Epoxy Compounds Research Articles

Atmospheric persistence and toxicity evolution for fluorinated biphenylethyne liquid crystal monomers unveiled by in silico methods

It is essential to understand the atmospheric fate of liquid crystal monomers (LCMs), an important component in liquid crystal displays (LCDs); however, limited information is available at present. In this study, the atmospheric reaction mechanism, kinetics and toxicity evolution of three fluorinated biphenylethyne LCMs (1,2,3−trifluoro−5−(2−(4−methylphenyl)ethynyl)benzene (m−TEB), 1,2,3−trifluoro−5−(2−(4−ethylphenyl)ethynyl)benzene (e−TEB), 1,2,3−trifluoro−5−(2−(4−propylphenyl)ethynyl)benzene (p−TEB)) are investigated by theoretical calculations. Results show that the initial reactions of·OH addition to −C ≡ C− groups and hydrogen abstraction from alkyl groups (−CH3, −C2H5, −C3H7) are dominant pathways. The resulting transformation products (TPs) for m-TEB are mainly highly oxidized multi-functional compounds such as benzil-based compounds, benzoic acid, alcohols, aldehydes, diketone and epoxy compounds. Results also show that some TPs exhibit higher aquatic toxicity than the parent. The calculated rate constants of m−TEB, e−TEB and p−TEB with·OH at 298 K are in the ranges of (1.3 −8.6) × 10−12 cm3 molecule−1 s−1, and the corresponding atmospheric half-lives are 3.8−9.3, 2.2−5.4 and 0.6−1.4 days, respectively. This evidences that m−TEB and e−TEB may have atmospheric persistence and could undergo long-range transport. The results herein could be helpful for clarifying the atmospheric fates, persistence and risks of fluorinated LCMs with ethynyl benzene center.

Effect of Cross-Linking Density on Horizontal and Vertical Shift Factors in Linear Viscoelastic Functions of Epoxy Resins

Epoxy resins are an important class of thermosetting resins, and their network structure, obtained by the curing reaction of epoxy and amine compounds, plays an important role in the material properties. We here revisited a time–temperature superposition (TTS) principle applied to the dynamic viscoelastic functions of epoxy resins, in which the network was well defined and systematically varied on the basis of the length of n-alkyl diamine. The superimposition of isothermal curves in the frequency domain required not only a horizontal shift but also a vertical shift, regardless of the length of n-alkyl diamine. The temperature dependence of the horizontal shift factor, aT, could be well expressed by the Williams–Landel–Ferry equation. The fitting parameter, called C2, increased with decreasing alkyl chain length of the diamine, meaning that the thermal expansion of the free volume was suppressed due to greater cross-linking density. This was qualitatively confirmed by a full-atomistic molecular dynamics (MD) simulation. Meanwhile, the vertical shift factor, bT, increased with increasing temperature, and the extent was smaller with increasing cross-linking density. This can be explained in terms of the entropic contribution to the modulus in the temperature region above the glass transition temperature. The entropy change estimated using the isobaric molar heat capacity from the MD simulation strongly supported this hypothesis. The knowledge here obtained should be useful for a better design of thermosetting polymers as well as for the prediction of long-term durability.

Delamination and Engineered Interlayers of Ti3C2 MXenes using Phosphorous Vapor toward Flame-Retardant Epoxy Nanocomposites.

As recently created inorganic nanosheet materials, more and more light has been shed on MXenes, which have emerged as a hotspot of intensive investigations. The simple exfoliation method for MXenes attracts numerous studies to pay efforts on. Compared with the extensive research about ultrasonication and mechanical milling, gas-assisted exfoliation has never been carried out for MXenes. Meanwhile, MXene-based nanocomposites are always prepared after exfoliation step by step. In this work, a facile way to fabricate a few-layered Ti3C2 MXene delaminated using phosphorous vapor evolved from commercial red phosphorous (RP) is put forward. The vapor deposits on the surface of Ti3C2 and also partially intercalates into the interlayers to obtain a novel two-dimensional RP/Ti3C2 nanocomposite directly. The P element strongly connects with the substrate by a covalent bond that improves the safety problems for RP during storage and usage. Due to the versatile feature of MXenes, the nanocomposite has the potential to be applied in a variety of fields. Herein, it is employed as a flame retardant for epoxide resin and effectively reduces fire disaster. The one-step exfoliation plus nanocomposite fabrication provides a more feasible way for the practical application of MXenes.

