bluuebunny/crossref_metadata_2025 huggingface dataset:
Primary to quaternary protein structure determination with electrospray ionization and magnetic sector mass spectrometry
Authors: Loo Joseph A. , Loo Rachel R. Ogorzalek , Andrews Philip C.
Published: May 2005

Electrospray ionization with a forward‐geometry magnetic sector mass spectrometer was used for collisionally activated dissociation studies of multiply charged polypeptides and for studying non‐covalently bound protein systems. The high‐resolution capabilities of a high‐performance instrument allow the resolution of isotopic contributions for product ions and molecular ion species. Determination of product ion charge states by this method reduces difficulties in the interpretation of product ion mass spectra from multiply charged precursors, which are generated either in the atmospheric pressure/vacuum electrospray interface or in the collision chamber of the mass spectrometer. Extended tandem mass spectrometric experiments have the potential for sequencing larger polypeptides. However, evidence for isomerization of gas‐phase product ions from substance P and substance P analogues was observed, complicating the interpretation of product ion spectra. Non‐covalent complexes can also be studied by electrospray ionization magnetic sector MS. The higher m/z range of such an instrument is a major advantage for studying weakly bound systems, such as heme–protein systems (myoglobin, hemoglobin) and protein aggregates (concanavalin A), because of their tendency to form complex ions with relatively low charge states.
Mass spectrometry of some 10β‐Fluoro‐1,4‐estradien‐3‐oxo steroids
Authors: Desmarteau D. D. , Resnati G. , Seraglia R. , Traldi P.
Published: May 2005

The mass spectrometric behavior of some 10β‐fluoro‐1,4‐estradiene‐3‐oxo steroids under two different ionization conditions (electron inpact and fast atom bombardment) was studied with the aid of mass‐analyzed ion kinetic energy spectroscopy. The influence of fluorine in the fragmentation pattern was investigated by comparison with the behavior of 10‐methyl analogs. In particular, the presence of fluorine at position 10 seems to reflect the weakening of C(9)C(10) bond. Further, when an acyloxy moiety is present at position 17, the primary ring cleavages typical of steroids become disfavored and fragment ions related to the acyloxy substituents are detected.
Mass spectrometric study of 2‐acyloxy‐4,6‐dimethoxy‐1,3,5‐triazines
Authors: Sochacki Marek , Kami Zbigniew J.
Published: May 2005

Electron impact ionization mass spectra of 2‐acyloxy‐4,6‐dimethoxy‐1,3,5‐triazines were examined. Two general pathways of fragmentation were found: (i) formation of an acylium ion typical for all the compounds studied, and (ii) rearrangement followed by loss of carbon monoxide, characteristic of derivatives of aromatic carboxylic acids.
Collision‐induced decompositions of metal‐cationized methyl‐6‐deoxy‐6‐bromo‐α‐D‐glucopyranoside derivatives
Authors: Madhusudanan K. P. , Dhami T. S. , Katiyar S. , Suryawanshi S. N.
Published: May 2005

Collision‐induced decompositions (CIDs) of the [M + H]+, [M + Li]+, [M + Na]+, [M + K]+ and [M + Ag]+ ions of some methyl‐6‐deoxy‐6‐bromo‐α‐D‐glucopyranoside derivatives are discussed. Elimination of MeOH resulting in the glycosidyl cation is the predominant reaction of the [M + H]+ ion. This process is completely suppressed during CID of the metal‐cationized species, which, surprisingly, show elimination of the added metal in the form of RCOO‐metal and metal bromide in the case of the ester derivatives. These reactions appear to be assisted by neighbouring group participation. Because of the proximity of the C(3)‐oxygen with C(6), the benzyl ether derivative is characterized by the loss of PhCH2Br from the [M + metal]+ ion.
Li+‐ and Ag+‐cationized per‐O‐acetyl‐ and Per‐O‐benzyl‐α‐D‐thioglycosides: a collision‐induced decomposition study
Authors: Madhusudanan K. P. , Dhami T. S. , Katiyar S. , Suryawanshi S. N.
Published: May 2005

The collision‐induced decompositions of the [M + Li]+ and [M + Ag]+ ions of per‐O‐acetyl‐ and per‐O‐benzyl‐α‐D‐thioglycosides having phenyl sulphide, phenyl sulphoxide and phenyl sulphone as the aglycone moieties were studied. The [M + Li]+ ion of the acetyl derivative of the phenylthioglucoside shows loss of AcOLi, whereas its [M + Ag]+ ion shows elimination of PhSAg. Their sulphoxide and sulphone derivatives lose the C(1) and C(2) substituents to form the glucal under both Li+ and Ag+ cationization conditions. The corresponding benzyl derivatives do not show the loss of metal. The formation of glucal leads to ring fragmentation by retro‐Diels‐Alder reaction in the ring‐activated benzyl derivatives.
Reactivity of vinylamine radical cation with neutral dienes
Authors: Bouchoux Guy , Penaud‐Berruyer Florence
Published: May 2005

The gas‐phase ion—molecule reactions between ionized vinylamine ([CH2  CHNH2]+.) as a set of conjugated and unconjugated dienes were studied by Fourier transform is observed. Conjugated dienes lead to the elimination of NH3 or of an hydrocarbon radical from the adduct [M + CH2  CHNH2]+.. In the case of unconjugated dienes a regiospecific cyclobutanation‐cycloreversion process is observed. Reaction mechanisms are proposed to explain these experimental findings.
Rapid screening technique for tetrachlorodibenzo‐p‐dioxins in complex environmental matrices by gas chromatography/tandem mass spectrometry with an ion‐trap detector
Authors: Plomley Jeffry Blaise , Koester Carolyn Jean , March Raymond Evans
Published: May 2005

