Showing papers on "Epoxy published in 1996"
TL;DR: In this article, a new class of phenolic-like thermosetting resins has been developed that is based on the ring-opening polymerization of a benzoxazine precursor, which combines the thermal properties and flame retardance of phenolics with the mechanical performance and molecular design flexibility of advanced epoxy systems.
Abstract: A new class of phenolic-like thermosetting resins has been developed that is based on the ring-opening polymerization of a benzoxazine precursor. These new materials were developed to combine the thermal properties and flame retardance of phenolics with the mechanical performance and molecular design flexibility of advanced epoxy systems. The polybenzoxazines overcome many of the traditional shortcomings of conventional novolak and resoletype phenolic resins, while retaining their benefits. The physical and mechanical properties of these new polybenzoxazines are investigated and are shown to compare very favorably with those of conventional phenolic and epoxy resins. The ring-opening polymerization of these new materials occurs with either near-zero shrinkage or even a slight expansion upon cure. Dynamic mechanical analysis reveals that these candidates for composite applications possess high moduli and glass transition temperatures, but low crosslink densities. Long-term immersion studies indicate that these materials have a low rate of water absorption and low saturation content. Impact, tensile, and flexural properties are also studied. Results of the dielectric analysis on these polybenzoxazines demonstrate the suitability of these materials for electrical applications. © 1996 John Wiley & Sons, Inc.
711 citations
TL;DR: In this paper, the authors describe the preparation of hard carbon samples from epoxy resins and show that these materials incorporate small nanopores between the single layers, which are about 15 A in diameter.
610 citations
TL;DR: The percolation threshold for composites made by dispersing anisometric, single-crystal graphite flakes in either an epoxy resin or a polyurethane polymer matrix is examined.
Abstract: We examine the percolation threshold for composites made by dispersing anisometric, single-crystal graphite flakes in either an epoxy resin or a polyurethane polymer matrix. Analysis is based on empirical and excluded-volume approaches and the results are compared with a similar treatment using literature data of carbon-fiber based composites. \textcopyright{} 1996 The American Physical Society.
485 citations
TL;DR: In this paper, a new class of phenolic-like thermosetting resins was developed that is based on the ring opening polymerization of a benzoxazine precursor, which is copolymerized with an epoxy resin in order to modify their performance.
425 citations
TL;DR: In this paper, the mechanical properties of sisal fiber composites of several thermoset resin matrices, [polyester, epoxy, phenol-formaldehyde] and a thermoplastic matrix [low density polyethylene (LDPE)] were evaluated with respect to fibre length and fibre loading.
224 citations
TL;DR: In this paper, the activation energies for polymerization of intra- and extragallery monomer, as determined by DSC measurements, are 84 and 130 KJmol −1, respectively.
200 citations
TL;DR: In this article, the authors used a dynamic mechanical analyzer (DMA) to characterize the viscoelastic properties of a commercial epoxy resin and developed master curves of stress relaxation behavior during cure.
Abstract: Epoxy resins and other thermosetting polymers change from liquids to solids during cure. A precise process model of these materials requires a constitutive model that is able to describe this transformation in its entirety. In this study the viscoelastic properties of a commercial epoxy resin were characterized using a dynamic mechanical analyzer (DMA). Specimens were tested at several different cure states to develop master curves of stress relaxation behavior during cure. Using this experimental data, the relaxation modulus was then modeled in a thermorheologically complex manner. A Prony (exponential) series was used to describe the relaxation modulus. An original model was developed for the stress relaxation times based on similar work by Scherer (16) on the relaxation of glass. Shift functions used to obtain reduced times are empirically derived based on curve fits to the data. The data show that the cure state has a profound effect on the stress relaxation of epoxy. More important, the relaxation behavior above gelation is shown to be quite sensitive to degree of cure.
187 citations
TL;DR: In this article, the mechanical properties of carbon fiber reinforced composites and Al2O3particles dispersed carbon fiber hybrid reinforced composite were investigated, and the effects of hybridization effects on mechanical properties with nano-and micron-sized Al 2O3 particles were discussed.
