bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic determination of the in‐situ composition of epoxy matrices in glass fiber reinforced composites
Authors: Antoon M. K. , Zehner B. E. , Koenig J. L.
Published: May 2005

Computerized infrared analysis is applied to the characterization of a glass‐reinforced crosslinked polyester. The method of factor analysis determines the number of independent components which constitute the polymeric matrix. Subsequently, the spectra of those components are fitted by a least‐squares criterion to spectra of the multicomponent matrix, or, if the glass spectrum is included as an additional component, to the spectra of composites. The least‐squares coefficients yield the matrix composition in terms of the initial reactant composition and the extent of crosslinking.
Mica composites of improved strength
Authors: Newman S. , Meyer F. J.
Published: May 2005

Mineral fillers of flake configuration such as mica can, in principle, produce large increases in modulus and strength especially if the flake is oriented predominantly in a plane. Additionally, the resulting composites have the advantage of possessing isotropic properties in the plane of orientation, thereby minimizing the warpage normally associated with the injection molding of fiber‐reinforced thermoplastics. However, to properly transmit stress from the matrix to the mica and minimize the effect of defects in morphology, a ductile matrix is required with adequate interaction or adhesion between phases. Many of the above conclusions are documented in the literature and are confirmed by our investigations of the system mica‐polypropylene. The novelty of this effort rests upon (1) successful attempts to identify specific non‐silane additives which by co‐blending suitably modify the mica‐polypropylene interface, (2) to demonstrate the remarkable effects of time‐temperature during melt processing on the behavior of this system; and, (3) to show the relation between composition and time‐temperature effects on resultant mechanical, physical, and thermal properties. Most notably, large improvements in tensile and flexural strength and heat distortion temperature can be attributed to the use of small amounts of chlorinated organic compounds blended under carefully selected melt process conditions. Some speculation concerning the mechanism of interaction will be discussed and the resultant potential for increased application will also be outlined.
Test method evaluation for fiber‐reinforced molding materials
Authors: Taggart David G. , Pipes R. Byron , Mosko John C.
Published: May 2005

Standard test methods ASTM D‐651 for determining tensile properties and ASTM D‐790 for flexure properties are evaluated. Heterogeneous fiber distributions due to molding flow conditions are shown to yield test specimens wherein fiber orientation near surfaces is highly collimated while orientations in central regions are oriented approximately transverse to the specimen axis. In addition, the converging and diverging flow fields in the dog bone (ASTM D‐651) specimen with end gate are shown to yield a variation in fiber orientation along the specimen length. Finite element analysis of the dog bone (ASTM D‐651) reveals that stress concentrations and a non‐uniform stress distribution are introduced due to the required gripping arrangement of the test standard. The flexural specimen is decomposed into two elements of a collimated and transverse fiber orientations and a mathematical model is developed which reflects the composite behavior of the beam specimen. Finally, it is concluded that the D‐651 and D‐790 test methods do not reveal intrinsic design data for fiber reinforced molding materials.
Flow and flow orientation of composites containing anisometric particles
Authors: Utracki L. A.
Published: May 2005

There is a growing commercial and academic interest in polymeric composites filled with short fibers and/or glass or mica flakes. Here, the properties depend strongly on the flow induced morphology and on the distribution of residual stresses. To optimize processing and properties, it is important to know both the melt rheology and the orientation of the dispersed phase. The industrial formulations are notoriously very complex. However, it is possible to understand, and sometimes predict, their behavior by a systematic comparison with simpler, better known systems, i.e., suspensions. This review concentrates on two main aspects of flow of polymer melts containing anisometric particles, namely yield phenomena and orientation.
Determination of the orientation of mica in composites
Authors: Malik T. M. , Prud'Homme R. E. , Rémillard B.
Published: May 2005

A wide angle x‐ray diffraction technique has been used to determine the orientation of mica flakes in composites. The mica used was a fine grade Phlogopite, and the polymers were polystyrene, polycarbonate and poly(vinyl chloride). Composite samples of varying mica contents and orientations were prepared. The x‐ray method can give the orientation distribution function of mica flakes across and parallel to the surface of the sample. From this function, an average orientation parameter was calculated. The results show that there is no orientation of mica across the surface of the sample (the x‐ray beam is normal to the surface), but that there is a strong orientation in a direction parallel to this surface, the average orientation parameter being strongly dependent upon the particle size of mica and mode of preparation.
Measurement of fiber and matrix orientations in fiber reinforced composites
Authors: Kamal Musa R. , Song Li , Singh Peter
Published: May 2005

Short glass fiber reinforced polypropylene was employed in a study to determine the effect of molding and mold design variables on the distrubution of fibers and their orientations, and consequently, on the distributions of mechanical properties in the molded article. In this paper, a variety of experimental techniques were employed to evaluate the distributions of fibers and their orientations. Moreover, techniques were developed to evaluate the orientation and crystallization of the matrix. The results yield significant information regarding the development and control of both the microstructure and the properties of short fiber reinforced composites.
Use of grafted aspen fibers in thermoplastic composites: IV. Effect of extreme conditions on mechanical properties of polyethylene composites
Authors: Kokta Bohuslav V. , Daneault Claude , Beshay Alphons D.
Published: May 2005

