Organic/inorganic hybrid epoxy nanocomposites based on octa(aminophenyl)silsesquioxane

Octa(aminophenyl)silsesquioxane (OAPS) was used as the curing agent of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin. A study on comparison of DGEBA/OAPS with DGEBA/4,4′-diaminodiphenyl sulfone (DDS) epoxy resins was achieved. Differential scanning calorimetry was used to investigate the curing reaction and its kinetics, and the glass transition of DGEBA/OAPS. Thermogravimetric analysis was used to investigate thermal decomposition of the two kinds of epoxy resins. The reactions between amino groups and epoxy groups were investigated using Fourier transform infrared spectroscopy. Scanning electron microscopy was used to observe morphology of the two epoxy resins. The results indicated that OAPS had very good compatibility with DGEBA in molecular level, and could form a transparent DGEBA/OAPS resin. The curing reaction of the DGEBA/OAPS prepolymer could occur under low temperatures compared with DGEBA/DDS. The DGEBA/OAPS resin didn’t exhibit glass transition, but the DGEBA/DDS did, which meant that the large cage structure of OAPS limited the motion of chains between the cross-linking points. Measurements of the contact angle indicated that the DGEBA/OAPS showed larger angles with water than the DGEBA/DDS resin. Thermogravimetric analysis indicated that the incorporation of OAPS into epoxy system resulted in low mass loss rate and high char yield, but its initial decomposition temperature seemed to be lowered.     

Chemically induced phase separation in the preparation of porous epoxy monolith

A methodology for preparing porous epoxy monolith via chemically induced phase separation was proposed. The starting system was a mixture of an epoxy precursor, diglycidyl ether of bisphenol‐A (DGEBA), a curing agent, 4,4′‐diaminodiphenylmethane (DDM), and a thermoplastic polymer, polypropylene carbonate (PPC). As DGEBA was cured with DDM, the system became phase‐separated having PPC particles dispersed in epoxy matrix. After PPC particles were removed by thermal degradation, a porous structure was obtained. The phase separation mechanism was determined by the initial composition and illustrated by a pseudophase diagram. The pore size increased with increasing the concentration of PPC and raising the curing temperature. The intermediate and final morphologies of the system were studied using optical and scanning electron microscopy, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Evaluation of furfurylamines as curing agents for epoxy resins

Epoxy resin adhesives are widely used because of their strength, versatility, and ability to bond a variety of substrates. Furfurylamines represent a potential, new class of epoxy curing agents. Furfuryl amine (FA), tetrahydrofurfuryl amine (THFA), and 5,5′-methylenebis-2-furanmethanamine (DFA) were studied as possible epoxy curing agents. The utility of FA and THFA are limited by their volatility at the temperatures needed to effect cure of diglycidyl-ether of bisphenol A (DGEBA) based epoxy resins. DFA is a very effective epoxy curing agent with the ability to cure DGEBA at rates similar to that of standard epoxy curing agents such as liethylenetriamine.     

Phase behavior and morphology in epoxy resin/poly(L-lactide) blends. Comparison with epoxy resin/poly(L,D-lactide) blends

Thermoset/thermoplastic blends were prepared with epoxy–aromatic diamine mixtures and poly(L-lactide) (PLLA), as semicrystalline thermoplastic, in concentrations ranging from 4 to 25 wt.%. In some cases, poly(L,D-lactide) (PDLLA), an amorphous thermoplastic, was used instead for comparative purposes. Diglycidyl ether of bisphenol-A (DGEBA) was employed as epoxy resin and 4,4′-diaminodiphenylmethane (DDM) as curing agent. Phase behavior and morphology were studied during curing at 140 °C. Initially, all blends were homogeneous; however, the curing reaction of the epoxy resin caused a liquid–liquid phase separation. A co-continuous morphology was formed at the beginning of the phase separation in all the considered blend compositions. Blends evolved to a particle/matrix structure or to a phase-inverted structure depending on the initial blend composition. At 140 °C, crystallization only occurred in blends with 16 and 25 wt.% PLLA. This crystallization originates changes in the surface of the epoxy-rich droplets developed with the phase separation.     