A capillary column gas chromatographic/ion‐trap tandem mass spectrometric (GC/MS/MS) technique was applied to the determination of tetrachlorodibenzo‐p‐dioxins (TCDDs) in complex environmental matrices. A detection limit of 500 fg μl‐1 injected, with a signal‐to‐noise ratio of 6:1, was obtained when MS/MS was combined with broadband ion ejection of matrix ions and selected ion isolation. Calibration graphs were constructed from extracted fragment ion mass chromatograms and were found to be linear over the range 0.5‐200 pg. Concentrations of total TCDDs and of 2,3,7,8‐TCDD were determined for extracts from fish, air and soil; in most cases, the results found by GC/MS/MS were comparable to those obtained by high‐resolution MS and triple quadrupole MS.
Tandem mass spectrometry of peptides: Mechanistic aspects and structural information based on neutral losses. II—Tri‐ and larger peptides
Authors: Cordero Marcela M. , Wesdemiotis Chrys
Published: May 2005

The neutral products arising during the collisionally activated dissociation of protonated oligopeptides (MH+) are post‐ionized by collision and detected in neutral fragment‐reionization (+NfR+) mass spectra. For the isomeric tripeptides Ala‐Gly‐Gly, Gly‐Ala‐Gly and Gly‐Gly‐Ala, the amino acid and dipeptide losses from the C‐terminus and the diketopiperazine losses from the N‐terminus allow for differentiation. These neutral fragments are identified in the corresponding +NfR+ spectra by comparison to reference collision‐induced dissociative ionization (CIDI) mass spectra of individual amino acids, dipeptides and diketopiperazines. Peptides with distinct C‐termini but otherwise identical sequences are found to yield +NfR+ products that are characteristic of the respective C‐terminal amino acid. This is demonstrated for several peptide pairs, including leucine‐ and methionine‐enkephalin. In general, +NfR+ spectra are dominated by the heavier neutral losses; further, +NfR+ and CIDI cause extensive dissociation, indicating that the collisional ionization process imparts high average internal energies.
Side‐chain effects on the fragmentation behaviour of alkylthiophenes
Authors: Lange D. , Budzikiewicz H.
Published: May 2005

The processes leading to the fragment ions formed from alkylthiophene molecule ions by benzylic cleavage without and with transfer of one hydrogen from the side‐chain to the ring and the influence of additional methyl groups on the relative importance of these two fragmentation reactions were investigated.
Unimolecular neutral and ion kinetics by variable‐time neutralization—reionization mass spectrometry
Authors: Kuhns David W. , Turecek Frantisek
Published: May 2005

A new method is described for the determination of rate parameters of unimolecular dissociations of neutral intermediates and ions produced by collisional neutralization and reionization at kiloelectronvolt kinetic energies. The method utilizes variable time‐scales for neutral and ion dissociations to obtain time‐dependent survivor and product ion yields. Kinetic analysis then provides phenomenological rate constants for both neutral and ion dissociations. Neutralization with CH3I, NO, (C2H5)2O, C6H6 and Xe of methyl iodide cation radicals is shown to produce the intermediate neutral molecules with different internal energies, resulting in different rates of neutral and ion dissociations. Vibrational excitation in neutralized CH3I results in neutral dissociations with rate parameters in the (1–3) × 105 s–1 range. The origin of neutral excitation by fast collision is explained by the intermediate formation of highly excited Rydberg states that decay by photon emission to the vibrationally excited ground state of the molecule.
Electrospray vs. matrix‐assisted laser desorption/ionization. 1. Some examples in the protein field
Authors: Favretto Donata , Seraglia Roberta , Traldi Pietro , Curcuruto Ornella , Hamdan Mahmoud
Published: May 2005

Several proteins in the relative molecular mass (RMM) range 1150–29000 are examined by means of both positive electrospray and matrix‐assisted laser desorption/ionization mass spectrometry. Accuracy of the measured RMMs, resolution and overall sensitivity are discussed. The presence of more than one component in a number of the investigated compounds permitted the assessment of both desorption methods for the analysis of mixtures. Solvent‐induced conformational changes are linked to charge‐state distribution shifts observed in some positive electrospray mass spectra.
Negative‐ion fast atom bombardment mass spectrometry in the characterization of deoxyfluorinated sugars
Authors: Coppola M. , Favretto D. , Traldi P. , Resnati G.
Published: May 2005

Negative‐ion fast atom bombardment mass spectrometry and metastable ion studies were applied to the characterization of three isomeric fluorine‐containing sugars. Peculiar fragmentation processes were evidenced for each isomer, enabling their differentiation. Comparison with the behaviour of a non‐fluorinated analogue allowed investigation of the role of fluorine in the decomposition processes of these compounds.
Translational energy losses of LiF cluster ions
Authors: Vékey Károly , Ludányi Krisztina
Published: May 2005

