bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrospray mass spectrometry: Ethylene glycol as a solvent and its effects on ion desorption
Authors: Guevremont R. , Le Blanc J. C. Y. , Siu K. W. M.
Published: May 2005

Ethylene glycol solutions of gramicidin S, myoglobin and tetrabutylammonium bromide were analysed by means of electrospray mass spectrometry and their spectra were compared with those of aqueous solutions. The evaporation of water and ethylene glycol droplets, initially at room or elevated temperature, in air at room temperature was modelled. It was found that under conditions where a water droplet's radius would shrink by ∼30%, an ethylene glycol droplet shrinks negligibly. Further, droplets that are initially hot (such as those that are ejected from a heated electrospray needle) cool very rapidly owing to evaporation and heat loss to ambient air, and subsequently evaporate much like droplets that are initially at room temperature. For gramicidin S, the ion abundances in ethylene glycol as solvent were ∼200 times lower than those in water under room temperature operating conditions. In experiments where the spray probe was heated to ∼100°C to reduce the viscosity of ethylene glycol, the gramicidin response difference between the solvents decreased to about a factor of 40. Similar trends were observed for myoglobin and the tetrabutylammonium ion. The gramicidin abundances in ethylene glycol, relative to those in water, are orders of magnitude too large to be accounted for using the conventional solvent evaporation model. It is speculated that decreasing the viscosity increases the velocity of ions drifting in ethylene glycol towards the solution/air interface and increases the total number of analyte ions desorbed at the Taylor cone during electrospray.
Effect of electrospray ionization conditions on low‐energy tandem mass spectra of peptides
Authors: Kilby Greg W. , Sheil Margaret M.
Published: May 2005

The effect of electrospray ionization (ESI) conditions on low‐energy tandem mass spectra of peptides in the relative molecular mass range 400–1200 was examined. For singly charged peptide ions the source skimmer potential (which determines the degree of acceleration of the ions through the intermediate pressure region in the source) can strongly influence the extent of fragmentation observed in tandem mass spectra, especially at low collision energies. For each peptide there is an optimum skimmer potential which represents a balance between generating ions with sufficient internal energy for subsequent tandem mass spectrometric experiments and inducing the onset of other processes such as source fragmentation. The fragmentation which can be achieved in tandem mass spectra with high skimmer potentials differs from ESI source fragmentation for the same peptides. We have found that fragmentation in ESI mass spectra depends both on skimmer potential and on solvent pH, presumably because the latter determines the proportion of doubly charged species generated from a given peptide. Low‐energy tandem mass spectra of peptides following ESI are equally as sensitive to peptide structure and the type of adduct studied (e.g. [M + H]+ vs. [M + NH4]+) as tandem mass spectra obtained following older ionization methods such as fast atom bombardment.
Suppression of metastable interference in matrix‐assisted laser desorption/ionization (MALDI) spectra in a reflecting time‐of‐flight mass spectrometer
Authors: Ens Werner , Spicer Victor , Standing Kenneth G. , Zhou Jie
Published: May 2005

Metastable interference in matrix‐assisted laser desorption/ionization (MALDI) spectra is reduced by modulating the accelerating potential (by <∼100 V) on alternate laser shots. Both parent and daughter ions are reflected on every second shot but only daughter ions are reflected on the next shot. The parent‐ion spectrum is then obtained by subtraction. In order to ensure the necessary well defined energy distributions, signals with similar intensity (preferably small) are selected by transferring each transient to a computer for examination. This procedure decreases the complexity in reflected spectra (especially spectra of mixtures) in the lower mass range and improves the mass resolution in the intermediate mass range around 10 000 u. Continuous background in reflected spectra is also suppressed by the technique.
On‐target deuteration for peptide sequencing by laser mass spectrometry
Authors: Spengler Bernhard , Lützenkirchen Frank , Kaufmann Raimund
Published: May 2005

Hydrogen–deuterium exchange was evaluated as a tool for sequence analysis of peptides by matrix‐assisted laser desorption–ionization utilizing post‐source decay (PSD‐MALDI). The number of exchangeable hydrogens (EH) of precursor ions and product ions can be determined from the mass difference between ion signals originating from the deuterated and the non‐deuterated form of a peptide, resulting in a second dimension of structural information. The reliability of sequence determination by combinatorial algorithms or pattern recognition techniques is considerably increased by employng this ‘EH spectroscopy.’ On‐target deuteration is a simple preparatory step which can be performed reversibly with the already mass‐analysed sample within a few minutes and without consumption of additional sample material. The efficiency of hydrogen–deuterium exchange with this technique is about 98.5%. In addition to supporting sequence analysis, deuteration can be used to investigate fundamental fragmentation mechanisms of peptides in PSD‐MALDI. Inconsistencies with expected fragmentation pathways have been found for fragments a1–a3 of substance P.
Gas‐phase protonation of simple inorganic molecules: A stimulating interplay between theory and experiment
Authors: Grandinetti Felice
Published: May 2005

