Cured Epoxy Resin Research Articles

Thermo-Mechanical Properties and Phase-Separated Morphology of Warm-Mix Epoxy Asphalt Binders with Different Epoxy Resin Concentrations.

The performance and phase-separated microstructures of epoxy asphalt binders greatly depend on the concentration of epoxy resin or bitumen. In this paper, the effect of the epoxy resin (ER) concentration (10-90%) on the viscosity, thermo-mechanical properties, and phase-separated morphology of warm-mix epoxy asphalt binders (WEABs) was investigated using the Brookfield rotational viscometer, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and laser scanning confocal microscopy (LSCM). Due to the high reactivity of epoxy resin, the viscosity of WEABs increases with time. Furthermore, the initial viscosity of WEABs decreases with the ER concentration. Depending on the ER concentration, the viscosity-time behavior of WEABs is divided into three stages: slow (10-40%), fast (50-80%), and extremely slow (90%). In the slow stage, the viscosity slightly increases with the ER concentration, while the fast stage shows an opposite trend. DSC and DMA results reveal that WEABs with 10-80% ER exhibit two glass transition temperatures (Tgs) for cured epoxy resin and bitumen. Moreover, the Tgs of epoxy resin and bitumen increase with the ER concentration. However, WEAB with 90 % ER has only one Tg. LSCM observation shows that phase separation occurs in all WEABs. For WEABs containing 10-40% ER, spherical epoxy particles act as the discontinuous phase and disperse in the continuous bitumen phase. However, in WEABs with 50-90% ER, phase inversion takes place. Contrarily, bitumen particles disperse in the continuous epoxy phase. The damping properties of WEABs with the continuous epoxy phases increase with the ER concentration, while the crosslinking density shows an opposite trend. The occurrence of phase inversion results in a sharp increase in the tensile strength of WEABs. For WEABs with the continuous epoxy phases, the elongation at break increases with the ER concentration. The toughness first increases and then decreases with the ER concentration. A maximum toughness value shows at 70% ER.

Experimental characterization of epoxy/quartz composite material exposed to PDs

Failures due to the degradation of polymeric insulation in components of electrical power systems are difficult to predict. Partial discharges (PDs) are one of the main phenomena that contribute to polymeric insulators’ aging. Therefore, a better understanding of the aging process due to PDs is crucial to develop effective models that predict degradation, optimize materials and propose diagnostic indicators. Here we present an experimental characterization, via Fourier-transform Infrared spectroscopy (FTIR), of a composite material exposed to PDs. The material consisted of cured epoxy resin mixed with silica (quartz). Aging tests with surface discharges, using a needle-plate configuration, were conducted considering two atmospheres (air and CO2) and four exposition times (6, 24, 72 and 120 hours). To aid the interpretation of spectroscopic data, we included a series of simulation results. The main effect observed was the erosion and removal of epoxy resin from the surface of the samples, proportionally to treatment time and distance from the needle. Along with erosion, new chemical species (possibly oxalate salts) were detected on the surface exposed to air-plasma. These species were likely formed and then removed due to plasma activity over time. On the other hand, samples aged in CO2 atmosphere underwent only epoxy resin erosion.

Thermal curing of epoxy resins at lower temperature using 4‐(methylamino)pyridine derivatives as novel thermal latent curing agents

AbstractTo expand the application fields of epoxy resins, there has been a growing demand for thermal latent curing agents that combine a lower curing temperature with a long storage lifetime for a one‐component epoxy formulation. Herein, we present the use of novel thermal latent curing agents for epoxy resins that are effective at lower curing temperatures compared to epoxy resins containing imidazoles as curing agents—they are based on 4‐(methylamino)pyridine (4MAPy), with reactivity suppressed by different amide protecting groups. We revealed reaction mechanism of epoxy polymerization by the thermal latent 4MAPy, using Matrix‐assisted laser desorption ionization–time‐of‐flight mass spectrometry, Fourier transform infrared spectroscopy (FT‐IR), and 1H NMR analyses of the model polymerization of phenyl glycidyl ether. The amide protecting groups decomposed to form the highly reactive 4MAPy by nucleophilic acyl substitution with the propagating alkoxide. Furthermore, FT‐IR data and pencil hardness tests revealed that thermal latent 4MAPy derivatives, particularly those with electron‐rich pyridine rings, can cure epoxy resins at lower curing temperatures, notably 90°C. The thermal latent 4MAPy derivatives with epoxy resin exhibited a storage lifetime of at least 6 days at 3°C, in contrast to 4MAPy with epoxy resin that cured within a day after mixing.

