Uncured Epoxy Research Articles

Self-healing woven glass fabric/epoxy composites with the healant consisting ofmicro-encapsulated epoxy and latent curing agent

This paper reports a study of self-healing woven glass fabric reinforced epoxy composites.The healing agent was a two-component one synthesized in the authors’ laboratory, whichconsisted of epoxy-loaded urea-formaldehyde microcapsules as the polymerizable binder andCuBr2(2-methylimidazole)4 (CuBr2(2-MeIm)4) as the latent hardener. Both the microcapsules and the matching catalyst werepre-embedded and pre-dissolved in the composites’ matrix, respectively. Whenthe microcapsules are split by propagating cracks, the uncured epoxy can bereleased into the damaged areas and then consolidated under the catalysis ofCuBr2(2-MeIm)4 that was homogeneously distributed in the composites’ matrix on a molecular scale. As aresult, the cracked faces can be bonded together. The influence of the content of theself-healing agent on the composites’ tensile properties, interlaminar fracturetoughness and healing efficiency was evaluated. It was found that a healing efficiencyover 70% relative to the fracture toughness of virgin composites was obtainedin the case of 30 wt% epoxy-loaded microcapsules and 2 wt% latent hardener.

Study of Amine-Cured Epoxy Resin/Aluminium Oxide Interfacial Interaction

The interfacial structure and interactions of amine-cured epoxy resin (EP) / aluminium oxidie system were investigated in this presentation. The competitive chemisorption of uncured epoxy resin on Al2O3 particles were measured by FTIR and XPS. The interphase structure and the morphology at different depths of the broken-surface of the samples were characterized by XPS and SEM. The results showed that the nitrogenous molecules in the system formed the adsorbed monolayers on the interface based on the coupling interaction of the adsorption and cure. The composition, binding energy and chemical properties of the interphase deviated considerably from that of the bulk.

Sources of variability in uncured aerospace grade unidirectional carbon fibre epoxy preimpregnate

Two sources of variability have been investigated in uncured unidirectional carbon epoxy preimpregnate (prepreg). The variability in mass/unit area properties has been measured at various scales and compared to the specification limits as defined by the manufacturer. Both random variability and a structured variation in mass properties across the width of the roll can be detected; and as might be expected the variability rises rapidly as the scale on which the measurements are performed is reduced. The variability in fibre straightness has been studied in two ways, by direct measurements of fibre misalignments in as-delivered prepreg, and by inference from measurements of the tensile load response of uncured prepreg. A significant level of fibre misalignment is detectable in as-delivered prepreg, largely as in-plane wrinkling, although both macroscopic out of plane wrinkling and very localised small scale out of plane wrinkling can also be detected. This misalignment increases with forming, both in and out-of plane wrinkling becoming more severe. The influence of these variabilities on laminate and component response are considered.

Nanostructural Control of Carbon Nanofiller/ Epoxy Composite by Using an Alternating Electric Field

It is well known that carbon nanofillers (CNFs) enhance the stiffness, electric conductivity and thermal conductivity of polymers. Alignment of carbon nanofillers in polymer is expected to increase the performances in the aligned direction. Several papers have reported that applying alternating electric field to a liquid suspension including CNFs causes alignment of CNFs in the electric field direction. Only a few papers have reported the fabrication of nanostructurally controlled composites by using AC field, but the conditions to let CNFs align have not been investigated. In this study, unidirectionally aligned carbon nanofiller/epoxy composite was fabricated under AC electric field, and the alignment of CNFs was in-situ observed during fabrication by using an optical microscope. Then, the effects of applied voltage, frequency and the weight fraction of CNFs on nanostructure were investigated. As a result, it is found that CNFs in uncured epoxy resin align in the AC electric field and form a chain-like network, and that in the end the network structure is hold with cured epoxy. It is also shown that the applied voltage and weight fraction affect the morphology of the network. Furthermore, the network morphology was quantified by using texture analysis. Local homogeneity in the longitudinal and transverse directions of the AC electric field was used. It is found that there is strong relationship between the changes of local homogeneity and network morphology.

