Conventional Epoxy Research Articles

Insights into biobased epoxidized fatty acid isobutyl esters from biodiesel: Preparation and application as plasticizer

Biodiesel was used to prepare epoxidized fatty acid isobutyl esters (Ep-FABEs) as a biobased plasticizer in this work. Transesterification of biodiesel with isobutanol catalyzed by tetrabutyl titanate was carried out in a gas-liquid tower reactor. The conversion achieved nearly 100% within 5 h under the reaction temperature, the mass ratio of catalyst to fatty acid methyl esters (FAMEs), and isobutanol to FAMEs total molar ratio of 180 °C, 0.4 %(mass), and 5.4:1, respectively. In addition, kinetic model of the transesterification reaction was developed at 150–190 °C. The calculated activation energy was 48.93 kJ·mol−1. Then, the epoxidation of obtained fatty acid isobutyl esters (FABEs) was conducted in the presence of formic acid and hydrogen peroxide. The Ep-FABEs was further analyzed for its plasticizing effectiveness to replace dioctyl phthalate (DOP) and compared with conventional epoxy plasticizer epoxidized fatty acid methyl esters (Ep-FAMEs). The results indicated that the thermal stability and mechanical properties of PVC films with Ep-FABEs plasticizer were significantly improved compared with those plasticized with DOP. In addition, the extraction resistance and migration stability of Ep-FABEs were better than those of Ep-FAMEs. Overall, the prepared Ep-FABEs via structural modification of biodiesel proved to be a promising biobased plasticizer.

A robust and eco-friendly waterborne anti-corrosion composite coating with multiple synergistic corrosion protections

Environmentally friendly waterborne coatings have received significant attention recently due to their lower volatile organic compounds (VOCs) emission than solvent-based coatings, but their practical applications are severely limited by poor barrier properties. Herein, a novel and robust waterborne OBN-PA-Zn-D/WEP anti-corrosion composite coating was successfully fabricated by utilizing hydroxyl-functionalized h-BN (OBN) nanosheets , phytic acid (PA), Zn 2+ and dicyandiamide. Due to the π-π interactions between OBN and organic-inorganic PA-Zn-D complex, the dispersibility of OBN-PA-Zn-D nanosheets was improved, which was beneficial for enhancing the physical barrier properties of OBN-PA-Zn-D/WEP composite coating. After adding dicyandiamide, the interface compatibility between OBN-PA-Zn-D nanosheets and the waterborne resin matrix was significantly improved, greatly reducing the defects inside the OBN-PA-Zn-D/WEP composite coating. In addition, PA and Zn 2+ formed protective layer in the defect area to inhibit the corrosion of anode and cathode . Therefore, under the effect of multiple synergistic corrosion protections , the eco-friendly waterborne OBN-PA-Zn-D/WEP composite coating exhibited unique anti-corrosion performance that was greatly improved compared with the conventional waterborne epoxy coatings . • A robust and eco-friendly waterborne anti-corrosion composite coating was prepared. • OBN-PA-Zn-D/WEP composite coating provided strong corrosion protection. • Physical barrier, corrosion inhibition and interface enhancement synergistically enhance anti-corrosion ability.

Impacts of Resveratrol and Pyrogallol on Physicochemical, Mechanical and Biological Properties of Epoxy-Resin Sealers.

This study aimed at evaluating the physicochemical and biological properties of experimental epoxy-resin sealers containing polyphenols such as resveratrol and pyrogallol. A conventional epoxy resin (OB) was modified by adding different concentrations of resveratrol (RS) or pyrogallol (PY) to its composition. Antibacterial and antioxidant activities, mechanical properties, along with wettability and morphological changes were investigated. The results were statistically analyzed using ANOVA and multiple comparison tests (α = 0.05). The incorporation of the tested polyphenols into the epoxy resin enhanced its mechanical properties. PY demonstrated much better antioxidant and antibacterial activities than RS, which were associated with a higher release of PY. In contrast, PY showed a higher cytotoxicity than OB and OB doped with RS. OB containing PY presented a rougher surface and higher water absorption than OB doped with RS. Both tested polyphenols caused no notable changes to the overall porosity of OB. Resveratrol and pyrogallol may not only influence the morphology and mechanical properties of epoxy-resin sealers, but could also enhance antioxidant activity and antibacterial effects against Enterococcus faecalis. Most epoxy-resin sealers currently available in the market can be considered as “passive” materials. Thus, doping their composition with specific polyphenols may be a suitable strategy to confer some antibacterial properties, antioxidant potential, along with improvement of some mechanical properties.

