Epoxy-silica Hybrid Research Articles

Epoxy-silica hybrids by nonaqueous sol–gel process

The epoxy-silica hybrids have been prepared by the non-aqueous sol–gel process and the in situ generation of nanosilica from tetraethoxysilane was initiated with borontrifluoride monoethylamine (BF3MEA). The DGEBA based epoxy networks with aliphatic, cycloaliphatic and aromatic amines were used as matrices. The solventless technique made it possible to avoid drawbacks of the classical aqueous procedure. The “non-aqueous” systems show improved homogeneity and thermomechanical properties in particular at the application of the coupling agent glycidyloxypropyl trimethoxysilane. Mechanism of the non-aqueous sol–gel process under BF3MEA action and evolution of the hybrid structure during polymerization, followed by chemorheology, are discussed. The nanosilica structure growth is slower under the non-aqueous procedure thus facilitating a better structure control. The hybrids with both particulate and bicontinuous morphologies were prepared and the epoxy-silica interphase bonding and crosslinking through the formed silica domains was proved. The hybrid hierarchical structure and morphology were determined by NMR, SAXS, TEM and DMA.

Epoxy-silica hybrid organic–inorganic electrolytes with a high Li-ion conductivity

Organic–inorganic hybrid electrolytes were prepared by co-hydrolysis and co-condensation of 3-glycidoxipropyltrimethoxysilane (GPTMS) and tetraethyl orthosilicate (TEOS) doped with lithium acetate as self-supported materials and thin-films. The effects of the relative molar content of LiAc on the physicochemical properties of electrolytes, such as morphology, thermal, chemical and electrochemical properties were investigated. Two and four probes test cells were designed for comparative studies of ionic conductivity of hybrid electrolytes using electrochemical impedance spectroscopy (EIS). Similar ionic conductivities were obtained using both measurement methods, reaching a maximum ionic conductivity value of around 10−6S/cm at 25°C. The conductivity mechanism presents Arrehenius behavior with the increase of the temperature from 25°C to 120°C. The electrochemical stability window is found to be in the range of 0–5V, which ensures that hybrid organic–inorganic materials are potential electrolytes for solid-state rechargeable lithium ion batteries.

Novel Epoxy-Silica Hybrid Adhesives for Concrete and Structural Materials: Properties and Durability Issues

Novel epoxy-silica hybrid systems based on silane-functionalized epoxy resins containing interpenetrating silica domains were investigated as structural adhesives with the aim to achieve a good retention of properties when the adhesives are exposed to severe environmental conditions or weathered. Durability experiments have been conducted on the experimental hybrid adhesives by monitoring their mechanical properties, on both cast specimens and on adhesive joints composed of cylindrical concrete or masonry blocks, in ordinary conditions or after exposure to different environmental agents (moderate temperature, immersion in water, outdoor exposure).

Evolution of transient states and properties of an epoxy–silica hybrid cured at ambient temperature

An epoxy–silica hybrid was produced from a mixture of an amine-silane functionalized bisphenol-A resin and a siloxane precursor derived from tetraethoxysilane with small amounts of glycidoxypropyltrimethoxysilane coupling agent. The low temperature curing characteristics and final properties of the hybrid system were compared to those of two epoxy controls. Examinations were carried out by differential scanning calorimetry, dynamic mechanical analysis, electron microscopy, thermogravimetric analysis, UV–Vis spectroscopy, SAXS and densitometry. The modulus, strength and ductility were measured in 3-point bending mode at 23 and 50°C.The siloxane hybridization of the original epoxy resin was found to increase the glass transition temperature (Tg) of cold cured systems by more than 10°C and to produce large improvements in mechanical properties. The study has also provided new insights for the events taking place during gelation, vitrification and curing to the equilibrium state.

