Amine-cured Epoxy Research Articles

Chemical degradation of amine-cured DGEBA epoxy resin in supercritical 1-propanol for recycling carbon fiber from composites

Chemical degradation of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured with an aliphatic amine in supercritical 1-propanol was investigated under different reaction temperature and time. The combination of GC-MS and LC-MS proved that the epoxy resin was decomposed to five main products including phenol, 4-isopropylphenol, 4-isopropenylphenol, bisphenol A, and 4,4'-(cyclopropane-1,1-diyl)diphenol. The 13 C-NMR results verified the chemical structures of the degradation products. The change of the productsyield with time was evaluated by an effective means of HPLC. In addition, the GPC analysis confirmed the formation of soluble low molecular weight clusters during the degradation reaction. A possible free-radical reaction mechanism was proposed for chemical depolymerization of the epoxy resin in supercritical 1-propanol. After the homolytic cleavage of the aromatic ether linkages, the resulting bisphenol A biradical either produced 4,4'-(cyclopropane-1,1-diyl)diphenol after intramolecular rearrangement or generated bisphenol A after capturing hydrogen from 1-propanol.

Thermal stability and fire retardancy of polyurea and epoxy nanocomposites using organically modified magadiite

The purpose of this study is to investigate the effect of the surface modification of a layered silicate (magadiite) on the flammability of both polyurea and amine-cured epoxy resin. Based on the surface chemistry of magadiite, both quaternary alkyl ammonium and silane modifier can be employed for the organo-modification. Nanocomposites of both polymers were prepared via ultrasound-assisted in situ polymerization. Dispersion of magadiite was investigated through X-ray diffraction and high-resolution transmission electron microscopy. Thermal stability and flammability were evaluated by thermogravimetric analysis and cone calorimetry, respectively. The addition of small amount of magadiite resulted in significant improvements in flame resistance with not much change in thermal stability for both polymers. Ammonium-modified magadiite improves the flame resistance, whereas silane modification helps to increase time to ignition of both polymers.

Facile fabrication of superhydrophobic films with fractal structures using epoxy resin microspheres

A simple method has been developed to fabricate superhydrophobic surfaces with fractal structures with epoxy resin microspheres (ERMs). The ERMs is produced by phase separation in an epoxy-amine curing system with a silica sol (SS) dispersant. The transparent epoxy solution becomes cloudy and turns into epoxy suspension (ES) in this process. The fractal structure (two tier structure) generated by synthetic epoxy resin microspheres (ERMs) and deposited nanoincrutations on the surfaces of these ERMs, which have been observed by scanning electron microscope (SEM). The curing time of ES is an important condition to obtain films with good comprehensive performances. Superhydrophobic films can be prepared by adding extra SS into ES with a curing time longer than 5h. The optimal curing time is 10h to fabricate a film with good mechanical stability and high superhydrophobicity. In addition, a surface with anti-wetting property of impacting microdroplets can be fabricated by prolonging the curing time of ES to 24h. The gradually decreased hydrophilic groups resulted from a longer curing time enable the surface to have smaller surface adhesions to water droplets, which is the main reason to keep its superhydrophobicity under impacting conditions. The coated surface is highly hydrophobic and the impacting water droplets are bounced off from the surface.

Towards the rational design of polymers using molecular simulation: Predicting the effect of cure schedule on thermo-mechanical properties for a cycloaliphatic amine-cured epoxy resin

