Bifunctional Epoxy Research Articles

Nanoindentation Response of Structural Self-Healing Epoxy Resin: A Hybrid Experimental-Simulation Approach.

In recent years, self-healing polymers have emerged as a topic of considerable interest owing to their capability to partially restore material properties and thereby extend the product's lifespan. The main purpose of this study is to investigate the nanoindentation response in terms of hardness, reduced modulus, contact depth, and coefficient of friction of a self-healing resin developed for use in aeronautical and aerospace contexts. To achieve this, the bifunctional epoxy precursor underwent tailored functionalization to improve its toughness, facilitating effective compatibilization with a rubber phase dispersed within the host epoxy resin. This approach aimed to highlight the significant impact of the quantity and distribution of rubber domains within the resin on enhancing its mechanical properties. The main results are that pure resin (EP sample) exhibits a higher hardness (about 36.7% more) and reduced modulus (about 7% more), consequently leading to a lower contact depth and coefficient of friction (11.4% less) compared to other formulations that, conversely, are well-suited for preserving damage from mechanical stresses due to their capabilities in absorbing mechanical energy. Furthermore, finite element method (FEM) simulations of the nanoindentation process were conducted. The numerical results were meticulously compared with experimental data, demonstrating good agreement. The simulation study confirms that the EP sample with higher hardness and reduced modulus shows less penetration depth under the same applied load with respect to the other analyzed samples. Values of 877 nm (close to the experimental result of 876.1 nm) and 1010 nm (close to the experimental result of 1008.8 nm) were calculated for EP and the toughened self-healing sample (EP-R-160-T), respectively. The numerical results of the hardness provide a value of 0.42 GPa and 0.32 GPa for EP and EP-R-160-T, respectively, which match the experimental data of 0.41 GPa and 0.30 GPa. This validation of the FEM model underscores its efficacy in predicting the mechanical behavior of nanocomposite materials under nanoindentation. The proposed investigation aims to contribute knowledge and optimization tips about self-healing resins.

Equol-based epoxy resin as an ideal substitute for the diglycidyl ether of bisphenol A (DGEBA)

The development of high-performance bio-based epoxies with excellent mechanical properties, heat resistance and flame retardant properties is essential to mitigating the resource and environmental burdens caused by the widespread utilization of petroleum-based epoxies. This work focuses on the synthesis of a bifunctional epoxy resin (EEU) with the rigid tetrahydrobenzopyran ring derived from equol. The structure of the EEU epoxy resin was characterized, and using 4,4′ diamino diphenyl sulfone as the curing agent, the rheological properties, curing behavior and comprehensive properties of cured resin were studied. The results demonstrate that EEU-DDS presents the same curing behavior as DGEBA-DDS. The mechanical properties heat resistance and flame retardant properties of EEU-DDS are superior to DGEBA-DDS. The tensile strength, tensile modulus and glass transition temperature reached to 94.0 MPa, 3.62 GPa and 221 °C, respectively, higher than those of DGEBA-DDS (83.2 MPa, 2.81 GPa and 203 °C). EEU-DDS reached the V-1 rating in UL-94 tests with a high limiting oxygen index (LOI) (28 %), and the peak heat release rate and smoke release rate of 631 kW/m2 and 0.155 m2/s were significantly lower than that of DGEBA-DDS. The flame retardant mechanism was proven to be gas-coacervated phase synergistic flame retardant. In addition, the interlamellar shear strength (ILSS), bending strength, and impact strength of carbon fiber reinforced resin matrix composites prepared by EEU-DDS reached 97.9 MPa, 1281 MPa, and 81.3 kJ/m2, respectively, higher than those of DGEBA-DDS. Therefore, equol-based epoxy resin can serve as an ideal alternative to petroleum-based bisphenol A-type epoxy resin, offering superior comprehensive properties.