187 citations
TL;DR: The first examples of organic polymer-layered silicic acid nanocomposites have been prepared by formation of a cured epoxy polymer network in the presence of organo cation exchange forms of magadite as mentioned in this paper.
Abstract: The first examples of organic polymer-layered silicic acid nanocomposites have been prepared by formation of a cured epoxy polymer network in the presence of organo cation-exchange forms of magadite. The transparency of the exfoliated magadiite hybrid is an especially notable property.
183 citations
TL;DR: In this article, near and mid-infrared spectroscopy techniques were used to study the cure reaction of accelerated diphenyldimethylurea (Diuron) epoxy formulation based on diglycidyl ether of bisphenol A (DGEBA) prepolymer curing with dicyandiamide (DDA) hardener.
165 citations
TL;DR: In this paper, the dielectric properties of the diglycidyl ether of Bisphenol A with 4,4‘-diaminodicyclohexylmethane in the temperature range 290−353 K were studied.
Abstract: Dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC) have been used simultaneously as a means of following the isothermal cure of the diglycidyl ether of Bisphenol A with 4,4‘-diaminodicyclohexylmethane in the temperature range 290−353 K. The dielectric permittivity and dielectric loss of the thermosetting mixture have been measured as a function of reaction time over the frequency range 101.2−105 Hz. The evolution of the dielectric properties was studied as the curing temperature was lowered to values close to the solidification of a sample. The kinetics of the cure have also been determined, using calorimetry, for four reaction temperatures over the whole range of conversion up to the point where the system vitrifies and the reaction becomes diffusion-controlled. Correlations between the changes in molecular dynamics and the chemical kinetics occurring during the thermosetting process have been made in some detail, and a theoretical working model has been developed that a...
IBM1
TL;DR: A series of cycloaliphatic diepoxides with cleavable acetal links were synthesized and characterized in this paper, which can extend the utility of thermosetting epoxies by preserving their positive attributes while eliminating their well known intractability after curing.
Abstract: A series of cycloaliphatic diepoxides with cleavable acetal links were synthesized and characterized. These materials were shown to undergo thermosetting reactions with cyclic anhydride in very similar fashion to a commercial cycloaliphatic epoxide, but cured samples were easily dissolved in a variety of acid-containing solvent mixtures. Such materials can extend the utility of thermosetting epoxies by preserving their positive attributes while eliminating their well known intractability after curing. The latter property is particularly a problem for manufacturers designing products for disassembly at end of use in order to facilitate recycling. © 1996 John Wiley & Sons, Inc.
TL;DR: In this article, a new phosphorus-containing oxirane, bis-(3-glycidyloxy)phenylphosphine oxide (BGPPO), was synthesized.
Abstract: A new phosphorus-containing oxirane, bis-(3-glycidyloxy)phenylphosphine oxide (BGPPO), was synthesized. Further curing BGPPO with diamine curing agents, dicyanodiamide (DICY), 4,4′-diaminodiphenylmethane (DDM), and 4,4′-diaminodiphenylsulfone (DDS), respectively, resulted in several phosphorylated epoxy resins. Compared with Epon 828, Eponex 1015, and DER 732, BGPPO showed relatively high reactivity toward diamine agents via DSC studies. Furthermore, the reactivity of the three curing agents toward BGPPO were found to be in the order of DDM > DICY > DDS. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorylated resins showed lower weight loss temperatures and higher char yields than did the Epon 828-based resins. The high char yields as well as high limited oxygen index (LOI) values of the BGPPO-based resins confirmed the effectiveness of phosphorus-containing epoxy resins as flame retardants. © 1996 John Wiley & Sons, Inc.
TL;DR: In this paper, the electrical conduction of (0,degree) unidirectional (UD) CFRP parallel to the fibers is modeled using the parallel resistance approach, which can be taken as an indicator of the evolution of various types of damage in classical longitudinal UD but also in ({+-} 45{degree}) CFRP laminates.
Patent•
04 Oct 1996
TL;DR: Aqueous thixotropes for waterborne systems are disclosed in this paper, including an aqueous dispersion of fumed silica and a waterborne resins.
