Showing papers on "Epoxy published in 1997"

Mechanical properties and failure behaviour of carbon fibre-reinforced polymer composites under the influence of moisture

Abstract: The effect of moisture on the mechanical properties and the failure behaviour of fibre-reinforced polymer composites was investigated. Moisture was introduced into the specimens by immersion in distilled water. Three materials were investigated, which were all reinforced with continuous carbon fibres. Two thermosetting matrices (unmodified and toughness-modified epoxy) and one thermoplastic matrix (polyetheretherketone) were used. The results showed that the absorbed moisture decreases those properties of both epoxy-based composites which were dominated by the matrix or the interface. The influence of water on the fibre-dominated values, as well as on the properties of the thermoplastic material, was not detectable. The distinct fall of the matrix- and interface-based values due to moisture can be ascribed to the weakening of bonding between fibre and matrix and softening of the matrix material.

Durability characteristics of concrete beams externally bonded with FRP composite sheets

Abstract: The strengthening of concrete structures in situ with externally bonded fiber reinforced plastic (FRP) composite sheets is increasingly being used for repair and rehabilitation of existing structures. This paper provides information in the area of long-term durability of concrete beams externally bonded with FRP sheets. It was intended to study the effect of harsh environmental conditions such as wet/dry cycling using salt water on the performance of FRP-bonded concrete beams and on the interfacial bond between the fiber and the concrete. Concrete beams were strengthened with four different types of FRP sheet: two carbon and two glass. Three different types of two-part epoxy were used. Test variables included (1) the type of fiber, (2) the type of epoxy system, and (3) the environmental exposure condition. The specimens were conditioned in two different environments: (a) room temperature (+20 °C), and (b) 300 wet/dry cycles (salt water was used for the wet cycles and hot air at 35 °C and 90% humidity for the dry). At the end of each exposure, load-deflection curves of the specimens were obtained in order to evaluate their maximum capacity, stiffness, and ductility. The performance of the wet/dry exposed specimens was compared with those kept at room temperature. Results showed that specimens subjected to wet/ dry environmental conditions and those kept at room temperature exhibited significant improvement in flexural strength when FRP sheets were bonded to the tension face of the concrete beams. However, the specimens subjected to wet/dry conditions showed less improvement than those kept at room temperature. None of the specimens failed due to FRP rupture but rather due to the debonding between the FRP sheet and the concrete interface. The selection of epoxy was shown to be very important for using the FRP strengthening technique, especially in a marine environment.

Phosphorus-containing epoxy for flame retardant. III: Using phosphorylated diamines as curing agents

Abstract: Two phosphorus-containing diamine compounds, bis(4-aminophenoxy)-phenyl phosphine oxide and bis(3-aminophenyl)phenyl phosphine oxide, were synthesized for use as curing agents of epoxy resins. Phosphorylated epoxy resins were obtained by curing Epon 828 and Eponex 1510 with these two diamine agents. For raising the phosphorus contents of the resulting epoxy resins, the phosphorus-containing epoxy, bis(glycidyloxy)phenyl phosphine oxide (BGPPO), was also used. These two diamine agents showed similar reactivity toward epoxies. Their reactivities were higher than DDS and lower than DDM. High char yields in TGA evaluation were found for all the phosphorylated epoxy resins, implying their high flame retardancy. The excellent flame-retardant properties of these phosphorylated epoxy resins were also demonstrated by the high limiting oxygen index (LOI) values of 33 to 51. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 895–901, 1997

Coated abrasive article and method of making same

Abstract: A coated abrasive article comprises a backing, a first binder (i.e., a make coat) on the backing, and a plurality of abrasive particles in the first binder. The first binder precursor is an energy-curable melt-processable resin containing an epoxy resin, a polyester component, a polyfunctional acrylate component, and a curing agent for cross-linking the epoxy resin that is cured to provide a cross-linked make coating. The invention also relates to a method of producing such coated abrasive articles and a surface-treated porous cloth material.