Effect of water absorption on the wear behavior of sol-gel processed epoxy/silica hybrids

The aim of this study is to investigate the wear behavior of epoxy-silica hybrids. These hybrids were obtained through the addition of sol-gel prepared silica nanoparticles to epoxy resin. In this study, the effect of nanosilica content on the mechanical properties and wear behavior of epoxy-silica hybrid materials was investigated. Tensile strength, impact strength, hardness, water absorption and wear tests were conducted on the epoxy-silica hybrid specimens. The results demonstrated that the composition of hybrids was of significant importance on mechanical, water uptake and wear properties. Water absorption was found to be highly effective on the wear behavior of hybrids.

Ethoxysilyl-modified hyperbranched polyesters as mulitfunctional coupling agents for epoxy-silica hybrid coatings

Partially ethoxysilyl-modified hyperbranched aliphatic–aromatic polyesters (HBPs) were effectively used as toughening as well as multi-site coupling agents in the preparation of organic–inorganic UV-thermal dual-cured epoxy/TEOS coatings. Through chain transfer reaction of the phenolic terminal units of the HBPs effective incorporation in the epoxy resin is achieved in the photo-initiated cationic polymerization whereas the ethoxysilane groups allow effective formation of a strongly interconnected inorganic–organics network during the in-situ sol-gel process with TEOS by binding the organic to the inorganic phase. Under those conditions, the addition of the inorganic precursor to the epoxy/HPB (20 wt%) system induced an increase of the storage modulus and more important, an improvement of the viscoelastic properties by extending the performance of the elastic modulus to higher temperatures. Thus, highly transparent hybrid coatings with enhanced thermal-mechanical and surface hardness properties resulted by the use of the partially ethoxysilyl-modified HBPs as multifunctional coupling agents.

A comprehensive study of the bicontinuous epoxy–silica hybrid polymers: I. Synthesis, characterization and glass transition

This paper presents a novel two-stage chronological procedure developed for the synthesis of bicontinuous epoxy–silica hybrid polymers. The epoxy–silica polymers are produced by solvent-free hydrolysis of tetraethylorthosilicate into the liquid epoxy resin, followed by the crosslinking of epoxide groups with a diamine curing agent. The two types of bicontinuous epoxy–silica hybrid polymers prepared in this way contain 0–30 wt.% silica and differ only in the absence or presence of (3-glycidoxypropyl)trimethoxysilane ( GLYMO); minimal amount of which is used for the in situ functionalization of silica. GCMS and DSC analyses provide an insight into the reaction mechanism, and reveal that total conversion of silanes as well as epoxy groups is feasible in this way. The free-standing epoxy–silica polymer films are subsequently characterized by the attenuated total reflectance FTIR spectroscopy and AFM. The AFM micrographs exhibit a very fine dispersion of nanoscale silica into the organic matrix that is further enhanced on addition of GLYMO. The presence of GLYMO substantially affects the particle size and distribution, augments the adhesion of the two phases, and inhibits the macroscopic phase separation. The glass transition temperatures of epoxy–silica polymers are also improved by 20.4%; which is attributed to the formation of entangled epoxy–silica networks.

Synthesis, thermal properties, and flame retardance of phosphorus‐containing epoxy‐silica hybrid resins

AbstractA novel epoxy resin modifier, phosphorus‐containing epoxide siloxane (DPS) with cyclic phosphorus groups in the SiO network, was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with polyhedral‐oligomeric siloxanes, which was synthesized by the sol–gel reaction of 3‐glycidoxypropyltrimethoxysilane. DPS was confirmed by Fourier transform infrared and 29Si NMR measurement, and then was employed to modify epoxy resin at various ratios, with 4,4‐diaminodiphenyl‐methane as a curing agent. In order to make a comparison, DOPO‐containing epoxy resins were also cured under the same conditions. The resulting organic–inorganic hybrid epoxy resins modified with DPS exhibited a high glass transition temperature (Tg), a good thermal stability, and a high limited oxygen index. In addition, the tensile strength of cured products was also rather desirable. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Effect of Amino-Modified Silica Nanoparticles on the Corrosion Protection Properties of Epoxy Resin-Silica Hybrid Materials

