Showing papers on "Epoxy published in 1999"

Transparent Nanocomposites with Ultrathin, Electrospun Nylon-4,6 Fiber Reinforcement

Abstract: Transparent sheets of epoxy resin reinforced with nylon-4,6 nanofibers are described. The 30-200 nm diameter fibers, obtained by electrospinning from formic acid solutions, are reported to provide significant improvement in strength and stiffness to the epoxy film. The Figure is a scanning electron microscopy image of the electrospun nanofibers.

Mechanical properties of composites using ultrafine electrospun fibers

Abstract: The objective of this research was to show the reinforcing effects of nanofibers in an epoxy matrix and in a rubber matrix using electrospun nanofibers of PBI (polybenzimidazole). The average diameter of the electrospun fibers was around 300 nanometers, which is less than one tenth the diameter and 1/100 the cross sectional area of ordinary reinforcing fibers. The ultrafine fibers provide a very high ratio of surface area to volume. The nanofibers toughened the brittle epoxy resin. The fracture toughness and the modulus of the nanofiber (15 wt%)-reinforced epoxy composite were both higher than for an epoxy composite made with PBI fibrids (17 wt%), which are whisker-like particles. In an elastomeric matrix, The Young's modulus and tear strength of the chopped nanofiber-reinforced styrene-butadiene rubber (SBR) were higher than those of the pure SBR. Micrographs of the fracture surfaces were obtained by scanning electron microscopy (SEM).

Morphology and toughness/stiffness balance of nanocomposites based upon anhydride‐cured epoxy resins and layered silicates

Abstract: Basic correlations between polymer morphology, silicate superstructures, glass temperature, stiffness and toughness of thermoset nanocomposites were investigated as a function of layered silicate type and content. The nanocomposites were based upon hexahydrophthalic anhydride-cured bisphenol A diglycidyl ether and layered silicates such as synthetic fluoromica (Fmica), purified sodium bentonite and synthetic hectorite, all of which were rendered organophilic by means of ion-exchange with various mono- and difunctional alkyl ammonium ions. Enhanced toughness was associated with the formation of dispersed anisotropic laminated nanoparticles consisting of intercalated layered silicates. Nanocomposite superstructures were imaged by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM).

Intelligent Material Systems Using Epoxy Particles to Repair Microcracks and Delamination Damage in GFRP

Abstract: The objective of this study is to propose an intelligent material system that can perform a self-repairing operation against initial damage that might occur in GFRP laminates. Specifically, we highlight the development of a novel actuator to be used in such self-repairing operations. There has been much research on sensor systems to detect damage and some actuators to control the shape of the structure or to control the vibration. However, no literature can be found on the actuator aiming at the self-repair of damage. For this purpose, a small grain particle-type adhesive is embedded in a glass/epoxy composite (GFRP) laminate. The diameter of the particle is approximately 50 μm. Hence, in the developed intelligent material system, coldsetting epoxy resin is used as the matrix, uni-directionally arranged glass fiber is used as the reinforcement, and a thermosetting epoxy particle is used as a repairing actuator. The volume fraction of the particles in the matrix was approximately 40%. The embedded particles can repair the damage, when melted by heat. Basic characteristics of the particles were investigated first, and we confirmed that the embedded particles in the matrix can melt by heat and flow to repair the crack. We also confirmed that the embedded particles do not deteriorate the stiffness of the GFRP laminate. Then we investigated the efficiency of the repairing operation against initial damage such as microscopic matrix cracks and delamination, by conducting two typical tests, i.e., static three-point bending of [0/90] laminate and tensile fatigue of [0/90] s laminate. Damage was observed by CCD camera. As a result, the decrease in the stiffness due to initial damage has been recovered and consequently increased the residual fatigue life.