Hardwood fibers of aspen in the form of chemithermo‐mechanical pulp (CTMP) have been used as reinforcement in linear low density polyethylene (LLDPE). The effect of composite treatment (immersion in boiling water, heat exposure at 105°C for seven days or at a temperature of −40°C) on resulting mechanical properties were evaluated. The grafted aspen CTMP composites showed by far the best results with regard to secant modulus, tensile strength, energy, and strain when compared to those of wood flour, mica or glass–fiber filled LLDPE, as well as to virgin LLDPE. Finally, the dimensional stability of CTMP aspen‐filled LLDPE composites immersed for four hours in boiling water was better than that of mica or glass–fiber filled LLDPE.
Ultrasonic evaluation of filled polymers: I. Techniques and models for the elastic moduli of a resin filled with iron spherical inclusions
Authors: Piché L. , Hamel A.
Published: May 2005

The ultrasonic technique for the nondestructive evaluation of elastic moduli is described. Its use in the application to polymers, whereby viscoelastic effects are eliminated, is discussed. Experimental results are given for composites containing high contrast (iron) spherical inclusions. The measurements are discussed in terms of available theoretical models. It is clearly demonstrated that models that account for the microscopic details of the material offer the best description of the bulk properties.
Buckling of composite cylinders under external pressure
Authors: Ouellette P. , Hoa S. V. , Sankar T. S.
Published: May 2005

Experimental results from buckling tests on thin shell structures made of filament‐wound glass fiber reinforced plastic are compared to values calculated with three different procedures. These procedures are: (1) a linear stability analysis for anisotropic, heterogeneous, thin, cylindrical shells, (2) a proposed design code, and (3) a national standard. Imperfection surveys in the circumferential direction were conducted and were found to be much larger than imperfections typical for metallic thin shells. All three procedures yield design pressures lower than observed buckling pressures. The analytical method and the standard are less conservative than the proposed design code and may possibly permit the fabrication of safe and more economical structures.
Crystallization and fiber/matrix interaction during the molding of PEEK/carbon composites
Authors: Denault J. , Vu‐Khanh T.
Published: May 2005

The objective of this work was to investigate the effects of molding conditions (molding temperature, residence time at melt temperature, and cooling rate) on the crystallization behavior and the fiber/matrix interaction in PEEK/carbon composites made from both prepreg and commingled forms. In order to investigate the crystallization behavior of the PEEK matrix, the molding process was simulated by differential scanning calorimetric analysis, DSC. The results show that the prepreg and commingled systems do not have the same matrix morphology; prepreg tape was found to be at its maximum of crystallinity, whereas the commingled system was found to be only partially crystalline. The results show that processing must be carried out at a temperature sufficiently high to destroy the previous thermal history of the PEEK matrix; this is an essential requirement to produce efficient fiber/matrix adhesion in the commingled fabric system. Optical microscopic observations also suggest that matrix morphology near the fibers is dependent on the melting conditions; a well‐defined transcrystalline structure at the interface is observed only when the melt temperature is sufficiently high. However, the high temperature of molding can easily result in degradation of the PEEK matrix such as chain scission and crosslinking reactions. Thermal degradation of the matrix during processing is found to affect the crystallization behavior of the composites, the fiber/matrix adhesion, and the matrix properties. This effect is more important in the case of a commingled system containing sized carbon fibers because the sizing agent decomposes in the molding temperature range of PEEK/carbon composites. This produces a decrease of the matrix crystallinity and an elimination of the nucleating ability of the carbon fibers. A transition between cohesive and adhesive fracture is observed when the cooling rate increases from 30°C/min to 71°C/min for the composite made from the commingled fabric. This critical cooling rate is found to closely correspond to a change in the mechanism of crystallization of the PEEK matrix.
Blends of semicrystalline and amorphous polymeric matrices for high performance composites
Authors: Torre L. , Kenny J. M.
Published: May 2005

The compatibility and crystallization behavior of blends of semicrystalline and amorphous polymers, traditionally used as matrices of high performance composites, has been studied. The analysis has been focused on blends of semicrystalline poly(etheretherketone) (PEEK) with amorphous poly(etherimide) (PEI) prepared by melt mixing. Differential scanning calorimetry and thermogravimetric analysis have been used to analyze the influence of blend constituents and processing conditions on the compatibility, on the crystallization kinetics and on the final crystalline content. An Avrami model has been applied to the crystallization of PEEK in a PEEK/PEI 50/50 blend and the results have been compared with the behavior of the neat PEEK resin. The results of the characterization can be applied to predict the behavior of such blends when processed as matrix of composites or when used in the “amorphous bonding” procedure.
Structure and properties of poly(p‐xylylene) composites made by electrochemical and vapor deposition polymerization
Authors: Li Hong , Moshonov Aharon , Muzzy John D. , Olsen Roger A.
Published: May 2005