A brief account of some of the results obtained recently during the investigation of the gas‐phase protonation of some simple inorganic molecules. The combined use of structurally diagnostic mass spectrometric techniques, such as mass‐analyzed ion kinetic energy (MIKE) and collisionally activated dissociation (CAD) spectrometry and ab initio calculations allows the successful probe of the corresponding potential energy surfaces. Information is obtained on the structure and the stability of the various protonated intermediates, as well as on the details of the mechanisms of their interconversion and unimolecular decomposition processes.
Cross‐chiral examinations of molecular enantioselective recognition by fast atom bombardment mass spectrometry: Host–guest complexations between chiral crown ethers and chiral organic ammonium ions
Authors: Sawada Masami , Okumura Yasuo , Yamada Hitoshi , Takai Yoshio , Takahashi Shigetoshi , Kaneda Takahiro , Hirose Keiji , Misumi Soichi
Published: May 2005

Using fast atom bombardment (FAB) mass spectrometry (MS), cross‐chiral relationships were confirmed for the first time for the diasteromeric host‐guest complexations between the chiral crown ether host (1) and the chiral organic ammonium ion guest (2) on the basis of the relative peak intensities (RPI). Both host–guest combinations (R, R, R, R) – 1, (R) – 2 and (S, S, S, S) – 1, (S) – 2 obviously provided larger RPI values than the combination of both (R, R, R, R) – 1, (S) – 2 and (S, S, S, S) – 1, (R) – 2 by a factor of 1.6 as an averaged value: 1.87 (n = 4)/1.16 (n = 4) = 1.6. These results are consistent with the expected stabilities of the host‐guest complexations by CPK model examinations. Successfully observed cross‐chiral examinations strongly suggest a potentially useful FABMS/RPI methodology for rapidly searching newly designed and synthesized crown ether‐like host compounds with a higher degree of enantioselectivity.
Competitive formation of M+˙ and [M + H]+ ions under fast atom bombardment conditions
Authors: Takayama Mitsuo , Tanaka Yoshiaki , Nomura Taro
Published: May 2005

The competitive formation of molecular ions M+˙ and protonated molecules [M + H]+ under fast atom bombardment (FAB) conditions was examined using various kinds of organic compounds. The use of protic/hydrophilic matrices such as thioglycerol and glycerol resulted in relatively large values of the peak intensity ratio I([M + H]+)/I(M+˙) compared with the use of relatively aprotic/hydrophobic matrices such as m‐nitrobenzyl alcohol and o‐nitrophenyl octyl ether. The change of matrix from thiol‐containing such as thioglycerol and dithiothreitol to alcoholic such as glycerol and pentamethylene glycol increased the I([M + H]+)/I(M+˙) ratio. Furthermore, the change of matrix increased the peak intensity ratio of the doubly charged ion [M + 2H]2+ to [M + H]+ in the FAB mass spectra of angiotensin I and gramicidin S. The addition of acids to the matrix solution increased the I([M + H]+)/I(M+˙) ratio, although such an effect did not always occur. The acetylation of simple aniline compounds markedly increased the I([M + H]+)/I(M+˙) ratio. It was concluded from these results that the hydrogen bonding interaction between hydroxyl groups(s) of the matrix and basic site(s) of analyte molecules in solution acts advantageously as a quasi‐preformed state for [M + H]+ formation, and that the presence of significant proton acceptor(s) such as carbonyl group in analytes hinder the M+˙ formation which may generally occur under FAB conditions. The formation of M+˙ and [M + H]+ ions seemed to occur competitively, reflecting or according to the interaction or solvation states between the analyte and matrix molecules in solution and the structural characteristics of the analytes.
Computer processing and interpretation of mass spectral information. Part IX—generalized characteristics of mass spectra
Authors: Sukharev Yu. N. , Nekrasov Yu. S. , Molgachova N. S. , Tepfer E. E.
Published: May 2005

The formation of numerical generalized characteristics (indices) of mass spectra by using one or two experimental parameters (mass numbers and/or ion peak amplitudes) is suggested. The influence of the measuring error of peak amplitudes on the statistical characteristics of indices was studied. It was ascertained by four classes of organometallic compounds that within an isolated class the value of each index is distributed by a normal law. The possibility of using mass spectral indices for the identification of unknown compounds is demonstrated.
Radical‐type reactivity of the methylenedimethylsulfonium ion, (CH3)2S+CH2˙
Authors: Smith Rebecca L. , Chyall Leonard J. , Stirk Krista M. , Kenttämaa Hilkka I.
Published: May 2005

Ab initio molecular orbital calculations at the MP2/6–31G*//6–31G* + ZPVE level of theory suggest that the ion (CH3)2S+CH2˙ is 75 kJ mol−1 higher in energy than ionized ethyl methyl sulfide. However, this distonic ion is stable toward isomerization to the conventional structure: the two ions show distinctly different reactivity in a dual‐cell Fourier transform ion cyclotron resonance mass spectrometer. Molecular orbital calculations further indicate that the charge site of the ion is on the sulfur atom whereas the odd‐spin density is localized on the CH2 group. The chemical properties of the ion reflect this description. The coordinatively saturated sulfonium charge site is chemically inert. This radical cation possesses unique chemical reactivity in that its reactions are associated with the radical site. Most of these reactions involve a homolytic bond cleavage in the neutral molecule, resulting in abstraction of an atom or a radical by the ion. The reaction efficiency correlates with the homolytic bond dissociation energy of the bond being broken in the neutral molecule, suggesting a simple radical abstraction mechanism for these reactions. Hence, the methylenedimethylsulfonium ion is best described as on electrophilic radical with an inert charge site.
Reactive ion–surface collisions: Application of ionized acetone‐d6, DMSO‐d6 and pyridine‐d5 as probes for the characterization of self‐assembled monolayer films on gold
Authors: Kane Thomas E. , Somogyi Árpád , Wysocki Vicki H.
Published: May 2005

