Epoxy Adhesives Research Articles

Experimental evaluation of interface adhesion of a flax fiber composite patch with epoxy and polyurethane adhesives for the reinforcement of steel structures

Using fiber-reinforced composite patches for repairing damaged structures made of metal or/and concrete is an interesting and widely available solution on the market using synthetic materials. These repairing patches are bonded on the structures’ surfaces to increase their strength against internal stresses, as well as protect them from external physico-chemical attacks, thereby limiting crack propagation. Natural fibers offer a potential alternative to replacing glass or carbon fibers commonly used for bonded repair patches. Similarly, bio-based polymers represent an important sustainable alternative for partially or entirely replacing the petroleum-based polymers. In this study, an epoxy matrix reinforced with flax fiber is proposed as the material for the patches, and bonded to a steel plate using four different types of adhesive materials, including a castor-oil derived polyurethane resin. Floating roller peel tests were performed to assess the adhesion and viability of these new patches. The resulting peeling loads and fracture surface analysis are presented. Polyurethane demonstrates promising performance for epoxy-to-steel joints, but major improvements of the bio-based polyurethane application process and curing conditions may be necessary for its successful industrial implementation.

An experimental study for using nano-alumina to improving mechanical properties of epoxy resin for assembling glass artifacts

Purpose This study aims to assess the efficacy of nano-alumina (nano-Al2O3) in improving the performance of epoxy adhesives used to assemble archaeological glass. The conservators face a significant problem in assembling this type of artifact. Therefore, the assembling process is considered one of the important stages that must be taken care of to preserve these artifacts from damage and loss. Design/methodology/approach To evaluate the stability of adhesives, the samples were subjected to artificial aging under varying environmental conditions. Some investigative techniques and mechanical testing were used in this study to evaluate the selected materials. It includes a transmission electron microscope, X-ray diffraction, visual assessment, digital microscope, scanning electron microscopy (SEM), color change and tensile strength test. Findings The visual evaluation and the digital microscope results showed that the epoxy/nano-Al2O3 greatly resisted artificial aging. Although slight yellowing was present, it did not significantly affect the general appearance of the samples. On the other hand, the pure epoxy sample showed cracks of different sizes on its surface due to aging, as evidenced by SEM examination. Furthermore, epoxy/nano-Al2O3 has a better tensile strength (11.27 MPa) and slight color change (ΔE = 2.06). Originality/value The main objective of the experimental study was to identify appropriate adhesive materials that possess key properties such as non-yellowing and improved tensile strength by conducting various tests and evaluations. Ultimately, the goal was to identify materials that could serve as effective adhesives for assembling the archaeological glass.

Experimental Investigation of Mechanical and Physical Properties on Epoxy Resin with Wood Timber for Furniture Application

ABSTRACT Composites are attracting the attention of researchers nowadays because of their strength-to-stiffness ratio. The development of wood particle composites reinforced for practical purposes has been successfully attempted. This paper focuses on the application of an epoxy/hardener ratio with wood particle-reinforced polymers to develop high-strength wood composites. The percentage of wood particles in the composition varied as follows: 5, 15, and 25 wt%, with epoxy/hardener ratios of 5:0.3, 10:1, and 5:0.8. Appropriate surface modifications were made by different treatments with 0.6, 0.8, and 1 g of NaOH in 10 liters of distilled water and 0.2% KMnO4 for better adhesion of particles and epoxy. Flexural strength, impact strength, water absorption, and SEM were investigated. Nine experiments were investigated based on the Taguchi orthogonal array blend design. The composite was successfully fabricated using the conventional hand lay-up technique. The highest mean S/N ratio considered was found for wood content composition (15%), epoxy resin to hardener ratio (10%), and NaOH (1%), i.e. the main factors affecting the mean flexural and impact strength were the wood particle contents in the matrix. Water absorption was investigated. Water absorption was found to increase with wood particle content.