Poly(para‐xylylene)(PPX)/carbon fiber towpregs were produced by two different in‐situ polymerization processes: Electrochemcal polymerization (ECP) and vapor deposition polymerization (VDP). The monomer used for the ECP process was α, α′ ‐dibromo‐para‐xylylene and di‐para‐xylylene was the starting material for the VDP process. A series of tests, including FTIR, WAXD, DSC, TG, and SEM were carried out to identify and compare these two composite towpregs. It has been confirmed that the PPX samples obtained by the two different polymerization processes were basically chemically identical. However, the polymer coating on the fiber surface produced by the VDP process was much smoother than that produced by the ECP process, which produced a porous coating.
Impact modification of poly(vinyl chloride) with chlorinated polyethylene I. Blend morphology
Authors: Siegmann A. , Hiltner A.
Published: May 2005

The solid state morphology of chlorinated polyethylene (CPE)‐modified poly(vinyl chloride) (PVC) and the relationship of blend structure to impact strength and mode of fracture have been investigated. Selective staining of the CPE phase showed that the morphology of the two phase system changes with increasing CPE content from a dispersion of discrete CPE particles to a network structure enveloping the primary PVC particles. The network formation coincides with a transition from brittle to ductile impact fracture. When the blend was mixed for too long a time or above the fusion temperature of the primary PVC particles, the CPE network was destroyed. The resulting indistinct domain structure is associated with a reduction in the impact properties.
Analysis of the evolution of microcreep during physical aging and mechanical deformation in poly(methyl methacrylate) using a microstructural model
Authors: Shankar N. Gowri , Bertin Y. A. , Gacougnolle J. L.
Published: May 2005

The evolution of poly(methyl methacrylate) (PMMA) during physical aging at 90°C is followed by torsional microcreep tests. On the aged specimen a longitudinal stress is applied which induces a strain of 5 percent after 30 days of creep. The torsional microcreep tests are performed during the longitudinal creep in order to compare the structure evolution of PMMA caused by straining with its evolution measured during aging. The microcreep, for the first 800s, follows a reversible logarithmic law. In this stage the mobile defects achieve their activated form which is perfectly reversible when unloaded. The physical aging reduces this logarithmic part of microcreep. This is due to the decrease of either the number or the volume of the mobile defects. Beyond a critical elongation ϵ = 1 percent, the longitudinal straining has just the opposite influence, i.e., the logarithmic part of microcreep increases. This critical elongation ϵ = 1 percent corresponds to the beginning of the steady state longitudinal creep. The transient that precedes this steady state has no detectable influence on the structure of the specimen.
Deformation behavior of plasticized poly(vinyl chloride) membranes with barium content
Authors: Abu‐Samra M. A. , Ahmad M. S. , Zihlif A. M.
Published: May 2005

Barium complexes were embedded in plasticized poly(vinyl chloride) (PVC) membranes. Effects of these metallic complexes were followed as a function temperature and strain rate. It was found that both the elastic modulus and yield stress decrease with barium content. This behavior is attributed to a lack of uniform structure and the existence of irregularities and voids in the bulk membranes. Another factor which may reduce the tensile strength is te internal and interfacial residual stresses developed at the metal‐matrix interface. These internal stresses and the structural nonuniformity influence the electrical conduction mechanism and performance of the PVC matrix ion‐selective electrodes during aging. Also, it was observed that the yield stress of these membranes has a strain rate and temperature dependence.
Temperature measurements of polymer melts in the heating barrel during injection molding. Part 3: Effects of screw geometry
Authors: Amano Osamu , Utsugi Shirou
Published: May 2005

We have developed a new method to measure the true temperature of the polymer melt and its three‐dimensional distribution of a shot stored in the reservoir during injection. By means of this method, it is demonstrated that the temperature distribution of the polymer melt stored in the reservoir is strongly dependent on the setup molding conditions, the polymer investigated, and the geometry of the screw used. Further, it is noted qualitatively that there are two major effects of screw geometry on the temperature distribution of polymer melts. One, which governs strongly the temperature in the high temperature zone, is shear heat generated within the polymer itself in the metering zone of the screw during the transporting process. The second is the ability to preheat and plasticate the polymer in the compression zone, which is indispensable for uniform plastication.
Theoretical model for flow of polymer melts in the screw channel
Authors: Steller Ryszard T.
Published: May 2005

Isothermal and nonisothermal flows of polymer melts in a screw channel are discussed. An exact solution for the isothermal flow of a power law fluid in a rectangular channel including both longitudinal and transverse velocity components is presented. A method to describe the effects of flights and curvature on flow behavior is proposed. The results are extended to deal with various nonisothermal flow conditions. The proposed theory has been numerically verified.
Design of a composite polymer plant using a simulation system
Authors: Lin Linda , Sommerfeld Jude T. , McKendry Margaret L.
Published: May 2005