Thermal and viscoelastic property of epoxy-clay and hybrid inorganic-organic epoxy nanocomposites

Abstract: The properties of nanostructured plastics are determined by complex relationships between the type and size of the nanoreinforcement, the interface and chemical interaction between the nanoreinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this article, we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nanoreinforcement, namely, organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nanocomposites were studied using differential scanning calorimetry (DSC). Small-strain stress relaxation under uniaxial deformation was examined to provide insights into the time-dependent viscoelastic behavior of these nanocomposites. Since the size of the POSS macromer is comparable to the distance between molecular junctions, as we increase the amount of POSS macromers, the glass transition temperature Tg as observed by DSC, increases. However, for an epoxy network reinforced with clay, we did not observe any effect on the Tg due to the presence of clay reinforcements. In small-strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely, the characteristic relaxation time, as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS–epoxy nanocomposites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1993–2001, 1999

Parametric studies on self-repairing approaches for resin infused composites subjected to low velocity impact

Abstract: Low velocity impact response of glass reinforced polymer composites, which have the potential to self-repair both micro- and macro-damage, has been investigated. This class of material falls under the category of passive smart polymer composites. The self-repairing mechanism is achieved through the incorporation of hollow fibers in addition to the normal solid reinforcing fibers. The hollow fibers store the damage-repairing solution or chemicals that are released into the matrix or damaged zone upon fiber failure. Plain-weave S-2 glass fabric reinforcement, vinyl ester 411-C50 and EPON-862 epoxy resin systems were considered for this study. Different tubing materials were investigated for potential use as storage materials for the repairing chemicals instead of the actual hollow repair fibers and included borosilicate glass micro-capillary pipets, flint glass pasteur pipets, copper tubing and aluminum tubing. composite panels were fabricated by using a vacuum assisted resin transfer molding process. The present investigation addressed fabrication of self-repairing composite panels and some of the parameters that influence the response of self-repairing composites to impact loading. Specific issues addressed by this study include: the processing quality; the selection of storage material for the repairing solution; release and transportation of the repairing solution; the effect of the number, type and spatial distribution of the repairing tubes, specimen thickness, matrix material and impact energy level.

Vapor grown carbon fiber composites with epoxy and poly(phenylene sulfide) matrices

Abstract: Vapor grown carbon fibers (VGCF, Pyrograf III™ from Applied Sciences, Inc.), with 100–300 nm diameters and ∽10–100 μm lengths, were formulated in various fiber volume fractions into epoxy (thermoset) and into poly(phenylene sulfide) (thermoplastic) composites. Increases in stiffness were observed as with previous VGCF/organic matrix composites. Large increases in flexural strengths were achieved in both systems demonstrating for the first time that discontinuous randomly oriented Pyrograf III™ can give strength increases and has substantial potential as a reinforcement in composites. Here-to-fore, addition of VGCF caused strength decreases. Voids, residual thermal strains (as the fiber surface area is ∽35 times greater than 7 μm-diameter PAN fiber), or uncertainties about fiber strength, fiber–matrix bonding and the degree of fiber dispersion, could cause losses of strength. Thermal conductivity properties of VGCF/ABS (acrylonitrile–butadiene–styrene from GE Plastics) and VGCF/epoxy composites with various fiber volume fractions were measured. Thermal conductivity increased with an increase in fiber volume fraction. However, these increases were not significant enough to make these VGCF fiber/organic matrix composites candidates for thermally conductive materials.

Effect of Ag particle size on electrical conductivity of isotropically conductive adhesives

Abstract: The present work is to introduce nanoparticles in micro-sized metal particles to study particle distribution in polymer matrix. Previous examinations of the silver-filled particles reveal that the micro-sized particle fillers appear as full density silver flakes, while nanoparticle fillers appear as highly porous agglomerates, similar to open-cell foams. Actually little work has been carried out to study the cross-sectional area of a particle-particle-contact in isotropically conductive adhesives (ICA). In this study, transmission electron microscope is chosen as a main measure to analyze the distribution of different-sized particles. The percentage of the nanoparticles varies from 20 wt% and 50 wt% to full percentage within micro-sized particles, and the total metal content in epoxy resin is 70 wt%. So the change of contact area and contact behavior with various volume ratio of nano-sized and micro-sized particles was investigated. At the same time, the electrical resistivity was measured, which is compared with the different level of the filler loading.

