Epoxy-amine Mixtures Research Articles

Kinetics of the interfacial curing reaction for an epoxy-amine mixture.

A better understanding of the chemical reaction between epoxy and amine compounds at a solid interface is crucial for the design and fabrication of materials with appropriate adhesive strength. Here, we examined the curing reaction kinetics of epoxy phenol novolac and 4,4'-diaminodiphenyl sulfone at the outermost interface using sum-frequency generation spectroscopy, and X-ray and neutron reflectivity in conjunction with a full atomistic molecular dynamics simulation. The reaction rate constant was much larger at the quartz interface than in the bulk. While the apparent activation energy at the quartz interface obtained from an Arrhenius plot was almost identical to the bulk value, the frequency factor at the quartz interface was greater than that in the bulk. These results could be explained in terms of the densification and orientation of reactants at the interface, facilitating the encounter of the reactants present.

Features of Preparation of Multilayer Ultrathin Coatings from Thermosetting Epoxy Amine Systems by Spin-Coating Technique

The basic factors influencing the quality of thin films prepared by the spin-coating technique from thermosetting stoichiometric epoxy-amine mixtures have been studied. It has been shown that films 2.5–3.0 nm thick are formed on silicon supports from a 0.025 wt % solution of the stoichiometric mixture of epoxy resin and amine in toluene. Multilayer polymer coatings with thickness up to 40 nm have been prepared from successively deposited partially cured epoxy-amine layers. The thickness of these coatings grows linearly with an increase in the number of layers, while their surface energy decreases. The revealed features may be used for creating multilayer polymer coatings, the properties of which vary along the coating thickness.

Synthesis of Pluri-Functional Amine Hardeners from Bio-Based Aromatic Aldehydes for Epoxy Amine Thermosets.

Most of the current amine hardeners are petro-sourced and only a few studies have focused on the research of bio-based substitutes. Hence, in an eco-friendly context, our team proposed the design of bio-based amine monomers with aromatic structures. This work described the use of the reductive amination with imine intermediate in order to obtain bio-based pluri-functional amines exhibiting low viscosity. The effect of the nature of initial aldehyde reactant on the hardener properties was studied, as well as the reaction conditions. Then, these pluri-functional amines were added to petro-sourced (diglycidyl ether of bisphenol A, DGEBA) or bio-based (diglycidyl ether of vanillin alcohol, DGEVA) epoxy monomers to form thermosets by step growth polymerization. Due to their low viscosity, the epoxy-amine mixtures were easily homogenized and cured more rapidly compared to the use of more viscous hardeners (<0.6 Pa s at 22 °C). After curing, the thermo-mechanical properties of the epoxy thermosets were determined and compared. The isophthalatetetramine (IPTA) hardener, with a higher number of amine active H, led to thermosets with higher thermo-mechanical properties (glass transition temperatures (Tg and Tα) were around 95 °C for DGEBA-based thermosets against 60 °C for DGEVA-based thermosets) than materials from benzylamine (BDA) or furfurylamine (FDA) that contained less active hydrogens (Tg and Tα around 77 °C for DGEBA-based thermosets and Tg and Tα around 45 °C for DGEVA-based thermosets). By comparing to industrial hardener references, IPTA possesses six active hydrogens which obtain high cross-linked systems, similar to industrial references, and longer molecular length due to the presence of two alkyl chains, leading respectively to high mechanical strength with lower Tg.

Mesoscopic Heterogeneity in the Curing Process of an Epoxy–Amine System

Epoxy resins are composed of a three-dimensional network formed by chemical reactions between epoxy and amino compounds, which plays an important role in the mechanical properties. Thus, to use epoxy resins in various applications, it is necessary to gain a better understanding of their network structure. Here, we study the structural heterogeneity evolved in an epoxy–amine mixture during the curing process on the basis of a particle tracking technique, in which the thermal motion of probe particles in the mixture was tracked, small-angle X-ray scattering measurements in conjunction with coarse-grained molecular dynamics simulation. The heterogeneous environment was generated even at the initial stage of the curing process. Notably, the characteristic length scale was on the order of several hundreds of nanometers down to several tens of nanometers, depending on the extent of curing. Once a reaction occurs between a pair of epoxy and amino groups, the temperature at the site is locally elevated due to the...