Nanostructured thermoset epoxy resin templated by an amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) diblock copolymer

AbstractAn amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006

New method for the synthesis of clay/epoxy nanocomposites

AbstractA new liquid–liquid method for the synthesis of epoxy nanocomposites was developed. This new method improved the dispersion and exfoliation of the organoclay in the polymer matrix, thus improving the end‐use properties. The microstructure and physical properties of the clay/epoxy nanocomposite synthesized by the new method were studied. Rheological tests of the uncured epoxy–organoclay system demonstrated that this method resulted in a great increase in viscosity, much more than the most commonly used direct‐mixing method. The Krieger–Dougherty model successfully described the dispersion of the clay layers in the uncured epoxy. In the 5 wt % organoclay nanocomposite, compressive tests on the cured samples showed that there was a 45% increase in the maximum strength, a 10% increase in the yield strength, and a 26% increase in the modulus over the pure epoxy–amine cured system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4286–4296, 2006

Nonlinear Constitutive Model of Uncured Epoxy Resin

The Bingham model characterizes the yield stress of a viscous fluid but does not take into account the shear‐thinning effect; on the other hand the power‐law fluid model characterizes the shear‐thinning effect but does not incorporate a yield stress. Based on rheologic test results, a new epoxy resin constitutive equation is proposed with mathematical justification. It is different from the existing models because every term and every coefficient in it have physical meaning, which clarifies the essence of viscoelasticity of resin materials. The proposed model indicates that the yield stress is one of the main reasons for the shear‐thinning effect, and it reveals why some materials have double Newtonian regions with the shear viscosity value in the first region higher than that in the second region.

12-Tungstophosphoric Acid Composites with Sulfonated or Unsulfonated Epoxies for High-Temperature PEMFCs

The use of 12-tungstophosphoric acid (HPW) as the ionomer in high temperature, >100 °C, proton exchange membrane fuel cells (PEMFCs) was investigated. Since HPW is a crystalline solid, the material is more conveniently studied in membranes fabricated from composites of polymers and HPW. A commercially available high-temperature epoxy was chosen as the polymer for our initial studies. The ionomer was added, either by mixing the HPW with the uncured epoxy or by soaking a cured epoxy membrane in an aqueous solution of HPW. Sulfonated and unsulfonated epoxy membranes, with and without HPW, were fabricated. The structure of the composite membranes was characterized using attenuated total reflectance infrared spectroscopy, small angle X-ray scattering, scanning electron microscopy, and thermal gravimetric analysis. Fuel cell polarization curves were obtained for the membranes under varying conditions of temperature and humidification. A trend of increasing current density was noted with increasing temperature for the HPW-doped sulfonated epoxy membrane. All of the membranes exhibited sufficient mechanical strength to 165 °C. Where the sulfonated epoxy, without HPW, failed at temperatures above 165 °C, the sulfonated membranes with HPW functioned in the fuel cell to ⩽200 °C. © 2004 The Electrochemical Society. All rights reserved.

Sensitivity of surface free energy analysis methods to the contact angle changes attributed to the thickness effect in thin films

AbstractThe surface tension of thin, uncured epoxy films spun‐cast onto oxidized silica wafers was analyzed as a function of their thickness in the range of 5 to 75 nm. Based on contact angle measurements with polar and apolar liquids, the surface free energies of various films were analyzed and compared using Lifshitz–van der Walls/acid–base (LW/AB), harmonic mean (of Wu), geometric mean, and Zisman approaches. Results of harmonic mean and Zisman surface tension analyses, in spite of significant changes in contact angle attributed to changes in thickness, did not show significant changes. However, geometric mean and LW/AB methods did reveal limited changes in free energy of epoxy surface attributed to variations in thickness. The surface tension components showed a similar trend to that of contact angle changes. It seems that it is better to use surface free energy analysis methods, which use several liquids with different polarities, to reveal the accumulative effect of different group free energy densities on total surface free energy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1972–1980, 2004