In this paper, a series of organic-inorganic hybrid materials consisting of epoxy resin frameworks and dispersed nanoparticles of amino-modified silica (AMS) were successfully prepared. First of all, the AMS nanoparticles were synthesized by carrying out the conventional acid-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) in the presence of (3-aminopropyl)-trimethoxysilane (APTES) molecules. The as-prepared AMS nanoparticles were then characterized by FTIR, 13C-NMR and 29Si-NMR spectroscopy. Subsequently, a series of hybrid materials were prepared by performing in-situ thermal ring-opening polymerization reactions of epoxy resin in the presence of as-prepared AMS nanoparticles and raw silica (RS) particles. The as-prepared epoxy-silica hybrid materials with AMS nanoparticles were found to show better dispersion capability than that of RS particles existed in hybrid materials based on the morphological observation of transmission electron microscopy (TEM). The hybrid materials containing AMS nanoparticles in the form of coating on cold-rolled steel (CRS) were found to be much superior in corrosion protection over those of hybrid materials with RS particles when tested by a series of electrochemical measurements of potentiodynamic and impedance spectroscopy in 5 wt% aqueous NaCI electrolyte. The increase of corrosion protection effect of hybrid coatings may have probably resulted from the enhancement of the adhesion strength of the hybrid coatings on CRS coupons, which may be attributed to the formation of Fe-O-Si covalent bond at the interface of coating/CRS system based on the FTIR-RAS (reflection absorption spectroscopy) studies. The better dispersion capability of AMS nanoparticles in hybrid materials were found to lead more effectively enhanced molecular barrier property, mechanical strength, surface hydrophobicity and optical clarity as compared to that of RS particles, in the form of coating and membrane, based on the measurements of molecular permeability analysis, dynamic mechanical analysis, contact angle measurements and ultraviolet-visible transmission spectra, respectively.

Molybdate doping of networks in epoxy–silica hybrids: Domain structuring and corrosion inhibition

Epoxy–silica hybrids were prepared from a silane-functionalized resin mixture of two diglycidyl ether bis-phenol A oligomers with different molecular weights, using molybdate anions as dopants for the siloxane domains. The functionalization of the epoxy resin was carried out using suitable trimethoxysilane compounds, respectively, containing amine and mercaptan reactive groups. The molybdate anions were added as “bound” species in the form of salts produced from pre-reactions with a fractional amount of the cycloaliphatic amine hardener, and as “free” molybdic acid. The co-continuous silica domains within the epoxy networks were produced by the incorporation of pre-hydrolysed mixtures of tetraethoxy silane and γ-glycidoxyl trimethoxysilane into the precursor solution used for the production of epoxy–silica hybrids. The addition of a source of molybdate anions to the hybrid precursor solution gave rise to the formation of a denser siloxane network and to a substantial increase in the T g of the organic phase. This resulted also in a large increase in the rubbery-plateau modulus, and in a substantial reduction in both the rate of solvent uptake and the equilibrium amount of solvent absorption. It was shown that the presence of organic–inorganic hybrid networks allows the “entrapped” molybdate anions to be released at a slow and controlled rate. Furthermore, when the precursor solution mixtures for the formation of such doped networks are used as coatings for ferrous metal substrates, the molybdate anions slowly migrate to the interface and provide an enhanced mechanism for the passivation of the metal substrate. The enhancement of the corrosion protection capability of the coatings was found to be greater when the molybdate anions were added in “bound” form, as amine molybdate, than as “free” molybdic acid.