Optimization of novel two-step curing method for die stack epoxy bonding to reduce voids in Ball Grid Array packages for high-density interconnect applications

This research explores the optimization of epoxy curing parameters to minimize void formation in 3-IC-Chip-MAPBGA packages, a subset of BGA packages, crucial components in high-density interconnect applications. The study utilizes a systematic approach involving design of experiments (DOE) assisted by statistical JMP tool to manipulate curing profiles, aiming to achieve void reduction while preserving adhesion properties. Various analytical techniques, including X-ray imaging, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), die shear strength tests, and C-Sam analysis for delamination, are employed to analyze void formation, material characteristics, mechanical properties, and structural integrity. The findings demonstrate that the sample with a 2nd step curing profile, identified as sample#3, which includes a ramp time of 15 min, a 1st step curing temperature of 90 °C with a soak time of 20 min, and a 2nd step ramp time of 20 min, exhibits the most favourable outcome in void reduction. This sample shows a notably lower void presence of 3.66 % and the highest die shear strength of 126 MPa. In contrast, the control sample, serving as a reference, displays a void percentage of 7.28 %, nearly twice as high as that of sample#3, and much lower die shear strength of 80 MPa at 25 °C. Adopting the curing profile of sample#3 also leads to a substantial 18.75 % reduction in cycle time compared to the control sample. The study highlights the importance of balancing curing parameters to mitigate void formation and maintain optimal mechanical properties, offering valuable insights for improving the reliability of high-density interconnect applications.

Preparation and evaluation of Urea‐F amine crosslinkers

AbstractThis study presents the preparation of a long‐chain amine solution, employing the concept of urea‐formaldehyde synthesis. We also investigate the performance shifts in the cured product post‐urea addition. The Urea‐F curing agent is prepared by reacting EDA/DETA/TETA/TEPA, formaldehyde, and urea, and crosslinked with bisphenol A epoxy resin (E51). The crosslinking agent solves the problem of urea not being suitable for curing epoxy resin, and it improves the problem of low mechanical strength of traditional amine crosslinked epoxy resin cured materials. The cured product underwent evaluation through acid and alkali resistance solution measurement and mechanical and thermal tests. The results show enhanced heat resistance in the cured product, with its maximum thermal decomposition rate exceeding 350°C. The cured products have better mechanical properties than the amine monomers, with enhanced bending strength and superior acid–base solution resistance. The scanning electron microscopy micrograph indicates that the cured product fractures have a tight internal structure.

Size Effect of Graphite Nanosheet-Induced Anti-Corrosion of Hydrophobic Epoxy Coatings

In order to broaden the selectivity of graphite nanosheet additives on epoxy resin-based coatings and verify the size effect, this work aims to dope graphite nanosheets of different sizes into the three-dimensional structure produced by cross-linking and curing epoxy resin and polyamide resin. In addition, a micro-nano level secondary structure and a surface with special roughness are constructed to obtain the composite epoxy hydrophobic coating. The influence of the size effect of graphite nanosheets on the hydrophobic performance and corrosion resistance of the coating is summarized as well. Among them, the optimized doping size (2.2 μm) of graphite nanosheets in the epoxy coating showed the largest impedance arc of 2.58 × 108 Ω cm2, which could form an excellent nano-network covering the micropores to impede the diffusion of corrosive medium. Through simulation calculation analysis, we also found that the edge site of graphene is more effective in capturing H2O and O2; therefore, a smaller size of graphene with a large edge can be more favorable. This work will be used as a reference for the industrial application of graphite anti-corrosive coating.

UV-heat dually curable epoxy resin composites with low filler contents and high curing speed

Epoxy resin composites are a type of polymer-based materials with wide application scopes. A mass of fillers was added to improve thermal properties which may degrades mechanical properties at the same time. In addition, the common heat-curing process takes several hours to completely cure. To improve the performance of epoxy resin composites of low-content fillers, we prepare UV-heat dually curable epoxy resin with silicate ester. The overall curing time of UV-heat curing process is about half of the traditional thermal-curing process. The breakdown voltage of epoxy resin modified by silicate ester is up to 181 MV/m, which is increased by 50 % compared to pure epoxy resin. The silicate ester curing agent can react with both epoxy resin and silica fillers and can thus improve the dispersion of the fillers in the matrix and enhance the interaction between fillers and the resin. As a result, the coefficient of thermal expansion (CTE) of the composites was greatly reduced. The CTE of silicate ester-modified epoxy resin composites is 93 ppm/K and 137 ppm/K over the temperature range below and above its Tg, respectively, which is 25 % lower than those of normal epoxy resin composites.