Polymerization Processes of Epoxy Matrix Composites under Simulated Free Space Conditions

The creation of large-size space constructions by deploying structures needs a method for making the shell material rigid after unfolding. The best method is a chemical reaction. There is a negative influence of space environment (high vacuum, atomic oxygen flux, cosmic rays, sun irradiations, sharp temperature variations) on a liquid polymer matrix and on the polymerization process. The authors suggest that the space environment can initiate the polymerization reaction, for example a curing reaction of epoxy resin composition. This paper contains the results of experiments on polymerization processes under the action of separate space environment factors: vacuum and plasma action. For the simulation of space plasma a discharge of microwave plasma and radio-frequency plasma were used. Structures of polymer materials cured under plasma and in the usual curing conditions were compared. The results on degradation processes in uncured epoxy resin under plasma action were taken into account for the curing kinetic study. The fornation of new active groups in liquid composition under plasma action and the ability of new groups to take part in the curing reaction was analysed. A process of layer mixing in uncured epoxy resin during plasma action was observed. The mixing of oxidized layers with initial bulk layers of resin leads to an acceleration of the curing reaction. Due to layer mixing the plasma treatment becomes a method for bulk modification of polymers. A method of utilization of negative free space factors for the curing process of composite materials in free space is proposed. The space plasma can be used for the polymerization process of composite materials on Earth orbit. The composite samples of glass fibres impregnated by the epoxy matrix with 5 mm thickness were polymerized in plasma discharge at low pressure without formation of bubbles.

Effects of irradiation and design basis accident conditions on thermal properties of epoxy coating system for nuclear power plant

In this work, the thermal properties of epoxy coating system on carbon steel liner in an atomic reactor container have been investigated in terms of irradiation and design basis accident (DBA) conditions. Two epoxy coating systems were irradiated by different dose rates, i.e. 1×10 6 and 5×10 5 rad/h in a total dosage of 2×10 8 rad/h. And, DBA tests were applied to them based on the specification. The glass transition temperature ( T g) and thermal stability of the epoxy coating systems after tests were measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. As a result, the irradiation led to the fracture of internal structure in cured epoxy systems, resulting in significantly decreasing the thermal stability, as well as, the T g. Also, the higher dose rate made a relaxation of epoxy resins to reduce the hardening of the network system. Whereas, the DBA test made an important role in the thermal stability in the epoxy coating systems, resulting in post-curing of the uncured epoxy resins. Consequently, it could be found that the thermal properties of the epoxy coating system were greatly influenced on the irradiation and DBA tests, which were probably due to the modification of internal network structure of the epoxy resins.

Crystallization and Equilibrium Melting Behavior of Poly(Butylene Terephthalate)/Epoxy Blends

Blends of poly(butylene terephthalate) (PBT) with epoxy resin (diglycidyl ether of bisphenol-A) have been prepared by blending in a mini-mixer and then cured using a 4-functional amine curing agent at 175°C for 4 hr. Melting and crystallization behavior of the uncured and cured blends has been studied using differential scanning calorimetry. Isothermal crystallization studies of the uncured, as well as cured, blends have been carried out to determine the induction time for the onset of the nucleation process. The equilibrium melting behavior of cured and uncured blends has been studied using Hoffman‐Week's linear extrapolation method. From the equilibrium melting temperature γ, the proportionality factor between initial thickness of chain-folded lamella and final thickness was calculated. The Flory interaction parameter, χ, between PBT and epoxy resin has been calculated using the Nishi–Wang equation. The interaction parameter is found to be negative, indicating that PBT forms a thermodynamic stable mixture with the epoxy monomer. It has been shown that PBT forms miscible blend with uncured epoxy, which affects the crystallization and equilibrium melting behavior of PBT. After curing, due to the phase separation of PBT and epoxy, the melting and crystallization behavior of cured blends is closer to that of pure PBT.