Translation energy loss (TEL) values have been measured in the collision‐induced fragmentation of Li6F5+ cluster ions. TEL values varied between 1 and 8 eV in single collisions and showed a strong dependence on the centre‐of‐mass (com) collision energy. At large com collision energies (>800 eV) the TEL was small (˜1.5 eV) and is explained by internal excitation. At lower com collision energies, TEL values were larger (up to 8 eV), and these are explained in terms of kinetic energy uptake by the target gas. TEL values observed using LiF and CsI clusters are compared.
Mass spectral fragmentation pathways in some glycoluril‐type explosives. A study by collision‐induced dissociation and isotope labeling
Authors: Yinon J. , Bulusu S. , Axenrod T. , Yazdekhasti H.
Published: May 2005

Electron impact (EI), chemical ionization and negative‐ion chemical ionization (NCI) mass spectra of 1,4‐dinitroglycoluril (DINGU), its 15N‐ and 2H‐labeled analogues and the dimethyl‐substituted derivatives were recorded. Tandem mass spectrometry with collision induced dissociation was used to study the fragmentation pathways of these compounds. It was found that the main EI fragmentation processes of DINGU are due to the cleavage of CN bonds and some rearrangement reactions.
Investigation of cationic organic dyes used as molecular probes by liquid secondary ion mass spectrometry
Authors: Carlson Richard E. , Busch Kenneth L.
Published: May 2005

The positive‐ion mass spectra of twelve organic dyes used as molecular probes were measured using liquid secondary ion mass spectrometry (LSIMS). Nine of the twelve dyes were singly charged cations and the other three were doubly charged cations. The mass spectra of each of the dyes in m‐nitrobenzyl alcohol contain abundant signals for the intact cation, C+ (singly charged cation dyes), or for singly‐charged forms of the doubly charged cation formed by proton loss, [C2+ H+]+, or halogen counter ion attachment, [C2+ + X−]+. Fragmentation is usually minimal under the conditions used. However, the cations of five of the singly charged compounds appear to undergo charge‐remote fragmentation. Collision‐induced dissociation experiments on a hybrid mass spectrometer of EBqQ geometry at collision energies up to 300 eV failed to access this fragmentation pathway. In contrast to the LSIMS of many other doubly charged organic compounds, two of the dicationic dyes produced a doubly charged ion of reasonable abundance (2–20%) in the mass spectrum. When glycerol was used as a matrix solvent, the addition of the matrix modifier trifluoroacetic acid increased the abundance of C2+.
Fragment ion formation from n‐alkanes and cycloalkanes by plasma desorption
Authors: Betts R. L. , Park M. A. , Shirey E. Lynn , Schweikert E. A.
Published: May 2005

The plasma desorption of hydrogen loss fragment ions from frozen films of several classes of aliphatic volatile hydrocarbons was investigated with 252Cf plasma desorption mass spectrometry. A time‐of‐flight instrument suitable for the reproducible sampling and analysis of volatile hydrocarbons in the solid state was designed for this study. Representative compounds from the n‐alkanes and cycloalkanes were analyzed. For all the compounds studied, radical molecular ions. M+., and hydrogen loss fragment ions, [M  mH]+ with m varying from 1 to 10, were produced. The length of the alkane chain, the size of the alkane rings and the stability of the resulting H‐loss ions affected the number and abundance of these ions. Smaller molecules underwent proportionally more hydrogen loss than larger molecules of the same class.
Fast atom bombardment mass and tandem mass spectra of protonated and alkali cationized aldobiouronic and pseudoaldobiouronic acid per‐O‐methyl derivatives
Authors: Kováčik Vladimír , Hirsch Ján , Heerma W. , de Koster C. G. , Haverkamp J.
Published: May 2005

The positive‐ion fast atom bombardment mass spectra of permethylated aldo‐ and pseudoaldobiouronic acids can be used to distinguish these classes of compounds. The collisional‐induced dissociation spectra of the [M + H]+ ions show fragment ions resulting from glycosidic bond cleavage and successive losses of methanol molecules. These spectra together with those of the [M + H  MeOH]+ oxonium ions allow the identification of the type of interglycosidic linkage. Collisional activation of the relatively stable [M + Na]+ ions show many fragmentations which are common to alkali cationized permethylated saccharides. Moreover, fragment ions resulting from two‐bond ring cleavage processes yield additional information with respect to the linkage between the hexose and uronic acid units.
Reactions of ionized dibutyl ether
Authors: Bowen Richard D. , Suh Dennis , Terlouw Johan K.
Published: May 2005

The reactions of ionized di‐n‐butyl ether are reported and compared with those of ionized n‐butyl sec‐butyl and di‐sec‐butyl ether. The main fragmentation of metastable (CH3CH2CH2CH2)2O+. is C2H5⋅ loss (˜85%), but minor amounts (2–4%) of CH3⋅, C4H7⋅, C4H9⋅, C4H10 and C4H10O are also eliminated. In contrast, C2H5⋅ elimination is of much lower abundance (20 and 4%, respectively) from metastable CH3CH2CH2CH2OCH(CH3)CH2CH3+. and [CH3CH2(CH3)CH]2O+., which expel mainly C2H6 and CH3⋅ (35–55%). Studies on collisional activation spectra of the C6H13O+ oxonium ions reveal that C2H5⋅ loss from (CH3CH2CH2CH2)2O+. gives the same product, (CH3CH2CH2CH2 +OCHCH3) as that formed by direct cleavage of CH3CH2CH2CH2OCH(CH3)CH2CH3+.. Elimination of C2H5⋅ from (CH3CH2CH2CH2)2O+. is interpreted by means of a mechanism in which a 1,4‐H shift to the oxygen atom initiates a unidirectional skeletal rearrangement to CH3CH2CH2CH2OCH(CH3)CH2CH3+., which then undergoes cleavage to CH3CH2CH2CH2+OCHCH3 and C2H5⋅. Further support for this mechanism is obtained from considering the collisional activation and neutralization‐reionization mass spectra of the (C4H9)2O+. species and the behaviour of labelled analogues of (CH3CH2CH2CH2)2O+.. The rate of ethyl radical loss is suppressed relative to those of alternative dissociations by deuteriation at the γ‐position of either or both butyl substituents. Moreover, C2H5⋅ loss via skeletal rearrangement and fragmentation of the unlabelled butyl group in CH3CH2CH2CH2OCH2CH2CD2CH3+. occurs approximately five times more rapidly than C2H4D⋅ expulsion via isomerization and fission of the labelled butyl substituent. These findings indicate that the initial 1,4‐hydrogen shift is influenced by a significant isotope effect, as would be expected if this step is rate limiting in ethyl radical loss.
Resin/fiber thermo‐oxidative interactions in pmr polyimide/graphite composites
Authors: Alston William B.
Published: May 2005

