Base Epoxy Research Articles

Carbon fiber-reinforced composites based on an epoxy resin containing Schiff base with intrinsic anti-flammability, good mechanical strength and recyclability

A new renewable material, comprising a Schiff base epoxy thermoset derived from furan derivatives, was successfully synthesized. This innovative material not only possesses remarkable carbon fiber recyclability but also exhibits favorable mechanical properties and flame retardancy. After being cured with the bio-based curing agent, 5,5′-methylenedifurfurylamine, the cured Schiff base epoxy thermoset exhibited an ultra-high char yield of 54% and a glass transition temperature of 207 °C. Compared to bisphenol A epoxy resin, it achieved a 100% higher yield. Furthermore, the cured Schiff base epoxy thermoset demonstrated a high storage modulus (at 30 °C) of 2695 MPa and a tensile modulus of 60 MPa, surpassing bisphenol A epoxy resin. Remarkably, the exceptional structure of the Schiff base epoxy thermoset imparted intrinsic flame retardancy, resulting in a V-0 rating in the UL-94 test. The thermoset also exhibited considerable recyclability in carbon fiber composites due to its Schiff base network. Moreover, it could be nondestructively and quickly recycled under mildly acidic conditions, enabling efficient recycling of the carbon fiber composites.

A bio-based epoxy resin derived from syringaldehyde with excellent mechanical properties, flame retardant and high glass transition temperature

Due to increasing environmental concerns, global warming, and the decline of oil reservoirs, the use of bio-epoxy resins derived from sustainable resources is recommended. The development of bio-based epoxy resins with considerable thermal stability, mechanical strength, and appropriate intrinsic flame retardant potential is highly demanded. In this study, a new Schiff-based epoxy monomer, triglycidyl ether of syringaldehyde (SA-TAG-EP), was synthesized from renewable syringaldehyde. After the 4,4′-diaminodiphenylmethane (DDM)-based curing process, an intrinsically flame-retardant resin (SA-TAG-EP/DDM) with C, H, N, and O elements was achieved. SA-TAG-EP/DDM showed higher glass transition temperature (224.9°C) and greater mechanical strength, including a tensile strength of 66.8 MPa and an elongation at break of 3.91%, compared to petroleum-based bisphenol A epoxy thermoset. It also passed the V-0 flammability rating in the UL-94 test and exhibited a 38.5% limiting oxygen index, 48.9% char yield under N2, and a lower peak heat release rate than that of petroleum-based bisphenol A epoxy thermoset. We proposed a simple and sustainable route for the synthesis of Schiff base epoxy compounds from biomass-derived resources, which demonstrates significant mechanical properties and increased flame retardant potential.

Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single-atom Cu/O Lewis pair for acetylene hydrochlorination

Simultaneously boosting acetylene hydrochlorination activity and avoiding formation of explosive copper acetylide over Cu-based catalyst, which represented a promising alternative to Hg-based and noble metal catalysts, remained challenging. Herein, we fabricated a frustrated single-atom Cu/O Lewis pair catalyst (Cu/O-FLP) by coupling epoxide group (C–O–C) with atom-dispersed Cu-cis-N2C2Cl center to address this challenge. The basic epoxy site modulated the electron-deficient state of Lewis-acidic Cu center and paired with the Cu-cis-N2C2Cl moiety to preferentially break HCl into different electronegative Cu–Clδ− and C–O–Hδ+ intermediates, which further induced both an extra localized electric field to polarize acetylene and a upshift of the d-band center of catalyst, thereby promoting adsorption and enrichment of acetylene by enhancing the dipolar interaction between acetylene and active intermediates. Moreover, the generated Cu–Clδ− and C–O–Hδ+ drastically reduced the energy barrier of rate-limiting step and made vinyl chloride easier to desorb from the Lewis-basic oxygen-atom site rather than traditional Lewis-acidic Cu center. These superiorities ensured a higher activity of Cu/O-FLP compared with its counterparts. Meanwhile, preferential dissociation of HCl endowed single-atom Cu with the coordination-saturated configuration, which impeded formation of explosive copper acetylide by avoiding the direct interaction between Cu and acetylene, ensuring the intrinsic safety during catalysis.