Epoxy-Based Nonlinear Optical Polymers from Post Azo Coupling Reaction

Abstract: A series of novel second-order nonlinear optical (NLO) polymers have been developed based on a precursor polymer prepared from the diglycidyl ether of Bisphenol A and aniline. The precursor polymer was postfunctionalized by azo coupling reaction and tricyanovinylation to form a number of NLO polymers with different conjugation lengths and electron acceptors. Post azo coupling reaction enabled the introduction of chromophores and extension of the conjugation lengths of the chromophores to take place in a single-step reaction. The chromophores introduced in the polymer system through covalent bonding not only define the NLO properties but also significantly modify other physical properties of the polymers. In this work, the correlation between chromophore structure and NLO polymer properties was extensively studied and the knowledge base was used to optimize polymer properties at the same time. The d33 value of 66 pm/V at 1.542 μm was determined for a representative polymer of the class containing tricyanov...

Nanoscale Indentation of Polymer Systems Using the Atomic Force Microscope

Abstract: The use of the atomic force microscope (AFM) to measure surface forces has been developed to optimize its operation as a surface imaging tool. This capability can potentially be extended to evaluate nanoscale material response to indentation and would be ideal for the evaluation of multi-component polymer systems, such as adhesives and composites. In this paper, previous work related to the development of the AFM as a nanoindentation device is reviewed, and a technique is proposed which allows the AFM to be used to probe local stiffness changes in polymer systems. Cantilever probes with spring constants ranging from 0.4–150 N m were used to investigate a number of polymer systems, including an elastomer, several polyurethane systems, thermally cured epoxies, a thermoplastic polymer-thermosetting polymer adhesive system, and a thermoplastic matrix composite.

Polyetherimide-modified epoxy networks: Influence of cure conditions on morphology and mechanical properties

Abstract: The morphologies and mechanical properties of thermoplastic-modified epoxy networks generated through the reaction-induced phase separation procedure were studied as a function of isothermal cure conditions. The selected model system was diglycidyl ether of bisphenol A cured with 4,4′-methylenebis [3-chloro,2,6-diethylaniline] in the presence of a nonfunctionalized polyetherimide. Appropriate precuring and postcuring schedules were selected. The precure temperature had a strong effect on final morphologies because it affected the viscosity of the system at the cloud point and the extent of the separation process. The morphologies generated are discussed in connection with phase separation mechanisms. The ratio of the height of the loss peaks corresponding to each phase was an appropriate parameter to qualitatively predict the shape of morphology and to determine if the system was phase-inverted or not. The fracture toughness, KIc was significantly improved only when bicontinuous or inverted structures were generated, resulting from the plastic drawing of the thermoplastic-rich phase. Before phase inversion, KIc was hardly higher than that of the neat matrix due to poor interfacial adhesion. Nevertheless, the thermoplastic-rich particles constitute obstacles to the propagation of the crack and contribute to the toughening of the material, measured through impact resistance measurements. The observation of fracture surfaces revealed the occurrence of microcracking and crack-pinning. Strain recovery experiments showed that particle-induced shear yielding of the matrix was present as well. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2433–2445, 1997

Determination of Bisphenol A Migrating from Epoxy Can Coatings to Infant Formula Liquid Concentrates

Abstract: Migration of bisphenol A (BPA) from epoxy-coated can surfaces to infant formula concentrates is reported. Levels of BPA in the undiluted concentrates surveyed in this study range from 0.1 to 13 parts per billion (ppb) as determined by solid phase extraction/high-pressure liquid chromatography with fluorescence detection and confirmation by gas chromatography with mass selective detection. Fourier transform infrared spectroscopy with 30° specular reflectance/transmittance was used to screen formula cans for epoxy coatings. Keywords: Bisphenol A; epoxy; can coating; migration; infant formula

Effects of environmental exposure on fiber-reinforced plastic (FRP) materials used in construction

Abstract: A major hindrance to the acceptance of polymer composites in civil engineering applications is the susceptibility of the polymeric matrix to weathering. The polymer matrix is prone to degradation initiated by ultraviolet (UV) radiation, moisture, temperature, and high pH environments. The objective of this study was to characterize chemical and physical changes in polymeric matrix resins following exposure to these environments. The ultimate goal is to identify factors that contribute to matrix resin degradation under environmental and mechanical stresses. Resin systems studied included vinylester and isophthalic polyester, both of which are commonly used in construction applications. Neat polymer films were exposed to UV radiation, moisture, alkaline, and saline environments. Diffusion of water, alkali, and saline solution into the polymers was calculated from gravimetric measurements. Changes in strength, viscoelastic response, and thermal properties were evaluated through tensile testing, dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC). Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were also used for detecting changes in the polymer surface following UV exposure.

