Epoxy Film Research Articles

Derivation and characterization of epoxidized soybean oil and epoxy resin film produced using a three step-washing neutralization process

The scientific community has recently focused on developing high-value-added epoxidized soybean oil and green bio-based epoxy resins using sustainable resources because of their cost-effectiveness and eco-friendliness. A part of this developing epoxy resin includes the replacement of conventional petroleum-based resins with their green counterparts, that is, bio-based epoxy resins. The long-term goal of this research is to develop low-cost, value-added, and bio-based epoxy resins from conventional soybean oils and commercialize the technology to be scaled up for epoxy resin production for chemical industries. Epoxidized soybean oil (ESO) was developed through the synthesis of conventional soybean oil by applying deep eutectic solvent catalysts, such as choline chloride–oxalic acid (DES-02) and choline chloride–butyric acid (DES-06) followed by three steps of washing neutralization processes. The impact of the catalysts on the epoxidation process was verified using titration methods in combination with infrared and nuclear magnetic resonance spectroscopies. The results showed an optimal carbon–carbon double bond conversion with a high selectivity of 73% when soybean oil was epoxidized with bifunctional DES-02 catalysts. The conventional epoxidized soybean oil synthesis without deep eutectic catalysts yielded relatively low carbon–carbon double bond conversions with 5% selectivity. Various novel bio-based epoxy resins with equal amounts of ESO and acrylic acid as monomers were developed, followed by injection molding. Bio-based epoxidized soybean resin films were characterized by dynamic mechanical and thermomechanical analyses. The results showed that resin films catalyzed by DES-02 and DES-06 improved the storage modulus (ca. 2000 MPa) and loss modulus (ca. 390 MPa).

Binary Resin-Curing Agent Systems for Fabricating Epoxy and Graphene Oxide-loaded Epoxy Films

In this research, diglycidyl ethers of bisphenol-A (BADGE) and polyethylene glycol (PEGDGE) were binarily cured with a mixture of diamine curing agents including isophorone diamine and polyethylene glycol diamine (PEGDA) in the absence/presence of aminated graphene oxide nanoplatelets (AGNPs, 0.5 wt.%). Four molar ratios of diglycidyl ethers and curing agents were used stoichiometrically in isothermal curing systems. The films prepared from the epoxy networks were entirely strong and pliable. All epoxy thermosets were evaluated using field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and diffuse reflectance-ultraviolet/visible spectroscopy (DR-UV/vis). The absorption coefficients of the epoxy and AGNPs-loaded epoxy materials decreased with increasing the molar ratio of PEGDGE resin and polyethylene glycol diamine curing agent. According to dynamic mechanical analysis no phase heterogeneity occurred in the structure of the prepared thermostats. When the thermoset materials were loaded by AGNPs filler, the peaks associated with alpha relaxations shifted to higher temperatures. Moreover, thermogravimetric analysis demonstrated that the thermal stability of the prepared epoxy thermosets slightly increased after the addition of the nanoplatelets. In addition, the thermal resistance of the prepared thermosets decreased to some extent by increasing the participation rate of monomers containing polyoxyethylene.

Surface modification of carbon nanotubes by a bifunctional amine silane; effects on physical/mechanical/thermal properties of epoxy nanocomposite

Weak interfacial interactions between MWCNTs and epoxy matrix causes agglomeration of the nanotubes and declines in the nanocomposite performances. In this study, MWCNTs were surface modified by a bifunctional amino silane (i.e. Bis (3-triethoxysilylpropyl)amine) at different concentrations. The nanotubes were previously functionalized through acid oxidation to increase silane grafting ratio. The pure, functionalized and silanized carbon nanotubes were characterized to assess the success of silane grafting. The pure and modified nanotubes were applied at different contents (0.5, 1 and 2 wt%) to epoxy resin. The tensile, flexural and compressive properties of the nanocomposites were evaluated. The nanocomposites were also characterized using water contact angle test, DSC, DMTA and FE-SEM/EDS analysis. It was observed that silanization of nanotubes caused considerable increment (32°) in the water contact angle of epoxy films. The results showed that incorporating the pure nanotubes (at 0.5 wt%) to epoxy resin enhanced the mechanical strengths but decreased the modulus of the epoxy sample. It was found that incorporating 0.5 wt% of modified MWCNT into epoxy binder caused 33, 53 and 40 % improvement in the tensile, flexural and compressive strengths and 56, 85 and 110 % increment in the tensile, flexural and compressive modulus compared to the pure MWCNT containing nanocomposite. The modified MWCNTs participated in curing of epoxy resin through reaction of silane amide groups with resin epoxide groups that this increased enthalpy of curing up to 25 %.

