Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Epoxy

  • neat epoxy
  • pure epoxy

  • Terms modified by Epoxy

  • epoxy alcohol
  • epoxy aldehyde
  • epoxy blend
  • epoxy composite
  • epoxy group
  • epoxy groups
  • epoxy ketone
  • epoxy matrix
  • epoxy monomer
  • epoxy nanocomposite
  • epoxy network
  • epoxy phase
  • epoxy resin
  • epoxy resin composite
  • epoxy specimen
  • epoxy system

  • Selected Abstracts

    An analytical approach to evaluate the coefficients of thermal expansion of textile composite materials

    POLYMER COMPOSITES, Issue 5 2000
    Yasser Gowayed
    An analytical approach is developed to evaluate the coefficients of thermal expansion (CTE) of textile reinforced composites. At the micro level, a cylindrical composite model is employed to model the fiber/matrix thermal and mechanical interactions. The effects of voids and fiber coating on the thermal expansion coefficients of composites are considered at this level. The cylindrical model was then embedded in a macro hybrid finite element solutio structure to calculate the value of the CTE for textile composites. AS-4/epoxy balanced plain weave textile composites were manufactured. Five different fiber volume fractions were tested for CTE. Evaluatio of the thermal expansion coefficients using the current model was compared to experimental data for in-plane and out-of-plane directions. [source]

    Epoxy-based production of wind turbine rotor blades: occupational dermatoses

    CONTACT DERMATITIS, Issue 6 2004
    A. Pontén
    Occupational dermatoses were investigated in a factory producing rotor blades for wind turbines by an epoxy-based process. In a blinded study design, 603 workers were first interviewed and thereafter clinically examined. Based on a history of work-related skin disease, clinical findings of dermatitis, or both, 325 (53.9%) of the workers were patch tested with a specially profiled occupational patch-test series and the European standard patch-test series. Calculated on all investigated workers, 17.1% of the workers were diagnosed with occupational dermatoses caused by work. Occupational allergic contact dermatitis was found in 10.9% of the workers. The estimated frequency of irritant contact dermatitis caused by work was 6.1%. Dermatitis on the hands was associated with contact allergy to epoxy resin (P = 0.017). The number of days on leave before the clinical examination was negatively associated with the presence of dermatitis (P = 0.001). Among workers employed 7,12 months, the frequency of occupational contact allergy was higher than that among workers employed for ,6 months (P = 0.004). Females both washed their hands more often (P < 0.001) and used more moisturizers/protection creams at work (P < 0.001) than males. No sex differences were found concerning dermatitis on the hands. [source]

    Kinetics and mechanism of esterification of epoxy resin in presence of triphenylphosphine

    Neelam Pal
    The kinetics of esterification of bisphenol-A based epoxy resin with acrylic acid in presence of triphenylphosphine has been studied. The reaction exhibits a first-order rate dependence with respect to [Epoxy] and [Catalyst]. A first-order dependence of rate with respect to [Acid] has been observed during a particular kinetic run. However, a retarding effect of [Acid] on the rate has been observed by increasing the initial concentration of acid. A suitable mechanism consistent with the kinetic data is proposed and discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 280,285, 2004 [source]