A Comparative Study on the Properties of Rosin-Based Epoxy Resins with Different Flexible Chains

This study aims to reveal the effects of flexible chain lengths on rosin-based epoxy resin’s properties. Two rosin-based epoxy monomers with varying chain lengths were synthesized: AR-EGDE (derived from ethylene glycol diglycidyl ether-modified acrylic acid rosin) and ARE (derived from acrylic acid rosin and epichlorohydrin). Diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) with different flexible chain lengths were used as curing agents. The adhesion, impact, pencil hardness, flexibility, water and heat resistance, and weatherability of the epoxy resins were systematically examined. It was found that when the flexible chains of rosin-based epoxy monomers were grown from ARE to AR-EGDE, due to the increased space of rosin-based fused rings, the toughness, adhesion, and water resistance of the rosin-based epoxy resins were enhanced, while the pencil hardness and heat resistance decreased. However, when the flexible chains of curing agents were lengthened, the resin’s performance did not change significantly because the space between the fused rings changed little. This indicates that the properties of the rosin-based resins can only be altered when the introduced flexible chain increases the space between the fused rings. The study also compared rosin-based resins to E20, a commercial petroleum-based epoxy of the bisphenol A type. The rosin-based resins demonstrated superior adhesion, water resistance, and weatherability compared to the E20 resins, indicating the remarkable durability of the rosin-based resin.

A high-throughput technique to evaluate the probability distribution of strength of adhesively bonded joints after moisture absorption

ABSTRACT The reliability of adhesive bond strength influences the applicability of structural adhesives in industries. The statistical probability distribution of the strength of adhesive joints is an essential indicator when designing and choosing adhesives. In this study, we experimentally studied the probability distribution of the strength of adhesive joints. The strength data were collected using a novel high-throughput technique consisting of a sample preparation method and shear testing device. Numerous cylindrical butt shear-joint specimens were prepared by mechanical machining and tested using a self-developed shear testing device. The effect of moisture absorption by the adhesive was specifically considered. The probability distribution of the shear strength of the epoxy adhesive joints was characterized using five probability distribution functions: Normal, Lognormal, Exponential, Weibull, and Gamma. Quantile – quantile plots were employed to determine the suitability of each distribution function. The results suggested that the Weibull and Normal distributions were best suited for describing the probability distribution of the strength of the epoxy adhesive joints. The Weibull distribution is particularly suitable for brittle epoxy adhesives. Moisture absorption reduced both the mean and variance of the shear strength, which might be attributed to the plasticization of the adhesives. The high-throughput method proposed in this study significantly improved the efficiency of testing adhesive joints. It not only contributes to the study of the strength distributions of adhesive joints but also helps to shorten the research and development cycle of new adhesives by facilitating rapid strength evaluation.

Chemical Structure Evaluations of Amine Hardeners to Ensure and Predict the Performance of Wet Adhesion of Epoxies

Abstract The relationship between the chemical structure and performance of a water-sorbed epoxy adhesive (wet adhesion) provides fundamental data for epoxy adhesives for application in wet and underwater environments. However, data on the effect of the chemical structure on wet adhesion remains insufficient. This study systematically examined the wet adhesion strengths of epoxies comprising bisphenol A diglycidyl ether and various amines. The use of numerical parameters quantifying the features of the chemical structure and physicochemical properties via theoretical calculations to analyze the correlation between wet adhesion and the chemical structure of amine yielded clear linear relationships. This enabled the extraction of the amine molecular structural features that were superior in wet adhesion, in addition to quantification of the certainties of the features contributing to the physical properties. Furthermore, a prediction model for wet adhesive strength was prepared using machine-learning least absolute shrinkage and selection operator regression analysis. The model exhibited a reasonable accuracy, even using only 14 experimental values, and its effectiveness was verified experimentally. This process facilitates the rational design and selection of amine hardeners for preparing epoxies with excellent performance in wet conditions and underwater environments.

