Type Epoxy Research Articles

Intrinsic flame-retardant epoxy resin composite containing schiff base structure with satisfied flame retardancy and mechanical properties

To solve the non-renewable and flammability of traditional epoxy composites, a new type of intrinsic flame-retardant epoxy (VH/GF) composite was fabricated from vanillin-based epoxy resin (VH) and glass fibre (GF). The T5% of VH/GF was higher than that of DGEBA/GF, and CY800 of VH/GF reached above 84 wt%. VH/GF obtained a limiting oxygen index as high as above 90 % and passed UL-94 V-0 rating. Compared with DGEBA/GF, the total heat release, total smoke production, maximal smoke density of VH/GF reduced by more than 72 %, 91 % and 81 %, respectively. The physical barrier of glass fibre and excellent char formation ability of VH endowed VH/GF composite with good condensed phase flame-retardant effect. When the mass ratio of matrix and glass fibre was 5:5, the storage modulus and glass transition temperature of VH/GF were 6.34 GPa and 205 °C, and its tensile strength and elongation at break were 348.36 MPa and 4.01 %. This work provides new research insights for bio-based epoxy resin in high-performance fire safety composites.

Experimental investigation on shear behavior of PVA-ECC keyed joints

Keyed joints play a critical role in ensuring the overall behavior of a precast concrete segmental bridges. However, these joints can exhibit poor shear capacity and durability as well as brittle failure. Polyvinyl alcohol fiber-reinforced engineered cementitious composites (PVA-ECCs) exhibit high shear strength and ductility as well as excellent fracture performance, making them attractive for use in the joints of segmental bridges. This study fabricated 16 Z-shaped specimens with number of keys (one, two, or three), concrete materials (normal concrete or PVA-ECC), and types (monolithic, epoxy, or dry) to investigate their failure modes, cracking loads, shear capacities, residual capacities, and shear stress–vertical displacement curves. The results indicated that the keyed joints exhibited shear failure at the root of a shear key, and an increase in the number of keys increased the residual strengths and ductility of both the dry and epoxy joints, but it had a negative effect on the shear strengths. When PVA-ECC was applied instead of normal concrete, the cracking resistance index for all joints improved significantly and the shear strengths and ductility of the monolithic and keyed epoxy joints increased. Generally, the shear strengths of the epoxy joints were 6.3–29.1% higher than those of the corresponding dry joints; however, the ultimate displacements of the epoxy joints were 46.6–72.4% lower. Finally, a method for calculating method of the shear capacities of keyed PVA-ECC joints was proposed and verified to accurately predict the behaviors of previously tested joint specimens.

High performance, self-healable and recyclable epoxy thermosets by integrating dynamic hindered urea bonds

During recent decades, intrinsic self-healable thermosetting materials by integrating dynamic covalent bonds (DCBs) have been widely used. In this study, through the molecular structure design, a flexible polyurethane curing agent based on hindered urea bonds (HUBs) was successfully prepared by the reaction of Hexamethylene diisocyanate trimer (THDI) and sterically hindered secondary amine, which was further used as a curing agent to cure epoxy resin. Therefore, a new type of epoxy thermosetting material (TBEP) with dynamic hindered urea bond was synthesized and the preparation and performance of TBEP were confirmed and characterized by infrared spectroscopy, thermomechanical analysis and thermal stability test. The results show that the HUBs are successfully integrated into the epoxy resin and endow the epoxy thermosets with brilliant self-healable, reprocessable, recyclable and shape memory properties. Simultaneously, the existence of flexible polyurethane chain in the crosslinking network effectively solves the brittleness problem of epoxy resin, promotes the mechanical performance of epoxy thermosets, and further broadens the its application field. This work provides a simple and efficient method to design flexible and self-healable epoxy thermosets with brilliant mechanical performance, which solves the contradiction between outstanding mechanical properties and self-healing ability of epoxy resin to some extent, and is environmentally friendly and cost-effective in acquisition and application.