Low‐energy collisions of ionized acetone‐d6, DMSO‐d6 and pyridine‐d5 with alkanethiolate self‐assembled monolayer (SAM) surfaces prepared on gold were investigated. These experiments can be used to monitor routinely the condition of the surfaces and to determine whether a surface is acceptable for a given application. In addition to the surface‐induced dissociation of the molecular ions, intense peaks corresponding to the addition of H (or D) to the ionized molecules are observed in the ion–surface collision spectra. The relative abundance of the [M + H(D)]+ reaction products was found to be dependent on several variables, including (i) the chemical composition of the monolayers (alkanethiolate, perdeuteroalkanethiolate, fluorinated alkanethiolate), (ii) the chain length of the alkanethiolate monolayers, (iii) the time for which the vapor‐deposited Au surfaces are exposed to the thiol solution during surface preparation and (iv) the degree of deliberate damage of the SAM film (70 eV Ar+˙ beam bombardment). The variation in [M + H(D)]+ abundance with induced surface changes illustrates the utility of these adduct ions for the characterization of the quality of the monolayers. The general trend observed is an increase in the [M + H]+ peak with the increased presence of hydrocarbon adsorbates, which in turn is believed to be directly related to increased disorder (inherent or induced) of the monolayer film. The increase in [M + H]+ is seen with a decrease in chain length, with shorter monolayer preparation times, and with an increase in surface damage. In general, a fluorinated surface that has been intentionally damaged by an Ar+˙ beam retains its highenergy deposition characteristics and is appropriate for use as a collision target for many types of projectiles.
Collision‐induced dissociation studies of protonated alcohol and alcohol—water clusters by atmospheric pressure ionization tandem mass spectrometry. 1Methanol
Authors: Karpas Z. , Eiceman G. A. , Harden C. S. , Ewing R. G. , Smith P. B. W.
Published: May 2005

Cluster size distribution and collision‐induced dissociation (CID) studies of protonated methanol and protonated methanol—water clusters yield information on the structure and energetics of such ions. Ions were formed at atmospheric pressure in a corona discharge source, and were subjected to CID in the center quadrupole of a triple quadrupole mass spectrometer. Cluster ions containing up to 13 molecules of methanol and/or water were observed and examined using CID experiments. The CID of all (CH3OH)n · H2O · H+ clusters, where n ⩽ 8, showed that water loss was statistically favored over methanol loss and that the preferred dissociation channel involved loss of water with methanol molecules. These results support a model employing a chain of hydrogen‐bonded solvent molecules rather than one in which fused rings of ligands surround a central hydronium ion. However, CID of larger clusters, where n ⩾ 9, showed that loss of one methanol was equal to or less than loss of water, reflecting a change in structure.
A new window on fullerene chemistry: An electrospray mass spectrometric study of the amination of C60
Authors: Wilson Stephen R. , Wu Yunhui
Published: May 2005

Polyamines derived from C60 were characterized by electrospray ionization mass spectrometry in 1:1 methanoltoluene containing 2.5% trifluoroacetic acid. Peak assignments are consistent with the formula C60On(RNH2)m for the protonated products. The preferential formation of the hexaaminated product C60O6(RNH2)6 was also observed.
Significant differences in site of protonation and extent of fragmentations in chemical ionization and fast atom bombardment mass spectrometry of simple bifunctional compounds. A mechanistic implication for formation of protonated molecules
Authors: Nakata Hisao , Arakawa Naofumi , Mizuno Rika
Published: May 2005

Chemical ionization (CI) and fast atom bombardment (FAB) mass spectra of simple bifunctional aromatic compounds were compared. Some significant differences were revealed with respect to the site of protonation and extent of fragmentations. Unlike conventional CI ionization, the protonated molecule formation by FAB could not be accounted for by ordinary proton transfer reactions in the gas phase. The observed ions under FAB conditions appear to be regulated by proton exchange reactions through frequent collisions in some particular region between the matrix and the gas phase.
Multiply charged ions of ruthenium(II), rhodium(III) and cobalt(III) complexes in electrospray ionization mass spectrometry
Authors: Arakawa Ryuichi , Matsuo Takekiyo , Ito Hiroyuki , Katakuse Itsuo , Nozaki Koichi , Ohno Takeshi , Haga Masa‐Aki
Published: May 2005

Multiply charged ions from electrospray ionization (ESI) were observed for ruthenium‐bidentate ligand complexes, such as [RuL2B]X2 and [(RuL2)2B]X4, where L is 2,2′‐bipyridine, B are tetradentate ligands of 2,2′‐bis(2′‐pyridyl)bibenzimidazole and 2,6‐bis(2′‐pyridyl)benzodiimidazole, bidentate ligand of 2‐(2′‐pyridyl)benzimidazole and related compounds and X is CIO4‐ or CI‐. ESI mass spectra showed a simple mass pattern for easy structural assignment and detecting impurities. The mass spectra for binuclear complexes provide a charge state distribution ranging from 4+ to 2+ for Ru(II)—Ru(II) compounds and 5+ to 2+ for Ru(II)—Rh(III) compounds. It was found that different multiply charged ions are generated by loss of counterions and by protonation/deprotonation at the proton site of ligands B. The abundances of these ions are qualitatively explained in terms of the acidity of metal complexes depending on the bridging ligand structures and the charge of the metal ions. Ions produced by removal of ligands were hardly observed.
Dimethyl ether and dimethyl‐d6 ether chemical ionization mass spectrometry of nitramines, nitroaromatics and related compounds
Authors: Burrows Elizabeth P.
Published: May 2005