Evaluation of the strength characteristics of polymer materials for the manufacture of personal electric vehicle elements

The properties of materials for airless wheel propulsion of vehicles, including electric ones, have been studied. The experimental substantiation of the choice of the type of polymer matrices and compositions of reinforcing fillers for the manufacture of an airless wheel mover of electric vehicles has been carried out. To test the basic epoxy matrix, part of the samples without the addition of reinforcing fibers was cured at room temperature (L-285H), and the rest (L-285G) – when heated to 60 °C. In order to improve the strength characteristics of the epoxy matrix L-285G, glass reinforcement was carried out with EC16 1600T-16(400) glass reinforcement. The Smooth-Cast 300 Series was chosen as the matrix for performing samples based on injection-molded polyurethanes. Samples are made of base polyurethane under various conditions: at atmospheric rejection (SC), under vacuum 0.8 kPa (SC-0.8) and during vibration-induced curing (SCV). Comparative tests were carried out, which showed differences in the mechanical properties of the base matrices based on epoxy resins and injection-molded polyurethanes, in particular, the relative elongation of samples from injection-molded polyurethane by more than 2 times. It is established that the most rational use of injection-molded polyurethane is application as damping elements, and the material for manufacturing spokes dampers is composite SCV-S-20. It is advisable to manufacture products from the resulting composite when vibrations are applied to the mold and with preliminary vacuuming at a vacuum of 0.8 kPa of the components of the polyurethane matrix, which reduces the number of internal defects in the form of shells. Since vacuuming of the product during polymerization does not give a significant effect due to the presence of a set of specialized deaeration additives in the base matrix, it is proposed to carry it out under constant control, since exceeding the vacuum in the range from 0.8 to 0.9 kPa entails decomposition of individual matrix components with foam formation.

Dynamic mechanical and thermal mechanical analysis of Cyperus malaccensis sedge fiber reinforced GO-incorporated epoxy nanocomposites: a short communication

The sedge fiber extracted from the Cyperus malaccensis (CM) plant has recently been found as a promising reinforcement of polymer composites. Incorporation of 30 vol.% CM sedge fibers improved the impact resistance and tensile elastic modulus of epoxy composites with only slight differences in their thermogravimetric parameters. However, dynamic mechanical viscoelastic behavior is still needed to complete these composites characterization for possible engineering applications. This complementary research work extends the previous study to dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) for GO-incorporated epoxy matrix nanocomposites incorporated with 30 vol.% of CM sedge fibers. In comparison to basic epoxy (control sample) the damping factor (tan δ), as the ratio between DMA loss and storage moduli, is significantly increased from 0.45 to 0.75 for 30 vol.% CM fiber composite. TMA findings disclosed only slight variations in the glass transition temperature (119–124 °C) as well as in the thermal expansion coefficient (168 x 10–6 to 220 x 10–6/°C). These DMA and TMA results confirms the promising CM sedge fiber reinforcing effect on GO-incorporated epoxy nanocomposites and its mechanical/thermal viscoelastic contribution.

STUDY OF INTERFACIAL ADHESION OF PAVEMENT SEALANTS BASED ON MOLECULAR DYNAMICS

To study the performance of bitumen mixture pavement sealants from their micro-mechanisms, the physical properties of base bitumen, SBS-modified bitumen and epoxy resin sealant as well as the adhesive properties of sealant-aggregate interfaces were studied using a molecular dynamics simulation. The adhesion of a sealant-pavement crack wall was studied using a contact angle test based on the surface energy theory. The results show that the epoxy resin sealant has excellent adhesion properties. Its physical properties and interfacial adhesion work are more significant than those of base bitumen and SBS-modified bitumen. An increase in the SBS can improve base bitumen’s mechanical properties and interfacial interaction. The interaction between three kinds of crack sealants and aggregate is identified as mainly the physical adsorption behavior. The van der Waals force plays a significant role in the adhesion behavior of bitumen crack sealant-aggregate interface. In contrast, the electrostatic force and van der Waals forces significantly affect the epoxy resin binder-aggregate interface. The adhesion work of 90# base bitumen, SBS-modified bitumen and epoxy resin binder for the asphalt pavement crack wall is (37.76, 44.86 and 77.63) mJ/m2, respectively.