Sandwich structures of aluminium skins and egg-box-shaped cores made with biobased foam and composites

Sandwich panels composed of aluminium skins and egg-box-shaped cores made with natural fibre composites are tested in three-point bending and evaluated statistically and through failure analysis. The corrugated cores are assessed with filled bio-based foam. In order to produce these sandwich panels, preliminary investigations on natural fibre composites, and their use as egg-box-shaped structures are conducted. A full factorial design is performed to assess the effects of fibre reinforcement (sisal or coir) and polymer matrix types (epoxy or castor oil) on the physical-mechanical properties of flat composite laminates. These composites are also used to manufacture the egg-box shaped structures in different sizes, which are characterized under compression testing. A new analytical approach called RJS Method is used to determine the flexural and shear modulus of the proposed sandwich panels and estimate the shear contribution. The results reveal that flat laminated composites and their corresponding egg-box shaped cores, composed of sisal fibres and epoxy polymer, achieve higher absolute and specific mechanical properties. The corrugated core also leads to sandwich panels with higher mechanical properties, increasing the skin and core shear stresses by up to 60 and 76%, respectively, compared to the coir fibre castor-oil cores. The failure modes of the sandwich panels are limited to the core and are chronologically established through foam tearing, foam-egg-box shaped composite debonding, and final egg-box cell-wall flattening. The findings demonstrate that the sandwich panel based on egg-box shaped core made from natural resources is feasible for scaling up in different structural applications.

Understanding the effect of solid lubricants on scratch behavior in epoxy resins: An experimental and statistical approach

AbstractEpoxy resins inherently have low resistance to scratching. To increase the scratch resistance of epoxy resins, reinforcing solid lubricants into the resin is an option. For this purpose, in this study, polytetrafluoroethylene (PTFE) and graphite were reinforced in two different epoxy resins (rigid and toughened) at different reinforcement ratios (5, 10, and 15 wt%). The effects of solid lubricant reinforcement on the scratch behavior of rigid and toughened epoxy resins were examined both experimentally and statistically. Scratch tests were performed throughout a distance of 10 mm using a test apparatus under a load of 15 N and a scratch speed of 30 mm/min. Following the scratch tests, the COF (Coefficient of Friction) values, scratch hardness, scratch width, and depth of all samples were determined and compared to neat epoxy for each resin. In general, it has been determined that solid lubricant reinforcement at higher reinforcement ratios has a positive effect on the COF value (15 wt%). In the case of 15 wt% graphite reinforced rigid and toughened epoxy, a decrease of 15.90% and 17.77%, respectively, was obtained in the COF value compared to the neat epoxy. After the scratch tests, statistical analysis was performed according to RSM to support the experimental results, and ANOVA tables were obtained.Highlights Epoxy adhesives exhibit low scratch resistance. Examining the impact of PTFE and graphite reinforcement on scratch behavior. Two types of epoxy and varied reinforcement ratios (5, 10, and 15 wt%) were studied. Solid lubricant reinforcement to epoxy positively affected scratch behavior.

Mechanical and Thermal Analysis of Duroplastic Matrix Composites over a Range of Temperatures.

It is commonly acknowledged that polymer composites in service are often subjected to not only intricate mechanical loads but also harsh environmental conditions. The mechanical and thermal properties of five particular composites are explored here. The composites are composed of laminates of glass cloth type "E" sheet infilled with a duroplastic matrix. This is a thermoset polymer-epoxy resin with different molecular weights. The composites were fabricated by IZOERG company, which is based in Poland. The final articles were 1.5 mm thick by 60 cm long and 30 cm wide, with the glass layers arranged parallel to the thickness. Young's modulus and tensile strength were measured at room temperature. Using the thermal analysis of dynamic mechanical properties (DMTA), the values of the storage modulus and the loss modulus were determined, and the damping factor was used to determine the glass transition temperature (Tg). It was revealed that the nature of changes in the storage modulus, loss modulus, and damping factor of composite materials depends on the type of epoxy resin used. Thermal expansion is a crucial parameter when choosing a material for application in cryogenic conditions. Thanks to the TMA method, thermal expansion coefficients for composite materials were determined. The results show that the highest value of the coefficient of thermal expansion leads the laminate EP_4_2 based on brominated epoxy resin cured with novolac P. Duroplastic composites were characterized at cryogenic temperatures, and the results are interesting for developing cryogenic applications, including electric motors, generators, magnets, and other devices.

