Epoxy Film Research Articles

An active ester‐cured resveratrol‐based epoxy film with excellent thermal and dielectric performances for high‐frequency applications

An active ester‐cured resveratrol‐based epoxy film with excellent thermal and dielectric performances for high‐frequency applications

An intelligent CFRP bolt with embedded carbon nanotube eddy current sensors for damage self‐diagnosis of bolted composite joints

AbstractRecognizing the critical demand for composite bolts and the damage‐mode complexity of composite bolt joints, this study introduces the concept of an intelligent carbon fiber reinforced polymer (CFRP) bolt, which achieves self‐monitoring of damage in small and complex CFRP bolted joints. The proposed eddy current sensor (ECS) is mainly composed of a coil made of carbon nanotube film and encapsulated with epoxy resin film. This achieves homogeneous embedding of the sensor by using the same material for both sensor and bolt. The CFRP bolt is fabricated by molding process, with the proposed ECS embedded in bolt shank. The numerical simulation results indicate that hole‐edge damages impact the distribution of induced current density and eddy current flow in CFRP plates. Additionally, the impedance amplitude of the ECS effectively monitors bearing damage propagation. Shear tests confirm that the integration method of the proposed ECS within the CFRP bolt introduces negligible intrusion to the host bolt's integrity. Experimental results demonstrate that the intelligent CFRP bolt can effectively monitor the damage propagation at the hole edge, with an accuracy for bearing damage exceeding 0.5 mm. At a working frequency of 10 MHz, the sensor's sensitivity in detecting a 0.5 mm bearing damage reaches 4.20%.Highlights An intelligent CFRP bolt was fabricated using the molding method. The embedding of the ECS did not cause adverse effects on the bolt. The proposed EC sensor is composed of carbon nanotube and epoxy resin adhesive films. The eddy current distribution at the hole edge of the CFRP bolted joints is analyzed. The ability of intelligent bolts to monitor hole edge damage is verified by experiments.

A novel bio-based epoxy resin curing agent of gluconic aldehyde amine for the preparation of epoxy resin film

To resolve the shortage of fossil resources, gluconic aldehyde amine (GAA) was prepared from glucose via Mannich reaction, and then was used to cure E901 epoxy resin to prepare glucose-based epoxy resin film (GAAF). Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy indicated the successful synthesis of GAA. With the increase of Mannich reaction temperature, the tensile strength and elongation at break of GAAF firstly increased and then decreased, as well as the thermal stability increased. The GAAF-60 sample exhibited maximum tensile strength of 47.5 MPa, which were higher than that prepared by petroleum-based phenolic amine and lignin-based phenolic amine, respectively. The synthesis of GAA presented a novel bio-based epoxy resin curing agent for the preparation of epoxy resin film.

Preparation and characterization of Epoxy/TiO2 thin films for Anti-UVB coating

Thin films of pure epoxy and Epoxy/TiO2 were successfully prepared using the spin coating method. The epoxy was doped with different weight ratios of TiO2 nanoparticles for the purpose of studying the effect of increasing its percentage on the properties of epoxy thin films. The surface topography of the prepared films was studied using an atomic force microscope (AFM), which showed that the surfaces of the samples became rougher with an increase in the doping of TiO2 nanoparticles. The functional groups were measured using a Fourier infrared spectrometer (FTIR), which showed the presence of TiO2 bonds in the epoxy matrix at wave numbers 400 and 862 cm-1. Optical measurements for absorbance, transmittance, and reflectivity showed a clear effect of TiO2 nanoparticles on the optical properties of the prepared samples through high absorbance for ultraviolet ray’s B (UVB) and low absorbance for visible light. Reflectivity decreases at the wavelengths of UVB and increases at the wavelengths of visible light with an increasing doping ratio. This makes these thin films candidates for use in anti-UVB coatings.

