Strength Of Epoxy Research Articles

A transparent, strong, moldable wood laminated composite as a sustainable decorative building material

Delignified wood (DW) retaining its microstructure has increasingly been used as an alternative to synthetic or natural fibers in the preparation of fiber-reinforced composites for novel light-transmitting, high-strength structural materials. In this study, wood laminated composite (WLC) was prepared by impregnating with cycloaliphatic epoxy resin (CAE) and laminating using DW as a continuous reinforcing fiber. Results showed that DW effectively strengthened the resin matrix, increasing the epoxy resin's strength by 25.44 %, while CAE modified the wood's opacity, achieving a transmittance of up to 74.83 %. The mechanical and optical properties of the WLC can be effectively tuned through various lamination combinations. Additionally, due to the UV curing properties of CAE and its infiltration of DW, uncured WLC had long-term shade storage capability and excellent processability. The WLC developed in this study combines good processing, mechanical, and optical properties, making it an attractive option for sustainable home decoration and lightweight structural materials.

Flame retardant, high mechanical strength, transparent and water-resistant epoxy composites modified with chitosan derivatives

Adding bio-based flame retardants to improve the flame retardancy of polymer materials without sacrificing other properties is a great challenge. Herein, a novel flame-retardant CS-DOPA was prepared from chitosan and 10-hydroxy-9,10-dihydro-9-oza-10-phosphaphenanthrene-10-oxide by acid-base neutralization reaction and fully characterized. The 4 wt% CS-DOPA modified EP showed good flame retardancy in both gaseous and condensed phase. The peak heat release rate, total smoke production, CO production, and smoke production rate of EP composites containing 4 wt% CS-DOPA were reduced by 55 %, 34 %, 45 %, and 46 %, respectively, to pass the UL-94 V-1 rating with a limiting oxygen index of 34.1 %. The CS-DOPA contributes to the formation of the condensed phase of the thermo-oxidation-resistant high-quality char layer with non-flammable other and phosphorus-containing free radicals released in the gas phase. In addition, EP/4CS-DOPA has good water resistance, mechanical properties, and transparency, with tensile and flexural strength improved by 12.7 % and 13.9 %, respectively, and still has high strength even after water treatment. The present work provides a green and facile strategy to use chitosan as a main raw material to manufacture EP materials with high performance.

Self-assembly strengthening-toughening epoxy/Graphene composites through intermolecular π-π interactions with ultralow Graphene content

Dispersion of Graphene (GE), high cost of massive usage of GE, and synergistic efficiency of GE and other fillers on epoxy resin (ER) are still challenges. This work not only achieves the uniform dispersion of few-layered GE through π-π interaction between GE and phenyl glycidyl ether (PGE), but also presents an equation in calculating the synergistic efficiency of multiple tougheners. The results show that the strength, modulus, elongation at break, and impact strength of ER can be simultaneously improved when D8 (an epoxy resin with side aliphatic chains) and PGE/GE are used together (D8/PG-X samples) or alone, and the D8/PG-X samples exhibit incomparable positive synergistic efficiency in both strength and toughness with ultralow GE content. The improvement of the impact strength, elongation at break, tensile modulus, and tensile strength in the optimum D8/PG-5 system is 115.5 %, 45.7 %, 17.8 %, and 28.3 % compared with unmodified ER system. We demonstrate that the improved comprehensive properties of the D8/PG-X samples as well as the improved interlaminar shear strength (ILSS) of the carbon fiber (CF)/ER composites can be ascribed to synergistic strengthening-toughening effect of self-assembly effect of aliphatic chains in D8 and uniformed dispersed GE (by π-π interaction). The impressive synergistic strengthening-toughening strategy can provide theoretical guidance for the preparation of high-performance ER with ultralow GE content.