Dimethyl ether (DME) chemical ionization mass spectrometry with introduction by direct exposure desorption was utilized for the characterization of a variety of nitramines, nitroaromatics and related compounds. For the nitramines and for many of the nitroaromatics the most abundant ions were fragment‐molecule adduct ions resulting from ion‐molecule reactions with the reagent gas. Nitroaromatic positional isomers were readily distinguished by large differences in the abundances of the various adduct ions. For the nitramines, collision‐induced dissociations of the prominent methoxymethylene adduct ions were studied and contrasted with those of the corresponding adducts derived from DME‐d6 as reagent gas.
Structural analysis of rapamycin and related compounds using [M + Li]+ ions generated by liquid secondary ion mass spectrometry
Authors: Kiplinger J. P. , Guadliana M. A.
Published: May 2005

Cationization of the macrocyclic immunosuppressant rapamycin with lithium ion upon liquid secondary ion mass spectrometric ionization yields a number of fragment ions, which are observable in the full‐scan spectrum. These are clearly assigned using B/E linked scanning (fragment ion scanning), B2/E linked scanning (precursor ion scanning) and peak matching for accurate mass measurement. Many of the fragments are produced by processes that open the macrocyclic ring, and it is possible to observe several different pieces of the molecule as fragment ions. The diversity of fragments produced facilitates the elucidation of new rapamycin‐like structures through mass spectrometry. Three structurally modified rapamycin analogues have been examined by this technique, and the modifications to the molecule may be located based on the nominal masses of their fragments.
The potential of pyrolysis/gas chromatography/mass spectrometry for determining the progress of lignification: An investigation of maturing asparagus sclerenchyma tissue
Authors: Mellon Fred. A. , Waldron Keith W. , Selvendran Robbie R. , Galletti Guido C.
Published: May 2005

Sclerenchyma tissues from semi‐mature and mature asparagus spears were analysed by pyrolysis/gas chromatography/mass spectrometry and by conventional chemical methods in order to determine the degree of lignification and compare analytical techniques. The pyrolysis data are similar to those obtained by a chemical method involving alkaline extraction at 70°C followed by spectrophotometric determination of phenolic content. The pyrolysis method was more rapid, sensitive and informative than the chemical technique and shows considerable potential for studying the chemical basis of the textural development of plant foods.
Pyrolysis/gas chromatography/mass spectrometry of asphaltene fractions
Authors: Nali M. , Calemma V. , Montanari L.
Published: May 2005

Two n‐heptane‐precipitated asphaltene samples, characterized by elemental analysis and nuclear magnetic resonance spectrometry, were fractionated according to relative molecular size by gel permeation chromatography (GPC). Both the whole asphaltene samples and their fractions were analysed by pyrolysis/gas chromatography/mass spectrometry. The data obtained from the pyrograms (average side‐chain length, aromaticity index, sulphur compounds vs. aliphatic compounds, presence of SO2 and CO2) demonstrated that, in the case of asphaltenes, GPC fractionation results in the separation of different chemical structures ranging from lower molecular mass, highly aromatic and polar compounds to higher molecular mass, less polar and aromatic compounds.
Fast atom bombardment mass spectrometry of reaction products between C3O2 and stabilized phosphorus ylides
Authors: Seraglia Roberta , Traldi Pietro , Bertani Roberta , Facchin Giacomo , Pandolfo Luciano
Published: May 2005

A fast atom bombardment (FAB) mass spectrometric study on the open‐chain compound 1,3‐bis(cyanomethylenetriphenylphosphorane)propane‐1,3‐dione and on the cyclic zwitterionic compounds 4‐oxy‐5‐triphenylphosphonium‐6‐methyl‐2‐pyrone and 4‐oxy‐5‐triphenylphosphonium‐6‐phenyl‐2‐pyrone, obtained by reaction of carbon suboxide, C3O2, with stabilized phosphorus ylides, Ph3PCHX (XCN, COMe, COPh), is described. The FAB mass spectrometric behaviour of these compounds is compared with that shown by tri‐phenylphosphoranilideneketene, Ph3P  C  C  O, and by 4‐hydroxy‐6‐methyl‐2‐pyrone, with the aid of metastable ion data and collision spectroscopy.
Characterization of modification sites during peptide synthesis using liquid secondary ion/collision‐induced dissociation mass spectrometry and a computer program
Authors: Rozenski Jef , Samson Isabelle , Janssen Gerard , Busson Roger , Van Aerschot Arthur , Herdewijn Piet
Published: May 2005

