Epoxy Molecules Research Articles

Molecular Simulation of the Interfacial Properties of an Epoxy Composite Reinforced Using a Carbon Nanotube/Carbon Fiber Hybrid

Molecular simulations of the interfacial properties of (1) a composite with an epoxy(EP) matrix and a carbon nanotube(CNT)/carbon fiber(CF) multi-scale reinforcement and (2) a traditional CF/EP composite were performed employing Materials Studio 4.0 software. Results indicate that the interfacial atom concentration of material 1 is higher that that of material 2 by interfacial molecular structure analysis, and there are many benzene rings in both material 1 and material 2 which are parallel to the crystal layers of CF. The contact layer thickness of material 1 and material 2 is 0.25 and 0.10 nm, respectively. The concentration distribution calculation of EP molecules in the interface shows that the most concentrated part of EP in material 2 appears in the carry-forward area of the contact layer, while it is more close to the contact layer in material 1.

Interactions between silica nanoparticles and an epoxy resin before and during network formation

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica nanoparticles and an epoxy resin based on diglycidyl ether of bisphenol-A (DGEBA) have been studied before and during network formation (curing). Rheology and mainly temperature modulated differential scanning calorimetry (TMDSC) have been used to investigate interactions between the silica nanoparticles and molecules of the epoxy oligomer or molecules of the growing epoxy network. Measurements of the complex specific heat capacity before curing showed that interactions between the nanoparticles and DGEBA molecules are very weak. An expression for an effective specific heat capacity of the silica nanoparticles could be deduced. Examination of the isothermal curing process after addition of an amine hardener yielded evidences for a restricted molecular mobility of the reactants in the cause of network formation. These restrictions could be overcome by increasing the curing temperature. No evidences for an incorporation of the silica nanoparticles into the epoxy network, i.e. for a strong chemical bonding to the network, were found. Interactions between the silica nanoparticles and the epoxy resins under study are assumed to be of a physical nature at all stages of network formation.

Noncatalytic polymerization of ethylene glycol and epoxy molecules for rigid polyurethane foam applications

AbstractThe study investigated an approach to incorporate modified epoxidized soy‐based vegetable oil polyol as a replacement for petroleum‐based polyether polyol and to substantially reduce the isocyanate loading in the rigid foam formulation. Noncatalytic polymerization of epoxidized bodied soybean oil and ethylene glycol (EG) was carried out in a closed batch reaction. Cleavage of the oxirane rings and hydroxyl group attachment at optimum conditions provided the desired polyol products. The polyols were characterized based on its hydroxyl numbers, acidity, viscosity, iodine number, and Gardner color index for quality purposes. Reactions of oxirane ring and EG were verified by spectroscopic FTIR. Crosslinking performance was evaluated by extractability analysis on the polyurethane (PU) elastomer wafers. Rigid foaming performed at 50 and 75% petroleum‐based polyether polyol replacements have shown excellent thermoinsulating and mechanical properties compared with epoxidized soybean oil (ESBO) alone or petroleum‐based polyether polyol alone. A reduction of up to 8% of the polymeric diphenylmethane diisocyanate was achieved using the synthesized ESBO‐EG‐based polyols. A higher average functionality polyol is key component to the reduction of isocyanate in PU synthesis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Tribological properties of epoxy/polyurea composite

AbstractThe tribological behavior of epoxy/polyurea composite under dry friction was investigated. The worn surface morphologies of epoxy and epoxy/polyurea composite have been analyzed using scanning electron microscopy (SEM), and the functional group of epoxy and epoxy/polyurea composite before and after wear have been analyzed by a Fourier transform infrared spectrometer (FT‐IR). It has been found that epoxy terminal groups, which exist in an epoxy molecule, can react with the end group amine of the polyurea copolymer, generating more HO bonds, which enhances the deformation capacity. Polyurea particles are dispersed uniformly in epoxy matrix before wear, while plastic deformation and distorted domains occur on the worn surface of epoxy/polyurea composite. This indicates that the wear resistance of epoxy/polyurea composite was greatly improved by the addition of polyurea elastomer, which led to low frictional coefficients and wear mass losses. Copyright © 2008 John Wiley & Sons, Ltd.