Urethane golf ball covers using epoxy compounds with a polyamine or glycol as curing agents

Abstract: A golf ball cover is produced from a composition comprising an isocyanate-functional prepolymer and a curing agent of a polyamine or glycol, and an organic compound having at least one epoxy group such as the diglycidyl ether of bisphenol A.

Irreversible interactions between water and DGEBA/DDA epoxy resin during hygrothermal aging

Abstract: Two approaches were adopted to examine the irreversible interactions between water and a model epoxy resin (DGEBA/DDA). One was to employ XPS to investigate the changes of the chemical structure of the resin after immersion in water at a temperature of 90°C and followed by completely drying. The other was to use XPS and FTIR to characterize the degradation products formed during hygrothermal aging. The results clearly showed that irreversible interactions occurred between water and the resin at elevated temperature. Water can lead to the incorporation of C—O and N—CO—N groups in the resin and cut the epoxy backbone chain. Based on the results obtained, a tentative degradation mechanism is proposed and found to explain the results reasonably well. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:449–458, 1997

Effect of moisture content on the properties of silanized jute‐epoxy composites

Abstract: The composites investigated in this article were epoxy resins reinforced with jute-fibers. The jute-fibers were modified with an epoxyfunctional-y-glycidoxypropyltrimethoxy-silane (A-187 from Osi-Specialtis GmbH, Germany), which works as a coupling agent between fiber and matrix. The introduction of the coupling agent distinctly influences the mechanical properties of the composite: Dynamic modulus was doubled, damping was reduced by about 50%, and the Wohler curves showed fatigue limits increased by about 20%. The investigations pointed out further that the moisture uptake of composites with silanized fibers was reduced by about 10-20%. Moisture at equilibrium and kinetics of absorption increase with increasing fiber content. Finally, the application of the coupling agent caused a reduction of moisture effects on mechanical properties. Tensile strength, tensile modulus, and fatigue strength under repeated tensile stress were reduced up to 30%. This tendency was not duplicated in the results for flexural strength and flexural modulus.

Synthesis, characterization, thermal, and flame retardant properties of phosphate-based epoxy resins

Abstract: A new phosphorus-containing oxirane bis-glycidyl phenylphosphate (BGPP), and a diamine, bis(4-aminophenyl)phenylphosphate (BAPP), were synthesized. Both of these two phosphorus-containing compounds lead to phosphate-containing epoxy resin via curing reaction. The kinetics of the curing reaction of BGPP with various curing agents, including BAPP, were studied. The introduction of electron-withdrawing group into the compounds increases the BGPP and decreases the BAPP reactivity in the curing reaction. The thermal and the weight loss behavior of the cured epoxy resins were studied by TGA. High char yields (32–52%) as well as high limiting oxygen index (LOI) values (34–49) of these phosphorylated resins were found, confirming the usefulness of these phosphorus-containing epoxy resins as flame retardants. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 565–574, 1997.

Dental visible light curable epoxy system with enhanced depth of cure

Abstract: A visible-light photopolymerizable composition comprising a) a cationically polymerizable epoxy resin, b) a hydroxyl-containing material c) an aryliodonium salt and d) a visible light sensitizer that is an alpha-dicarbonyl compound having an extinction coefficient less than about 1000. Particularly preferred compositions of the present invention are dental materials.

Damage tolerance of a stitched carbon/epoxy laminate

Abstract: Polymer composite laminates are prone to delamination when impacted. This behaviour generally results in a low damage tolerance, which is of great concern for load carrying applications. The possibility of improving the low velocity and ballistic impact damage tolerances of a carbon fibre brittle epoxy laminate by stitching has been investigated by determination of damage width, compression strength and other properties after falling weight and ballistic impact. The damage tolerance of the stitched laminate was found to be much better than that of a prepreg laminate with a brittle epoxy matrix (914C), better than that of a laminate with a toughened epoxy matrix (6376C) and about equal to that of a laminate with a very tough thermoplastic matrix (APC-2). The compression strength after a 45 J low velocity impact of a quasi-isotropic laminate 3 mm thick was 150 MPa for the 914C laminate and 270 MPa for the stitched laminate. In the ballistic case compression strength was increased by about 50% for near quasi-isotropic laminates of thickness 5 mm.