Curing and Failure Monitoring of Composite Material Single-Lap Joint Based on CNT/PSF Sensor

Abstract Composite bonded structures are widely used in the field of aerospace. The safety of composite structures can be ensured by the health monitoring and early warning of their whole life. In this paper, a composite CNT/PSF film sensor based on asymmetric porous PSF film was designed and prepared. Through integrated molding with epoxy film, in-situ monitoring of gel point (142.1°C) and curing time (36min) of epoxy film is realized. After optimization of curing process, tensile strength of epoxy film casting body is increased by 86.3%. The single lap shear strength of the composite is increased by 45.7%. The CNT/PSF film sensor with composite material has high response sensitivity (GF≈1.4) and linearity (0.998) to cyclic strain (0-3000με). In the shear experiment of composite single lap joint, the adhesive layer presents a typical cohesive failure mode of first compression, then tensile and finally failure. The resistance changes of CNT/PSF film sensor first decreases from 0 to -1‰, and then rises to 2.7‰. Finally, the fracture response is good, and the in-situ failure behavior monitoring of the joint can be fully realized.

Epoxy composite films of superior dielectric properties promoted by active ester hardeners for applications in electronic packaging

Epoxy composites with ultralow dielectric dissipation factors (Df) are highly desired in advanced electronic packaging architectures to cater for high-frequency signal transmission. However, Df of epoxy systems traditionally cured by amine, anhydride or phenolic resin is too high due to the generated high-polarization groups like hydroxyl moieties. Using active esters as curing agents is an effective strategy to reduce polarization of cured epoxy by replacing hydroxyl moieties with ester groups. Herein, diallyl-based active ester hardeners (DAAE) are synthesized via one-step esterification reaction with a high yield of > 90 %. When DAAE is used to cure epoxy films containing SiO2 fillers, the cured epoxy composite films (DAAE-ECFs) demonstrate low dielectric constant (Dk, ∼3.0) and low Df (∼0.005) above 5 GHz at 25 ℃. Importantly, whether immersed in room-temperature water for 24 h or in boiling water for 1 h, DAAE-ECFs absorb < 0.6 wt% water with stable Dk and slightly increased Df (<0.0085). Moreover, DAAE-ECFs show excellent thermal stability (Td5% >365 ℃), dimensional stability (CTE of ∼ 30 ppm ℃-1 below 80 ℃), high storage modulus (∼10 GPa at 30 ℃). The appealing dielectric, thermal and mechanical properties imply that DAAE-ECFs could serve as promising candidates for electronic packaging materials in high-frequency signal transmission.

Zn–Al with NO2− as a corrosion inhibitor epoxy-coated carbon steel under artificial atmospheric conditions

This study evaluated Zn–Al–NO2− layered double hydroxide as a corrosion inhibitor in a high-thickness epoxy resin coating (200 µm). The layered double hydroxide was tested in a NaCl solution, using electrochemical impedance spectroscopy. The formed oxides were analysed by X-ray diffraction and energy dispersive X-ray spectroscopy. The corrosion resistance of the epoxy coating (with and without layered double hydroxide) was analysed by electrochemical impedance spectroscopy after exposure to a NaCl solution, salt spray, or a weather-O-meter chamber in a simulated atmospheric environment. The electrochemical impedance spectroscopy measurements for the free layered double hydroxide in a NaCl solution revealed that layered double hydroxide prompted the formation of a compact, protective, and insoluble oxide layer on the carbon steel surface. The Cl− permeability through the epoxy resin film was 5.88 times lower for the film containing layered double hydroxide than for the control. The layered double hydroxide was added to the epoxy coating at a 5 wt-% to evaluate the behaviour of the coating in aggressive environments. The entry of aggressive ions was controlled by the ability of the layered double hydroxide to capture them and release the corrosion inhibitors. Thus, the layered double hydroxide worked as a trap for these aggressive ions and enhanced the performance of the coating. Therefore, a layered double hydroxide addition could benefit a high-thickness coating exposed to an aggressive environment and UV radiation.