Improving the Fracture Toughness and Strength of Epoxy Resin Using NH2‐silica‐C8H17 Janus Nanosheets

AbstractIn this work, a NH2‐silica‐C8H17 Janus nanosheet with short n‐octyl chains on one side and aminopropyl groups on the opposite side was prepared by the sol‐gel method. This nanosheet was used to improve the toughness and strength of epoxy resin. The morphologies and structures of Janus nanosheets and the properties of NH2‐silica‐C8H17/epoxy nanocomposites were characterized. Results show that the addition of Janus nanosheets not only increases the storage modulus and glass transition temperature of nanocomposites, but also improves their mechanical performance and thermal stability. The tensile strength, elongation at break, fracture toughness and impact strength of nanocomposites are increased by ca. 57, 80, 74 and 63 %, respectively, at the 0.5 wt.% loading of Janus nanosheets. These findings suggest that NH2‐silica‐C8H17 Janus nanosheets exert an effective influence on the toughness and strength of ultimate nanocomposites, which is attributed to the fact that NH2‐silica‐C8H17 Janus nanosheet simultaneously contains n‐octyl and aminopropyl groups on both sides, thus improving the nanosheet/matrix interface adhesion.

Effect of Multiwall Carbon Nanotubes on Tensile Strength of Cross Lap Joint

Abstract: This paper compares the tensile strength of an adhesively bonded single cross lap joint with and without the addition of multiwall carbon nanotubes (MWCNT) in the adhesive. Tensile strength analysis of adhesively bonded cross lap joint is done by applying pulling load which produces tensile stress at overlap between two substrates which joined together by using adhesive. Cross lap joint were created using Al-Al substrates. Five tests were performed on Al-Al substrates with and without the addition of MWCNT in the adhesive for each specimen. MWCNT filler particles increase the toughness and strength of epoxy resin when compared to epoxy resin that does not contain MWCNT. MWCNT fill epoxy resin increases toughness and resists crack formation, increasing the interface strength between two substrates.

Influence of the Addition of Alumina Nanofibers on the Strength of Epoxy Resins

The paper describes the effect of the addition of alumina nanofibers on the mechanical properties of the epoxy resin. Alumina nanofibers functionalized with epoxypropyl functional groups are used in this work. The dependence of the mechanical characteristics on the amount of the additive, as well as the features of its distribution in the material, is investigated. In the work, nanocomposites were obtained, which are epoxy resin with aluminum oxide nanofibers. The mechanical properties of the samples were studied by bending tests and differential mechanical analysis (DMA). It has been shown that the addition of alumina nanofibers leads to an increase in ultimate flexural strength. The maximum of this increase is near the percolation threshold of alumina nanofibers in epoxy resin. With the addition of 0.2% alumina nanofibers, the ultimate flexural strength increases from 41 to 71 MPa. It is shown that after exceeding the percolation threshold of nanofibers, the ultimate strength decreases. In this case, the elastic modulus increases from 0.643 to 0.862 GPa. DMA is shown that the glass transition temperature decreases with increasing amount of the additive. This indicates a decrease in the molecular weight of the polymer. By implication, this suggests that the hardener connects the epoxypropyl functional groups on the nanofibers and the epoxy groups in the resin, and as a result of this process, the nanofibers become natural polymer chain length limiters. The data obtained from mechanical testing and differential mechanical analysis can be used to strengthen epoxy resins in polymer composite materials and molding compositions.

A fully bio-based, anti-flammable and non-toxic epoxy thermosetting network for flame-retardant coating applications