Water Uptake in Epoxy Ionic Liquid Free Film Polymer by Gravimetric Analysis and Comparison with Nondestructive Dielectric Analysis.

Due to their high surface coverage, good adhesion to metal surfaces, and their excellent corrosion resistance, epoxy thermosets are widely used as protective coatings. However, anticorrosion protection of these coatings can be improved against water uptake and can be tuned by changing the chemical nature of the curing agents. In this work, a comparative study has been performed on the water uptake of an epoxy–amine based on bisphenol A diglycidyl ether (DGEBA) cured with an aliphatic amine and the same epoxy initiated with a phosphonium ionic liquid (IL). Thus, the epoxy networks were immersed in saline water solution in a controlled temperature environment. Gravimetric and electric impedance measurements were carried out for a maximum of 3 months. Results were analyzed in order to assess the water diffusion coefficients and water saturation limits. Two models, the Brasher–Kingsbury and a novel mixing rule, were applied on permittivity values. Results highlighted that epoxy–ionic liquid systems are less sensitive to water uptake than conventional epoxy–amine networks. Due to their higher hydrophobic properties the water diffusion coefficient of epoxy–ionic liquid systems are two times less compared to epoxy–amine samples and the water saturation limit is more than four times less. The analysis also shows that the novel mixing rule model proposed here is prone to better estimate the water uptake with accuracy from electrical impedance measurements.

A life cycle assessment comparison of materials for a tidal stream turbine blade

Electricity generated from tidal streams via underwater turbines has significantly lower greenhouse gas emissions than fossil-fuel derived electricity. However, tidal stream turbine blades are conventionally manufactured from non-recyclable reinforced polymer composite materials. Tidal stream capacity is forecast to be over 1GW by 2030, which using current methods will ultimately produce around 6000 tonnes of non-recyclable blade waste. This waste is currently disposed of in landfill or incinerated, both of which have greenhouse gas and human health impacts. To address a growing waste management problem, this high-level study considers for the first time a range of conventional and bio-based materials, manufacturing methods, and end-of-life treatments to determine the blade materials and designs likely to have low environmental impact. A finite element model is used to develop material cases and Life Cycle Assessment is used to study the impacts of each over a ‘cradle to dock, dock to grave’ scope. The impact of material choices on cost and modifications to the wider turbine are considered. Compared to a glass fibre composite turbine blade, steel blades are around 2.5 times heavier, and incur additional environmental impact due to upgrades required to the wider turbine. Carbon fibre composite blades weigh less than glass fibre, but cause greenhouse 80% greater gas emissions, and human and ecosystem health risks, so are also not recommended. The best environmental performance of the cases considered was a flax fibre composite. This material offers greenhouse gas emissions around 50% lower than glass fibre materials when manufactured using conventional epoxy resin, and around 40% lower when manufactured using recyclable epoxy resin, which also enables the reuse of the fibre and may further reduce environmental impact. Initial results suggest that the cost of these materials are similar to or lower than conventional composite materials.

Synthesis characterization and application of hexafunctional epoxy resin and comparison against commercial epoxy resin

Current study compares the various analytical results of hexafunctional epoxy resins based on bisphenol-A with conventional epoxy resins. Reaction of bisphenol-A, formaldehyde, and epichlorohydrin produces hexafunctional epoxy resin. The curing properties of commercial epoxy resin and hexafunctional epoxy resin were determined using a variety of hardeners, including diethylenetriamine, triethylenetetramine, phenalkamine, polyamido amines, and polyamides. The epoxy equivalent weight (EEW), hydrolyzable chlorine content, volatile content, Brookfield viscosity, weight average molecular weight, elemental analysis (C, H, N, O analysis), and Fourier transform infrared spectroscopy were used to characterize the hexafunctional resin (FT-IR). Jute and glass reinforced composites were also prepared by using hexafunctional epoxy resins and commercial epoxy resins. Mechanical properties (tensile strength, flexural strength, Izod impact strength, and Rockwell hardness), thermal properties, and chemical resistance were determined for each composite. Hexafunctional epoxy resin-based composites exhibited superior mechanical characteristics, thermal resistance, and chemical resistance properties than commercial epoxy resin-based composites.