Optimal Thickness of Double-Layer Graphene-Polymer Absorber for 5G High-Frequency Bands

A new analytical approach to optimize the thicknesses of a two-layer absorbing structure constituted by a graphene-based composite and a polymer dielectric spacer backed by a metallic layer acting as perfect electric conductor (PEC) is proposed. The lossy sheet is made by an epoxy-based vinyl ester resin filled with graphene nanoplatelets (GNPs) characterized by known frequency spectra of the complex permittivity. The optimal thicknesses are computed at the target frequencies of 26, 28, and 39 GHz in order to obtain a –10 dB bandwidth able to cover the 5G frequency bands between 23.8 and 40 GHz. The resulting absorbing structures, having a total thickness lower than 1 mm, are excited by transverse magnetic (TM) or electric (TE) polarized plane waves and the absorption performances are computed in the 5G high frequency range.

Effect of crack and vibration of waste tyre rubber hybrid composite for energy absorption applications

Composites reinforced with landfill waste materials have find the applications in engineering materials and they can lead to reduce the environmental pollutions. Waste tyre rubber, broken ceramic tiles and wood particles are creating the environmental hazard to the surroundings. In particular, the recycling of used tyre rubber is highly challenging, but it has very good property to absorb the energy. The reinforcement of rubber as single filler in composite has the limitations in processing and applications. Hence, the above waste materials are incorporated to prepare the composite in the present work. The fracture toughness and shear strength of composites were evaluated and compared with other combinations along with pure epoxy specimen. In order to find the application of composite in dynamic conditions the vibration analysis were done. The presents of rubber decreased the fracture toughness and at the same time the incorporation of ceramic largely improved the fracture toughness of epoxy composite. The shear strength of composites increased with the addition of ceramic and wood particles. But the rubber particle has the great influence on the damping behavior of ceramic base epoxy composites. The addition of ceramic with the epoxy increased the natural frequency and decreased the damping factor. This can be compensated by the inclusion of rubber with ceramic in epoxy resin matrix. 15 wt % addition of rubber with ceramic and epoxy increased the natural frequency of 18.52% and damping factor of 288% than 5 wt % of rubber with ceramic and epoxy. The natural frequency and damping factor of ceramic and rubber based epoxy composite have the highest amount of all combinations and can be used for vibration applications to absorb the energy at high frequencies.

Analysis of boron epoxy resin composite in morphology, neutron radiography, and thermal neutron shielding performance

This study aims to analyze the effect of boron fillers in epoxy resin composites. Three samples of the shield were prepared: pure epoxy resin, epoxy resin with 5 %wt boron, and epoxy resin with 10 %wt boron. The morphology of the samples was studied using a scanning electron microscope. The dispersion of the boron powder was observed using neutron radiography. The samples were also tested with a thermal neutron attenuation experiment using the TRIGA Mk-II reactor in the Malaysian Nuclear Agency. The SEM images show that boron affected the structure of the base resin matrix. Agglomerates and white spots can be observed which might be the boron filler. The radiographs reveal several dark spots in the composite, suggesting the inhomogeneity of the boron powder. From the attenuation experiment results, the transmission ratio, the removal cross-section, the mean free path, the half-value layer, and the tenth-value layer were calculated. It was found that increasing the boron content improved the shielding performance of the base epoxy resin by at least 21% if 5 %wt boron was added.

Pyrolysis Combustion Characteristics of Epoxy Asphalt Based on TG-MS and Cone Calorimeter Test.

To examine the pyrolysis and combustion characteristics of epoxy asphalt, the heat and smoke release characteristics were analyzed via TG-MS and cone calorimeter tests, and the surface morphology of residual carbon after pyrolysis and combustion was observed via scanning electron microscopy. The results showed that the smoke produce rate of epoxy asphalt was high in the early stage, and then sharply decreased. Moreover, the total smoke produced was close to that of base asphalt, and the surface of residual carbon presented an irregular network structure, which was rough and loose, and had few holes, however most of them existed in the form of embedded nonpenetration. The heat and smoke release characteristics of epoxy asphalt showed that it is not a simple fusion of base asphalt and epoxy resin. Instead, they promote, interact with, and affect each other, and the influence of epoxy resin was greater than that of base asphalt.