Cure Kinetics of Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine System

The cure kinetics of epoxy based on the diglycidyl ether of bisphenol A (DGEBA) modified with different amounts of poly(acrylonitrile-butadiene-styrene) (ABS) and cured with 4,4′-diaminodiphenylsulfone (DDS) was investigated by employing differential scanning calorimetry (DSC). The curing reaction was followed by using an isothermal approach over the temperature range 150–180°C. The amount of ABS in the blends was 3.6, 6.9, 10 and 12.9 wt%. Blending of ABS in the epoxy monomer did not change the reaction mechanism of the epoxy network formation, but the reaction rate seems to be decreased with the addition of the thermoplastic. A phenomenological kinetic model was used for kinetic analysis. Activation energies and kinetic parameters were determined by fitting the kinetic model with experimental data. Diffusion control was incorporated to describe the cure in the latter stages, predicting the cure kinetics over the whole range of conversion. The reaction rates for the epoxy blends were found to be lower than that of the neat epoxy. The reaction rates decreased when the ABS contents was increased, due to the dilution effect caused by the ABS on the epoxy/amine reaction mixture.     

Thermal degradation of a reactive flame retardant based on cyclotriphosphazene and its blend with DGEBA epoxy resin

Hexaglycidyl cyclotriphosphazene (HGCP) was synthesized, and characterized by FTIR, ³¹P, ¹H, and ¹³C-NMR. This compound was used as a reactive flame retardant to blend with commercial epoxy resin DGEBA (Diglycidyl ether of bisphenol A). Its effect on the DGEBA decomposition pathways was characterized by studying both gas and solid phases produced during thermogravimetric analysis (TGA). The gases evolved during TGA in air were studied by means of thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), while the solid residues were analysed by FTIR and scanning electron microscopy (SEM). The results showed that HGCP presents a good dispersion in DGEBA, and the blend thermoset with 4,4′-methylene-dianiline (MDA) curing agent leads to a significant improvement of the thermal stability at elevated temperature with higher char yields compared with pure DGEBA thermoset with the same curing agent. Improvement has also been observed in the fire behaviour of blend sample.     

Fracture toughening of epoxy matrices with blends of resins of different molecular weights and other modifiers

The microstructure and fracture behavior of epoxy mixtures containing two monomers of different molecular weights were studied. The variation of the fracture toughness by the addition of other modifiers was also investigated. Several amounts of high‐molecular‐weight diglycidyl ether of bisphenol A (DGEBA) oligomer were added to a nearly pure DGEBA monomer. The mixtures were cured with an aromatic amine, showing phase separation after curing. The curing behavior of the epoxy mixtures was investigated with thermal measurements. A significant enhancement of the fracture toughness was accompanied by slight increases in both the rigidity and strength of the mixtures that corresponded to the content of the high‐molecular‐weight epoxy resin. Dynamic mechanical and atomic force microscopy measurements indicated that the generated two‐phase morphology was a function of the content of the epoxy resin added. The influence of the addition of an oligomer or a thermoplastic on the morphologies and mechanical properties of both epoxy‐containing mixtures was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3920–3933, 2004     

Preparation of crosslinked epoxy microparticles via phase inversion

Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) studies have been performed to reveal a crosslinked epoxy nature of the spherical particles formed in cured epoxy/DDS/PMMA blends. An interesting phase inversion phenomenon was observed in cured DGEBA/DDS/PMMA blends, which occurred at a relatively low thermoplastic composition of 20 phr PMMA in blends. A unique method of preparing crosslinked epoxy spheres of controlled sizes based on cure-induced phase inversion is described in this report. Several factors have been found to affect the geometry of the formed epoxy spheres. The volume fraction of PMMA in the blends strongly dominates the influence. With the increase of PMMA volume fraction in the blends, the spheres not only become smaller in sizes, but also more regular in the spherical geometry due to less impingement. The crosslinking density (DDS phr in the blends) has been found to influence the average sizes of the spheres. The cure temperature has relatively limited effects only when the PMMA loadings in the blends are relatively small. Various potential applications for the epoxy microspheres may be investigated in future studies. © 1996 John Wiley & Sons, Inc.     

