transition. The dissipation factor‐concentration curves for different carbon blacks show maximum values in the vicinity of the critical concentration values. The dielectric properties of these systems are discussed in terms of interfacial Maxwell‐Wagner polarization effects.
A free radical copolymerization model for simulating reactive processing of unsaturated polyester resins
Authors: Huang Y. J. , Fan J. D. , Lee L. J.
Published: December 2004

A free radical copolymerization model is proposed for simulating the reaction rates and conversions of styrene monomer and unsaturated polyester resins during curing. This model is based on film theory in which the rate constants reflect both reaction and diffusion resistances. Differential scanning calorimetry in combination with Fourier transform infrared spectroscopy is used to measure the overall and individual reactivities of reacting species. Model parameters are determined from experimental data. The applicability of this model is demonstrated in a cure simulation.
Microspheres and microcapsules, a survey of manufacturing techniques Part II: Coacervation
Authors: Arshady Reza
Published: December 2004

A methodological survey of coacervation/phase separation techniques employed for the preparation of microspheres and microcapsules is presented. Basic features of macromolecular coacervation are discussed, and a classification of different coacervation procedures (i.e., simple, complex, aqueous, and nonaqueous) is provided. Microsphere formation and microencapsulation techniques based on coacervation/phase separation of gelatin, gelatin‐acacia, and ethylcellulose are described, and those of a wide range of other polysaccharide derivatives and synthetic polymers are tabulated. The dependence of microsphere/microcapsule characteristics on manufacturing parameters and performance evaluation of microspherical/microcapsular products are also discussed.
An experimental and theoretical investigation of transient melt temperature during injection molding
Authors: Dontula N. , Sukanek P. C. , Devanathan H. , Campbell G. A.
Published: December 2004

An in‐depth study of the effect of molding parameters on melt temperature was carried out, in which the melt temperature was measured with infrared probes. The effect of screw speed, back pressure, shot size, and polymer viscosity on melt temperature during plastication was determined. The melt temperature was not constant during injection, and was found to be as much as 44°C above the barrel temperature. The temperature rise results from viscous dissipation during plastication and adiabatic compression during injection. Measured temperatures are in qualitative agreement with a first order model of the process.
The performance of the emulsion polymerization of styrene in a continuous loop tubular reactor
Authors: Lee Der‐Yuan , Wang Jenn‐Hwa , Kuo Jen‐Feng
Published: December 2004

The emulsion polymerization of styrene in a continuous loop tubular reactor (CLTR) has been used to study the process kinetics under eigth levels of sodium lauryl sulfate (SLS) concentration, eight levels of potassium persulfate (KPS) concentration, and three levels of styrene monomer (St) concentration. A critical surfactant concentration for the overshoot phenomenon in the monomer conversion exists between 8.02 and 12.40 g‐SLS/1‐water. Overshoot was not eliminated by changing concentrations of the initiator and monomer. The overshoot in the number concentration of polymer particles was observed in all the polymerizations studied. The dependences of the rate of polymerization and the number concentration of particles in the steady state on the SLS and KPS concentrations are presented. The growth of the average cumulant diameter of particles shows a transient period followed by a steady state. The dependences of the volumetric growth rate of polymer particles on diameter are of the order of 1 for the lower SLS concentration and 0.5 for the higher SLS concentration, respectively. The steady state cumulant diameter depends on an order of −0.24 for the SLS concentration.
Fabrication and electrical properties of ceramic superconductor/polymer composites
Authors: Sarkar Asok K. , Peterson T. L.
Published: December 2004

Superconductor/polymer composites were prepared by mixing powders representing the Y‐Ba‐Cu‐O and Bi(Pb)‐Sr‐Ca‐Cu‐O systems with high‐density polyethylene. Their electrical resistivities were measured as a function of temperature. By controlling the powder preparation techniques, it was possible to fabricate composites with superconductive transition to zero resistivity in the Bi(Pb)‐Sr‐Ca‐Cu‐O system. These composites can be fabricated in certain desired shapes.
New wood‐polymer composites containing ethyl α‐hydroxymethyl acrylate polymers
Authors: Wright J. R. , Mathias L. J.
Published: December 2004

Ethyl α‐hydroxymethyl acrylate (EHMA) was synthesized and evaluated as a candidate for wood impregnation and in‐situ polymerization. Southern Pine softwood was impregnated under a variety of conditions with EHMA alone and with various comonomers plus free radical initiator. Following thermal polymerization, the wood‐polymer composites were tested for increased dimensional stability (water soaking swell resistance) and mechanical properties over untreated wood. The greatest increase in dimensional stability was attained using EHMA alone, while the maximum compression modulus was achieved by impregnating with 1:1 EHMA‐styrene and styrene alone. The composites were further characterized by 13C CP/MAS solid state NMR and scanning electron microscopy.
Structure and physical properties of biaxially stretched polyethylene terephthalate sheet after heat‐setting
Authors: Maruhashi Yoshitsugu , Asada Tadahiro
Published: December 2004