The amounts of resin weight loss and fiber weight loss in four PMR polyimide/graphite fiber composites were calculated from the composite weight losses and the fiber/resin ratios of the composites after long term thermo‐oxidative aging in 600° F air. The accelerating effect of graphite fiber on resin weight loss, compared to neat resin weight loss, indicated the presence of a deleterious resin/fiber thermo‐oxidative interaction, presumably due to fiber impurities. Similarly, the declerating effect of the protective matrix resin on fiber weight loss, compared to bare fiber weight loss, was also demonstrated. The amount of hydrazine indigestible resin and the amount of loose surface graphite fiber that formed during 600° F exposure of the composites were quantitatively determined. The indigestible residual resin was also qualitatively studied by scanning electron microscopy.
Stress dependence of water diffusion in epoxy resin
Authors: Fahmy A. A. , Hurt J. C.
Published: May 2005

The effect of stress on the diffusion of water in glassy polymers is analytically treated. Utilizing the free volume concept the effect of stress on the free volume fraction is established and in turn is related to the diffusion coefficient yielding the following formula: Dσ = Doe(6 to 10)σ/G where Dσ and Do are the diffusion coefficients in the presence and absence of stress respectively, G is the shear modulus, and σ is the stress. Experiments are described which demonstrate that in a bent epoxy bar, more water is picked up at the tension side than at the compression side. Theory and experiment are discussed and compared.
Quality assurance of epoxy resin prepregs using liquid chromatography
Authors: Hagnauer Gary L.
Published: May 2005

Liquid size exclusion, adsorption, and bonded‐phase high performance liquid chromatographic (HPLC) methods have been developed to monitor the chemical compositions of epoxy resin prepregs. Examples are given to illustrate how multiple detectors and oligomer analysis techniques may be used to identify prepreg components and to discriminate between epoxy resins obtained from different manufacturers. The results of a case study in which HPLC methods were used to monitor compositional variations in batches of a commercial prepreg over a four year period are discussed. Finally, examples demonstrate how HPLC may be applied to monitor prepreg aging and to measure the extent of prepreg staging.
Mechanical properties of glass microsphere‐filled composite materials
Authors: Micliaresi C. , Nicolais L. , Nicododemo L. , Di Benedetto A. T.
Published: May 2005

The mechanical behavior of epoxy, hydroxyethymetherylate and polystyrene composites containing various percentages of glass microspheres was investigated over a wide range of temperature. The effect of filler concentration of the ductile‐brittle transition and on the glass‐transition temperature of the composites is reported. The utility of various predictive models for the effect of filler concentration on mechanical properties is assessed.
Heat transfer in polymeric composites containing “thermally active” fillers
Authors: Migliaresi C. , Astarita G. , Nicolais L. , Joshi S.
Published: May 2005

Thermal properties of polystyrene composites with a filler showing a solid‐solid phase transition have been studied. Differential calorimeter analysis and typical insulation tests have been performed. An analysis of the experimental results has been done, by using the Stefan moving boundary theory, showing that it is inadequate to predict the thermal behavior of composites of the type studied.
Compounding of glass fiber‐reinforced polypropylene and investigation of its mechanical properties under simple and complex loading
Authors: Pandit S. N. , Gupta V. B. , Subramanian K.
Published: May 2005

Polypropylene is one of the important thermoplastics that has been reinforced with glass fibers to give a reasonably good engineering plastic. Because of its inert nature, it does not easily adhere to the glass surface and hence some improvement in mechanical properties. In the present study a vinyltriethoxysilane coupling agent in polymeric form has been tried and seen to improve the properties. Tests have been carried out at (a) constant strain rate (in the Instron testing machine), and (b)constant stress rate (water loading on a biaxial testing machine). Under constant strain rate only tensile properties have been studied while under constant stress rate, the tensile, torsional and combined tensile‐torsional tests have been carried out. In each of the above cases, a considerable improvement in elastic modulus has been observed. The Tensile strength is improved to the extent of about 25 percent. There is only a slight improvement in torsional strength. Different fiber volume contents were used and their effect studied on modulus and strength. The mechanical data for reinforced‐polypropylene samples have been discussed in terms of the fiber‐length distribution in the composite. Detailed analysis of tensile data suggests that at low strains, when the critical length is relatively low, the fibers contribute to a high modulus. With increasing strain the critical length increases and the load carrying capacity of the fibers is reduced. Consequently the gain in strength is relatively less. The effect of fiber length distribution in torsion and combined tension‐torsion tests would be expected to be similar and the results seem to confirm this.
Molding and torsional testing of tubular specimens of glass fiber‐reinforced polypropylene
Authors: Pandit S. N. , Gupta V. B.
Published: May 2005