Development of novel single-die hybridisation processes for small-pitch pixel detectors

Hybrid pixel detectors require a reliable and cost-effective interconnect technology adapted to the pitch and die sizes of the respective applications. During the ASIC and sensor R&D phase, especially for small-scale applications, such interconnect technologies need to be suitable for the assembly of single dies, typically available from Multi-Project-Wafer submissions. Within the CERN EP R&D programme and the AIDAinnova collaboration, innovative hybridisation concepts targeting vertex-detector applications at future colliders are under development. Recent results of two novel interconnect methods for pixel pitches of 25 µm and 55 µm are presented in this contribution — an industrial fine-pitch SnAg solder bump-bonding process adapted to single-die processing using support wafers, as well as a newly developed in-house single-die interconnection process based on Anisotropic Conductive Film (ACF). The fine-pitch bump-bonding process is qualified with hybrid assemblies from a recent bonding campaign at Frauenhofer IZM. Individual CLICpix2 ASICs with 25 µm pixel pitch were bump-bonded to active-edge silicon sensors with thicknesses ranging from 50 µm to 130 µm. The device characterisation was conducted in the laboratory as well as during a beam test campaign at the CERN SPS beam-line, demonstrating an interconnect yield of about 99.7%. The ACF interconnect technology replaces the solder bumps by conductive micro-particles embedded in an epoxy film. The electro-mechanical connection between the sensor and ASIC is achieved via thermocompression of the ACF using a flip-chip device bonder. The required pixel pad topology is achieved with an in-house Electroless Nickel Immersion Gold (ENIG) plating process. This newly developed ACF hybridisation process is first qualified with the Timepix3 ASICs and sensors with 55 µm pixel pitch. The technology can be also used for ASIC-PCB/FPC integration, replacing wire bonding or large-pitch solder bumping techniques. This contribution introduces the two interconnect processes and presents preliminary hybridisation results with CLICpix2 and Timepix3 sensors and ASICs.

Low-Profile Polymer Composite Radar Absorber Embedded With Frequency Selective Surface

This paper proposed a novel design for a thin, lightweight polymer composite Radar Absorber (RA) with broadband bandwidth in the frequency range 2.8-9.6 GHz. A 3-mm-thick, thin polymer composite structure comprised of glass fiber, epoxy resin, and FSS films was then fabricated using the hand layup process. The β-phase behaviour enhanced polyvinylidene fluoride (PVDF) through electrospinning was deposited on a frequency selective surface (FSS). The PVDF phase structure was evaluated using X-Ray diffraction (XRD). The formation of nanofibers was evaluated by scanning electron microscopy (SEM). A significant increase in the absorption of electromagnetic (EM) waves with a broad operational bandwidth is produced by the addition of FSS to the glass fiber. Experiments were carried out and assessed by comparing the results to numerical models in CST Microwave Studio, indicating that the RA integrated with PVDF coated FSS has an operational bandwidth of 2.8-9.6 GHz and a reflectivity of less than -10dB. Finally, the absorption and mechanical characteristics of the fabricated Radar Absorbing Structure (RAS) was also investigated.

Preparation and characterization of black liquor lignin-based epoxy composite film

To fully utilize black liquor from pulping and decrease its contribution to pollution, lignin-based epoxy resin composite films were prepared from black liquor lignin. Fourier transform infrared spectroscopy indicated the successful synthesis of lignin-based phenolic amine (LPAA). Using LPAA as a curing agent, the prepared epoxy resin films (LPAAF) presented good dispersion of the inorganic chemicals of black liquor and exhibited higher tensile strength of 30 MPa and thermal stability than that using the phenolic amine as a curing agent. Therefore, LPAAF prepared from black liquor lignin presents a novel utilization of black liquor.

