bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mechanism of photocure of inherently photosensitive polyimides containing a benzophenone group
Authors: Scaiano J. C. , Netto‐Ferreira J. C. , Becknell A. F. , Small R. D. 
Published: December 2004

AbstractThe photochemistry of an appropriately substituted bisimide has been studied in solution by conventional means and time resolved laser techniques as a model for the behavior of inherently photosensitive solvent soluble polyimides, whose photochemistry are not well understood. A mechanism for the photochemical insolubilization of the polymer systems is suggested based on the results for the model system, which is confirmed by time resolved laser studies of polyimide solutions. Phosphorescence quenching rate constants for the model compound indicate that the triplet excited state is about one order of magnitude more reactive than triplet benzophenone, an increase most likely due to the inductive effect of the imide moieties.
Basic functionalization of polyethylene in the melt
Authors: Simmons A. , Baker W. E. 
Published: December 2004

AbstractThe production of a polymer containing basic functional groups via the reactive processing of polyethylene was investigated. Grafting of dimethylamino ethyl methacrylate, DMAEMA, to linear low‐density polyethylene in the melt was carried out, and the effects of initiator type, feed composition, and reaction time and temperature were studied. The extent of grafting was determined by Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy, and the degree of cross‐linking was observed by measuring the products' melt indices. Thermal stability of the product was investigated using differential scanning calorimetry. Materials containing up to 3 wt% of grafted DMAEMA were prepared. The choice of appropriate feed compositions and reaction conditions allows the production of a material containing the maximum amount of grafted DMAEMA, while minimizing cross‐linking. The grafted polyethylene produced under these conditions is more stable than the starting material, suggesting an antioxidant effect of the grafted moieties. The functional polymer produced should be of interest for the preparation of polymer blends with acidic polymers by virtue of the miscibility enhancement that could occur as compared with the hydrocarbon precursor.
On correlations of primary normal stresses in polymer solutions
Authors: Ait‐Kadi A. , Choplin L. , Carreau P. J. 
Published: December 2004

AbstractPrimary normal stress difference data of some 32 different polymer solutions have been examined and correlated to the shear stress by a simple power‐law model. The normal stress at constant shear stress is shown to increase with the molecular weight of the polymer, but decreases with the polymer concentration. The method proposed by Abdel‐Khalik, et al., for predicting the primary normal stress difference from viscosity data for these polymer solutions is inadequate. The FENE‐P dumbbell model is used to obtain master curves combining normal stress and viscosity data as a function of a dimensionless shear rate. It is found that this presents several drawbacks. It predicts shear‐thinning effects with a power‐law slope of −2/3, which is found to be too restrictive. The model fails to predict shear‐thinning effects for dimensionless shear rates λEγ lower than approximately 0.5. It also fails to predict satisfactorily the low shear rate value of the dimensionless combination of viscosity and first normal stress coefficient Ψ1/λE(η − ηs). An empirically modified correlation is proposed. The fit for a series of polyacrylamide (Dow Separan AP‐30) solutions is very good. In the case of a series of monodisperse polystyrene solutions, the fit is not as good, as the data show a more pronounced effect of polymer concentration at high shear rates.
An analysis of the extrusion welding process
Authors: Michel P. 
Published: December 2004

AbstractA mathematical model has been developed for the heating phase of extrusion welding. It is shown that weld quality is mainly determined by melting a layer of the base material. All the parameters relevant to the heating phase are shown to affect weld quality through their effect on the thickness of the molten layer in the base material. It is shown that these parameters can be well controlled.
Computer‐aided optimization of the parameters of heated‐tool butt welding
Authors: Potente H. , Natrop J. 
Published: December 2004

AbstractWelding represents one of the key stages in the manufacture of injection molded or blow molded plastics products. One process frequently employed is heated‐tool butt welding. However, the high seam quality associated with this process can only be attained through reliable process control and optimized welding parameters. This paper presents a simple new method for determining these parameters. Mathematical and physical descriptions of the individual process stages and a computer‐controlled heated‐tool butt welding machine serve as the basis for determining the parameters.
The impact strength of butt welded vibration welds related to microstructure and welding history
Authors: Schlarb Alois K. , Ehrenstein Gottfried W. 
Published: December 2004