Electrical properties of a composite comprising epoxy resin and α-hematite nanorods

Electrical properties of pure epoxy and epoxy–hematite nanorod composites have been investigated. The nanorods were synthesized by the forced hydrolysis method and further mixed with epoxy to obtain the nanocomposite. TEM analysis revealed that they have an average diameter of about 8nm, with an average aspect ratio of 25. DC-conductivity and DC-current relaxation measurements showed a significant influence of Fe2O3 nanorods on the DC-electrical properties of the epoxy matrix. However, the observed effects of the filler below and above the glass transition are different. Because of their high specific surfaces, nanorods affected segmental mobility of epoxy molecules to a large extent, which resulted in an increase in the glass transition temperature (Tg) and a decrease in the real part of dielectric permittivity in high frequency/low temperature region. It is further observed that at elevated temperatures (above Tg) and low frequencies the real part of dielectric permittivity of the nanocomposite exceeds that of the pure matrix, i.e. there is a transition towards microcomposite-like dielectric behaviour.

Electrical conductivity enhancement of a polymer using butyl glycidyl ether (BGE)–lithium hexafluorophosphate (LiPF6) complex

In this study, we investigated the improvement in electrical conductivity of a polymer with the addition of dissolved lithium hexafluorophosphate (LiPF6) in an ether based solvent, butyl glycidyl ether (BGE). Thin film samples were fabricated by adding LiPF6 (up to 1 wt%) to poly (methyl-methacrylate) (PMMA). Film with 0.75% LiPF6 showed the highest improvement of electrical conductivity by three orders of magnitude. Both FTIR spectra and X-ray diffraction studies confirmed the formation of BGE–LiPF6 complex. Differential Scanning Calorimetry was used to characterize the PMMA/LiPF6 specimens further. Dielectric experiments revealed the existence of multiple composition dependent relaxation processes: β (high frequency) and β (low frequency) relaxation processes. The results suggest that electrical conductivity could be improved without influencing the domain polymer and the composite materials, including their processability. This work suggests that the conductivity of nanocomposites with various solid conductive fillers may be sufficiently enhanced in combination with this ion conduction approach involving a “liquid conductive filler.” Since BGE is compatible with epoxy molecules, further study is expected to lead to an effective solution to conductive epoxy composites in their wide field of applications including aircraft and multifunctional energy sources such as structural batteries.

Synthesis and characterisation of novel PBT and PCCD telechelic ionomers prepared by end capping

Poly(butylene terephthalate) (PBT) and poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) (PCCD) ionomers containing terminal ionic units, derived from a novel sodiosulfonate epoxy molecule, were synthesised using an end capping technique in solution. The sulfonated epoxide has the fundamental feature of selectively reacting with the polymer carboxylic terminal groups and therefore, creating polymers with terminal ionic groups. The presence of the sodiosulfonate end groups was confirmed by 1H NMR spectroscopy and titration of carboxyl end groups. Differential scanning calorimetry (DSC) indicated that the presence of ionic end groups has a different effect on the crystallisation process. In particular in PBT the ionic groups cause an increment of the crystallisation rate, whereas, in PCCD the opposite effect is observed.

Effect of reactive layered double hydroxides on the thermal and mechanical properties of LDHs/epoxy nanocomposites

LDHs particles, including LDH-amino benzoate (LDHs-AB) and LDH-carbonate (LDHs-CB) particles, were prepared with coprecipitation method. After the intercalation of the amino benzoate, LDHs-AB particles have reactive and hydrophobic properties. In the preparation of the LDHs-AB/epoxy nanocomposites, the pre-intercalation of the EPON 828 resin into the LDHs-AB interlayer galleries prior to the addition of DDM curing agent was performed. Subsequently, after the addition of the DDM monomers, cross-linking polymerization was performed in the LDHs-AB intragalleries. It expands the interlayer space and well separates these nanolayers from one another to achieve the exfoliated nanocomposites. In addition, the strong chemical bondings formed from the reaction of the reactive LDHs-AB nanolayers and epoxy molecules lead to excellent compatible nanocomposites. Accordingly, exfoliated and compatible LDHs-AB/epoxy nanocomposites exhibit outstanding performance in thermal and mechanical properties compared to the pristine epoxy resin. On the contrary, LDHs-CB/epoxy nanocomposites exhibit a little enhancement on their properties because of the stacked lamellar LDHs-CB particles and weak compatibility in the epoxy nanocomposites.