We report prediction of selected physical properties (e.g. glass transition temperature, moduli and thermal degradation temperature) using molecular dynamics simulations for a difunctional epoxy monomer (the diglycidyl ether of bisphenol A) when cured with p-3,3′-dimethylcyclohexylamine to form a dielectric polymer suitable for microelectronic applications. Plots of density versus temperature show decreases in density within the same temperature range as experimental values for the thermal degradation and other thermal events determined using e.g. dynamic mechanical thermal analysis. Empirical characterisation data for a commercial example of the same polymer are presented to validate the network constructed. Extremely close agreement with empirical data is obtained: the simulated value for the glass transition temperature for the 60°C cured epoxy resin (simulated conversion α=0.70; experimentally determined α=0.67 using Raman spectroscopy) is ca. 70–85°C, in line with the experimental temperature range of 60–105°C (peak maximum 85°C). The simulation is also able to mimic the change in processing temperature: the simulated value for the glass transition temperature for the 130°C cured epoxy resin (simulated α=0.81; experimentally determined α=0.73 using Raman and α=0.85 using DSC) is ca. 105–130°C, in line with the experimental temperature range of 110–155°C (peak maximum 128°C). This offers the possibility of optimising the processing parameters in silico to achieve the best final properties, reducing labour- and material-intensive empirical testing.

Enhancement of thermal and physical properties of epoxy composite reinforced with basalt fiber

The basalt chopped fiber reinforced epoxy composites using different curing systems were prepared in order to investigate the thermal characteristics of the composites. 2 different curing systems for bisphenol F type epoxy resin — an epoxy-amine curing system and an epoxy-anhydride curing system — were selected and used to investigate the interaction between matrix resin and basalt fiber in the means of thermal properties and physical properties. Through the evaluation of T g and thermal degradation behavior of both systems, it was deduced that the type of curing system as well as basalt fiber reinforcement have a great role in determining thermal properties of the composites. Also, the tensile and flexural properties of the composites were systematically evaluated in order to further understand the effect of curing agents on the interaction with basalt fiber.

Modelling of curing kinetics of amine cured epoxy resins for vacuum assisted resin infusion molding

AbstractEpoxy resin, along with a suitable reinforcement such as glass, is used to manufacture windmill blades by vacuum assisted resin infusion molding (VARIM) process. For the simulation of VARIM process, the sub models are required to describe the rheological and thermochemical behaviour of the epoxy resin. In the present paper, the curing kinetics of amine cured epoxy resin, which is mostly used for wind blade manufacturing, are presented. The kinetic study is performed by measuring the exothermal heat generated during the curing of the amine cured epoxy resin system, using Differential Scanning Calorimeter (DSC), at different temperatures. The range of the temperature for the study is selected between the reaction onset temperature, which is about 70°C, and the peak reaction temperature, which is nearly 120°C. The reaction exotherm, as measured by DSC, is processed to obtain the reaction kinetic data such as the degree of reaction and the rate of reaction at different times and temperatures. A suitable model is proposed to describe the reaction kinetic data obtained experimentally. The unknown parameters of the models are determined by a nonlinear regression analysis on experimental data, while the kinetic rate constants are obtained based on Arrhenius Law. The proposed model is also compared with the models available in the literature. It is found that the proposed model is the simplest model, which accurately captures both the degree of cure and rate of cure qualitatively and quantitatively.

New Phosphonate-Based Additives for Fortification in Model Epoxies

The bulk properties of polymers are often adjusted via addition of a complex blend of compounds collectively known as additives, where so-called molecular fortifiers (or antiplasticizers) may improve the mechanical properties. On the basis of our previous work, we have further explored the potential of reactive phosphonate based additives for enhancement of mechanical and thermal properties of an amine-cured model epoxy resin. In particular, successful fortification based on “ionic bond” formation was achieved for a series of novel custom-made compounds with systematic variation of side groups. Both cure temperature and chemical structure of the fortifier have significant impact on the epoxy’s properties as well as aging behavior. Long-term storage of the epoxies resulted in partial loss of initially achieved fortification. Bifunctional fortifiers revealed particularly robust and much superior performance compared to the previously recommended fortifier dimethyl methylphosphonate (DMMP), rendering them mo...