Bi-functional epoxy coating with long-term protection for Q235 steel prepared by incorporating melamine-grafted and carbon-black-modified graphene oxide

In recent years carbon materials, such as graphene oxide (GO) and carbon nanotube, have been became key materials for high-performance coatings for the protection of metals from corrosion. Here, a novel bi-functional epoxy coating was developed and formulated, which can replace traditional primers and topcoats. Furthermore, the effects of modified graphene oxide‑carbon black (MGC) on the corrosion resistance and weathering resistance of coated Q235 samples have been investigated using salt spray testing, UV accelerated aging testing, and electrochemical impedance spectroscopy. Results suggest that the incorporation of MGC leads to a considerable enhancement in the corrosion resistance and weathering resistance of coated samples. Notably, the bi-functional epoxy coating formulated with 0.2 wt% of MGC demonstrated the most effective anti-corrosion and weathering resistant properties. During the UV accelerated aging testing for 20 days, the low-frequency impedance modulus values of bi-functional epoxy coated samples were recorded to be 1.09 × 108 Ω·cm2, which is higher than pure epoxy coated samples (9.05 × 106 Ω·cm2). Also, the highest adhesion strength of bi-functional epoxy coated samples decreased from 2.51 MPa to 1.97 MPa. These observations suggest that the bi-functional epoxy maintained a significant portion of its adhesion strength even after undergoing UV accelerated aging, indicating its robustness and durability under such corrosion conditions.

Tailoring peel strength in UV-responsive, nonconductive adhesives via photocleavable epoxy for micro-LED bonding and repair

To develop a UV-responsive epoxy-based nonconductive adhesive (NCA) with adjustable peel strength, a bifunctional epoxy (NBE) was synthesized. This compound included an ortho-nitrobenzyl ester that decomposes upon UV absorption, exhibiting absorption in the 240350 nm wavelength range and a thermal decomposition temperature at 1% weight loss of 214 ℃. When coupled with an imidazole catalyst, the curing of NBE began at 100 ℃ and reached a maximum exothermic peak at 136 ℃. The NCA was formulated using NBE together with bisphenol F epoxy, cresol novolac epoxy, and nadic methyl anhydride as a curing agent. Despite the increasing NBE content in the NCA, the curing behaviour remained almost the same. However, the decomposition temperature of the NCA decreased in proportion to the NBE content. NCA tapes bonded to quartz glass substrates exhibited a 90° peel strength of 7.1910.39 N/in, depending on the NBE content. When exposed to excimer laser irradiation at 100 mJ/cm2, the 90° peel strength decreased significantly to nearly 0 N/in.

Analysis of the Effect of Network Structure and Disulfide Concentration on Vitrimer Properties.

A set of five vitrimers with glass transition temperatures in the range of 80-90 °C were designed to assess the effect of the network structure and disulfide concentration on their dynamic and mechanical properties, and to find the best performing system overall compared to the commercial Araldite LY1564/Aradur 3486 commercial thermoset system. Vitrimer networks were prepared by incorporating mono- and bifunctional epoxy reactive diluents and an amine chain extender into the Araldite LY1564/4-aminophenyldisulfide system.

Suppression of Supramolecular Disassembly of Pseudopolyrotaxane Nanosheet by End-Capping via Amine–Epoxy Click Reaction of Bifunctional Epoxy

Suppression of Supramolecular Disassembly of Pseudopolyrotaxane Nanosheet by End-Capping via Amine–Epoxy Click Reaction of Bifunctional Epoxy

Effect of Temperature on the Functionalization Process of Structural Self-Healing Epoxy Resin

This work deals with developing a self-healing resin designed for aeronautical and aerospace applications. The bifunctional epoxy precursor was suitably functionalized to enhance its toughness to realize good compatibilization with a rubber phase dispersed in the hosting epoxy resin. Subsequently, the resulting mixture was loaded with healing molecules. The effect of the temperature on the epoxy precursor’s functionalization process was deeply studied. Fourier trans-former infrared (FT-IR) spectroscopy and dynamic mechanical analyses (DMA) evidenced that the highest temperature (160 °C) allows for obtaining a bigger amount of rubber phase bonded to the matrix. Elastomeric domains of dimensions lower than 500–600 nanometers were found well distributed in the matrix. Self-healing efficiency evaluated with the tapered double cantilever beam (TDCB) method evidenced a healing efficiency for the system functionalized at 160 °C higher than 69% for all the explored fillers. The highest value was detected for the sample with DBA, for which 88% was found. The healing efficiency of the same sample functionalized at 120 °C was found to decrease to the value of 52%. These results evidence the relevant role of the amount and distribution of rubber domains into the resin for improving the resin’s dynamic properties. The adopted strategy allows for optimizing the self-healing performance.

Preparation of double-core microcapsules and tribological properties of epoxy composites

Double-core microcapsules were prepared via in situ polymerization using poly(urea-formaldehyde) (PUF) as the wall material as well as ionic liquid and linseed oil as the core material. The addition of microcapsules to epoxy matrices can result bifunctional epoxy composites with self-lubricating and self-healing properties. Frictional wear experiments indicated that compared with pure epoxy resin, the friction coefficient of the epoxy composite containing 7 wt% microcapsules was reduced by 93.5% and the wear rate of the composite was reduced by 98%. In addition, the composite material has excellent repair properties for scratches.

A bifunctional epoxy coating doped by cerium (III)-8-hydroxyquinoline: Early self-reporting and stimuli-responsive inhibition on corrosion of Al substrate

Recently, anti-corrosion coatings with auto-inhibition and self-reporting on their premature flaws are becoming more and more attractive. In this work, we engineered a cerium nitrate/8-hydroxyquinoline (Ce-HQ) hybrid pigment to endow epoxy coatings with corrosion self-inhibiting and fluorescent self-reporting performances via molecule design. The Ce-HQ pigments were synthesized by physical mixture and then dispersed into the commercial epoxy coating. Once the epoxy coating gets degraded, the underneath aluminum alloy matrix may corrode to produce Al3+ ions, which can compete with Ce3+ ions in the Ce-HQ complex, and then chelate with dissociative 8-HQ to form fluorescent Al-HQ complex, due to the higher bonding strength of Al3+ with 8-HQ than Ce3+ ions. Thus, not only the responsive releasing of Ce3+ ions and 8-HQ can inhibit the underlying Al alloy, but the newly formed Al-HQ complex could indicate the location and severity of coating flaws through fluorescent emission under UV light. Electrochemical impedance evidenced that the composite epoxy coating containing 1 % mass Ce-HQ presents high corrosion resistance even after 504 h of salt spray test, showing 90 % corrosion refraining efficiency. This work may enlighten an approach to developing self-healing and self-diagnosis coating for premature corroded Al alloy beneath coatings via reactive release and fluorescent visualization.

Synthesis of a Novel Bifunctional Epoxy Double-Decker Silsesquioxane: Improvement of the Thermal Stability and Dielectric Properties of Polybenzoxazine.

In this study a new type of bifunctional epoxy compound (DDSQ-EP) based on double-decker silsesquioxane (DDSQ) was synthesized by process of alkaline hydrolysis condensation of phenyltrimethoxysilane and corner capping reaction with dichloromethylvinylsilane, followed by epoxidation reaction of vinyl groups. The resultant structures were confirmed using Fourier transform infrared spectrometry, nuclear magnetic resonance spectrometry and time-of-flight mass spectrometry, respectively. The DDSQ-EP was incorporated into polybenzoxazine to obtain the PBZ/DDSQ-EP nanocomposites. The uniform dispersion of DDSQ-EP in the nanocomposites was verified by X-ray diffraction and scanning electron microscope. The reactions occurred during the curing of the composites and were investigated using infrared spectroscopy of segmented cures. Dynamic mechanical analysis and thermal gravimetric analysis indicated that the storage modulus, glass transition temperature and thermal stability of PBZ/DDSQ-EP were increased in comparison with pure benzoxazine resins. Assessment of dielectric properties demonstrated that the dielectric permittivity and dielectric loss of polybenzoxazine decreased slightly because of the addition of DDSQ-EP.

Preparation, characterization, and curing kinetics of elevated and cryogenic temperature-resistant epoxy resin composites