Abstract: Aqueous thixotropes for waterborne systems are disclosed including an aqueous dispersion of fumed silica and a waterborne resin. The waterborne resin is selected from the group consisting of alkyd, acrylic, polyester, polyether, silicate, urethane, epoxy, formaldehyde, vinyl, and mixtures thereof. The fumed silica has a surface area between about 85 m2/g and about 410 m2/g, and is present in the system in an amount between about 0.5 and about 10.0 % by weight, of total resin solids.
TL;DR: In this paper, a modified statistical theory for microcomposite strength as a function of length was developed to incorporate this a effect, where both the expected doubling and tripling of the Weibull shape parameter as compared to that of the fiber and the predicted a effect for micro composite length were observed.
TL;DR: In this paper, an analytical procedure was developed for modelling the kinetics of the cure process of a commercial epoxy resin for resin transfer molding (RTM) applications, using differential scanning calorimetry (DSC) in the isothermal and dynamic modes to obtain the experimental database.
Abstract: An analytical procedure has been developed for modelling the kinetics of the cure process of a commercial epoxy resin for resin transfer moulding (RTM) applications, using differential scanning calorimetry (DSC) in the isothermal and dynamic modes to obtain the experimental database. The overall reaction rate of the epoxide groups with amines was determined and fitted by an autocatalytic kinetic model. An improvement of the model to allow for diffusion limitation effects results in a good agreement between experimentally determined and predicted reaction rates. A non-linear least squares regression analysis method based on Marquardt's algorithm was used to fit the DSC reaction rate data with an appropriate model and to evaluate the activation energies and the reaction orders for this particular resin system. The Di Benedetto equation was utilised to establish the relationship between conversion and glass transition temperature (T g ), required to develop the diffusion-dominated part of the model.
TL;DR: In this paper, the improvement of flame-retardation of thermosetted epoxy-amine resins was attempted by chemically incorporating phosphorus-containing reagents, and the quantitative aspect of the addition of dialkyl (or aryl) phosphate onto glycidyle oxiranes was evaluated by elemental analysis.
Abstract: The improvement of flame-retardation of thermosetted epoxy–amine resins was attempted by chemically incorporating phosphorus-containing reagents. By reacting 4,4′-diglycidylether of bisphenol A (DGEBA) with dialkyl (or aryl) phosphate, it was possible to chemically modify the epoxy resin and then cure it in the presence of 4,4′-diaminodiphenylsulfone (DDS) to obtain epoxy-amine resin with good flame-retardant and thermal stability behaviors. The quantitative aspect of the addition of dialkyl (or aryl) phosphate onto glycidyle oxiranes was evaluated by elemental analysis of the modified epoxy-amine resins. Flammability and thermal behaviors of modified DGEBA/DDS resins depend on the nature of phosphate groups (the best flame-retardation was observed on resins bearing phenyl phosphate groups) and their concentration in the material. In relation to DGEBA/DDS samples containing additives of the same structure [trialkyl(or aryl) phosphate], cured resins incorporating chemically bonded phosphate groups show a better flame-retardation. On the contrary to the nonomodified DGEBA/DDS [with or without trialkyl (or aryl) phosphate as additive], combustion of modified DGEBA/DDS resins is accompanied by formation of intumescent char. Chemical modification of DGEBA by dialkyl (or aryl) phosphates can be carried out in situ during the curing of epoxy resins without change in the fire behavior. © 1996 John Wiley & Sons, Inc.
TL;DR: In this paper, three different routes were used to fabricate ceramic particle dispersed epoxy composites, and the wet ball-milling technique was found to be effective for homogeneous dispersion of ceramic particles.
TL;DR: In this paper, the authors measured the moisture absorption characteristics, longitudinal shear modulus and loss factor, and the interlaminar shear strength of polymer composites, with a view to assessing the feasibility of the use of dynamic measurements as a nondestructive tool for determining the structural integrity of polymer composite degraded by moisture.
TL;DR: In this article, the first step of electrolyte penetration through the coating is related to water uptake, when molecules of pure water diffuse in the micropores of polymer net according to Fick's law and it is independent of type and dimensions of ions in the electrolyte.