The effect of silicon sources on the mechanism of phosphorus–silicon synergism of flame retardation of epoxy resins

The effect of silicon source on the mechanism and efficiency of silicon–phosphorus synergism of flame retardation was studied. The studied systems composed of a phosphorus-containing epoxy resin and various types of silicon additives including nanoscale colloidal silica (CS), tetraethoxysilane (TEOS), and diglycidylether terminated polydimethylsiloxane (PDMS-DG). Thermal stability and degradation kinetics of cured epoxy resins, elemental analysis of degraded residues, and evolved gases analysis of degradation reactions were conducted with a thermogravimetric analyser, energy-dispersive X-ray spectrometry, and gas chromatography–mass spectrometry, respectively. Addition of silicon compounds showed significant effect on enhancing the thermal stability and char yields of the cured epoxy resins. During thermal degradation, TEOS and PDMS-DG exhibited silicon migration to sample surface and CS did not. Self-degradation of PDMS-DG resulted in a silicon loss for PDMS-DG-containing epoxy resin. From the results it was concluded that using TEOS as an additive for epoxy resins and formation of epoxy-silica hybrid structure through sol–gel reactions was a good approach for achieving phosphorus–silicon synergism in flame retardation.

Network density control in epoxy–silica hybrids by selective silane functionalization of precursors

AbstractFollowing previous work on the compatibilization of organic–inorganic hybrids through coupling reactions with the precursor components, the present study evaluates the relative efficiency of different types of coupling agents on the morphology and properties of epoxy–silica hybrids. In particular, this investigation compares the effects of introducing trialkoxysilane functional groups at the chain end (using amine‐ and mercapto‐silanes) with similar types grafted in the middle of the chain of the constituent resin (using an isocyanate silane). The use of coupling agents with a basic character (amine silane type) brings about the formation of denser networks in both constituent phases of the resulting epoxy–silica hybrid, which is manifest through a large increase in the Tg and a more extensive suppression of the molecular relaxations within the glass transition regions. Increasing the number of alkoxysilane functional groups at the chain end, with the use of a bis‐aminosilane, has a relatively minor effect on the morphology and dynamic mechanical spectra of the resulting epoxy–silica hybrids. It was also found that while the incorporation of small amounts of a high molecular weight epoxy resin causes considerable plasticization of the organic phase, much larger amounts of organic (aliphatic) co‐agent within the siloxane phase are required to deteriorate those properties that are related to the inorganic character of the hybrid material. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:91–102, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20033

Preparation and characterization of epoxy-silica hybrid materials by the sol-gel process

A transparent organic-inorganic epoxy/silica hybrid material was prepared by epoxy resin, functionalized-epoxy resin, which was partially functionalized by 3-aminopropyl triethoxylsilane(APTES), and highly reactive polysilcic acid (PSA), which was prepared through hydrolysis and condensation of metasilicate salt. The properties of hybrid materials such as impact strength, tensile strength, glass transition temperature (Tg), thermogravimetric temperature (TGA), and thermal effect of the hybrid materials were studied. The size of PSA particles in THF measured by dynamic light scattering technique, ranged from 10–28 nm. The results of experiment indicated that modified epoxy resin possed better roughness than that of the pure epoxy resin. The structure of the hybrid materials was characterized by FT-IR spectroscopy and 29SiNMR spectroscopy.

Epoxy-silica hybrid materials synthesized via sol-gel process

We have successfully utilized the sol-gel method to synthesize epoxy-silica hybrid material at nanoscale. Using the sol-gel process we could overcome many disadvantages of conventional composite materials. In this research, two different methods are recommended — a one-step process and a two-step process — to synthesize epoxy-silica hybrid materials. The coupling agent, γ-glycidoxypropyl-methyldiethoxysilane (KBE-402), was utilized to modify the surface properties of the silica via the sol-gel process. The role of the coupling agent is to provide covalent bonding between the epoxy resin and silica. This method could reinforce the interfacial force of the hybrid material and promote the thermal properties of the materials. The thermal properties of the epoxy-silica materials were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). From these results, we noted that the best reaction time in the one-step process is 2 days and the addition of the inorganic component enhanced the thermal stability of the hybrid materials. On the other hand, the two-step process led to a phase separation phenomenon after mixing epoxy resin and precursor without coupling agent. The coupling agent could avoid the phase separation problem of hybrid materials and enhance the thermal stability of the materials through this process. At the same time, the T g of the materials increased proportionally to the content of silica from 80°C to 113°C.