Construction of a nano-micro nacre-inspired 2D-MoS2-MOF-glutamate carrier toward designing a high-performance smart epoxy composite

For the first time, dual-functional pH-sensitive and water-barrier epoxy coating was prepared by introducing the monosodium-glutamate molecules into the ZIF-8@MS nano-hybrid. By performing the FTIR, XRD, BET, and FE-SEM investigations the successful production of ZIF-8 particles on the MS surface was proved. Based on the mesoporous nature of the ZIF-8 particles, they were utilized as a pH-responsive carrier to encapsulate the glutamate molecules and Zn2+-ions as effective corrosion inhibitors. Owing to the pH-responsive behavior of ZIF-8@MS, the corrosion resistance of the bare steel (Z 0.01 Hz = 7466 ohm.cm2) was improved in a saline solution containing particle extract. The ZIF-8@MS-filled epoxy resin provided excellent corrosion resistance after 21 days of exposure due to the excellent barrier impact of 2D MS sheets and the smart release of corrosion inhibitors. The self-healing capability of the epoxy coatings filled with glutamate and Zn2+ loaded ZIF-8@MS was demonstrated by FE-SEM, EIS, and salt spray tests. The synergistic anti-corrosion effect of the combined inhibitors was shown by EIS outcomes. The results have revealed a considerable improvement in the storage modulus, Tg, crosslink density, and tensile strength, which verified the effective duty of ZIF-8@MS particles in the epoxy film’s mechanical properties.

Fabrication and evaluation of epoxy resin film adhesive with excellent heat resistance and potential flame retardance

To obtain a heat-resistant and flame-retardant epoxy film system that can be stored for a long time, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was used to modify an imidazole curing agent, and thus a new reactive flame retardant curing agent (DMH) was successfully synthesized. A phenolic epoxy resin matrix with an oxazolidinone (EPO) structure was synthesized through the reaction of a phenolic epoxy resin (EPN) and toluene diisocyanate (TDI), and polyethersulfone (PES) was used as a toughening agent. After characterization of the material, the curing process was also considered. The results showed that the film adhesive maintained reaction inertness around room temperature and was effectively cured at a curing temperature of 130 °C and released moderate heat. Cone calorimetry testing further confirmed the excellent flame retardance of the film adhesive. The T5% temperature obtained from thermogravimetric analysis (TGA) was as high as 366 °C, which proved its good thermal stability. On this basis, the mechanical properties of the film adhesive didn't decrease, and the addition of PES ensured its good toughness. When used as the adhesive for cured resin aluminum-honeycomb sandwich samples, the lap shear strength (LSS) of the sample reached 35.6 MPa. Due to these advancements, the film adhesive system has the potential for application in a wide range of fields.

Poppy-leaf extract-derived biomolecules adsorption on the rGO-nanoplatforms and application as smart self-healing material for epoxy coating

Nowadays, low-dimensional materials have been utilized as potential materials for designing smart composite coatings. Not only the coating's barrier function but also its self-healing ability can be improved via the inclusion of nano-particles. Herein, the graphene oxide (GO) nanosheets are firstly functionalized by Poppy-leaf extract (MGO) and then modified with Zn (II) ions. Thereupon, the Zn@MGOs are incorporated into the epoxy coating (EC).First, Zn@MGOs were synthesized and then characterized by Raman, XRD, and FT-IR techniques. Second, the anti-corrosion impacts of Zn@MGOs in 3.5% NaCl media and after inclusion into the epoxy coating (EC) were investigated. The reason for applying the solution phase studies was to investigate the anti-corrosion behavior of the designed nano-hybrid in a neutral salty solution. In the coating phase, electrochemical studies were done on the scratched and intact coatings to investigate the self-healing behavior and barrier properties of the designed nano-composites. Also, other experiments including salt spray and cathodic delamination tests were carried out to further study the protection function of the designed composites. Outcomes from the EIS and polarization tests proved that the Zn@MGO could enhance the metal resistance against corrosion via a mixed-type inhibition mechanism in the solution phase. Besides, the EIS studies in the coating phase clarified that the epoxy film self-healing action and barrier function were simultaneously improved in the presence of the Zn@MGO.