The consumption of hot‐fillable poly(ethylene terephthalate) bottles is extremely large and is still increasing in Japan. This type of bottle is generally manufactured by the heat‐set method using hot molds after stretch‐blow molding. In this study, the method is simulated using a setting application in which sheets can be stretched constraining their sizes on a hot aluminum block. The crystallinities of the sheets are found to depend on the thermal history, i.e., the duration and temperature of the heat‐set cycle. Heat‐setting mitigates thermal‐shrinkage of the sheets which is due to the increase in crystallinity or in the tense segments in the amorphous region. The structure of the heat‐set sheet varies depending on the original stretched sheet. For a sample of low draw ratio, the crystallinity does not increase because of the heat‐set. For a sample of medium draw ratio, the crystallinity increases greatly and the tense segments in the amorphous region also increase because of heat‐set. For a sample of high draw ratio, the crystallinity increases a little but the numbers of the crystallite and tense segments in the amorphous region do not change with the heat‐set.
Characterization of blends of an amorphous polyamide with lightly sulfonated polystyrene ionomers
Authors: Sullivan M. J. , Weiss R. A.
Published: December 2004

Improved compatibility of blends of polystyrene and an amorphous polyamide was achieved by lightly sulfonating the polystyrene. Hydrogen bonding between amide groups and either sulfonic acid or metal sulfonate groups lowered the interfacial tension between the two polymers, which led to a much finer dispersed phase size in blends involving the sulfonated polystyrene. At relatively high sulfonate to amide ratios, the two polymers formed a miscible blend. Improved mixing of the phases was verified by shifts in the glass transitions, and the specific interactions that occurred were characterized by Fourier transform infrared spectroscopy.
Experimental characterization of processing‐performance relationships of resistance welded graphite/polyetheretherketone composite joints
Authors: Don Roderic C. , Gillespie John W. , Lambing Cynthia L. T.
Published: December 2004

A study to investigate fusion bonding (welding) of AS4 graphite/polyetheretherketone (PEEK) thermoplastic composites is presented. Processing studies are conducted for resistance welding preconsolidated AS4/PEEK laminates in both unidirectional and quasi‐isotropic configurations using PEEK and polyetherimide (PEI) film at the joint interface. All bonding was done under a constant displacement process. The influence of processing time, initially applied consolidation pressure, and the rate of heat generation on weld performance is examined through lap shear and Mode I interlaminar fracture toughness testing. A rapid increase in strength with processing time that asymptotically approaches the compression molded baseline is measured. Weld times for quasi‐isotropic lap shear coupons are significantly shorter than those with a unidirectional lay‐up. Variation of the initially applied consolidation pressure is shown to have little influence on the lap shear strength of PEEK film welded lap joints. A discussion of the mechanisms allowing void formation during the welding process is given. Bond strength test results are correlated with ultrasonic C‐scans of the weld regions.
Modeling of antioxidant loss from polyolefins in hot‐water applications. I: Model and application to medium density polyethylene pipes
Authors: Smith G. D. , Karlsson K. , Gedde U. W.
Published: December 2004

This paper is the first in a series of related papers describing the application of a diffusion/reaction model to the loss of antioxidants from polyolefins in hot‐water applications. The model, which is derived in detail, describes the time evolution of antioxidant concentration profiles in the exposed material in terms of adjustable parameters. The parameters describe the rates of diffusion, evaporation, extraction, and chemical reaction of antioxidant. Parameter values are determined by least‐squares fitting of the calculated concentration profiles to experimental profiles. The model is applied to a commercial medium density polyethylene pipe material, where antioxidant concentration data from thermal analysis is available for water/air (internal/external) exposure at three temperatures. A comparison of parameter values with literature data is undertaken. The temperature dependence of the parameters is considered and activation energies are compared with literature values. The relative importances of the loss mechanisms are discussed. The effect of boundary conditions on parameter values is considered by application of the model to a limited amount of available data for air/air and water/water exposures. The results indicate that for water/air exposure, extraction by the water phase is the dominating loss mechanism.
Numerical simulation of semicrystalline polymer flowing in an empty tube with solidification
Authors: Yang Ling C. , Charmchi M. , Chen S. J.
Published: December 2004

A methodology is set forth for the numerical solution of the transient freezing problem of a viscous power‐law fluid flowing in a cold empty tube with a frozen layer forming on the inside tube surface. The fluid considered is the melt of a semicrystalline polymer with temperature dependent viscosity. The solution domain encompasses both the liquid and solid phases. Coordinate transformations are employed to immobilize and to straighten the moving, curved interface. An implicit finite difference method is employed to solve the governing equations. Numerical results are analyzed by examining the effects of the Peclet number, Nahme number, Stefen number, and the power law index on the profiles of the frozen layer. Variations of the thickness of the frozen layer as a function of time and axial coordinate are also presented.
Single screw extrusion of poly(vinyl chloride): Effect on fusion and properties
Authors: Covas J. A. , Gilbert M.
Published: December 2004