This paper describes a torsion pendulum based on the free vibration method and designed for studies on tubular samples. The design and fabrication of the injection mold used for molding the tubular specimens is also described. Tubular specimens were injection molded form polypropylene and glass fiber‐reinforced polypropylene having different glass fiber contents. The sample, which is enclosed in an insulated chamber, can be cooled with the help of liquid nitrogen and heated electrically. The damped oscillations were recorded on a moving chart paper using a lamp and a photodyne between −40 to 100°C. The results indicate that both storage modulus and the logarithmic decrement are affected by the glass fiber and its content. The reinforcing effect of glass fiber and the suppression of viscoelastic effects are briefly discussed.
Notched strength of sheet molding compunds
Authors: Hoa S. V.
Published: May 2005

The Tensile strength of sheet molding compounds containing circular coutouts is investigated. The results show that sheet molding compounds contain inherent voids making the material unaffected by notches smaller than a certain size, The results show a reasonable fit with a three parameter model.
Comparison of primary and secondary aminosilance coupling agents in anhuydride‐curde epoxy fiberglass composites
Authors: Chiang Chwan‐Hwa , Koenig Jack L.
Published: May 2005

Fourier transform infrared spectroscopy (FT‐IR) has been utilized to investigate the interfacial chemical bonding at the interfaces of the aminosilanes and the nedic methyl anhydiride cured epoxy matrix in fiber‐reinforced composites. It is found that the nedic methyl anhydride can react with γ‐aminopropyltriethoxysilane (APS) and N‐methylaminoproplytrimethoxysilane (MAPS). In comparing the relative reactivities of two coupling agents to the epoxy resin, the secondary aminosilance has a higher reactivity than the primary aminosilance. An elevated temperature is required for the copolymerization to take place between the silane and the epoxy resin. The results indicate that covalent bonds form at the coupling agents. The molecular structure of the interface in MAPS treated fiberglass reinforced composites is different from that of the APS treated fiber composites. In addition, an accelerated copolymerization initiated by the coupling agent treated surface is also found in the resin interphase which may be important in determining the mechanical properties of the composites.
Fracture of adhesive joints
Authors: Wang S. S. , McGarry F. J. , Mandell J. F.
Published: May 2005

This paper presents some of the important results obtained from a series of studies on cohesive fracture in adhesively bonded joints. Due to the complex nature of the adhesive joint fracture, an accurate and efficient numerical method particularly suitable for the present problem has been developed, based on a hybrid‐stress finite element formulation. Fracture characteristics in adhesively bonded joints are described in terms of local crack‐tip deformation and stress fields in the polymeric adhesive layer. Effects of material properties, joint geometry, and bond‐line thickness on the crack behavior are studied for classical lap‐shear and currently used double‐cantilever‐beam joints. Of particular interest are the crack‐tip stress intensities in the adhesive layer; their values are obtained for several cases of practical importance.
Environmental testing of high strength molding compounds
Authors: Edwards Dale B. , Sridharan N. S.
Published: May 2005

Tensile and short beam shear tests were performed on five high strength vinyl ester molding compounds after immersion in water at various temperatures. These tests were conducted in order to characterize the degradation of these properties with environmental exposure and to isolate problem areas which contribute to the degradation. Reductions of up to 70 percent were found for both tensile and short beam shear strength, when tested at high temperatures. This loss of properties is primarily a result of degradation of the glass/resin interface and is essentially irreversible.
Joining strength of sheet molding compounds
Authors: Hoa S. V. , Feldman D.
Published: May 2005

Bonding and bolting strengths of a sheet molding compound (SMC‐R30) are investigated. Epoxy adhesives are found to give good bonding strength. Surface pretreatment does not affect bond strength. Artificial weathering has practically no effect upon bond strength. Bolting strength depends on the width of the specimen for a certain bolt size. Bolting gives stronger joints than bonding.
Application of a gripping system to test a uniaxial graphite fiber‐reinforced composite (PMR 15/celion 6000) in tension at 316°C
Authors: Whittenberger J. Daniel , Hurwitz Frances I.
Published: May 2005

A gripping system has been developed to test uniaxial, 0° orientation PMR 15/Celion 6000 composites at elevated temperatures. The method involves compression of grit‐blasted laminate between grit‐blasted metal to give a non‐slipping interface for load transfer. Tensile testing at both 316°C and room temperature indicated that deformation was elastic to fracture and that the variation in tensile properties for one laminate is the same as that for several panels. In addition, the tensile properties for uniaxial PMR 15/Celion 6000 are identical at 316°C and room temperature. For nominally 51 volume percent fiber, the elastic modulus is 119.6 GPa, the fracture stress is 1370 MPa, and the strain to fracture is about 1.15 percent. In addition, data are presented which indicate that the gripping system can be used for long term, elevated temperature testing of composite materials.
Influence of injection‐molding parameters on the morphology and mechanical properties of glass fiber‐reinforced polypropylene composites
Authors: Xavier S. F. , Tyagi D. , Misra A.
Published: May 2005