Colorfully Patterned Epoxy Resin Films with a Cholesteric Structure Prepared through a Photopolymerization Approach

Structurally colored epoxy resin films were prepared using a liquid crystalline (LC) epoxy monomer of E11M and a chiral additive of CA-iso through a photopolymerization approach. With the addition of the co-photoinitiator isopropyl thioxanthone and comonomer 3′,4′-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, the polymerization rate was increased. Since the epoxy resin films can be obtained within several seconds, they are feasible for large-area preparation on the coating line. The reflective wavelength was tunable by changing the concentration of CA-iso in the LC mixture. Diffuse-reflectance circular dichroism spectra indicated a right-handed helical supramolecular structure. Field-emission scanning electron microscopy images indicated a multilayer structure. Since the LC mixtures were thermochromic, colorfully patterned epoxy resin films were prepared by controlling the polymerization temperature. Moreover, LC gratings were also prepared, which were expected to be applied for anticounterfeiting.

Solution Uptake in Cylindrical Carbon-Fibre-Reinforced Polymer (CFRP) Tendons

Salt water exposure conditions relevant to carbon-fibre-reinforced polymer (CFRP) prestressed concrete structures in marine environments are investigated. The diffusion into relatively small diameter CFRP tendons can be a lengthy process so the prediction of the long-term moisture uptake using short-term experiments on thin films of epoxy would be advantageous. However, the fibre inclusions within a composite introduce complexities, and factors are typically required for correlation with pure epoxy specimens. Diffusion parameters based on moisture uptake result from CFRP tendons exposed to salt water solution at 20°C and 60°C are compared with those obtained using equivalent thin film specimens. The higher temperature is selected to accelerate the moisture uptake. It is found that the measured ratios of tendon and epoxy diffusivity were temperature dependent, and the combination of the higher temperature and salt solution leads to an increased propensity for moisture uptake in the tendon. Existing analytical models to predict the CFRP tendon diffusivity from that of a thin film of epoxy did not appear to capture the observed trends. However, predictions using a unit cell with a fibre interface zone suggest that this may be due to an increased diffusivity in the interphase region.

Accelerated‐curing epoxy structural film adhesive for bonding lightweight honeycomb sandwich structures

AbstractAccelerating the curing of epoxy/aromatic amine adhesives and improving their toughness are challenges in heat‐resistant epoxy structural adhesives. Herein, we report an epoxy/aromatic amine adhesive accelerated curing system with an oxo‐centered trinuclear (chromium III) complex, which is toughened using a thermoplastic block copolymer (TPBC). The reaction characteristics, heat resistance, microstructure, and bonding properties of the accelerated epoxy adhesives were analyzed. The reaction peak temperature of the epoxy with 3% catalyst was 113.1°C, which was 113.6°C lower than that of epoxy without catalyst, and the modified epoxy resin demonstrated a potential for rapid curing at medium temperature. The glass transition temperature of the TPBC‐toughened epoxy adhesive was 125°C after curing, indicating excellent thermal stability after medium temperature curing. The introduction of the TPBC increased the single‐lap shear strength of the epoxy adhesive without reducing its heat resistance. The shear strength at room temperature and 120°C of the modified epoxy adhesive with 50 phr of TPBC was 25.2 and 10.9 MPa, respectively. Moreover, the epoxy film adhesive exhibited outstanding bonding properties when used in the bonding of lightweight honeycomb sandwich structures.

Effect of Solvents on the Color Recovery Responses of Swollen Structural-Color Epoxy Films Based on Inverse Opal Photonic Crystals.

Photonic crystal (PC) films have been widely applied in color displays and the anticounterfeiting field due to their facile fabrication process and easily tunable properties. However, the method for improving the reusability of the color-changed swollen PC films is still a challenge. In this paper, we report the color recovery behavior of epoxy resin inverse opal photonic crystal (EP-IOPC) films, which show different responses after being infiltrated with ethanol, acetone, and dimethyl sulfoxide (DMSO) based on the swelling and deswelling process. DMSO achieved the best effect on the color recovery of the swollen EP-IOPC films compared to ethanol and acetone, and the reflection spectrum blue-shifted in a small range and finally stabilized at a 60 nm deviation from the original spectrum after 10 times recovery. This strategy of color recovery not only solved the problem that the swollen EP-IOPC film's color changes to a certain extent but also showed promising potential in the color display and anticounterfeiting field.