The behavior of unplasticized poly(vinyl chloride) (UPVC) during single screw extrusion was studied. The melting and gelation mechanisms under a variety of operating conditions were identified using microscopy, density measurements, and thermal analysis. The compound followed the behavior of wall‐slipping materials, the melt forming a pool near the passive flight of the screw. Gelation involved the progressive destruction of the original powder morphology and the development, upon cooling, of an entanglement network with primary and secondary crystallinity. Both the breakdown and internal fusion of the grains were observed, depending on the location of the material around the screw. Tensile yield parameters were found to be independent of the gelation level. The values of the post‐yield parameters reached a maximum for gelation levels in the range of 70% to 85%.
Aerodynamics in the blown film process
Authors: Campbell G. A. , Obot N. T. , Cao B.
Published: December 2004

Most industrial and laboratory blown film lines use an air ring with one or more lips to produce an annular air jet that cools the polymer extrudate. Experience in operating blown film lines indicates that the air flow around the bubble plays an important role in both heat transfer and momentum trasfer. The former has received some attention in the literature, but few investigations have been made on the latter. This paper deals with the aerodynamic aspect of the blown film process. An air flow field similar to that in the blown film process was produced by blowing air past a rigid model. Aerodynamic experiments were carried out to determine the velocity and pressure distributions, and the overall axial force on the rigid model. Theoretical predictions using the techniques of superposition of stream functions and macro‐balances of mass and energy were compared with experimental data.
The effect of axial pressure gradient on extruder mixing characteristics
Authors: Bigio David , Erwin Lewis
Published: December 2004

Many twin screw extruders are operated in the starve‐fed mode with the majority of the extruder having partially‐filled channels. There will always be regions of totally filled channels due to the presence of the die or reverse elements. The authors experimentally show the effect of the change of percent drag flow on the rate of distributive mixing in the co‐rotating and counter‐rotating twin screw extruder. Optimum operating conditions for distributive mixing are identified experimentally and verified theoretically.
Determination of the long‐term hydrolytic stability of polycarbonate engineering resins
Authors: Zinbo M. , Golovoy A.
Published: December 2004

The hydrolytic degradation of polycarbonate resins is a first‐order process in terms of the decrease in average molecular weights under a relative humidity (RH) and temperature. Two analysis procedures have been developed for making life‐cycle predictions of polycarbonate at any combination of humidity and temperature. The first prediction procedure uses an Arrhenius equation derived for determination of the activation energy of polycarbonate hydrolysis tested at various temperatures under a constant RH. The rate constants at any combination of temperature and RH can be determined for a new resin tested at three or more RHs under a temperature, since the logarithm of the Arrhenius intercept has a linear empirical relationship with RH. The second prediction procedure uses a linear relationship between the logarithm of the rate constant and RH derived from the humid‐aging of polycarbonate tested at various RHs under a constant temperature. The rate constants at any combination of temperature and RH can be determined for a new resin tested at three or more temperatures under a RH, since the intercept of the above linear relationship has another linear empirical relationship with temperature.
Predicting chain conformation and entanglement of polymers from chemical structure
Authors: Wu Souheng
Published: December 2004

The characteristic ratio C∞ and the entanglement molecular weight Me are two key molecular parameters that control melt viscoelasticity, solid mechanical (brittle/ductile) behavior, and adhesion of polymers. We show that the characteristic ratio C∞ and the entanglement molecular weight Me can be predicted from chemical structure by group additivity with uncertainties usually less than ∼ 7% for C∞ and ∼ 15% for Me, comparable with the accuracies of experimental values.
Percolation in injection molded polymer blends
Authors: Arends C. B.
Published: December 2004

Elastic moduli of injection molded blends of polycarbonate with poly(styrene‐co‐acrylonitrile) (SAN) have been obtained at temperatures between the glass transition temperatures of the two components. When compared with compression molded blends as a function of composition, the moduli were found to differ by as much as a factor of three at intermediate compositions. The variations are ascribed to differences in connectivity between minor component particles. The morphologies of these materials have been modeled using percolation concepts to quantify continuity of the individual phases. The effects of phase continuity resulting from composition as well as dispersed phase shape differences were evaluated. It was found that shape per se has only a minor effect on percolation. However, shape as reflected in the size of dispersed particles relative to the extent of the domain in which they reside is primary for developing a model for continuity of the phases. An empirical relation for percolation in finite domains was devised from Monte Carlo simulations. Modulus values calculated from these continuity considerations agree well with the observed data.
Fractography of injection molded polycarbonate acrylonitrile‐butadiene‐styrene terpolymer blends
Authors: Lee M.‐P. , Hiltner A. , Baer E.
Published: December 2004