Frontal Curing of Epoxy Resins: Comparison of Mechanical and Thermal Properties to Batch-Cured Materials

Abstract: The epoxy resin diglycidyl ether of bisphenol F (DGEBF) was cured by the aliphatic amine curing agent Epicure 3371 in a stoichiometric ratio both frontally and in a batch-cure schedule. Glass transition temperatures (Tg) were determined using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). DMA also was used for studying the storage modulus (E′) and tan delta (tan δ) of the cured samples. Tensile properties of epoxy samples were tested according to ASTM D638M-93. The properties of the frontally cured epoxy resin were found to be very close to that of batch-cured epoxy resin. Velocity of cure-front propagation was measured for both neat and filled epoxy. Rubber particles (ground tires) were used as a filler. The maximum percentage of filler in the epoxy resin allowing propagation was 30%. Because of convection, only descending fronts would propagate. Advantages and disadvantages of frontal curing of epoxy resins are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1209–1216, 1997

Fabrication and mechanical characterization of glass fiber reinforced UV‐cured composites from epoxidized vegetable oils

Abstract: Novel fiberglass-reinforced composites were fabricated by the ultraviolet and visible (solar) irradiation of epoxidized vegetable oils in the presence of onium salt cationic photoinitiators. A variety of layup techniques and experimental conditions were explored to optimize composite fabrication. It was demonstrated that composites prepared by wet layup techniques containing up to five plies of glass cloth could be cured by a direct, 25-min exposure to solar irradiation. A series of composite samples were prepared using mixtures of epoxidized vegetable oils and synthetic epoxy resins, and their mechanical properties were evaluated. Based on these measurements, it may be concluded that photochemical routes to the fabrication of composites derived from epoxidized vegetable oils provide a simple, direct, and inexpensive route to the fabrication of composites with many potential low-performance applications. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2073–2087, 1997

Liquid crystal polyester resin composition

Abstract: The present invention provides a liquid crystal polyester resin composition, which is manufactured at low cost and has favorable gas barrier properties and improved impact resistance, vibration-damping properties, thin-wall properties (mechanical properties of thin-wall molded articles), and film-forming properties, while maintaining excellent heat resistance and mechanical properties of a liquid crystal polyester. A liquid crystal polyester resin composition of the invention includes 55.0 through 99.9 percent by weight of a liquid crystal polyester as a component (A) and 0.1 through 45.0 percent by weight of an epoxy group-containing ethylene copolymer as a component (B), wherein the component (B) includes: (a) 50 through 96.5 percent by weight of an ethylene unit; (b) 0.5 through 30 percent by weight of an unsaturated glycidyl carboxylate unit or an unsaturated glycidyl ether unit; and (c) 3 through 40 percent by weight of an ethylenically unsaturated ester compound unit.

Flammability testing of flame‐retarded epoxy composites and phenolic composites

Abstract: Flame-retarded epoxy composites and phenolic composites containing fiberglass, aramid (Kevlar® 49), and graphite fiber-reinforcements were tested using the NASA upward flame propagation test, the controlled-atmosphere cone calorimeter test, and the liquid oxygen (LOX) mechanical impact test. The upward flame propagation test showed that phenolic/graphite had the highest flame resistance and epoxy/graphite had the lowest flame resistance. The controlled-atmosphere cone calorimeter was used to investigate the effect of oxygen concentration and fiber reinforcement on the burning behavior of composites. The LOX mechanical impact test showed that epoxy/fiberglass had the lowest ignition resistance and phenolic/aramid had the highest ignition resistance in LOX. The composites containing epoxy resin and/or aramid fiber reinforcement reacted very violently in LOX upon mechanical impact. © 1997 by John Wiley & Sons, Ltd.