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.

Effect of elastic properties modification on the vibrational density of states: A joint Brillouin and Raman scattering study

AbstractThe modification of the vibrational density of states in a reactive epoxy–amine mixture during isothermal polymerization at different temperatures was characterized by Brillouin and Raman scattering measurements. During the reaction, the system underwent the glass‐transition passing from the liquid to the glassy phase. The relative variations of the boson peak (BP) and the elastic moduli were investigated. We found that the intensity variation and the shift of the BP could be completely explained in terms of the elastic medium transformation. A master curve of the spectra in the BP region can always be obtained both as a function of the reaction temperature and as a function of the reaction time. Moreover, the Brillouin light‐scattering results gave evidence of the validity of a Cauchy‐like relation for the real part of the elastic moduli measured at finite frequencies also in a relaxing regime. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

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.

Nanostructuration in Thin Epoxy−Amine Films Inducing Controlled Specific Phase Etherification: Effect on the Glass Transition Temperatures

Inordertopreparecuredthin filmsthicknessesin the range of 90 300 nm, epoxy amine mixtures of di fferent concentrations in toluene are spin-cast onto oxidized silicon substrates. The glass transition temperature of the cured thin films is measured by microthermal analysis, revealing the existence of two distinct glass transitions temperatures for all the samples due to amine segregation at air/ film interface. These transitions are ascribed to two layers. The upper layer properties of the film due to the air/polymer interface are independent of the film thickness. This layer is around 30 nm thick, and its glass transition temperature is about 97 C and matches to a constant amine/epoxy composition at the air/ film interphase.Consecutively,the filmthicknessreductioninducesanincreaseoftheepoxyexcessinthesublayer,promotingsideepoxy reactions revealed by aliphatic ether bonds formation. Thus, signi ficant increase of the sublayer Tg, in comparison to the Tg of the bulk sample with an equivalent amine/epoxy ratio at the same amine conversion rate, is mainly due to these new ethers bonds for film thickness less than 160 nm. These bonds, surface catalyzed, are created at low temperature by the consumption of the epoxy excess. Etheri fication enhancement is finely controlled by the amine epoxy o ffstoichiometry in the sublayer tuned by its thickness and mainly results in glass transition temperature increase at lightly amine conversion. At complete epoxy and high amine conversion reached by postcuring, etheri fication in the sublayer leads to a constant amount whatever the thickness of the sample. The glass transition temperature of the sublayer postcured is around 180 C, equivalent to the bulk sample and does not bring out con finement e ffects.

Effect of polymerization on the boson peak, from liquid to glass

Reactive epoxy-amine mixtures during isothermal polymerization have been characterized by Raman scattering measurements in order to follow the modification of the vibrational density of states. In the initially liquid solutions an increasing number of Van der Waals bonds are replaced by stiffer covalent bonds. During the chemical reaction, the molecular diffusion slows down and ultimately the systems are frozen in a glassy structure. The transformation from reactive liquids to chemical glasses is accompanied by microscopic structural changes driven by the bonding process. During the reaction the samples density and the sound velocity increase, both of them contribute to significantly change the Debye level. By combining Raman with Brillouin inelastic X-ray scattering measurements, we compare the relative variations of the boson peak with that of the Debye level. We find that the shift and intensity variation of the boson peak are fully explained by the modification of the elastic properties of the medium and a boson peak master curve is obtained.

