Epoxy Surface Research Articles

Silane modification of semi-curing epoxy surface: High interfacial adhesion for conductive coatings

Weak interfacial bonding between epoxy resin and plated metallic layer limits the development of epoxy resin in electronic devices and multilayer circuits. In this work, we propose a surface silane graft strategy by utilizing the active epoxy groups of semi-curing epoxy resin, which can replace the alkali washing and coarsening steps before metallization and achieve higher interfacial adhesion strength to the metallic layer. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the chemical composition of the surface after the modification process. The effects of modification time and concentration of 3-mercaptopropyltriethoxysilane (MPTES) solution on the adhesion strength were studied by 180° peeling test. When the modification time reached 20 min or the concentration of MPTES solution was above 8 %, the adhesive strength was stable at 16 N/cm, showing a strong adhesive effect on the silver layer. This research may have positive implications for improving interfacial bonding between metal and polymer surfaces.

Increase in Leidenfrost point via plasma-activated water

We exploit plasma-activated water to increase the Leidenfrost point for application in spray cooling. Due to the presence of reactive oxygen and nitrogen species in the plasma-activated water, compared to deionized (DI) water, we observe up to an 18% increase in the solution density and up to 21% reduction in the surface tension. This gives rise to a significant increase in evaporation rate using the plasma-activated water compared to DI water and also leads to a shift in Leidenfrost point. Specifically, in the nucleate and transition boiling regimes, we observe a considerable reduction in the surface temperature when the plasma-activated water droplet is impinging on the heated plate as compared to the DI water droplet, i.e., up to 220%. We further demonstrate the practicality of plasma-activated water droplets as a viable alternative to replace DI water droplets in spray cooling through a commonly used graphene–epoxy surface coating enhancement technique. With the plasma-activated water droplet, we show a further reduction in the surface temperature of the heated plate by up to 11% as compared to the DI water droplet. Given that plasma-activated water can be easily produced and its bacterial inactivation characteristic can circumvent bacteria growth, these promising results highlight its potential applicability to replace DI water as a coolant in practical cooling systems.

Effect of seawater and stress coupling on the durability of carbon fibre-reinforced polymer

Using pre-stressed carbon fibre reinforced polymer/plastic (CFRP) to strengthen bridge structures is currently considered a promising technology and the durability of the structure is closely related to the material property. CFRP have good corrosion resistance, but they also experience different degrees of swelling, corrosion and hydrolysis in water immersion environments. Stress accelerates this effect and leads to deterioration of the mechanical properties of the materials. This work aims to investigate the durability of CFRP grids under water, wet-dry cycles of seawater, seawater immersion and 0% fu ( fu is the ultimate tensile strength of the tested CFRP grids and it is constant stress in this paper), 30% fu, 60% fu coupled environments.Test aging time at room temperature (25°C) of 30, 60, 120, 180, 270, 360 days. The results indicate that the surface of epoxy resin is smooth at the initial moment by comparing of scanning electron microscope (SEM) image. With the increase of deterioration degree with aging time, the cavities and cracks appeared in the matrix. The epoxy resin content between the fibers decreased, and the adhesion force decreased. When the aging time is short, the tensile damage section of CFRP grid is flaky and the matrix is tightly bonded with the fiber. The later damage is mainly blow-up damage, which the fracture section is typical filiform. After CFRP grids aged for 360 days, the tensile strength decreased by 6.2%, 10.2%, 10.9% in the water, seawater solution and seawater wet-dry cycle environments. The tensile strength decreased by 10.2%, 12.3% and 20.2% under the coupling of seawater and different stress levels. A semi-empirical model of durability is proposed to provide a good reference value for the durability prediction of FRP materials.

