Showing papers on "Epoxy published in 1994"

Complete acoustic band gaps in periodic fibre reinforced composite materials: the carbon/epoxy composite and some metallic systems

Abstract: We present results of elastic band structure for two-dimensional composite materials, composed of periodical square arrays of parallel cylinders in a background. We reveal, for the first time, the existence of several very large complete band gaps in the band structure of a material of practical interest such as a C fibre reinforced epoxy composite. Within these gaps the propagation of acoustic waves is forbidden. The influence of the geometry of the cylinders and the effect of the composition of the composite material on the band structure are studied. We also compare these results with those obtained for metallic composites such as W (Al) cylinders in an Al (W) matrix. The complete band gaps are observed in the cases of C cylinders in epoxy or W cylinders in Al, but not in the opposite situations. We discuss the existence of these gaps in relation to the physical parameters of the materials involved.

Thermoplastic-toughened epoxy polymers

Abstract: The microstructure and properties of two epoxy-resin systems which have been modified with varying amounts of a thermoplastic to improve the toughness of the thermosetting epoxy polymers, have been studied. The curing agent was 4,4′ diaminodiphenylsulphone and the thermoplastic was a reactively terminated poly (ether sulphone) copolymer. Different microstructures were found to occur as the concentration of the thermoplastic component was steadily increased. In particular, the relationships between the microstructures and values of stress-intensity factor, KIc, and fracture energy, GIc, were explored.

Plate bonding : strengthening of existing concrete structures with epoxy bonded plates of steel or fibre reinforced plastics

Abstract: This thesis deals with several aspects of the plate bonding problem, i.e. when steel or fibre reinforced plastics (FRP) plates are bonded to a concrete structure with the use of an epoxy adhesive. ...

Reduction of residual stress in montmorillonite/epoxy compounds

Abstract: An epoxy resin was cured while in intimate contact with small amounts of epoxyphilic montmorillonites. It was determined that cured epoxy exists within the montmorillonite interlayer by the observation of very high interlayer spacings, even greater than 8 nm, Generally, epoxy compounds containing montmorillonites that had been swollen in the curing agent prior to curing exhibited larger interlayer spacings, especially among the non-dispersed montmorillonite layers. The maximum observed residual stress was reduced by greater than 50% in the epoxyphilic montmorillonite/epoxy compounds over that of the pure epoxy. The epoxyphilic montmorillonite/epoxy compounds generally exhibited higher values of glass transition temperature, flexural modulus, and ultimate flexural strength than the pure epoxy. The tyramine-montmorillonite compounds typically had the highest values overall.

Physical aging studies in epoxy resins. I. Kinetics of the enthalpy relaxation process in a fully cured epoxy resin

Abstract: The physical aging of an epoxy resin based on DGEBA cured by a hardener derived from phthalic anhydride has been studied by DSC. The isothermal curing of the epoxy resin was carried out in one step at 130°C for 8 h, obtaining a fully cured resin whose T g was 98.9°C. Samples were aged at temperatures between 50 and 100°C for periods of time from 15 min to a maximum of 1680 h. The enthalpy relaxation was found to increase gradually with aging time to a limiting value where structural equilibrium is reached

Lifetime Prediction for Organic Coatings on Steel and a Magnesium Alloy Using Electrochemical Impedance Methods

Abstract: Electrochemical impedance studies were conducted on an epoxy polyamide-coated AISI1010 steel (UNS G10100) and an epoxy/chromate conversion-coated magnesium (Mg) alloy ZE41A-T5 (UNS M16410)...

Erosion resistant surface protection

Abstract: A coating for protection of airfoil surfaces from erosion caused by the impingement of particles in the incoming air stream of a gas turbine engine or on helicopter blades. The coating consists of an epoxy film toughened with hard particles to improve the erosion resistance and softer particles which impede the progression of cracks through the coating. A method for applying the coating is also described.