Influence of substrate chemistry and the network homogeneity of ultra‐thin cross‐linked polymer films cured at their surface on the main relaxations temperatures probing by microthermal analysis

AbstractThin 200‐nm epoxy–amine mixtures were cured on silicon wafers with different surface chemistry to quantify the effect of the chemistry on the glass transition temperature evolution in ultra‐thin thermosetting films. Two surface treatments were investigated: the first one only consisted in the activation of the silanols groups at the silicon surface, whereas the second one consisted in the grafting 3‐aminopropyltrimethoxysilane (APTMS) monolayer on the silicon wafers. The epoxy films were deposited on these chemistry modified wafers by spin coating a toluene solution of DGEBA–amine mixture at stoichiometric ratio. The same cure processing was used for both samples. Thin films were analysed not only using microthermal and thermomechanical analysis to determine the relaxation transitions temperatures of these films but also using FTIR in infrared reflection absorption spectroscopy mode to determine the curing rate of these networks. It was found that all these thin films showed two different glass transitions, the first one at 96 °C and was independent of the surface treatments, whereas the second one increasing from 142 °C for the oxidised wafers surface to 167 °C for the aminosilane grafted on the silicon wafer. The substrate chemistry extent on the film network structure, the interfacial bonds and interactions are discussed. This work also illustrates the interest in using microthermal analysis to obtain relevant temperature glass transition of thin film at sub‐micrometre scale, strongly dependant of local structure and chemistry composition. Copyright © 2009 John Wiley &amp; Sons, Ltd.

An Investigation on the Capillary Wetting of Glass Fiber Tow and Fabric Structures with Nanoclay-Enriched Reactive Epoxy and Silicone Oil Mixtures

Capillary wetting of a biaxially-oriented glass fabric and the tow comprising the fabric was examined via the Washburn equation with silicone oil and a reactive epoxy-curative system containing 0-4 wt % nanoclay reinforcement. Capillary wetting of silicone oil was used to measure the hydraulic constant of the fabric and tow. The wetting rates for fabric were found to be greater than those for tow and this was based on the larger pore radii of fabric compared to tow. Reynolds and capillary numbers calculated from wetting rate data indicated that the flow is dominated by interfacial tension. The presence of nanoclay offered a significant perturbation to capillary wetting behavior. Wetting rates indicate that the effect of nanoclay is 2-fold: blocking of tow pores and increasing the wetted area. This suggests that nanoclay particles are aggregating and the flow field is such that the particles are not dispersed additionally under the present conditions. Capillary wetting rates of fabric and tow samples were measured with reactive epoxy-amine mixtures at various nanoclay loadings. The presence of nanoclay offers another level of complexity to the Washburn equation. In addition to the liquid/fabric or tow interfacial tension, the interfacial tension of the liquid/nanoclay interface has to be reconciled. As a consequence, hydraulic constant, surface tension, and contact angle are convoluted in such a binary system.

Raman-Scattering Measurements of the Vibrational Density of States of a Reactive Mixture During Polymerization: Effect on the Boson Peak

Raman-scattering measurements are used to follow the modification of the vibrational density of states in a reactive epoxy-amine mixture during isothermal polymerization. Combining them with Brillouin light and inelastic x-ray scattering measurements, we analyze the variations of the boson peak and of the Debye level while the system changes from liquid to glass upon increasing the number of covalent bonds among the constituent molecules. The shift and intensity variation of the boson peak are explained by the modification of the elastic properties throughout the reaction, and a master curve for the boson peak can therefore be obtained. Surprisingly, bond-induced modifications of the structure do not affect this master curve.

Bond-Induced Ergodicity Breakdown in Reactive Mixtures

We have studied by inelastic x-ray scattering, at wave vectors 1 nm < or =q< or =15 nm(-1), the high-frequency dynamics of epoxy-amine mixtures as the monomers irreversibly polymerize. We find that chemical bonding, while inducing molecular ordering on a mesoscopic length scale, also efficiently realizes the mechanism of dynamical arrest described by the mode-coupling theory, as manifested by a cusp singularity in the behavior of the nonergodicity factor as a function of the number of chemical bonds. These results confront positively the mode-coupling theory with a new control parameter.