Side‐reactions often occur during peptide synthesis resulting in modified amino acid moieties. To identify these residues, liquid secondary ion/collision‐induced dissociation mass spectra were recorded. The main fragments are generated by cleavage of the peptide bond. To facilitate interpretation of the spectra and assignment of the structure, a simple, but flexible and efficient, computer program is presented. The program allows the verification of the correct structure of the synthesized peptides and the deduction of the type of side‐products formed, such as alkylation of tryptophan residues.
Determination of tetrahydrocannabinolic acid—carrier protein conjugate by matrix‐assisted laser desorption/ionization mass spectrometry and antibody formation
Authors: Goto Yuri , Shima Yumi , Morimoto Satoshi , Shoyama Yukihiro , Murakami Hiroki , Kusai Akihiko , Nojima Kazutetsu
Published: May 2005

In order to form the monoclonal antibody against tetrahydrocannabinolic acid (THCA), THCA was coupled with bovine serum albumin (BSA) or human serum albumin (HSA) using β‐alanine as a linker or without β‐alanine to produce individual antigen conjugates. The number of haptens contained in the antigen conjugates was determined by matrix‐assisted laser desorption ionization mass spectrometry using BSA or HSA as an internal standard. The formation of monoclonal antibody is also discussed.
Characterization of chlorins within a natural chlorin mixture using electrospray/ion trap mass spectrometry
Authors: Chillier Xavier Fr. D. , Van Berkel Gary J. , Gülaçar Fazil O. , Buchs Armand
Published: May 2005

Chlorins in a sedimentary mixture were characterized, without prior isolation of individual components, using electrospray ionization combined with ion trap mass spectrometry. Collision‐induced dissociation in the atmospheric sampling interface and multi‐step mass spectrometry (i.e. MSn where n ⩾ 2) were used in order to obtain structural information about the macrocycle. Fragmentation pathways are proposed for different macrocycle types based on data from model chlorins. Three unknown chlorins (RMM = 888, 844 and 790) are assigned as having bacteriochlorophyll macrocycle types esterifled to unusual side‐chains (i.e. dihydrophytol for the unknown with a bacteriopheophorbide a structure, phytol and an alcohol with a molecular mass of 242 u for the two unknowns with a proposed bacteriopyropheophorbide d structure).
Chemical reactions occurring at the interface of epoxy matrix and aminosilane coupling agents in fiber‐reinforced composites
Authors: Chiang Chwan‐Hwa , Koenig Jack L.
Published: May 2005

The chemical reactions at the interface between an anhydride‐cured epoxy resin and an aminosilane treated fiber have been investigated using Fourier transform infrared methods (FT‐IR). The results indicate that chemical bonds are formed in the interfacial region between the matrix and the coupling agents. The amount of interfacial bonding depends on the composition and the processing conditions.
Interferometric measurement of inhomogeneous swelling
Authors: Sargent J. P. , Ashbee K. H. G.
Published: May 2005

Differential thermal contraction between matrix and fiber materials in composites and between adhesive and adherend materials in adhesive joints occurs during cooling from the resin cure temperature and gives rise to non‐uniform internal stress fields. Resin swelling associated with water uptake during service gives rise to inhomogeneous stress, the magnitude and distribution of which is the subject of the present investigation. Thin layers of cured epoxy resin have been allowed to absorb water at their edges only, and the swelling normal to these layer planes has been measured by studying optical interference patterns. The stresses resulting from inhomogeneous swelling, a few tens of bars, are of similar magnitude to those resulting from inhomogeneous shrinkage during cooling from resin cure temperatures.
Fiber rearrangements during the molding of continuous fiber composites. I. Flat cloth to a hemisphere
Authors: Robertson R. E. , Hsiue E. S. , Sickafus E. N. , Yeh G. S. Y.
Published: May 2005

The goal of this series of reports is to develop rapid computational procedures for determining the rearrangement of fibers that occurs during the molding of continuous fiber composite components for flat layups. This report considers the shaping of a cloth into a hemisphere. /the numerical procedure developed predicts that a cloth can be shaped into a hemisphere without wrinkling. This prediction is compared with experiment, and various paramenters connected with the shaping calculation are discussed.
Elevated temperature testing for comparison of glass/resin composites
Authors: Silverman E. M.
Published: May 2005

Static test methods were used to evaluate and compare the thermal and mechanical properties of several glass/thermoset laminated composites between 25° and 400°C. The unidirectional matrix composites consisted of phenolic‐modified epoxy, epoxy novolac, epoxy, and modified phenolic resins. These materials were selected as potential alternative materials for rotary compressor vanes. Dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) techniques were selected to evaluate elevated temperature performance. The short‐beam shear test was chosen to measure interlaminar shear properties. The results indicated that an elevated‐temperature matrix, such as the modified phenolic resin, may not result in optimum composite strengths. Instead, an epoxy resin reinforced with glass fibers provides a better balance between elevated‐temperature performance and interlaminar shear strength. The test results of this study, in addition to being adequate for discriminating the materials for initial selection purposes, were obtained quickly and easily. Moreover, the thermal results provide a more realistic understanding of composite elevated‐temperature characteristic than do those of the present standard test.
Polymerization of filled propylene: A new principle for formation of conducting composites
Authors: Berlin Y. , Beshenko S. I. , Zhorin V. A. , Galashina N. M. , Enikolopian N. S.
Published: May 2005