Synergistic fracture toughness enhancement of epoxy-amine matrices via combination of network topology modification and silica nanoparticle reinforcement

A strategy for enhancing fracture toughness of nanosilica particle (NSP) reinforced high T g epoxy thermosets via topological rearrangement of cross-linked networks is presented. Hybrid systems consisting of NSP with an average particle size of 20 nm and monoamine functionalized partially reacted substructures (mPRS) were prepared using high T g tetraglycidyl ether of diaminodiphenylmethane (TGDDM) and a low T g diglycidyl ether of bisphenol A (DGBEA) epoxies cured with Jeffamine D230. A synergistic effect on fracture toughness improvement was observed for all hybrid systems. For the high T g TGDDM system, the fracture energy of the base epoxy polymer showed a moderate increase from 119 J/m 2 to 203 J/m 2 with the addition of 10 wt% NSP. Modifying the network topology of this system using 15 wt% mPRS tripled the fracture energy to 652 J/m 2 . It was found that the addition of mPRS results in hybrid modified systems capable of exceptional tensile failure strains, thus significant plastic shear deformation is induced near the crack-tip region enhancing NSP debonding and subsequent void growth and energy dissipation . Fracture morphologies of the hybrid systems using scanning electron microscope (SEM) showed increasing number of voids and enhanced void growth with increasing weight ratio of mPRS. Impact tests showed the role of these toughening mechanisms on high strain rate deformation and energy dissipation.

Effect of hybrid carbon nanofillers at percolation on electrical and mechanical properties of glass fiber reinforced epoxy

AbstractMulti walled carbon nanotubes and graphene nanoplatelets are novel fillers possessing exceptional intrinsic characteristics, such as high aspect ratio, strength, and good compatibility. These fillers are integrated into a glass fiber reinforced epoxy using a pultrusion process with a mixing ratio of 2:3 to attain the synergetic effect. The electrical and mechanical properties of the composites containing combinations of multi walled carbon nanotubes (0.4 wt%), graphene nanoplatelets (0.6 wt%) and micron aluminum trihydrate (2 wt%) fillers is studied. Significant improvement in electrical and mechanical properties is achieved. This study reveals that the incorporation of hybrid carbon nanofillers into epoxy leads to improved dielectric constant, AC conductivity and mechanical properties as compared with the base epoxy composite with glass reinforcement. The AC conductivity increases from 10−9 to 10−1 S/m and dielectric constant from 3.6 to 100 due to carbon fillers. The mean tensile strength improves from 433 MPa of the base epoxy composite to 508 MPa in carbon‐filled composite. The compressive strength improves from 630 to 681 MPa due to incorporation of carbon fillers signifying the improvement in load transfer effectiveness. The effect of carbon fillers on the flexural strength and hardness is minimal. The experimental data on mechanical parameters have been validated using theoretical modeling and a good correlation is established.

Sustainable Manufacture of Natural Fibre Reinforced Epoxy Resin Composites with Coupling Agent in the Hardener

Lignocellulosic natural fibres are hydrophilic, while many matrix systems for composites are hydrophobic. The achievement of good mechanical properties for natural fibre-reinforced polymer (NFRP) matrix composites relies on good fibre-to-matrix bonding at the interface. The reinforcement is normally coated with an amphiphilic coupling agent to promote a strong interface. A novel alternative approach is to dissolve the coupling agent in the hardener for the resin before creating the stoichiometric mix with the base epoxy resin. During composite manufacture, the hydrophilic (polar) end of the coupling agent migrates to surfaces (internal interfaces) and bonds to the fibres. The hydrophobic (non-polar) end of the coupling agent remains embedded in the mixed resin. Mechanical testing of composite samples showed that silane added directly to the matrix produced a NFRP composite with enhanced longitudinal properties. As pre-process fibre coating is no longer required, there are economic (shorter process times), environmental (elimination of contaminated solvents) and social (reduced worker exposure to chemical vapours) benefits arising from the new technique.