A fully bio-based epoxy thermosetting network was prepared by curing a renewable luteolin-derived epoxy resin (DGELU) with a furan-derived hardener, 5, 5′-methylenedifurfurylamine (DFA). For comparison, a control sample was prepared by curing the petroleum-based commercial epoxy diglycidyl ether of bisphenol A (DGEBA) with a petroleum-based hardener, 4, 4′-diaminodiphenylmethane (DDM). The glass transition temperature (Tg) was found to be 216 °C for the cured DGELU/DFA, which was 67 °C higher than that of the cured DGEBA/DDM. The storage modulus at 30 °C and the tensile strength of the cured DGELU/DFA were 82.5 % and 23.2 % higher than those of the cured DGEBA/DDM. The benzopyrone unit of the luteolin structure was conducive to exceptional charring, and the char yield for thermal decomposition in the nitrogen of the cured DGELU/DFA was 3.2-fold higher than that for the cured DGEBA/DDM. As expected, the cured DGELU/DFA displays a relatively high limiting oxygen index (LOI) of 38.0 % and a UL-94 V-0 classification, whereas the petroleum-based counterpart exhibited a much lower LOI of 24.0 % and no classification in the UL-94 test. An in-vitro cytotoxicity study indicated that the cured DGELU/DFA showed no cytotoxic effect against normal fibroblast cells after 24 and 72 h. Because of these fascinating features, the DGELU/DFA thermosetting network was deposited onto wood surfaces for evaluation as a flame-retardant coating. Compared with the wood treated using the cured DGEBA/DDM coating, wood coated with the cured DGELU/DFA showed a super fire-safe property that could lead to a 55.8 %, 12.4 %, and 11.5 % decrease in peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP), respectively. An anti-flammable, high strength and non-toxic bio-derived epoxy thermosetting network for highly safe epoxy coating applications has been developed.

Processing of post-industrial unidirectional prepreg tapes using SMC equipment

The aerospace industry has an issue of disposing of waste, unused carbon fiber unidirectional prepreg tapes. This paper explores producing chips using sheet-molding compounding equipment (SMC) for conversion into products via compression molding, which are stronger than traditional glass-reinforced SMC parts due to the carbon fiber and high strength epoxy resin. Without a means to convert the continuous tape prepreg into chips, it will not be possible to convert the prepreg into a useful product and provide a way to reduce flow to the landfill and produce less expensive, lighter, and stronger parts for the transportation industry. The cure state of the epoxy resin in the prepreg tapes, which is affected by the amount of time the material has spent stored at elevated or room temperatures, significantly changes the ability of the material to be chopped into short fiber chips. In addition, equipment-related factors affect the material’s ability to be chopped by the SMC equipment. This paper accounts for each of these factors and uses statistical methods to design experiments to investigate the impact each of these material-related and equipment-related factors on the success of the cutting portion of the process. The level of cure, as defined by endothermic peak, glass-transition temperature (Tg), or heat of reaction/degree of cure, has the greatest impact on the cutting process. For material with a moderate level of cure, the sharpness of the blades in the cutting roller also has a major impact on the success of the process. The cutting pressure, roller speed, and tape tension also have an impact on the success of the process, but impact of these factors lessens for feedstock prepreg with a sufficiently high level of cure. An optimal setup was determined, and general rules of thumb for selecting material and equipment settings were established.

The Behavior of RC Beams Retrofitted with Carbon Fiber Reinforced Polymers (CFRP)

The need for the introduction of economical and quicker retrofitting techniques is increasing due to the ever-aging infrastructure and damages produced by major catastrophic events around the world. The application of Carbon Fiber Reinforced Polymers (CFRP) for strengthening and retrofitting of reinforced concrete structures is gaining popularity due to its higher strength, lightweight, durability, corrosion resistance, and aesthetic value. This study presents the results of two strengthened and two retrofitted beams in comparison to control specimens. Two specimens were strengthened and two were retrofitted by attaching CFRP (Sika Carbo-Dur S812 or Sika-Wrap 230C) to the tension side of the beams using high strength epoxy. The results show that one CFRP strip/wrap simply attached at the tension side can help the damaged beam regain/pass the original strength. All specimens fail due to debonding of CFRP from the concrete surface emphasizing the need for efficient anchorage systems. Among the four patterns adopted, CFRP strips along with u-shaped anchorages at the ends provided the highest strength enhancement of 17.36%.

