Showing papers on "Epoxy published in 1992"

Chemistry and Technology of Epoxy Resins

Abstract: Introduction to the chemistry, synthesis, manufacture and characterization of epoxy resins, B. Ellis curing agents for epoxy resins, W.R. Ashcroft the kinetics of cure and network formation, B. Ellis additives and modifiers for epoxy resins, S.J. Shaw fracture behaviour of epoxy resins, W.J. Cantwell and H.H. Kausch electrical properties of epoxy resins, G.P. Johari epoxy resin adhesives, S.J. Shaw composite materials, F.R. Jones coatings and other applications of epoxy resins, X.M. Chen and B. Ellis.

Organic Coatings : Science and Technology

Abstract: What are Coatings? Polymerization and Film Formation. Flow. Mechanical Properties. Exterior Durability. Adhesion. Corrosion Protection by Coatings. Latexes. Amino Resins. Binders Based on Isocyanates: Polyurethanes. Epoxy and Phenolic Resins. Acrylic Resins. Polyester Resins. Drying Oils. Alkyd Resins. Other Resins and Cross--Linkers. Solvents. Color and Appearance. Pigments. Pigment Dispersion. Pigment Volume Relationships. Application Methods. Film Defects. Solvent--Borne and High Solids Coatings. Water--Borne Coatings. Electrodeposition Coatings. Powder Coatings. Radiation Cure Coatings. Product Coatings for Metal Substrates. Product Coatings for Nonmetallic Substrates. Architectural Coatings. Special Purpose Coatings. Perspectives on Coatings Design. Appendix. Index.

Modelling of the toughening mechanisms in rubber-modified epoxy polymers

Abstract: The finite element method has been employed to study the micromechanics and micromechanisms in rubber-toughened cross-linked-epoxy polymers. A two-dimensional plane-strain model has been proposed and has successfully been used to identify the stress fields associated with the dispersed rubbery phase and to simulate the initiation and growth of localized plastic shear-bands running between the rubbery particles. The effects of the microstructure and mechanical properties of the multiphase polymer on the nature and magnitude of the stress fields have also been examined.

Compression Failure Mechanisms in Unidirectional Composites

Abstract: Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model.

Effects of particle size on mechanical and impact properties of epoxy resin filled with spherical silica

Abstract: Effects of particle size on the mechanical and impact properties of cured epoxy resins are studied. This resin was filled with spherical silica particles prepared by hydrolysis of silicon tetrachloride. Particles were sorted into five kinds of different mean sizes in the range from 6–42 μm. A static flexural and tensile tests and an instrumented Charpy type impact test were carried out. Flexural strength, tensile strength, and impact-absorbed energy increased with a decrease in the particle size. Fractured surfaces were observed using a scanning electron microscope to clarify the initiation point of fracture.

Modelling of the toughening mechanisms in rubber-modified epoxy polymers: Part II A quantitative description of the microstructure-fracture property relationships

Abstract: A mathematical model has been developed to quantify the relationships between the microstructure and fracture properties of multiphase rubber-toughened epoxy polymers. Good agreement between predictions from the model and experimental results have been found. The model also reveals that localized plastic shear banding in the epoxy matrix, running between the rubbery particles, is the dominating mechanism under all testing conditions

Fiber-Matrix Adhesion and Its Effect on Composite Mechanical Properties: IV. Mode I and Mode II Fracture Toughness of Graphite/Epoxy Composites

Abstract: To optimize the level of fiber-matrix adhesion an understanding of the relationship between fiber-matrix interfacial bond strength and the mechanical and frac ture behavior of composites is essential. This study establishes the relationship between fiber-matrix interfacial shear strength (ISS) and interlaminar fracture toughness (both Mode I and Mode II) and failure modes for graphite/epoxy composites. A well defined and characterized graphite fiber/epoxy system was chosen in which the level of adhesion be tween fiber and matrix was changed by using the same graphite fibers with different sur face treatments. These surface treatments changed the level of adhesion between the fiber and matrix thus resulting in an increase of the fiber-matrix ISS by over a factor of two while the fiber and matrix properties remained unchanged. The Mode I and Mode II tests were conducted by the double cantilever beam (DCB) and end-notch flexure (ENF) tests methods, respectively. The Mode I fracture toughness (GIC) of composi...