Fire performance studies on glass-reinforced plastic laminates

Abstract: Polyester, epoxy and phenolic glass-reinforced laminates were compared in terms of their fire properties in the cone calorimeter. The presence of a gel coat on the polyester and epoxy products had some effect, mainly in the FR grades. The FR polyester with a brominated flame retardant showed a marked decrease in rate of heat release and in rate of smoke production. Aluminium hydroxide (commonly called alumina trihydrate of ATH) caused a significant delay in ignition time for the epoxy product and some reduction in rate of heat release but rate of smoke release was still relatively high. Phenolic laminates showed a long ignition time and relatively low rate of heat release (RHR). The peak RHR was further reduced by the presence of aluminium hydroxide and by changing the type of glass reinforcement. The influence of thickness was explored for a series of phenolic laminates in both cone calorimeter and the International Maritime Organization (IMO) surface flammability test. Ignition delay time was significantly affected and the cone calorimeter results showed that the shape of the RHR curve was also changed as the thickness increased. However, the heat release measurements in the IMO test were not sensitive enough to pick up the differences in this property. The type of substrate under the laminate significantly altered the burning rate but this may have been because they were not glued or mechanically fixed.

In situ cure monitoring of epoxy resins using fiber-optic raman spectroscopy

Abstract: Fiber-optic Raman spectroscopy was used to monitor the curing of epoxy resins in situ for eventual application to polymer composite processing. A 200-μm diameter quartz fiberoptic sensor immersed in liquid resin was used to obtain Raman spectra for a concentration series of diglicidyl ether of bisphenol-A in its own reaction product with diethylamine using an 820 nm continuous-wave diode laser excitation. A Raman peak at 1240 cm−1 was assigned to a vibrational mode of the oxirane (epoxide) ring and its normalized intensity was found to be linearly related to the concentration of epoxide groups in the resin mixtures. Raman peaks at 1112 and 1186 cm−1 associated with phenyl and gem-dimethyl resin backbone vibrations, respectively, did not change in intensity due to the curing reaction and were used as internal references to correct the Raman spectra for intensity changes due to density fluctuations and instrumental variations during the experiments. Fiber-optic Raman spectroscopy was used to monitor the extent of reaction in situ for the room-temperature cure of phenyl glicidyl ether with diethylamine. The extent of reaction of the epoxide groups calculated from the Raman spectra were in excellent agreement with kinetic data from Fourier transform near-infrared absorbance measurements made under the same conditions. © 1994 John Wiley & Sons, Inc.

Ultimate properties of epoxy resins modified with a polysiloxane-polycaprolactone block copolymer

Abstract: Mechanical and fracture mechanics properties of transparent multiphase epoxy resins toughened with various amounts of compatibilized silicone liquid rubbers consisting of polycaprolactone-block-poly(dimethylsiloxane)-block-polycaprolactone triblock copolymer have been investigated. At silicone liquid rubber contents < 10 wt % significantly improved toughness has been achieved without adversely affecting thermal and mechanical properties. Fractographic and interferometric methods have been applied to study crack propagation in such silicone-modified resins. © 1994 John Wiley & Sons, Inc.

Method of preparing layered silicate-epoxy nanocomposites

Abstract: An epoxy-silicate nanocomposite is prepared by dispersing an organically modified smectite-type clay in an epoxy resin together with diglycidyl ether of bisphenol-A (DGEBA), and curing in the presence of either nadic methyl anhydride (NMA), and/or benzyldimethyl amine (BDMA), and/or boron trifluoride monoethylamine (BTFA) at 100°-200° C. Molecular dispersion of the layered silicate within the crosslinked epoxy matrix is obtained, with smectite layer spacings of 100 Å or more and good wetting of the silicate surface by the epoxy matrix. The curing reaction involves the functional groups of the alkylammonium ions located in the galleries of the organically modified clay, which participate in the crosslinking reaction and result in direct attachment of the polymer network to the molecularly dispersed silicate layers. The nanocomposite exhibits a broadened T s at slightly higher temperature than the unmodified epoxy. The dynamic storage modulus of the nanocomposite was considerably higher in the glassy region and very much higher in the rubbery plateau region when compared to such modulus in the unmodified epoxy.