    Epoxy,siloxane hybrid coatings by a dual-curing process

    Giulio Malucelli
    Abstract Coatings based on a hybrid organic,inorganic epoxy system were prepared by a dual-curing mechanism, via cationic photopolymerization in the first step at room temperature and a subsequent hydrolysis/condensation reaction of a trialkoxy-silane compound (sol,gel process) at high temperature. To this end, a high Tg epoxy resin (3,4-epoxycyclohexylmethyl-3,-cyclohexenyl-methyl adipate, UVR 6128) was added in increasing amounts to a precursor for the inorganic-like phase (3,4-epoxycyclohexylethyltrimethoxysilane, EETMOS). The mixture contained triphenylsulfoniumhexafluoroantimonate as a cationic photoinitiator. By this method, the strongly acid environment generated by the photolysis of the triarylsolfunium salt in the first step induces the hydrolysis of EETMOS alkoxy-silane groups. The films produced in the first step of the process were thermal treated to promote the condensation reactions of the siloxane moieties. The kinetics of the reactions of photopolymerization and condensation was investigated. It was found that the presence of EETMOS increases both the polymerization rate and the final consumption of epoxy groups. Thermogravimetric analyses performed in air have revealed an increased stability of the hybrid coatings with respect to the films produced from formulations without EETMOS. A significant increase in surface hardness was also observed for the hybrid coatings. The thermo-mechanical properties were found to be strongly affected by the temperature used in the thermally induced reactions in the second step. The hybrid coatings on a low-density polyethylene substrate were found to decrease the diffusivity of oxygen and to increase the oxygen solubility within the coating. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:77,85, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20149 [source]

    Nanoclay and long-fiber-reinforced composites based on epoxy and phenolic resins

    Gang Zhou
    Abstract In this study, high-performance thermoset polymer composites are synthesized by using both long fibers and nanoclays. Epoxy and phenolic resins, the two most important thermoset polymers, are used as the polymer matrix. The hydrophobic epoxy resin is mixed with surface modified nanoclay, while the hydrophilic phenolic resin is mixed with unmodified raw nanoclay to form nanocomposites. Long carbon fibers are also added into the nanocomposites to produce hybrid composites. Mechanical and thermal properties of synthesized composites are compared with both long-fiber-reinforced composites and polymer- layered silicate composites. The optimal conditions of sample preparation and processing are also investigated to achieve the best properties of the hybrid composites. It is found that mechanical and thermal properties of epoxy and phenolic nanocomposites can be substantially improved. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Studies on thermal and morphological properties of 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane-epoxy-bismaleimide matrices

    K. Dinakaran
    Abstract A new cyanate ester monomer, 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane has been synthesized and characterized. Epoxy modified with 4, 8 and 12% (by weight) of cyanate ester were made using epoxy resin and 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane and cured by using diaminodiphenylmethane. The cyanate ester modified epoxy matrix systems were further modified with 4, 8 and 12% (by weight) of bismaleimide (N,N,-bismaleimido-4,4,-diphenylmethane). The formation of oxazolidinone and isocyanurate during cure reaction of epoxy and cyanate ester blend was confirmed by IR spectral studies. Bismaleimide-cyanate ester-epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. Thermal studies indicate that the introduction of cyanate ester into epoxy resin improves the thermal degradation studies at the expense of glass transition temperature. Whereas the incorporation of bismaleimide into epoxy resin enhances the thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influences the thermal properties according to their percentage content. DSC thermogram of cyanate ester modified epoxy and bismaleimide modified epoxy show unimodel reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured bismaleimide modified epoxy and cyanate ester-epoxy systems increased with increasing bismaleimide content. The morphology of the bismaleimide modified epoxy and cyanate ester-epoxy systems were also studied by scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    ChemInform Abstract: An Efficient Synthetic Method for 3-Bromofuran Derivatives via Stereoselective Cyclization of ,,,-Epoxy-(E)-,-bromoacrylates.

    CHEMINFORM, Issue 23 2009
    Fumihiko Yoshimura
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Synthesis of Hexabromo, Hydroxy, Epoxy, Methoxy and Nitroxy Derivatives of Tetralins and Naphthalenes.

    CHEMINFORM, Issue 7 2005
    Ramazan Erenler
    No abstract is available for this article. [source]

    Oxazolinyloxiranyllithium-Mediated Stereoselective Synthesis of ,-Epoxy-,-amino Acids.