Thermal stability of epoxy-silica hybrid materials by thermogravimetric analysis

The thermal degradation behavior and thermal stability of epoxy-silica nanocomposites were studied with thermogravimetric analysis (TGA). Detailed and precise factors on the thermal stability based on the initial decomposition temperature (IDT), temperature of maximum rate of weight loss ( T max), integral procedure decomposition temperature (IPDT), decomposition temperature range, and activation energy ( E a) of the decomposition reactions were studied. Introduction of nanoscale silica into epoxy resins certainly improved their thermal stability and reduced their weight loss rates, and the improvement can be further enhanced with using a phosphorous compound as the curing agent. The activation energies of the thermal degradation reactions of the nanocomposites were calculated from various methods, and the results from the Ozawa method provided reliable data. It was shown that the presence of nanoscale silica leveled up the values of the activation energies of the degradation reactions, and phosphorus group depressed the values of E a.

Preparation, thermal properties, and flame retardance of epoxy–silica hybrid resins

AbstractA novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003

Flame-retardant epoxy resins: An approach from organic-inorganic hybrid nanocomposites

Phosphorus-containing epoxy-based epoxy–silica hybrid materials with a nanostructure were obtained from bis(3-glycidyloxy)phenylphosphine oxide, diaminodiphenylmethane, and tetraethoxysilane in the presence of the catalyst p-toluenesulfonic acid via an in situ sol–gel process. The silica formed on a nanometer scale in the epoxy resin was characterized with Fourier transform infrared, NMR, and scanning electron microscopy. The glass-transition temperatures of the hybrid epoxy resins increased with the silica content. The nanometer-scale silica showed an enhancement effect of improving the flame-retardant properties of the epoxy resins. The phosphorus–silica synergistic effect on the limited oxygen index (LOI) enhancement was also observed with a high LOI value of 44.5. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 986–996, 2001

Formation and structure of the epoxy-silica hybrids

The organic-inorganic hybrid interpenetrating network (IPN) composed of an epoxide-amine network and silica was prepared and studied. Formation of the inorganic phase from tetraethoxysilane (TEOS) by sol-gel process was characterized by 29Si n.m.r. spectroscopy, gas chromatography, small-angle X-ray scattering and electron microscopy. Kinetics of the silica structure build-up in the organic matrix, its final structure and morphology depend on the method of IPN hybrid preparation. The large compact silica aggregates, 100–300 nm in diameter, are formed during the one-stage polymerization. The two-stage process with the acid prehydrolysis of TEOS leads to an acceleration of gelation and formation of more open and smaller silica structures: 50–100 nm in diameter. The most homogeneous hybrid morphology with the smallest silica domains of size 10–20 nm, appears in the sequential IPN. The development of the silica structure is restricted by a rigid reaction medium of the preformed epoxide network.

Structure evolution in epoxy–silica hybrids: sol–gel process

The evolution of heterogeneous structure during polymerization in the epoxy–silica hybrid was followed by small-angle X-ray scattering using a position-sensitive detector. The organic–inorganic hybrid was composed of an epoxide–amine system and the silica formed by the sol–gel process from tetraethoxysilane (TEOS). Silica structure evolution is determined by catalytic conditions and the way of preparation: one- or two-stage process. The one-stage polymerization was base-catalyzed by an amine used as a cross-linker of the epoxide. The reaction results in formation of large overlapping polysiloxane clusters from the very beginning of the reaction. During polymerization more branched domains gradually appear within the structure. The polymer shows a compact structure with fractal dimension increasing during the polymerization to D m =2.5. The two-stage procedure consisting in acid prehydrolysis of TEOS and basic catalysis in the second step leads to an acceleration of gelation. Primary particles are formed in the first step followed by aggregation into clusters in the second step. The inner structure of the clusters described by a fractal dimension does not change during the polymerization. The diffusion-limited cluster–cluster reaction may be responsible for a more open structure with a fractal dimension D m =1.7.