Synthesis and Characterization of Non-Isocyanate Polyurethanes using Diglycidyl Ether of Bisphenol Acetone (DGEBPA) Epoxy Resin

Present work focuses on synthesis of non-isocyanate polyurethane (NIPU) using the conventional epoxy resin, diglycidyl ether of bisphenol acetone (DGEBPA). The conventional polyurethanes (PUs) are prepared by reaction of the toxic diisocyanates and polyols. The epoxy resin contains two epoxy groups which are converted to cyclic carbonate groups when reacted with carbon dioxide. In this work, the epoxy resin (ER) was converted into the cyclocarbonated epoxy resin (CCER) using methyltriphenylphosphonium iodide (MePh.I) as the catalyst and ethyl cellsuolve as the reaction medium. The reaction was carried out in a carbon dioxide atmosphere, slightly above the atmospheric pressure, for 20 h. The progress of reaction was monitored by percent oxirane oxygen content (%OOC). The FTIR study confirms the disappearance of epoxy groups at 910 cm-1 and appearance of cyclic carbonate groups at 1800 cm-1. The films of the resulting resin were prepared by curing with diethylamine (DEA), ethylene diamine (EDA) and reactive polyamide resin (70% NV). The formation of urethane linkage was confirmed by FTIR spectrum. The mechanical, chemical and appearance properties of the resulting NIPU were studied. The results were satisfactory, like improvement in adhesion and alkali resistance, but reduction in gloss and colour retention was observed. This eco-friendly route for synthesis of polyurethane can be used easily and variation in properties can be obtained by selecting the suitable epoxy compound as well as curing agent.

Comparative analysis of Basalt/E-Glass/S2-Fibreglass-Carbon fiber reinforced epoxy laminates using finite element method

This paper aims to numerically analyse (using finite element methods) the static loading effects on basalt/E-glass/S2-fibreglass-carbon fibre reinforced epoxy hybrid composites, an alternative to the conventional and expensive pure carbon fibre epoxy composites. Structural properties of few hybrid composites are evaluated through static tests for validation purpose. The composite specimens comprising of four layers of carbon fibre and four layers of either basalt/E-glass/S2-fibreglass combined with LY556 resin in six varying stacking sequences are analysed for failure based on Tsai-Wu failure criteria. Commercial finite element software ANSYS Composite PrepPost (ACP) and ANSYS Mechanical were employed for this study. All specimen dimensions, boundary conditions and loading were adopted as per ASTM Standards. Results and discussion are followed by a significant comparison of static test results between basalt, E-glass, and S2-fibreglass each combined with carbon fibre epoxy. Finally, the optimal stacking sequence was found to be S2 - [02C/±45 M/0M]S. Basalt-carbon hybrids produced superior results in tensile and flexural tests while the brittle glass-carbon hybrids proved to be better in compression and in-plane shear. Laminates with carbon fibre at the outer layers showed improved performance among contemporaries.

Application of Prosopis juliflora based bio oil in natural fibre reinforced composite laminates

Improved life style and liberal economic policies across the globe created a vast gap between the supply and demand of energy. Further, the need for materials of required characteristic in different engineering disciplines prompt researchers to explore alternate sources both in energy sector as well as material domain. In this work, the invasive species especially Prosopis juliflora which imposes a serious threat to the environment is subjected to thermal decomposition at different temperatures based on the decomposition range to obtain various products particularly bio oil and biochar. Further, the bio oil collected during the thermal decomposition process is collected and characterized by employing Fourier-transform infrared spectroscopy (FTIR) to use it as a supplementary to fossil fuel based phenolic resin. It is observed that, the tensile and flexural properties of the coir fibre reinforced composite laminates admixed with bio oil and conventional epoxy resin exhibit a higher strength in comparison to that of the neat epoxy resin based composites.