Properties and Morphology of Bulk Epoxy Composites Filled with Modified Fumed Silica-Epoxy Nanocomposites

Modified fumed silica-epoxy nanocomposites were obtained by refluxing epoxy molecule with fumed silica using imidazole as catalyst. The modified fumed silica was then used as filler in epoxy resin with amine as curing agent. The properties of the surface modified silica and their effect as fillers in bulk epoxy composite were characterized by Fourier Transform Infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance Spectroscopy (1H-NMR), Thermogravimetri Analysis (TGA), Differential Scanning Calorimeter (DSC), Coefficient of Thermal Expansion (CTE), Tensile testing, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectrometry (EDX). From FTIR, 1H-NMR and TGA analysis, it was found that the epoxy resin was chemically bonded onto silica surface. From the DSC and CTE analysis, the addition of modified silica filler in the composite matrix highly influences thermal properties. This new synthesis filler shows higher glass transition temperature and more stable CTE data compared to unmodified filler when introduce into composite matrix. The tensile properties of composite matrix with and without the addition of filler show no significant difference in their tensile properties. SEM-EDX analysis show modified fillers have better adhesion with composite matrix compared to unmodified filler.

Study of the cross‐linking mechanism of a copolymer containing an electrooptic chromophore

AbstractThe mechanism of the cross‐linking reaction occuring between an NLO chromophore copolymerized with a glycidyl epoxide unit (polymer PIII) was rationalized using magic angle spinning (MAS) NMR spectroscopy. A first study conducted on a system composed of a model chromophore and a simple epoxy molecule enabled us to attribute the NMR changes that accompany the epoxy ring opening. Further, the use of a guest–host system made of an azo chromophore dispersed in an MMA–GMA copolymer matrix indicated a quantitative yield of the carboxyl/epoxy anchorage reaction after 30 min of heating at 140°C. The 13C cross polarization (CP)/MAS NMR spectroscopic study showed unambiguously that the cross‐linking reaction in polymer PIII is due to a nucleophilic opening of the epoxy rings by the carboxylic groups of the chromophores resulting in carboxylic ester bond formation. Finally, the blue shift of the ca 500 nm absorption band was modeled with a computational study. It is concluded that the esterification of the acid carboxylic group of the chromophore causes the torsion of the azo molecule. Copyright © 2005 John Wiley & Sons, Ltd.

Adverse effects of thermal dissociation of alkyl ammonium ions on nanoclay exfoliation in epoxy–clay systems

It has been shown recently that storage modulus of intra-gallery epoxy plays a crucial role in producing exfoliated clay structures in epoxy-nanoclay systems. In this study, the possibility of thermal dissociation of alkyl ammonium ions used as cation exchange agents of layered silicate clays and its effects on plasticization of epoxy networks and the growth of storage modulus of intra-gallery epoxy were investigated. It was found that at cure temperatures higher than the dissociation temperature, primary amines were generated from the thermal dissociation of alkyl ammonium ions and the excess chloride salt, which reacted readily with the epoxy molecules and formed linear chains. In addition, such reactions resulted in an excess of diamine curing agents, which in turn caused additional plasticization of epoxy networks and lowered the values of intra-gallery storage modulus. In such cases, only intercalated epoxy composites were produced.

Hydrodynamic Effect on Secondary Phase Separation in an Epoxy Resin Modified with Polyethersulfone

AbstractSummary: The evolution of the morphologies in blends of epoxy/4,4′‐methylenebis(2,6‐dimethylaniline)/polyethersulfone was followed by time‐resolved light scattering, optical microscopy and scanning electron microscopy. The results suggest that, once the diffusion of epoxy molecules cannot follow the geometrical growth, a secondary phase separation occurs, even in the droplet morphology, in which the size of the epoxy‐rich domain grows as usual. The viscoelastic effect of polyethersulfone is also discussed.Development of morphologies followed by OM: bicontinuous phase separation in the PES‐15.9 blend cured at 140 °C after 80 s.magnified imageDevelopment of morphologies followed by OM: bicontinuous phase separation in the PES‐15.9 blend cured at 140 °C after 80 s.

Preparation and properties of LDHs/epoxy nanocomposites

Layered double hydroxides (LDHs)/epoxy nanocomposites were prepared by mixing the amino laurate intercalated LDHs, EPON 828 resin, and Jeffamine D400 as a curing agent. The organo-modified LDHs with hydrophobic property easily disperse in epoxy resin, and the amino laurate intercalated LDHs with large gallery space allow the epoxy molecules and the curing agents to easily diffuse into the LDHs galleries at elevated temperature. After the thermal curing process, the exfoliated LDHs/epoxy nanocomposites were formed. X-ray diffraction was used to detect the formation process of the exfoliated LDHs/epoxy nanocomposites. TEM was used to observe the dispersed behavior of the LDHs nanolayers, and the LDHs nanolayers were exfoliated and well dispersed in these nanocomposites. Owing to the reaction between the amine groups of the intercalated amino laurate and epoxy groups, the adhesion between the LDHs nanolayers and epoxy molecules makes these LDHs/epoxy nanocomposites more compatible. Consequently, the tensile properties from tensile test and the mechanical properties from DMA were enhanced, and the T g of these nanocomposites from DMA and TMA were increased. Coefficients of thermal expansion (CTEs, below and above T g) of these nanocomposites from TMA decreased with the LDHs content. The thermal stability of these nanocomposites was enhanced by the well dispersed LDHs nanolayers.