    CHEMINFORM, Issue 47 2003
    Renzo Luisi
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]

    ChemInform Abstract: Stereospecific ,-Lithiation of Oxazolinyloxiranes: Synthesis of ,,,-Epoxy-,-butyrolactones

    CHEMINFORM, Issue 37 2002
    Vito Capriati
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Mechanical and viscoelastic properties of semi-interpenetrating polymer networks of poly(vinyl chloride)/thermosetting resin blends

    Charles U. Pittman Jr.
    Semi-interpenetrating polymer networks (SIPNs) of PVC/thermoset were prepared by premixing porous, 150 ,m diameter particles of PVC and a small quantity (from 5 to 15% by weight) of a single thermosetting liquid preresin from one of five types (e.g. methylene bis-phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), toluene diisocyanate (TDI) prepolymer, epoxy, and vinyl ester resins, respectively). Two roll milling of these mixtures was followed by hot-press curing. Mechanical testing indicated that most of these blends exhibited increased tensile, impact, and flexural strengths. The strength increments were greater when going from 0 to 5% thermoset content than when going from 5 to 10% or 10 to 15% thermoset. In many cases, increasing thermoset content from 10 to 15% gave slightly decreased or unchanged tensile, impact, and flexural strengths. This behavior is in accord with a "thermoset dilution effect" in PVC. Most of these SIPN blends exhibited a tan , peak temperature lower than that for pure PVC in the glass transition region. The tan , peak temperatures were progressively lowered as the amounts of thermoset increased. Also, a single distinct peak existed in the E, curves for most of the blends. Only the PVC/epoxy (90/10) blend showed two peak maxima in E, vs. temperature curves. All blends exhibited peak E, values at a lower temperature than those of PVC which had been exposed to the same processing temperatures. These observations seem to rule out the presence of large domains of PVC, which are phase-separated from PVC/thermoset SIPN, and pure thermoset domains. A substantial amount of the added thermoset appears to exist in SIPN type phases in these five blend types. [source]

    Porous epoxies by reaction induced phase separation of removable alcohols: Control of spheroidal pore size by mass fraction, cure temperature, and reaction rate,

    Robert J. Klein
    Abstract Porous organic and inorganic materials with both random and controlled microstructures have utility in a variety of fields including catalysis, sensors, separations, optical platforms, tissue engineering, hydrogen storage, micro-electronics, medical diagnostics, as well as other applications. This work highlights a simple and general technique for tuning the pore size in crosslinking polymeric systems by adding a solvent poragen that phase separates during the curing process (reaction induced phase separation). The pore size can be controlled over large length scales ranging from microns to well below 100 nanometers. In this system an amine cured epoxy resin was reacted in the presence of the sacrificial poragen octadecanol, which is removed by vacuum-assisted evaporation once the epoxy components have reacted to form a solid, porous matrix. The importance of the present approach is based on the simplicity of the chemical formulation, the ease by which other epoxide or amine chemistries may be substituted for the two reactive components, and the control of pore size down to the nanometer scale by the addition of a small amount of catalyst. © 2010 Wiley Periodicals, Inc., J Appl Polym Sci, 2010 [source]

    Moisture absorption behavior of epoxies and their S2 glass composites

    Amit Chatterjee
    Abstract The influence of moisture exposure on the behavior of three toughened epoxy,amine systems (scrimp resins SC11, SC15, and SC79, Applied Poleramic, Inc., Benicia, CA) was investigated. Neat resin samples were conditioned by immersion in distilled water at 71°C and in an environmental chamber at 85% relative humidity and 87.8°C until saturation. The equilibrium weight gain ranged from 1.8 to 3.8% for the resins. The long-chain, low-crosslink-density epoxy system (SC11) absorbed the highest amount of water and was saturated first, and it was followed by the medium-crosslink-density (SC15) and high-crosslink-density materials (SC79). The moisture diffusivity decreased with the increasing crosslink density of the resins. The percentage reduction of the glass-transition temperature (Tg) at equilibrium moisture absorption was highest for the low-crosslink molecule. The percentage reductions for the medium-crosslink and higher crosslink systems were comparable. A net weight loss after drying was observed for the SC11 and SC79 resin systems. Fourier transform infrared analysis confirmed the segment breakage and leaching of molecules from the epoxy,amine network. The effects of moisture cycling on Tg were dependent on the epoxy,amine morphology. During the drying stage, Tg increased to a value higher than that of the unaged dry systems. The S2 glass composite samples were conditioned under identical conditions for the resin system. Composite systems absorbed less moisture than the neat resins as expected. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