Influence of chain length of organic modifiers in hydrophobization process on epoxy resin properties

Resins have been widely used in a variety of industry fields for more than a century, such as coatings, adhesives, or automotive. Their low cost and workability are extremely useful in creating more and more advanced materials due to their chemical structure (Ghaffari et al. in Surf Interfaces 17:100340, 2019). Common problem today is the wetting tendency of various materials which in the end can result in further damage in the structure because of atmospheric conditions. Nowadays, scientists are trying to find better ways to improve the properties of coatings or composites in cases like hydrophobicity or icephobicity. One of the examp les are fluorinated organic compounds with good linking properties to the substrate (Qin et al. in Mater Today Commun 22:100770, 2020). Because o f that, to im prove the properties of a basic epoxy resin, its chain has been modified with hydrophobic compounds with different chain lengths. Influence of modifiers’ molecule size on hydrophobic and ice adhesion properties of obtained epoxy resins has been tested. Chemical composition of prepared coatings was analyzed by FTIR. Moreover, their thermal stability was investigated using TG and DSC measurements. Additionally, wettability of the samples was analyzed with a goniometer. Furthermore, their ice adhesion tests were performed on a dedicated apparatus. As a result, presented work provides a critique overview and concept of promising icephobic and hydrophobic coatings in the industry. Moreover, these products have a high chance to be developed further.

Steel-reinforced resin for bolted shear connectors: Confined behaviour under quasi-static cyclic loading

Injections bolts were initially conceptualized to repair riveted connections in bridges with long service lifetime and now they are widely used in steel and composite structures. Injecting steel-reinforced epoxy resin in bolted connections with oversized holes is a novel approach to enable fast and easy assembly of composite structures while limiting slip between the components. The performance of these bolted shear connectors is mainly dependent on the injected material. In this paper, short-term mechanical properties of an epoxy-based resin mixed with steel shots (steel-reinforced resin) are evaluated to consider it for bolted shear connectors. Uniaxial static tests allowed to compare the stiffness and ductility of resin and steel-reinforced resin and to define a hardening law, while multiaxial tests were conducted under quasi-static cyclic loading in order to characterize the material behaviour under confined conditions. Steel-reinforced resin specimens showed a stiffness under confined conditions 2.6 times higher compared to the bare resin specimens. This increase of stiffness is fundamental to achieve slip resistant behaviour when resin-injected shear connectors are used in significantly oversized holes. The linear Drucker-Prager plastic model was used to define the material behaviour. The good agreement observed indicates that future investigations on numerical and experimental performance of bolted shear connectors can be implemented with the parameters proposed in this paper.

A thermal latent imidazole complex containing copper (II) as the curing agent for an epoxy-based glass fiber composite

Epoxy-based glass fiber composites are widely used in various fields, such as automotive, marine, and aircraft, owing to their high strength and light weight compared to traditional metal materials. However, the epoxy-based resins or prepregs cannot be stored for a long time at room temperature owing to their high reactivity. In this study, 1-cyanoethyl-2-ethyl-4-methylimidazole (CEMI) is a complex with copper chloride to improve its thermal latency towards epoxy resins, and the epoxy-based glass fiber composite is made by prepreg processing. The composition of the imidazole–copper (II) complex (Complex-S) is characterized by elemental analysis and inductively coupled plasma optical emission spectrometry. Thermal dissociation of Complex-S is conducted by differential scanning calorimetry and Fourier transform infrared spectroscopy. With Complex-S as a latent curing agent, the thermal and mechanical properties of epoxy resins are studied. The epoxy systems show distinctly prolonged shelf life at room temperature. Moreover, the composite with Complex-S has a higher flexure strength and modulus comparable to that with CEMI.

Comparative Study of Different Methods of Synthesis and Their Effect on the Thermomechanical Properties of a Halogenated Epoxy-Based Flame-Retardant Resin.

The work presented in this paper deals with the comparative synthesis of diglycidyl ether-based tetrabromobisphenol-A(TBBPA) using both conventional and nonconventional methods in order to explore materials for better industrial applications with respect to effective yield, cost, and time consideration. The conventional method involved the polycondensation of TBBPA and epichlorohydrin in the presence of an alkali catalyst. The nonconventional routes adopted for the synthesis of the material involved ultrasonication, microwave irradiation, and UV light exposure. The Fourier transform infrared spectroscopy spectra of all the synthesized materials of the resin were found to be identical, and the X-ray diffraction analysis showed the material as amorphous. The mechanical studies of the resins revealed that all these resins synthesized by different methods are strong and possess high viscosity. Based on the overall thermal, rheological, and excellent hydrophobic properties, it can serve as an excellent flame retardant.