Patent•
IBM1
TL;DR: In this paper, an aluminum or copper heat sink is attached to a ceramic cap or exposed semiconductor chip using flexible-epoxy to provide improved thermal performance, which is useful for CQFP, CBGA, CCGA, CPGA, TBGA, PBGA, DCAM, MCM-L, single layer ceramic, and other chip carrier packages.
Abstract: An aluminum or copper heat sink is attached to a ceramic cap or exposed semiconductor chip using flexible-epoxy to provide improved thermal performance. The aluminum may be coated by anodizing or chromate conversion or the copper may be coated with nickel. Such structures are especilly useful for CQFP, CBGA, CCGA, CPGA, TBGA, PBGA, DCAM, MCM-L, single layer ceramic, and other chip carrier packages as well as for flip chip attachment to flexible or rigid organic circuit boards. These adhesive materials withstand thermal cycle tests of 0° to 100° C. for 1,500 cycles, -25° to 125° C. for 400 cycles, and -40° to 140° C. for 300 cycles; and withstand continuous exposure at 130° C. for 1000 hours without loss of strength. Flexible-epoxies have a modulus of elasticity below 100,000 psi and a glass transition temperature below 25° C., are much stronger than typical silicone adhesives, and do not contaminate the module or circuit board with silicone. The flexible epoxy may contain a material having a low coefficient of thermal expansion (CTE) in order to provide a CTE between that of the silicon die and the metal of the heat sink.
TL;DR: In this paper, the use of biocomposite materials in the construction of amperometric biosensors is discussed. But the authors do not discuss the application of such composites in the biomedical field.
Abstract: This paper reviews the use of biocomposite materials in the construction of amperometric biosensors. These rigid composites are formed by dispersing graphite particles in assorted polymers (especially epoxy resins). These composites are bulk-modified biologically (adding enzymes and cofactors) and chemically (blending mediators and catalysts).
TL;DR: In this paper, the non-isothermal vitrification and devitrification of two epoxy thermosetting systems have been studied using modulated differential scanning calorimetry (MDSC).
TL;DR: In this paper, the micromechanics of reinforcement of a model composite consisting of continuous high-modulus fiber embedded in epoxy resin has been investigated as a function of fiber sizing.
Abstract: The micromechanics of reinforcement of a model composite consisting of continuous high-modulus fibre embedded in epoxy resin has been investigated as a function of fibre sizing. The composite was subjected to incremental tensile loading up to full fragmentation, while the stress in the fibre was monitored at each level of applied strain with the new technique of remote laser Raman microscopy. The two systems exhibited differences in the residual stress field with the unsized fibre being in compression. The average stress in the fibre increased linearly with applied matrix strain up to first fracture. After fracture, the stress in the fibre was found to build from the tips of the fibre breaks, reaching a maximum value at the middle of each fragment. The shape of the stress transfer profiles indicated minor differences between the two systems at moderate strains. At high strains, the stress transfer profiles of the two systems were distinctly different possibly owing to the presence of two different interfacial failure modes in the two types of model composites. The maximum interfacial shear stress for both systems was of the order of 40 MPa with the sized system exhibiting slightly better adhesion. SEM examination of the fracture surfaces revealed clear interfacial failure for the unsized system whereas the sized system indicated areas of good adhesion.
TL;DR: In this paper, the influence of blend morphology on mechanical behavior of rubber-toughened polymers was investigated, and it was found that a blend with a connected microstructure provides significantly higher fracture toughness compared to a similar blend containing uniformly dispersed particles.
Abstract: The influence of blend morphology on mechanical behaviour of rubber-toughened polymers was investigated. Diglycidyl ether of bisphenol A epoxies toughnened by core-shell rubber particles were employed as the model systems. The blend morphology was varied by changing the composition of the shell of particles, the curing agent, and the extent of agitation prior to casting. It is shown that the most uniform dispersion of particles is obtained when the shell of the modifiers contains reactive groups. In the absence of the reactive groups and when a slow curing agent is employed, however, a highly connected microstructure is obtained. It was found that a blend with a connected microstructure provides significantly higher fracture toughness compared to a similar blend containing uniformly dispersed particles. The reason for this observation is that the connected morphology enables the shear bands to grow further from the crack tip and thus consume more energy before fracture occurs. Also, the yield strength in uniaxial tensile testing is significantly lower in the blend with the connected morphology. Therefore, it should contribute to a larger plastic zone size.