Sound deadening and structural reinforcement compositions and methods of using the same

Abstract: Expandable sealant and baffle compositions and methods of forming and using such compositions are provided wherein the compositions comprise a first thermoplastic resin, an epoxy resin, preferably a second thermoplastic resin different from the first thermoplastic resin, and optionally a compound selected from the group consisting of pigments, blowing agents, catalysts, curing agents, reinforcers, and mixtures thereof. The resulting compositions are formed as self-sustaining bodies which can be heat-expanded into a lightweight, high strength product for sealing hollow structural members of vehicles, substantially decreasing the noise which travels along the length of those members as well as strengthening those members with minimal increases in their weights. In a preferred embodiment, the first thermoplastic resin is an SBS block co-polymer, the epoxy resin is a bisphenol A-based liquid epoxy resin, the second thermoplastic resin is a polystyrene, and the reinforcer is hydrated amorphous silica. The compositions can be formed into free-standing, self-sustaining parts or into U-shaped members supported on lattice-type nylon supports.

Synthesis and properties of phosphorus-containing epoxy resins by novel method

Abstract: Novel phosphorus-containing epoxy resins (1–3% phosphorus content) were synthesized by the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and the diglycidyl ether of bisphenol A and then cured with 4,4′-diaminodiphenyl sulfone or phenol novolac. Differential scanning calorimetry, high performance liquid chromatography, and epoxide equivalent weight titration were used to trace the reaction between the DOPO and the epoxy. The thermal stability and flame retardancy were checked by thermal gravimetric analysis, the limiting oxygen index, and the UL-94 vertical test. The glass transitions were measured by dynamic mechanical analysis. The relation between these properties (thermal stability, flame retardancy, and glass transition) and the DOPO contents (phosphorus content) were discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3903–3909, 1999

Polyester molding composition

Abstract: A thermoplastic resin composition with enhanced elongation and good appearance comprising a compatible resin blend of a polyester sulfonate salt ionomer and a polyamide and an effective amount of at least one difunctional epoxy compound wherein the difunctional epoxy compound has at least one cyclohexane ring moiety and having two terminal epoxy functional groups, wherein at least one of the two terminal epoxy functional groups is a substituent on the at least one cyclohexane ring moiety; and optionally an effective amount of a catalyst compound or rubbery impact modifier.

Epoxy−Diamine Thermoset/Thermoplastic Blends. 2. Rheological Behavior before and after Phase Separation

Abstract: The phase separation process in a thermoplastic-modified epoxy system was studied using rheological dynamic analysis (RDA) and differential scanning calorimetry (DSC). Transmission electronic microscopy (TEM) was used to get direct representation of morphologies at different times during the phase separation process. The selected thermoset system was bisphenol A diglycidyl ether (DGEBA) cured with 4,4‘-methylenebis[3-chloro,2,6-diethylaniline] (MCDEA) in the presence of various compositions of polyetherimide (PEI), 10−64 wt %. As rheology is a signature of connectivity, the rheological behavior at phase separation was found to be greatly dependent on the initial concentration of PEI. Experimental results showed that when PEI concentration was lower than 10−15 wt %, phase separation induced a rapid decrease of the viscosity. For concentrations close to the phase inversion composition, a rheological behavior characteristic of a bicontinuous morphology appeared with a strong dependence on frequency. When PEI...

Sorption and diffusion of water, salt water, and concrete pore solution in composite matrices†

Abstract: In recent years, the use of fiber-reinforced polymer composites in civil infrastructure has been promoted as a solution to the deterioration of bridges, buildings, and other structures composed of traditional materials, such as steel, concrete, and wood. Any application of a polymer composite in an outdoor environment invariably involves exposure to moisture. There is also potential for exposure to saline conditions in waterfront or offshore structures, and alkaline environments, as would be encountered by a reinforcing bar in a cementitious material. This study characterizes the sorption and transport of distilled water, salt solution, and a simulated concrete pore solution in free films of vinyl ester, isophthalic polyester (isopolyester) and epoxy resins, all commercially important materials for use in structural composites. Diffusion of all three liquids in each of the three materials was observed to follow a Fickian process. Mass loss was observed for the isopolyester in salt water and concrete pore solution at 60°C, suggesting hydrolysis that was accelerated by the high temperature exposure. Both the rate of uptake, as well as the equilibrium uptake, were greater at 60°C, compared with ambient conditions. Diffusion coefficients calculated from the mass uptake data revealed that, although the epoxy resin had the highest equilibrium uptake, it had the lowest diffusion coefficient. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 483–492, 1999