Biomimetic epoxy adhesive capable of large-scale preparation: From structural underwater bonding to hydrothermal durability

Biomimetic adhesives inspired by mussels are promising bonding materials in both dry and wet conditions. However, few such materials are suitable for application as underwater construction adhesives, where much higher bonding performance (≥5 MPa) and scale production are urgently required. Herein, a biomimetic catechol-based Mannich base epoxy curing agent (CMB) was prepared by the one-pot condensation reaction of 4-tert-butylcatechol, paraformaldehyde, and diethylene triamine on a hectogram scale. Further, a fast-curing two-part epoxy adhesive was designed by combining the CMB with the diglycidyl ether of hydrogenated bisphenol A. Benefiting from the independent crosslink-point strategy and synergic conditions, the CMB epoxy adhesive could maintain its dry bonding strength (9.0 MPa), even in a 4 °C underwater environment, which is the highest value that has been achieved to the best of our knowledge. Moreover, with a moderate post-curing process, the dry bonding strength on sandblasted Al (20.4 MPa) matches that were obtained on anodized Al and siloxane-treated Al, on which the obtained bonding strength represents the upper limit of an adhesive because of their well-known optimal surfaces for bonding. To the best of our knowledge, no previously reported catechol-assisted adhesive could achieve the same strength as siloxane-treated surfaces. Accelerated ageing experiments showed that the catechol groups had good endurance under hydrothermal conditions. The developed CMB epoxy adhesive has great potential as a high-performance structural adhesive and the findings of this study contribute to the understanding of the important chemical properties necessary for the design of biomimetic adhesives.

Siloranes–Suitability of a Novel Adhesive for Orthodontic Bracket Bonding

Recently, an epoxy-based resin-Filtek Silorane-has been proposed for restorative fillings. It was the aim of the investigation to evaluate the suitability of this novel resin for orthodontic bracket bonding on unground enamel. Shear bond strength was measured for two adhesives-Filtek Silorane, Transbond XT-in combination with steel, ceramic and polymer brackets. For Filtek Silorane etching was performed with the Silorane self-etching primer, as well as phosphoric acid. The Transbond XT samples were etched with phosphoric acid only and served as the control group. All samples were thermo-cycled (1000×, 5–55 °C). Shear testing was carried out with an Instron 3344. In addition, ARI scores were evaluated. The Shear bond strength showed a weak adhesion of Filtek Silorane to unprepared enamel, either with the self-etching primer or the conventional etching (0.87–4.28 MPa). The Shear bond strength of the control group was significantly higher (7.6–16.5 MPa). The ARI scores showed a clear failure at the enamel-adhesive interface for all Filtek Silorane samples. For the combination of Transbond XT and different brackets the failure was found at the adhesive–bracket interface. The novel epoxy-based resin Filtek Silorane is not appropriate for bracket bonding to unprepared enamel.

Fully bio-based epoxy resin derived from vanillin with flame retardancy and degradability

There are many applications for epoxy resin as a coating material in the automotive, electronics, and aerospace industries. However, when derived from petrochemical industries, adversely affect the environment, as they are rigid and resistant to recycling due to inherent cross-linked structure. In the present study, we prepared green epoxy resin from renewable resources, able to replace the conventionally produced DGEBA thermoset. Initially, we synthesized an epoxy thermoset from vanillin-derived Schiff base epoxy monomer (VTA-EP) that was thermally cured with bio-based 5, 5′-methylenedifurfurylamine (DFA). Due to the unsaturated double bond in cured VTA-EP/DFA thermoset displayed a relatively high glass transition temperature (Tg ~ 170 °C) than the DGEBA/DDM system. Also, tensile strength (60 MPa), storage modulus (3271 MPa), and elongation at break (2.8%) were higher. Additionally, the peak of heat release rate (PHRR) and the total heat release (THR) of the cured VTA-EP/DFA resin decreased, and LOI and UL-94 ratings were improved. The green epoxy thermoset exhibited good dissolution in various acidic conditions due to the degradability of the Schiff base network in contrast to DGEBA/DDM. This work demonstrates that the combination of biomass with Schiff base structure provides a versatile platform for the fabrication of multifunctional vanillin-derived epoxy thermosets.