Polypropylene reinforced with glass fiber (28 percent by weight) was injection molded under different processing conditions. The influence of injection‐molding parameters such as pressure, injection speed, and injection temperature on the morphology and mechanical properties was studied using standard techniques, viz. polarizing microscope, scanning electron microscope, and Instron Universal testing machine. The observed mechanical properties were explained in terms of skin‐core‐morphology, transcrystallinity, fiber orientation and void volume. This study attempts to correlate processing conditions with morphology and mechanical properties. Such a study would help in optimizing processing conditions to give composites with desired properties.
Melt processible fluoropolymer composites
Authors: Crosby J. M. , Carreno C. A. , Talley K. L.
Published: May 2005

A series of melt‐processible fluoropolymer compounds including ethylene‐tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVF2), ethylene‐chlorotrifluoroethylene copolymer (ECTFE), perfluoroalkoxy modified tetrafluoroethylene (PFA), and fluorinated ethylene‐propylene copolymer (FEP) containing reinforcing glass fiber, milled glass fiber, carbon fiber, minerals, poly(tetrafluoroethylene) (PTFE) lubricant powder, graphite powder and MoS2 were prepared and characterized. The mechanical, physical, thermal, and tribiological properties of these composites were compared and ranked for suitability in various applications. These composites represent the first comprehensive evaluation of reinforced and filled meltprocessible fluoropolymer composites.
Polymer impregnation of tuff
Authors: Aurisicchio S. , Masi P. , Nicolais L. , Evangelista A. , Pellegrino A.
Published: May 2005

Polymer impregnation has been proven to increase environmental and mechanical resistance of tuff (a soft volcanic rock), suggesting its potential application for restoration of monuments or reinforcement of structures. The influence of monomer viscosity and applied pressure on the penetration rate of the liquid into pores, the monomer evaporation from the pores, and the effect of the curing temperature on the polymerization rate were studied. The data are analyzed in terms of the existing phenomenological or analytical models. The results can be used to develop a practical and economical large‐scale process.
Exact and approximate strain‐optic laws for photoelastic composites
Authors: Agarwal B. D. , Chaturvedi S. K.
Published: May 2005

An exact strain‐optic law for othotropic materials has been derived using Pockels' theory of crystalline photoelasticity. The law requires three experimentally determined photoelastic constants. Photoelastic response of materials such as glass‐fiber‐reinforced epoxy or polyester composites subjected to any state of strain can be predicted through this law. However, due to practical difficulties, this law is not sufficient to solve for principal strain differences or the direction of principal strain from conventional measurements in a polariscope. An approximate strain‐optic law, which has been derived by minimizing square of the error between predictions of exact and approximate laws, can be employed to estimate the difference between principal strains and their directions. The error in using the approximate law appears to be small. The approximate strain‐optic law has been found to be preferable over an approximate stress‐optic law.
Forced torsional properties of PMR composites with varying nadic ester concentrations and processing histories
Authors: Hurwitz Frances I.
Published: May 2005

PMR polyimide resin was prepared from 4,4′‐methylenedianiline (MDA), the dimethyl ester of 3,3′,4,4′‐ benzophenonetetracarboxylic acid (BTDE) and the monomethyl ester of 5‐norbornene‐2,3‐dicarboxylic acid (NE). The NE group serves as a chain terminator and crosslinking site. PMR/Celion 6000 composites were fabricated from resins having varying NE concentrations using two molding processes, and the laminates characterized in forced torsion. Glass transition temperatures (Tg) of 360–390°C were observed in the crosslinked resins, as compared with the literature value of 284°C reported for the uncrosslinked systemTgdidnotdecrease with decreasing NE concentrations over the range from 2.0 to 1.25 moles. Stoichiometry, within the range studied, showed little influence on shear properties; however, a 25% variation in matrix shear modulus with processing was observed. TheG12values determined in forced torsion were in excellent agreement with those reported from tensile tests of ±45° laminates. A branching and possible secondary crosslink mechanism is proposed based on dynamic mechanical behavior and infrared spectra of the composites.
The effect of glass fibers on the rheological behavior of polypropylene melts between rotating parallel plates
Authors: Mutel A. T. , Kamal M. R.
Published: May 2005

The Rheometrics mechanical spectrometer has been employed in the parallel plate mode to study the rheological behavior of pure polypropylene resin and melts filled with 10, 20, 30, and 40 percent by weight glass fibers. Steady‐state shear data show that, for loadings above 20 percent fiber, increasing fiber loading leads to an increase in viscosity of the melt. The effect of increasing fiber content becomes smaller at higher shear rates. For the same loading range, fiber addition increases the first normal stress difference, and the effect of fiber loading becomes smaller with increasing shear rate. At 10 percent loading, the viscosity of the filled polymer melt is lower than that of the pure resin melt. These results require further confirmation.