Influence of Interfacial Interaction Between Various Metal Substrates and Epoxies on Bonding Reliability Under High Temperture

The shift from gel encapsulation to epoxy encapsulation has been driven by the need to reduce the size of power modules. However, the dissimilar bond between the encapsulation epoxy and substrate is seen as a potential weak point. Previous studies have largely focused on the impact of epoxy materials on package reliability. Our prior research has highlighted the crucial role played by interfacial interactions between copper substrates and epoxy. In this study, we investigate the influence of interfacial interactions between three metal substrates (copper, Ag-plated copper, nickel-plated copper) and epoxy on the reliability of epoxy encapsulation under high temperature. Two types of epoxy (bisphenol A and cycloaliphatic) were used to encapsulate metal substrates. Encapsulated packages were subjected to a high-temperature storage test (HST) at 200°C for 1000 hours, and changes in bonding strength were measured. We then analyzed the fracture surface and bonding interface at the nanoscale. Our results indicate that substrate material has a significant impact on the reliability of epoxy encapsulation. Both epoxies exhibited the highest initial bonding strength with copper, followed by Ag-plated copper and nickel-plated copper. After HST, we found that the catalytic effect of metals caused the epoxy in contact with the metal substrate to decompose. The decomposition was most significant in epoxy in contact with Ag, followed by copper, which resulted in a significant drop in bonding strength. In contrast, epoxy in contact with nickel showed little decomposition and only little change in bonding strength. These findings will greatly benefit power module design.

Effect of hygrothermal conditioning on compressive strength after impact in carbon fiber/epoxy composites

AbstractCarbon fiber‐reinforced polymers have been widely applied in structural parts and components in several sectors, in addition to being constantly used in environments with the presence of humidity and high temperatures, which can affect their density, hardness, and rigidity. In this work, the influence of hydrothermal conditioning on carbon fiber (CF)/epoxy composites was investigated using three types of epoxy resin and two different CF fabric reinforcements, that is, plain weave and eight harness satin (8HS) arrangements. The CF/epoxy composites were subjected to compression after impact (CAI) test by 28 and 40 J energy and then exposed to hydrothermal conditioning for 8 weeks. After the CAI tests, the visual analysis of all composites presented microbuckling mechanisms. The composites tested with 40 J energy absorbed only 2% more moisture compared with the other composites, nonimpacted, and tested with 28 J, indicating that the impact damage did not cause delamination between the layers of the composites, which could facilitate the absorption of water. All composites analyzed showed resistance to CAI even after exposure to humidity, with decreases ranging from 2.8% to 23.8% about the unconditioned specimens. The decrease in CAI also shows the influence of the type of epoxy matrix and the arrangement of the CF in fabrics.

Phosphorus acid: an asset for flame-retardant sustainable vitrimers

Three biobased epoxy resins from vanillic alcohol, linseed oil and cardanol were crosslinked with phosphoric acid to prepare vitrimers.

Investigation of the kinetics of heat treatment of epoxy polymers

The study examines the effect of the concentration of modifiers (BDI) on the annihilation characteristics of cured epoxy polymers using the positron annihilation method. The results show that both the concentration and size of microcavity defects decrease, which can be explained by the formation of densely sewn areas due to the production of additional bridges. The supramolecular structure of the formed epoxy polymer is discussed, with the identification of several distinct areas, including polymer globules formed by stacking chains of simple polyester macromolecules around polymerization centers, and the interglobular space consisting of the ends of macro chains and low molecular weight products. The end groups of polymerization-cured epoxy polymers, such as double bonds of the vinylidene type, hydroxyl and unreacted epoxy groups, create conditions for the splitting of BDI in the interglobular space. The study also demonstrates that at optimal concentrations of modifiers, there is a decrease in the radius and concentration of micropore defects, as well as a general decrease in the proportion of free volume. The curing processes of epoxy polymers and their heat treatment in the presence of modifiers are investigated, with BDI having a significant effect on the formation of the epoxy polymer structure.

Examination of the relationship between variants in the gene region encoding soluble epoxy hydrolase enzyme hydrolytic activity and type 2 diabetes

Examination of the relationship between variants in the gene region encoding soluble epoxy hydrolase enzyme hydrolytic activity and type 2 diabetes

Application of 3PHV60 Type Epoxy Resin for the Repair of Timber Structures

This article deals with the issue of repairing wooden structures with 3PHV60 type resin. The first step of the research was to understand the material properties of 3PHV60 resin. The information provided by the resin manufacturer and the tests based on fracture tests have greatly contributed to the proper study of the behaviour of this material. The use of resin for the repair of timber structures is discussed in relation to the type of internal forces.