Kinetic method by using calorimetry to mechanism of epoxy-amine cure reaction

A combination of kinetic method and DSC measurements was used to examine the system of resorcinol diglycidylether-aniline. The purpose of this study is to obtain information about linear polycondensation in epoxy-amine system. The reaction of resorcinol diglycidylether (RDGE) with aniline falls into the family of epoxy-amine reaction mixtures, within of which the functional groups varies only. The molar heats and the rate constants for the three pathways were evaluated by nonlinear regression analysis of the data assuming that reaction mechanism proposed for simple molecular epoxy-amine system such as phenylglycidylether-aniline would be operative in the reaction between resorcinol diglycidylether and aniline. A feature of the present reaction system is that it proceed through the structural changes occurred with the heat effect. The loss of catalytic activity by the molecules of the reaction product was used as indicator for the structure forming in the reaction medium.

Clustering and Cooperative Dynamics in a Reactive System

We study the dependence of the dynamics on the size of particle clusters that grow by stepwise aggregation in a reactive epoxy-amine mixture. The data reveal the cluster property involved in the glasslike arrest and its quantitative link with the structural relaxation time. We find that the number-average cluster size xn governs the formation of a glassy phase as distinct from a gel phase, and that xn correlates to the size of the "cooperatively rearranging regions" postulated by the Adam-Gibbs model for glass forming liquids. These results suggest that the step polymerization process generates clusters that behave much like dynamical heterogeneities observed in supercooled liquids.

A phosphorus‐containing diamine for flame‐retardant, high‐functionality epoxy resins. I. Synthesis, reactivity, and thermal degradation properties

AbstractA phosphorus‐containing amine, bis(4‐aminophenoxy)phenyl phosphine oxide (BAPP), suitable for curing epoxy resins with improved fire performance was synthesized and characterized with Fourier transform infrared spectroscopy and nuclear magnetic resonance. The reactivity of the amino group was evaluated by differential scanning calorimetry of the epoxy–amine mixture and by proton nuclear magnetic resonance of the amino unit. With BAPP as a curing agent, a range of high‐functionality, aerospace epoxy resins were cured, and the dynamic kinetic parameters calculated from Kissinger's and Ozawa's models were compared with those from the more widely used amines. The thermal degradation properties of the phosphorus‐containing epoxy resins were studied by thermogravimetric analysis, the degradation activation energy was calculated, and a multistep thermal degradation process was observed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2093–2100, 2004

Chemorheology and ultimate behavior of epoxy-amine mixtures modified with a liquid oligomer

Chemorheology and ultimate behavior of epoxy-amine mixtures modified with a liquid oligomer

Chemorheology and ultimate behavior of epoxy-amine mixtures modified with a liquid oligomer

Rubber toughening of epoxy resins has been actively studied since the 1960s with clear progress in understanding of the ultimate properties: microstructure relationships. The morphology, obtained after curing of the modified thermosetting matrix, is a function of the process conditions as well as of the materials used because both influence the thermodynamics and the kinetics of phase separation. In this work several amounts of poly(oxypropylentriamine) (POPTA), have been added as modifier to a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy matrix cured with a cycloaliphatic amine. Molecular weight of the neat resin and amine/epoxy stoichiometric ratio have also been used as variables. This investigation has focused upon the importance of cure chemorheology for microstructure formation by using both physicochemical (isothermal and dynamic calorimetry) and rheological techniques. In the second part of this study, the influence of the molecular weight of the epoxy resin in the ultimate properties of 15 wt % POPTA-modified epoxy matrices is also analyzed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1269–1279, 2000

Rheological monitoring of curing reaction of an epoxy system: effect of heating rate

In this work, we present a rheological study of the non-isothermal curing reaction of an epoxy resin, diglycidyl ether of bisphenol A, with aliphatic amines of different functionalities. The reaction was carried out under a linear temperature program and the epoxy-amine mixtures were prepared at different epoxy groups to amine-hydrogen ratios. The effect of vitrification on the curing reaction is analyzed as a function of the heating rate. At low heating rates, the viscous modulus, G″, presents two peaks. The first peak is due to the vitrification-devitrification phenomenon that takes place during cure. At the second peak, the sample is completely cured and the decrement is G″ is only due to the temperature increment.