A new approach to the formation of electrically conducting polymeric materials has been formulated. It is based on the phenomenon of pressure‐induced injection of charge carriers from conducting particles into dielectric media. This process has been recently discovered by the authors. In practice, this approach can be accomplished by synthesizing macromolecules of proper dielectric next to the surface of a conducting filler. The experiments supporting the validity of the main assumptions are used to provide a background for the “polymerization filling” concept. The application of this principle makes it possible to obtain systems with larger specific conductivity than with the usual “blended” composites.
Extensional flow of mica‐filled polyethylene
Authors: Utracki L. A. , Lara J.
Published: May 2005

Extensional flow of mica‐filled high density polyethylene was studied at 150°C in a Rheometrics elongational rheometer. The constant strain‐rate mode at a rate of 10−3 to 1.0 s−1, and the constant stress mode were used. The mica content was 0, 25, 40, and 60 weight percent. In both testing modes, the steady state elongational viscosities were obtained; those for the filled samples were about ten to twenty times larger than the shear viscosity at corresponding (low) rates of deformation.
Jute reinforced polyester structures
Authors: Semsarzadeh Mohammad A. , Lotfali Abdol R. , Mirzadeh Hamid
Published: May 2005

Large diameter pipes and structures are manufactured with jute reinforced polyester resin. A modified filament winding machine is used to take the jute cloth on the rotating mold acting as a collapsible mandrel. The effect of calendering, fillers and poly(vinyl acetate) on jute reinforcing cloth and the results on the ultimate mechanical properties of the composite are studied. The effect of load during the curing of polyester and its effect on the strength of structure is reported. These findings are used in manufacturing of large diameter structures with improved mechanical properties.
Effect of particulate reinforcement on creep behavior of polyurethane foams
Authors: Alperstein D. , Narkis M. , Kenig S. , Siegmann A.
Published: May 2005

The compressive creep behavior of rigid unreinforced and particulate reinforced polyurethane foams at different densities, filler contents, temperatures, and loads was investigated. The creep behavior could be described by a power function of time and its temperature dependence by an Arrhenius type relation. The addition of particulate rigid fillers enhances the creep resistance as well as the foam elastic modulus. Particulate reinforcement of polyurethane foams was found to be efficient for the higher foam densities, especially for higher filler levels.
Mechanical degradation of glass fibers during compounding with polypropylene
Authors: Fisa B.
Published: May 2005

The objective was to study the fiber length degradation during compounding of glass fiber with polypropylene. The effect of parameters such as viscosity, total work, concentration on fiber length and dispersion was studied using an automatic particle size analyzer. The length degradation is most severe during the very first stage of the process, i.e., when fiber bundles are being filamentized. The mode of glass fiber incorporation into the melt (fiber addition to the molten resin versus to polypropylene powder prior to compounding) was found to have no effect on the final fiber length. Matrix resin viscosity affects the fiber length significantly. Concentration dependencies of fiber length for different times of compounding suggest that the degradation results from both fiber‐fiber and fiber‐melt interactions.
Mechanical properties of drawn poly(methyl methacrylate) filled with ultrafine particles
Authors: Sumita Masao , Shizuma Tadao , Miyasaka Keizo , Ishikawa Kinzo
Published: May 2005

The elastic and yield properties of drawn poly(methyl methacrylate) (PMMA) filled with ultrafine SiO2 are described as functions of filler content and size. The drawn PMMA composites were made by uniaxially drawing to x4.0 at 100°C and at a rate of 20 mm/min. Four compliance values, i.e., S33, S11, S13, and S44 were determined. These values decreased with filler content and decreasing filler size. The relative compliance values Sde/Sdo(Sde is the compliance of drawn PMMA composites and Sdo is that of drawn unfilled PMMA) are almost equivalently changed with changes in filler content. The elastic properties of drawn PMMA composites are thus reinforced isotopically. This is characteristic of PMMA which has a large side group. The yield behavior of drawn PMMA composites have similar filler size and content dependence to those of elastic properties except that the transverse yield stresses become more brittle with filler content. The anisotropy in yield stress is relatively larger than that of elastic properties. This is probably because the anti‐reiforcing effect, such as fibrillation becomes prominent with increasing filler content in the perpendicular direction.
Structure‐property relations in polypropylene mica composites
Authors: Xavier S. F. , Sharma Y. N.
Published: May 2005

Polypropylene composite samples with concentrations of mica of 10, 20, 30, 40, 45, 50, and 60 wt percent were prepared under identical conditions by injection molding. The influence of mica concentration on the structure and mechanical properties of the composites was investigated using a polarizing microscope, scanning electron microscope, differential scanning calorimetry, and stress‐strain characteristics. Flexural and impact strengths show an initial rise and then gradual fall with increasing mica concentration. An optimum of these properties occurred at ∼20 wt percent mica. Tensile modulus and heat distortion temperature show a continuous rise; whereas the percent elongation decreased with mica content. These changes in properties are discussed in terms of a skin‐core morphology, transcrystallinity, crystallinity, fracture surface morphology, flake orientation, and interfacial adhesion in these composites. This study helps in optimizing the mica concentration for injection molded composites.
The effect of thermal stresses on the EMI (electromagnetic interference) shielding of conductive plastics
Authors: Bigg D. M.
Published: May 2005