Novel Crosslinked Anion Exchange Membranes Based on Thermally Cured Epoxy Resin: Synthesis, Structure and Mechanical and Ion Transport Properties.

Limitations in existing anion exchange membranes deter their use in the efficient treatment of industrial wastewater effluent. This work presents an approach to fabricating novel anion-conducting membranes using epoxy resin monomers like hydrophobic or hydrophilic diglycidyl ether and quaternized polyethyleneimine (PEI). Manipulating the diglycidyl ether nature, the quantitative composition of the copolymer and the conditions of quaternization allows control of the physicochemical properties of the membranes, including water uptake (20.0-330%), ion exchange capacity (1.5-3.7 mmol/g), ionic conductivity (0.2-17 mS/cm in the Cl form at 20 °C), potentiostatic transport numbers (75-97%), as well as mechanical properties. A relationship was established between copolymer structure and conductivity/selectivity trade-off. The higher the quaternized polyethyleneimine, diluent fraction, and hydrophilicity of diglycidyl ether, the higher the conductivity and the lower the permselectivity. Hydrophobic diglycidyl ether gives a much better conductivity/selectivity ratio since it provides a lower degree of hydration than hydrophilic diglycidyl ether. Different mesh and non-woven reinforcing materials were also examined. The developed membranes demonstrate good stability in both neutral and acidic environments, and their benchmark characteristics in laboratory electrodialysis cells and batch-mode dialysis experiments are similar to or superior to, commercial membranes such as Neosepta© AMX, FujiFilm© Type1, and Fumasep FAD-PET.

AC breakdown characteristics of ultra violet curable epoxy resin with nitrogen fine bubbles

AbstractWe investigated AC breakdown characteristics of ultra violet curable epoxy resin (UV‐EP) with nitrogen fine bubbles (FBs) in order to improve insulating properties of UV‐EP. As a result, it was found that self‐made FB generator mainly add FBs with a diameter between 60 and 150 nm to FB‐EP before curing. In addition, SEM images revealed that FB‐EP has FBs after curing. Bubble diameter in FB‐EP after curing was estimated between 55 and 140 nm due to resin shrinkage. Furthermore, partial discharge inception voltage and electric strength of FB‐EP with FB addition for 10 min were almost the same as No FB‐EP.

Performance evaluation of new epoxy resin-based composite phase change materials and their asphalt mixture

In recent years, the temperature-adjusted asphalt pavement has been an extensive concern by scholars in various countries, and this pavement can reduce temperature-related diseases. In this study, the shaped composite phase change materials (CPCMs) were successfully synthesized by two processes, which are vacuum impregnation and epoxy curing. Firstly, the applicability of CPCMs in asphalt mixtures was evaluated by microscopic characterization, chemical compatibility, thermal properties, durability, and leakage stability. Secondly, CPCMs were applied to the asphalt mixture to evaluate its temperature-adjusted characteristics and pavement performance. Finally, the performance of the temperature-adjusted asphalt mixture was analyzed by integrating all factors. The research shows that the prepared CPCMs have excellent thermal properties and durability, the phase transition temperature is 48.93 °C, and the phase transition enthalpy is 106.5 J/g, which fully meets the requirements for use in pavement. The temperature-adjusted asphalt mixture could alleviate the occurrence of extreme temperature, which was 4.9 °C lower than the conventional mixture. The pavement performance of the temperature-adjusted asphalt mixture can meet the specified standards for humid areas. Considering the factors, the recommended amount of CPCMs is 1.5%. The research results provide a basis for the promotion of temperature-adjusted asphalt pavement and effectively support the development of pavement engineering technology.

Study on preparation and properties of polyurethane modified epoxy resin lotion cementing slurry

To solve the problems of poor cementing quality and weak consolidation performance of deep-water shallow cementing cement, a low-temperature curable polyurethane-modified epoxy resin lotion (WER) was prepared with epoxy resin and polyurethane as raw materials, and its hydrophilic groups (carboxyl and ether bonds) were self emulsified. The results show that the modified WER lotion cement slurry has good fluidity and stability. Its thickening transition time is less than 16 min, which can effectively prevent gas channeling. In addition, its low-temperature mechanical properties have been significantly improved, and its compressive strength has increased by 42.4% and 44.5% compared to net slurry cement within 3 and 7 days, while its elastic modulus has decreased by 34.1% and 42.4%, respectively.