Processing of Composite Rod with Embedded Optical Fiber

Polymer composite rods have promising uses in telecommunications as cable strength members, in maritime structures because of their resistance to various environmental in uences, and as railway insulating rods. The use of optical ®bers as sensors for this structure enables the chance of real-time damage and strain assessment in structural applications. The investigations performed by past researchers differ in the variety of the laminate composite structure, optical ®ber coating, and type of testing (three-point bending, fatigue and, impact). One of the ®rst applications of optical ®ber sensors was that of the impact damage detection via ®ber breakage sensors [1, 2]. Waite and Sage [3] described the failure of silane solution-treated and acrylate buffered optical ®bers, which were either embedded in polymer composites or loaded individually. In another study by the same author [4], conclusive results were obtained by using hard clad silica and strippable co-polymer coated optical ®bers for the detection of fatigue damage. To the authors' best knowledge, no results have thus far been presented for embedding an optical ®ber in composite rod structures. It is dif®cult to integrate optical ®bers precisely into composites that do not have a ply structure. In our previous study [5], we detailed the development of an experimental facility for manufacturing composite rods with embedded optical ®bers by vacuum molding. Vacuum in®ltration involves placing the reinforcing ®bers and the optical ®ber in a die, applying a vacuum at one end of the die and a source of epoxy matrix at the other, and then using the vacuum to draw the resin through the die to impregnate the ®bers. The ®berous reinforcement used in the composite was E-glass ®ber Etex R2105 roving. An acrylatecoated multimode optical ®ber (with core=cladding= coating equal to 62.5=125=250 im) was chosen due to its relatively easy handling, simplicity of mounting, low cost of fabrication, and simple electronic detection. The matrix material was based on a diglycidyl ether or bisphenol A, together with an aromatic amine hardener (Araldite CY 223=HT972, Ciba-Geigy). The epoxy-amine mixtures were prepared by heating the resin in an oil bath to 70 8C, and adding the curing agent with continuous stirring until a clear homogeneous solution was obtained. The exural, impact, and fatigue resistance of a composite rod structure is related to the strength of the material at the surface. The specimen initially has a tensile force acting on the top surface, while the bottom surface is compressed. The fatigueor impact-induced rod bending causes tension on the rear surface, inducing strain in the matrix and the optical ®ber embedded at that location. When the strain in the exed rod exceeds the ultimate strain of the optical ®ber, it will fracture. Therefore, embedding optical ®bers near the die=composite interface is considered to be essential from the standpoint of strain sensing. The degree of cure of a composite is important in many aspects because the amount of cure can in uence the mechanical properties of the product and probably melt the buffer on the optical ®ber. In order to achieve a uniform degree of cure in the cross-section of a composite rod, the die temperature is the most important processing variable. Control of the die temperature requires information about the curing reactions taking place inside the die. A mathematical model has been developed to simulate the vacuum molding process, namely, the pro®les of temperature and the degree of cure in the radial direction in a die of cylindrical shape. A similar approach was taken by several authors [6±8], who were interested in modeling the pultrusion process. The kinetic parameters of the epoxy resin were obtained from the differential scanning calorimeter (DSC) scans. From the data shown in Fig. 1 and the peak obtained by scanning a standard Indium sample (Perkin Elmer DSC-2), the calculated reaction heats (yAH) at 423.15 K and 443.15 K were 579.3 J=g resin and 535.7 J/g resin, respectively. Other kinetic parameters were calculated by a nonlinear curve®tting method. The reaction rate equation used in this study was: