Synthesis Of Epoxy Resins Research Articles

Straw Tar Epoxy Resin for Carbon Fiber-Reinforced Plastic: A Review.

The massive consumption of fossil fuels has led to the serious accumulation of carbon dioxide gas in the atmosphere and global warming. Bioconversion technologies that utilize biomass resources to produce chemical products are becoming widely accepted and highly recognized. The world is heavily dependent on petroleum-based products, which may raise serious concerns about future environmental security. Most commercially available epoxy resins (EPs) are synthesized by the condensation of bisphenol A (BPA), which not only affects the human endocrine system and metabolism, but is also costly to produce and environmentally polluting. In some cases, straw tar-based epoxy resins have been recognized as potential alternatives to bisphenol A-based epoxy resins, and are receiving increasing attention due to their important role in overcoming the above problems. Using straw tar and lignin as the main raw materials, phenol derivatives were extracted from the middle tar instead of bisphenol A. Bio-based epoxy resins were prepared by replacing epichlorohydrin with epoxylated lignin to press carbon fiber sheets, which is a kind of bio-based fine chemical product. This paper reviews the research progress of bio-based materials such as lignin modification, straw pyrolysis, lignin epoxidation, phenol derivative extraction, and synthesis of epoxy resin. It improves the performance of carbon fiber-reinforced plastic (CFRP) while taking into account the ecological and environmental protection, so that the epoxy resin is developed in the direction of non-toxic, harmless and high-performance characteristics, and it also provides a new idea for the development of bio-based carbon fibers.

Preparation and self‐healing properties of epoxy vitrimer materials based on imine bonds

AbstractVitrimer materials have machinability and stability because of their shape remodeling and self‐healing properties at high temperatures. This article reports the synthesis of epoxy resin using vanillin, p‐aminophenol, and epichlorohydrin as raw materials, and polyetheramine‐400 as a curing agent. To study the effect of free amine on the mechanical and self‐healing properties, two materials with epoxy and amine stoichiometric ratios of 1:1 and 1:1.2 were studied, respectively. The experimental results show that when the molar ratio of epoxy to amine stoichiometric is 1:1.2 (V1:1.2), the tensile strength of vitrimer materials can reach 5.4 MPa and the self‐healing efficiency can reach 99.5% after 6 h of healing at 120°C. When the molar ratio is 1:1 (V1:1), the obtained epoxy material has a higher tensile strength of 9.5 MPa. After 24 h of healing at 120°C, the self‐healing efficiency can reach 83.4%. In addition, epoxy vitrimer materials can be remodeled at 120°C, and the self‐healing and mechanical properties are not influenced after remodeling. This work proposes a novel preparation method for epoxy vitrimer materials, which is beneficial to the development of high‐strength remodelable self‐healing materials.

Oxone in microemulsion for diastereoselective epoxidation of R-limonene to trans-limonene dioxide

Some catalytic processes developed for the synthesis of epoxy resins, polycarbonates or even non-isocyanate polyurethanes from cis/trans-limonene dioxide exhibit low or complete absence of reactivity of cis-limonene dioxide (cis-LDO). This study focuses on the development of a process for exclusively producing trans-LDO. The technique involves uses a chiral ketone as a catalyst that reacts with oxone to form the corresponding chiral dioxirane which epoxidises R-limonene. The effect of various organic solvents and the importance of the surfactant (for micelle formation) were evaluated. It was found that when epoxidation is performed using a chiral ketone in presence of a microemulsion, high conversion and diastereoselectivity was reached. The chiral ketone catalyst tested in this way gave an LDO yield close to 100%, consisting almost exclusively of trans-LDO (97%). When acetone catalyst was employed instead of the chiral ketone, a mixture of cis and trans-LDO was obtained with a selectivity to trans diastereoisomers of only 39%. The diastereoselective epoxidation process developed is easy to reproduce and could be considered ready for industrial implementation.