Dicyanamide ionic liquid mixtures for curing and modifying flax-fiber reinforced epoxy resin composites

Epoxy composites reinforced with natural fibers are a research area that has been growing tremendously in recent years, with increasing reports providing a better understanding of the interactions within such structures, resulting in newer and more specialized applications. This article presents a comprehensive study on the design and application of ionic liquids (ILs) in the development of flax fiber-reinforced epoxy composites with tailored mechanical properties. Three distinct ILs, namely 1-hexyl-3-methylimidazolium dicyanamide [HMIM][DCA], 1-hexyl-1,4-diazabicyclo[2.2.2]octan-1-ium dicyanamide [DABCO-C6][DCA], and trimethyloctadecylammonium dicyanamide [N11118][DCA], were strategically engineered to incorporate longer carbon chains, with the primary objective of influencing the mechanical parameters of the resulting composites, specifically aiming for enhanced flexibility and resistance to bending and stretching. Using these designed ILs, two mixtures were developed and crafted to facilitate the effective curing of epoxy resin, which was examined using Differential Scanning Calorimetry (DSC). Investigation of the resin crosslinking process revealed that the mixtures of ILs exhibited a lower total enthalpy of thermal conversion than single-IL systems. Moreover, shifts in the polymerization onset temperatures were observed for the mixtures, with some systems displaying dual temperature peaks during crosslinking, indicative of potential parallel polymerization reactions.

The effects of the contents of modified‐diatomite on the properties of modified‐diatomite/epoxy resin composites

AbstractExternal plasticization is one of the effective ways to toughen epoxy resins. In this study, an inorganic filler (EMD) was prepared by chemical modification of diatomite and was used to fill epoxy resin matrix. The effects of different amounts (5%, 10%, 15%, and 20%) of raw diatomite (RD) and modified‐diatomite (EMD) on the mechanical and thermal properties of epoxy resin composites were studied. The mechanical results showed that the impact strength, tensile strength, and bending strength of EMD/EP were higher than those of RD/EP. The impact strength of EMD‐15/EP reached 5.39 KJ/m2, which was 36.8% higher than that of RD‐15/EP. Thermogravimetric analysis showed that the thermal stability of EMD/EP was better than that of RD/EP. The results of DMA show that the glass transition temperature of EMD/EP was lower than that of RD/EP. Non‐isothermal differential scanning calorimetry study showed that the apparent activation energy of EMD‐15/EP was much lower than that of RD‐15/EP, which proved that EMD could promote the curing of epoxy resin. The Malek method was used to determine that both the RD‐15/EP and EMD‐15/EP curing systems were autocatalytic (Šesták–Berggren) models.

Synthesis of Radiation Curable Trimethylolpropane Epoxy Acrylate

Synthesis of Radiation Curable Trimethylolpropane Epoxy Acrylate

Applicability Evaluation of Modified Epoxy Resin in the Repair and Reinforcement of Ancient Building Timber Members

To investigate the potential of modified epoxy resin for repairing and strengthening historical wooden structures, this study utilized polyurethane and silicone-modified epoxy resin as the base, alongside a polyamine curing agent. The resin mixture was cured at ambient temperature, resulting in the creation of ten unique epoxy resin systems. Investigation into the chemical structure and alterations to the glass transition temperature were conducted. The study conducted tests and characterization of viscosity, curing rate, mechanical properties, stress failure mode, hygrothermal aging resistance, and bonding properties. The results reveal that the curing degree of the two modified epoxy resins is high after being cured at room temperature, and the chemical structure and curing rate show insignificant changes. The range of the glass transition temperature for the modified epoxy resin is between 61.31 °C and 70.51 °C. The incorporation of polyurethane and silicone molecular chains into the epoxy resin cross-linking curing system enhances the toughness of the epoxy resin. The modified resin achieves a maximum elongation at break that is 5.18 times greater than that of the unmodified resin, along with a maximum tensile strength and a compressive strength that are 7.94 and 1.74 times, respectively, higher than those in the Chinese technical specifications for the maintenance and reinforcement of ancient wooden structures. The increase in toughness changes the failure mode of the cured epoxy resin. The modified epoxy resin exhibits great bonding ability to aged wood, with a shear strength of up to 9.6 MPa along the grain. As a result, the modified epoxy resin meets the requirements for the reinforcement and repair of the timber members of ancient buildings.

Monitoring of Curing Process of Epoxy Resin by Long-Period Fiber Gratings.

The curing of epoxy resin is a complex thermo-chemical process that is difficult to monitor using existing sensing systems. We monitored the curing process of an epoxy resin by using long-period fiber gratings. The refractive index of the epoxy resin increases during the curing process and can be measured to determine the degree of curing. We employed long-period fiber gratings that are sensitive to the refractive index of an external medium for the measurement of refractive index changes in the resin. We observed that the resonances of long-period fiber gratings increased their depth with the increased refractive index of the resin, which was well described by our simulation taking the coupling to radiation modes into account. We demonstrated that the degree of cure can be estimated from the depth of the grating resonances using a phenomenological model. At the same time, long-period fiber gratings are sensitive to temperature variations and internal strains that are induced during curing. These factors may affect the measurements of curing degree and should also be addressed.