AbstractA study has been made of vibration butt welds between plaques of polypropylene. The quality of the welds, as determined by impact tests, has been examined as a function of the welding variables: pressure and vibration amplitude. In addition, the microstructure of the welds has also been examined, classified, and correlated with the welding variables and weld quality. Penetration as a function of time shows three distinct regimes and It is shown that the impact strength of the welds is independent of time once the third regime is reached. The time required to reach the third regime decreases as pressure or amplitude increases and is more sensitive to amplitude of vibration than to pressure. The highest quality welds were produced at low pressure and low amplitude with corresponding long times to reach regime three and exhibited a unique, readily identifiable microstructure.
On the modeling of continuous mixers. Part II: The cokneader
Authors: Elemans P. H. M. , Meijer H. E. H. 
Published: December 2004

AbstractThe Buss cokneader is a single‐screw extruder with interrupted flights. Pins from the barrel are inserted into the screw channel. The screw is both rotating and oscillating. Due to this action, screw flights are continuously wiped by the pins. During one passage of the pin, the material is not only subjected to high shear stress, but it is reoriented as well, thus promoting the distributive mixing process by the local weaving action of the pins and screw flights. Attempts to model the cokneader tend to focus on a single pin passing through the hole in a screw flight (1, 2). However, a more comprehensive model can start with the same equations that apply to the corotating twin‐screw extruder (3). Because the effect of leakage flows on the local pressure gradient has to be considered along with the effect of the local dragging action of the pins (neglecting the oscillatory action), experiments with model liquids have been performed to evaluate the comprehensive model. Additional experiments with a Plexiglas‐wailed cokneader support the calculations concerning filled lengths in various screw geometries. These results, and those of model calculations, which are extended to the nonisothermal, non‐Newtonian situation, are presented.
Modeling nonisothermal impregnation of fibrous media with reactive polymer resin
Authors: Chan Albert W. , Hwang Sun‐Tak 
Published: December 2004

AbstractThe manufacture of polymer composites through resin transfer molding (RTM) or structural reaction injection molding (SRIM) involves the impregnation of a fibrous reinforcement in a mold cavity with a reactive polymer resin. The design of RTM and SRIM operations requires an understanding of the various parameters, such as materials properties, mold geometry, and mold filling conditions, that affect the resin impregnation process. Modeling provides a potential tool for analyzing the relationships among the important parameters. The present work provides the physical model and finite element formulations for simulating the mold filling stage. Resin flow through the fibers is modeled using two‐dimensional Darcian flow. Simultaneous resin reaction and heat transfer among resin, mold walls, and fibers are considered in the model. The proposed technique emphasizes the use of the least squares finite element method to solve the convection dominated mass and energy equations for the resin. Excellent numerical stability of the proposed technique provides a powerful numerical method for the modeling of polymer processing systems characterized by convection dominated transport equations. Results from example numerical studies for SRIM of polyurethane/glass fiber composites were presented to illustrate the application of the proposed model and numerical scheme.
A rheological method for the study of crosslinking of ethylene acetate and ethylene acrylic ester copolymer in a polypropylene matrix
Authors: Cassagnau P. , Bert M. , Verney V. , Michel A. 
Published: December 2004

AbstractTransesterification may be used to crosslink a copolymer such as ethylene vinyl acetate with poly(ethylene acrylate‐co‐propylene) in the presence of dibutyltin oxide as a catalyst. A rheological study of the mechanism of this exchange reaction has been made: The kinetics of the crosslinking reaction was determined by studying the time and temperature dependence of the dynamic storage modulus G′(t, T)ω. Kinetic curves obtained for different reactive blends (EVA, PP/EVA, and PPf/EVA) allowed for the evaluation of the activation energy of the reaction and, thus, specified the appropriate parameters (temperature and time) for carrying out this reaction in a molten state.
Flow field analysis of the kneading disc region in a co‐rotating twin screw extruder
Authors: Yang Haur‐Horng , Manas‐Zloczower Ica 
Published: December 2004