Synthesis of epoxy and phenyl groups‐containing polyhedral oligomeric silsesquioxane of large Si16O24 cage and its flame retardant and mechanical performances on epoxy resins

AbstractA kind of the epoxy and phenyl groups‐containing POSS of the regular cage of 16 silicon atoms (EPHPOSS) was synthesized successfully via the hydrolysis‐condensation reaction of phenyltrimethoxysilane and 2‐(3,4‐glycidoxypropyl) propyltrimethoxysilane, and its chemical structure was characterized. To improve the comprehensive performances of the epoxy resin (EP), EPHPOSS in different ratios was incorporated into the EP by thermal curing technology. It is obtained that the EPHPOSS has a homogeneous dispersion in the EP composites and plays an important role in enhancing the bending strength and thermal properties of the EP composites. The EP composite with 10 wt% EPHPOSS has a limiting oxygen index (LOI) value of 27.8%, higher than the LOI of 23.2% of the pure EP. The peak of heat release rate, total heat release, and total smoke release of the EP composites with the EPHPOSS are reduced obviously. In flame retardant mechanism of the EPHPOSS on the EP, the microstructures of the burning char and TG‐FTIR of the EP composites were achieved, it is suggested that the EPHPOSS promotes the formation of compact and continuous char layers and reduces the production of the organic combustible gases.

Bisphenol‐A free bio‐based gallic acid amide epoxy thermosets

AbstractBisphenol‐A (BPA)‐based epoxy thermoset has been used commercially due to its many impressive properties. However, it has toxic effects on human health, and it is obtained from petrochemicals so environmentally friendly bio‐based alternatives to substitute BPA for the synthesis of epoxy resins are essential. In this context, a gallic acid amide was synthesized from renewable gallic acid, and diethanol amine. The epoxy resin of the synthesized amide was obtained by the condensation reaction with epichlorohydrin in an alkaline medium. The synthesized epoxy resin was cured with a combination of two hardeners, aliphatic bio‐based poly(amido amine) and aromatic 2‐aminophenyldisulfide at varying weight percentages. The chemical structure of the synthesized epoxy resin was characterized by FTIR and NMR spectroscopic analyses. The synthesized epoxy thermosets showed a maximum tensile strength of 20.04 MPa along with elongation at break of 62.63%, high impact resistance (>19.3 kJ/m2), high scratch hardness (up to 8.5 kg), and high adhesive strength for metal–metal substrates. Moreover, the thermo‐gravimetric analysis showed good thermostability with an initial degradation temperature of 224°C, while the microbial broth culture test confirmed the biodegradability of the thermosets. Thus, this bio‐based epoxy thermoset could find different potential applications including as a binder for eco‐friendly coatings and paints.

Bio-sourced alternatives to diglycidyl ether of bisphenol A in epoxy–amine thermosets

Since the 1940s, bisphenol A (BPA) has been used in the plastic industry, reaching production of 10 Mt in 2022. More than 30% of the produced BPA is used in the production of epoxy resins. Decades of research has now provided enough evidence that BPA has endocrine-disrupting activity. Hence, it is an urgent matter to replace BPA in the production of epoxy resins. In the past years, considerable efforts have been put into finding alternatives to the toxic BPA. However, not only does the diglycidyl ether of BPA exhibit high polymerization reactivity, but also the presence of aromatic rings confers interesting thermomechanical resistance to epoxy networks therefrom. Hence, these properties are also expected from potential alternatives to BPA. In this review, first, the elements leading to toxicity of BPA are explained and then thorough accounts of possible bio-sourced aromatic alternatives to BPA are gathered. The reported synthetic routes for each of these alternatives and their toxicity are described. Also, their use in synthesis of epoxy resins and how the new alternatives influence the mechanical properties are discussed. This is a concise summary of the structure–property and structure–toxicity relationship for possible bio-sourced substitutes of BPA in synthesis of epoxy resins.

In-situ pyrolysis kinetic analysis and fixed-bed pyrolysis behavior of ex-service wind turbine blades

