Showing papers on "Epoxy published in 1983"

Adhesion of Graphite Fibers to Epoxy Matrices: I. The Role of Fiber Surface Treatment

Abstract: Adhesion between graphite fibers and epoxy matrices is a necessary and sometimes controlling factor in achieving optimum performance. Manufacturers′ proprietary fiber surface treatments promote adhesion without providing a basic understanding of the fiber surface properties altered through their use. This study has combined fiber surface chemistry, morphology, interfacial strength measurements and fracture characterization in order to elucidate the role of surface treatments. The results of this investigation lead to the conclusion that surface treatments designed to promote adhesion to epoxy matrix materials operate through a two-part mechanism. First, the treatments remove a weak outer fiber layer initially present on the fiber. Second surface chemical groups are added which increase the interaction with the matrix. Increases in fiber surface area are not an important factor in promoting fiber-matrix adhesion. In some cases the upper limit to fiber-matrix interfacial shear strength is the intri...

Curing of Epoxy Matrix Composites

Abstract: Models were developed which describe the curing process of composites constructed from continuous fiber-reinforced, thermosetting resin matrix prepreg materials. On the basis of the models, a computer code was developed, which for flat-plate composites cured by a specific cure cycle, provides the temperature distribution, the degree of cure of the resin, the resin viscosity inside the composite, the void sizes, the temperatures and pressures inside voids, and the residual stress distribution after the cure. In addition, the computer code can be used to determine the amount of resin flow out of the composite and the resin content of the composite and the bleeder.

Adhesion of Graphite Fibers to Epoxy Matrices: II. The Effect of Fiber Finish

Abstract: Reinforcing fibers are available from various manufacturers with matrix compatible “finishes” applied to them. Usually these finishes or coatings are 100–200 nm thick resin layers applied after surface treatment. Their function has been hypothesized as being to enhance adhesion through either protecting the fiber from handling damage, protecting the fiber surface reactivity, or improving fiber wettability. This study of finished and unfinished graphite fibers concludes that the mechanism by which an epoxy compatible finish operates is different from what has been hypothesized to date. The finish layer creates a brittle interphase layer between the fiber and matrix which increases the interfacial shear strength but at the expense of changing the failure mode from interfacial to matrix.

Adhesion aspects of polymeric coatings

Abstract: I. General Overviews.- Acid Base Interactions Between Oxide Surfaces and Polar Organic Compounds.- Adhesion of Polymers to Metals: The Role of Surface Topography.- Recent Progress in the Studies of Molecular and Microstructure of Interfaces in Composites, Coatings and Adhesive Joints.- Adhesion and Internal Strain in Polymeric Coatings.- Determining the Locus of Failure with Modern Surface Analysis Techniques.- II. Factors Influencing Adhesion.- Processing Conditions and the Adhesion Properties of Styrene/Acrylic Polymers.- Variables Affecting the Adhesion of Aliphatic Amine-cured Epoxy Resin to Metal and Ceramic Adherends.- The Relationship of Sulfuric-Chromic Acid (FPL) Etch Composition to the Surface Properties of 2024 T-3 Aluminum Alloy.- Adhesion of Plasma-Polymerized Films (A Model Study on Water Sensitivity of Adhesion).- Epoxy Adhesion to Copper.- Infrared Spectroscopic Investigation of Polymer Coating-Metal Substrate Interaction.- The Relationship Between Adhesion and Polyelectrolyte Solution Conformation as Studied by Fourier Transform IR Spectroscopy.- Conformation and Dynamics of Adsorbed Polymer Molecules Subjected to Flow.- PTFE Film Adhesion to Electronically Conducting Materials.- III. Bond Durability.- Durability of Metal Polymer Bonds.- Correlation of Surface Chemistry and Durability of Aluminum/Polymer Bonds.- A Case Study of Water Sensitivity of Polymeric Coating-Substrate Interface for Two Aluminum Surface Preparations.- Adhesion of Organic Coatings and its Loss due to Corrosion.- The Effects of Environment on Paint Adhesion to Steel.- Effect of Aging of Pigmented Polymeric Films on Adhesion to Metal Substrates.- IV. Adhesion Promotion Via Coupling Agents.- Silane Adhesion Promoters for Polymeric Coatings.- Structure and Effects of Organosilane or Organo-titanate Adhesion Promoters on Al203/Polyethylene Joints.- Improved Wet Strength Adhesion of Epoxy Coatings to Steel.- The Use of Coupling Agents to Improve the Adhesion of Polymer Matrices for Electronic Applications.- Adhesion Promotion and Polymer Composite Performance with Titanate Coupling Agents.- Synthesis and Testing of ?-Diketone Coupling Agents for Improved Durability of Epoxy Adhesion to Steel.- Interfacial Coupling by Alkoxytitanium and - Zirconium Tricarboxylates.- V. Resist Adhesion.- Adhesion, Wettability and Surface Chemistry.- Organosilanes as Process Compatible Adhesion Promoters for Resist Materials.- Recognition and Discussion of Basic Adhesion Mechanisms in Photopolymeric Systems.- Factors Affecting Dry Film Photoresist Adhesion on Electroless Copper Surfaces.- VI. Adhesion Measurement.- Pull-off Test, an Internationally Standardized Method for Adhesion Testing - Assessment of the Relevance of Test Results.- Quantifying the Tape Adhesion Test.- Indentation-Debonding Test for Adhered Thin Polymer Layers.- Thermographic Detection of Polymer/Metal Adhesion Failures.- Ultrasonic Inspection Potential for Polymeric Coatings.- About the Contributors.