Insulation degradation affected by micron metal particles attached on epoxy surface: charge accumulation and flashover voltage

The micron metal particles are inevitably produced in long-term operation condition of high voltage direct current SF6 insulated apparatus, which could frequently cause the surface discharge. Degradation of long-term surface discharge will be a severe threat to the insulation strength. Aiming at this problem, the surface charge accumulation and flashover voltage of epoxy itself before and after discharge degradation by particles were compared in this paper. The composition after degradation was measured by EDS and FTIR. The microstructure was observed by SEM. The roughness was measured as well. The trap distribution was measured by SPD. The mechanism of degradation and its effect on insulation characteristics were analyzed. The results show that the surface charge accumulation increase three times after degradation. Additionally, flashover voltage decreases 19% after degradation. The smoothly surface after degradation decrease the trap energy level for 14%, which might be the change reason of surface charge accumulation and flashover voltage. This paper can offer as a reference for the effect of micron metal particles on insulation degradation in SF6 gas insulated equipment.

Effect of epoxy concentrations on thermo-mechanical properties of kenaf fiber – recycled poly (ethylene terephthalate) composites

The effect of different concentrations of epoxy surface coating treatment on the thermal and mechanical properties of kenaf fiber reinforced recycled poly (ethylene terephthalate) (RPET) composites was studied. Silane-treated kenaf fibers (SKF) were epoxy-coated with optimized coating concentrations (in the ratios of 1:4, 1:5, and 1:6 epoxy to acetone solutions) to improve the thermal degradation/decomposition resistance and interfacial bonding with RPET matrix. The different epoxy coated-silane treated kenaf fibers 1:4 ESKF, 1:5 ESKF, and 1:6 ESKF were compounded with RPET at an optimized temperature of 240°C, and their constituents’ composites KF/RPET, 1:4 ESKF/RPET, 1:5 ESKF/RPET, and 1:6 ESKF/RPET were subjected to thermal, mechanical and microstructural investigation. The obtained results showed some remarkable effects of epoxy concentrations on the chemical and surface structures of the treated fibers. Thermal properties of both ESKF and ESKF/RPET composites were more stable and improved with different concentrations of epoxy treatment compared to the untreated counterparts. 1:4 ESKF and 1:5 ESKF were the most thermally stable with onset degradation and DTG decomposition temperatures of 331.6°C and 381.7°C, and 324.0°C and 388.7°C respectively. Mechanical properties of the epoxy-coated composites were higher and further improved with epoxy concentrations and fiber loadings compared to uncoated composites. Hence, the epoxy concentration of 1:4 gave the maximum tensile and impact properties, and at 10 wt. % fiber loading within the lower loading regions, followed by 1:5 with outstanding flexural properties. The coated-treated composites showed strong fiber/matrix bonding with no evidence of fiber decomposition compared to the untreated composites with poor fiber/matrix interaction. The current research findings are original and valid for improving the thermal degradation resistance and stability of natural fibers, and the mechanical properties of natural fiber reinforced engineering thermoplastic composites. The epoxy coated – silane-treated textile kenaf fibers reinforced with recycled PET composites have the potentials to be utilized in high-temperature industrial and engineering applications.

Tribological and mechanical analysis of hybrid epoxy based polymer composites with different in situ liquid lubricants (silicone oil, PAO and SN150 base oil)

This study compares the tribological, thermal and mechanical properties of epoxy-based composites with solid fillers (ultrahigh molecular weight polyethylene, molybdenum disulphide), and different in situ liquid lubricants in different volume proportions. Liquid lubricants used in this paper are three types of silicon oil with different viscosities, base oil and polyalphaolefins (PAO). The base oil-epoxy composite showed superior tribological performance among the three. The coefficient of friction of 0.1 and specific wear rate in the range of 10−7 mm3/Nm were obtained at an apparent pressure of 0.611 MPa. Transfer film formation with oil pockets on both the tribo-pair surfaces was identified as the main friction and wear reduction mechanisms. The surface of epoxy became hydrophobic, reducing adhesive interaction and friction.