After the peak of rapid wind power development, a large amount of wind turbine blades reach/exceed their service life due to aging or damage. These ex-service wind turbine blades (EWTB) will increase the issue of its high-efficient utilization in the future decades. Among several treatment methods, pyrolysis has been considered as a promising solution to separate inorganic fiberglass and make organic epoxy resin (OER) high-value-added converted. However, the pyrolysis mechanism, chemical composition, and fiberglass separation of EWTB have not been deeply studied. In this paper, the synthetic model compound of epoxy resin was firstly used to investigate the thermal weight loss and pyrolysis kinetics, the thermal weight loss temperature range of which was 300 ∼ 480 °C. The apparent activation energy was minimum when the conversion rate was 0.6, and the pyrolysis mechanism was determined by the Coats-Redfern method as a diffusion control. On this basis, a lab-scale fixed-bed was conducted to study fast-heating pyrolysis characteristics of EWTB. It could be analyzed that the chemicals in the pyrolytic liquid were a series of phenolics with methyl and vinyl substituted benzene rings (e.g., bisphenol A, p-isopropenyl phenol, and phenol). Bisphenol A presented a relatively high selectivity of 51.02%, which could be recycled as the main raw material for the synthesis of epoxy resins. Furthermore, clean fiberglass could be separated by combusting the residual carbon in pyrolytic solids. These results might be useful for achieving the separation and resource utilization of organic and inorganic components of EWTB.

Evolution of Charge Trapping and Insulating Performances of Epoxy Materials Containing Hydrolyzable Chlorine During Hygrothermal Aging

Hydrolyzable chlorine is a well-known residue issued from the synthesis of epoxy resin, which may impart specific dielectric properties. In this work, the changes in distributed energy levels and charge trap depths of the molecule containing such defects are investigated using quantum chemical calculations. These changes are analyzed from the microscopic perspectives of electron energy structure and electron cloud offset. The charge transport and charge injection behavior in epoxy materials before and after the hydrolysis are predicted using the analysis results. The volume resistivities and space charges of epoxy materials with three different hydrolyzable chlorine contents are tested at different hygrothermal aging times, which are consistent with the previous predictions. These results are used to explain the ac breakdown strength of these epoxy materials at different hygrothermal aging times. It is indicated that the structural changes (electronegativity and atomic position changes) of the molecule containing hydrolyzable chlorine before and after hydrolysis change the spatial distribution of electron cloud density between and on valence bonds, and in turn, change the energy levels of different molecular segments. This results in a large increase in the overall electron trap depth and a small decrease in the overall hole trap depth of the molecule after hydrolysis.

Thermo-healing and recyclable epoxy thermosets based on dynamic phenol-carbamate bonds

In recent years, the reversible addition reaction of isocyanates and active hydrogen compounds has aroused wide concern. The synthesis of a novel dynamic covalent system based on phenol-carbamate bonds (PCBs) and its application in the preparation of thermo-healing and recycled epoxy resins have become a research hotspot. Herein, a compound with a phenolic hydroxyl group was designed and synthesized, which was used to react with isocyanate to obtain the dynamic covalent system of PCBs. Based on PCBs, a cross-linked polyurethane curing agent and the epoxy thermosetting resin with recyclability and thermo-healing ability were prepared. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), stress relaxation analysis and tensile test were carried out on the synthesized epoxy resins based on PCBs (PCBs-EP). The results showed that the dynamic PCBs endow epoxy thermosets with outstanding reprocessability, thermo-healing, welding, recycling and shape memory properties. Based on the reversible dynamic phenol-carbamate bonds, PCBs-EP can be thermally healed within 2 h under 100 °C, and the thermo-healing effect is obvious. More surprisingly, the tensile strength of PCBs-EP reaches 95.89 (±1.06) MPa, and its tensile strength still maintains 74.13% of the original after healed and 70.6% of the original after welded. Therefore, the strategies for incorporating dynamic covalent PCBs into thermosetting epoxy resins provide a feasible strategy for preparing cross-linked epoxy thermosets with high thermo-healing efficiency and high mechanical strength in a cost-effective manner.

Bio-based epoxy resins derived from diphenolic acid via amidation showing enhanced performance and unexpected autocatalytic effect on curing

Bisphenol A (BPA) is the main precursor in the synthesis of epoxy resins. However, because of its toxic and nonrenewable nature, BPA is unsuitable in the sustainable preparation of epoxy resins. In contrast, Diphenolic acid (DPA) is renewable but its carboxyl group limits its applications in bio-based thermosets. In this study, we report a novel amidation route to tailor DPA to produce epoxide monomers that present epoxy resins with a high performance. The diphenolic amides exhibited very low toxicities when compared with that of BPA, and also provided an unexpected autocatalytic effect on the curing reactions when succinic anhydride (SA) was used as the hardener. Dynamic mechanical analyses (DMA) and tensile test results confirmed the remarkable thermomechanical properties of the cured epoxy resins, which may be attributed to the increased cross-linking density and enhanced hydrogen bonding by the amide groups. Among the SA-cured epoxy resins, diglycidyl ether of diphenolic ethylamide exhibited the best performance, which included a high Tg of 114 °C, char yield (CY) of 20%, tensile strength of 60.2 MPa, and toughness value of 185 MPa. In addition, the DPA-derived epoxy resins have great potential in the preparation of bio-based composites because they act as excellent interfaces between the resin and cotton fibers (CoFs). Our study presents a new strategy to prepare bio-based epoxy resins with a high performance, emphasizing the greater potential of amidated DPA derivatives to replace BPA in the epoxy resin market.

