Epoxy-amine System Research Articles

Studying the curing of epoxyamine mixtures via dynamic light scattering and differential scanning calorimetry

The curing of epoxy oligomers with different structures and reactivity using an aliphatic amine curing agent was studied and quantitatively characterized by the methods of dynamic light scattering and differential scanning calorimetry. The presence of disperse phase in the initial reagents, as well as in the reacting systems is established. It is shown that the particles of the disperse phase are involved in the process of curing even in the early stages. By changing the width of the devitrification region, the change in the molecular homogeneity of epoxyamine systems during curing is estimated.

DSC-TG studies on kinetics of curing and thermal decomposition of epoxy–ether amine systems

The cure behavior of diglycidyl ether of bisphenol A with a simple ether amine (4,7,10, trioxa -1,13, tridecane diamine), system I and a polyether amine (polypropylene glycol block polyethylene glycol block polypropylene glycol bis 2 amino propyl ether), system II was compared by Differential Scanning Calorimetry. The exothermicity of the curing reaction of system I is higher than that of system II (316 ± 15 J g−1 for System I and 230 ± 15 J g−1 for system II). Kinetic parameters viz., activation energy, pre-exponential factor, and rate constant for curing were evaluated by Kissinger method and Kissinger–Akahira–Sunose isoconversion method. Both systems showed low glass transition temperatures and System II shows a much lower T g (−38 °C) than system I (26 °C). The thermogravimetric analysis of the two cured epoxy amine systems showed comparable thermal stability.

Manipulation of Interfacial Amine Density in Epoxy-Amine Systems as Studied by Near-Edge X-ray Absorption Fine Structure (NEXAFS)

In this work, we investigate the ability to tune the quantity of surface amine functional groups in the interfacial region of epoxy-diamine composites using NEXAFS, a technique that is extremely sensitive to surface composition. Thereby, we employ a model surface (silicon wafer with the native oxide present) and, after deposition of an epoxy functionalized silane, we immersed the wafers in various diamines, followed by reaction with a diepoxy acting as a molecular probe. These results show that the number of available surface amines depends on the diamine chosen, wherein smaller molecular weight diamines provide more reaction sites. Subsequent experiments with mixtures of diamines undergoing competitive adsorption show that the amine quantity can be tailored by choice of the diamine mixture. Further experiments of diamine treated 3-(glycidoxypropyl) trimethoxysilane layers in a reacting epoxy/diamine showed that the surface reaction site density differences observed for adsorption experiments persisted in the reacting epoxy, implying that the surface reaction rate (and by extension, the surface amine concentration) dictate interfacial cross-link density up to the point of gelation.

Interpretation of Gel Points of an Epoxy-Amine System Including Ring Formation and Unequal Reactivity: Measurements of Gel Points and Analyses on Ring Structures.

Gel points are investigated as the critical extent of reaction at gelation by FT-IR and viscoelastic measurements for the network formed by the epoxy–amine system. The reaction systems examined are comprised of diglycidyl ether of bisphenol A (DGEBA) and polyoxypropylene (POP) diamine of different chain lengths with various degrees of dilution. The experimental results are obtained as the delay of gel point, that is the delay from the gel point expressed by the Flory–Stockmayer formula, and interpreted in terms of ring formation caused by intramolecular reaction which is characterized by the ring forming parameter of λ0. This parameter relates with the internal concentration (in mol L–1) of reactive groups Pab, for RAfa + R′Bfb type polymerization. The analyses of the conversion curve (p vs t curve, where p denotes the extent of reaction) obtained by FT-IR measurement are carried out on the basis of the kinetic model of the epoxy-amine reaction to find the ratio of rate constant. For all the reaction syst...

Interpretation of Gel Points of an Epoxy–Amine System Including Ring Formation and Unequal Reactivity: Reaction Scheme and Gel-Point Prediction.

First, the kinetics of the reaction of a polyoxypropylene (POP) diamine and the diglycidyl ether of Bisphenol A (DGEBA), taking account of the induced unequal reactivity (substitution effect) of th...

Isothermal Cure of Bisphenol Epoxy Resin with a Nonlinear Aliphatic Polyamine Hardener

An amine terminated polypropylenimine dendrimer (DAB-dendri-(NH2)4), was employed as a new nonlinear aliphatic curing agent for diglycidyl ether of bisphenol A (DGEBA). Isothermal curing reaction kinetics of DGEBA/DAB was investigated with a differential scanning calorimeter (DSC). The autocatalytic model proposed by Kamal was demonstrated for simulating the reaction kinetic in the initial stage of the cure. It was found that the overall reaction order, m + n, was in the range 2.3688–2.5980. The rate constants of k l and k 2, showed a good Arrhenius fit to temperature and the associated activation energies was estimated to be 60.41 kJ/mol and 55.66 kJ/mol, which showed in agreement with values reported for common epoxy-amine systems. In the latter stage of curing, diffusion control was considered and a diffusion factor was incorporated into the autocatalytic model; therefore, it was possible to accurately predict the cure kinetics over the whole range of conversion.