Structural behaviour of reinforced concrete beams strengthened by epoxy bonded steel plates.

Abstract: The development of synthetic adhesives based on epoxy resins has opened new possibilities for bonding structural materials together. The present work was concerned with the use of epoxy resins to strengthen reinforced concrete beams by externally bonded steel plates. It was found in the first part that the assessment of the properties of the epoxy adhesive is of paramount importance as they varied considerably with the thickness of the test specimen and the rate of loading. The adhesive proved to offer a bond stronger than concrete in shear and resulted in a composite action between the beams and steel plates. Preloading the beams prior to strengthening them did not have any adverse effect on their behaviour. The added strength from the plates was fully exploited even in beams which were held under a preload of 70% of their ultimate strength while being strengthened. Stopping the plate in the shear span, short of the support, created a critical section where premature bond failure occurred beyond a certain plate thickness. Failure was caused by the combination of high peeling and bond stresses present in the region where the plate was stopped. These stresses were due to the transfer of tensile forces from the plate to the bars in that region and were higher with thicker plates. Bonding steel plates on the tension face of the beams increased their shear capacity by 9 to 15%. This may have been due to dowelling action from the plates which had a greater contact area with concrete than an equivalent amount of internal steel bars. The use of externally bonded steel as shear reinforcement was effective but requires further investigation. The external web strips failed prematurely as compared to equivalent stirrups. The long term deformations in plated beams were highly affected by the conditions of their environment but despite 47 month exposure no visual deterioration of the concrete-epoxy-steel joint was observed.

Surface Charging on Epoxy Spacer at DC Stress in Compressed SF 6 Gas

Abstract: The charge accumulation and its mechanisms are studied based on the experiments of post and conical epoxy spacers subjected to high dc voltages in compressed SF 6 gas. The charge measurement is performed using electrostatic probe and dust figure techniques. The charge accumulation is strongly influenced by the surface condition of epoxy spacer. Heterocharge deposits locally on the surface of untreated spacer. The flashover voltage of highly charged spacer decreases considerably at the time of polarity reversal. In the case of epoxy surface treated with horning, only a small quantity of charge is deposited uniformly on the surface of spacer. The mechanism of inhomogeneous surface conduction is suggested by the local surface charging on the untreated spacer. Field emission is also found as the other charging mechanism on the conical spacer set in rough finish electrode system.

Statistical analysis of multiple fracture in 0°/90°/0° glass fibre/epoxy resin laminates

Abstract: Measurements of the distributions of crack spacings developed in the 90° ply of 0°/90°/0° glass fibre/epoxy resin laminates under tensile loading show that the ply has a variable strength. As a consequence the strain at which cracking begins is very dependent on the specimen length. The observed distributions of crack spacing are not consistent with the assumption of a uniform strength for the 90° ply. A statistical model provides a good description of the cracking behaviour particularly when the cracks are widely spaced. Magnification of the stress in the matrix between the relatively stiff glass fibres leads to debonding which is observed as a reversible “stress-whitening.” The distributions reveal a lower probability of crack formation in the under-stressed region close to the existing cracks and provide estimates of the size of this region. The method of analysis can be applied to many systems which exhibit multiple fracture.

Dielectric studies of water in epoxy resins

Abstract: Dielectric measurements are reported on amine-cured epoxy resin samples over a frequency range from 200 Hz to 200 kHz and a temperature range from −60°C to 70°C as a function of molecular weight of the diglycidyl ether and water content. The effects of change of the molecular weight of the diglycidyl ether on the dielectric relaxation are small in comparison with the changes observed on the introduction of water into the matrix. Analysis of the data indicates the presence of cluster—free and bound—molecularly dispersed water. The former are presumed to be found in voids and cavities which arise in curing powder samples. The conductivity of the water-doped samples reflects the mobility of the water and is compared with the predictions of theories for amorphous materials.