New insights into brominated epoxy resin type WPCBs pyrolysis mechanisms: Integrated experimental and DFT simulation studies

Pyrolysis is a recycling technology for waste circuit boards (WPCBs) with a wide range of applications. In this research, the brominated epoxy resin (BER) type WPCBs were taken as the research object, and the optimal pyrolysis process parameters were determined. Combined with experiments and density functional theory (DFT) calculations, the pyrolysis gaseous generation pattern and product distribution of BER type WPCBs were analyzed, and the generation mechanism of phenol, bromide and other pyrolysis products was investigated in depth. The results of the study showed that the pyrolysis rate of WPCBs exceeded 95 % under optimal reaction conditions. In the initial phase of the pyrolysis of WPCBs, the BER's CO bonds and a portion of Ph-Br bonds will be broken, leading to the production of intermediates such propylene oxide, bisphenol A, isopropyl alcohol, tetrabromobisphenol A and HBr. Among them, propylene oxide can generate ethylene oxide through free radical reaction. In the second stage, intermediates such as bisphenol A undergo homolytic cleavage and radical addition to form phenols, bromides, alcohols, ketones and other pyrolysis products.

Curing and thermal degradation behavior of epoxy‐based vitrimers

AbstractEpoxy with associative covalent adaptable networks (CANs), called vitrimer, is reported to be promising to realize the recyclable utilization. The typical epoxy vitrimers are synthesized from diglycidyl ether of bisphenol A and dicarboxylic catalyzed by triazabicyclodecene (TBD). The study on the curing and thermal degradation behavior facilitates in‐depth understanding of the associative CANs. In this work, the effect of TBD on the curing and thermal degradation behavior is investigated via curing kinetics and thermal degradation performance analysis. The results reveal that the activation energy of curing reaction is increased as the amount of TBD is increased. EST‐5 has an average activation energy of 70.1 kJ/mol, while EST‐15 reaches as high as 75.1 kJ/mol. Especially, when the conversion is up to 50%, the activation energy shows an obvious increment. In addition, it has been demonstrated that TBD accelerates the thermal degradation of cured networks at lower temperature and increases the amount of volatiles during thermal decomposition.

Synchronously Improving Mechanical and Thermal Performances of Cured Epoxy Resins by Epoxidized Polyether Sulphones as Modifiers

AbstractAs an effort to improve toughness of epoxy resins without scarifying their heat resistance, four novel polyether sulphones (PESs) with epoxy groups (PES‐Es) are developed as efficient toughness modifiers of epoxy resins. The influences of PES‐E on the mechanical property, curing kinetics, thermal, and mechanical properties of the diglycidyl ether with bisphenol‐A (DGEBA) are investigated. The impact strength of PES‐E/DGEBA composites is significantly improved from 16.6 to 28.9 kJ m−2 with optimal content of PES‐E. Different from the composites of typical PES and epoxy which have two‐phase structure, PES‐E/DGEBA composites exhibit a single‐phase structure owing to the participation of PES‐E in the curing reaction of epoxy groups and good solubility of PES‐E in DGEBA. Furthermore, the thermal stability of the PES‐E/DGEBA composites is slightly increased compared to the neat epoxy resin due to the formation of crosslinked semi‐interpenetrating polymer networks. The glass transitionnal temperature (Tg) of PES‐E/DGEBA composites is up to about 184 °C, 46 °C higher than the neat epoxy resin with the same hardener, which have great potential in high‐performance composites. The method developed in this seminal report makes it possible to improve the toughness of epoxy resins without trading‐off the Tg and tensile strength.

Implementation of the PECVD process to produce a novel range of filler-polymer-coated perlites for use in epoxy composites

This study examines the use of expanded perlite powder (ExP), a natural rock, as reinforcement in bisphenol-A type epoxy resin. The surface of ExP has been coated using the PECVD method with different polymers such as poly(hexafluorobutyl acrylate) (PHFBA) and poly(glycidyl methacrylate) (PGMA). ExPs before and after the coating process underwent characterization using various techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Scanning Electron Microscopy (SEM). The effects of filler ratio and different polymer coatings on composite properties were investigated. The higher tensile strengths for uncoated, PHFBA-coated, and PGMA-coated ExP composites were determined as 109 MPa, 132 MPa, and 152 MPa, respectively. The surfaces of the polymer-coated ExP composites were found to be hydrophobic and water sorption was lower in these composites. ExPs have improved thermal stability and flammability properties. In addition, PHFBA-coated ExP composite was found more resistant to UV radiation and the hydrothermal environment.