A moisture-tolerant route to unprotected \u03b1/\u03b2-amino acid N-carboxyanhydrides and facile synthesis of hyperbranched polypeptides

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups. Here we report a robust method for preparing unprotected NCA monomers in air and under moisture. The method employs epoxy compounds as ultra-fast scavengers of hydrogen chloride to allow assisted ring-closure and prevent NCA from acid-catalyzed decomposition under moist conditions. The broad scope and functional group tolerance of the method are demonstrated by the facile synthesis of over 30 different α/β-amino acid NCAs, including many otherwise inaccessible compounds with reactive functional groups, at high yield, high purity, and up to decagram scales. The utility of the method and the unprotected NCAs is demonstrated by the facile synthesis of two water-soluble polypeptides that are promising candidates for drug delivery and protein modification. Overall, our strategy holds great potential for facilitating the synthesis of NCA and expanding the industrial application of synthetic polypeptides.

Mechanical properties of unmodified and montmorillonite-modified epoxy compounds. Part I: compression test

The aim of the article was to determine the compressive strength and compressive strain of an unmodified and a modified epoxy compounds containing a montmorillonite filler, as well as to determine the effect of temperature and an aging time on the mechanical parameters of the considered epoxy compounds. The subject of the research was both the unmodified and the modified adhesive compounds. The unmodified epoxy compounds were made in four variants, which included the epoxy resins based on a bisphenol A as well as the curing agents: a triethylenetetramine and a polyamide curing agent. The modified compounds containing the montmorillonite filler, were also made in four variants. The samples were subjected in a thermal chamber at 80 °C for 1 and 2 months and in a thermal shock chamber in the temperature range from − 40 °C to 80 °C for 1 and 2 months. The reference samples were seasoned at room temperature 20–25 °C. The epoxy compounds samples were subjected to the compression strength tests in accordance with ISO 604 standard. The compressive strength is influenced by the environment and temperature, the aging time and the presence of the modifying agent. The epoxy compounds subjected at elevated or variable temperatures have higher compressive strength than the reference epoxy compounds. The operation of the climatic chamber or the thermal shock chamber makes the samples more deformable than the reference samples.

Novel bio-based epoxy resins from eugenol as an alternative to BPA epoxy and high throughput screening of the cured coatings

A novel vinyl ether monomer from eugenol, 2-eugenoloxyvinyl ether (EEVE), was synthesized and used as a building block for polymeric epoxy resins. The EEVE monomer was polymerized via cationic polymerization of the vinyl ether group leaving the allylic functionality of eugenol available for further epoxidation. Epoxidized poly(EEVE) resins varying in levels of epoxidation (epoxy equivalent weights from 360 to 870 g/eq) were produced and cured with twelve amine curatives at ambient and elevated temperatures for different time intervals to evaluate and optimize the curing regime. The cured coatings were screened with high throughput dye extraction and “conventional” coating testing methods and compared to coatings produced from diglycidyl ether of bisphenol-A (DGEBA). Results showed that coatings derived from epoxidized poly(EEVE) [Epoly(EEVE)] can be tuned from soft and elastic with hardness <50 GPa and glass transition temperatures (Tgs) < 20 °C to hard and brittle with hardness >500 GPa and Tgs > 60 °C by varying the extent of epoxidation and the nature of curative, whereas DGEBA resulted in hard and brittle coatings irrespective of the type of curative used in the study. Compared to DGEBA resin, coatings with similar or higher crosslink densities and hardness were obtained from Epoly(EEVE) resins with >50% epoxidation of EEVE moieties using the same curative and curing regime. These partially biobased epoxy compounds derived from eugenol have the potential to be competitive with petroleum-based DGEBA resins in coatings applications.