Comparison between Synthetic and Biodegradable Polymer Matrices on the Development of Quartzite Waste-Based Artificial Stone

The development of artificial stone from the agglutination of polymeric resin using industrial wastes can be a viable alternative from a technical, economic, and sustainable point of view. The main objective of the present work was to evaluate the physical, mechanical, and structural properties of artificial stones based on quartzite waste added into a synthetic, epoxy, or biodegradable polyurethane polymer matrix. Artificial stone plates were produced through the vacuum vibration and compression method, using 85 wt% of quartzite waste. The material was manufactured under the following conditions: 3 MPa compaction pressure and 90 and 80 °C curing temperature. The samples were characterized to evaluate physical and mechanical parameters and microstructure properties. As a result, the artificial stone plates developed obtained ≤0.16% water absorption, ≤0.38% porosity, and 26.96 and 10.7 MPa flexural strength (epoxy and polyurethane resin, respectively). A wear test established both artificial quartzite stone with epoxy resin (AS-EP) and vegetable polyurethane resin (AS-PU) high traffic materials. Hard body impact resistance classified AS-EP as a low height material and AS-PU as a very high height material. The petrographic slides analysis revealed that AS-EP has the best load distribution. We concluded the feasibility of manufacturing artificial stone, which would minimize the environmental impacts that would be caused by this waste disposal. We concluded that the production of artificial rock shows the potential and that it also helps to reduce environmental impacts.

Study of fiber delamination on silane modified ramie fiber/OMMTnano‐clay epoxy composite under low‐velocity impact, shear load, and high‐speeddrilling

AbstractIn this present study, the effect of silane treated ramie fiber addition along with organically‐modified montmorillonite (OMMT) nano clay in epoxy resin composite was investigated in drop load impact, shear loading, and high‐speed drilling. The main aim of this research study was to develop a high‐laminar shear strength epoxy structural composite for various engineering applications. To improve the laminar adhesion the fiber was treated using silane via acid hydrolysis technique. The OMMT nanoclay also added with fiber in order to improve the load bearing effect and adhesion phenomenon. The composites were prepared using hand layup method with postcuring. The adhesion behavior of composites was tested based on American society for testing and materials standards and compared. According to the results, the treated ramie fiber possesses high resistance to impact loading. The ballistic resistance of composite is increased three fold when compare with as‐received fiber‐epoxy composites. The interlaminar shear strength of composite designation C1.5 gives highest shear strength of 35 MPa. The drilling study revealed highest dimensional stability for treated fiber. No fiber chip off and pull out at the drilled hole surface. The fractography analysis confirms no lamina delamination occurs even at high‐speed drilling. These delamination resistance epoxy‐based composites are suitable in automobile, structural and defense gadget manufacturing applications.

Fully aminated rigid-rod aramid reinforced high strength epoxy resin and its composite with carbon fibers

Poly(p-aminophenylene aminoterephthalamide) ((NH2)2-PPTA), a new organo-soluble fully aminated rigid-rod aramid has been synthesized by the polycondensation of nitroterephthalic acid and 2-nitro-1,4-phenylenediamine and then hydrogenation-reduction of the nitro side groups. (NH2)2-PPTA was then used as the modifier of epoxy resin (EP) and carbon fiber (CF)/EP composites and their mechanical properties were systematically investigated. Because all the benzene rings in (NH2)2-PPTA contain amino side groups, (NH2)2-PPTA has excellent solubility in organic solvents and EP. In addition, the amino side groups are able to react with the matrix so as to effectively integrate the rigid-rod (NH2)2-PPTA into the cross-linked molecular network of EP and facilitate the stress transfer between EP and (NH2)2-PPTA. The tensile and flexural properties and notch impact strength of EP are greatly increased with the addition of only 0.5 wt% (NH2)2-PPTA. Unusually high tensile strength and flexural strength have been achieved, which reach 140.6 ± 4.1 MPa and 237.9 ± 12.3 MPa, respectively. Moreover, addition of a small amount of (NH2)2-PPTA also significantly improves the flexural strength, toughness and the interlaminar shear strength of CF/EP composites. Compared with previously reported nanofillers and other rigid-rod polymers, (NH2)2-PPTA shows better reinforcing and toughening effect for EP and CF/EP composites owing to its great solubility, reactivity and inherent great mechanical properties.