    Phase behavior and photo-responsive studies of photoactive liquid crystalline hyperbranched polyethers containing benzylidene moiety

    V. Srinivasa Rao
    Abstract Two sets of hyperbranched polyether epoxies were synthesized to study the effect of substituent, rigidity, and nature of photoactive unit on the thermal and photoresponsive properties. Each set was comprised of one molecule with an acyclic moiety in the repeating unit, and two molecules with a cyclic moiety of varying rigidity (cycle size) in the repeating unit. Two substituents on aromatic rings in the repeating unit were present in one set, and other set was without a substituent. The mesogenic and photoresponsive properties were studied and correlated to the varied structural parameters. The effects of varied molecular structural parameters on phase behavior and photoresponsive properties were very prominent. Out of six monomeric diols, only four have exhibited liquid crystalline phase while the polymers corresponding to all monomeric diols revealed mesophase. The findings in photoresponsive properties were further supported by molecular modeling studies. The changes in refractive index, photoviscosity, and fluorescence intensity with irradiation time substantiated the spectral pattern observed in UV-Vis spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2774,2786, 2009 [source]

    Effect of molecular architecture and size of mesogen on phase behavior and photoactive properties of photoactive liquid crystalline hyperbranched polyester epoxies containing benzylidene moiety

    V. Srinivasa Rao
    Abstract A series of photoactive liquid crystalline linear and hyperbranched polyester epoxies were synthesized by polyaddition of photoactive bis benzylidene alkanone diol monomers and terephthalic acid and trimesic acid respectively with good yield. The effect of molecular architecture (linear and hyperbranched), size of mesogenic unit (cyclic and acyclic units) on the physicochemical, thermal, mesogenic, and photoactive properties of hyperbranched polymers were studied and compared. Degree of branching of hyperbranched polymers was found to be in the range of 0.46,0.49. Monomers containing cyclic moieties only exhibited nematic mesophase, while all polymers exhibited typical nematic mesophase. Intermolecular photo cycloaddition reaction was studied by ultraviolet,visible spectra (UV,vis) and NMR spectroscopy and photo viscosity measurement of UV irradiated polymer solutions. Faster photo induced behavior of hyperbranched polymers containing acyclic alkanone moiety, as compared to polymers containing cycloalkanone moieties, was observed. The change in the refractive index was found to be in the range of 0.02,0.024. Substantial variation of refractive index indicates that this polymer could be used for optical recording. All the polymers were also found to be fluorescent in nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 552,563, 2008 [source]

    Influence of substituents on the kinetics of epoxy/aromatic diamine resin systems

    Heping Liu
    Abstract Eleven different epoxy/diamine systems, including tetraglycidyl-4,4,-diaminodiphenylmethane (TGDDM), triglycidyl p -aminophenol (TGAP), and diglycidyl ether of bisphenol A (DGEBA) with 4,4,-diaminodiphenylsulfone (DDS), diethyltoluenediamine (DETDA), dimethylthiotoluenediamine (DMTDA), and meta -phenylenediamine (m -PDA), were studied with near-infrared spectroscopy at different temperatures. The reactivities of the epoxies were determined and found to be in the following order when reacted with the same amine: DGEBA > TGAP > TGDDM. When the primary amine was reacted with the same epoxy, the order was DETDA > DDS > DMTDA; for the secondary amine, the order was DETDA > DMTDA > DDS. The relative reaction rates of the secondary amine to the primary amine were compared and discussed in terms of the structural differences and the corresponding substitution effect. It was concluded that the increase in the secondary amine reactivity of DETDA and DMTDA was caused by the deconjugation of the benzene-ring , electrons from the lone pair on the N atom. The overall order of the secondary amine relative reactivity was DMTDA > DETDA > DDS for the same epoxy and TGDDM > TGAP > DGEBA for the same amine. The m -PDA systems had no significant positive or negative substitution effects. Molecular orbital calculations were performed, and the results showed the most significant deconjugation effect in the secondary amine of DETDA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3143,3156, 2004 [source]