СОСТАВ И НЕКОТОРЫЕ СВОЙСТВА ЭПОКСИДНЫХ ОЛИГОМЕРОВ НА ОСНОВЕ ГЕКСАХЛОРЦИКЛОТРИФОСФАЗЕНА И ДИФЕНИЛОЛПРОПАНА

Phosphazene-containing oligomers (FEO) were synthesized by the one-pot method by reacting hexachlorocyclotriphosphazene, diphenylolpropane, and epichlorohydrin at 80 °C in the presence of solid KOH. In contrast to analogous oligomers previously obtained at a lower temperature, according to MALDI-TOF spectrometry data, they contain about 10% of compounds with two or three phosphazene rings linked by one or two oxyaryleneoxy radicals, while the total number of epoxy groups in the molecules of these compounds is from 4 to 8. FEO are cured with polyamine hardeners to form compositions with increased fire resistance, retaining at the same time the basic properties of conventional epoxy materials.

Recyclable and reformable epoxy resins based on dynamic covalent bonds – Present, past, and future

Epoxy resins, as a typical class of thermosetting polymers, have widespread industrial applications such as adhesives, coatings, electronic encapsulants, and polymer matrices for advanced composites, owing to their excellent mechanical performance, adhesive capacity, dimensional stability, heat, and chemical resistance. However, conventional epoxy resins cannot be reprocessed, repaired, or recycled due to their permanent crosslinked structures, making it a long-standing challenge to process and recycle the ever-increasing epoxy and epoxy-based composite similar to thermoplastics. Therefore, both economic and environmental factors are driving the development of reformable and recyclable epoxy resins. In this paper, various such epoxy vitrimers containing dynamic covalent bonds are reviewed. Future potentials of these epoxy vitrimers are also discussed.

On the structural damping response of hollow carbon composite shafts with room temperature curable novel acrylic liquid thermoplastic resin

Current research investigates the structural damping response of hollow tubular structures with novel acrylic liquid thermoplastic Elium® resin (EL) and thin ply carbon(TPC) and woven carbon(WC) as the reinforcement. The results are compared with the baseline tubes manufactured with conventional epoxy (EP) resin systems. The structural damping results have shown 26.7% higher structural damping for TPC/EL and 27.3% higher damping for WC/EL compared to TPC/EP and WC/EP tubular configuration respectively at all the accelerometer positions during the modal analysis tests. The viscoelastic presence in acrylic Elium® and its amorphous chemical structure as opposed to the cross-linked state in epoxy resin and good fibre matrix interfacial bonding is the major contributing factor towards this increase. Damping results have also shown that the thickness of the tube has a positive effect of the structural damping (1.6 mm as opposed to 1.1 mm) and on the contrary, an increase in the fibre volume fraction (64% as opposed to 41%) has an adverse effect on the damping phenomenon, 10% higher and 85% lower respectively.

Self-healing Ability of Epoxy Vitrimer Nanocomposites Containing Bio-Based Curing Agents and Carbon Nanotubes for Corrosion Protection

Epoxy is extensively used for anti-corrosion coatings on metallic materials. Conventional epoxy coatings have a permanent crosslink network that is unable to repair itself when cracks and damages occur on the coating layer. This study aims to develop self-healing epoxy vitrimer/carbon nanotube (CNTs) nanocomposite for coating. Two bio-based curing agents viz., cashew nut shell liquid (CNSL) and citric acid (CA) were employed to create covalent adaptable networks. The 0–0.5 wt% CNTs were also incorporated into epoxy/CNSL/CA matrix (V-CNT0-0.5). Based on the results of our study, thermomechanical properties of V-CNT nanocomposites increased with increasing CNTs content. The bond exchange reaction of esterification was thermally activated by near infrared (NIR) light. The V-CNT0.5 showed the highest self-healing efficiency in Shore D hardness of 97.34%. The corrosion resistance of coated steel with V-CNT0 and V-CNT0.5 were observed after immersing the samples in 3.5 wt% NaCl for 7 days. The corrosion rate of coated steel with V-CNT0.5 decreased from 9.53 × 102 MPY to 3.12 × 10–5 MPY whereas an increase in protection efficiency of 99.99% was observed. By taking advantages of the superior self-healing and anti-corrosion properties, V-CNT0.5 could prove to be a desirable organic anti-corrosion coating material.