Curing epoxy resins with anhydrides. Model reactions and reaction mechanism

Abstract: The mechanism of acid curing of epoxy resins catalyzed with tertiary amines was investigated by using model systems composed of phenylglycidyl ether and benzoic acid or acetic acid anhydrides in the presence of benzyldimethylamine. The reaction was studied by NMR spectrometry, liquid chromatography, and ozone absorption. The main findings are that (1) the tert-amine is bound chemically and irreversibly during the reaction under the formation of a quaternary ammonium salt and (2) 1-phenyloxypropanediol-2,3-dibenzoate or diacetate is the main reaction product. The suggested reaction mechanism involves initiation in which the tertiary amine reacts with the epoxy group, giving rise to a zwitterion that contains a quaternary nitrogen atom and an alkoxide anion; the latter immediately reacts with the anhydride and quaternary salt is formed. In a later stage the carboxy anion of the quaternary salt reacts first with the epoxy group, then with the anhydride. By this reaction diester is formed and the carboxy anion is regenerated.

Process for producing epoxy resins

Abstract: An improved process for reacting vicinal epoxides with phenols or thiophenols is described. This process is conducted at essentially anhydrous conditions and temperatures less than 175° C. The resulting resins are generally more linear and less colored than advanced resins produced via prior art processes. Also the phosphonium catalyst remains active to promote subsequent advancement or curing reactions. The catalyst can be deactivated in a separate step to produce a resin of exceptional purity.

Sealing resin composition

Abstract: PURPOSE: To obtain a sealing resin composition excellent in moldability and moisture resistance and forming easily removable flashes on the leads of an electronic or electrical component, by adding a spherical silica powder and a crushed silica powder to an epoxy resin containing a novolac phenol resin as a curing agent. CONSTITUTION: This sealing resin composition essentially consists of an epoxy resin (A), a novolac phenol resin (B), a spherical silica powder (C) and a crushed silica powder (D), wherein the total of powder C and powder D is 25W90wt.% based on the total resin composition. Although a connectional resin composition formed by adding a crushed fused silica powder or a crystalline silica powder to resin A containing resin B as a curing agent is excellent in moisture resistance, removal of flashes formed on leads in the molding step has been difficult. By adding powders C and D to such a resin composition, it is possible to obtain a resin composition which is excellent in moisture resistance and moldability and does not cause deformation of leads because flashes can be easily removed from them. COPYRIGHT: (C)1989,JPO&Japio

Reaction injection molded elastomers

Abstract: The invention relates to reaction injection molded elastomers derived from high molecular weight amine terminated polyethers and/or high molecular weight polyols, a chain extender, a polyisocyanate and an epoxy modified filler material. The reaction injection molded (RIM) elastomers of this invention are useful, for example, as automobile body parts.

Latent curing agents for epoxy resins

Abstract: A latent curing agent for epoxy resin, characterized in that the latent curing agent is an adduct obtained by reacting (a) a polyfunctional epoxy compound, (b) a compound having at least one OH, NH 2 , NH or SH group together with a tertiary amino group in the molecule and (c) a carboxylic acid anhydride is a good curing agent for epoxy resins. The present curing agent is useful in formulating storable, one-package, heat-curable epoxy resin-based compositions.

Flame retardant B-staged epoxy resin prepregs and laminates made therefrom

Abstract: A prepreg useful in flame resistant copper clad printed circuit boards is made by impregnating a porous substrate with an impregnant containing: either a prebrominated epoxy resin or a mixture of a non-halogenated epoxy resin and flame retarding additive containing bromine, and phenolic hydroxyl groups. A phenolic novolac oligomer having an average of over 2.5 phenolic hydroxyl groups per oligomeric unit is used as curing agent. Optionally, a suitable catalyst may be included. The impregnated substrate is heated to cure or advance the resin to the "B"-stage.

Preparation of epoxy resins

Abstract: Epoxy resins are prepared by reacting an excess of an epihalohydrin with a phenolic hydroxyl-containing compound in the presence of the incremental addition of a basic catalyst while removing water by codistilling with a solvent and epihalohydrin.

Resilient cellular polymers from amine terminated poly(oxyalkylene) and polyfunctional epoxides

Abstract: An absorbent, flexible, resilient, cellular polymer is provided which comprises the reaction product of at least one epoxy resin and amine terminated poly(alkylene oxide).

Epoxy resin composition for encapsulating semiconductor

Abstract: An epoxy resin composition for encapsulating semiconductors and semiconductor elements is disclosed. This epoxy resin composition mainly comprises (a) a polyfunctional epoxy compound, (b) a styrene type block copolymer or styrene type block copolymer and liquid rubber, (c) a hardener for the epoxy compound and (d) an inorganic filler.

Ultraviolet radiation-curable silicone controlled release compositions

Abstract: Ultraviolet radiation-curable epoxyfunctional silicone controlled release compositions are provided. Polyfunctional epoxy monomers, when added to UV-curable epoxy silicones provide quantitative variable release, depending on the amount of epoxy monomer added.