Ar/HMDS Plasma Jet as a Tool for Superhydrophobic Coatings on Epoxy Resin

During actual operation, the superhydrophobic surface provides excellent resistance to condensation and icing due to its low wettability. This study used an Ar/HMDS mixture as the working gas and a low-temperature plasma jet induced in an atmospheric pressure environment to create a superhydrophobic coating with a water contact angle of up to 172.6°, utilized a typical epoxy resin plate as the substrate. XPS analysis indicated the presence of a significant number of low surface energy functional groups containing Si and O on the epoxy resin surface. Scanning electron microscope (SEM) revealed the presence of dense microstructure and nanostructure on the surface. The process of plasma jet water-repellent modification of epoxy resin surface was further analyzed from two perspectives: particle collision in the electric field, molecular bond breaking and reorganization reaction of monomer, and grafting reaction of free radicals formed on the surface of epoxy resin by high-energy jet bombardment, combined with XPS test of high-purity discharge products in the jet tube. The results indicate that the epoxy resin surface modified by plasma jets achieves superhydrophobicity. The modification time is extended to 180 s, and the static water contact angle is increased from 72.4° to 172.6°. Dense microparticle and nanoparticle are formed on the surface. For the secondary binary composite rough structure, the percentage of Si and O elements increased to 41.3% and 27.8%, respectively. The Si(CH₃)O_3/2 system contributed the most, accounting for 40.5%.

Peel Adhesion Strength between Epoxy Resin and Hydrated Silica Surfaces: A Density Functional Theory Study.

Adhesive strength is known to change significantly depending on the direction of the force applied. In this study, the peel and tensile adhesive forces between the hydroxylated silica (001) surface and epoxy resin are estimated based on quantum chemical calculations. Here, density functional theory (DFT) with dispersion correction is used. In the peel process, the epoxy resin is pulled off from the terminal part, while in the tensile process, the entire epoxy resin is pulled off vertically. As a result of these calculations, the maximum adhesive force in the peel process is decreased to be about 40% of that in the tensile process. The adhesion force–displacement curve for the peeling process shows two characteristic peaks corresponding to the process where the adhesive molecule horizontally oriented to the surface shifts to a vertical orientation to the surface and the process where the vertical adhesive molecule is dissociated from the surface. Force decomposition analysis is performed to further understand the peel adhesion force; the contribution of the dispersion force is found to be slightly larger than that of the DFT force. This feature is common to the tensile process as well. Each force in the peel process is about 40% smaller than the corresponding force in the tensile process.

Study on tribological properties of epoxy resin composites

Abstract Epoxy resin has been widely used in many fields. The improvement of friction and wear property can further expand the application range of epoxy resin. Filling modification can improve the tribological state of epoxy resin and improve the friction and wear property of epoxy resin. This paper summarizes the research of epoxy resin composite material tribology performance at the forefront of progress. The influence of different fillers on the friction and wear properties of epoxy resin composite materials was discussed from the aspects of the single filling of nano-filler, organic materials and inorganic lubricating fillers and the compound filling of inorganic or organic-inorganic fiber-filler. Many researching literature shows. The mechanical properties of epoxy resin composites are strengthened by adding filler to epoxy resin to improve the load bearing capacity of epoxy resin composites during friction. At the same time, add filler to reduce the surface of epoxy resin and the friction pair of duality between the caking property, and in the process of friction is easy to form transfer film, transfer film to isolate the direct contact of the friction surface, composite materials and the dual friction between surfaces into composite materials and transfer film, the friction between improved tribological condition between the friction pair, reduce the friction coefficient and wear rate of epoxy resin composites multiple fillers can improve the wear resistance and reduce the friction coefficient of epoxy resin composites, so that the epoxy resin composites have better tribological properties.

Study on the Morphology Characteristics of Epoxy Resin of Composite Insulator under Acid-heat Condition