Enhanced thermal conductivity of bio-based epoxy-graphite nanocomposites with degradability by facile in-situ construction of microcapsules

To efficiently disperse micro/nano thermally conductivity (TC) fillers without pretreatment is still considered as a major technical issue to prepare high TC polymeric composites. Here, a new bio-based epoxy thermoset (BE) that contains the Schiff base structure was synthesized. BE/GNP (graphite nanoplatelets) powder with microcapsule structure was constructed by a grinding process, and its nanocomposites were then fabricated by hot-press technique. The relationship between GNP dispersion and TC of BE/GNP nanocomposites were systematically investigated. Results showed that the dispersion of GNP was enhanced significantly and TC network was constructed efficiently. The nanocomposite exhibited a higher TC (2.21 Wm−1K−1) with only 10 wt% of GNP content, which is ~10 fold higher than that of conventional epoxy (EP). Moreover, modified Hashin-Shtrikman model demonstrated that its thermal resistance (0.031 m2KW−1) can be decreased efficiently by ~30.8% lower than EP/GNP nanocomposites (0.0448 m2KW−1) based on this strategy. The prepared nanocomposite is used as the heat sink of LED chips, which shows potential practicability in thermal management. In addition, the Schiff base BE/GNP nanocomposite network could be degraded completely, and GNP could be nearly nondestructive recycled. This work may open up future opportunities to directly incorporate thermal conductive filler without pretreatment to fabricate “green” and highly thermal conductive polymeric composites.

Facile synthesis of lignin-based epoxy resins with excellent thermal-mechanical performance

Up to now, various approaches have been used to fabricate lignin-based epoxy thermosets by utilizing lignin or lignin-derivatives, but there is still lack of a simple, effective and environmental-friendly pathway for producing lignin-based epoxy resins from industrial lignin. In this work, a novel strategy - one-pot to synthesize phenolated lignin incorporated novolac epoxy networks (PLIENs) was proposed. As expected, PLIENs obtained from the novel route exhibited preferable mechanical and thermal properties compared with the epoxy resins which obtained from common route. Moreover, increasing the loading of lignin did not significantly deteriorate the thermal-mechanical performance of cured epoxy resins. However, the Tg of PLIENs was slightly lowered compared with conventional petroleum-based epoxy resins (DGEBA). Nonetheless, the flexural strength and storage modulus of PLIENs were higher than that of DGEBA. Especially, the char yield of PLIENs at 800 °C was up to 28.9%, much higher than that of DGEBA (only 6.9%), which indicated that lignin has a certain promoting effect on the flame retardancy of epoxy resins. This research provides a new insight for producing commercially viable lignin-based epoxy thermosets.

Degradation of Thermal-Mechanically Stable Epoxy Thermosets, Recycling of Carbon Fiber, and Reapplication of the Degraded Products

Conventional epoxy resins can meet the requirement for engineering applications in which high glass transition and thermal stability are essential, but they show no degradability or recyclability. ...

The Working Principles of a Multifunctional Bondline with Disbond Stopping and Health Monitoring Features for Composite Structures

In comparison to bolted joints, structural bonds are the desirable joining method for light-weight composite structures. To achieve a broad implementation of this technology in safety critical structures, the issues of structural bonds due to their complex and often unpredictable failure mechanisms have to be overcome. The proposed multifunctional bondline approach aims at solving this by adding two safety mechanisms to structural bondlines. These are a design feature for limiting damages to a certain size and a structural health monitoring system for damage detection. The key question is whether or not the implementation of both safety features without deteriorating the strength in comparison to a healthy conventional bondline is possible. In previous studies on the hybrid bondline, a design feature for damage limitations in bondlines by means of disbond stopping features was already developed. Thus, the approach to evolve the hybrid bondline to a multifunctional one is followed. A thorough analysis of the shear stress and tensile strain distribution within the hybrid bondline demonstrates the feasibility to access the status of the bondline by monitoring either of these quantities. Moreover, the results indicate that it is sufficient to place sensors within the disbond stopping feature only and not throughout the entire bondline. Based on these findings, the three main working principles of the multifunctional are stated. Finally, two initial concepts for a novel multifunctional disbond arrest feature are derived for testing the fundamental hypothesis that the integration of micro sensors into the disbond stopping feature only enables the crack arrest and the health monitoring functions, while reaching the mechanical strength of a conventional healthy epoxy bondline. This work therefore provides the fundamentals for future investigations in the scope of the multifunctional bondline.