Phase Separation of Poly(ether sulfone imide) Modified Epoxy Resins

Amine terminated poly(ether sulfone imide) (PESI) with various imide and ethersulfone contents but similar polymer molecular weights were blended with diglycidyletherbisphenol-A (DGEBA) and cured with diaminodiphenylsulfone (DDS). The imide group, a tertiary amine, is a catalyst of the curing reaction of DGEBA with DDS, but it is poorly compatible with uncured epoxy resin. The ethersulfone group is not a catalyst of the curing reaction of DGEBA with DDS, but it has a similar chemical structure as DDS and is compatible with epoxy resin while it is at a low degree of curing. Since PESIs used in this study had similar molecular weights, increasing imide content of PESI would reduce ethersulfone content. The influence of imide and ethersulfone contents of PESI on the phase separation and curing reaction of DGEBA/DDS/PESI blend was investigated using differential scanning calorimetry (DSC), time-resolved light scattering (TRLS), and polarized optical microscopy (POM). Though the imide group has a catalysis effect on the curing reaction of DGEBA with DDS, however, its poor compatibility with epoxy resin retards the curing reaction. Our experimental results revealed the morphology of the cured blends and the curing behavior was a compromise result of catalysis and compatibility of PESI with epoxy resin.

Epoxy Compounds: Aromatic Diglycidyl Ethers, Polyglycidyl Ethers, Glycidyl Esters, and Miscellaneous Epoxy Compounds

Epoxy Compounds: Aromatic Diglycidyl Ethers, Polyglycidyl Ethers, Glycidyl Esters, and Miscellaneous Epoxy Compounds

Dewetting of Unreacted Epoxy/Amine Mixtures on Silica

We employ a direct method, time-of-flight secondary ion mass spectroscopy (ToF-SIMS), to determine experimentally the chemical compositions of the wetted and dewetted regions of an uncured epoxy thin film. Determining the composition of the dewetted region indicated the presence of a very thin sublayer of resin in what was thought to be a region devoid of resin. The capability of ToF-SIMS to probe small 65×65 μm 2 areas of the surface has permitted us to directly compare the SIMS spectra of the wetted and dewetted regions to the survey spectra of the reactants. This may indicate the strength of resin/silica interactions, which determine interface formation and properties.

建築用エポキシ樹脂接着剤から溶出するビスフェノールAの定量分析

It has been pointed out that bisphenol A has possibility to be one of the endocrine disruptors. It is considered that bisphenol A is included in epoxy resin minutely; therefore, it is essentially important to know how much amount of bisphenol A is eluted from epoxy resin adhesives for construction works. In this context, quantitative analysis of bisphenol A eluted from two brands of commercial epoxy resin adhesives for construction was conducted in the study. The results obtained can be summarized as follows; 1) 0.1x10^<-6>grams and 11x10^<-6>grams of bisphenol A were eluted with acetonitrile from 1 gram of the two brands of uncured epoxy resin adhesives, respectively. 2) 0.030x10^<-6>grams and 0.017x10^<-6>grams of bisphenol A were eluted from 1 gram of the two brands of cured epoxy resin adhesives with 60℃ water. 0.077x10^<-6> grams and 0.064x10^<-6>grams of bisphenol A were eluted from 1 gram of the same cured epoxy resin adhesives with 60℃ alkaline water.

Miscibility, crystallization and real-time small-angle X-ray scattering investigation of the semicrystalline morphology in thermosetting polymer blends