The elevated-and-cryogenic temperature resisting composites were prepared using tetrafunctional (AG-80) and bifunctional (E-42) epoxy resin blend as the matrix, polyetheramine (D400), and m-xylylene diamine (MXDA) as hybrid curing agents, silane coupling agent (KH-560) as a toughening agent, and micron-sized silicon oxide particles as fillers. The curing kinetics of the composites was investigated by differential scanning calorimetry (DSC), the effect of reaction temperature on the resin system's viscosity, the variation of gel time with temperature, and the heat resistance of the resin system were tested by thermogravimetric analysis. The apparent activation energy and reaction level of the curing reaction was calculated, the curing process was developed, and the elevated and cryogenic mechanical properties set at different times were tested. The results showed that the resin system's viscosity decreased with increasing temperature, 40 °C was determined as the optimum operating temperature, and the heat resistance of the composite was good. The gel time test developed a strategy of pre-curing by vacuum at 40 °C and curing at 60 °C. The compressive strength of the resin system was 99.55 MPa and 159.12 MPa after placing at −196 °C and 160 °C for 4 h, respectively. This study presents a theoretical basis for the curing process and optimization of curing parameters for elevated and cryogenic resistant modified epoxy resin composite and provides a potential application for its future in-situ utilization in deep space exploration and lunar construction.

Spatially controlling the mechanical properties of 3D printed objects by dual-wavelength vat photopolymerization

To date, the 3D printing of polymers with heterogeneous and locally controlled material properties is still a challenging area in additive manufacturing. In terms of vat photopolymerization 3D printing, the fabrication of multi-material objects typically relies on an automatic material exchange of different resin vats. However, along with the high complexity of the printing equipment, this technique suffers from a low build speed and often yields 3D printed objects with week interlayer adhesion across the various material interfaces. Herein, we use chemo-selective wavelengths to fabricate objects with multi-material properties by dual-wavelength vat photopolymerization 3D printing employing a single vat. The photopolymers’ stiffness and flexibility are conveniently controlled by two photoreactions working at two different wavelengths. In particular, a dual photocurable resin is applied containing multi-functional acrylates, which are cured by a radical induced chain growth reaction at 405 nm, and bi-functional epoxy monomers, which additionally undergo cationic curing upon UV exposure (365 nm). FT-IR experiments confirm the wavelength selective network formation whilst dynamic mechanical analysis and tensile tests give evidence of the distinctive difference of the related mechanical properties. By being able to produce soft (ε = 24%, σ = 1.0 MPa) and stiff (ε = 4%, σ = 39.1 MPa) networks with a single resin vat, we demonstrate the efficient fabrication of 3D structures with locally controlled mechanical properties using a dual-wavelength 3D printer operating at 405 and 365 nm. In contrast to previous work in this field, we were able to significantly expand the range of mechanical properties by appropriate selection of the acrylic components and to drastically accelerate the build speed by changing the cationic photoinitiator and using a customized printer with high intensity LED sources.

A dieugenol-based epoxy monomer with high bio-based content, low viscosity and low flammability

A renewable eugenol-based biphenyl bifunctional epoxy monomer (DEUEP) is synthesized via a facile method. Eugenol is coupled into 5,5′-dieugenol and then glycidized to yield DEUEP with a potentially 100% biobased content in a high purity (96%). DEUEP displays a lower viscosity (9.2 vs. 20.6 Pa·s at 25 ℃) and a flow activation energy (60.4 ± 0.4 vs. 81.1 ± 0.4 kJ/mol) than a commodity bisphenol A-based epoxy prepolymer (E54) does. With a 3,3′-diaminodiphenylsulfone (33DDS) hardener, DEUEP/33DDS is found to express the reactivity identical to E54/33DDS with a similar activation energy (~62 kJ/mol). The cured DEUEP/33DDS thermoset is systematically examined and compared with E54/33DDS in terms of dynamic mechanical properties, thermal stability, flammability, flexural, impact and shear properties, fracture behaviors, water resistance, and wettability. DEUEP/33DDS has a lower flammability as indicated by the increased limited oxygen index (26.4% vs. 22.1%), the decreased heat release rate (HRR), total heat release (THR) and heat capacity (HR) by 46%, 33% and 46%, respectively. DEUEP/33DDS has Tg of 120.9 ℃, a storage modulus of 2.57 GPa (25 ℃), a higher char yield of 32.2% (750 ℃ in N2), and a higher water-contact angle of 110.6°.