Robust Dynamic Epoxy Adhesives with High Environmental Tolerance Enabled by the Coordination of Small-Molecule Coupling Agents with Boroxine

Robust Dynamic Epoxy Adhesives with High Environmental Tolerance Enabled by the Coordination of Small-Molecule Coupling Agents with Boroxine

Effect of the Presence of a Silane Coupling Agent on Reaction Kinetics of Cationic Thermopolymerization of Epoxy Resin Adhesive

The effect of the presence of a silane coupling agent containing different functional groups on the reaction kinetics and physical properties of epoxy resin generated via cationic thermopolymerization was investigated. The kinetics of cationic polymerization of epoxy resin was studied using a nonisothermal DSC method. The polymerization is propagated by activated chain end (ACE) and activated monomer (AM) processes. With an increase in silane content, the ACE apparent activation energy first decreased and then increased, while the AM apparent activation energy increased. Moreover, the shear strength, coefficient of linear thermal expansion, gelation time, environmental testing of damp heat, and steady state with varied contents of silane coupling agents were evaluated. The results indicated that the presence of a silane coupling agent has more adhesion and lower water absorption than pure EP. The coefficient of linear thermal expansion and gelation time increased with the increase in silane content, while the water absorption decreased with the increase in silane content. Comparing the overall performance of three silane coupling agents used in the research, the curing system obtained by blending with vinyltrimethoxysliane (VTS) is a much better option for practical application as an adhesive.

Polydopamine/Silane Composite Coating on Electrolytic Copper Foil as Epoxy Adhesion Promoter and Corrosion Inhibitor

Polydopamine/Silane Composite Coating on Electrolytic Copper Foil as Epoxy Adhesion Promoter and Corrosion Inhibitor

Influence of cure time, temperature, and moisture on mechanical properties of a fast cure adhesive for post-installed rebar application

The use of chemical adhesives to post-install rebars and anchor elements in existing concrete structures has been widely developed in the previous years. The progress of the adhesive market in civil engineering has led to various commercialized structural adhesives targeting post-installation of steel elements in existing concrete structures. Regardless of the diversity of chemistries of adhesive types on the market today, existing mechanical theoretical descriptions and product evaluation methods are common to all adhesives.This paper presents the influence of moisture, cure time and temperature on the tensile behavior (resistance and stiffness) of a fast cure industrial adhesive used for post-installed rebar application. Results are compared to other studies on slow cure (epoxy) adhesives also used for the same application. The influence of temperature of the initial cure exothermic reaction is quantified through thermal measurements. Tensile tests performed at different times with samples stored at 50 % RH and 100 % RH show increase of strength and stiffness with cure time and highlighted the weakening effect of water. Finally, tensile tests performed directly at high temperatures (50 °C, 80 °C and 110 °C) on samples that had been previously pre-heated at these same temperatures or below were performed. Material strengthening caused by thermally induced post-cure (as observed for step polymerized products designed for the same application) is not distinguishable for the fast-cure adhesive. The progressive decrease of strength and stiffness with temperature appears unchanged by the thermal history.

A study on the bond strength of interface between post-fire concrete and different epoxy resin adhesives

In order to investigate the influences of temperature that concrete has undergone on the resin/concrete interface bonding performance for different epoxy resin adhesives, 40 tensile specimens and 24 three-point bending specimens were heated to 200, 300, and 600 ℃, respectively. After natural cooling, resin was injected to form tensile specimens and sandwich specimens, which were subjected to pull-out tests and three-point bending tests, respectively. The interface bond-separation constitutive relationship was obtained to study the influence of fire temperature and different epoxy resin adhesives on the properties of the resin/concrete interface bonding. The results showed that the reinforcement of high-temperature concrete with different permeable epoxy resin adhesives caused the crack initiation load, interface strength, and fracture energy of the concrete/resin interface to increase slightly and then decrease sharply as the temperature of the concrete in the fire increased. When the fire temperature was 200 ℃, the peak value of the bonding performance of high-temperature concrete/resin interface was higher than that at room temperature.

Impact of 3D-printed PLA coatings on the mechanical and adhesion properties of AM60 magnesium alloys

This article investigates the impact of PLA (Polylactic Acid), an emerging bioplastic coating, fabricated with an additive manufacturing method (3D printing) on AM60 magnesium alloys. In addition to tensile testing, the adhesion of PLA on magnesium alloys with two epoxy and polyvinyl pyrrolidone adhesives was checked with the pull-off experiment. The strength of the bond between PLA and AM60 magnesium alloy was tested using two different adhesives, polyvinyl pyrrolidone and epoxy glue. The polyvinyl pyrrolidone adhesive resulted in an adhesion strength of 0.3 ± 0.02 MPa, whereas the epoxy glue resulted in a much stronger adhesion strength of 4.29 ± 0.71. Coating the AM60 magnesium alloy with PLA led to enhancements of 5.26 % in the yield stress (Syt), 7.79 % in the ultimate stress (Sut), 2.40 % in the elongation, and 2.34 % in the elastic module, as compared to the uncoated specimen. The fracture surface was also checked with FESEM (field-emission scanning electron microscopy) images. It was found that the fracture type for AM60 magnesium alloys with and without PLA coatings was brittle under tensile loading.