Syntheses and characterizations of thermally reworkable epoxy resins II

Abstract: In flip-chip technology, the development of reworkable underfill materials has been one of the keys to the recovery of highly integrated and expensive board assembly designs through the replacement of defective chips. This article reports the syntheses, formulations, and characterizations of two new diepoxides, one containing secondary ester linkages and the other containing tertiary ester linkages, that are thermally degradable below 300 °C. The secondary and tertiary ester diepoxides were synthesized in three and two steps, respectively. Both compounds were characterized with NMR and Fourier transform infrared spectroscopy and formulated into underfill materials with an anhydride as the hardener and an imidazole as the catalyst. A dual-epoxy system was also formulated containing the tertiary ester diepoxide and a conventional aliphatic diepoxide, 3,4-epoxy cyclohexyl methyl-3,4-epoxycyclohexyl carboxylate (ERL-4221E), with the same hardener and catalyst. The curing kinetics of the formulas were studied with differential scanning calorimetry (DSC). Thermal properties of cured samples were characterized with DSC, thermogravimetric analysis, and thermomechanical analysis. The dual-epoxy system showed a viscosity of 18.7 and 0.87 P at 25 and 100 °C, respectively. The cured secondary, tertiary, and dual-epoxy formulas showed decomposition temperatures around 265, 190, and 220 °C, glass-transition temperatures around 120-140, 110-157, and 140-157 °C, and coefficients of thermal expansion of 70, 72, and 64 ppm/°C below their glass-transition temperatures, respectively. The shear strength of the cured dual-epoxy system decreased quickly with aging at 230 °C. The reworkability test showed that the removal of a chip underfilled with this material from the board was quite easy, and the residue on the board could be thoroughly removed with a mechanical brush without obvious damage to the solder mask. In summary, the synthesized tertiary epoxide can be used as a reworkable underfill for flip-chip applications.

Interfacial studies on surface modified Kevlar fibre/epoxy matrix composites

Abstract: Kevlar fibre/epoxy composites with superior interfacial strength were developed, by chemical treatment of the fibre surface with organic solvents. Multiple fibre pullout tests revealed that it is possible to raise the interfacial strength to 63 MPa from a value of 39 MPa normally exhibited by untreated Kevlar fibre/epoxy composites. A physicochemical and morphological characterization of the chemically treated fibre surface by microscopic and spectroscopic techniques, aids in the understanding of the observed interfacial properties. The importance of surface oxygen content in matrix bonding and mechanical interlocking of the fibre and matrix was established. Failure analysis of the pullout specimens reveals a strong correlation between the fracture features and the observed test data.

Coated abrasive article

Abstract: A coated abrasive article comprises a backing, a first binder on the backing, and a plurality of abrasive particles in the first binder. The first binder precursor is an energy-curable preferably, melt-processable resin containing an epoxy resin, an ethylene-vinyl acetate copolymer, and a curing agent for crosslinking the epoxy resin that is cured to provide a crosslinked make coating. The above binder precursors of the invention are preferably free of homopolymers and copolymers of olefinic monomers. In another aspect, the invention also describes an energy curable first binder precursor containing an epoxy resin, an ethylene-vinyl acetate copolymer, a polyfunctional acrylate component and a curing agent for crosslinking the epoxy resin that is cured to provide a crosslinked make coating. The invention also relates to a method of producing such coated abrasive articles and a surface-treated backing material.

Phosphorus-containing epoxy resin for an electronic application

Abstract: A phosphorus-containing epoxy resin, 6-H-dibenz[c,e][1,2] oxaphosphorin-6-[2,5-bis(oxiranylmethoxy)phenyl]-6-oxide (DOPO epoxy resin), was synthesized and cured with phenolic novolac (Ph Nov), 4,4′-diaminodiphenylsulfone (DDS), or dicyandiamide (DICY). The reactivity of these three curing agents toward DOPO epoxy resin was found in the order of DICY > DDS > Ph Nov. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorus-containing epoxy resin showed lower weight loss temperature and higher char yield than that of bisphenol-A based epoxy resin. The high char yields and limiting oxygen index (LOI) values as well as excellent UL-94 vertical burn test results of DOPO epoxy resin indicated the flame-retardant effectiveness of phosphorus-containing epoxy resins. The DOPO epoxy resin was investigated as a reactive flame-retardant additive in an electronic encapsulation application. Owing to the rigid structure of DOPO and the pendant P group, the resulting phosphorus-containing encapsulant exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the regular encapsulant containing a brominated epoxy resin. High LOI value and UL-94 V-0 rating could be achieved with a phosphorus content of as low as 1.03% (comparable to bromine content of 7.24%) in the cured epoxy, and no fume and toxic gas emission were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 353–361, 1999