Colloidal Lignin Particles and Epoxies for Bio-Based, Durable, and Multiresistant Nanostructured Coatings.

There is a need for safe and sustainable alternatives in the coating industry. Bio-based coatings are interesting in this perspective. Although various oils and waxes have been used as traditional wood coatings, they often lack sufficient durability. Lignin is an abundant natural polyphenol that can be used to cure epoxies, but its poor water solubility has impeded the use of unmodified lignin in coatings in the past. To address this issue, water-dispersible colloidal lignin particles (CLPs) and an epoxy compound, glycerol diglycidyl ether (GDE), were used to prepare multiprotective bio-based surface coatings. With the GDE/CLP ratios of 0.65 and 0.52 g/g, the cured CLP–GDE films became highly resistant to abrasion and heat. When applied as a coating on wooden substrates, the particulate morphology enabled effective protection against water, stains, and sunlight with very thin layers (less than half the weight of commercial coatings) while retaining the wood’s breathability excellently. Optimal hydrophobicity was reached with a coat weight of 6.9 g(CLP)/m2, resulting in water contact angle values of up to 120°. Due to their spherical shape and chemical structure, the CLPs acted as both a hardener and a particulate component in the coating, which removed the need for an underlying binding polymer matrix. Light interferometry measurements showed that while commercial polymeric film-forming coatings smoothened the substrate noticeably, the particulate morphology retained the substrate’s roughness in lightweight coatings, allowing for a high water contact angle. This work presents new strategies for lignin applications in durable particulate coatings and their advantages compared to both currently used synthetic and bio-based coatings.

Double-Layer Nitrogen-Rich Two-Dimensional Anionic Uranyl-Organic Framework for Cation Dye Capture and Catalytic Fixation of Carbon Dioxide.

A novel two-dimensional double-layer anionic uranyl-organic framework, U-TBPCA {[NH2(CH3)2][(UO2)(TBPCA)], where H3TBPCA = 4,4',4″-s-triazine-1,3,5-triyltripamino-methylene-cyclohexane-carboxylate}, with abundant active sites and stability was obtained by assembling UO2(NO3)2·6H2O and a triazine tricarboxylate linker, TBPCA3-. Due to the flexibility of the ligand and diverse coordination modes between carboxyl groups and uranyl ions, U-TBPCA exhibits an intriguing topological structure and steric configuration. This double-layer anionic uranyl-organic framework is highly porous and can be used for selective adsorption of cationic dyes. Due to the presence of high-density metal ions and basic -NH- groups, U-TBPCA acts as an effective heterogeneous catalyst for the cycloaddition reaction of carbon dioxide with epoxy compounds. Moreover, the various modes of coordination between the tricarboxylic ligand and uranyl ion were studied by density functional theory calculations, and several simplified models were established to probe the influence of hydrogen bonding between carbon dioxide and U-TBPCA on the ability of U-TBPCA to bind carbon dioxide. This work should aid in improving our understanding of the coordination behavior of uranyl ion as well as the development and utilization of new actinide materials.

Experimental study of a virtual allowables approach for the design of composite aircraft structures

Statistically derived allowables are representative for the behavior of a composite material system in a given structural context where data variability needs to be contemplated. In particular, they define the strength of the material as characterized by various coupon tests according to ASTM standard procedure subjected to the actual manufacturing process and layup stacking sequences. The current paper presents a detailed comparison between virtual allowables predictions obtained using MSC Digimat and the experimentally determined values of a certified material backed up by a 3x2x3 (batch/panel/specimen) stochastic approach. Tests generate the required data for building material model ab initio of carbon fibers reinforced epoxide resin in form of 2x2 twill woven fabric used for qualifying an innovative composite wing for the Next Generation Tilt Rotor (NGCTR). Numerical models of in-plane tension, compression and shear test methods have been assembled along with an associated material model allowing numerical predictions to be validated with the coupon level experimental results as final purpose. Standard statistical model has been adopted in order to include material and manufacturing process variabilities to define B-basis allowables. The calibrated statistical FEM method performed for different layup configurations have been used to fully characterize the mechanical behavior of the analyzed CFRP material and to predict performances for thicker laminates.