Fractography has been used in the post‐failure analysis of single edge notched specimens of injection molded blends of polycarbonate (PC) and acrylonitrile‐butadiene‐styrene terpolymer (ABS). The mode of ductile tensile fracture of single edge notched specimens depended on comosition. Plane stress shear tearing was observed in the composition range PC/ABS 90/10 to 70/30 by weight where PC was the continuous phase. Intermediate compositions, PC/ABS 60/40 to 40/60, had a co‐continuous or almot co‐continuous phase morphology; these blends fractured by mixed mode pop‐in, where a tunneling center crack relieved the triaxiality and permitted plane stress shear lips to form near the edges. Herringbone fracture, a plane strain mode characterized by discontinuous crack growth, was observed when ABS was the continuous phase, PC/ABS 30/70 to 10/90. An S‐shaped relationship was observed between the ductile‐to‐brittle transition temperature and the composition. Addition of ABS to PC increased ductility up to PC/ABS 70/30 and 60/40, which were the most ductile compositions. Further addition of ABS decreased the ductility, and the least ductile compositions were PC/ABS 30/70 and 10/90.
Effects of UV exposure and thermal history on properties of a preimidized photosensitive polyimide
Authors: Ree Moonhor , Chen K.‐J. Rex , Czornyj George
Published: December 2004

The structure and properties of a preimidized photosensitive polyimide (Probimide PSPI, a copolyimide of benzophenonetetracarboxylic dianhydride with alkyl groups substituted aromatic diamines) were studied with variations of UV exposure energy and bake temperature by means of wide angle X‐ray diffraction, dynamic mechanical thermal analysis, stress‐strain analysis, and residual stress analysis. The X‐ray diffraction patterns patterns indicate that the PSPI is amorphous in the solid state. The Tg was 378°C ∼ 410°C, depending upon the thermal history over the range of 350°C ∼ 400°C. At the glass transition region, the dynamic storage modulus E′ was very sensitive to both i‐line exposure energy and thermal history. However, the mechanical stress‐strain behavior at room temperature was primarily dependent on the thermal history. The mechanical properties were 2.6 GPa ∼ 2.9 GPa Young's modulus, 131 MPa ∼ 168 MPa tensile strength, 10% ∼ 12% yield strain, and 16% ∼ 74% elongation at break, depending upon the baking or annealing. These dynamic and static mechanical properties indicate that on the PSPI backbone, crosslinks are formed thermally as well as photochemically. The thermal crosslinks might be formed through thermal liberation of the labile alkyl groups of aromatic diamine moieties and subsequent coupling of the radicals. The thermal degradation was also evidenced in the mechanical properties degraded by baking above 375°C or annealing above 350°C. In addition, during baking and cooling, the residual stress was dynamically measured on Si wafers as a function of temperature. The stress at room temperature was 48 MPa ∼ 52 MPa for the PSPI films baked at 350°C or 400°C, regardless of i‐line exposure.
Vacuum metallization of polyetherimide: Interfacial chemistry and adhesion
Authors: Porta Gregory M. , Foust Donald F. , Burrell Michael C. , Karas Bradley R.
Published: December 2004

Vacuum deposition of metal coatings on polyetherimide was investigated. High levels of adhesion (>170 g/mm) with evaporated copper were achieved through a primarily chemical interaction. Changes in the interfacial chemistry were correlated with metal/polymer adhesion. Vacuum deposition of aluminum onto polyetherimide was also examined and found to yield much lower adhesion.
Steady melting of rectangular thermoplastic bars induced by hot contacting surfaces
Authors: Poslinski A. J. , Stokes V. K.
Published: December 2004

The steady melting of rectangular thermoplastic bars in contact with hot surfaces is analyzed by solving a simplified set of the momentum and energy balance equations, assuming a temperature and shear‐rate dependent melt viscosity. A numerical model is developed for predicting the flow field and the temperature distribution in the solid and molten regions of the bar and the location of the solid/melt interface. Computer simulations show that the steady melting rate of the thermoplastic solid is mainly affected by the temperature sensitivity of the melt viscosity, by the pressure applied on the end of the bar, and by a balance between heat conduction and the convection of colder material into the molten region. For the amorphous and semicrystalline polymers considered, heat convection in the outflow direction of the molten material, viscous dissipation, and shear‐thinning of the melt viscosity have a much smaller effect on the melting process. These results provide an insight into conduction‐induced melting with forced melt removal caused by pressure‐induced flow; they also provide a basis for developing a transient model for the hot‐tool welding process.
Description of thermal and mechanical properties of drawn polymers over a wide temperature range
Authors: Bronnikov S. V. , Vettegren V. I. , Frenkel S. Ya.
Published: December 2004

Temperature dependencies of the thermal expansion coefficient for segments of macromolecular helices, α(T), were obtained for polymers by infrared (IR) spectroscopy. It was shown that the α(T) are complicated (nonlinear) over a wide temperature range. Wunderlich and Bauer's idea concerning “freezing out” of normal vibrations of polymer chains was used to describe them. It was shown that the substitution of the classical rather than quantum statistics for both torsional and bending vibrational modes of macromolecules causes complications in α(T). Mechanical properties of drawn linear polymers are connected with the thermal expansion. Therefore, such an approach may be used to describe the temperature dependence of Young's modulus and failure strength for drawn polymers in the range from cryogenic to melting temperatures.
On the interrelation of rubber elastic stress‐strain curves under different types of strain
Authors: Eckert G. , Pechhold W. , Schmid M.
Published: December 2004