Strain sweeps employing dynamic measurements in conjunction with the parallel plate mode of the Mechanical Spectrometer were carried out. In general, it was found the dynamic properties are strain dependent. Steady shear data employing the cone‐and‐plate mode were not repeatable.
Rheology of mica‐reinforced polyethylene melts
Authors: Fisa B. , Utracki L. A.
Published: May 2005

Seven samples of HDPE containing 0, 2, 5, 10, 25, 40 and 60 weight percent of mica were prepared on a roll mill at 200°C. The samples were tested at T = 150, 170, 190 and 210°C for a wide range of rate of deformation from 10−2 to 2 × 104 s−1. Both capillary and rotational rheometers were used. The samples were found to be thermally stable. The results indicate that η, G′, and G″ increase with mica content for the whole range of deformation rates. The relaxation time spectrum for the sample containing 60 weight percent of mica showed a particulate contribution. The zero shear viscosity was discussed in terms of suspension theories.
Particle flow and sintering processes in extrusion
Authors: Swanson C. L. , Fanta G. F. , Bagley E. B.
Published: May 2005

The flow mechanism of particulate polymers during processing is reviewed. The extrusion of starch‐g‐poly(methyl acrylate) polymers is a good example of this type of processing, since graft copolymers retain their granular appearance and do not melt, even at high temperature, due to the rigid starch matrix. The formation of a continuous plastic by extrusion is accomplished by the sintering of heat‐deformed granules in the high‐pressure zone of the extruder die. Photomicrographs confirm this mode of formation. Plots of flow rate through the extruder die versus pressure in the die are presented. Tensile strengths and percent elongation of extruded specimens are not greatly affected by variations in flow rate. The equilibrium moisture content (about 5 percent) of starch‐g‐poly(methyl acrylate) plasticizes the starch component and thus reduces the operating pressure in the die. Tensile strengths, however, are unaffected by the presence of equilibrium moisture. Final traces of residual acid (resulting from initiator solution) are difficult to remove from starch‐g‐poly(methyl acrylate), and prolonged heating of the graft copolymer in the presence of this acid results in polymer degradation.
Thermoplastic vs. thermosetting structural composites
Authors: Muzzy John D. , Kays Ancil O.
Published: May 2005

High performance composites are normally fabricated from continuous fiber and fabric reinforcements embedded in a thermosetting resin. Currently, thermoplastics are receiving considerable attention as matrix materials in structural composites. These thermoplastic composites can be fabricated by novel techniques which are less cumbersome and potentially faster than curing in an autoclave. In this paper, fabrication techniques and physical properties of thermosetting composites will be compared. Applications where thermoplastic composites are particularly well suited will be presented.
Stress‐rupture lifetime of a poly(ethylene terephthalate)/glass composite under an alkaline solution environment
Authors: Schultz J. M. , Lhymn Chang
Published: May 2005

Stress corrosion testing of injection molded, short‐fiber (E‐glass) reinforced poly(ethylene terephthalate) (PET), in a 10 weight percent NaOH solution, indicated that a PET‐matrix degradation mechanism was operating. This is in direct contrast to the fiber degradation observed in acidic (10 weight percent HCl solution) stress corrosion tests on this material. Stress‐rupture lifetime in the alkaline solution was shorter than that in the acidic solution, suggesting that the alkaline attack on the PET matrix is more aggressive than the acidic attack on the E‐glass fibers. In both environments, fiber/matrix interface deterioration was also observed. Alkaline lifetime versus toughness behavior has been analyzed by established statistical methodology, using the empirical lifetime expression and the Weibull distribution function.
Fatigue crack propagation in composites with spherical fillers‐II effect of the size of the filler
Authors: Gadkaree K. P. , Salee G.
Published: May 2005

A study of the effect of spherical glass beads of mean diameters of 46 microns, 89 microns, and 133 microns, on fatigue crack propagation rates, was carried out at ten and thirty weight‐percent beads. The resin was a low‐molecular‐weight [Mn= 8200, (MwMn) = 2.04] Bisphenol A‐terephthalate/isophthalate thermoplastic copolyester. Fatigue crack‐grwoth rates were measured using compliance method. The relationship between logarithm of stress intensity factor change and logarithm of crack‐growth rate is linear for 46 micron beads. For the 89 micron beads, the relationship is still approximately linear. The incorporation of 133 micron beads, however, results in large fluctuations in crack‐growth rates with changes in stress intensity factor range. A mechanism is proposed to explain this behavior. A relationship between interparticle distance and fatigue crack‐growth resistance is also observed.
Polyfunctional epoxies: Part I. rubber‐toughened brominated and nonbrominated formulations for graphite composites
Authors: Nir Z. , Gilwee W. J. , Kourtides D. A. , Parker J. A.
Published: May 2005

A new trifunctional epoxy resin, Tris‐(hydroxyphenyl)methane triglycidyl ether, was compared to a state‐of‐the‐art resin, 4,4′‐diaminodiphenyl methane (TGDDM), in graphite composites. Rubber‐toughened brominated and nonbrominated formulations were compared for their mechanical performance, environmental stability, thermochemical behavior, and flame retardancy. It was found that the new resin performs almost the same way as the TGDDM does, but has some improved properties. The fracture toughness of the various formulations was studied carefully and the overall performance of the new resin is discussed.
The matrix phase microstructure of a glass poly(ethylene terephthalate) injection‐molding compound
Authors: Lhymn Chang , Schultz J. M.
Published: May 2005

Microscopic observations of thermoplastic poly(ethylene terephthalate) reinforced with short E‐glass fibers revealed a unique matrix microstructure influenced by the orientation of densely packed glass fibers. The observed platelets tend to surround a fiber in a cylindrical sheath pattern. This observation of the crystalline platelet morphology is possible by the combination of ion‐etching and the shadowing effect of protruding fibers.
Three‐phase carbon microballoon syntactic foam composites
Authors: Kenig S. , Raiter I. , Narkis M.
Published: May 2005