The electrical properties of a number of filled and coated plastics were examined after subjecting the materials to rigorous thermal cycling between −20 and 80°C. Filled compounds that obtained their conductivity through the addition of carbon based conductive fillers maintained their conductivity throughout the thermal cycling. Compositions which contained metal fillers were able to maintain their conductivity only when a high temperature thermally stable polymer was used as the polymer matrix. Plaques coated by a zinc arc spray or with acrylic paints containing graphite, silver, and nickel particles were unaffected by thermal cycling. Plaques coated with an acrylic paint containing copper particles lost most of their conductivity during the changes in sample temperature.
Mechanical and rheological properties of multicomponent polypropylene blends
Authors: Pukánszky Béla , Tüdõs Ferenc , Kelen Tibor
Published: May 2005

Polypropylene (PP) compositions containing CaCO3 filler, EPDM (ethylene‐propylene‐ethylidenenorbornene) elastomer, and a non‐reactive surfactant were investigated in the mixing chamber of a plastograph. Rheological properties were determined from the registered torque (M) vs. time and temperature (T) vs. time curves, while tensile characteristics of the blends were measured on compression molded plates. The homogenization process can be followed with the aid of 1 n M vs. 1/T diagrams. In the first few minutes of the mixing, beside homogenization, a significant breaking down of the elastomer takes place, and the size of the particles attains an equilibrium value. Dispersion time increases with increasing amount of EPDM and surface active‐agent. Morphological investigations indicate the presence of a continuous PP phase containing dispersed CaCO3 and elastomer particles. The rheological and tensile characteristics are seemingly determined by the total amount of additives, which imply that the elastomer and the filler has the same effect on the properties of the composite. Separation of the effects proved, however, that the effect of the two components are dissimilar, the filler exerts a larger influence on the investigated properties.
Statistical distribution of strength of fiber‐reinforced composite materials
Authors: Wetherhold Robert C.
Published: May 2005

The Weibull distribution is presented as a physically consistent description of strength distribution in brittle composites. Methods are developed for obtaining point and one‐sided interval estimates for the parameters of the Weibull distribution. Strength data are obtained for 25 replicates of nine different sheet molded and injection molded composites, and the developed statistical methods are applied to these data. Details of the materials and processing are given. Strength results indicate that the reliability calculations using the one‐sided interval estimates are uniformly conservative for all materials. In addition, it is shown that composites produced with a less automated production process show more strength variability. Machining of an injection molded composite surface appears to lower strength and increase strength variability by introducing flaws which act as fracture initiation sites.
Measurement of the thermal conductivity of composites using heat flow sensors
Authors: Penn B. G. , Ledbetter F. E. , White W. T. , Clemons J. M.
Published: May 2005

A thermal conductivity measuring apparatus that uses heat flow sensors to measure the heat flux through samples was constructed of inexpensive materials. This device was used to measure the thermal conductivity (k) of two composites used in the space program that consist of fibrous or granular components embedded in a resin matrix. The k‐values that were determined ranged from 0.035 to 0.059 Btu/h‐ft2‐°F/ft (−163 to 553°F) and 0.029 to 0.035 Btu/h‐ft2‐°F/ft (77 to 212°F). Thermal conductivity values of the composites conformed to the rule of mixture. The accuracy of the system was found to be comparable to the guarded hotplate and it requires neither a skilled operator nor extensive maintenance.
Air entrapment in sheet molding compounds (SMC)
Authors: Slotfeldt‐Ellingsen Dag , Magnus Elisabeth , Ekern Eric , Holtmon Egil , Corneliussen Lars
Published: May 2005

Entrapped air can commonly lead to large delaminations in thick walled sheet molding compound (SMC) products. In this work different sources of air entrapment in SMC are investigated. The critical process is shown to be the impregnation of the fibers. If no surface active additives are used, large volumes of air may be entrapped in this process, unless the viscosity of the compound is very low. In this situation of poor wetting, the viscosity of the compound during fiber impregnation will critically determine the interlaminar, tensile strength of the product. However, if surface active additives are used, the air escapes entrapment even at relatively high viscosities. The lowering of the viscosity, which is a side effect of the additives, has practically no importance under these conditions of good wetting. Large numbers of small air bubbles are also entrapped during the mixing of the components, but it is shown that these bubbles have very little effect on the mechanical properties of the finished part.
The effects of tension on the absorbance of water into neat and glass‐bead‐filled, cross‐linked polyester
Authors: Janas V. F. , Smith L. S. , McCullough R. L.
Published: May 2005

The effects of tension on the absorbance of water at 60°C into neat and glass‐bead‐filled, cross‐linked polyester are reported. Experimental apparatus and procedure to determine water uptake for these materials subjected to three tensile stresses in the range of 0 to 30 percent of the breaking stress of the neat dry polyester are described. It was found, for bead‐filled samples, that a load of approximately 4.9 × 106 N/m2 caused the absorption level to increase by 30 percent over that of an unloaded sample. Tensile load was found to have no effect on the absorption characteristics of neat polyester. However, breaking stress was reduced to less than 15 percent of that in the dry neat material. Optical microscope examinations of damage at the fracture surfaces and at the sample cores indicate that the excess moisture uptake in bead‐filled samples was not due to microcrack formation.
The effect of chemical exposure on the EMI shielding of conductive plastics
Authors: Bigg D. M.
Published: May 2005