With specially shaped samples it is possible to study the stress‐strain relation σ(γ) in simple shear up to large shear deformation γ. Measurements of σ(γ) on synthetic polyisoprene, IR 305, differently crosslinked with dicumylperoxide, are reported and compared with those for uniaxial extension on the same materials. Using the simple deformation geometry including shearbands proposed in the meander model (1), both stress‐strain relations can be converted into each other. These results favor the applied superstructural model and moreover show that the deformation behavior of rubbers is governed by one material law, σ(γ).
Effect of filler concentration on the phase separation in poly(vinyl acetate)‐poly(methyl methacrylate) mixtures
Authors: Lipatov Yuri S. , Nesterov Anatoly E.
Published: December 2004

The temperatures and kinetics of phase separation have been studied as a function of filler concentration in a polymer mixture of poly(vinyl acetate)‐poly(methyl methacrylate). The filler was shown to have a marked effect on the cloud point position and the phase separation kinetics at various temperatures. The effects observed are dependent upon the component ratio.
Characterization and cure of dielectric and conducting polymer thick films
Authors: Prime R. Bruce
Published: December 2004

Polymer thick films are screenable polymer pastes which vary from electrically non‐conducting to electrically conducting. These materials typically contain significant amounts of high boiling solvents, and cure therefore involves removal of solvent in addition to crosslinking of the polymer matrix. In this study thermogravimetric analysis and dynamic mechanical analysis were utilized to characterize the residual solvent and glass transition behavior, respectively, with cure of the polymer thick films. Thickness was maintained constant at approximately 25μ and 100μ by using stainless steel mesh substrates. Results showed that IR curing, although able to heat more rapidly, did not accelerate the cure beyond that expected from time at temperature. Time‐temperature superposition kinetics were employed to measure activation energy of cure, generate master cure curves, and to quantify IR cure time‐temperature profiles. Cure models describing Tg and residual cure as a function of time, temperature, and film thickness were developed.
The effect of cyclic stress on the physical properties of a poly(dimethylsiloxane) elastomer
Authors: Fitzgerald John J. , Martellock Arthur C. , Nielsen Paul L. , Schillace Robynn V.
Published: December 2004

The dynamic creep behavior of a filled poly(dimethylsiloxane) elastomer was studied under cyclic stress. The stress level was chosen such that the increase in the internal temperature was small and that microcracks were not observed. This work has demonstrated that cyclic stress in combination with high temperature accelerates the degradation of the elastomer. The results suggest that because of the applied force, breaks in the load‐bearing chains of the network occur. These breaks, while relieving the mechanical stress, create highly reactive ionic fragments. It is believed that because of the subsequent reactions of the ionic fragments, changes in the specific gravity, storage modulus, effective crosslink density, and length of the sample (creep) are observed. The observed decrease in the storage modulus is thought to occur because of the reaction of the ionic fragments with moisture, which results in the formation of silanol chain ends that reduce the effective crosslink density. The results also show that contrary to the prediction of the Boltzmann's Superposition Principle, the rate of creep is greatly enhanced when the sample is subjected to a sinusoidally varying dynamic load as compared to a comparable static load. The polymer weight loss was found to be linear with time and strongly dependent on the level of applied dynamic and static force. In addition, the weight loss and rate of creep were also found to be strongly dependent upon temperature.
Optical characterization of three‐dimensional surface and bulk anisotropy in high refractive index polymers
Authors: Cha Cheol Y. , Moghazy Samir , Samuels Robert J.
Published: December 2004

Interest in the development of polymeric materials for high temperature, electronic and microelectronic applications has led to an increasing number of new polymers. Many of these polymers have complex organic ring structures and semirigid backbones, characteristics that have posed some difficulties for structural analysis. The purpose of this paper is to test and compare two practical nondestructive optical techniques, polarized optical microscopy and polarized refractometry, for the determination of three‐dimensional surface and bulk anisotropy in these advanced materials. The optical techniques are first tested on a series of optically homogeneous uniaxially oriented isotactic polypropylene films and then applied to the analysis of high refractive index Kapton (PMDA‐ODA) polyimide films. The study includes a test of the validity of the compensator method, including the effect of fringe jumping, the use of polymer retarders, and the tilting technique of Stein.
Noncontact measurement of parison thickness profiles affected by swell and sag in continuous extrusion blow molding
Authors: Diraddo R. W. , Garcia‐Rejon A.
Published: December 2004