Assessment of the mechanical behavior of bonded glass-to-glass transparent epoxy adhesive joint at elevated temperatures for load-bearing elements

Glass is increasingly used as a structural material in buildings, not only for enclosing spaces but also for bearing loads. To meet architect requirements for a uniform structure without appearance disturbance, adhesively bonded joints are preferred over mechanical fasteners. However, in the construction industry, most technical guidelines cover only soft structural silicone sealants, while stiffer adhesives like epoxy resins are not considered. Alternatively, the specific transparent epoxy adhesives offer a high potential for bonded glass assemblies, enabling thinner joints and a fully transparent junction. Indeed, under real service conditions, elevated temperatures are one of the worst factors affecting the mechanical properties of structural bonded joints. Therefore, in this paper, an experimental program was conducted to evaluate the performance of transparent bonded glass joints with epoxy resin over a wide range of temperatures. Tensile and shear tests were performed on bulk-cured adhesive samples and bonded glass-to-glass block shear specimens respectively, at room temperature (RT), 40, 60, and 80 °C. The differences in surface characteristics such as roughness, wettability, and surface free energy (SFE) between both glass sides were examined. The results showed that tensile and shear strengths decreased with increasing temperatures. Furthermore, the shear strength was influenced by the surface properties of the glass sides. At all tested temperatures, the rougher bonded glass side specimens revealed higher shear strength coupled with a mixed failure while a loss of adhesion characterised the smoother glass surfaces.

Crater array generated on Al alloy surface by nanosecond laser: Surface characteristics and bonding strength

The strength of aluminium (Al) alloy adhesive joints is critical for aerospace and automotive applications. This work uses an infrared nanosecond laser to create a crater array (CA) and thereby modify the substrate bonding area and enhance the strength of 7075-T6 Al alloy joints bonded by epoxy resin adhesives. We study how the parametrisation (crater overlap ratio β and pulse energy density Ф) of the CA affects the surface texture features (surface roughness Sa and fractional increase Sdr in surface area), wettability, chemical properties, and shear strength τ. The mechanism by which CA affects τ is revealed by the surface characteristics and failure modes. Sandblasted specimens were used as a reference. The results show that, for laser treatment, Sdr, Sa, and τ are closely related to β but not to Ф. When β = 30 % or 60 %, the CA surface is superhydrophilic. Regardless of β and Ф, the substrate absorbs carbon-containing pollutants from the air, so that the contact angle of the CA surface gradually increases over time until, 15 days after the laser treatment, the CA surface becomes hydrophobic. Zn, Cu, and Fe are uniformly distributed over the alloy surface, whereas C, O, Mg, and Al are unevenly distributed. The C content decreases with increasing β but is not correlated with Φ. The O content increases with the increasing β and Φ. When β = 30 %, the area of cohesive failure in the substrate bonding area is maximal. When β ≤ 0, the untreated area outside the craters is susceptible to adhesive failure. When β ≥ 60 %, the substrate bonding area is covered by a thin layer formed by molten residue, which is susceptible to substrate failure. Laser treatment is more effective than sandblasting in modifying the texture, wettability, and chemical properties of the bonding area, which can further improve the bonding strength. The maximum strength of the bonded joint obtained by laser treatment is 26.89 MPa at Φ = 21.6 J/cm2 and β = 30 %, which is 16.2 % stronger than sandblasting.

Failure Study of BFRP Joints with Two Epoxy Adhesives under Hygrothermal Coupling.