PVT behavior of thermoplastic poly(styrene-co-acrylonitrile)-modified epoxy systems: relating polymerization-induced viscoelastic phase separation with the cure shrinkage performance

The volume shrinkage during polymerization of a thermoplastic modified epoxy resin undergoing a simultaneous viscoelastic phase separation was investigated for the first time by means of pressure-volume-temperature (PVT) analysis. Varying amounts (0-20%) of poly(styrene-co-acrylonitrile) (SAN) have been incorporated into a high-temperature epoxy-diamine system, diglycidyl ether of bisphenol A (DGEBA)-4,4'-diaminodiphenyl sulfone (DDS) mixture, and subsequently polymerized isothermally at a constant pressure of 10 MPa. Volume shrinkage is highest for the double-phased network-like bicontinuous morphology in the SAN-15% system. Investigation of the epoxy reaction kinetics based on the conversions derived from PVT data established a phase-separation effect on the volume shrinkage behavior in these blends. From subsequent thermal transition studies of various epoxy-DDS/SAN systems, it has been suggested that the behavior of the highly intermixed thermoplastic SAN-rich phase is the key for in situ shrinkage control. Various microscopic characterizations including scanning electron microscopy, atomic force microscopy, and optical microscopy are combined to confirm that the shrinkage behavior is manipulated by a volume shrinkage of the thermoplastic SAN-rich phase undergoing a viscoelastic phase separation during cure. Consequently, a new mechanism for volume shrinkage has been visualized for the in situ polymerization of a thermoplastic-modified epoxy resin.     

固化剂对环氧树脂/聚砜共混物层状结构形成的影响

不同含量的聚砜(PSF)对环氧树脂(EP)/PSF共混物相结构有重要影响,通过对反应分相后的样品进行断面观察,发现一定PSF含量时,体系形成了层状结构.这种层状结构通常为3层,包括上下2个外层、由聚砜和环氧树脂的颗粒-基体结构组成,以及1个双连续结构形成的中间层.研究表明,这种层状结构由反应诱导相分离开始之初形成的双连续结构发展而来,由于反应和相分离的进一步发展热塑性树脂富集相的体积分数逐渐减小、以及组分间的动力学不对称而最终形成的.在一定PSF浓度范围内,不同温度固化样品时均得到了这种层状结构.改变固化剂类型,层状结构的形貌受到影响,当固化剂活性较高时,外层变薄中间层增厚.当组分间的相容性较好时,双连续结构甚至不能演化发展到层状结构.     

Study of cure kinetics of epoxy-silica organic-inorganic hybrid materials

Cure kinetics of organic-inorganic hybrids based on epoxy resin was investigated, using differential scanning calorimetry (DSC). Thermoset hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) as organic precursor, and 3-glycidyloxypropyltrimethoxysilane (GLYMO) as inorganic precursor. Precursors were polymerised simultaneously using poly(oxypropylene)diamine (Jeffamine D230) as a curing agent. Isothermal DSC characterisation of DGEBA/Jeffamine system and two hybrid DGEBA/GLYMO/Jeffamine systems, with DGEBA and GLYMO mixed in mass ratios of 2:1 and 1:1, respectively, was performed at different temperatures. Applicability of empirical models, commonly used to describe the curing kinetics of thermosets, to hybrid systems was investigated, and the resulting parameters were tested on dynamic DSC scans. Additionally, prepared materials were studied by FTIR and the extraction in tetrahydrofuran. The presence of inorganic phase was found to hinder complete cross-linking of organic phase and influence the kinetics of cure.     

Morphologic and kinetic study of an epoxy-poly(ethyleneoxide) system. The fluorescence to predict miscibility

The kinetic of the curing process in the ethylenediamine (EDA)-poly (bisphenol A-co-epichlorohydrin) glycidyl end-capped (DGEBA) mixture modified with poly(ethylene oxide) (PEO) was studied. The epoxy component was labeled with a fluorescence group (dansyl) treating the DGEBA with the reactive dansyl derivative DNS-EDA. Dynamic DSC experiments were carried out and from their results the effect of the PEO composition on the epoxy curing was discussed. Furthermore, the effect of cure temperature and PEO composition on the morphology and crystallinity of the blend were studied as well. The morphologic study was carried out using complementarily optical transmission (TOM) and epifluorescence (EFM) microscopy. It was observed that: i) the addition of a non-reactive thermoplastic leads to a dilution effect of the reactive groups and therefore a decrease of the epoxy amine reaction rate; ii) the PEO composition does not seem to affect the non catalyzed process of the epoxy curing, while an increase in the PEO fraction within the epoxy/PEO mixture seems to change the mechanism of the cure reaction; iii) dynamic DSC scans, TOM and EFM images and steady state fluorescence spectra of the cured samples suggest that when the curing temperature increases there is an increase in the miscibility between PEO and the epoxy-amine reaction mixture; and iv) a reduction in the PEO/cured epoxy miscibility as the fraction of PEO increases was observed.     