Optimization of final part thickness distributions is crucial in the extrusion blow molding process in order to minimize resin usage. Prediction of part thickness distributions from basic process and material parameters would be ideal. However, attempts to do so have been unsuccessful, largely because of the inability to predict parison thickness profiles. One must therefore resort to measurement of the parison thickness profile and estimation of the final part thickness distribution by computational methods. This paper describes a new technique for the noncontact estimation of parison thickness profiles in continuous extrusion blow molding. The method accounts for sag and requires no previous knowledge of rheological data. It can be employed on‐line for the purposes of process monitoring and control. The approach is based on the measurement of the parison length evolution with time during extrusion, the parison diameter profile, the flow rate, and the melt temperature gradient along the length of the parison. These parameters are utilized in conjunction with a theoretical approach that describes the extrusion of a parison under the effects of swell, sag, and extrusion into ambient conditions. Results are presented for three resins of various molecular weight distributions. The degree of sag is minimal at the top and bottom of the parison, and reaches a maximum near the center of the parison. Results are also presented to demonstrate the versatility of the method under other process conditions, such as varying flow rate, die temperature, and die gap.
The melt rheology of poly‐ε‐caprolactam/polypropylene alloy: A VAMAS round‐robin study
Authors: Samurkas T. , Rogers M. G.
Published: December 2004

The melt rheology of commercial poly‐ε‐caprolactam/polypropylene blend, Orgalloy R‐6000 was studied by a number of university, industrial, and government laboratories as part of the Versailles Project on Advanced Materials and Standards (VAMAS), Technical Working Party on polymer blends round‐robin research program. The objective of the organization is to facilitate the development of standard test methods for the characterization of such complex materials. The program was established to evaluate proposed test methods for characterization of the melt rheology of commercial blends. Orgalloy R‐6000 was studied in both shear and extensional flows. A number of the laboratories also compared its rheology to that of a polypropylene and a polyamide that are similar to those that were used to produce it. This material showed all the viscoelastic properties expected of molten thermoplastics but was found to be significantly more elastic than its constituent materials. The poor quantitative agreement of the interlaboratory results indicate that improvements in the standardization of test methodologies and sample conditioning for such hydroscopic materials is necessary.
Orientation of miscible and immiscible polymer blends
Authors: Abtal Essaid , Prud'Homme Robert E.
Published: December 2004

Polystyrene (PS) and poly(vinylmethylether) (PVME) were used to study the orientation of miscible and immiscible polymer blends. A miscible blend containing 60 wt% PS was prepared by casting the sample from a benzene solution. The immiscible blend was made by annealing the initially miscible mixture above its lower critical solution temperature for different times and temperatures. Fourier transform infrared spectroscopy and birefringence were used to measure the orientation of PS and PVME, before and after phase separation. Stress‐strain curves were also measured for the two types of systems. It was found that the two polymers orient differently and that phase separation induces an increase in the overall orientation of the mixture, in the modulus and in PS orientation. The differences observed between pure PS and PS in the blend were attributed to changes in specific interactions and density of entanglements. The variations with phase separation were attributed to a change in the morphology of the system.
Morphology‐Properties relationship of a ternary polymer alloy
Authors: Kojima Takayuki , Kikuchi Yutaka , Inoue Takashi
Published: December 2004

A ternary alloy of polyamide‐6 (PA), poly(phenyleneether) (PPE), and rubber has a three‐phase structure, in which PPE particles with rubber inclusions are dispersed in a PA matrix. This is an excellent thermoplastic with high impact strength and high heat resistance. To understand the morphology‐properties relationship, we undertook a two‐dimensional finite element method (FEM) analysis on the deformation mechanism of the ternary alloy. A three‐phase model was constructed so that five hybrid particles of PPE‐shell and rubber‐core were embedded in the PA matrix. When the model was deformed at room temperature, the rubber domain induced yielding of the PPE‐shell and the PA‐matrix and at large strains the yielded zone expanded to pervade the whole space. This suggests that the toughening mechanism is essentially the same as in the binary alloy of PA and rubber (rubber‐toughened PA). At higher temperatures (e.g., at 100°C) the stress concentration occurred not only in the PA matrix but also in the PPE‐shell. It implies that the PPE‐shell is highly responsible for bulk deformation, even though it is part of the dispersed phase. At high temperatures, the rigidity of PPE affects the alloy bulk rigidity so that the ternary system exhibits high heat resistance.
Morphological characterization of simulated polymer blends by light scattering
Authors: Bélanger C. , Cielo P. , Utracki L. A. , Favis B. D. , Patterson W. I.
Published: December 2004

The morphology and the properties of polymer blends are closely related to processing conditions. A skin/core morphology, with a minor phase undergoing variations in orientation and aspect ratio from the surface to the core of the material is observed in processes such as the injection molding of blends. The use of optical inspection to control the stability and the quality of the product on‐line is an interesting tool. In this paper, polymer composites made from glass fibers and glass microspheres embedded in a matrix of PS are used to simulate two‐phase polymer blend morphology with a skin/core configuration. The relationships between the morphology of two‐phase systems and the diffuse pattern scattered from an incident light beam are investigated through an analysis of the iso‐intensity plots. Information can be obtained from the ratio of the axes of the ellipsoidal iso‐intensity domains for depth‐invariant blend morphology, and from the variation of this ratio as a function of the distance from the center of the pattern for depth‐varying morphology samples. It is shown that one can differentiate the skin morphology and thickness effects.
Curing of unsaturated polyester resins—effects of pressure
Authors: Huang Yan‐Jyi , Lu Tian‐Jyh , Hwu Wei
Published: December 2004