Probing the prediction of effective properties for composite materials

This article presents different micromechanical modelling techniques based on analytical and numerical approaches to determine the effective elastic and piezoelectric (piezoelastic) properties of graphene-based composite materials. Different types, orientations and shapes as well as different geometrical parameters of fiber reinforcement are considered for estimating the effective properties. The effective properties of composite are predicted with and without considering the strong covalent bond which provides interaction and in-plane stability of 2Dcrystalline graphene or strong van der Wall forces formed between graphene layers and the matrix. It is revealed that the axial, transverse and shear effective piezoelastic properties of graphene reinforced piezoelectric composite (GRPC) are significantly enriched due to the incorporation of graphene into the epoxy matrix. The importance of incorporating graphene as nanofillers/interphase into the conventional epoxy matrix to form an advanced composite and its effective properties are illustrated while these results show excellent agreement with previously reported experimental estimates. These results reveal that due to incorporation of graphene nanofillers, there is a significant enhancement in effective properties of composite. The results would also help to recognize the most important material properties with respect to different shapes and orientation of reinforcements which influences the performance of system significantly. To confirm safety, robustness and sustainability of the structure, it is the most prior requirement to determine the effective properties of composites considering different parameters for the different static and structural analyses.

The properties and suitability of commercial bio‐based epoxies for use in fiber‐reinforced composites

AbstractEnvironmental concerns about fiber composites are leading manufacturers to consider bio‐based alternatives to petroleum‐derived epoxies. Such a substitution is hindered by a lack of information, so commercially available bio‐based epoxy systems have been compared, their mechanical properties measured, and fiber composites produced by vacuum infusion. Most high bio‐based content resins for infusion use conventional curing agents. Bio‐based content is generally added using Epicerol, but also other bio‐based precursors. A diglycidyl ether of bisphenol A system produced using Epicerol achieves 20 % bio‐based content, but achieves higher contents when Epicerol is used in diluents. Fully bio‐based monomers can be deleterious to the mechanical properties and glass transition temperature (Tg), so are used sparingly. The most‐promising systems (28 % to 43 % bio‐based) compare well to conventional epoxies, possessing good strength, stiffness, toughness, and a reasonable Tg. These partially bio‐based epoxies offer an immediate lower‐carbon alternative for vacuum‐infused composites in marine, sports equipment, and wind energy.

Recyclable High-Performance Epoxy-Anhydride Resins with DMP-30 as the Catalyst of Transesterification Reactions.

Epoxy-anhydride resins are widely used in engineering fields due to their excellent performance. However, the insolubility and infusibility make the recycling of epoxy resins challenging. The development of degradable epoxy resins with stable covalent networks provides an efficient solution to the recycling of thermosets. In this paper, 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) is incorporated into the epoxy-glutaric anhydride (GA) system to prepare high-performance epoxy resins that can be recycled below 200 °C at ordinary pressure via ethylene glycol (EG) participated transesterification. The tertiary amine groups in DMP-30 can catalyze the curing reaction of epoxy and anhydride, as well as the transesterification between ester bonds and alcoholic hydroxyl groups. Compared with early recyclable anhydride-cured epoxy resins, the preparation and recycling of diglycidyl ether of bisphenol A (DGEBA)/GA/DMP-30 systems do not need any special catalysts such as TBD, Zn(Ac)2, etc., which are usually expensive, toxic, and have poor compatibility with other compounds. The resulting resins have glass transition temperatures and strengths similar to those of conventional epoxy resins. The influences of GA content, DMP-30 content, and temperature on the dissolution rate were studied. The decomposed epoxy oligomer (DEO) is further used as a reaction ingredient to prepare new resins. It is found that the DEO can improve the toughness of epoxy resins significantly. This work provides a simple method to prepare readily recyclable epoxy resins, which is of low-cost and easy to implement.