This paper describes the use of the General Purpose Simulation System (GPSS) to simulate the manufacture of a typical line of thermotropic liquid crystal polymer resins. Specifically considered were composite polymers based on parahydroxybenzoic acid with glass, graphite, or talc added as a filler or reinforcing agent. The process examined consists of a combination of batch and semicontinuous operations. Product campaigning and equipment cleaning requirements were also incorporated into the GPSS model. Different equipment configurations and manpower distributions were simulated to aid in the design of such a polymer plant. The simulation results were analyzed, and the calculated return on investment was used to select the final plant design.
On the synthesis of poly(ε‐caprolactam)—poly(butadiene‐co‐acrylonitrile) block copolymers for the reaction injection molding process
Authors: Stehlíček Jaroslav , Lednický Frantiček , Baldrian Josef , Šebenda Jan , Neuhäusl Emil
Published: May 2005

The liquid rubbers Hycar ATBN and HTBN were used in the preparation of poly(ε‐caprolactam)—poly(butadiene‐co‐acrylonitrile) block copolymers intended for reaction injection molding by the anionic polymerization of ε‐caprolactam. The conversion of Hycar end groups to polymerization growth centers and the conditions of polymerization influence the crystallization, morphology, and mechanical properties of the product through its molecular structure. The contribution of individual reactions to this molecular structure is discussed.
Laser interferometry: A measurement technique for diffusion studies in thin polymer films
Authors: Saenger K. L. , Tong H. M.
Published: May 2005

Laser interferometric techniques have many applications in the area of thin film science and technology due to their sensitivity, simplicity, and low cost. Typically, changes in thickness and/or refractive index of a transparent polymer film sample are detected from changes in film reflectivity, as measured by variations in the intensity of reflected laser light. Diffusion related properties such as solvent uptake/swelling, dissolution, and drying rates are accessible with laser interferometry since each of these processes involves a change in the film's thickness and/or refractive index. The principles and basic experimental considerations common to these three applications will be discussed. Illustrative examples from our lab will include n‐methyl‐2‐pyrrolidone diffusion in polyimide, and methanol diffusion in poly(methyl methacrylate).
Dynamic melt rheology. I: Re‐examining dynamic viscosity in relationship to the steady shear flow viscosity
Authors: Khanna Y. P.
Published: May 2005

Since 1950's, theoretical as well as experimental efforts have been made to explain the similarity between the shear rate dependence of the steady flow apparent viscosity and the frequency dependence of the dynamic viscosity. The literature points out agreements, as well as occasional disagreements, between the two viscosity terms, depending on the polymer system. In this manuscript, some critical results are presented which suggest that the strain rate dependence of the two viscosities, has entirely different origins and that it is only a coincidence that these data happen to be closer for the common polymers. A time‐temperature dependence of viscoelastic parameters is brought into the discussion to argue the observed pseudo‐plasticity in dynamic melt rheology and to demonstrate, in principle, that the strain rate dependence of the dynamic and steady flow viscosities should be different. Nevertheless, we must mention that the dynamic and steady flow measurements have their own merits and these techniques can complement each other very well.
Electrically conductive adhesives: Effect of particle composition and size distribution
Authors: Lyons Alan M.
Published: May 2005

The effects of particle composition and size distribution on the electrical properties of conductive adhesives were studied. Silver‐plated glass and silver‐plated nickel particles with both narrow (37‐44 μm) and broad (< 44 μm) size distributions were dispersed in an epoxy matrix. In all cases, formulations incorporating narrow particle size distributions required greater concentrations of particles to exceed the percolation threshold for electrical conduction than when broad particle distributions were used. Differences between glass and nickel particles were observed and attributed to the higher density of nickel particles, as well as subtle variations in particle size distributions.
Structure development during flow of polyblends containing liquid crystalline polymers
Authors: Beery D. , Kenig S. , Siegmann A.
Published: May 2005

The microstructure development during capillary flow of polyblends containing Liquid Crystalline Polymers (LCPs) was studied. In the present investigation the wholly aromatic LCP constituent was the minor phase suspended in polycarbonate (PC), poly(butyleneterephthalate) (PBT) or Nylon 6 (N‐6), in addition to previously studied amorphous nylon matrix Experimental results showed that the viscous forces acting at the components' interface are predominating the elongational deformation and the resulting structure development of the LCP phase. In cases where the viscosity of the suspending matrix was higher than the LCP one (PC, amorphous nylon) scanning electron micrographs indicated that fibrillar structure developed. In cases where the viscosity of the matrix polymers was lower than the LCP suspended phase, fibrous structures developed only at very high shear rates. Due to velocity rearrangement effects at the capillary exit a skin core morphology was observed. Since the polymers viscosity depends both on shear rate and temperature, the in situ composite structure development depends on the specific processing methods and conditions that the LCP containing polyblends experience.
Methods of describing oxidation reactions in fractal spaces
Authors: Kozlov GV , Afaunova ZI , Zaikov GE
Published: May 2005