A bi-functional self-healing epoxy composite coating based on coordinated functionalized attapulgite/graphene oxide

Applications for graphene oxide (GO) in the field of corrosion protection will be severely constrained by the material’s poor dispersion and compatibility with epoxy resins, as well as the absence of self-healing corrosion protection in GO-based epoxy coatings. In this work, we developed a bi-functional 2-mercaptobenzothiazole (MBT) inhibitor-encapsulating GO-based nanocomposite (GAM) with pH-responsive release by implanting attapulgite (ATP) nanorods on the surface of GO. Additionally, GO-based nanocomposite can form covalent connections with epoxy resins and be evenly distributed in epoxy film via a ring opening process. Moreover, improved epoxy film compatibility and dispersion result in elevated mechanical strength and better impermeability, which prevent corrosion in both the active and passive modes. The corrosion resistance of GAM self-healing coating increased as the submersion period exceeded 24 h up to 0.54 M Ω cm2, resulting in the release of MBT inhibitor to form a passivation film at the defective region. Moreover, the improved charge transfer resistance (Rct) and the coating’s resistance to corrosive species (Rc) attribute to the self-healing ability of the GAM coating. The incorporation of GAM (2 %) nanocomposites into epoxy films enables long-term protection of AA2024-T3 by combining passive and self-healing corrosion prevention.

Rheo-kinetics and thermodynamics of oxazolidone modified epoxy film adhesive

Rheo-kinetics and thermodynamics of oxazolidone modified epoxy film adhesive

Low energy impact damage characteristics of epoxy coating on the surface of sandwich composites

AbstractWhen composite honeycomb sandwich structures are subjected to low energy impacts, the upper panel or the honeycomb core often suffers large damages, which are invisible, but affects the structural safety. To achieve non‐destructive detection of these damages, an epoxy resin film (ERF) was designed as a functional coating to display the internal failure features on structure surface. The effect of low energy impacts on the damage modes of the ERF was first investigated, and then the correspondence between the ERF damage characteristics and the structural internal failure was established. Simulation and experimental results showed that with the increase of impact energy, cracks on the ERF expanded from the radial radiation with a small extension range to the circumferential pattern with an increased damage area. Meanwhile, localized delamination appeared inside the upper panel, while the degree of flexure and crushing damage to the core continued to increase. Based on the analysis of the crack extension pattern of the ERF and the damage state of the upper panel and honeycomb core, a specific link between the ERF crack characteristics and the internal damages to the sandwich structure was obtained, which might offer a novel non‐destructive testing method for composite impact damages.Highlights Low energy impact damage in honeycomb sandwich structures was a concern. Impact damage response of epoxy resin film on sandwich composites was studied. Crack extension of the film showed a particular change from radial to annular. Specific link between film crack and sandwich structure damage was established. The results would be helpful for damage detection in sandwich composites.

Epoxy fiber derived all‐polymer films for high performance electrostatic energy storage dielectrics

Dielectric films with high discharged energy density are highly desired in electrical and electronic systems. Adding inorganic nanoparticles, especially for 1D inorganic fillers, in polymer films is recognized as one of the most effective methods to improve the electric breakdown strength, which is a key parameter of energy storage. However, 1D inorganic fillers added into thin films will undoubtedly introduce many defects and reduce the electric insulation performance. Herein, homogeneous epoxy fiber derived all‐polymer films were fabricated by electrospinning, laminating, and curing in sequence. The existing 1D structure of the epoxy films significantly enhanced the dielectric constant and electric breakdown strength, resulting in a very high enhancement of 2.7 times the discharged energy storage density at 25 °C, up to 9.6 J/cm3. Assisted by the simulation analysis, the enhanced dipole polarization and reduced current density are found to be the main reasons for the improved energy storage performances. Preparing all‐polymer films with fiber structure has proved to be an effective way to find advanced energy storage dielectric films.This article is protected by copyright. All rights reserved.