Synthesis, characterization, thermal and flame‐retardant properties of silicon‐based epoxy resins

Abstract: A new silicon-containing oxirane triglycidyl phenyl silane oxide (TGPSO) and its corresponding silicon-containing epoxy resins are synthesized and characterized. The activation energies of TGPSO curing reaction with various curing agents, including 4,4-diaminodiphenylmethane, 4,4-diaminodiphenylsulfone, and dicyanodiaminde, are found to be 180, 196.5, and 154 kJ/mol. The curing reaction of TGPSO with diamines is determined to be a first-order reaction through means of Arrhenius plots. The introduction of the silicon-containing group results in higher curing reactivity. This silicon-containing resin possesses higher char yield as well as higher limiting oxygen index (LOI = 35) than the commercial epoxy resins, confirming the usefulness of these silicon-containing epoxy resins as flame retardants. Char yields and LOI measurements demonstrate that incorporating silicon into epoxy resins is able to improve their flame retardancy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1231–1238, 1999

Mechanical properties of flax fibre reinforced epoxy composites

Abstract: Flax fibre reinforced epoxy composites were prepared by autoclave moulding technique. Influence of various fibre parameters such as lignin content, pectin content and degree of polymerisation on the composite properties was investigated. Fibre surface modifications such as alkali treatment, silane treatment and isocyanate treatment were done to improve the fibre-matrix interactions. The modified fibre surface was characterised by scanning electron microscopy, atomic force microscopy, thermogravimetric analysis and differential scanning calorimetry measurements. It was found that treatment of fibre has significant influence on the mechanical properties of the composites. Morphological studies of the fracture surfaces were carried out using scanning electron microscopy.

Toughening of epoxy resin using hydroxyl-terminated polyesters

Abstract: Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by relatively low toughness. Several approaches to improve epoxy resin toughness include the addition of fillers, rubber particles, thermoplastics, or their hybrids, as well as interpenetrating networks and flexibilizers, such as polyols. It seems that this last approach did not receive much attention. So in an attempt to fill this gap, the present work deals with the use of hydroxyl-terminated polyester resins as toughening agents for epoxy resin. For this purpose, the modifier, that is, a hydroxyl-terminated polyester resin (commercially referred to as Desmophen), which is a polyol, has been used at different concentrations. The prepared modified structure has been characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. Two types of Desmophen (800 and 1200) have been used as modifiers. The obtained results showed that hydroxyl-terminated polyester improves the epoxy toughness. In fact, the impact strength increases with Desmophen content and reaches a maximum value of 7.65 J/m at 10 phr for Desmophen 800 and 9.36 J/m at 7.5 phr for Desmophen 1200, respectively. At a critical concentration (7.5 phr), Desmophen 1200 (with higher molecular weight, longer chains, and lower branching) leads to better results. Concerning Kc, the effect of Desmophen 800 is almost negligible; whereas a drastic effect is observed with Desmophen 1200 as Kc reaches a maximum of 2.41 MPa m1/2, compared to 0.9 MPa m1/2 of the unmodified epoxy prior to decreasing. This is attributed to the intensive hydrogen bonding between epoxy and Desmophen 1200, as revealed by FTIR spectroscopy. Finally, the SEM analysis results suggested that the possible toughening mechanism for the epoxy resin being considered, which might prevail, is through localized plastic shear yielding induced by the presence of the Desmophen particles. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 29–38, 1999

Influence of surface treatment of glass fibres on the dynamic mechanical properties of epoxy resin composites

Abstract: In this study the influence of the interface of differently treated glass fibres in epoxy resin composites is investigated by dynamic mechanical analysis. These results are compared with mechanical measurements of adhesion. It is found that the flexural storage modulus E′ of the composites with improved interfacial bonding is increased over the whole investigated temperature range. Decrease of the magnitude of tan δ at the α-relaxation associates with an improvement of interfacial bonding too. The behaviour differences can only be attributed to interfacial phenomena because all other parameters were kept constant. The dynamic mechanical analysis is an additional possibility for quantifying interfacial interactions.