Three methods for describing kinetic curves of oxygen consumption using the scaling approach and fractal analysis are offered. These models are used for the description of the polymer melt structure. All three methods account for the nonuniformity of this structure, which is characteristic for a fractal object, and give the correct description of kinetic curves of the autodecelerated type. Copyright © 2005 Society of Chemical Industry
Chemical and Morphological Characterization of Ultra‐Thin Fluorocarbon Plasma‐Polymer Deposition on 316 Stainless Steel Substrates: A First Step Toward the Improvement of the Long‐Term Safety of Coated‐Stents
Authors: Haïdopoulos Marie , Turgeon Stéphane , Laroche Gaétan , Mantovani Diego
Published: May 2005

Summary: Metallic intravascular stents are medical devices used to scaffold a biological lumen, most often diseased arteries, after balloon angioplasty. They are commonly made of 316L stainless steel or Nitinol, two alloys containing nickel and chromium, which are classified as potentially toxic and carcinogenic by the International Agency for Research on Cancer. Their long‐term safety is therefore controversial, since the corrosion processes may lead to the release of several metallic compounds potentially toxic. Therefore, the strategy behind this work was to develop a process aiming the complete isolation of the devices from the body fluids by a thin, cohesive and strongly adherent coating of a plasma‐polymerized fluoropolymer. Ultra thin fluorocarbon films were deposited on pre‐treated stainless steel surfaces by radio frequency glow discharge plasma. Chemical composition, structure, hydrophobicity and morphology of the plasma‐polymer films were investigated by X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, water contact angle measurements and atomic force microscopy. Results show that the films were partially hydrogenated, amorphous, highly hydrophobic, smooth and pinhole‐free. Deposition on as‐received substrates however leads to partially hydrogenated, porous fluorocarbon coatings that consisted of heterogeneously distributed nanospherical particles. Thus, careful pre‐treatment prior to deposition proved essential, as demonstrated by its strong influence on the chemical composition of the interface, as well as the chemical structure and the morphology of the plasma‐polymer films. Finally, plasma‐polymer films were validated with respect to impermeability in a medium reproducing the physiological conditions that prevail in coronary arteries.

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Nanoporous Organosilicate Glass Films via Chemical Vapor Deposition onto Colloidal Crystal Templates
Authors: Wu Qingguo , Ross April D. , Gleason Karen K.
Published: May 2005

Summary: Templated nanoporous organosilicate glass (OSG) films with extremely low dielectric constants and refractive indeces, as low as 1.4 and 1.067 respectively, were fabricated via chemical vapor deposition. Well‐ordered assemblies of polymer nanospheres serve as templates for the pores. To enable three‐dimensional crystal templates to form on substrate areas larger than 10 cm2, a method using rapid evaporation‐induced self‐assembly of polystyrene (PS) nanospheres was developed. Conformal plasma‐enhanced CVD using dimethylsilane and oxygen precursors fills the interstices of the colloidal crystal to form the OSG matrix. With subsequent annealing at 500 °C the labile polymer beads decompose, resulting in a nanoporous organosilicate thin film.

TEM image of nanoporous OSG film using the 15 nm bead template.

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TEM image of nanoporous OSG film using the 15 nm bead template.
Particle Characterization, Present State and possible Future Trends
Authors: Leschonski Kurt
Published: May 2005

The investigations of single and combined properties of particles or of particulate matter still belongs to the most important areas of present research and practical applications of Particle Characterization. Methods to measure single particle properties, as for instance particle size, shape, composition and velocity, are of much higher sophistication than before and they still aim at improved accuracy and higher resolution. There still is a considerable lack of understanding, and lack of theoretical interpretation and of experimental evidence of the differences seen in the correlation of different equivalent diameters, obtained when analysing the same irregularly shaped particle, or a distribution of particles, using different physical principles. Furthermore, there still is a lack of understanding of the influence of shape on the results obtained with optical methods using diffraction, light scattering etc., thus asking for more information with respect to the transferability of results from one physical principle to another. The measurement of combined particle properties comprises the simultaneous measurement of, for instance, size, velocity and concentration, which is of particular importance in the comprehensive description of multiphase flow systems. Those instruments which are in working order are highly complicated, not easy to use and to handle and they are in most cases special adaptations for a limited range of the variables to be analysed. There is also growing interest in the evaluation of socalled property functions. Particle Characterization will remain for quite a number of years just as exciting as it has been in the past. If industrial demand enforces the use of on‐line instrumentation it might even become more interesting.
Applications of Condition Numbers A‐priori Analysis of Moment Method for Describing Size Distributions
Authors: Gentry James W. , Calabrese Richard V.
Published: May 2005

A procedure for estimating the effectiveness of algorithms which retrieve size distribution parameters from cumulative fractions or moments is described. The principle of the algorithm is to select moments, or cumulative fractions, which minimize the condition number. Extensive tests of the algorithm for a distribution consisting of the sum of two log normal distributions were carried out. This procedure can be easily extended to use different numbers and types of constituent functions. The simulations indicated that moment methods which include positive and negative moments give the best result. When the means of the constituent distribution are close, the large condition numbers indicate that no algorithm will give unambiguous values for the parameters.
Triboelectric Charging of Polymer Particles by Impact
Authors: Yamamoto Hideo , Scarlett Brian
Published: May 2005