Consolidatable particulate material and well treatment method

Abstract: A well treating composition comprising: a gelled carrier; a particulate material; an epoxy resin system including at least one epoxy resin; and a finely-divided hardening agent which, when dissolved, is operable for hardening the epoxy resin. The finely-divided hardening agent is dispersed in the epoxy resin system. A method of treating a subterranean zone located in a well comprising the steps of: (a) preparing the above-described treating composition; (b) injecting the treating composition into the well such that the treating composition is placed in the subterranean zone; and (c) maintaining the finely-divided hardening agent under conditions such that, prior to injecting the treating composition into the well, the finely-divided hardening agent does not substantially dissolve.

Thermoplastic resin composition

Abstract: A resin composition comprising (a) 100 parts by weight of a block copolymer composed of polyphenylene sulfide segments and polyphenylene sulfide sulfone segments and (b) 0.01 to 20 parts by weight of at least one compound selected from the group consisting of epoxy resins, maleimide compounds, N,N'-diarylcarbodiimide compounds and organosilane compounds and as required, (c) an inorganic filler.

Analysis and modelling of electrical tree growth in synthetic resins over a wide range of stressing voltage

Abstract: A simple accumulated damage analysis method and an empirical field-driven tree growth model are proposed to characterize and describe the spatial and temporal development of electrical trees. Examples are presented for trees grown in CT200 and CY1311 epoxy resin pin-plane samples subjected to a wide range of 50 Hz alternating current electrical stress. It is shown that a material's resistance to treeing may be described quantitatively, allowing the relative performance of different synthetic resins to be easily compared. For CY1311 epoxy resin, tree structural characteristics change progressively from branch to bush structures as the stressing voltage is increased. It is shown that the time to failure is primarily influenced by the local electric field and the resultant tree geometry and fractal dimension of tree growth and is not simply dependent on the applied voltage.

Methods for forming and positioning moldable permanent magnets on electromagnetically actuated microfabricated components

Abstract: A low temperature batch method for forming and positioning permanent magnets on electromagnetically actuated micro-fabricated components, such as electrical switches employs a first adhesive, such as a Siltem/epoxy blend of an epoxy resin and a siloxane polyimide polymer, to releasably attach a mold layer of Kapton polyimide to a substrate, which may be the movable portion of a micromechanical structure, or a precursor to such movable portion. A well-shape cavity is formed in the mold layer, and filled with a slurry of rare earth NdFeB magnetic particles suspended in a second adhesive, which is cured to form the body of a magnet. The second adhesive is an SPI/epoxy blend, also of an epoxy resin and a siloxane polyimide polymer, but with a greater adhesion strength and a higher temperature softening point compared to the Siltem/epoxy blend. The entire structure is heated, and the mold layer is pulled off the substrate, while the body of magnetic material remains firmly attached. Selective etchants may be subsequently employed to remove metal sacrificial layers, while the NdFeB magnetic particles are protected from attack by the etchant by being effectively encased in plastic.

Thermosetting cure diagrams : calculation and application

Abstract: The time–temperature–transformation (TTT) isothermal cure diagram and the continuous-heating-transformation (CHT) cure diagram are calculated from a reaction model for a high-Tg epoxy/amine system that has been developed to describe both epoxy/amine and etherification reactions in kinetically and diffusion-controlled reaction regimes. The cure diagrams are applied to various processing operations. The optimization of processing and of material properties by exploiting gelation and/or vitrification during cure is discussed. © 1994 John Wiley & Sons, Inc.

Process for the production of compounds based on silanes containing epoxy groups

Abstract: A process is disclosed for the production of compounds based on hydrolysables silanes containing epoxy groups. The process involves adding one of the following substances to a pre-hydrolysed silicon compound A with at least one hydrolytically non-separable group which includes an epoxy ring: i) a particulate substance B which can be selected from oxides, oxyhydrates, nitrides or carbides of Si, Al and B and of transition metals, the particle size bein 1-100 nm; ii) a surface-active agent, preferably non-ionic; iii) an aromatic polyol with an average molecular weight not exceeding 1000. The compounds obtained through this process can be used to produce coatings and moulded bodies with a range of properties, in particular high scratch resistance, lasting hydrophilic characteristics, corrosion resistance, good adsorption and transparency.