bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microspheres and microcapsules, a survey of manufacturing techniques Part II: Coacervation
Authors: Arshady Reza 
Published: December 2004

AbstractA 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

AbstractAn 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

AbstractThe 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

AbstractSuperconductor/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

AbstractEthyl 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

AbstractThe 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

AbstractImproved 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

AbstractA 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

AbstractThis 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

AbstractA 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

AbstractThe 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

AbstractMost 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

AbstractMany 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

AbstractThe 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

AbstractThe 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

AbstractElastic 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

AbstractFractography 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

AbstractThe 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

AbstractVacuum 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

AbstractThe 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

AbstractTemperature 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

AbstractWith 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

AbstractThe 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.