Epoxy/poly(benzyl methacrylate) blends: miscibility, phase separation on curing and morphology

Diglycidyl ether of bisfenol-A (DGEBA)/polybenzyl methacrylate (PBzMA) blends cured with 4,4’-diaminodiphenylmethane (DDM) were studied. Miscibility, phase separation, cure kinetics and morphology were investigated through differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Non-reactive DGEBA/PBzMA blends are miscible over the whole composition range. The addition of PBzMA to the reactive (DGEBA+DDM) mixture slows down the curing rate, although the reaction mechanism remains autocatalytic. On curing, initially miscible (DGEBA+DDM)/PBzMA blends phase separate, arising two glass transition temperatures that correspond to a PBzMA-rich phase and to epoxy network. Cured epoxy/PBzMA blends present different morphologies as a function of the PBzMA content.     

Cure behavior and thermal stability of an epoxy: new bismaleimide blends for composite matrices

A new bismaleimide (BMI) resin was synthesized to formulate epoxy(tetraglycidyl diaminodiphenyl methane; TGDDM) – bismaleimide thermoset blends for composite matrix applications. 4,4′-diaminodiphenyl methane (DDM) was used as an amine curing agent for the TGDDM. A Fourier transform infrared (FTIR) spectroscopy was employed to characterize the new BMI resin. Cure behavior of the epoxy–BMI blends was studied using a differential scanning calorimeter (DSC). DSC thermograms of the thermoset blends indicated two exothermic peaks. The glass transition temperature of the thermoset blends decreased with BMI content. Thermogravimetric analysis (TGA) was carried out to investigate thermal degradation behavior of the cured epoxy–BMI thermoset blends. The new BMI resin reacted partially with the DDM and weak intercrosslinking polymer networks were formed during cure of the thermoset blends.     

Flame retardant and toughening behaviors of bio‐based DOPO‐containing curing agent in epoxy thermoset

Based on bio‐based furfural, a phosphorus‐containing curing agent (FPD) was successfully synthesized, via the addition reaction between 9,10‐dihydro‐9‐oxa‐10 phosphaphenanthrene‐10‐oxide (DOPO) and furfural‐derived Schiff base. Then, as co‐curing agent, FPD was used to prepare flame retardant epoxy thermosets (EP) cured by 4, 4′‐diaminodiphenyl methane. The incorporated FPD improved the flame retardancy and toughness of epoxy thermoset, simultaneously. When 5 wt% FPD was added into EP, the FPD/EP achieved 35.7% limited oxygen index (LOI) value and passed UL94 V‐0 rating, meanwhile. In FPD/EP thermoset, the incorporated FPD reduced the thermal decomposition rate, increased the charring capacity, and inhibited the combustion intensity of epoxy thermoset. Through gas‐phase and condensed‐phase actions in weakening fuel supply, suppressing volatile combustion, and enhancing charring barrier effect, FPD decreased the heat release of burning epoxy thermoset, significantly. For the outstanding effectiveness on both flame retardancy and toughness, the study on FPD provides a promising way to manufacture high‐performance epoxy thermoset.     

A systematic study of the microwave and thermal cure kinetics of the DGEBA/DDS and DGEBA/DDM epoxy‐amine resin systems

The microwave and thermal cure processes for the epoxy-amine systems (epoxy resin diglycidyl ether of bisphenol A, DGEBA) with 4,4′-diaminodiphenyl sulphone (DDS) and 4,4′-diaminodiphenyl methane (DDM) have been investigated for 1 : 1 stoichiometries by using fiber-optic FT-NIR spectroscopy. The DGEBA used was in the form of Ciba-Geigy GY260 resin. The DDM system was studied at a single cure temperature of 373 K and a single stoichiometry of 20.94 wt% and the DDS system was studied at a stoichiometry of 24.9 wt% and a range of temperatures between 393 and 443 K. The best values of the kinetic rate parameters for the consumption of amines have been determined by a least squares curve fit to a model for epoxy/amine cure. The activation energies for the polymerization of the DGEBA/DDS system were determined for both cure processes and found to be 66 and 69 kJ mol⁻¹ for the microwave and thermal cure processes, respectively. No evidence was found for any specific effect of the microwave radiation on the rate parameters, and the systems were both found to be characterized by a negative substitution effect. Copyright © 2002 John Wiley & Sons, Ltd.     