AbstractCo‐rotating, intermeshing twin screw extruders are widely used in polymer compounding and blending. Among the different modules of the co‐rotating twin screw extruder, the kneading discs are the dominant ones in determining mixing efficiency. The major difficulty in solving the flow problem in the kneading disc region arises from the complex geometry and the time‐dependent flow boundaries as the discs rotate. In this work, a fluid dynamics analysis package—FIDAP—using the finite element method was employed to simulate the flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK‐30 co‐rotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter λ quantifying the elongational flow components. The last two parameters are the most important ones in analyzing mixing efficiency. The influence of design variables (stagger angle, right or left handed configuration) and processing conditions (rpm, axial pressure gradient) on the flow characteristics was analyzed.
Compatibilization of a polystyrene‐polyethylene blend through reactive processing in a twin screw extruder
Authors: Teh J. W. , Rudin A. 
Published: December 2004

AbstractDirect grafting of polystyrene onto polyethylene has been carried out in a twin screw extruder with an organic peroxide and a crosslinking co‐agent. The reaction extruded blends exhibited enhancement in impact properties at an optimum level of peroxide and co‐agent. Further improvement was achieved by introducing styrene monomer into the system during reactive extrusion. The structure and morphology of the blends were studied using differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy, and size exclusion chromatography.
Liquid crystalline polymer/fluoropolymer blends: Preparation and properties of unidirectional “prepregs” and composite laminates
Authors: Dutta D. , Weiss R. A. , Kristal K. 
Published: December 2004

AbstractExtruded films of liquid crystalline polymer (LCP)/fluoropolymer blends were melt drawn to develop uniaxial orientation of a microfibrillar dispersed LCP phase. The anisotropy of the films increased with increasing draw and LCP content in the blend. Laminated composite plates were prepared using the extruded sheets as prepreg. The mechanical properties and coefficient of thermal expansion (CTE) of the prepreg and laminates agreed well with predictions from composite lamination theories. The potential for replacing glass fiber reinforced fluoropolymers with LCP/fluoropolymer blends in applications such as microwave circuit boards is discussed.
Thermoplastic character of polyimide blends
Authors: Han B. J. , Park Jae M. , Gryte Carl C. 
Published: December 2004

AbstractPolyimide blends consisting of pyromellitic dianhydride/4,4′‐oxydianiline (PMDA/ODA) and biphenyl‐tetracarboxylic dianhydride/p‐phenylene diamine (BPDA/PDA) show a distinct glass transition behavior at temperatures lower than each component does. Disruption of molecular packing by blending of polymers having dissimilar interaction sites leads to a significant increase in molecular mobility at much lower temperatures. This is examined by laminating two pieces of film cast from the blend and measuring the adhesive strength at the interface. A strong adhesion, 11.5 N/cm (6.6 lbf/in) by 180° peel test, was achieved indicating interpenetration of polyimide molecules. It was also found that the polyimide blends can be converted into highly ordered states by mechanical deformation of the blends above their glass transition temperatures (Tgs).
The microwave processability of semicrystalline polymers
Authors: Chen M. , Hellgeth J. W. , Siochi E. J. , Ward T. C. , McGrath J. E. 
Published: December 2004

AbstractThe overall objective of these studies was to investigate the relationship between polymer structure and microwave absorptivity. In this paper, the microwave processing of semicrystalline polymers such as poly(ether ether ketone) (PEEK), nylons, and poly(ethylene terephthalate) (PET), via a cylindrical resonance wave cavity and a rectangular standing wave applicator is described. These polymeric materials were irradiated in low power (< 50W) electric fields at 2.45 GHz. Silicone flexible molds were necessary for improved processing of nylons and PEEK at temperatures below their Tc Rapid heating rates were observed between the glass transition temperature, Tg, and the melting temperature, Tm, for all these polymers provided that Tc was exceeded. Both dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA) spectra were utilized to predict the heating phenomena between amorphous and semicrystalline materials and to explain the rapid crystallizing rate of PEEK. above its glass transition temperature. Correlations were drawn between (a) the apparent activation energy and the critical temperature (Tc) and (b) the shape of the dielectric spectra at 2.45 GHz and its shape in kHz region.
Interaction of nonhomogeneous shear, nonlinear viscoelasticity, and yield of a solid polymer
Authors: Wineman A. S. , Waldron Jr. W. K. 
Published: December 2004