Усиление внутреннего слоя многослойного композита базальтопластиком в виде сотовой структуры

In our studies we present a multilayer structure consisting of outer layers of two-ply basalt composed of basalt fabric impregnated with an epoxy compound and an inner layer of polyurethane reinforced with basalt, having the same composition, formed in conjugate hexagonal prisms, and forming a cellular framework. The main part describes the technological sequence of obtaining basalt face layers, basalt hexagonal cellular frame, and filling it with a liquid reaction mass of rigid polyurethane system. The formation of a single multilayer composite structure is shown. We also present the results of the experimental research of strength of a laminated composite and its inner layer without facing layers when tested for static bending with concentrated load increasing at a constant rate and compression testing up to 10% of relative deformation. It describes the effect of the size of hexagonal prismatic cells of the frame on the physical and mechanical characteristics of the middle layer. The reduction of the cell size results in the increase of the composite strength. The dependence of the composite density on the size of the cells of the basalt frame has been studied.

Performance of two epoxy compounds against corrosion of C38 steel in 1 M HCl: Electrochemical, thermodynamic and theoretical assessment

Performance of two epoxy compounds against corrosion of C38 steel in 1 M HCl: Electrochemical, thermodynamic and theoretical assessment

Improving the tensile and flexural properties of reinforced epoxy composites by using cobalt filled and carbon/glass fiber

In this paper, the study concentrates on the flexural and tensile characteristics of the cobalt filler and fiber-reinforced epoxy composites used in the car body parts. Glass fiber (GF) and carbon fiber (CF) filled with the epoxy compound were prepared by hand lay-up varying the percentage of weight (wt.%) of cobalt from (0.4 to 1.0 wt.%). GF tensile and flexural strength were available at approximately 96.9 MPa and 120 MPa, respectively, while tensile and flexural strength of the reinforced CF was combined found in 194.82 MPa and 393.34 MPa. A 55.64% increase in flexural and tensile strength of the specimen was obtained compared to pure epoxy which represents a significant improvement. The use of a 0.6 wt.% Cobalt (Co) filler content for the combination of GF and CF epoxy reinforces positive results in the strength test. In addition, Field Emission Scanning Electron Microscopy (SEM) was done to investigate the microstructural characterization, the performance of GF and CF epoxy reinforced composite.

Facile Synthesis, Spectral and Electrochemical Properties and Catalytic Efficiencies of β-Octabromo Vanadyl Porphyrin

Selective oxidation of olefins to epoxy compounds has always been an interesting area of research for chemists owing to their great importance in the production of highly valued commodity chemicals such as polyurethanes, unsaturated resins, glycols, surfactants, and other products. Further, oxidative bromination of thymol and other phenolic derivatives has industrial importance. Iron and manganese porphyrins have been widely utilized as effective homogeneous catalysts for such oxygenation reactions in the last few decades. The major drawbacks of homogeneous MTPP-based catalysts are the macrocyclic ring which is liable to oxidative self-destruction, aggregation of metalloporphyrins through π–π interactions, lower turnover frequency (TOF) and poor product selectivity. Notably, vanadyl porphyrins have gained significant interest as useful molecules with applications in the fields of therapeutics, catalysis and 3D supramolecular assemblies. Herein, we synthesized vanadyl complex of β-octabromo-meso-tetraphenylporphyrin (VOTPPBr8) by self-catalytic reaction of VOTPP in excellent yield ar room temperature under mild bromination conditions using KBr/H2O2 in presence of HClO4. Further, VOTPPBr8 was utilized as an efficient catalyst for the epoxidation and oxidative bromination reactions. In this presentation, we will present facile synthesis, spectral and electrochemical properties and catalytic efficiencies of VOTPP and VOTPPBr8 in detail.

Fused Filament Fabrication Based on Polyhydroxy Ether (Phenoxy) Polymers and Related Properties.