Pull‐off capacity of FRP–concrete composite bonded with epoxy/geopolymer at elevated temperature

AbstractExternally bonded strengthening technique to the concrete has been widely used with epoxy adhesive. However, the adhesive is considerably weak against high temperatures, which has been regarded as the critical point in the loss of integrity of the strengthened system. Alternatively, geopolymer materials have shown an excellent performance at high temperatures, thus, their potential to be used as adhesive material has been investigated in this work. In experimentation, the composite specimens were developed using both types of adhesives, epoxy and geopolymer, and their performance was evaluated at three temperature levels (20, 60, and 120°C) by conducting pull‐off strength tests and classifying their failure modes. It was observed that the strength of concrete and epoxy was reduced with temperature. In contrast, the strength of geopolymer‐based adhesives strength was increased due to the reactivity of the precursor at high temperatures. Also, bond strength was reduced for both composite specimens at elevated temperatures. The highest bond strength was observed for the epoxy‐based adhesive system at 20°C, and about 70% loss in bond strength was observed when exposed to 120°C. The failure mode was also shifted from concrete to adhesive interface failure, that is, failure between the adhesive and the fiber fabric layer. The geopolymer‐based adhesive system has lower strength than its counterpart at all temperature levels, and the failure mode was adhesive interface failure. To enhance the bonding capacity at high temperatures, efforts are being made by adding different minerals has been employed. From the experimental results, it was found that there were some improvements, however, it was still less than that of epoxy‐based system. Further optimization of the geopolymer adhesive using minerals is required and then high‐thermal resistance geopolymer adhesive can be established.

Contribution of surface roughness and oxygen-containing groups to the interfacial shear strength of carbon fiber/epoxy resin composites

The interfacial shear strength (IFSS) between carbon fibers (CFs) and the matrix is crucial to the performance of CF-reinforced polymer composites. To evaluate the contribution of mechanical interlocking and chemical anchoring at the interfaces of a polyacrylonitrile-based CF (TORAYCA T800SC-12000-10E)-reinforced epoxy resin (EP: bisphenol A type epoxy resin and tetrafunctional epoxy resin) composites, the surface roughness and content of oxygen-containing functional groups of the CFs were respectively altered by ammonia treatment and electrochemical oxidation. The results showed that ammonia treatment increased the surface roughness without much change to the surface elemental composition, while electrochemical oxidation increased the number of surface oxygen groups without changing the surface roughness. The IFSS of CF/EP composites was tested by the micro-droplet method. The relationships between IFSS, and surface roughness and oxygen content were obtained by linear fitting. The results showed that in the interfacial bonding of CF to epoxy resin, the contribution of chemical anchoring to the IFSS is larger than that of mechanical interlocking.

Novel Low Df Thermosetting Film and Photo Imageable Film

There are various demands for interlayer insulation film. One typical demand is to interlayer insulation film with low Df for substrate to decrease transmission loss, and another typical demand is to low warpage, fine via type photo imageable interlayer insulation film for RDL. We have developed two types of the novel interlayer insulation films, one was low Dk/Df thermosetting film and another was fine via type photo imageable film. Epoxy based interlayer insulation film, which was mainly used for substrate, showed high transmission loss at mm wavelength due to its high Df, especially at high temperature. But it showed good processability and reliability due to its thermosetting property. PPE was known as low Df resin, but it had poor processability and reliability due to its thermoplastic property. Thus we have synthesized the novel curable PPE resin, and by using the resin, we have developed the novel thermosetting PPE based interlayer insulation film for substrate. It showed far lower Df and far lower transmission loss compared to the low Df type epoxy based interlayer insulation film. We have developed the novel photo imageable interlayer insulation film for RDL. Ordinally photo imageable PI solution was used for RDL, but it showed high CTE, which caused warpage and reliability issue, high surface roughness, which required post processing process, and high curing temperature. We have used the novel epoxy acrylate and developed the novel photo imageable film, which showed low CTE, low surface roughness and low curing temperature.

Synthesis And Applications of Bisphenol-A Epoxide Resins - A Review

Epoxy resin is a widely used substance for coatings, adhesives, composites, electrical components, LEDs, paintbrush manufacturing, fiber-reinforced plastic materials, and consumer product manufacturing (such as cases, kits, and snowboards). Epoxy resin is highly versatile due to its properties. One of the most commonly used types of epoxy resin is Bisphenol-A Epoxy resin, which is excellent for high-temperature applications, the adhesion of a variety of substrates, compression, bends, electrical insulation, mortar, grouts, adhesion, and high-tensile-strength applications. There are several types and applications of Bisphenol-A epoxy resin. This paper aims to review the types, synthesis, and applications of Bisphenol-A epoxy resin.