AbstractA constitutive equation for small strain viscoelastic response is considered in which stress relaxation. occurs faster as strain increases. The constitutive equation is of single integral type and has a psuedo‐ or material time function which is calculated from a strain dependent shift function. First, it is shown that such a constitutive equation can account for yield as observed in polymers for a number of different stress and strain histories. Next, the constitutive equation is used in the analysis of the problem in which a hollow cylinder is fixed at its inner surface and a moment history is applied to its outer surface. This causes the cylindrical surfaces to rotate about the central axis, thereby inducing a radial shear strain distribution. It is shown that there is a time when the material near the inner support begins to yield and a layer of large shear strain gradient begins to grow rapidly. It is also shown that the stress or strain history at a material element will generally not be one of the standard histories used to study yield.
Review of stabilization of polyolefin insulated conductors. Part I: Theory and factors affecting stability
Authors: Hendrickson L. , Connole Kent B. 
Published: December 2004

AbstractThe understanding of the failure mechanism causing cracks in insulated telephone wire is critical to developing a solution to the problem. This paper reviews the antioxidant and metal deactivator theory as it applies to polyolefins and reviews the factors, both internal to the polymer and external which affect stability. Degradation theory in vacuum and air is reviewed. Primary and secondary antioxidants are discussed as are multifunctional metal deactivator/antioxidant molecules. The internal factors affecting thermal stability which are discussed include: polymer synthesis process, molecular weight, molecular weight distribution, crystallinity, phase state, orientation, amount of antioxidant, amount of metal deactivator, and amount of blowing agent. The external factors affecting long term life are: temperature, oxygen, ozone, stress, filling compound, and presence of copper.
Numerical simulation of fiber orientation in injection molding of short‐fiber‐reinforced thermoplastics
Authors: Chung S. T. , Kwon T. H. 
Published: December 2004

AbstractThe present study develops a numerical simulation program to predict the transient behavior of fiber orientations together with a mold filling simulation for short‐fiber‐reinforced thermoplastics in arbitrary three‐dimensional injection mold cavities. The Dinh‐Armstrong model including an additional stress due to the existence of fibers is incorporated into the Hele‐Shaw equation to result in a new pressure equation governing the filling process. The mold filling simulation is performed by solving the new pressure equation and energy equation via a finite element/finite difference method as well as evolution equations for the second‐order orientation tensor via the fourth‐order Runge‐Kutta method. The fiber orientation tensor is determined at every layer of each element across the thickness of molded parts with appropriate tensor transformations for arbitrary three‐dimensional cavity space.
Steady‐State and dynamic properties of concentrated fiber‐filled thermoplastics
Authors: Greene Joseph P. , Wilkes James O. 
Published: December 2004

AbstractRheometric data for short‐fiber‐filled thermoplastics are presented using a parallel‐plate viscometer. Polypropylene tensile bars contain short and long fibers with glass weight percentages of 0%, 5%, 10%, 20%, and 30%, polycarbonate tensile bars with glass percentages of 0%, 5%, and 10% long fibers, and nylon 6/6 tensile bars with 0%, 15%, 30%, and 45% short fibers. The short fibers were initially 3 mm in length and 12.7 microns in diameter. The long fibers were initially 6 mm in length and 10 microns in diameter. In the steady‐state experiments, the fibers increase the viscous stresses and the normal stresses in proportion to the concentration of fibers. At low shear rates, the viscosity is increased by the addition of the fibers, but at high shear rates the viscosity approaches that of the neat resin. In dynamic testing, the fibers increase the viscous and elastic components as measured by the complex viscosity and modulus. The fibers increase the viscous and elastic nature of the fiber‐filled composite at low frequencies and to a lesser extent at higher frequencies. The fibers increase the elastic component more than the viscous component at low frequencies and less at higher frequencies as demonstrated by tan δ.
Particle Size Distribution and Aspect Ratio of Organic Pigments
Authors: Grubenmann Arnold 
Published: December 2004