    Synthesis, characterization, and thermal properties of ladderlike polyepoxysiloxanes

    Yuhui Lin
    Abstract Starting from trichlorosilanes and using 1,4-phenylenediamine as a template, we have synthesized some ladderlike poly(glycidyl- co -alkyl/aryl)siloxanes (polyepoxysiloxanes or polyepoxies for short). The structures of copolymers were confirmed through IR, 1H NMR, elemental analyses, and gel permeation chromatography. Curing behaviors of these polyepoxies in the absence and presence of a curing agent have been studied with DSC. It was shown that these epoxies could be cured without any curing agent. Copolymers having aromatic groups showed higher curing reactivity than those having alkyl groups. The experimental results also demonstrate that the curing reaction occurred solely via epoxy functionality, not via the condensation reaction of the hydroxy groups located at the end of polymer main chains. The thermal stability of the cured polymers was examined by thermogravimetric analysis. The results confirm that polyepoxies with aromatic groups had better thermal stability than those with alkyl groups. It was also found that polyepoxies cured with a diamine have a higher thermal stability than those cured in the absence of a curing agent. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2215,2222, 2001 [source]

    Effects of rubber-rich domains and the rubber-plasticized matrix on the fracture behavior of liquid rubber-modified araldite-F epoxies

    Keqin Xiao
    The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl-terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, KIC, measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber-rich domains and the structure of the rubber-rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy-residing dispersed rubber phase and the rubber-dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process. [source]

    Novel epoxy compositions for vibration damping applications

    D. Ratna
    Abstract Three epoxy compositions have been developed by using polyether amine hardeners having varying chain lengths of polyethers. Unlike normal epoxies, the compositions show low glass transition temperatures (0,45°C). Dynamic mechanical analysis and time,temperature superposition of the isotherms indicate that they have broad and high loss factor values over broad frequency and temperature ranges suggesting their application as viscoelastic materials in constrained layer damping of structural vibrations. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Contact allergy to epoxy (meth)acrylates

    CONTACT DERMATITIS, Issue 1 2009
    Kristiina Aalto-Korte
    Background: Contact allergy to epoxy (meth)acrylates, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]propane (bis-GMA), 2,2-bis[4-(2-hydroxy-3-acryloxypropoxy)phenyl]-propane (bis-GA), 2,2-bis[4-(methacryl-oxyethoxy)phenyl] propane (bis-EMA), 2,2-bis[4-(methacryloxy)phenyl]-propane (bis-MA), and glycidyl methacrylate (GMA) is often manifested together with contact allergy to diglycidyl ether of bisphenol A (DGEBA) epoxy resin. Objective: To analyse patterns of concomitant allergic reactions to the five epoxy (meth)acrylates in relation to exposure. Methods: We reviewed the 1994,2008 patch test files at the Finnish Institute of Occupational Health (FIOH) for reactions to the five epoxy (meth)acrylates, and examined the patients' medical records for exposure. Results: Twenty-four patients had an allergic reaction to at least one of the studied epoxy (meth)acrylates, but specific exposure was found only in five patients: two bis-GMA allergies from dental products, two bis-GA allergies from UV-curable printing inks, and one bis-GA allergy from an anaerobic glue. Only 25% of the patients were negative to DGEBA epoxy resin. Conclusions: The great majority of allergic patch test reactions to bis-GMA, bis-GA, GMA and bis-EMA were not associated with specific exposure, and cross-allergy to DGEBA epoxy resin remained a probable explanation. However, independent reactions to bis-GA indicated specific exposure. Anaerobic sealants may induce sensitization not only to aliphatic (meth)acrylates but also to aromatic bis-GA. [source]