Synthesis and properties of high temperature self-curing epoxy resin

A new bifunctional epoxy resin was synthesized by the reaction of replacing the hydrogen atom of amino groups from 4,4-diaminodiphenylmethane and epichlorohydrin taken in a double excess in dichloroethane. In order to remove HCl formed during the synthesis, which can interact with the initial diamine, as well as with the oxirane rings of both epichlohydrin and the synthesized product, an excess of potassium carbonate was introduced into the reaction mixture. The structure of the synthesized epoxy resin - 4,4′-methylenebis (N- (oxiran-2-ylmethyl) aniline) was characterized and proved by the methods of FTIR spectroscopy, nuclear magnetic resonance and elemental analysis. The kinetic parameters of the synthesized resin were characterized by differential scanning calorimetry. Using the Kissinger method, the activation energy of the self-curing reaction was calculated, the value of which was 1.139 kJ / mol. Such a low activation energy of epoxy resin allows to cure at low temperatures, but shortens the storage time. Two curing modes were studied: 1 mode - 10 hours at 150 ° C, 2 step mode - 10 hours at 150 ° C + 3 hours of postcuring at 180 ° C.

Thermal and Dielectric Properties of Cyanate Ester Cured Main Chain Rigid-Rod Epoxy Resin.

Thermal and dielectric properties of rigid-rod bifunctional epoxy resin 4,4-bis(2,3-epoxypropoxy) biphenyl epoxy (BP) and commercial epoxy resin diglycidyl ether of bisphenol A (DGEBA) were studied using differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), thermal mechanical analyzer (TMA) and dielectric analyzer (DEA). These two epoxies were cured with cyanate ester hardener 2,2’-bis(4-cyanatophenyl) propane (AroCy B10). The BP/B10 system consisting of a rigid-rod structure exhibited better thermal properties than the DGEBA/B10 system with a flexible structure. Anisotropic BP/B10 (2:1) had the highest 5% weight loss temperature, the highest amount of residue and a smaller thermal expansion coefficient than the commercial DGEBA/B10 system. The BP/B10 system, which cured at the LC phase temperature, had higher Tg than the commercial DGEBA/B10 system, as found from dynamic mechanical analysis. The BP/B10 system also demonstrated better dielectric properties than the commercial DGEBA/B10 system when enough curing agent was provided.

Studies on the Modification of Commercial Bisphenol-A-Based Epoxy Resin Using Different Multifunctional Epoxy Systems

The tensile fracture mechanics and thermo-mechanical properties of mixtures composed of two kinds of epoxy resins of different chemical structures and functional groups were studied. The base resin was a bi-functional epoxy resin based on diglycidyl ether of bisphenol-A (DGEBA) and the other resins were (a) distilled triglycidylether of meta-amino phenol (b) 1, 6–naphthalene di epoxy and (c) fluorene di epoxy. This research shows that a small number of multifunctional epoxy systems, both di- and tri-functional, can significantly increase tensile strength (14%) over neat DGEBA while having no negative impact on other mechanical properties including glass transition temperature and elastic modulus. In fact, when compared to unmodified DGEBA, the tri-functional epoxy shows a slight increase (5%) in glass transition temperature at 10 wt.% concentration. The enhanced crosslinking of DGEBA (90 wt.%)/distilled triglycidylether of meta-amino phenol (10 wt.%) blends may be the possible reason for the improved glass transition. Finally, the influence of strain rate, temperature and moisture were investigated for both the neat DGEBA and the best performing modified system. The neat DGEBA was steadily outperformed by its modified counterpart in every condition.

Trifunctional cycloaliphatic epoxy-based thermoset polymers: Synthesis, polymerization, and characterization

High-performance thermoset materials derived from epoxy resins have excellent properties, and are widely used. Diglycidyl ether bisphenol A (DGEBA) is an extensively used monomer in the epoxy network, but despite its many advantages, its precursor, bisphenol-A, is considered toxic to human health. As an alternative to DGEBA, cycloaliphatic resins have attracted significant interest. Herein, the synthesis of trifunctional cyclohexylepoxide (CHE) and the polymerization of trifunctional cyclohexyl-epoxide with curing agents such as imidazole (IM), aliphatic, and aromatic amines are reported. The polymers are characterized using NMR spectroscopy, FT-IR, differential scanning calorimetry, and dynamic mechanical analysis. The polymer derived from CHE and IM shows different thermal stabilities based on the molar percentage of IM per epoxide. CHE/diaminodiphenylmethane (DDM) epoxy/amine thermoset shows the highest thermal mechanical stabilities. To understand and compare the polymerization of CHE with aliphatic and aromatic curing agents, the activation energies for the polymerization reactions are calculated based on the polymerization temperature at different heating rates. Further, the CHE/amine polymers are compared with the commercially available DGEBA (bifunctional epoxy) and trifunctional epoxy-containing N,N′-diglycidyl-4-glycidyloxyaniline (DGGHA) epoxy/amine polymers.