A dielectric, mechanical, rheological and electron microscopy study of cure and properties of a thermoplastic-modified epoxy resin

Abstract: The effect of varying the proportion of a blended thermoplastic, poly(ether sulfone), on the cure and properties of an epoxy resin system, an aromatic diamine cured trifunctional aromatic epoxide, was studied. The initial mixture, prepared by solution casting, is homogeneous, but phase separation occurs rapidly in the initial stages of curing. Analysis of the dielectric data from the cured material shows the existence of a relaxation process which can be ascribed to polarization of a conducting occluded phase. Correlation of these data with the electron micrograph data indicates that the type of phase structure changes with thermoplastic content

Solid state NMR investigation of cationic polymerized epoxy resins

Abstract: Cationic UV-polymerized resins, based on cycloaliphatic epoxides with aryl sulfonium salts as photoinitiators and polypropylene glycols of variable length as flexibilizers, have been investigated with respect to the network-forming reactions and the morphology of the resulting polymers. The combination of UV-curing and thermal postcure makes the chemical process complex and dependent on many variables, such as photoinitiator, exposure time, reaction temperature, and polyol components. Structure and curing of the epoxide were investigated by 13C CPMAS NMR. Morphology and domain sizes were studied by spin diffusion experiments using the novel “dipolar filter” technique for selective magnetization of mobile components.

Craze-like damage in a core-shell rubber-modified epoxy system

Abstract: Toughening mechanisms of a core-shell rubber-modified epoxy were investigated using various microscopic techniques. It was found that the crack tip damage zone of the rubber-modified epoxy appeared to consist of multiple craze-like damage and massive shear banding using optical microscopy. The craze-like damage was further analysed using transmission electron microscopy (TEM) and actually found to be a collection of line arrays of highly cavitated rubber particles. The matrix material around the cavitated particles appeared to have plastically deformed, while the material outside of the array was undeformed. The structure and physical nature of this highly localized dilatational process are substantially different from those of the commonly known craze. The sequence of events leading to the formation of these craze-like line arrays is discussed.

Epoxy resin adhesive composition

Abstract: An epoxy resin adhesive composition has excellent adhesive properties such as impact resistance, tensile shear strength and T-peel strength as well as excellent semi-gelling property. An epoxy resin adhesive composition comprising ionic crosslinking in a polymer utilized as the impact resistance modifier has not only excellent semi-gelling property and mechanical properties of cured products but also excellent storage stability for a long time and it is advantageously utilized when the application occasionally requires storage or standing of the material for one month to one year at the room temperature. The epoxy resin adhesive composition comprises an epoxy resin, a powder core/shell polymer and a heat activation type hardener for epoxy resins. The powder core/shell polymer is composed of a core comprising an acrylate polymer or a methacrylate polymer having a glass transition temperature of -30° C. or lower and a shell comprising an acrylate polymer or a methacrylate polymer comprising crosslinking monomer units having a glass transition temperature of 70° C. or higher and weight ratio of the core to the shell is in the range from 10/1 to 1/4.

Low-Velocity Impact Response of Foam-Core Sandwich Composites

Abstract: The low-velocity impact response of foam-core sandwich composites with fiberglass/epoxy face sheets is treated by a combination of computational and experimental methods. Linear elastic constitutive models are used for the face sheets and epoxy bond layer in conjunction with a foam constitutive model that includes nonlinear hardening plasticity and coupling between volumetric and deviatoric deformation. A transient finite- element code, utilizing four-noded uniform strain quadrilaterals, is used to explicitly solve the equations for balance of mass and momentum. The resulting deformation histories are compared to the experimental results and show qualitative agreement. The computed transverse shear stresses are used to correlate ultrasonic measurement of damage in the core/epoxy interface. Comparison of the plate stiffness prior to and after impact illustrates the effect of damage on subsequent behavior.

Transverse cracking and stiffness reduction in cross ply laminates of different matrix toughness

Abstract: Cross ply laminates of (02,902)s configuration having AS4 graphite fibers in three epoxy resins of different toughness: 3501-6, Tactix® 556 and Tactix® 695, have been tested to determine their tran...