Unique Gelation of Polyethylene Glycol-Modified Lignin in Hot Ethanol and Its Application to the Synthesis of Epoxy Resin with a Large Lignin Content

Glycol lignin is one of the novel lignin derivatives extracted from softwood meal and is expected to be an industrially important organic resource. Here, we show the peculiar aggregation behavior of glycol lignin in ethanol and the production of an ethanol-containing gel. The gel could be simply obtained by stirring glycol lignin powder in hot ethanol for several minutes. Furthermore, the gelled glycol lignin could be easily and homogeneously mixed with a traditional epoxy chemical, bisphenol A diglycidyl ether, in any ratio without any additional solvent and/or heating, resulting in an easy production of epoxy resin using wood-based lignin resources. Since the residual ethanol in the mixture could be easily evaporated before the curing process, thermosetting hard epoxy resin with glycol lignin contents of up to 90 wt % was prepared through the homogeneous mixing with the gel. Quantitative analysis of the equilibrium reaction between ethanol and glycol lignin using a gas adsorption analysis tool was investigated to understand the gelation behavior. It was suggested that the ethanol molecules were stored between polyethylene glycol molecular chains in glycol lignin, which generates a unique chemical character of this novel lignin derivative material.

Rheological Analysis of the Synthesis of High-Molecular-Weight Epoxy Resins from Modified Soybean Oil and Bisphenol A or BPA-Based Epoxy Resins.

The research undertaken in this work is one of the examples of the engineering of modern polymer materials. This manuscript presents studies on the gelation process which might occur during the synthesis of epoxy resin using the modified vegetable oil via the epoxy fusion process conducted in bulk. Based on obtained results we determined rheological parameters related to the properties of reacting mixture during the polyaddition process, especially before and after occurring the phenomenon of gelation (via (1) theoretical determination of the gel point using the degree of conversion of reactants before occurring the gelation process of reacting mixture and (2) experimentally—the dynamic mechanical properties such as storage modulus, G′; loss modulus, G″; and loss tangent, tg δ). Theoretical investigations show that for both systems: epoxidized soybean oil and bisphenol A (ESBO_BPA), as well as the hydroxylated soybean oil and low molecular weight epoxy resin (SMEG_EPR), theoretical values of the degree of conversion at the gel point are characterized by similar values (ESBO_BPA: xgel-theoretical = 0.620, xgel-theoretical = 0.620 and SMEG_EPR: xgel-theoretical = 0.614, xgel-experiment = 0.630, respectively), while the one determined based on the initial assumptions are greater than the above-mentioned (ESBO_BPA: xgel-assumed = 0.696 and SMEG_EPR: xgel-assumed = 0.667). Moreover, experimental studies in the viscoelastic fluid stage showed that the SMEG_EPR system is characterized by lower values of G′ and G″, which indicates lower elasticity and lower viscosity than the epoxidized derivative. It was found that alike during the conventional polyaddition reaction, both systems initially are homogeneous liquids of increasing viscosity. Wherein gradual increase in viscosity of the reaction mixture is related to the fusion of oligomer molecules and the formation of higher molecular weight products. In the critical stage of the process, known as the gelation point, the reaction mixture converts into the solid form, containing an insoluble cross-linked polymer.