This paper describes an experimental investigation of the charge acquired by a single polymer particle when striking a plate. The particle was projected from a pneumatic gun with variable velocity and angle of impact. The deflected particle was then captured in a Faraday cup and the net acquired charge so measured. The measurements of charge are related, particularly, to the initial potential of the surfaces and to their work functions.
Estimation of Particle Size Distributions Using Pipet‐Withdrawal Centrifuges
Authors: Dumm Timothy F. , Hogg Richard
Published: May 2005

The mathematical treatments used in the evaluation of particle size distribution from pipet‐withdrawal centrifuge data are reviewed. An error in the published procedure for multiple‐sample withdrawal systems is pointed out and a corrected formulation is presented. An alternative treatment, based on a piece‐wise linearization of the size distribution is described. Computer simulations of the analytical and data evaluation procedures indicate that the errors in the original formulation are not generally serious and that the corrected and alternative procedures lead to very similar estimates. Except for some cases involving very narrow size distributions, the alternative approach appears to give slightly closer estimates of the size distribution. Comparisons based on actual experimental data are also described.
Observations during Reactions and Melting of Freely Suspended Solid Particles
Authors: Straubel Harald , Straubel Edith
Published: May 2005

With the three‐plate‐capacitor method, as described previously by the author, reactions and heating processes in freely suspended particles (diameter 5‐50 μm) were investigated by using the diffraction pattern of a laser beam. Change of weight can be registered, during operation, by the a. c. and d. c. voltage connected to a capacitor. This device enables information to be obtained, from inside the droplets, on the gradient of density or the precipitation of small particles and on the formation and solution process of a crystal nucleus in anorganic and low molecular organic substances. The behaviour of high polymer materials was studied during heating in the central region ca. 4 μm of the droplet.

The diffraction patterns are similar to those of crystals (micells), but they do not show any crystal nucleus in the center. The application of heat, up to the softening point, gradually diffuses this cell arrangement. Such phenomena have not previously been studied within a droplet.
Explosive desensitization studies via chemical group modification. Nitroso‐Derivatives of RDX and 3‐Amino‐TNT
Authors: Iyer S.
Published: May 2005

With aims toward desensitizing RDX and TNT via molecular modification, mono‐ and trinitroso‐derivatives of RDX and 3‐amino‐TNT were synthesized and subjected to sensitivity tests. Impact and shock sensitivity data show these compounds to be markedly desensitized. Explosive yield measurements indicate that the changes in power output due to these molecular modifications are minor.
A contribution to the Study of Decomposition and Combustion of HMX. influence of some additives
Authors: Cohen‐Nir E. , Sannier H.
Published: May 2005

The work presented is an initial step in the attempt to obtain higher burning rates with nitramine‐based propellants. We have studied the influence of some boron and sodium compounds on the decomposition mechanism and on the burning rate of HMX. Results indicate that additives such as hydrazine monoborane, sodium boron hydride and methylamine monoborane lead to a significant increase of the decomposition heat of HMX and reduce as well as the activation energy and the temperature of maximum decomposition rate.

Experimental results about rb(p) and rb(To) laws of HMX and HMX/additive mixtures are presented. Quantitative investigations show that the burning rate of HMX can be increased by approximately a factor of 3 by addition of 10% boron compounds. Moreover, the pressure exponent is reduced from 0.9 to 0.6.
Some physicochemical problems of extraction of explosives from ammunition
Authors: Kondrikov Boris N.
Published: May 2005

Heat exchange peculiarities, burning heat instability phenomena, and the possible ways of initiation of a charge of explosive at dismantlement of ammunition are considered as the physico chemical ground for elaboration of the dismantlement methods of the higher productivity and safety. Melting of the explosive, contact and non‐contact mechanical technologies, unscrewing, cutting, milling, and turning of the ammunition are studied in outline from the point of view of the considered physicochemical processes importance, and some proposals concerning augmentation of safety and productivity of the dismantlement methods are formulated.
Modelling of the Shaped Charge Jet Break‐Up
Authors: Hennequin E.
Published: May 2005

A new model for shaped charge jet break‐up was devised. For this purpose, the fragments of a shaped charge jet were analyzed and their characteristics compared against the ones predicted by the break‐up proposed by Pfeffer, Hirsch, Chou und Haugstad. As the predictions provided by these models are not fully satisfactory, the break‐up process was analyzed in order to develop a new break‐up model which provides a better estimation of the break‐up time and the accumulated length of the jet. This model makes use of one parameter, the fragment shape index, which can be determined ex‐ perimentally. This parameter characterizes the type of jet break‐up (ductile or brittle) and is hence indicative of the jet quality.
Rheology of HTPB Propellant: Development of generalized correlation and evaluation of pot life
Authors: Muthiah Rm. , Krishnamurthy V. N. , Gupta B. R.
Published: May 2005