Basalt Fibre Reinforced Polymer (BFRP)-bonded structures are lightweight, high strength, economical, and environmentally friendly, which is very advantageous in the civil sector. The aim of this paper is to provide a comprehensive account of the hygrothermal degradation and failure mechanisms of BFRP-bonded structures by comparing the residual properties of two epoxy adhesive BFRP single-lap joints after ageing for 240 h, 480 h, and 720 h in an extreme hygrothermal environment with pure water at 80 °C. The hydrophilicity and thermal stability of the two adhesives were firstly compared by water absorption and Thermogravimetric Analysis (TGA) tests, and the hygrothermal degradation of the molecular chains and the reduction in Tg were characterised by Fourier Transform Infra-Red (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC) curves. The failure strength and load-displacement curves of the two joints were then compared, and it was found that the strength and stiffness had different trends, while the paired t-test was used to demonstrate the correlation between the failure strength and the adhesive Tg, as well as the difference in the failure mechanisms of the two joints caused by the water absorption rate. The analysis of macrosections and Scanning Electron Microscope (SEM) images summarised the process and reasons for the transition of the failure mode from fibre tearing to hybrid failure, and finally, the changes in elemental concentration and O/C values were analysed by Energy Dispersive X-ray Analysis (EDX), which proved that the degree of hydrolysis could not be used as a judgement of the degradation degree of the joint alone, and provided data support for the application of the BFRP-bonded structure in the humid and hot environment.

A sustainable alternative? A comparative life cycle assessment of epoxy adhesives

AbstractIn response to the imperative of eco‐friendly material substitution, a comparative cradle‐to‐gate life cycle assessment (LCA) of two epoxy adhesives is presented: a traditional epoxy resin and an innovative self‐curing epoxy derived by epoxidizing poly‐beta‐myrcene (a constituent of Chios Mastic natural resin). Employing ReCiPe 2016 indicators and standard normalization, our study reveals that epoxidized poly‐beta‐myrcene outperforms conventional epoxy in 9 of 18 assessed midpoint indicators, with minimal impact in 7, and marginally higher impact in 2. The superiority of epoxidized poly‐beta‐myrcene extends to all three ReCiPe Endpoint protection areas. Atom economy and the E‐factor are also considered and related to the LCA results. Furthermore, the evaluation demonstrates epoxidized poly‐beta‐myrcene's remarkable environmental favorability compared to a literature bio‐based epoxy across multiple CML‐IA‐baseline indicators. In summary, epoxidized poly‐beta‐myrcene emerges as a promising, ecologically sensitive alternative to current conventional and bio‐based epoxy options.

Effect of incorporating carbon- and silicon-based nanomaterials on the physico-chemical properties of a structural epoxy adhesive

Various carbon-based (i.e. carbon nanofibres (CNF), cellulose nanocrystals and graphite nanopowder) and silicon-based nanomaterials (i.e. silica nanopowder and MMT nanoclay) were incorporated into neat structural epoxy (NE) adhesive (Sikadur®-30) at 0.5, 1.0 and 1.5% by weight and mixed using a simple and cost-effective approach to produce the nanomaterial-modified epoxy adhesives (NMEAs). The impact of incorporating these nanomaterials into the NE on its chemical composition was investigated using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. X-ray diffraction (XRD) measurements were also used to identify the changes in the physical structure (i.e. the degree of crystallinity) that may occur in the NE with the addition of nanomaterials. Furthermore, the microstructure of the NE and NMEAs (in terms of the degree of dispersibility of the nanoparticles through the matrix) was investigated through scanning electron microscopy (SEM) analysis. A porosity analysis was also conducted across all samples. The results obtained from various tests were correlated to investigate the changes that occurred in the different properties of the matrix and the corresponding nanocomposites effectively and more critically. The SEM images showed some particle agglomeration, which increased with increasing wt%. An increase in the % porosity ratio of all nanocomposites over that of the NE was also observed, accompanied by a decrease in crystallinity compared to the NE. As per the FTIR spectroscopy, the chemical bonds in the NE and carbon-based NMEAs were observed to have different intensities, which were changed in the NMEAs, with the type and wt. % of the nanomaterials. No new bonds were formed by incorporating any of the nanomaterials (i.e. carbon- and silicon-based), except when adding 1.0 wt% CNF, where a bond at 1710 cm−1 was observed indicating a new CO stretching bond. As shown by Raman spectroscopy, all CNF and graphite NMEAs exhibited higher ID/IG values than those of the corresponding pristine materials.