Evaluation of the complex hygrothermal behaviors of epoxy–amine systems

AbstractIn this study, the complex hygrothermal behavior of two epoxy systems used for strengthening applications was studied. In these systems, property loss by plasticization simultaneously occurred with property gain during additional curing. A comparison of the changes in the glass‐transition temperature (Tg) and crosslink density with water immersion at different temperatures clearly showed that the two effects of additional curing by a postcuring reaction and plasticization by water absorption were in competition with each other during the exposure. The changes in the conversion with different exposure conditions suggested that water accelerated the postcuring reaction, even at low temperatures; this resulted in a significant difference in the postcuring reaction between unexposed and exposed epoxies. The construction of the plot of Tg versus conversion for the unexposed system and the placement of the Tg for exposed systems onto this master plot provided a method for evaluating the plasticization effect while excluding the influence of additional curing. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of Cure Conditions on the Generated Morphology and Viscoelastic Properties of a Poly(acrylonitrile–butadiene–styrene) Modified Epoxy–Amine System

The curing behavior, phase morphology, and dynamic mechanical characteristics of an epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylsulfone (DDS), modified with different amounts of poly(acrylonitrile–butadiene–styrene) (ABS), were investigated by employing differential scanning calorimetry (DSC), field-emission scanning electron microscopy (FESEM), and dynamic mechanical thermal analysis (DMTA). The effects of different curing conditions on the generated morphologies and viscoelastic properties were evaluated. The amounts of ABS in the epoxy blends were 3.6, 6.9, 10, and 12.9 wt %. The rate of the curing reaction decreased with increasing thermoplastic content and with decreasing curing temperature. Morphological analysis revealed a phase-separated morphology for the blend systems. The storage modulus (E′), loss modulus (E″), and tan δ values of the systems were measured as functions of temperature and are discussed based on the morphological behavior of the epoxy blends with different amount of ABS.

Experimental Studies on Epoxy-Amine System Using Microwave and Conventional Curing Approaches

In this present work attempts have been made to study the difference between microwave heating and conventional thermal heating in curing the epoxy-amine system of di-glycidyl ether bisphenol-A(DGEBA) with the curing agent of 4,4′Diamino diphenyl methane(DDM). Curing behaviors and mechanical properties of the system were studied through a number of experiments. Differential scanning calorimetry (DSC) technique was implemented to measure the glass transition temperature and kinetic parameters, and fourier transform infrared spectroscopy(FT-IR) was used to analyse the cure reaction mechanism of the resin system. Finally, microstructure of microwave-cured materials was also studied by using a scanning electron microscope(SEM) in order to analyze the morphology of cured specimens.

Interfacial kinetics of a model epoxy–amine addition reaction

The kinetics of the addition reaction at a solid interface for a model epoxy-amine system composed of monofunctionalized phenyl glycidyl ether and hexylamine was examined. The chemical character for the reaction of this system at the interface was the same as that in the bulk, while the physical nature was significantly different. Slowing down of the diffusion for the reactants in close proximity to the solid interface was also addressed by interfacial selective spectroscopy.

Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine Systems Analyzed by FTIR and Modulated DSC

Epoxy networks based on diglycidyl ether of bisphenol A (DGEBA) and diamino diphenyl sulfone (DDS) as curing agent were prepared in the presence of poly(acrylonitrile-butadiene-styrene) (ABS). Blends containing 3.6, 6.9, 10, and 12.9 wt% ABS were obtained by a melt mixing technique. Infrared spectroscopy was employed to follow the curing progress by determining the decrease of the band intensity caused by the epoxide groups. The evolution of glass transition temperatures (T g) and heat of reaction (ΔH) of the blends cured for different times were studied in detail by modulated DSC and used for evaluation of the overall curing degree. The increase in the epoxy network density was detected from the magnitude of the decrease in heat capacity change at T g, which reduces with conversion. The addition of ABS decreases the degree of cure and the epoxy network density due to the dilution of the reactants with the thermoplastic.

Fabrication of Super-Hydrophobic Surfaces with Long-Term Stability

A novel approach was proposed to fabricate super-hydrophobic surfaces by depositing aggregates of fumed silica modified with hydroxy-terminated poly-dimethylsioxane and γ-aminopropyltriethoxysilane on surfaces of glass plates. The glass plates were treated with 2,3-epoxy propoxy propyltrimethoxysilicane based on an epoxy-amine system in advance. Aggregates of fumed silica were found to be chemically bonded to the treated glass surfaces and a surface possessing dual micron- and nanoscale hierarchical structures was observed on the super-hydrophobic surfaces. The laboratory testing results showed that the obtained surfaces possessed long-term super-hydrophobicity in air and maintained its super-hydrophobicity over a wide pH range.

Thermodynamic analysis of polymerization-induced phase separation of a polystyrene in epoxy/monoamine–diamine systems. Effect of monoamine–diamine proportion on the phase diagram

Polymerization-induced phase separation of a polystyrene in various epoxy-amine systems where the amino groups were provided by a monoamine and a diamine mixed in different proportions was thermodynamically studied. A model based on the Flory–Huggins theory extended by Koningsveld and Staverman approach where the interaction parameter was dependent on temperature, composition and conversion, and polydispersity of the components was considered, was used. A general equation for the evolution during polymerization of the epoxy-amine species distributions according to the monoamine–diamine ratio was derived from the Stockmayer distribution. The interaction parameters continuously decreased with conversion. Phase diagrams of the blends were obtained and the critical composition was between 5 and 6 vol.% PS in all blends.