    Epoxy-based production of wind turbine rotor blades: occupational dermatoses

    CONTACT DERMATITIS, Issue 6 2004
    A. Pontén
    Occupational dermatoses were investigated in a factory producing rotor blades for wind turbines by an epoxy-based process. In a blinded study design, 603 workers were first interviewed and thereafter clinically examined. Based on a history of work-related skin disease, clinical findings of dermatitis, or both, 325 (53.9%) of the workers were patch tested with a specially profiled occupational patch-test series and the European standard patch-test series. Calculated on all investigated workers, 17.1% of the workers were diagnosed with occupational dermatoses caused by work. Occupational allergic contact dermatitis was found in 10.9% of the workers. The estimated frequency of irritant contact dermatitis caused by work was 6.1%. Dermatitis on the hands was associated with contact allergy to epoxy resin (P = 0.017). The number of days on leave before the clinical examination was negatively associated with the presence of dermatitis (P = 0.001). Among workers employed 7,12 months, the frequency of occupational contact allergy was higher than that among workers employed for ,6 months (P = 0.004). Females both washed their hands more often (P < 0.001) and used more moisturizers/protection creams at work (P < 0.001) than males. No sex differences were found concerning dermatitis on the hands. [source]

    Mechanical Characterization of Particulate Aluminum Foams,Strain-Rate, Density and Matrix Alloy versus Adhesive Effects

    Dirk Lehmhus
    Abstract The study evaluates mechanical properties of APM particulate aluminum foams built up from adhesively bonded Al foam spheres. Foams of matrix alloy AlSi10 are compared, with PM AlSi7 foams used as reference. The influence of density is studied both for quasi-static and dynamic compressive loading in a range from ,0.35 to 0.71,g,cm,3. The effect of varying the bonding agent is evaluated for a single density and both strain rate levels by replacing the standard, high-strength epoxy-based adhesive with a polyamide of greatly increased ductility. The result is a clear shift of fracture events to higher strain levels, as well as the introduction of a strain-rate dependency of strength. [source]

    Immunocytochemical characterization of ectopic enamel deposits and cementicles in human teeth

    Dieter D. Bosshardt
    Despite the relative frequency and clinical relevance of radicular enamel deposits and cementicles, their etiology and nature are unknown. The purpose of the present study was therefore to evaluate the presence and distribution of mineralization-associated non-collagenous matrix proteins (NCPs) in various types of root-associated ectopic mineralizations. Human teeth were processed for embedding in epoxy or acrylic resins. Tissue sections were incubated with antibodies to amelogenins (AMEL), bone sialoprotein (BSP), and osteopontin (OPN). Radicular enamel deposits contained residual organic matrix that labeled for AMEL. In contrast, BSP and OPN were not detected in the residual enamel matrix, they were found in the cementum deposited on its surface as well as in collagen-free cementicle-like structures in the adjacent periodontal ligament. True cementicles consisted of a collagenous matrix intermixed with a non-collagenous ground substance. Labeling for BSP and OPN was mainly associated with the interfibrillar ground substance. No immunoreactivity for AMEL was detected in cementicles. These data indicate that ectopic enamel deposits on the root retain a high amount of AMEL, whereas cementicles contain BSP and OPN, two NCPs typically found in bone and cementum. These NCPs may, like in their normal tissue counterparts, play a role in the mineralization process. [source]

    J -Based Analysis and DFT,NMR Assignments of Natural Complex Molecules: Application to 3,,7-Dihydroxy-5,6-epoxycholestanes