Morphology and interphase formation in epoxy/PMMA/glass fiber composites: effect of the molecular weight of the PMMA

In this work ternary composites based on an epoxy thermoset modified with a thermoplastic polymer and reinforced with glass fibers were prepared. The aim of this study is to analyze the influence of the molecular weight of the thermoplastic polymer on the final morphologies. To obtain tailor made interphases four poly(methylmethacrylate), PMMA, which differ in their molecular weight (34,000, 65,000, 76,000 and 360,000 g/mol) were chosen to modify the epoxy resin. The amount of PMMA in the composites was fixed to 5 wt.%. Neat polymer matrices (epoxy-PMMA without fibers) were also prepared for comparison. To study all systems dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used. Although all the systems showed the typical phase separation in the epoxy/PMMA blend, DMA experiments revealed a new phase with more restricted mobility when the glass fibers are present. The amount of this phase increases as molecular weight of PMMA does. The morphologies as well as the fracture surface in the immediate surroundings of the fibers were found to be different from those observed further away from the surface of the fiber, suggesting therefore that, in this case, different fracture mechanism operates. These observations allow us to conclude that an interphase with specific properties is formed. This interphase is based on a polymer or a polymer blend (epoxy-PMMA) enriched in the component with lower mobility.     

Visualization of the morphology at the interphase of glass fibre reinforced epoxy-thermoplastic polymer composites

This work deals with the effect that the use of glass fibres has on the morphology developed by a thermoplastic polymer modified epoxy. In particular, three surface modifications of the glass fibres were studied: calcinations desizing, activation with hydrochloric acid and coating with 3-aminopropyltriethoxy silane. As the epoxy polymer, a model system based on the full reaction of DGEBA and 2-methyl-1,5-diaminopentane was used. As the modifiers of the epoxy thermoset, two thermoplastic polymers were used: poly(methylmethacrylate) and polystyrene. The morphologies were examined either in the polymer bulk or at the interfaces by means of scanning electron microscopy and atomic force microscopy. After a thoroughly examination of the samples it was found that the thermoplastic polymers preferentially accumulate at the interfaces of these materials when activated and silanized glass fibres are used. These results might be attributed to a gradual phase separation process due to stoichiometric gradients which, on the other hand, seems to be conditioned by the nature of glass fibres surface.     

Curing behavior and kinetics of epoxy resins cured with liquid crystalline curing agent

This article describes the synthesis of a liquid crystalline curing agent 4,4′-bis-(4-amine-butyloxy)-biphenyl (BABB), and its application as a curing agent for the epoxy resin (DGEBA) in comparison with normal curing agent, 4,4′-diaminobiphenyl (DABP). BABB was investigated with polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scatting, and the results showed that BABB displayed smectic liquid crystalline phase. The curing behaviors of DGEBA cured with BABB and DABP were studied by using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and dynamic mechanical analysis (DMA). The results indicated that BABB showed a higher chemical reactivity than DABP. The kinetics was studied under isothermal conditions using an isoconversional method, and the isothermal DSC data can be fitted reasonably by an autocatalytic curing model. The nematic droplet texture was observed for the resulting polymer network of DGEBA/BABB system, while the DGEBA/DABP system showed an isotropic state. The storage modulus of DGEBA/BABB system was enhanced in comparison with DGEBA/DABP system because of the formation of LC phase, whereas the glass transition temperatures decreased because of the introduction of flexible spacer group.     

环氧树脂/聚砜共混体系相结构的调控研究——环氧预聚物分子量的影响

研究了不同分子量的环氧预聚物对双酚A型双官能团环氧树脂 /聚砜 (PSF) /固化剂 (二氨基二苯基砜 ,DDS)体系相分离结构的影响 .通过红外光谱 (FTIR)和动态热机械分析 (TMA)对反应转化率、玻璃化温度以及固化温度的关系的研究 ,表明环氧预聚物分子量较小时 ,凝胶点和玻璃化是影响相结构的关键因素 ;环氧分子量较大时 ,环氧扩链后粘度的变化则成为抑制相分离的重要因素 .电子显微镜 (SEM)结果表明改变环氧预聚物分子量可以达到调控相结构的目的 ,随着预聚物分子量的增大 ,体系的微区尺寸减小 .