Whether epoxy resin is degraded or not in composite insulators is the most direct criterion to distinguish Decay-like fracture from brittle fracture and normally mechanical fracture. During the actual operation of composite insulators, the nitric acid produced by partial discharge and abnormal heating will accelerate the degradation and deterioration of epoxy resin of composite insulators. In this paper, the experimental platform under acid-heat condition is built by using heating furnace, grinding bottle and serpentine condensation tube, and the acid-heat deterioration experiments are carried out under 60 °C (3 mol/L and 5 mol/L) and 80 °C (3 mol/L and 5 mol/L) condition. The macroscopic and microscopic morphologies of epoxy resin after acid-heat deterioration are analyzed, and the morphology changes of epoxy resin under the influence of acid-heat coupling field are studied. Firstly, it is concluded that the epoxy resin changes directly from colorless to light yellow, and then from light yellow to dark yellow under the influence of acid-heat deterioration. In addition, in the early stage of deterioration, the bulge on the surface of epoxy resin decreases gradually. Meanwhile, the maximum height difference and standard deviation of the surface profile of epoxy resin also gradually decreases, and the roughness decreases. In the later stage of deterioration, cracks appear on the surface of epoxy resin and some epoxy resins fall off. At the same time, the maximum height difference and standard deviation of surface profile of epoxy resin increases.

Investigation of physical, flexural, and dynamic mechanical properties of alumina and graphene nanoplatelets filled epoxy nanocomposites

AbstractIn this research, the different weight percentages of alumina and graphene nanoplatelets were homogeneously dispersed in the epoxy resin by a sonication and ball milling mixing process. The effect alumina and graphene nanoplatelets filled epoxy nanocomposites of physical, flexural, and dynamic mechanical properties were investigated. The epoxy nanocomposites showed a significant enhancement of 43.5% flexural strength and 29.5% flexural modulus for the combined filler loading of 2 wt% of alumina and 0.5 wt% of graphene nanoplatelets sample (EA2G0.5) than the neat epoxy. The EA2G0.5 epoxy nanocomposites sample showed an enhancement of 68.1% for the storage modulus. The loss modulus peak shifts toward the right side than the neat epoxy, which is showing better thermal stability of the composite. The differential scanning calorimetry technique was used to study the curing characteristics of the epoxy and epoxy nanocomposites. The scanning electron microscopy images of a fractured surface of the neat epoxy and alumina and graphene nanoplatelets filled epoxy nanocomposites showed the dispersion of the fillers, which is the sole cause of the enhancement of flexural properties. In general, these developed nanocomposites are suitable to be used as parent material in electrical and electronic packaging applications.

Bio-inspired robust superhydrophilic/underwater superoleophobic coating with lubrication, anti-crude oil fouling and anti-corrosion performances

The crude oil spill accidents cause numerous crude oil contaminations and oily wastewater. Underwater superoleophobic coating has excellent ability to resist crude oil contamination and separate oily wastewater. But it’s hard to keep stable performance against the physical or chemical attack. Herein, a robust underwater superoleophobic coating was fabricated by spraying the mixture of polyethyleneimine (PEI) and TiO2 on epoxy resin (E44) surface. Besides the good physical and chemical stability, the coating exhibited better drag reduction, anti-fouling performance and anti-corrosive performance in water compared with the commercially hydrophilic coating. The stainless steel mesh (SSM), coated by the E44/PEI/TiO2 coating, could separate different oil-water emulsions with a high oil rejection greater than 99.7%.

Study on discharge characteristics and improving surface hydrophobicity of epoxy resin by nanosecond pulse excited argon/hexamethyldisiloxane jet array

Surface flashover of insulating materials induced by pollution and moisture environment is one of the main reasons for the damage of power system and electrical equipment. The improvement of the insulating materials surface hydrophobicity is key important, which can prevent the pollutants and water attachment, and enhance the insulating performance. In this paper, the super-hydrophobic film is formed on the surface of epoxy resin by a one-dimensional (1D) argon (Ar) jet array driven by nanosecond pulse power supply with hexamethyldisiloxane (HMDSO) addition. The influences of the processing time and HMDSO content on the epoxy resin surface hydrophobicity are investigated. It shows that with 0.04 % HMDSO, the jet array achieves a best hydrophobic treatment effect on the epoxy resin surface. After 60 s treatment, the apparent contact angle (ACA) of the epoxy resin surface increases from 60.3° of the untreated surface to 150.0°. The wettability of epoxy resin surface does not change too much as the treatment time beyond 60 s. The maximum ACA value 153.4° appears at 120 s processing time, which is just slightly higher than that of 60 s treatment time. The epoxy resin surface morphology and chemical feature before and after plasma processing are characteristics by the scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infra-red spectroscopy and X-ray photoelectron spectroscopy. It shows that the treated epoxy resin surface is covered with dense coral like particles in nanoscales, the original C=O、C-H and other organic functional groups are replaced by Si-(CH3), Si-O-Si and other silicon containing groups, and the Si content increases from 0.4% to 28.0%. The experimental results provide important references to develop jet array as an efficient tool to enhance the surface hydrophobicity and insulating performance of insulating materials.