Mitigating the Degradation of MAPbI3 Perovskite Solar Cells Under Continuous Light Soaking with ZnO@CdS:Epoxy Short‐Wavelength Sunlight‐Shielded Films

The stability of MAPbI3‐based (MA stands for methylammonium) perovskite solar cells (PVSCs) has been carefully examined by ZnO@CdS nanoparticle‐embedded epoxy films (EP‐ZC films), device encapsulation (of glass sheet and UV‐curing gel), and in different temperatures, 10 °C, room temperature (no temperature control), and 65 °C. EP‐ZC films are used for shielding the short wavelength of the sunlight (UV, near UV, violet, and deep blue) which causes the photodegradation of MAPbI3 and hence the decline of power conversion efficiency (PCE) of PVSCs. Some external quantum efficiency spectra of the device are recorded alongside of the 500 h continuous light‐soaking measurement of current density (J)−voltage (V) of the devices. The time‐of‐flight secondary‐ion mass spectroscopy analysis is performed for a quantitative comparison of the iodide derived from the degradation of MAPbI3 in the encapsulated devices with or without the light‐shielding EP‐ZC films at 10 °C and 65 °C, respectively. The EP‐ZC6 film shows the best protection for encapsulated PVSCs with 98% of the initial PCE at 10 °C after 500 h continuous light soaking. Herein, from the continuous light‐soaking results, one can prioritize the moisture, temperature, and light in the influence of the stability of PVSCs.

Controllable construction of hollow Fe3O4/Ag particles for microwave absorption and photocatalysis

Hollow metallic composite particles are widely used in microwave absorption and catalysis due to their unique cavity structures, and favorable physical and electromagnetic properties. In this work, we propose an approach to prepare highly dispersed Fe3O4/Ag composite particles with a hollow structure using water-soluble green template method combined with in-situ growth process. The as-prepared cubic Fe3O4/Ag composite particles with an average size of 3.19 μm of hollow Ag and 11.65 nm of Fe3O4 coating on the surface were used as fillers for preparing microwave absorption epoxy resin films, showing a minimum reflection loss of −62.37 dB at 16.63 GHz with 7.5 mm thickness. An effective absorption bandwidth of 4.80 GHz can be observed in the frequency bands of 4.70–6.09 and 14.59–18.00 GHz. This mechanism is attributed to the internal cavity of the Fe3O4/Ag particles realizing multiple reflections of electromagnetic waves, and the synergistic effect of Fe3O4 and Ag. Moreover, this perspective is confirmed by their photocatalytic performance. The Fe3O4/Ag particles achieve a high photocatalytic degradation efficiency of 99.84% for Congo red dye within 30 min of light exposure and maintain a value of 96.62% after 6 cycles, demonstrating an outstanding reusability.

Thermal conductivity of epoxy resin films doped with a polythiophene/graphene complex or aluminum nitride

AbstractPolymer composites with thermal conductivity are attractive for heat dissipation in electronic devices. We prepared epoxy resin‐based composite films filled with polythiophene [poly(3‐hexylthiophene‐2,5‐diyl)] (P3HT)/graphene complex or aluminum nitride (AlN). The composite films were characterized by electron microscopic observation, thermogravimetric analysis, and thermal conductivity measurements. The addition of a small content of P3HT/graphene complex (&lt;1 wt%) increased both the out‐of‐plane and in‐plane thermal conductivities of the epoxy resin. The addition of AlN also increased thermal conductivity, but ≥40 wt% was required to obtain thermal conductivity comparable with that of an epoxy resin film doped with 0.9 wt% P3HT/graphene complex. The present results illustrate the potential of P3HT/graphene complexes as fillers for improving the thermal conductivity of epoxy resins without affecting their insulating properties.Highlights Polythiophene/graphene fillers increased epoxy resin films' thermal conductivity. To raise the thermal conductivity of epoxy resin films high AlN content was needed. In‐plane/out‐of‐plane epoxy resin films' thermal conductivities were evaluated.