Sensing the onset of epoxy coating degradation with combined Raman spectroscopy/atomic force microscopy/electrochemical impedance spectroscopy

The paper presents the results of investigation on epoxy resin durability upon 12-week exposure to UV radiation. The aim was early determination of the onset of epoxy degradation and for this purpose an epoxy film on steel substrate systems were periodically inspected using Raman spectroscopy, atomic force microscopy and electrochemical impedance spectroscopy. The behaviour of examined polymer could be divided into three periods: immunity, degradation initiation and failure. Early degradation initiation could be sensed only with Raman spectroscopy and AFM topography imaging where decrease in intensity of particular Raman peaks and discrete changes in topography constituted the fingerprints of UV-induced changes. At this stage electrochemical impedance spectroscopy and local dc current mapping with AFM did not provide any signs of forthcoming degradation since the epoxy film still exhibited sufficient barrier properties. Obtained results can be helpful in proper selection of investigation techniques in the situations where precise evaluation of polymer degradation onset is of key importance.

Enhancement of surface electrical performances of epoxy film by blending with fluorinated and crosslinking monomer

• Fluorinated monomers were synthesized through a facile method to prepare fluorinated epoxy films. • Effects of introducing –CF 3 groups on physicochemical characters of the films are studied. • Electrical strength of the fluorinated film was evidently enhanced. In order to introduce fluorine-containing functional groups into epoxy resins to stably enhance the surface electrical properties of thin films, the trifluoromethyl group containing diglycidyl ethers bisphenol A (F-DGEBA) monomer was prepared by a simple and environmentally friendly method. Further, the film was obtained by blending the prepared monomers with DGEBA in different proportions and curing at high temperature with methyl tetrahydrophthalic anhydride (MTHPA). The prepared films not only have improved hydrophobic properties, but also exhibit better surface electrical properties. With the increase of the content of F-DGEBA, the epoxy resin films have higher surface insulation strength and better potential decay performance, which is due to the existence of –CF 3 groups changing the distribution of deep and shallow traps. Compared with the non-fluorinated film, the flashover voltage of the fluorinated film with the best electrical properties is increased by 32.2%, and the potential decay rate is also much faster.

Analysis of low-energy impact damage to epoxy resin film based on surface damage characteristics

For fiber reinforced epoxy resin composites, when low-energy impact events occur, although the surface damage of the structure is invisible, a large area of delamination might have appeared inside. In order to detect these less noticeable impact damages, epoxy resin is intended to be used as an indicative coating to show obvious surface characteristics when the impact damage occurs. On that basis, the main purpose of this study is to establish the correspondence between the damage patterns of the epoxy resin film and the low-energy impact. First, a three-dimensional progressive finite element model was established and the impact damage mechanism of the film was analyzed. Then both numerical simulation and experimental investigation were conducted for the low-energy impact response of the film, and they were in good agreement with each other. The results showed that the damage characteristics of the epoxy resin film were clearly visible and changed regularly with the impact, as reflected by the fact that the damage area, the number of cracks and the crack distribution obviously depended on the magnitude of the impact energy. Therefore, the established simulation model can be used to predict and obtain systematic damage patterns of the film and offers the potential to evaluate the invisible impact damage of composite structures based on the regular damage patterns if the film is used as the indicative coating.