    Jesús Javier Poza
    Abstract In order to reproduce the stereochemical dispositions of the epoxy and hydroxy functionalities, four 3,,7-hydroxy-5,6-epoxycholestanes were easily prepared from cholesterol, and their NMR spectroscopic data were experimentally obtained from 1D and 2D NMR experiments. An exhaustive QM- J -based analysis was then performed to replicate the experimental H,H and C,H coupling constants as well as the 13C NMR chemical shifts. The B3LYP GIAO methodology with the 6-311-G(d,p) basis set was chosen and showed that the data obtained from rings A and B were sufficient to calculate the correct stereochemistry of the 5,6-epoxy and 7-hydroxy groups. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Asymmmetric Diamino Functionalization of Nanotubes Assisted by BOC Protection and Their Epoxy Nanocomposites

    Yao Zhao
    Abstract Homogenous dispersion and strong interfacial bonding are prerequisites for taking full advantage of the mechanical properties of nanotubes in a composite. In order to simultaneously achieve both conditions, a highly efficient and mechanically non-destructive functionalization of nanotubes is developed. With fluoronanotubes as the precursor, asymmetric diamine molecules, N -BOC-1,6-diaminohexane, are used to replace fluorines on the wall of fluoronanotubes and construct covalent bonding to the surface of the nanotubes. A BOC de-protection reaction is conducted and the resulting exposed amino groups create strong covalent bonds with the matrix in the course of epoxy ring-opening etherification and curing chemical reactions. In comparison with the conventional functionalization based on symmetric diamine molecules, the functionalized nanotubes derived from the BOC-protected diamine molecule are more dispersed within the epoxy matrix. Dynamic mechanical analysis shows that the functionalized nanotubes have better crosslinking with the matrix. The composites reinforced by the nanotubes demonstrate improvement in various mechanical properties. The Young's Modulus, ultimate tensile strength, and storage modulus of composites loaded with 0.5 wt% functionalized nanotubes are enhanced by 30%, 25%, and 10%, respectively, compared with the neat epoxy. The increase of the glass transition temperature, as much as 10 °C, makes the composites suited for engineering applications under higher temperatures. The new functionalization method allows for an competitive enhancement in the composite performance in use of relatively low cost raw nanotubes at a small loading level. The reinforcement mechanism of the functionalized nanotubes in the epoxy resin is discussed. [source]

    Effects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae

    FEBS JOURNAL, Issue 6 2000
    Till Böcking
    Photodynamic treatment of the yeast Saccharomyces cerevisiae with the singlet oxygen sensitizer toluidine blue and visible light leads to rapid oxidation of ergosterol and accumulation of oxidized ergosterol derivatives in the plasma membrane. The predominant oxidation product accumulated was identified as 5,,6,-epoxy-(22E)-ergosta-8,22-dien-3,,7,-diol (8-DED). 9(11)-dehydroergosterol (DHE) was identified as a minor oxidation product. In heat inactivated cells ergosterol is photooxidized to ergosterol epidioxide (EEP) and DHE. Disrupted cell preparations of S. cerevisiae convert EEP to 8-DED, and this activity is abolished in a boiled control indicating the presence of a membrane associated enzyme with an EEP isomerase activity. Yeast selectively mobilizes ergosterol from the intracellular sterol ester pool to replenish the level of free ergosterol in the plasma membrane during singlet oxygen oxidation. The following reaction pathway is proposed: singlet oxygen-mediated oxidation of ergosterol leads to mainly the formation of EEP, which is enzymatically rearranged to 8-DED. Ergosterol 7-hydroperoxide, a known minor product of the reaction of singlet oxygen with ergosterol, is formed at a much lower rate and decomposes to give DHE. Changes of physical properties of the plasma membrane are induced by depletion of ergosterol and accumulation of polar derivatives. Subsequent permeation of photosensitizer through the plasma membrane into the cell leads to events including impairment of mitochondrial function and cell inactivation. [source]

    Functionalization Strategies for Protease Immobilization on Magnetic Nanoparticles