The results of the study of a completely miscible thermosetting polymer blend containing a crystallizable component are reported. Blends of poly(ϵ-caprolactone) (PCL) and bisphenol-A-type epoxy resin (ER) cured with 4,4′-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA) were prepared and compared with blends of PCL with uncured bisphenol A-type epoxy resin, i.e. diglycidylether of bisphenol A (DGEBA). The miscibility, crystallization behavior and spherulitic morphology of both uncured DGEBA/PCL blends and MCDEA-cured ER/PCL blends were investigated by differential scanning calorimetry (DSC), optical microscopy, and Fourier-transform infrared (FTIR) spectroscopy. It was found that PCL is completely miscible with both DGEBA and MCDEA-cured ER in the melt and in the amorphous state over the entire composition range, as shown by the existence of a single composition-dependent glass transition temperature (Tg). The overall crystallization rate and crystallinity of PCL in the MCDEA-cured ER/PCL blends decrease much more rapidly with increasing amorphous content than those of the DGEBA/PCL blends. The spherulitic morphology of PCL in both the uncured and the cured blends is characteristic of miscible crystalline/amorphous blends, and the PCL spherulites in these blends are always completely volume-filling. The miscibility of the uncured DGEBA/PCL blends is considered to be due predominately to the entropic contribution, whereas that of the cured ER/PCL blends is due to the enthalpic contribution. FTIR investigations indicated hydrogen bonding interaction between the hydroxyl groups of MCDEA-cured ER and the carbonyl groups of PCL in the cured system, which is an important driving force for the miscibility of the cured ER/PCL blends. Real-time small-angle X-ray scattering (SAXS) experiments revealed that the amorphous cured ER segregated interlamellarly during the crystallization process of PCL, which is considered to result from the low chain mobility of the cured ER in the ER/PCL blends. On the basis of the SAXS results, a model describing the semicrystalline morphology of MCDEA-cured ER/PCL blends is proposed. The amorphous fraction of PCL, the branched ER chains and imperfect ER network are located between PCL lamellae in the crystallized blend.

Wetting Dynamics of an Oil-accommodating Adhesive

Oil-accommodating adhesives are widely used industrially to avoid the necessity of degreasing metals before bonding. We have undertaken a study of the behaviour of drops of an uncured model epoxy adhesive on both degreased and oiled, galvanized, steel sheet during temperature increase. Contact angle, θ, vs. time, t, behaviour is significantly different for the two cases. On a degreased substrate, wetting rate initially increases with temperature, therefore time, due to decreasing viscosity, and then becomes reduced as equilibrium is approached. For oiled substrates, there is a central pseudo-plateau in the θ vs. t curve, corresponding to a modified capillary balance, itself caused by significant absorption of the oil by the adhesive. This behaviour is modelled semi-quantitatively. In the case of spreading on a degreased substrate, a simplified model is proposed to explain dynamic effects related to reduced viscosity during temperature rise.

Film Thickness Effects on Interfacial Fracture of Epoxy Bonds

ABSTRACTNanoindentation test techniques were combined with deposition of highly stressed overlayers to study the interfacial fracture susceptibility of spin coated Epon 828/T403 on aluminized glass substrates as a function of film thickness. The test techniques required to induce fracture differed between samples. Nevertheless, the resulting interfacial fracture energies decreased monotonically with film thickness to a value near 0.5 J/m2. This value is higher than the ‘true work of adhesion' for uncured epoxy oliogomers on a methyl-terminated aluminum surface. However, it may indicate that we have irreversible specific interactions such as hydrogen bonding. Then 0.5 J/m2 may be near the fundamental value for such an interaction, or the ‘practical work of adhesion’.

Forming discontinuous fiber arrays by fracture of lubricated carbon-filament tows

This paper presents the results of a set of continuous-filament-tow fracturing experiments designed to produce highly collimated discontinuous-fiber-arrays with well-dispersed fractures. Discontinuous-fiber-arrays have at least two uses: reinforcing a matrix phase at high volume fraction and, when impregnated with a fluid, performing as a microrheometer. The lubricating fluid used for these experiments is uncured TCR epoxy, which may be stored at room temperature for up to one year. Tows with gauge lengths of 287, 362 and 400 mm were fractured into discontinuous fibers arrays during extension at four percent strain/min. Weibull analysis showed singlet failures were responsible for the fracture process of the two largest gauge length samples and multiplet failures accounted for the bulk of fracture at the shortest gauge length. Normal distributions approximated the filament length distribution at all gauge lengths. The longest gauge sample had the best distribution of filament breaks and had an average fiber length of 207 mm and a standard deviation of 65 mm.