Synthesis and properties of high temperature self-curing epoxy resin

A new bifunctional epoxy resin was synthesized by the reaction of replacing the hydrogen atom of amino groups from 4,4-diaminodiphenylmethane and epichlorohydrin taken in a double excess in dichloroethane. In order to remove HCl formed during the synthesis, which can interact with the initial diamine, as well as with the oxirane rings of both epichlohydrin and the synthesized product, an excess of potassium carbonate was introduced into the reaction mixture. The structure of the synthesized epoxy resin - 4,4′-methylenebis (N- (oxiran-2-ylmethyl) aniline) was characterized and proved by the methods of FTIR spectroscopy, nuclear magnetic resonance and elemental analysis. The kinetic parameters of the synthesized resin were characterized by differential scanning calorimetry. Using the Kissinger method, the activation energy of the self-curing reaction was calculated, the value of which was 1.139 kJ / mol. Such a low activation energy of epoxy resin allows to cure at low temperatures, but shortens the storage time. Two curing modes were studied: 1 mode - 10 hours at 150 ° C, 2 step mode - 10 hours at 150 ° C + 3 hours of postcuring at 180 ° C.

Development of fiber-reinforced transparent composites

In this study, a continuous glass fiber-reinforced composite is manufactured using the vacuum assisted resin transfer molding (VARTM) process. The composite is manufactured from an S-glass fiber acting as reinforcement and an epoxy resin as matrix. Unlike a traditional E-glass fiber reinforcement, S-glass fibers give higher stiffness and provide easier manufacturability due to the value of the refractive index of S-glass lying within the range of refractive indices of the epoxy resin. The epoxy resin is synthesized Epon 826, Epalloy 5200, and hexahydropthalic anhydride and tailored to match refractive indices of the S-glass fibers. After synthesis of the resin, composite panels are manufactured from the synthesized epoxy resin and S-glass fibers with a bi-directional [0°/90°] 8-harness satin weave. VARTM process was utilized to manufacture the composite panels. Composite panels are visually inspected for transparency, and tensile, flexural, and impact testing is performed. Mechanical tests showed consistent results for tensile modulus, tensile strength, flexural modulus, flexural strength, and impact damage resistance.

Synthesis and Properties of Furan Derivatives for Epoxy Resins

The discovery of huge petroleum reserves in the 19th century was a golden opportunity that promoted the industrial revolution, by offering a wide variety of cheap raw materials and a reliable source of energy. This caused an unprecedented increase of commodity and production of specialty chemicals in order to fulfill the needs of the global markets. However, as the global warming and the environmental issues has become a hazardous and worried situation, researchers are looking for bio renewable monomers with low toxicity in order to produce more sustainable polymers. This policy was also applied to epoxy resin materials because of their high volume production in industry for a wide range of applications. This review highlights the recent advances in the preparation of diamines and diepoxy monomers for the synthesis of epoxy resins, mainly from 2-furfural, 5-(hydroxymethyl)furfural (5-HMF), and 2,5-furandicarboxylic acid (FDCA), obtained from natural cellulose and hemicellulose feedstocks, respectively, and able to replace phthalic moieties in polyethylene terephthalate. In addition, the processes involved in the monomers preparation, such as reductive amination, etherification, esterification and carbonatation are listed. This review, reporting quasi-exhaustive synthetic pathways of epoxy precursors containing furanic moieties and describing the resulting resins, is composed of seven main parts, based on the synthesis of glycidyl derivatives containing one or two or four furan nuclei bearing or not a spacer between the furan ring and the function. The influence of the substituents on furan moieties (O, CO, CH 2) and the spacer between these groups have also been evaluated. Finally, thermal and a few mechanical properties of the obtained bio-sourced epoxy resins were compared to their fossil fuel analogues (from bisphenol A), featuring the high potential of bio-based monomers as substituents for non-renewable ones.

Novel Cycloaliphatic Cashew Nut Shell Liquid Derivatives and their use as Isocyanate Protective Groups

Cardanol (3-pentadecenyl-phenol), a well-known non-edible natural oil obtained as a by-product of the Cashew Industry, represents a valid alternative to petro-based derivatives, thanks to its peculiar chemical structure. When selected as polymer building block in the synthesis of epoxy curing agents or polyols and diols for polyurethane applications, cardanol can impart unique benefits, like chemical resistance, hydrolytic stability, thermal resistance and balanced mechanical properties. Once used in polyurethane prepolymers, it demonstrates various benefits, including favorable and easily tunable deblocking conditions, lower viscosity of resulting NCO-blocked prepolymers and excellent storage stability in comparison to commonly used phenolic compounds (phenol, nonylphenol, in particular). In this paper, novel cardanol-based fully cycloaliphatic derivatives (e.g. cyclohexanol, oxime, lactam-types) will be presented, investigating their use as innovative isocyanate protective groups with faster reactivity and lower deblocking temperatures than petro-derived benchmarks.