    Dan Li
    Abstract A comprehensive study on the general functionalization strategies for magnetic nanoparticles (MNPs) is presented in this work. Using well-established techniques as well as modified protocols, the wide range of functional moieties grafted on ,-Fe2O3 (maghemite) nanosurfaces include those of amine, aldehyde, carboxylic, epoxy, mercapto, and maleimide ends. Among the modified protocols are the one-step water-catalyzed silanization with mercaptopropyltrimethoxysilane, resulting in dense distal thiols, and the direct functionalization with a heterogeneous bifunctional linker N -[p-maleimidophenyl]isocynanate (PMPI). The former results in a protective Stöber type coating while simultaneously reducing the iron oxide core to magnetite (Fe3O4). The conjugation of trypsin, hereby chosen as model biomolecule, onto the differently functionalized MNPs is further demonstrated and assessed based on its activity, kinetics, and thermo-/long-term stability as well as reusability. Besides aqueous stability and ease in recovery by magnetic separation, the immobilized trypsin on MNPs offers superior protease durability and reusability, without compromising the substrate specificity and sequence coverage of free trypsin. The MNP-based proteases can be used as valuable carriers in proteomics and miniaturized total analysis devices. The applicability of the functional surfaces devised in the current study is also relevant for the conjugation of other biomolecules beyond trypsin. [source]

    Graphite Oxides Obtained from Porous Graphite: The Role of Surface Chemistry and Texture in Ammonia Retention at Ambient Conditions

    Mykola Seredych
    Abstract Graphite oxides (GO) synthesized using Brodie and Hummers methods are tested for ammonia adsorption at ambient conditions with different contents of water in the system. Surface characterization before and after exposure to ammonia is performed using XRD, FTIR spectroscopy, potentiometric titration, thermal analysis, adsorption of nitrogen, and XPS. Oxidation of the same porous graphite using two methods results in materials with different textural and chemical features. On GO obtained using the Brodie method mainly epoxy and carboxylic groups are present whereas on the GO obtained using the Hummers method chemisorbed oxygen is also found. The contribution of the carboxylic groups in the latter material is greater. It also contains sulfur either in sulfones or as residual sulfuric acid. Ammonia is adsorbed either via reaction with surface groups or dissolution in water. The former is responsible for strong adsorption. The evidence of the catalytic effect of the carbon surface on activation of oxygen leading to surface oxidation is also observed. [source]

    Cone calorimeter testing of S2 glass reinforced polymer composites

    FIRE AND MATERIALS, Issue 7 2009
    Alexander B. Morgan
    Abstract With the ever increasing demand for fuel savings on vehicles, there is a strong push to replace metal with polymeric + fiber (carbon/glass) composites. However, the replacement of metal with polymeric composites can lead to additional fire risk. Our study focused on glass fiber reinforced polymer composites meant for vehicular structural applications, and flammability performance of these composites was studied by cone calorimetery. The effects of fiberglass loading, nanocomposite use (clay, carbon nanofiber) and polymer type (epoxy, phenolic) were studied under a heat flux of 50kW/m2 to better understand the potential effects that these variables would have on material flammability. It was found that as fiberglass loading increased, flammability decreased, but at a cost to structural integrity of the residual polymer + fiber char. The use of nanocomposites has little effect on reducing flammability in this set of samples, but the use of phenolic resins in comparison with epoxy resins was found to yield the greatest improvements in flammability performance. Further, the phenolic system yielded a higher level of structural integrity to the final polymer + fiberglass char when compared with the other polymer systems of low heat release. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Self-Healing Materials: A Facile Strategy for Preparing Self-Healing Polymer Composites by Incorporation of Cationic Catalyst-Loaded Vegetable Fibers (Adv. Funct.

    Discontinuous sisal fibers carrying extremely active (C2H5)2O·BF3 are embedded in epoxy matrix together with epoxy monomer-loaded microcapsules to fabricate self-healing composite based on the healing mechanism of cationic chain polymerization. This approach, described by D. S. Xiao et al. on page 2289, skips the encapsulation of high activity chemicals, reducing the risk of their deactivation during handling. It provides a facile strategy for making extrinsic self-healing polymeric materials. [source]