The electrical properties of a number of filled plastics were examined after subjecting the materials to exposure to isopropyl alcohol, a 25°C detergent/water solution, an 80°C detergent/water solution, and at various chemical plant sites. Compositions which contained metal fillers maintained their conductivity only when a high temperature thermally stable polymer was used as the polymer matrix, while compositions which are made conductive through a carbon filler network maintained their conductivity under most of the exposure conditions examined even when low temperature polymers were used as matrices.
Some features of the injection molding of short fiber reinforced thermoplastics in center sprue‐gated cavities
Authors: Darlington M. W. , Smith A. C.
Published: May 2005

This paper describes an investigation into the fiber orientation in a number of center sprue fed cavities in short glass fiber filled polypropylene and nylon. The data have been interpreted in terms of a generalized five‐layer structure resulting from the frozen skin formation and the high and low shear levels in the flowing melt. The implications for scaling up the mold size are discussed from the results obtained with different shot volumes. The fiber structure was observed to depend on location in the molding, local injection time, and injection rate. In addition the occurrence of fiber‐free layers within the moldings using the filled polypropylene increases with an increase in shot volume, which produces an inherent ‘scale‐up’ problem. Notwithstanding the mold geometry subtleties, the fiber orientation in all the moldings follows similar patterns and trends.
A cure‐rate model for the shuttle filament‐wound case
Authors: Cagliostro D. E. , Islas A. , Hsu Ming‐ta
Published: May 2005

An epoxy and carbon fiber composite has been used to produce a light‐weight rocket case for the Space Shuttle. A kinetic model is developed which can predict the extent of epoxy conversion during the winding and curing of the case. The model accounts for both chemical and physical kinetics. In the model, chemical kinetics occur exclusively up to the time the transition temperature equals the reaction temperature. At this point the resin begins to solidify and the rate of this process limits the rate of epoxy conversion. A comparison of predicted and actual epoxy conversion is presented for isothermal and temperature‐programmed cure schedules.
Self‐Reinforced melt processible polymer composites: Extrusion, compression, and injection molding
Authors: Isayev A. I. , Modic M.
Published: May 2005

Rheological properties, extrusion, fiber spinning, compression, and injection molding of blends of polycarbonate and two thermotropic liquid crystal polymers based on wholly aromatic copolyesters have been studied. Blends were prepared using an internal Banbury mixer and static Koch mixer. Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentrations. During extrusion and injection molding at high strain rates, it has been observed that thermotropic liquid crystal polymer at concentrations 2.5, 5, and 10 percent by weight in situ forms high modulus and high strength fibers within the polycarbonate matrix leading to self‐reinforced polymer composites. The tensile strength of the composite containing 10 percent of liquid crystal polymer exceeds that of the pure components. In addition, anisotropy of properties of the injection molded parts has been found to substantially reduce in a comparison with that of liquid crystal polymer. The processing conditions and technique for the production of self‐reinforced polymer composite during processing of the blends have been identified. This has been done by measurements of mechanical properties, direct observation of morphology, and by theoretical calculation using simplified composite theory for the unidirectional continuous fiber‐reinforced composites. At the high concentrations, 25 and 50 percent by weight, thermotropic liquid crystal polymer forms large spherical droplets inside polycarbonate leading to highly brittle material. This is in distinction from the fibrous, high modulus tough composites formed at the lower concentrations.
Thermoanalytical investigation of composite lamination
Authors: Gotro J. , Appelt B. , Yandrasits M. , Ellis T.
Published: May 2005

Glass cloth reinforced epoxy resins are commonly used to make composites. The performance of these laminates depends strongly on optimizing cure kinetics and rheology for a given chemical composition and temperature/pressure profile. Aborted flow tests (weight percent resin squeezed out during a given temperature/pressure cycle) is frequently used to emulate lamination processes and/or to evaluate new formulations. The cure reaction was monitored using differential scanning calorimetry, rheology, and dielectrometry. These techniques show that the cure kinetics are controlled by the temperature profile. The viscosity and the macroscopic flow, however, are affected by the temperature profile, i.e. decrease in viscosity with rising temperature, as well as the cross‐linking kinetics which lead to an increase in viscosity. Gravimetric and thickness measurement indicated a non‐uniform resin distribution across the laminate, with a lower resin content found at the edges. Macroscopic flow is controlled by three dimensional heat transfer, which leads to a dynamic temperature distribution and, concomitantly, to a cure/rheology profile. This was demonstrated graphically by marking layers of reinforced resin and monitoring the movement of the markers.
Viscoelastic response of unidirectionally reinforced thermoplastic composites to off axis deformation
Authors: Tomkinson Gayle D. , Vallance Michael A.
Published: May 2005

Measurements of dynamic viscoelastic in‐plane shear modulus have been made for unidirectional carbon fiber composites with amorphous engineering thermoplastics as the binder resins. The viscoelastic response is modeled by a three‐phase, finite‐element model in which fiber placement in the plane perpendicular to the fiber axes is largely disordered. In the model, fibers tend to chain with the distance of closest approach dictated by several factors, including the tendency for the resin to wet the entire fiber surface. Polished section microscopy supports the assumed microstructure. The model includes an adsorbed primer layer at the fiber interface with perturbed viscoelastic response. The model is useful throughout the temperature range up to and including the glass transition of the binder resin.