Tack of epoxy resin films for aerospace-grade prepregs: Influence of resin formulation, B-staging and toughening

Aerospace-grade prepreg resin films based on multifunctional tetraglycidyl-4,4′-methylenedianiline (TGMDA), triglycidyl p-aminophenol (TGAP), Bisphenol A diglycidyl ether (DGEBA) and curing agent 4,4'diaminodiphenyl sulfone (DDS) are investigated in terms of tackiness by probe testing. The model epoxy systems are modified regarding the thermoplastic toughener content (polyethersulfone, PES) and the B-stage level, which is adjusted by cure prediction based on a model-free isoconversional method (Flynn-Wall-Ozawa). Additional DSC and rheological analysis are performed to study the thermal and viscoelastic material behavior in conjunction to its impact on temperature-dependent tack. Maximum achievable tack is found to decrease as a function of both degree of conversion and toughener content. Meanwhile, both influencing factors shift the tack maximum towards higher temperatures corresponding to increased flow characteristics attributed to evolving network formation and the incorporation of high molecular weight PES. In terms of absolute tack level and corresponding temperature, probe tack values similar to commercial prepreg systems (∼100 μJ mm−2) are recorded for TGMDA-based formulations containing 10 wt% PES at 20% pre-cure. Model formulations, which have neither been exposed to B-staging nor toughened, show exceptionally high tack below room temperature for all investigated epoxy prepolymers and are therefore not considered processable by automated fiber placement.

Enhanced damping and stiffness trade-off of composite laminates interleaved with recycled carbon fiber and short virgin aramid fiber non-woven mats

This paper proposes composite laminates interleaved with recycled carbon fiber and short virgin aramid fiber non-woven mats to enhance the trade-off of mechanical damping and stiffness. Compared with their virgin counterparts, recovered carbon fibers (rCFs) have the potential for damping enhancement at the cost of only minimal degradation in strength. A papermaking method was used to convert rCFs and virgin aramid fibers (vAFs) separately into 60 g/m2 non-woven mats, which were then sandwiched between two layers of 125 g/m2 epoxy resin films before interleaving. A vacuum-assisted compression molding process was then used to produce the laminates. The effect of a titanate coupling agent on the adhesion between the mats and the epoxy matrix was studied. The experimental results showed that the titanate coupling agent was an effective sizing agent for rCF and vAF mats with epoxy matrix. The laminate with a single core layer of sized rCF mat showed better flexural properties and dynamic performance than those with the sized vAF mat. The flexural modulus and dynamic properties were found to depend on the stacking sequence of the added non-woven mats. Compared with the control sample, the best laminate had a figure of merit of 0.73 GPa, which was 23.7% higher.

Experimental Study on Repairing Corroded Cracks by Electrophoretic Deposition

The corrosion of reinforced concrete could reduce its mechanical properties and cause concrete cracking. Electrophoretic deposition is a new method for repairing rust-cracked reinforced concrete. In this study, we observed the crack surface morphology, mass growth, epoxy resin film thickness, ultrasonic rate, and epoxy resin filling depth of rust-cracked reinforced mortar specimens during the repair process and investigated internal microstructure and phase composition of the repaired mortar, and clarified the principle behind the electrophoretic deposition of cationic epoxy resin and curing agent molecules in the repair solution. The result of research shows that longer repair times decreased the carbonization depth and water absorption of the specimens. After repair, the porosity of the surface mortar decreased, owing to the filling of epoxy resin, and the newly generated epoxy resin film had a dense structure. Thus, the carbonization resistance and waterproof performance of the repaired specimens improved. The repair process of electrophoretic deposition can be divided into the immersion, repair, and curing stages, and the physical and chemical principles of each stage were explained.

Probing water uptake gradient in an epoxy matrix via scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is used to detect and observe the presence of water inside polymeric film at the microscopic scale around 200–500 μm. The principle is based on the use of SECM performed with a room temperature ionic liquid (RTIL) and K4Fe(CN)6 as redox sensor. The particular electrochemical behaviors obtained in such medium have been investigated by performing cyclic voltammetry and approach curves in negative feedback mode. Then, the cross-section of epoxy resin films has been repeatedly scanned using the SECM probe over several days of immersion in the RTIL. As the presence of water impacts the electrolyte viscosity, the electrochemical signal was sensitive to the amount of water around the microelectrode. The sensitivity of this technique to the presence of water released from the materials at the microscopic scale was demonstrated by comparing electrochemical signals obtained on dry and saturated specimens. Such results appeared to be very promising for the development of new methods to locally detect the presence of water in thick polymeric materials and to measure humidity gradient within the material thickness.