Curing, Spectral and Thermal Study of Epoxy Resin of Bisphenol-C and Its Polyester Polyols Based Polyurethanes

Epoxy resin of bisphenol-C (EBC), its ricinoleate- and linoleate-based polyols have been cured using 5–25 wt% triethylamine and toluene-2,4-di-isocyanate at 100° and 140°C, respectively. Cured resins are insoluble in common solvents and characterized by IR, DSC and TGA. Amine-cured resin was thermally stable up to about 309–318°C and followed 1.5-order degradation kinetics. Ricinoleate-based polyurethane was thermally stable up to about 215°C and followed 0.43-, 0.75-, and 1.12-order degradation kinetics. Linoleate-based polyurethane was thermally stable up to about 260°C and followed, respectively, 1.9- and 0.93-order degradation kinetics. Kinetic parameters are interpreted in light of resin structure and nature of hardeners used. Amine-cured epoxy resin possesses better thermal properties than those of its polyols-based polyurethanes.

Glass transition dependence of ultrahigh strain rate response in amine cured epoxy resins

Ultrahigh strain rate performance in a series of model amine cured epoxy resins was investigated as a function of the glass transition temperature (Tg) of the cured polymer network, where the network Tg was systematically varied through the monomer stiffness, structure, and size. The high rate response was characterized in terms of a projectile penetration velocity, V50BL(P) (ballistic limit, protection criteria), which describes the projectile velocity with a 50% probability of sample penetration. One factor that dictates the ballistic performance of the epoxy networks, at effective rates of 104–105 s−1, is the difference between the measurement temperature and the glass transition temperature of the network. Sub-Tg relaxations did not have a measurable effect on ballistic performance, and neither did the monomer structure and functionality outside of the influence of the resin Tg, while off-stoichiometric (excess amine) formulations improved V50BL(P) slightly with high Tg epoxies. The results have implications in protective materials for military, aerospace, transportation, and construction industries, where high strain rate insults from airborne debris, high rate collisions, and natural events are increasingly considered during product design.

Nanoscale-confined crystallization in epoxy resin and polyethylene-block-poly(ethylene oxide) diblock copolymer blends

In this paper, the nanoscale-confined crystallization behavior and crystallization kinetics in blends of double-crystalline polyethylene-block-poly(ethylene oxide) (PE-b-PEO) diblock copolymer with diglycidyl ether of bisphenol A epoxy resin were investigated. The results showed that there appeared three crystallization regimes related to the crystallization of the PE block within three different microenvironments in the epoxy resin/PE-b-PEO blends. The Avrami index n is around 1.8–2.4, suggesting PE block of the copolymer in the blends exhibited nanoscale-confined crystallization behavior by homogeneous nucleation. The PE block nanoscale-confined crystallization is ascribed to the formation of the strong intermolecular hydrogen bonding interaction between hydroxyl groups of amine-cured epoxy and ether oxygen atoms of PEO, as seen from Fourier transform infrared spectroscopy spectra.

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.

Mechanical Properties of a Microcapsule-Containing Epoxy for Self-Healing Applications

The addition of microencapsulated healing agent or catalyst in a polymer matrix can potentially change its mechanical properties and processing characteristics. The extent of this change depends on the volume fraction of the additives, the level of interfacial interaction, and the inherent properties of the additives. For a self-healing concept to be viable, the healing performance should be achieved without compromising the overall processing and mechanical properties of the polymer matrix. In this study, tensile and dynamic mechanical properties were investigated and discussed for an amine-cured epoxy dispersed with different loadings of microcapsules.

Structure, thermal and fracture mechanical properties of benzoxazine-modified amine-cured DGEBA epoxy resins