Use of Carbon and Basalt Fibers with Adhesives to Improve Physical and Mechanical Properties of Laminated Veneer Lumber

Climate change is one of the main factors influencing the research of environmentally friendly materials. This is why the use of engineering fibers as a reinforcement technique in wood, in order to increase its mechanical properties, has recently been investigated. This research presents the results obtained from the use of carbon and basalt fiber fabrics as a reinforcement for microlaminated Radiata Pine wood panels at a laboratory scale using the adhesives epoxy resin and polyvinyl acetate. Tests were carried out in comparison to the control boards, relating the physical properties obtained in terms of thickness swelling by 48 h-water immersion with a decrease of 19% for the polyvinyl acetate and carbon fiber matrix reinforcement, about the mechanical properties evaluated, a better performance was obtained for the epoxy resin and carbon fiber matrix reinforcement and in terms of flexural stiffness and strength (in flatwise), tensile strength and Janka hardness, with an increment of 31%, 38%, 56% and 41%, respectively.

Torsional behaviour of RC beams strengthened by NSM GFRP bars

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is an innovative, serviceable, and beneficial method for strengthening reinforced concrete (RC) structures. Previous studies have proven that the epoxy-resin bonded NSM FRP method effectively achieved shear and flexural strengthening. However, only a few researches have employed this technique for improving torsion but, no research has been conducted on the use of NSM with GFRP bars and epoxy adhesives. This study investigates the behavior of RC beams subjected to combined torsion when they have been enhanced with NSM GFRP U-shaped and closed stirrups with different overlap sites. Four RC beams with dimensions of (150×250×2000) mm (width X depth X length) were considered in the experimental tests. One RC beam is not strengthened and used as a control beam (CB), while three beams are enhanced with NSM GFRP bars in different shapes and overlap configurations. The findings of the tests in terms of twist angle_applied torque curves, the torque of initial cracking, the ultimate torsional carrying capacity, and the ultimate angle of twist were all recorded and evaluated. It has also been shown that a considerable improvement in the performance of RC beams in twisting can be achieved by using NSM GFRP stirrups. From the different NSM strengthening configurations used in the tests, results have demonstrated that beams strengthened by closed GFRP stirrups at the opposite overlap with 100 cm spacing outperformed other strengthened beams of about 181.5% compared to the CB. In contrast, the beam, strengthened by U-shaped GFRP stirrups with spacing at 200 cm, had the lowest torsional strength of about 48.1% relative to the CB.

Interfacial bond characterization of epoxy adhesives to aluminum alloy and carbon fiber-reinforced polyamide by vibrational spectroscopy

Vibrational spectroscopic technique has been utilized to investigate interfacial bonding chemistry of two epoxy adhesive products, XP0012 and XP5005F, on plasma-treated AA6061 and carbon fiber-reinforced polyamide 66 (CFRP-PA66) surfaces. The change in vibrational peak ratios was measured by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to deduce bonding mechanisms. Both adhesives showed strong crosslinking polymerization of hydroxyl- and amine-initiated epoxy ring opening on AA6061 surface, but on CFRP surface XP0012 formed a simple amide linkage by the reaction of surface hydroxyl groups and nitrile groups of curing agent, and XP5005F formed a crosslinked network by hydroxyl-initiated epoxy ring opening polymerization. The different interfacial bonding formation of two adhesives on CFRP-PA66 surface is attributed to additive effect. Addition of additives to epoxy adhesives (XP5005F) changed the interfacial bonding mechanism on CFRP-PA66 surface, rather forming hydroxyl-initiated epoxy opening crosslinking polymerization than a simple amide bond formation (XP0012). The interfacial bonding chemistry was also proved by addition of bisphenol A (BA) to a simplified model diglycidyl ether of bisphenol A/dicyandiamide (DGEBA/DICY) epoxy system. When BA was added to the model DGEBA/DICY system, epoxy ring gradually decreased on CFRP-PA66 surface, while without BA, DGEBA/DICY showed only decrease in a nitrile peak intensity in ATR-FTIR. The foregoing different types of interfacial chemical bonds at the adhesive/CFRP-PA66 interfaces can affect the lap shear behavior of the joint.