This paper describes three‐phase syntactic foams consisting of microballoons, resin, and air voids. The microballoons comprise carbon and silica spheres in various proportions, always at a close‐packed structure (0.6 volume fraction). Compressive, electric, and dielectric properties are demonstrated as functions of parameters like resin content, temperature, and various carbon/glass proportions. The good combination of mechanical, thermal, and electrical properties may qualify these foams for applications including attenuation of electromagnetic radiation.
Composite‐material mechanics: Properties of planar‐random fiber composites
Authors: Bert Charles W. , Kline Ronald A.
Published: May 2005

This paper is primarily a literature review of over ten dozen papers on the methodology for predicting elastic stiffnesses, tensile strength, thermal expansion, and thermal conductivity of planar‐random fiber composites from the reinforcement geometry and appropriate properties of the constituent materials. Particular attention is devoted to the effects of fiber volume fraction, fiber curvature, fiber length, and fiber orientation, since variations in these properties can be introduced during the manufacturing process.
Cellulose‐Reinforced nylon‐reaction injection molded composites
Authors: Zadorecki Pawel , Abbås Kent B.
Published: May 2005

The properties of cellulose‐reinforced nylon‐6 block copolymers were studied. Composites were prepared by Reaction Injection Molding (RIM) of a nylon system in which one of the reactants contained cellulose fibers. Incorporation of cellulose fibers into the liquid reactant of the nylon‐RIM system resulted in increased viscosity, depending on the amount and the aspect ratio of cellulose fibers. After proper drying, cellulose did not disturb the polymerization of the nylon‐RIM system. The cellulose fibers increased the stiffness of the nylon‐6 block copolymer. The stiffening effect depended on the aspect ratio and surface treatment. The tensile strength of cellulose‐nylon composites was slightly decreased. Elongation at break and impact strength were reduced compared to glass fiber‐reinforced nylon. Dynamic mechanical measurements (DMA) showed that the cellulose improved the elastic modulus of the nylon, especially at elevated temperatures. Scanning Electron Microscopy (SEM) on fractured surfaces showed improved adhesion between fiber and matrix when a surface treated cellulose was used.
Characterization of the aramid: Epoxy and carbon: Epoxy interphases
Authors: Garton Andrew , Daly John H.
Published: May 2005

The matrix/reinforcement interphase in aramid fiber/epoxy and carbon fiber/epoxy composites were modeled by coating an internal reflection spectroscopy (IRS) element with a thin layer of an aramid or of carbonized poly(acrylonitrile) (PAN). The coated element was then used as a substrate on which the curing of an epoxy resin took place. Infrared (IR) spectroscopy was used to demonstrate that the simulated reinforcement surfaces modified the crosslinking chemistry in the first 200–400 nm of epoxy matrix adjacent to the surfaces, producing an interphase of matrix material with properties different from those of the bulk of the epoxy matrix. This hypothesis was confirmed by the fabrication and testing of a series of unidirectional aramid fiber/epoxy and carbon fiber/epoxy composites.
Dispersive mixing in roll‐mills
Authors: Manas‐Zloczower I. , Nir A. , Tadmor Z.
Published: May 2005

A theoretical model of the dispersive mixing process in roll‐mills is proposed. The model is based on the assumption that intensive mixing is dominated by agglomerate rupture in the narrow nip high shear flow field between the rolls. The dynamics of agglomerate size distribution and its dependencies on a number of variables and parameters are presented.
Composites containing glass spheres and fibers. I. Young's and flexural moduli
Authors: Dai S‐R. , Piggott M. R.
Published: May 2005

Experiments on sphere‐filled aligned fiber reinforced polyester resins show that the Young's and flexural moduli of the composites are increased by the presence of the spheres. The increase is particularly marked for composites made with flexible resins, and has potential for improving the properties of aligned fiber laminates. The moduli in the absence of fibers do not fit well with existing theory, and agreement with finite element analysis is only observed in the case of the rigid polyester. When fibers are present synergistic effects are observed.
Fiber orientation development in molding of polymer composites
Authors: Kenig S.
Published: May 2005

The hydrodynamics and heat transfer that take place during molding of short fiber polymer composites have been analyzed. Consequently, the fiber orientation development has been qualitatively modeled and the flow mechanisms that contribute to fiber orientation have been identified: 1. Spreading radial flow in the vicinity of the cavity gate, originates transverse orientation of fiber with respect to the flow direction. 2. The fountain flow in the advancing front contributes to orientation of fibers in the surface layer in the flow direction. 3. Converging type flow, as the melt front flattens, causes some alignment in the flow direction. 4. Shear flow, which in the nonisothermal case, contributes to fiber orientation in the flow direction, at some distance from the wall. As a result of these mechanisms a layered structure is formed, having distinct fiber orientations. The experimentally observed fiber distributions in injection molding of thermoplastics, transfer, and compression molding of thermosets, agree with the qualitative predictions. The suggested orientation mechanisms may guide the mold and product designers as to the effect of gate location, mold dimensions, and processing variables on the final properties of the article.
Experimental study and calculations of short glass fiber orientation in a center gated molded disc
Authors: Vincent M. , Agassant J. F.
Published: May 2005

Short glass fiber orientation in a center gated molded disc of polyamide is studied using optical microscopy techniques. The very different orientation between the core and the surface of the molding is quantified with an orientation function. The influence of the molding conditions is investigated. A numerical scheme is used for modeling the mold filling with a viscous melted polymer. A computation method is introduced to describe the fiber movement during the flow. The theoretical results are in good agreement with the experimental ones. In particular, the very different orientation between the skin and the core of the disc is well predicted.