Impact of Alpha Rays on the Optoelectronic Properties of Epoxy Resin Thick Films

Irradiated epoxy thick films are important for optical properties and may be used in many optical applications. This study aims to evaluate the effect of alpha irradiation on the optical and structural properties of epoxy thick films. Epoxy resin films were prepared by mixing epoxy resin (A) with hardener (B) at a mixing ratio of 3:1. Thus, specific thick films with thicknesses of 0.7 mm,0.8 mm and 1 mm were manufactured. Using visible and ultraviolet spectroscopy is one of the most important methods for studying polymers band gaps and electrical properties. The absorbance and transmittance spectra were used to investigate the optical properties of epoxy coatings of different thicknesses over a wavelength range of 300 nm–900 nm. Optical properties, such as absorption coefficient, refractive index, extinction coefficient, real dielectric constant, imaginary dielectric and optical band gap, were measured. The results show that the epoxy thick films have good optical transparency in the low-wavelength region. The results showed that increasing the thickness of the resin films decreased the optical energy gap and refractive index while increasing the absorption and extinction coefficients. In comparison, the effect of irradiation on an epoxy film of thickness 1 mm leads to an increase in the transmittance spectrum and energy gap and a decrease in the optical constants. The Fourier-transform infrared (FTIR) spectrum of the films was examined and showed the types of chemical bonds of the epoxy films before and after irradiation.

A new platform for designing high‐performance epoxy film adhesive with poly (butyl acrylate‐block‐styrene) block copolymer and alumina nano particles in aluminum–aluminum bonded joints: Preparation and analysis of the mechanical, adhesion, and thermal properties

AbstractEpoxy film adhesives are typically used in different industries. However, these adhesives suffer from brittleness, low flexibility, and thermal stability problems. In this research, phenolic resin (Novolac) and poly (butyl acrylate‐block‐styrene) were used in the formulation of epoxy film adhesive (Diglycidyl ether bisphenol A) to increase thermal stability and adhesion strength and as the toughening agent, respectively. Alumina nanoparticles were also employed to enhance the mechanical properties. The influence of block copolymer and alumina nano particles was also assessed on the mechanical and thermal properties of epoxy‐based film adhesives. The investigation of the mechanical properties of dumbbell‐shaped samples and adhesion strength of the Al‐Al bonded joints were evaluated by tensile, lap shear, and T‐peel tests. The thermal stability of the optimal samples was assessed by thermogravimetry analysis (TGA). SEM analysis was also utilized to study the toughening mechanism. Tensile test of the dumbbell‐shaped samples indicated that the incorporation of 2.5 phr block copolymer and 2 phr alumina nanoparticles enhanced the toughness to 250%. The shear and peel strengths of this sample also exhibited 51% and 76% increase, respectively, showing a remarkable synergistic effect. On the other hand, TGA results revealed that the incorporation of block copolymer improved the thermal stability of the adhesive matrix. The copresence of these two materials also showed a considerable synergistic effect on the thermal stability. The SEM results were also in line with the results of mechanical tests as the crack deviation, crack pinning, and debonding were the most important mechanisms of toughening.Highlights A new platform was developed for designing epoxy films adhesives with high mechanical, adhesion, and thermal properties. The hybrid of butyl acrylate block styrene copolymer, phenolic resin, and alumina nanoparticles showed synergistic effects on the lap shear and T‐peel strength. The greatest improvement in toughness was related to the epoxy adhesive containing 2.5 phr block copolymer and 2 phr alumina nanoparticles. Analysis of the fracture surface showed that by using hybrid of nanoparticles and block copolymers in the epoxy film adhesive formulation, the cohesive failure occurred. The use of hybrid additives in film adhesive formulations enlightened manufacture of adhesives for future studies on adhesive formulations.