High‐performance, semi‐bio‐based degradable epoxy resins and their application to recyclable carbon fiber composites

AbstractEpoxy resins containing dynamic covalent networks enable recycling of carbon fiber composites. However, the simultaneous realization of high performance and mild condition recycling of composites is still a challenge. In the present work, we mixed citric acid epoxy resin with bisphenol A epoxy resin to form a hybrid resin (DER) that meets the requirements of medium temperature curing epoxy resin, and prepared a carbon fiber reinforced resin composite material (DER@CF) that can rapidly degrade and recycle carbon fibers under mild conditions. The Tg of the DER was 125.67 °C, and the tensile strength (79.63 MPa) was comparable to that of the bisphenol A epoxy resin (79.90 MPa). It degraded rapidly after 2 h in ethylene glycol solution at 120 °C. The tensile strength of DER@CF was 825 MPa, and clean fibers could be obtained after 8 h of treatment in ethylene glycol solution at 120 °C. The results of SEM, Raman and tensile tests showed that the recycled fibers were similar to the original fibers in terms of morphology, chemical structure and mechanical properties. © 2024 Society of Chemical Industry.

Glycine-Ti3C2Tx Hybrid Material Improves the Electrochemical Corrosion Resistance of a Water-Borne Epoxy Coating.

Improving the dispersibility and compatibility of nanomaterials in water-borne epoxy resins is an important means to improve the protection ability and corrosion resistance of coatings. In this study, glycine-functionalized Ti3C2Tx (GT) was used to prepare an epoxy composite coating. The results of Fourier transform infrared spectroscopy and X-ray diffraction showed that glycine was successfully modified. The scanning electron microscopy and transmission electron microscopy results showed that the aggregation of Ti3C2Tx was alleviated. Electrochemical impedance spectroscopy test results show that, after 60 days of immersion, GT coating still shows the best protection performance, and the composite coating |Z|f = 0.01 Hz is 3 orders of magnitude higher than that of the pure epoxy coating. This is mainly because, after adding glycine, the -COOH group on the surface of glycine binds to the -OH group on the surface of Ti3C2Tx, improving the aggregation of Ti3C2Tx itself. At the same time, the -NH group of glycine can also participate in the curing reaction of epoxy resin to strengthen the bonding strength between the coating and the metal. The good dispersion of GT in epoxy resin makes it fill the pores and holes left by epoxy resin curing and strengthen the corrosion resistance. The easy availability and green properties of glycine provide a simple and environmentally friendly method for the modification of Ti3C2Tx.

Schiff base derivative flame-retardant endowing epoxy resin with toughness, transparency, and high flame retardancy

In this study, a novel phosphorus-containing flame retardant, SMAE, was prepared through a nucleophilic addition of N,N'-bis(salicylidene)ethylenediamine (SAED) and phenyl hypophosphite. SMAE can dissolve well in epoxy resin and provides molecular-level flame retardancy. By using SMAE as a co-curing agent and DDM to cure epoxy resin, EP/SMAE composites with excellent flame retardancy and good mechanical properties were obtained. As the dosage gradually increases, the limited oxygen index (LOI) values continue to rise. At a 5 % dosage, the Limiting Oxygen Index (LOI) value can reach 39.7 % and meet the UL 94 V-0 standard. It is observed that SMAE mainly exerts a blowing-out effect in EP. In addition, the use of SMAE as a co-curing agent can improve the impact strength of EP. The impact strength of 5 % SMAE/EP can reach 14.15 kJ/m2, which is 25 % higher than that of pure EP.

Substituting the epoxy curing agent with a greener solution-towards sustainability

Traditionally, resins and hardeners are produced by chemical and petroleum industries. These industries make use of non-renewable energy resources like fossil fuels for manufacturing the resins and curing agents. In addition, most of the conventional curing agents used in epoxy resins are highly noxious in nature causing skin allergies and asthma. The green epoxy resin is capable of reducing these toxic effects but have few shortcomings including its cost and the mechanical performance of cured epoxy resin. On the other hand, there is a dearth of investigation in the evolution of green or sustainable curing agents known as bio-binders. This paper presents the prediction of mechanical properties by replacement of conventional curing agent with amine derivative synthesized from bio-degradable resource in a thermoset epoxy resin system. The properties are predicted by molecular dynamics simulations using Materials Studio Software.Graphical