Mechanism of Exfoliation of Nanoclay Particles in Epoxy−Clay Nanocomposites

The mechanism of nanoclay exfoliation was investigated in epoxy−clay nanocomposites system. The elastic force exerted by cross-linked epoxy molecules inside the clay galleries was found responsible for exfoliation of clay layers from the intercalated tactoids. Complete exfoliation of clay galleries was observed under the conditions of slow increase of complex viscosity and fast rise of storage modulus. It was observed that faster intragallery polymerization, though expedited the exfoliation process, was not necessary for exfoliation. It was also observed that clays containing hydroxylated quaternary ammonium ions and quaternary ammonium ions with no polar functional groups produced exfoliated structures equally easily, provided the ratio of storage modulus to complex viscosity was maintained above 2−4 1/s. Both higher curing temperature and the presence of organically modified clay particles accelerated the formation of gels, and the gel time presented an upper bound of time available for exfoliation.

Adhesion of epoxy to hydrotalcite conversion coatings: II. Surface modification with ionic surfactants

Abstract Hydrotalcites (HT) are naturally occurring compounds being developed as environmentally benign conversion coatings for aluminum aerospace alloys. A successful conversion coating should provide corrosion resistance and act as a base for adhesion with subsequent organic layers. In the first paper of this series, the effect of interlayer anion substitution on the adhesion of epoxy primer was investigated. Interfacial tension and electrostatic interactions were found to influence adhesion between epoxy and conversion coatings. It was believed that increased adhesion could be attained by modification of these properties. This investigation examines the effect of ionic surfactants on the corrosion resistance and epoxy adhesion for HT-based conversion coatings. Post-treatment of a NO 3 HT conversion coating with a trialkyl ammonium surfactant (Adogen®-464) increased the pull-off tensile strength (POTS) of an epoxy coating by 55%. However, treatment with a linear anionic surfactant, sodium lauryl sulfate (SLS); a linear cationic surfactant, cetyltrimethylammonium bromide (CTAB); or a divalent cation (Ca 2+ ) had no effect on the epoxy POTS. Electrophoresis and the rising height method were employed to investigate the effect of the Adogen on electrostatic interactions and interfacial tension, respectively. Adogen decreased the isoelectric point (IEP) of NO 3 HT powders from 11.3 to 10.5. This was attributed to a shift in the Outer Helmholtz Plane (OHP) by the Adogen. A model epoxy molecule, N -methylethanolamine (NMEA), was used for contact angle measurements on conversion coating powders by the rising height method. The contact angle data was found to correlate with the epoxy dry adhesion rankings reported in Part 1 of this series. Adogen adsorption on NO 3 HT powders decreased the NMEA contact angle from 67.9 to 24.1°. Fourier Transform Infrared (FTIR) spectroscopy did not indicate primary bonding between NO 3 HT and Adogen. However, covalent bonding between NO 3 HT and NMEA (and, thus, epoxy) was suggested by FTIR. The improvement of epoxy adhesion on NO 3 HT by Adogen is believed to be due to the increased wettability of the HT.

Diffusion and reaction of epoxy and amine in polysulfone studied using Fourier transform infrared spectroscopy: experimental results

Multi-component diffusion of a diglycidyl ether of bisphenol A (DGEBA) epoxy and an aliphatic diamine, bis(p-aminocyclohexyl)methane (PACM 20) into amorphous polysulfone (PSU) using a Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (ATR-FTIR) technique has been studied. Results indicated that the diffusion of the larger epoxy molecule in polysulfone occurred more quickly when diffusing in the presence of the amine. This behavior and slight deviation of the experimental data from classical Fickian kinetics for amine diffusion into polysulfone were attributed to a finite amount of polysulfone swelling. The diffusion of a model end-capped (non-reactive) epoxy into a polysulfone film saturated with amine was studied to quantify the effect of the amine-induced polysulfone swelling on the diffusivity of the second component. In the DGEBA/PACM 20 system, simultaneous diffusion and reaction in PSU was quantified. Reaction rates in the PSU did not significantly deviate from intrinsic reaction rates of the bulk material. SEM studies of etched epoxy–amine–PSU interphases reveal a semi-interpenetrating network of cured epoxy–amine ranging from 0.6 to 2.4μm, depending on the processing temperature. The formation of this interphase structure is the primary method of load transfer between these dissimilar materials. This work demonstrates the diffusion, subsequent reaction, and final phase separation as the mechanism for interphase formation in the polysulfone/epoxy-amine system studied.