Preparation and characterization of tungsten oxide fortified poly(urea-formaldehyde) microcapsules for self-healing coatings

Radiation-resistant poly(urea-formaldehyde) (PUF) microcapsules with a bisphenol A diglycidyl ether/butyl glycidyl ether core were prepared via emulsion polymerization. Tungsten oxide (WO3) nanoparticles were incorporated into the polymer shell to improve radiation resistance of the resultant PUF microcapsules. Microcapsules prepared with modified WO3 nanoparticles had an average diameter of 117 μm, an encapsulation efficiency of 48%, and evenly dispersed nanoparticle incorporation of 3.5 wt%. Modification of dense WO3 nanoparticles was necessary for even dispersion into PUF microcapsule shells. The corrosion protection properties of epoxy films cast on mild steel were demonstrated via scratching and exposure to salt solution. Films containing modified WO3 fortified microcapsules demonstrated self-healing and retained corrosion protection properties. Under gamma irradiation, WO3/PUF microcapsules exhibited less degradation of epoxy healing core compared to microcapsules that were not fortified with WO3.

Covalent organic framework (COF)-decorated NH2-functionalized MXene sheets for thermomechanical and UV-shielding performance of epoxy nanocomposite coatings

Designing a multi-purpose epoxy nanocomposite with promising mechanical and weathering properties is yet a challenge to be explored. Meeting all above mentioned properties in one nanocomposite requires a rational design of hybrid nanomaterials benefiting from their synergistic effect. To this end, a robust imine-based COF was synthesized on an MXene substrate, forming an inorganic-organic assembly as filler for a multi-functional epoxy coating. As a proof of concept, the tensile strength of the loaded coating was almost twice the unloaded one, confirming the efficient stress transfer due to mechanically robust MXene and compatibility improvement of the hybrid assembly in the presence of the COF. Furthermore, the physical barrier of MXene, along with the nitrogen-rich structure of COF, resulted in efficient thermal insulating properties of the fabricated nanocomposite coatings. Moreover, the weathering test illustrated that the conjugated structure of the COF enhanced the epoxy film weathering stability after 7 days of UV exposure, which is promising among competitors. This high yield, facile processing, and rational design provide new insight into the application of MXene-conjugated COF in epoxy nanocomposite coatings.

BaSO4-Epoxy Resin Composite Film for Efficient Daytime Radiative Cooling.

Conventional cooling methods are based on active cooling technology by air conditioning, which consumes a large amount of energy and emits greenhouse gases. Radiative cooling is a novel promising passive cooling technology that uses external space as the cooling source and requires no additional energy consumption. Herein, we propose an approach to prepare highly dispersed BaSO4 nanoparticles (NPs) using a direct precipitation method combined with the in situ surface modification technology. The as-prepared PVP-modified BaSO4 NPs with an average size of 20 nm can be stably dispersed in ethanol for more than 6 months and then were used as building blocks to prepare spherical BaSO4 clusters with an average size of 0.9 μm using a scalable spray drying technique. The BaSO4 NPs/clusters (mass ratio 1:1) were used for preparing radiative cooling epoxy resin film, showing a high solar reflectance of 71% and a high sky window emissivity of 0.94. More importantly, this composite film displays superior radiative cooling performance, which can reduce the ambient temperature by 13.5 °C for the indoor test and 7 °C for the outdoor test. Compared with the commercial BaSO4 filled film, our BaSO4-epoxy resin composite film offers advantages not only in radiative cooling but also in mechanical properties with a 16.6% increase of tensile strength and 40.1% increase of elongation at break, demonstrating its great application potential in the field of building air conditioning.

A toughening indole‐based epoxy film with efficient anti‐counterfeiting properties driven by cation–π interaction

AbstractA strong and tough indole‐based epoxy film driven by cation–π interaction is designed, evading the trade‐off between stiffness and extensibility in epoxy resins. The film with high strength, toughness and effective anti‐counterfeiting properties induced by cation–π interaction is promising in the development of the fields of aerospace and electronic devices. © 2023 Society of Industrial Chemistry.