Lateral Cyclic Load Test of Masonry Infilled RC Frames Strengthened with Ultra-High Performance Concrete Diagonal Strips

Infilled frame structures have been a common form of construction. However, their behavior is one of the least understood and investigated among all the major construction systems. For a long time, these structures were built with a general lack of conclusive research and design information. An experimental program was undertaken which aims at investigating the behavior of masonry infilled RC frames strengthened with Ultra-High Performance Concrete (UHPC). In this study, UHPC cross diagonal strips, having a width of 355 mm, were bonded onto the masonry substrate using high strength epoxy mortar. Single-side strengthening layout was adopted due to the fact that it is frequently implemented in the case of external facade walls of existing masonry buildings to preserve the building exterior aesthetics and also on internal walls which have some sorts of artworks on one side. Regarding the CFRP strengthened infilled frame, 60% and 160% increase was achieved in the lateral load carrying capacity and energy dissipation, respectively, when compared to the reference frame. Furthermore, the drift capacity at failure was improved by 1.58 and 1.40 times for UHPC and CFRP strengthened specimens, respectively, when compared with the reference specimen.

A modified method to measure delamination strength of stabilizer free REBCO coated conductor under transverse tension

A setup of transverse tension measurements of high temperature superconductor (HTS) RE-Ba-Cu-O coated conductors are modified for simplicity. Modification includes using high strength epoxy films instead of solder as adhesive agents and changing the shape of contact surface between test samples and anvils. This method was designed to measure delamination strength of stabilizer free REBCO coated conductors with a width more than 10 mm. It is also applicable to REBCO coated conductors with copper or stainless-steel stabilizers. Samples made by the IBAD/PLD process were tested by this test. Effect of operation temperature on the delamination strength of coated conductors was investigated. In addition, fracture surfaces of delaminated samples were studied.

Exploitation of rubbery electrospun nanofibrous mat for fracture toughness improvement of structural epoxy adhesive bonded joints

The improvement of the fracture toughness of adhesive joints is a key factor in many structural applications. The ability of nylon electrospun nanofibrous mat to act as an adhesive carrier and reinforcing web in adhesive bonding has been demonstrated by the Authors in previous works. It has been shown that the impregnation method developed and refined during the previous studies allow generating high-quality pre-preg nanomats out of a 2k unfilled epoxy resin. By applying this methodology, in the present work, rubbery nanofibrous mats have been adopted for the first time to reinforce and increase the fracture toughness of adhesive joints. Rubbery nanofibers were produced by electrospinning of nitrile butadiene rubber (NBR) and poly(ε-caprolactone) (PCL). The addition of the semi-crystalline polymer (PCL) is exploited to maintain the nanofibrous morphology, which the rubber alone (NBR) would not be able to ensure due to its low glass transition temperature (Tg). The nanofibers thus obtained have been integrated into a two-component high strength epoxy resin for structural applications. S235 steel adherends for Double Cantilever Beam (DCB) tests have been manufactured and sandblasted to improve adhesion. An optimization of the sandblasting parameters (distance, pressure, angle and time) has been carried out evaluating the shear strength and the fracture surfaces on S235 steel Single Lap Joints (SLJ). Finally, DCB tests have been performed to compare the mode I fracture toughness with and without the rubbery electrospun nanomats.

Integration of nylon electrospun nanofibers into structural epoxy adhesive joints

The fracture toughness is a key parameter in the development of bonded joints for several structural applications. Adhesives are commonly toughened with fillers or modifying the resin chemical composition. Many studies also suggest that resin toughening could be achieved through electrospun polymer nanomat. In previous works, the Authors proved that nylon nanomats can be used as an adhesive carrier and reinforcing web for the adhesive layer. This allowed developing a laboratory route to produce high-quality prepregs of electrospun nylon carrier using medium viscosity, two-component, unfilled epoxy adhesive. By applying the same methodology, in the present work, electrospun nylon prepregs were produced using a high strength and high toughness 2k structural epoxy adhesive to toughen the joint. The wet nano-reinforced strips were placed between S235 steel sandblasted adherents and oven-cured to obtain Double Cantilever Beam (DCB) joints. DCB tests have been performed to compare the mode-I fracture toughness with and without the nanofibrous mat. Unlike previous works with medium-low toughness epoxies, this time the fracture toughness is reduced after the integration of an electrospun nano-reinforcement. From the Scanning Electron Microscope (SEM) images it seems that the nanomat hinders the ductile failure mechanism which instead develops in the neat resin.