Epoxy resin with excellent ultraviolet resistance and mechanical properties derived from renewable camphoric acid

AbstractGenerally, high‐performance epoxy resins, which are derived from aromatic compounds have two major disadvantages of yellowing and brittleness, and thus it presently remains a challenge for the facile synthesis of epoxy resin with excellent ultraviolet resistance and superior strength and toughness. Herein, a novel bio‐based epoxy resin diglycidyl ester of camphoric acid (DGECA) was synthesized from the renewable camphoric acid via an efficient and scalable route. The chemical structure of DGECA was carefully characterized by Fourier transform infrared (FT‐IR), nuclear magnetic resonance (NMR), and mass spectrometry before being cured with methylhexahydrophthalic anhydride (MHHPA). Compared with the cured diglycidyl ether of bisphenol A (DGEBA)/MHHPA, the cured DGECA/MHHPA system achieved 11.5%, 16.7%, and 109.4% increment in flexural strength (126 MPa vs. 113 MPa), modulus (2.8 GPa vs. 2.4 GPa), and impact strength (6.7 kJ/m2vs. 3.2 kJ/m2), respectively. Moreover, cured DGECA exhibited extremely lower ultraviolet absorption (0.038A) and better ultraviolet resistance than that of cured DGEBA. This work provides a new strategy to synthesize epoxy resin with excellent ultraviolet resistance and high toughness by using the unique structure of renewable feedstock.

Novel castor-oil-based flame-retardant and flexible epoxy resins: synthesis and properties

A novel castor-oil-based and phosphorus-containing epoxy resin (flame-retardant epoxy resin (FREP)) and a curing agent – castor oil polybasic acid (AACO) – with high flame retardancy and flexibility were successfully synthesized. The chemical structures of FREP and AACO were characterized by Fourier transform infrared spectrometry (FTIR) and hydrogen-1 (1H) nuclear magnetic resonance spectroscopy. The epoxy resin components were prepared by using bisphenol A epoxy resin (diglycidyl ether of bisphenol A (DGEBA)) with different mass contents of FREP and AACO. DGEBA with 40 wt% FREP (FREP40) possessed a large limiting oxygen index of 29.3%. Cone calorimetry showed that the heat release and smoke production were reduced for both DGEBA with 20 wt% FREP (FREP20) and FREP40 in comparison with those of pure resin (FREP0), indicating that the smoke release and fire hazard of epoxy resin composites with FREP were reduced. Thermogravimetry–infrared spectroscopy suggested that the yields of toxic carbon monoxide (CO), carbon dioxide (CO2) and other pyrolysis products were significantly reduced. FTIR and X-ray photoelectron spectroscopy showed that FREP40 outperformed FREP0 in carbon-forming capacity. The introduction of FREP and AACO effectively increased the elongation at break of pure epoxy resins. FREP and AACO provide a promising strategy for synthesis of epoxy resins with excellent flame retardancy, smoke suppression and flexible performance.

Migration of bisphenol A from epoxy coating to foodstuffs

Bisphenol A enters into the synthesis of epoxy resins; which are used as coating or food contact paint. Polymerization of epoxy resins may not be fully complete so Bisphenol A can migrate into solutions. The regulation allows a migration limit of 0.05 mg of BPA per kg of food. After development and characterization of an epoxy film by infrared and thermo gravimetric analysis, we followed the kinetics of this specific migration as a function of two key parameters; nature of the contact and temperature which varies between 40 and 70 °C. Three simulants were used in this study which represents three categories of food (water for aqueous foods, ethanol for alcoholic foods and acetic acid for acidic foods). The measurement of the amount of Bisphenol A migrated was detected using UV visible spectroscopy, and it’s found in compliance with regulation concerning water.

Synthesis of Epoxy Resin from Aromatic Oligomer Having Ether Ether Ketone Structure and Physical Properties of Its Cured Product

Synthesis of Epoxy Resin from Aromatic Oligomer Having Ether Ether Ketone Structure and Physical Properties of Its Cured Product