Estimating the molecular mass between epoxy-amine network junctions from glass-transition-temperature data

The average molecular mass between network junctions is estimated for several epoxy-amine systems of various compositions with comparable molecular masses of the epoxy oligomer and the curing agent. This estimation is based on the experimental data on glass-transition temperatures of curing epoxy-amine mixtures. The constant that relates these physicochemical characteristics is dependent on the nature of the epoxy-amine system and the rigidity of polymer chains located between network junctions. Correlations are found between the constant and the glass-transition temperature of the crosslinked epoxy-amine system and between the constant and the difference in the glass-transition temperatures of uncured and ultimately cured epoxy-amine systems.

Epoxy-amine composites with ultralow concentrations of single-layer carbon nanotubes

The physical and mechanical properties of composite materials based on epoxy-amine systems—diglycidyl ether of diphenylolpropane-eutectic mixture of aromatic amines (40 wt % m-phenylenediamine-60 wt % 4,4′-diaminodiphenylmethane) and epoxy-diane resin ED-20-eutectic mixture of aromatic diamines with ultralow contents (≤0.1 wt %) of single-layer carbon nanotubes—are studied. It is shown that, for the concentration dependence of the modulus of elasticity during tension, the additivity rule is obeyed only at the lowest concentrations of carbon nanotubes. In this case, the presence of near-surface layers of a matrix with an increased elastic modulus should be considered.

Physical ageing in ternary epoxy-amine curing systems of variable composition

Endothermal effects appearing close to the glass transition point in cured epoxy-amine systems of variable composition and connected with its physical ageing were investigated. The dependences of thermal effect parameters on ageing time and composition of curing system were determined.

Thermal behavior of blends based on a thermoplastic-modified epoxy resin with a crosslinking density variation

The thermal behavior of blends based on a polystyrene (PS) and several epoxy-amine systems where amino groups were provided by a monoamine (MA) and a diamine (DA) mixed in different proportions was investigated. This way, the crosslinking density of epoxy-amine polymer was controlled and continuously changed from a linear polymer (epoxy-MA) to a highly crosslinked polymer (epoxy-DA). The effect of the MA–DA proportion and PS modifier on the thermal stability, glass transition, and polymerization reaction was studied by differential scanning calorimetry and thermogravimetric analysis. The MA–DA ratio and modifier proportion did not affect the reaction heat but affected the reactivity. The thermal stability and glass transition temperature increased by increasing the DA proportion in the blend as a result of the higher degree of crosslinking. A study of miscibility of blends based on glass transitions was performed. The thermoplastic-modified materials generally showed two glass transitions with values close to the those of the pure materials, indicating that the mixtures were separated into phases.

Epoxy resin modified with a thermoplastic

The effect of cure temperature and modifier proportion on the miscibility of an epoxy–amine system with a thermoplastic modifier was studied by analysis of phase diagrams, morphologies, and glass transitions. Phase diagrams for the system before and during reaction were obtained from a thermodynamic analysis of phase separation using a model based on Flory–Huggins theory. Different types of morphologies were observed and analyzed in function of cure temperature and modifier proportion. The validity of the thermodynamic model was checked by comparing with observed morphologies. Two glass transitions were observed for most of the modified systems indicating that a phase separation was occurred.

Polymer blends based on an epoxy-amine thermoset and a thermoplastic

The effect of thermoplastic modification of an epoxy-amine system on the cure reaction, miscibility and thermal stability of the system was investigated. The cure kinetics showed an autocatalytic behavior. Modifier did not affect either the total reaction heat or the achieved maximum conversion but delayed the kinetics. The model of Horie-Kamal corrected by diffusion factor was used to adjust kinetics in the whole range of conversions. The modified systems showed two glass transitions indicating two separated phases, whose compositions were estimated using the Fox and Couchman equations. Modifier did not affect the thermal and thermooxidative stability of the system.

Phase diagram of different epoxy-amine precursors modified with a thermoplastic: Effect of structure of epoxy-amine system on miscibility

The miscibility of a thermoplastic with the precursors of different epoxy-amine systems was analyzed thermodynamically in which the dependence of interaction parameter on temperature and composition χ (T, ϕ) and the polydispersity of components were considered. The epoxy-amine precursors were different only in the nature of amino groups, which were provided by a monoamine and a diamine in different proportions. Cloud-point curves were measured for five unreacted modified systems resulting that miscibility of the system increased with the proportion of monoamine. The thermodynamic analysis was realized in two steps: first, the model was applied to each system individually and secondly, a general equation for χ (T, ϕ) depending on the monoamine–diamine proportion was searched and used to analyze all systems together. Theoretical calculations of cloud-point curves, shadow curves, spinodal curves, critical points, vitrification curves and species distributions were realized and discussed for those systems.