Interfacial Bond Properties between Normal Strength Concrete and Epoxy Resin Concrete

It is necessary to pay attention to the bonding strength of the interface between precast normal strength concrete (NSC) and cast‐in‐place epoxy resin concrete (EMR) when using EMR as a repair or filling material or an overlay in bridges’ rehabilitation. However, the performances of epoxy concrete are different due to differential mix ratios; thus, the bonding properties between various epoxy resin concrete and cement concrete are not completely the same. This article investigated the interfacial bond properties between NSC and ERC by direct tensile, push‐out, and slant shear test with specimens of special size and structure and observed the interfacial bond strength and corresponding failure modes. The minimum bond strength under direct tension was 0.72 MPa, while the minimum bond strength was 1.71 MPa and 3.19 MPa for the push‐out test and slant shear test, respectively. Results indicated that the slant shear test specimens with an inclination angle of 45° are not suitable for the slant shear test due to higher compressive stress. Furthermore, the cohesion and friction coefficient of interface bond strength were calculated inversely in accordance with the results obtained from the corresponding direct tensile and slant shear tests. The minimum cohesion value was 1.71 MPa, and the minimum friction coefficient value was 0.46.

High strength epoxy nanocomposites reinforced by epoxy functionalized aramid nanofibers

Thermosetting polymers have been demonstrated to exhibit improved mechanical properties when nanofillers are introduced. These improvements can be further increased through the introduction of covalent linkages between the polymer matrix and nanofillers that enhances the chemical interaction. Here, aramid nanofibers (ANFs) are functionalized using a glycidyl ether silane coupling agent and their effect on the mechanical properties of epoxy are investigated. The results show that Young's modulus and tensile strength of 1 wt % epoxy functionalized ANFs (EANFs) reinforced nanocomposites increase by 16.8% and 14.0%, respectively, and fracture toughness increases by 4.4 times with the addition of 1.5 wt % EANFs. Additionally, both an increase in storage modulus and glass transition temperature are observed during dynamic mechanical analysis with increasing percentage of EANFs. Thus, this work demonstrates that the EANFs can further enhance the mechanical properties of epoxy nanocomposites through chemical crosslinking between the epoxy matrix and ANFs.

Effect of carbon nanotubes on the interlaminar and fracture properties of carbon fiber/epoxy composites

The average properties of carbon fiber reinforced plastics (CFRPs) depend on the extent of interaction between the fiberand matrix. Any means, therefore, to modify either of the two constituents of CFRPs is the key to design the composite.Carbon nanotubes (CNTs) are often used to tailor the interface/interphase in conventional CFRPs either by mixing thenanotubes in matrix or by growing them on the surface of fiber. However, the incorporation of nanotubes, by either means, may affect the mechanical performance of the matrix and that of the composite as a whole. Experiments are carried out toassess the effect of CNT dispersion on the rate sensitivity of matrix, and the effect of CNT grafting on the averagemechanical properties of laminated composites. For better dispersion and interfacial interaction of nanotubes with matrix,molecular level designing of nanotubes is carried out by way of functionalization. It is found that the ultimate strength ofepoxy composites increases with applied loading rate, and that neat epoxy is more rate sensitive than CNT based epoxynano composites. Significant enhancements are also observed in the interlaminar and fracture properties of CFRPs after theincorporation of grafted nanotubes in the composite.

High strength epoxy system modified with soft block copolymer and stiff core-shell rubber nanoparticles: Morphology, mechanical properties, and fracture mechanisms

High strength epoxy system modified with soft block copolymer and stiff core-shell rubber nanoparticles: Morphology, mechanical properties, and fracture mechanisms