Castor Epoxy Fatty Acid Alkyl Ester Estolides as Bioplasticizers for Poly(Vinyl Chloride)

AbstractEpoxy fatty acid alkyl ester estolides were synthesized from castor oil to be used as biobased plasticizers for poly(vinyl chloride) (PVC) as a safer replacement for phthalate plasticizers. Initially, castor oil was transesterified with methanol or n‐butanol to quantitatively yield castor fatty acid alkyl esters. Acetylation of hydroxyl function with acetic anhydride led to the formation of estolide. The unsaturation was epoxidized, resulting in a bifunctional epoxy fatty acid alkyl ester estolide. The bioplasticizers were compounded with PVC and were evaluated for their functionality and compared with commercial phthalate plasticizer diisononyl phthalate (DINP) and nonphthalate 1,2‐cyclohexanoic acid diisononyl ester (DINCH). The bioplasticizers showed excellent gelation, efficiency, and compatibility, as well as plastisol viscosity and thermal properties, comparable to or better than the plastisols prepared with commercial controls DINP and DINCH. The volatility of the methyl ester was inferior to the butyl ester. Both compounds showed low water resistance properties. Further evaluation of the butyl ester under tropical conditions of high temperature and humidity confirmed limited compatibility. This indicates that the castor epoxy fatty acid ester estolides would be better suited for applications that do not come in contact with water for prolonged periods, such as flooring, artificial leather, wiring, or wall coverings.

An unexpected butadiene diolepoxide-mediated genotoxicity implies alternative mechanism for 1,3-butadiene carcinogenicity

1,3-Butadiene (BD) is abundant in combustion products such as cigarette smoke. While BD has been classified as a known human carcinogen, a long-standing question is the identity of the ultimate carcinogenic metabolite in humans. We hypothesize that 3,4-epoxybutane-1,2-diol (EBD) may play a critical role in human carcinogenesis due to its high bioavailability. We utilized a differential toxicity assay for BD metabolites and newly synthesized EBD analogs in a series of isogenic chicken cells lacking specific DNA repair proteins to address the mode of action of BD genotoxicity and infer a mode of action. Surprisingly, as with the diepoxide 1,2:3,4-diepoxybutane (DEB), the monoepoxide EBD showed remarkable toxicity to cells deficient in Fanconi anemia (FANC) genes. This observation suggests that EBD may be transformed into a bifunctional metabolite and forms interstrand cross-links. EBD and its analog with a hydroxy substituent at C1 were found to be highly toxic to FANCD2-deficient chicken and human cells. The Results suggest that EBD may be transformed to a bifunctional epoxy aldehyde, perhaps by alcohol dehydrogenase, to which the observed FANC sensitivity could be attributed. The implications of this study are very important in considering mechanisms by which EBD may cause leukemia and lymphoma in humans exposed to BD.

Silicone-epoxy block hybrid network to achieve high-performance and transparent polydimethylsiloxane materials

The preparation of highly compatible polydimethylsiloxane/epoxy system has been a challenging task. Here, we designed and synthesized a vinyl-containing bifunctional epoxy resin, which was chemically bonded with polydimethylsiloxane by hydrosilylation. A silicone-epoxy block hybrid network with restricted micromorphology and outstanding macro-performance was formed. The phase separation scale of polydimethylsiloxane/epoxy system was strictly restricted by molecular structure design and the modified PDMS was transparent. The mechanical test results showed that the tensile strength, elongation at break and shear strength of the hybrid material were increased by 391%, 78% and 292% respectively. More importantly, the initial thermal decomposition temperature of the hybrid material increased, and its thermal residue at 800 °C was kept at a high level. All these results indicate that we have prepared a transparent, high-performance polydimethylsiloxane material, which is expected to be applied in many prospects such as heat resistant adhesive and transparent surface coating.