First, traditional diamine hardeners of epoxy resins (EP) were checked as potential accelerators for the benzox- azine (BOX) homopolymerization. It was established that the acceleration effect depends on both the type and amount of the diamine compounds. In the follow-up work amine-curable diglycidyl ether bisphenol A (DGEBA) type EP was modi- fied with BOX keeping the EP/BOX ratio constant (75/25 wt.%). The amine hardeners, added in the EP in stoichiometric amounts, were of aliphatic and aromatic nature, viz. diethylenetriamine (DETA), 4,4!-diaminodiphenyl methane (DDM), and their 1/1 mixture. The thermal, viscoelastic, flexural and fracture mechanical properties of the EP/BOX hybrids were determined and compared to those of the reference EPs. Based on dynamic-mechanical thermal analysis and atomic force microscopy the formation of co-network between EP and BOX was concluded. Homopolymerized BOX was built in the network in nanoscaled inclusions and it was associated with internal antiplasticization. Incorporation of BOX improved the charring, enhanced the flexural modulus and strength, and reduced the glass transition of the parent EP. The fracture tough- ness and energy were not improved by hybridization with BOX.

Effect of TiO2 pigment type on the UV degradation of filled coatings

The objective of this study was to investigate the effect of the photoreactivity of titanium dioxide (TiO2) pigments on the photodegradation of polymeric coatings used in exterior applications. Two polymer matrices, an amine-cured epoxy (EP) and an acrylic urethane (AU), containing three types of TiO2 pigments, classified by different levels of photoreactivity, were studied. Specimens were exposed on an ultraviolet (UV) weathering chamber, the Simulated Photodegradation by High Energy Radiant Exposure device at the National Institute of Standards and Technology. Two exposure conditions were used: ambient, dry condition [25°C and 0% relative humidity (RH)] and high temperature, wet condition (55°C and 75% RH), which is similar to more severe outdoor exposures. The physical and chemical degradations of the filled coatings were monitored at periodic intervals using a combination of laser scanning confocal microscopy (LSCM) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Progression of degradation on the coating surfaces was characterized by LSCM in terms of changes in surface roughness and morphology, pigment agglomerate size, and the occurrence of pits or holes in the coatings. The observed physical changes were correlated to the chemical changes measured by ATR-FTIR as a function of UV exposure time. Both EP and AU systems showed less degradation in terms of surface roughness and morphological changes under the dry conditions compared to the wet exposure conditions. It was observed that both the pigment type (and hence photoreactivity) and particle dispersion strongly affected the degradation of both EP and AU systems.

Porous epoxies by reaction induced phase separation of removable alcohols: Control of spheroidal pore size by mass fraction, cure temperature, and reaction rate

AbstractPorous organic and inorganic materials with both random and controlled microstructures have utility in a variety of fields including catalysis, sensors, separations, optical platforms, tissue engineering, hydrogen storage, micro‐electronics, medical diagnostics, as well as other applications. This work highlights a simple and general technique for tuning the pore size in crosslinking polymeric systems by adding a solvent poragen that phase separates during the curing process (reaction induced phase separation). The pore size can be controlled over large length scales ranging from microns to well below 100 nanometers. In this system an amine cured epoxy resin was reacted in the presence of the sacrificial poragen octadecanol, which is removed by vacuum‐assisted evaporation once the epoxy components have reacted to form a solid, porous matrix. The importance of the present approach is based on the simplicity of the chemical formulation, the ease by which other epoxide or amine chemistries may be substituted for the two reactive components, and the control of pore size down to the nanometer scale by the addition of a small amount of catalyst. © 2010 Wiley Periodicals, Inc.† J Appl Polym Sci, 2010

The Diffusion Mechanism of Water Transport in Amine-Cured Epoxy Networks

In the present work, time-resolved attenuated total reflection Fourier transform infrared spectroscopy (ATR-IR), near-infrared (NIR) spectroscopy, and generalized two-dimensional (2D) correlation analysis were used to investigate water diffusion processes and the state of water molecules in six different epoxy resins. Positron annihilation lifetime spectroscopy (PALS) experimental results and IR results suggested that water diffusion is controlled by local chain reorientation and bond dissociation of water molecules from epoxy networks. Dynamic mechanical analysis (DMA) results of glass transition temperatures of epoxy resins after immersion in hot water correlated well with the PALS and IR results. In addition, four types of water molecules, termed nonbonded (S(0)), single bonded (S(1)), loosely double hydrogen bonded (S(2L)), and tightly double bonded (S(2T)), were detected. It was likewise found, as verified by rough estimation, that water molecules with double hydrogen bonds mostly accomplished diffusion.