The effects of pressure ranging from 0.1 to 6.21 MPa (0–900 psig) on the curing of unsaturated polyester resins at 110°c were investigated by an approach of integrated reaction kinetics‐rheology‐morphology measurements using a pressure differential scanning calorimeter (DSC), an infrared spectrophotometer (IR), a Haake rheometer, and by using scanning electron microscopy (SEM). Increasing pressure was found to delay the gel effect, and a previously unknown plateau of kinetic‐controlled region in the initial portion of the DSC rate profile was observed. The plateau region was mainly attributed to the crosslinking of C  C double bonds inside the microgel particles, as revealed by the conversions of styrene and polyester C  C bonds measured by IR, gel conversion data and SEM micrographs. The mechanisms of reaction kinetics both at atmospheric pressure and under pressures have also been elucidated by the progress of buildup of microgel structures.
Rheological and physical properties of polyarylate/LCP blend systems
Authors: Hong Soon Man , Kim Byoung Chul , Hwang Seung Sang , Kim Kwang Ung
Published: December 2004

A polyarylate Unitika U‐Polymer 100 (PAR) was melt blended with a thermotropic liquid crystalline polymer (LCP) Vectra A950, and the processingmorphology‐properties relations were investigated. Inclusion of LCP slightly reduced Tg of PAR. The PAR/LCP blend with the LCP content higher than 50 wt% exhibited a noticeable yield stress, particularly in the vicinity of crystal‐to‐nematic transition temperature (Tcn). LCP lowered the blend viscosity above Tcn and seemed to play a role as processing aid. The tensile strength of the blends was increased with increasing spin draw ratio and level of LCP, and the spinning temperature influenced tensile strength. The relaxation behavior under dynamic shear and resultant blend morphology based on WAXD and SEM analyses are discussed as well.
Mechanical properties of in‐situ composites based on partially miscible blends of glass‐filled polyetherimide and liquid crystalline polymers
Authors: Bafna S. S. , de Souza J. P. , Sun T. , Baird D. G.
Published: December 2004

The use of inorganic (glass) fiber reinforcement to enhance the mechanical properties and reduce the anisotropy of in situ composites based on blends of liquid crystalline polymers (LCPs) with polyetherimide (PEI) is discussed. It was found that the tensile and flexural moduli are increased and the anisotropy is reduced with increasing grass content (when compared at equivalent LCP weight fractions). The creep compliance of the PEI/LCP composites is reduced upon the addition of glass fibers. However, the disadvantage is that the processability worsens upon addition of glass fibers to the PEI/LCP in situ composites. The effect of adding glass reinforcement on the ultimate tensile strength is less clear, because the data do not show any consistent trend. Similarly, the elongation at break and toughness do not show any consistent improvement upon addition of glass reinforcement. Morphological studies show that there is considerable difference between the size and texture of the reinforcing glass fibers and LCP microfibrils.
Factors influencing the formation of elongated morphologies in immiscible polymer blends during melt processing
Authors: Gonzalez‐Nunez R. , Favis B. D. , Carreau P. J. , Lavallée C.
Published: December 2004

The morphology of the dispersed phase in immiscible polymer blends plays an important role in the determination of the final physical properties. This paper considers factors that influence the final state of deformation of the dispersed phase, and in particular, the formation of fibers and lamellae. Blends of polyethylene and nylon‐6 were extruded by ribbon extrusion at different draw ratios. Prior to single‐screw extrusion the materials were blended in a co‐rotating twin‐screw extruder, and the size of the dispersed phase was studied as a function of the viscosity ratio. As the blends are extruded into ribbons and drawn through the calender rolls, the morphology of the dispersed phase undergoes drastic transformations. The fiber formation is enhanced by increasing the draw ratio. At high draw ratios, long thin fibers are observed. Some biaxial deformation is obtained for the noncompatibilized systems when the extruded materials enter the calender with the maximum closing pressure applied to the rolls. The same effect is observed for the compatibilized systems with lower values of the viscosity ratio. As a general rule, it has been observed that the final dispersed phase deformation is diminished in interfacially compatibilized systems.
Fracture toughness of weldlines in thermoplastic injection molding
Authors: Tomari K. , Harada T. , Maekawa Z. , Hamada H. , Iwamoto M. , Ukai A.
Published: December 2004

Weldlines are fatal defects in many injection moldings of thermosetting resins and thermoplastics. Significant strength reduction by weldlines in thermoplastics is caused by poor adhesion, molecular orientation, and a V‐notch effect. These factors have been little investigated in detail, in spite of being well known. In the present article, the V‐notch effect on strength is discussed for two types of thermoplastics, polystyrene and polycarbonate. The depth of weldlines was obtained by milling on the weldline surface, and the fracture toughness was measured with a double edge notched specimen. Polystryrene, which was drastically weakened by weldlines, had relatively deeper V‐notch regions and the fracture toughness was also reduced by weldlines. Although polycarbonate had the same fracture toughness as polystyrene, it had strong weldlines since the depth of weldlines was negligibly small.
Comparison of microwave and thermal cure of epoxy resins
Authors: Wei Jianghua , Hawley Martin C. , Delong John D. , Demeuse Mark
Published: December 2004