AbstractParticle size and aspect ratio are amongst the most important parameters which determine the application properties of pigments, fillers and powders for ceramics. A statistical characterization of the samples is therefore needed. In this paper we discuss the measurement of bivariate size distributions of organic pigments and describe a correction procedure for particles with interchanged crystallographic axes. During the crystallization of a pigment, the larger aspect ratios usually result from faster growth rates.
A Rapid Method for Determination of Changes in Shape of Comminuted Particles Using a Laser Diffractometer
Authors: Austin Leonard G. , Trass Olev , Dumm Timothy F. , Koka Venkat R. 
Published: December 2004

AbstractThe size distributions of carefully screened √2 size fractions of ground materials were determined using a Microtrac laser diffractometer. The size distributions were fitted to the empirical function P(x) = 1/[1 + (x50/x)λ] where P(x) is cumulative mass fraction less than Microtrac size, x. The standard deviation of λ for a 50 second test time was approximately 0.5, so that seventeen test times give a mean with an estimated error within ± 0.25 (95% confidence level). Values of λ were 5.44, 4.82, 4.40 for a coal ground under different conditions, indicating statistically different shape distributions; the average value for mica was 2.91 owing to the high aspect ratio of the particles. The ratio of x50 to the geometric mean sieve size was 1.2 for the coal and 0.70 for mica.
Zur Geschichte des Zeiseschen Merkaptans und seines Namens (1833)
Authors: Diergart Paul 
Published: January 2005

AbstractDa die Erklärungen des Namens Merkaptan oft ungenau sind, wird in eine Untersuchung eingetreten. Zuvor wird begründet, warum der deutschen Schreibweise Merkaptan mit k heute der Vorzug zu geben ist, aber Mercaptum mit c. Die Zeitschriften zur Zeit der Entdeckung (1833) bringen verschiedenartige Ableitungen des Wortes Mercaptum, die sprachlich und chemisch dennoch zu rechtfertigen sind. Der aus der dänischen Urschrift beigebrachte Wille des Entdeckers und Namengebers Zeise ist maßgebend: mercaptum von mercurio aptum, merkaptan von mercurium captans. Nach näherer Begründung des Jahres 1833 als Entdeckungsjahr werden die Ansichten von Berzelius, Liebig und Wöhler über die Zeisesche Arbeit geschildert. Experimentell ist diese allen dreien vorzüglich, ja meisterhaft, aber beim Lesen der Abhandlung selbst ist ihnen mit Recht, „wie wenn man auf Schlitten durch Sand fährt”︁. Es wird dann ausgeführt, daß der Entdecker vor Liebig und Berzelius die Analogie zwischen Merkaptan und Alkohol ausgesprochen hat, und kurze Bemerkungen aus Zeises sonstigem Wirken bilden den Schluß. Alle notwendigen Belege sind angegeben.
Quantitative elektrolytische Reduktionen. II. Teil: Reduktion der Salpetersäure
Authors: Nietz Edgar 
Published: January 2005

Abstract
Bei der quantitativen Reduktion von Nitrat‐Ion zu Ammonium‐Ion an schwammig verkupferter Kathode kommen folgende Fehlerquellen in Betracht:

ein Teil des Stickstoffes entweicht als Gas. Die Maßnahmen zur Verringerung dieses Fehlers waren erfolglos.
Während des Spülens der Cu‐Kathode löst sich unter Verbrauch von Schwefelsäure etwas Kupfer auf. Durch Neutralisieren der reduzierten Lösung vor Unterbrechung des Stroms konnte dieser Fehler praktisch ausgeschaltet werden.
Die Amphoterie des Blei(2)‐ und des Blei(4) oxyds
Authors: Töpelmann Herbert 
Published: January 2005

AbstractDer allgemein‐chemische Charakter und die Amphoterie von Blei(2)‐ und Blei(4)oxyd werden in Zusammenhang mit den derzeitigen Kenntnissen vom Bau der Blei(2)‐ und Blei(4)‐ atomionen erörtert.
Über die Konstitution des Santenons und der Santensäure. Mit 3 Figuren
Authors: Enkvist Terje 
Published: January 2005

Abstract1. Bei einem Versuch zur Totalsynthese der Santensäure wurde nicht diese Säure, sondern eine mit derselben isomere, neue, anhydridbildende Säure, die Cis‐Allosantensäure erhalten, deren Struktur durch die Totalsynthese festgestellt ist, und die der gewöhnlich angegebenen ebenen Formel der Santensäure entspricht.