Composite solid propellants based on hydroxy‐terminated polybutadiene (HTPB) have become the workhorse propellants in the present‐day solid rocket motors world‐wide. Because of the high solid loading, the rheological behavior of such propellants is quite complex. The effect of solid loading, oxidizer particle size and aluminium content has been studied and reported. Similarly, the effect of temperature and mixer kinematics and mixing cycle time have also been studied and reported. In the present paper a generalized correlation has been developed for shear stress‐shear rate based on the rheological parameters like yield stress, consistency index and pseudoplasticity index which are in turn functions of solid volume fraction, cure time, t, and temperature, and has a correlation coefficient of 0.94 with the experimental values. Also a commonly used term in propellant industries, pot life, has been defined and evaluated for the HTPB propellant system.
Estimation of Aluminium in HTPB Based Composite Solid Propellants by hydrogen evolution method
Authors: Ajaz Aslam G.
Published: May 2005

Hydrogen gas evolution method has been applied to determine the percentage of aluminium (Al) in hydroxy‐terminated polybutadiene (HTPB) based composite solid propellants premix/pastes. The determination is not effected by the presence of Zn, Fe, Cu or small amounts of silicon but magnesium has been found to interfere in the analysis. The results are obtained with remarkable accuracy and reproducibility.
Thermoanalytical Investigations on the Effect of Atmospheric Oxygen on HTPB resin
Authors: Ninan K. N. , Krishnan K. , Rajeev R. , Viswanathan G.
Published: May 2005

TG‐DSC studies, carried out on hydroxy‐terminated polybutadiene (HTPB) in air and nitrogen atmospheres show three transitions which give rise to (1) an exothermic DSC peak and mass gain in TG at 170°C–240°C, seen only in air (2) exothermic peak and low mass loss, both in air and nitrogen, due to depolymerization, cyclization and cross linking, and (3) final mass loss corresponding to pyrolysis in nitrogen and combustion in air, appearing respectively as an endothermic peak and as a sharp exothermic peak in the two atmospheres. The FTIR spectrum of the product isolated from TG after the mass gain step shows addition of oxygen to the butadiene back bone. Arrhenius activation parameters (E and A) were computed for the exothermic oxygen addition reaction. The Ozawa method refined by MKN two‐term approximation for p(x) function gave results quite comparable to those from Kissinger method.
BKWC: An Empirical BKW Parametrization Based on Cylinder Test data
Authors: Fried Laurence E. , Clark Souers P.
Published: May 2005

A database containing mostly cylinder test data for 42 explosives composed of C, N, O, H, F, and Cl was collected. The resulting detonation velocities, C‐J pressure, adiabat energies, and total energies of detonation were used to reparametrize the BKW equation of state for the CHEETAH thermochemical code. The resulting parameter set, referred to as BKWC, reproduces detonation velocities and adiabat energies better than previous BKW parametrizations. The BKWR equation of state is found to be slightly better in yielding C‐J pressures.
Synthetic peptides corresponding to sequences of snake venom neurotoxins and rabies virus glycoprotein bind to the nicotinic acetylcholine receptor
Authors: Lentz Thomas L. , Hawrot Edward , Wilson Paul T.
Published: May 2005

Peptides corresponding to portions of loop 2 of snake venom curare‐mimetic neurotoxins and to a structually similar region of rabies virus glycoprotein were synthesized. Interaction of these peptides with purified Torpedo electric organ acetylcholine receptor was tested by measuring their ability to block the binding of 125I‐labeled α‐bungarotoxin to the receptor. In addition, inhibition of α‐bungarotoxin binding to a 32‐residue synthetic peptide corresponding to positions 173–204 of the α‐subunit was determined. Neurotoxin and glycoprotein peptides corresponding to toxin loop 2 inhibited labeled toxin binding to the receptor with IC50 values comparable to those of nicotine and the competitive antagonist d‐tubocurarine and to the α‐subunit peptides with apparent affinities between those of d‐tubocurarine and α‐cobratoxin. Substitution of neurotoxin residue Arg37, the proposed counterpart of the quatenary ammonium of acetylcholine, with a negatively charged Glu residue reduced the apparent affinity about 10‐fold. Peptides containg the neutotoxin invarint residue Trp29 had 10‐ to 100‐fold higher affinites than peptides lacking this residue. These results demonstrate that relatively short synthetic peptides retain some of binding ability of the native protein from which they are derived, indicating that such peptides are useful in the study of proetin interactions. The ability of the peptides to compete α‐bungarotoxin binding to the receptor with apparent affinites comparable to those of other cholinergic ligands indicates that loop 2 of the neurotoxins and the strucually similar segment of the rabies virus glycoprotein act as recognition sites for the acetylcholine receptor. Invarient toxin residues Arg37 and Trp29 and their viral homologs play important, although not essential, roles in binding, possibly by interaction with complementary anionic and hydrophobic subsites on the acetylcholine receptor. The α‐subunit peptide most likely contains all of the determinants for binding of the toxin and glycoprotein peptides present on the α‐subunit, because these peptides bind to the 32‐residue α‐subunit peptides with the same or greater affinity as to the intact subunit.
Calibration of effective van der Waals atomic contact radii for proteins and peptides
Authors: Iijima Hiroshi , Dunbar James B. , Marshall Garland R.
Published: May 2005