Stoichiometric mixtures of DGEBA (diglycidyl ether of bisphenol A)/DDS (diaminodiphenyl sulfone) and DGEBA/mPDA (meta phenylene diamine) have been isothermally cured by electromagnetic radiation and conventional heating using thin film sample configurations. Fourier transform infrared spectroscopy (FTIR) was used to measure the extent of cure. Thermal mechanical analysis (TMA) was used to determine the glass transition temperatures directly from the cured thin film samples. Well‐defined glass transitions were observed in the TMA thermograph for both thermal and microwave cured samples. Significant increases in the reaction rates have been observed in the microwave cured DGEBA/DDS samples. Only slight increases in the reaction rates have been observed in the microwave cured DGEBA/mPDA samples. Higher glass transition temperatures were obtained in microwave cured samples compared to those of thermally cured ones after gelation. The magnitude of increases of glass transition temperature is much larger for the DGEBA/DDS system than DGEBA/mPDA system. The microwave radiation effect was much more significant in DGEBA/DDS system than in DGEBA/mPDA system. DiBenedetto's model was used to fit the experimental Tg data of both thermal and microwave cured epoxy resins.
Phase structure related to the mechanical properties of poly (styrene‐co‐acrylonitrile)/polycarbonate blends
Authors: Kodama Minekazu
Published: December 2004

Dynamic mechanical and tensile properties were investigated for blends of poly(styrene‐co‐acrylonitrile) and bisphenol‐A polycarbonate prepared by the solution process. It is apparent from the dynamic mechanical properties that the as‐blended sample has a phase separated structure and the structure changes further with heat treatment. The phase structures of as‐blended and heat‐treated samples were estimated using the theories of Kerner and Davies for the modulus of two‐phase materials and the dynamic mechanical data. The tensile properties obtained at room temperature are not inconsistent with the phase structure estimated for the as‐blended and heat‐treated samples.
Estimation of kinetic parameters associated with the curing of thermoset resins. Part I: Theoretical investigation
Authors: Scott Elaine P. , Saad Zoubeir
Published: December 2004

This is a two‐part theoretical and experimental study on the estimation of kinetic parameters associated with the curing of a thermoset epoxy resin. In Part I, the estimation procedure is presented. This estimation procedure is based on a method referred to as the Box‐Kanemasu method, which involves the minimization of a least squares function, and it represents a new application of this method. The kinetic parameters under consideration were the Arrhenius constants associated with two rate constants in a kinetic model used to describe the curing rate of an amine epoxy resin. The use of differential scanning calorimetry (DSC) and dielectric data assuming isothermal and dynamic experimental conditions was first investigated in a sensitivity study. It was determined that the degree of cure should be treated as the dependent variable and that data from isothermal experiments should be used. The estimation procedure was then used to estimate the Arrhenius constants from simulated degree of cure data with added errors. These results compared favorably with those found using a linear regression method.
Mechanical hysteresis of a polyether polyurethane thermoplastic elastomer
Authors: Gorce Jean‐Noël , Hellgeth J. W. , Ward Thomas C.
Published: December 2004

The mechanical hysteresis of a polyether polyurethane thermoplastic elastomer was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature, Tg of the polymer where the material did not formally yield. At temperatures above the Tg of the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the hard segment domains to act as physical crosslinks. At elevated temperatures, percent hysteresis increased as the hydrogen‐bonded hard segment domains weakened. When mechanical hysteresis was considered on the basis of constant deformation energies, hysteresis values reached a maximum in the vicinity of the Tg of the polymer. These maxima existed as a consequence of two opposing trends: the decreasing resiliency of the polymer as it becomes a glass and the increase in the resistance of that glass to undergo deformations sufficient to cause plastic flow. Finally, a hysteresis response surface constructed as a function of deformation energy and temperature was found to be sensitive to both the strain‐induced crystallization of the rubbery soft segment matrix and to the strain‐induced yielding of the glassy soft segment matrix.
Experimental study of transcription of smooth surfaces in injection molding
Authors: Yoshii Masaki , Kuramoto Hiroki , Kato Kazunori
Published: December 2004

Signal deterioration of optical discs depends strongly on the substrate surface roughness. Characteristics of surface roughness of the molded substrate have been studied in order to clarify the transcription mechanism of smooth surfaces in injection molding of polycarbonate resin. When the melt temperature, mold temperature, and injecting rate are low, microscopic flow marks more than 5 nm deep are observed on the surface. These flow marks are formed when the melted resin near the mold wall is cooled to the no‐flow temperature of resin before it comes into contact with the mold wall. Molding transcription improves by optimizing the molding conditions for preventing these flow marks. As a result, the surface roughness of the molded substrate obtained is 3.2 nm in maximum height Rmax, which is nearly equal to that of the mold stamper at 2.7 nm in Rmax.