Finite element and experimental studies on the machining process of polymer/graphene nanoplatelet nanocomposites

Polymer matrix composites reinforced with graphene derivatives are receiving increasing attention in academia and industry. For future applications, however, the machinability of these materials needs to be understood. This study introduces the cutting mechanism of graphene nanoplatelet (GNP)-reinforced polymer matrix composites using the finite element (FE) method, where the cutting process is investigated in terms of stress distribution, chip formation, and surface morphology. The results show that the machined surface of polymer/GNP material has more defects compared with plain polymer and the presence of the GNPs influences the chip profiles. Small cavities/cracks can be found in about 40% area of machined surface in the epoxy/GNP, while no small cavities/cracks are found on the machined surface of plain epoxy. The machining conditions of epoxy/GNP should be selected in such a way that the material removal deformation falls in the regime without viscoplastic scaling/tearing and brittle cracking. The cutting model for polymer/GNP is validated with the machining experiments.

Plasma Surface Modification of Epoxy Polymer in Air DBD and Gliding Arc

We studied the epoxy polymer surface modification using air plasma treatment in a Gliding Arc (GA) plasma reactor and a pulsed Dielectric Barrier Discharge (DBD). We employed optical emission spectroscopy (OES) measurements to approximate the vibrational and rotational temperatures for both plasma sources, as well as surface temperature measurements with fiber optics and IR thermography to corelate with the corresponding hydrophilization of the epoxy material. Water contact angle measurements revealed a rapid hydrophilization for both plasma sources, with a slightly more pronounced effect for the air DBD treatment. Ageing studies revealed stable hydrophilicity, with water contact angle saturating at values lower than 50°, corresponding to a >50% decrease compared to the untreated epoxy polymer. ATR-FTIR spectroscopy studies showed an additional absorption band assigned to carbonyl group, with its peak intensity being higher for the DBD treated surfaces. The spectra were also correlated with the surface functionalization via the relative peak area ratio of carbonyl to oxirane and benzene related bands. According to SEM imaging, GA plasma treatment led to no apparent morphological change, contrary to DBD treatment, which resulted in nano-roughness formation. The enhanced surface oxidation as well as the nano-roughness formation on epoxy surface with the air DBD treatment were found to be responsible for the stable hydrophilization.

Microbial Depolymerization of Epoxy Resins: A Novel Approach to a Complex Challenge

The objective of this project is evaluating the potential of microbes (fungi and bacteria) for the depolymerization of epoxy, aiming at the development of a circular management of natural resources for epoxy in a long-term prospective. For depolymerization, epoxy samples were incubated for 1, 3, 6 and 9 months in soil microcosms inoculated with Ganoderma adspersum. Contact angle data revealed a reduction in the hydrophobicity induced by the fungus. Environmental scanning electron microscopy on epoxy samples incubated for more than 3 years in microbiological water revealed abundant microbiota. This comprised microbes of different sizes and shapes. The fungi Trichoderma harzianum and Aspergillus calidoustus, as well as the bacteria Variovorax sp. and Methyloversatilis discipulorum, were isolated from this environment. Altogether, these results suggest that microbes are able to colonize epoxy surfaces and, most probably, also partially depolymerize them. This could open promising opportunities for the study of new metabolisms potentially able depolymerize epoxy materials.

Shear adhesive strength between epoxy resin and copper surfaces: a density functional theory study.