Effective van der Waals radii were celebrated in such a way that molecular models built from standard bond lengths and bond angels reproduced the amino acid conformations observed by crystallography in proteins and peptides. The celebrations were based on the comparision of the Ramachandbran plots prepared from high‐resolution X‐ray data of protins and peptides with the allowed ϕ,ψ torsional angel space for the depeptide molecular models. The celebrated radii are useful as criteria with which to filter energetically improbable conformations in molecular modeling studies of proteins and peptides.
Crystal structure of subtilisin BPN′ variants containing disulfide bonds and cavities: Concerted structural rearrangements induced by mutagenesis
Authors: Katz Bradley , Kossiakoff Anthony A.
Published: May 2005

The X‐ray structure of four genetically engineered disulfide variants of subtilisin have been analyzed to determine the energetic and structural constraints involved in inserting disulfide bonds into proteins. Each of the engineered disulfides exhibited atypical sets of dihedral angles compared with known structures of natural disulfide bridges in proteins and affected its local structural environment to a different extent. The disulfides located in buried regions, Cys26–Cys232 and Cys29–Cys87 and Cys22–Cys87, which are located on the surface of the molecule. An analysis of the concerted changes in secondary structure units such as α‐helices and β‐sheets indicated systematic long‐range effects. The observed changes in the mutants were largely distributed asymmetrically around the inserted disulfides, reflecting different degrees of inherent flexibility of neighboring secondary structure types. The disulfide substitution in each variant molecule created some invaginations or cavities, causing a reorganization of the surrounding water structure. These changes are described, as well as the changes in side chain positions of groups that border the cavities.
Analysis of solvent structure in proteins using neutron D2OH2O solvent maps: Pattern of primary and secondary hydration of trypsin
Authors: Kossiakoff Anthony A. , Sintchak Michael D. , Shpungin Joseph , Presta Leonard G.
Published: May 2005

A method of determining the water structure in protein crystals is described using neutron solvent difference maps. These maps are obtained by comparing the changes in diffracted intensities between two data sets, one in which H2O is the major solvent constituent, and a second in which D2O is the solvent medium. To a good first approximation, the protein atom contributions to the scattering intensities in both data sets are equal and cancel, but since H2O and D2O have very different neutron‐scattering properties, their differences are accentuated to reveal an accurate representation of the solvent structure. The method also employs a series of density modification steps that impose known physical constraints on the density distribution function in the unit cell by making real space modifications directly to the density maps. Important attributes of the method are that (1) it is less subjective in the assignment of water positions than X‐ray analysis; (2) there is threefold improvement in the signal‐to‐noise ratio for the solvent density; and (3) the iterative density modification produces a low‐biased representation of the solvent density. Tests showed that water molecules with as low as 10% occupancy could be confidently assigned.

About 300 water sites were assigned for trypsin from the refined solvent density; 140 of these sites were defined in the maps as discrete peaks, while the remaining were found within less‐ordered channels of density. There is a very good correspondence between the sites in the primary hydration layer and waters found in the X‐ray structure. Most water sites are clustered into H‐bonding networks, many of which are found along intermolecular contact zones. The bound water is equally distributed between contacting apolar and polar atoms at the protein interface. A common occurence at hydrophobic surfaces is that apolar atoms are circumvented by one or more waters that are part of a larger water network. When the effects on surface accessibility by neighboring molecules in the crystal lattice are taken into consideration, only about 29% of the surface does not interface ordered water. About 25% of the ordered water is found in the second hydration sphere. In many instances these waters bridge larger clusters of primary layer waters. It is apparent that, in certain regions of the crystal, the organization of ordered water reflects the characteristics of the crystal environment more than those of trypsin's surface alone.
A novel approach to predicting protein structural classes in a (20–1)‐D amino acid composition space
Authors: Chou Kuo‐Chen
Published: May 2005

The development of prediction methods based on statistical theory generally consists of two parts: one is focused on the exploration of new algorithms, and the other on the improvement of a training database. The current study is devoted to improving the prediction of protein structural classes from both of the two aspects. To explore a new algorithm, a method has been developed that makes allowance for taking into account the coupling effect among different amino acid components of a protein by a covariance matrix. To improve the training database, the selection of proteins is carried out so that they have (1) as many non‐homologous structures as possible, and (2) a good quality of structure. Thus, 129 representative proteins are selected. They are classified into 30 α, 30 β, 30 α + β, 30 α/β, and 9 ζ (irregular) proteins according to a new criterion that better reflects the feature of the structural classes concerned. The average accuracy of prediction by the current method for the 4 × 30 regular proteins is 99.2%, and that for 64 independent testing proteins not included in the training database is 95.3%. To further validate its efficiency, a jackknife analysis has been performed for the current method as well as the previous ones, and the results are also much in favor of the current method. To complete the mathematical basis, a theorem is presented and proved in Appendix A that is instructive for understanding the novel method at a deeper level. © 1995 Wiley‐Liss, Inc.