Investigation on Recycling Technology of Carbon Fiber Reinforced Epoxy Resin Cured with Amine

An approach to chemical recycling of carbon fiber reinforced epoxy resin cured with amine has been investigated. Amine cured epoxy resin was decomposed totally when it was treated with nitric acid solution under certain conditions. The impacts of nitric acid concentration and decomposition temperature on recycling method were studied with decomposing time and the performance of carbon fiber as indexes. Epoxy resin matrix decomposed entirely after 23hrs at 95°C in the 8mol/L nitric acid solution. Scanning electron microscopy analysis (SEM) and monofilament strength were used to characterize the recycled carbon fibers.

Effect of chemical structure on the water sorption of amine-cured epoxy resins

In this investigation, water sorption behaviour of six epoxy systems with different chemical structure of amines and epoxies were monitored at five temperatures ranging from 35 to 75 °C. The sorption process was analyzed by gravimetric measurements, positron annihilation lifetime spectroscopy (PALS), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-IR). PALS measurements showed that the free volume fraction is not a decisive factor in governing the equilibrium water content, while the polarity of the system is the essential factor. ATR-IR curve fitting were consistent with the theoretical calculated results, and correlated to the diffusion coefficients from gravimetric measurements.

Variable-temperature measurements of the dielectric relaxation in carbon black loaded epoxy composites

Technologically, an understanding of the temperature influence on the transport properties is essential to the study of many random conductor-insulator composites, while fundamentally it is related to a variety of questions in statistical physics, dielectrics, and materials science, to name a few. Variable-temperature measurements of the frequency dependent complex effective permittivity were performed on amine-cured epoxy resins loaded with carbon black (CB). Two series of prepercolative samples differing from the kind of CB particles (Raven 2000 and Raven 5000) mixed in an amine-cured epoxy matrix (diglycidylic ether of bisphenol F) were studied. In this effort to contribute to our understanding of the role of frequency (100 Hz–15 MHz) and temperature (from ambient temperature up to 90 °C) on the complex effective permittivity which describes the linear response of the system to an electromagnetic wave, we investigate these composites with CB loadings below the percolation threshold. Two features are observed. First, our observations cannot be understood in the typical framework of a simple Debye-like dipolar process. In this analysis, we argue that the appearance of the broad temperature and frequency dependent maximum loss can be understood within the heuristic framework proposed by Jonscher which applies to disordered heterogeneous systems. This theoretical framework is consistent with several aspects of the experiments, notably the power-law decays of the real and imaginary parts of the effective permittivity characterized by two fractional exponents m and n. These exponents are both positive and smaller than unity. We further quantified their different temperature variations: while m is strongly decreasing with increasing temperature, n takes a value close to 1. Second, the observed maximum loss frequency found for each CB volume fraction shifts to higher frequencies with increasing temperature and exhibits a non-Arrhenius temperature dependence well represented by a Vogel–Tammam–Fulcher (VTF) fit. Well below the percolation threshold, the associated activation energy and ordering temperature of the VTF fit are not significantly sensitive upon the CB concentration. Such results are compared to previous related work.

Rate dependent multiscale modelling of fibre reinforced composites

A multiscale modelling technique has been developed to predict the strain rate dependent properties of a fibre reinforced composite system. The full stress–strain behaviour through yield of an amine cured epoxy resin matrix (tetraglycidyl 4,4′-diaminodiphenylmethane) has been predicted using group interaction modelling. These data are used in a three-dimensional finite element model to obtain strain concentration factors of fibres adjacent to a fibre break in a unidirectional composite. A Monte Carlo simulation is performed to predict the tensile failure strain of a single composite layer and by assembling these layers the ultimate failure strain of the composite system is predicted. The technique is repeated over three different strain rates and consistency with experiment is observed.