Adhesive strength varies greatly with direction; various adhesion tests have been conducted. In this study, the shear and tensile adhesive strength of epoxy resin for copper (Cu) and copper oxide (Cu2O) surfaces were estimated based on quantum chemical calculations. Here, density functional theory (DFT) calculations with dispersion correction were used. In the tensile process, the entire epoxy resin is peeled off vertically, whereas in the shear process, a force parallel to the adhesive surface is applied. Then, a bending moment acts on the adhesive layer, and a total force (stress) inclined at an angle θ with respect to the adherend surface is applied to the adhesive interface. We computed adhesive stress-displacement curves for each θ exhaustively and discussed the changes. When θ equals 90°, it corresponds to a tensile process. As θ decreases from 90°, the shear adhesive stress on both surfaces decreases slowly. When θ is less than 30°, the constraint to the surface causes periodic changes in the adhesive stress curves. The constraint to the Cu2O surface is especially strong, and this change is large. This periodicity is similar to the stick-slip phenomenon in tribology. To further understand the shear adhesive forces, force decomposition analysis was performed, revealing that the periodicity of the adhesive stress originates from the DFT contribution rather than the dispersion one. The procedure proposed in this study for estimating shear adhesive strength is expected to be useful in the evaluation and prediction of adhesive and adherend properties.

Partial discharge measurement and analysis under lightning impulse superimposed DC voltage in SF6 gas

The presence of lightning impulses (LIs) on the DC waveform can seriously influence the insulation performance of a GIL system. The waveshape can be a superposition of the DC and impulse waveform. In this study, the behaviour of partial discharge (PD) on an epoxy surface is investigated under DC and LI superimposed voltage in SF6. The lightning impulses with different polarities are superimposed on the epoxy surface under both positive and negative DC voltages, respectively. Positive lightning impulses are superimposed on a negative DC voltage with a 90% of the partial discharge inception voltage (PDIV) magnitude. The number and amplitude of the PDs are used to evaluate the insulation performance. The experimental results show that the LI with a different polarity applied to DC can excite the PDs on the epoxy surface. The excitation effect of positive LI superimposed on negative DC is more significant. According to the impulse amplitude and PD characteristics, the influence of superimposed LI on PD excitation can be divided into three stages. As the superimposed LI increases, the amplitude of the excited PD increases gradually, while the PD number first increases and then decreases. This study is expected to provide reference for manufacture and protection of power equipment.

Mechanism on improved surface flashover performances in vacuum of epoxy resin using fluorocarbon plasma treatment

To improve the insulation, strength of materials is a permanent topic in the fields of high voltage and insulation, and surface insulation is one of the difficulties. Research shows that the surface fluorination by a non-equilibrium plasma is a promising method to enhance the surface flashover characteristics of insulating materials. However, the determinants of flashover characteristics are so many that the mechanism is not well known. This paper aims to find out the reasons for the surface insulation improvement and optimise the plasma process parameters. The epoxy resin surfaces are modified by a fluorocarbon plasma, and the flashover voltages in vacuum and secondary electron emission yield are tested experimentally. Combined with the state of the art and the authors' previous work, the mechanism of improved surface flashover performances is investigated in depth from three aspects: the plasma process parameters, the surface physical and chemical properties and the surface electrical performances. A comprehensive understanding of the mechanism is concluded, of which the whole processes from the plasma surface modification of materials to the surface insulation performances are taken into account. It is hopeful to promote the practical applications of plasma fluorination in electrical engineering through the findings of this paper.

Corrosion Performance and Rust Conversion Mechanism of Graphene Modified Epoxy Surface Tolerant Coating

A graphene modified epoxy surface tolerant coating was prepared, and the corrosion performance and rust conversion mechanism of the prepared composite coating on rusty carbon steel substrate was investigated. Scanning electron microscope (SEM), X-ray powder diffractometer (XRD), and infrared (IR) spectrum were used to confirmed the iron rust conversion performance by the reaction of phytic acid and rust. electrochemical impedance spectroscopy (EIS), polarization curve, and salt spray test were used to evaluate the corrosion resistance of low surface treatment coatings. Results indicated most of the rust were dissolved and transformed with the reaction of phytic acid and rust on the rusty carbon steel; graphene could effectively improve the compactness and protective performance of the epoxy surface tolerant coating.