Patent•
12 Apr 1996
TL;DR: In this article, a linear motor has an epoxy core armature with dual cold plates attached to a top and a bottom of the armature to reduce heat build-up by providing paths of high thermal conductivity from any point in the armatures to the cold plates.
Abstract: A linear motor has an epoxy core armature with dual cold plates attached to a top and a bottom of the epoxy core armature to effect cooling of the epoxy core armature. The use of dual cold plates with circulating cooling fluid reduces heat build up by providing paths of high thermal conductivity from any point in the epoxy core armature to the cold plates. Another embodiment of the invention employs ceramic heat sink plates laminated to sides of the epoxy core armature to increase the thermal conductivity and the resultant power dissipation capacity of the epoxy core armature without introducing magnetic or electrically conducting materials. Other embodiments of the invention utilize cold plates formed from extrusions of aluminum or ceramic materials. Still other embodiments have forced air cooling wherein a U-frame of the linear motor has longitudinal flexible seals and air is forced through the U-frame in which the epoxy core armature travel. Yet another embodiment has a U-frame with ducts formed therein through which air is force. Orifices connect the ducts to an interior of the U-frame through which the epoxy core armature travels.
TL;DR: In this paper, a stable dispersion of polysiloxane thermoplastic polyurethane (TPU) particles in an epoxy resin matrix was achieved via epoxy ring opening with the isocyanate groups of urethane prepolymer to form an oxazolidone.
TL;DR: In this paper, a diglycidyl ether of bisphenol A epoxy resin was modified by incorporation of varying concentrations of hollow glass spheres (HGS) and/or reactive liquid rubber (CTBN).
Abstract: A diglycidyl ether of bisphenol A (DGEBA) epoxy resin was modified by incorporation of varying concentrations of hollow glass spheres (HGS) and/or reactive liquid rubber (CTBN). The fatigue crack propagation (FCP) behavior and mechanisms of such materials were studied in detail. A synergistic phenomenon reported for static fracture toughness was also observed in the FCP resistance of such composites. Optical microscopy studies revealed that the interactions between the stress fields of the crack-tip process zone and HGS cause plastic-zone branching, which in turn gave rise to synergistic toughening. It is also shown that process zone - second phase particle interactions cause a transition in FCP behavior of rubber-modified epoxy polymers, similar to that observed in metal alloys. Consequently, the process zone toughening mechanisms are active only above a certain stress intensity range. Conversely, FCP resistance of both modified and unmodified epoxies were the same below the transition.
TL;DR: In this paper, the interphase properties of glass fiber/polypropylene composites have been investigated using fibres sized with γ-aminopropyltriethoxysilane (A1100) and various polymer dispersions (polyethylene/polyurethane (PE/PUR).
Abstract: To ensure efficient transfer of stress between glass fibres and polypropylene (PP) matrix, the fibres are sized and the matrix is chemically modified. In this study, the interphase properties of glass fibre/PP model composites have been investigated using fibres sized with γ-aminopropyltriethoxysilane (A1100) and various polymer dispersions (polyethylene/polyurethane (PE/PUR). PP, PP/PUR and epoxy) and unmodified (PP) or modified (PPM) matrices. The acid-base properties of the fibre surface were characterized by zeta potential measurements in electrolyte solutions with varying pH. Fibre-melt interaction was characterized by direct wetting measurements of polymer melts on fibre surfaces and single-fibre pull-out tests under conditions comparable to processing conditions. Composite mechanical properties influenced by fibre—melt interaction were tested using continuous fibre-reinforced polypropylenes. The direct fibre—melt wetting experiments provided evidence for acid—base interactions together with interdiffusion effects in the interphase between sized glass fibres and the modified polypropylene matrix or physical interactions at the fibre—polymer melt interface. It was proved that these physical or chemical interactions influence the interfacial shear strength and the macromechanical properties. Differences in the interfacial shear strength correlated with different wetting kinetics due to the different formulations of film former used.