Dipole Dynamics in Liquid Crystalline Epoxies by Broad-Band Dielectric Relaxation Spectroscopy

Dipole dynamics of a series of thermotropic liquid crystalline (LC) epoxy prepolymers and an LC epoxy/amine network were studied by broad-band dielectric relaxation spectroscopy (DRS) over a wide range of frequency and temperature. Two relaxation processes were observed in the prepolymers below the melting point: the β process, associated with the rotational motions of the LC rigid rods about their molecular axis, and the γ process, whose origin lies primarily in the localized motions of the terminal group. The α process, associated with the segmental motions, emerges as a low-intensity process above the calorimetric glass transition and quickly shifts into the gigahertz frequency range with increasing temperature. The δ process, associated with the end-over-end motions in the mesophase, is largely absent because of a negligible longitudinal dipole moment in these LC epoxy molecules. An in-situ investigation of the formation of an LC epoxy/amine network was conducted by DRS and polarized optical microscopy (POM). The initial stage of cure in the mesophase was characterized by the formation of nematic droplets, which quickly coalesce to form larger structures. An interesting observation was the spontaneous formation and the subsequent change of homeotropic to planar orientation during curea trend analogous to that observed by X-ray diffraction. Three relaxations characterize the dynamics of cured networks: the α process due to segmental motions in the cross-linked network, the LC β process also observed in neat prepolymers, and the βOH process, associated with the localized motions of (primarily) hydroxyl groups.

Blends of epoxy resin with amine‐terminated polyoxypropylene elastomer: Morphology and properties

A liquid diglycidyl ether of bisphenol A (DGEBA) epoxy resin is blended in various proportions with amine-terminated polyoxypropylene (POPTA) and cured using an aliphatic diamine hardener. The degree of crosslinking is varied by altering the ratio of diamine to epoxy molecules in the blend. The mixture undergoes almost complete phase separation during cure, forming spherical elastomer particles at POPTA concentrations up to 20 wt %, and a more co-continuous morphology at 25 wt %. In particulate blends, the highest toughness is achieved with nonstoichiometric amine-to-epoxy ratios, which produce low degrees of crosslinking in the resin phase. In these blends, the correlation between GIC and plateau modulus (above the resin Tg), over a wide range of amine-to-epoxy ratios, confirms the importance of resin ductility in determining the fracture resistance of rubber-modified thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 427–434, 1999

Blends of epoxy resin with amine-terminated polyoxypropylene elastomer: Morphology and properties

A liquid diglycidyl ether of bisphenol A (DGEBA) epoxy resin is blended in various proportions with amine-terminated polyoxypropylene (POPTA) and cured using an aliphatic diamine hardener. The degree of crosslinking is varied by altering the ratio of diamine to epoxy molecules in the blend. The mixture undergoes almost complete phase separation during cure, forming spherical elastomer particles at POPTA concentrations up to 20 wt %, and a more co-continuous morphology at 25 wt %. In particulate blends, the highest toughness is achieved with nonstoichiometric amine-to-epoxy ratios, which produce low degrees of crosslinking in the resin phase. In these blends, the correlation between GIC and plateau modulus (above the resin Tg), over a wide range of amine-to-epoxy ratios, confirms the importance of resin ductility in determining the fracture resistance of rubber-modified thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 427–434, 1999

Epoxy-Polysulfone Networks as Advanced Matrices for Composite Materials

Compatibility between polysulfone (PSF) and epoxy oligomers in the melt state as well as the morphology and properties of alloys obtained were studied as a function of composition. The compatibility depends on the length and structure of epoxy molecules, and is best in the case of epoxysulfone oligomers (ESO). The properties of hybrid matrices are determined by their composition and morphology. The most pronounced effects are observed in the regions of small concentrations of either component. A small quantity of PSF significantly improves thermal stability and heat resistance of the epoxy resin as well as its impact strength. On the other hand, on addition to PSF of small amounts of epoxysulfone oligomers, the processability of the matrix can be substantially improved. In particular, the melt viscosity decreases, and wetting and impregnation of fibrous reinforcement is facilitated. Besides, the matrix adhesion to fibers is increased. Powdered PSF/ESO/curing agent mixtures are good for application in solvent-free technological processes of fibrous composites production, e.g. in electrostatic deposition of matrix particles onto a reinforcing fabric. Plastics based on hybrid matrices are distinguished by improved strength.