Foamable epoxy resin composition

Abstract: The present invention provides a foamable epoxy resin composition (A) 100 parts by weight of a liquid epoxy resin (B) 05-20 parts by weight of a latent curing agent, (C) 05-15 parts by weight of a foaming agent having a decomposition temperature of 100°-220° C, (D) 005-5 parts by weight of a surface active agent and (E) 10-200 parts by weight of a rubbery elastomer or a powdery halogen-free thermoplastic resin of 150 μm or less in average particle diameter, which composition has a melt viscosity of 25×10 3 -5×10 4 dPa·s at the decomposition temperature of said foaming agent The composition can provide a foamed material of rigidity and good heat resistance, having an expansion ratio of 5 times or more and a dense cell structure of 05 mm or less in average cell diameter

Thermosetting powder coating compositions

Abstract: Provided are novel thermosetting powder coating compositions which are useful for coating metal articles and protecting such articles from acidic corrosion. The compositions are comprised of an epoxy containing acrylic copolymer crosslinked with both an aliphatic dibasic acid and a blocked polyisocyanate.

Pressure dependence of free-volume hole properties in an epoxy polymer

Abstract: Positron annihilation spectroscopy has been applied to study free-volume properties in an amine-cured epoxy as a function of quasi-isotropic pressure in the range o-15 kbar. The orthopositronium lifetimes are found to decrease largely as a function of the increase of pressure while the corresponding intensities decrease slightly.

Synthesis and characterization of bismaleimides from epoxy resins

Abstract: Novel bismaleimides (BMIs) were prepared from functional monomaleimides and diglycidyl ether of bisphenol A (DGEBA) and some of them were shown to have good processibility and improved water resistance while retaining characteristic thermal stability of polyimide. Functional monomaleimides were synthesized via the condensation reaction of maleic anhydride with either aminobenzoic acid or aminophenol. Crosslinking reaction of thus obtained BMIs was carried out with or without catalyst at the temperature range of 100–250°C. The type of the functional group species and their position in monomaleimides significantly affected the crosslinking behavior of the resulting BMIs and the thermal property of their crosslinked products. BMIs with meta linkage, obtained from meta monomaleimides, exhibited much faster thermal crosslinking behavior than corresponding para BMIs. When the molecular weight of BMI was larger, the crosslinking density became smaller and Tg was lower as expected, while the viscosity started to increase at a higher temperature. Glass transition temperatures of the crosslinked resins were in the range of 160–250°C and these resins showed excellent thermal stability up to 370°C.

Effect of particle size on mechanical properties of epoxy resin filled with angular‐shaped silica

Abstract: Effect of particle size on the mechanical properties of cured epoxy resins has been studied. Resin was filled with angular-shaped silica particles prepared by crushing fused natural raw quartz. These particles were sorted into six groups having different mean sizes ranging from 2–47 μm. Flexural and compressive moduli of the cured epoxy resin slightly decreased with decrease in the particle size of the silica, whereas tensile modulus slightly increased. Flexural and tensile strengths increased with decrease in particle size. Fractured surfaces were observed using scanning electron microscopy to clarify the initiation point of fracture.

The mechanical and magnetic alignment of liquid crystalline epoxy thermosets

Abstract: The processing of a new series of liquid crystalline (LC) epoxy networks was evaluated. Above the glass transition temperature, the low crosslink density networks could be mechanically aligned. The mechanically oriented networks readily lost orientation upon heating. Highly anisotropic liquid crystalline (LC) epoxy networks were also prepared by aligning the mesophase of the prepolymer during the curing process under the influence of a magnetic field. Orientation parameters (f) of 0.13 to 0.57 were achieved by these processes as determined by x-ray diffraction analysis. The ability of the magnetically aligned networks to retain their orientation above the glass transition temperature was determined by time-resolved x-ray diffraction. The stability of the alignment of these networks was found to depend on crosslink density. The effect of the anisotropy of these networks was investigated by measuring the coefficient of thermal expansion (CTE). In the aligned networks, there was a substantial reduction in CTE parallel to the direction of the applied field compared to the randomly oriented networks. © 1992 John Wiley & Sons, Inc.