Thermokinetic modeling of an epoxy resin I. Chemoviscosity

Abstract: It is shown that the Williams-Landel-Ferry equation can be taken to describe the temperature dependence of viscosity of an amine-cured epoxy resin. Furthermore, for this resin system, the two parameters of the W-L-F equation can be expressed simply as functions of hardener concentration. Since the hardener concentration decreases with advancement, and since the reaction rate equation for advancement is readily determined and known, the viscosity can be calculated over any temperature (cure) cycle.

Epoxy resin fortifiers based on aromatic amides

Abstract: The reaction product of (i) an aromatic amide having the amine group of the amide attached to an aromatic ring, and (ii) a mono- or di-epoxide, has been found to be a good fortifier of epoxy resins. Epoxy resins have been found to attain increased strength and modulus (yet not brittle) by compounding: (a) a resin-forming polyepoxide, (b) an amine curing agent for (a), and (c) the above fortifier; and heat curing the mixture. Strengths as high as 130-150 MPa and modulus values to as high as 5000 MPa have been achieved yet with a ductile mode of fracture.

Addition of polyethersulphone to epoxy resins

Abstract: Phase separation of polyethersulphone from solution in epoxy resins has been studied as a function of polyethersulphone concentration, type of resin, and curing conditions. The resins chosen were a rapidly curing tetrafunctional and a trifunctional epoxy resin, hardened with either diaminodiphenylsulphone, or dicyandiamide. Fracture surfaces of some of the cured blends exhibited nodular features between 0.2μm and 6μm in diameter. Using X-ray microanalysis and scanning electron microscopy these nodules were shown to contain high concentrations of polyethersulphone. Mechanical properties, including fracture energy, dynamic mechanical relaxation and creep, were studied for the same range of blend compositions. Dynamic mechanical spectra provided further evidence for phase separation in certain blends, while elastic modulus, fracture toughness and creep showed little dependence upon composition.

The role of the polymeric matrix in the processing and structural properties of composite materials

Abstract: Introductory Remarks.- The Role of the Matrix in Fibrous Composite Structures.- Composites in Commercial Aircraft.- Current Material Research Needs in Aircraft Structures.- Chemical and Environmental Effects.- Characterization of the Matrix Glass Transition in Carbon-Epoxy Laminates Using the CSD Test Geometry.- Network Structure Description and Analysis of Amine-Cured Epoxy Matrices.- The Time-Temperature-Transformation (TTT) State Diagram and Cure.- Control of Composite Cure Processes.- A Study of the Thermo-Oxidative Process and Stability of Graphite and Glass/PMR Polyimide Composites.- Rubber Modified Matrices.- A Preliminary Study of Composite Reaction Injection Molding.- Characterization of High Performance Composite Matrices.- Environmental Aging of Epoxy Composites.- Factors Affecting the Development of New Matrix Resins for Advanced Composites.- A Stress Transfer Model for the Deformation and Failure of Polymeric Matrices under Swelling Conditions.- Short Fiber Reinforcement Effects.- Constitutive Relationships for Sheet Molding Materials.- Effects of Matrix Characteristics in the Processing of Short Fiber Composites.- Time Dependent Properties of Injection Moulded Composites.- Viscoelastic Properties of Particulate Reinforced Matrices.- On Feasibility of Accelerated Creep Measurements in Some Polymeric Materials.- Fatigue Crack Propagation in Short-Glass-Fiber-Reinforced Nylon 66: Effect of Frequency.- Creep and Fracture Initiation in Fiber Reinforced Plastics.- Effect of Fiber Aspect Ratio on Ultimate Properties of Short-Fiber Composites.- An Optical Technique for Measuring Fiber Orientation in Short Fiber Composites.- Low Cost Energy Storage Flywheels from Structural Sheet Molding Compound.- Reinforced Polyester Structural Foam.- Dimensional Stability of Reinforced Matrices.- Interfacial Effects.- Definition of Interphase in Composites.- In Situ Analysis of the Interface.- Internal Stresses in Fibre Reinforced Plastics.- Stress and Strength Analysis in and Around Composite Inclusions in Polymer Matrices.- Continuous Fiber Reinforcements and Design.- Design of Continuous Fiber Composite Structures.- Compression Fatigue Behavior of Notched Composite Laminates.- Consideration on the Fatigue Damage of Specimens Used for Composite Critical Component's Qualification.- Unresolved Stress Analysis Problems in Kevlar Composite Pressure Vessels.- Delamination in Graphite-Epoxy.- Industry-Academia and International Collaborative Research Efforts.- Finalized Researches on Polymeric Materials: Sub-project on Polymeric Materials of the Fine and Secondary Chemistry Research Program of the Italian National Research Council.- Industry-University Cooperation in Research.- Author Index.- Participants.