This paper describes the first-time application of polyhydroxy ether polymers, so-called phenoxy, to fused filament fabrication (FFF). Phenoxy is an amorphous thermoplastic polymer that is based on the same building blocks as epoxide resins. This similarity creates some unique properties such as dissolution to epoxide systems, which is why phenoxy is used as an additive for toughening. In this study, the processing parameters were characterized, a filament was extruded and applied to FFF printing, and the final mechanical characteristics were determined. The study concludes with a comparison with other standard FFF materials.

Shape memory epoxy vitrimers based on waste frying sunflower oil

AbstractThermoset polyesters are prepared from epoxidized waste frying sunflower oil (ESO), commercially available epoxy compounds and glutaric acid. Influence of the nature and concentration of bi‐ and trifunctionnal epoxy compounds on mechanical properties is studied. Static and dynamic mechanical tests are performed. The molar amount of commercial epoxy compounds used ranges from 20% to 80% regarding the molar amount of ESO. It enables to obtain thermosetting polyesters with glass transition temperatures ranging from 6°C to 102°C, as well as storage modulus ranging from 8 GPa to 14 GPa. 40% of trifunctional epoxy compound and 60% of commercial epoxy compound are found to be the best compromises between bio‐based content and mechanical properties. Furthermore, shape memory and vitrimer behavior of those epoxy‐acid based networks with 60% of commercial epoxy compounds are evaluated both qualitatively and quantitatively by cyclic thermo‐mechanical and stress relaxation tests. Excellent shape memory behavior with fixity ratios above 94% and recovery ratios above 98% is demonstrated. A transesterification catalyst is needed to obtain good vitrimer behavior. Overall, thanks to the previously mentioned properties of those partially biobased thermosets polyesters, industrial applications such as protective coatings, foams and temperature‐memory polymer actuators might be considered.

Sodium silicate/waterborne epoxy resin hybrid-modified Chinese fir wood

The use of fast-growing wood can reduce the environmental impact of the wood industry, but the low strength and flammability of these woods prevent their widespread application. Chinese fir not only has the general defect of fast-growing wood, but also has weak permeability due to aspirated pits. To improve its performance, environment-friendly modifier sodium silicate (SS) and WEP (waterborne epoxide resin) as the dipping solution, microwave pretreatment and multi-step emptying-pressure (MSEP) impregnation method were employed to prepare hybrid-modified wood. Microwave pretreatment was found to destroy pit membranes of Chinese fir and increase permeability. WEP addition reduced the wood’s -OH content and promoted formation of more Si–O–Si structures, while also forming a fusiform hybrid structure with SS through Si–O–C bonds. The mechanical properties and water resistance of SS/WEPW (hybrid-modified wood) were higher than those modified by SS alone. The bending strength, elastic modulus, compressive strength, and transverse, tangential, and radial hardness of SS/WEPW5% (5% WEP) reached 97.20, 8504.87, 57.73, 5113.50, 2536.37, and 2192.35 MPa, respectively. The water resistance performance was also significantly improved. Compared with SSW, the 7-day weight leaching ratio (WLR) and water absorption rate (WAR) were reduced by 49.26 and 11.09, respectively, and the 14-day anti-shrink efficiency (ASE) of SS/WEPW5% can reach 86.87%. Furthermore, the flame retardant and smoke suppression performances of hybrid-modified wood were also improved, with the heat release rate (HRR), smoke produce rate (SPR), mean carbon monoxide yield (mean COY), and mean carbon dioxide yield (mean CO2Y) of SS/WEPW5% significantly lower and the peak of CO and CO2 release almost 1/10th that of unmodified wood. SS/WEP hybrid-modified wood was improved in terms of mechanical properties, water resistance performance, and flame retardancy, which laid the foundation of its use as a high-performance wooden material.

Desorption of Inactive Solvent from Epoxy Compounds

Desorption of Inactive Solvent from Epoxy Compounds

Reliability and Failure Mode in Solid Tantalum Capacitors

The reliability and failure modes in surface mount Solid Electrolytic and Polymer Tantalum capacitors were investigated using the parts manufactured with conventional technology and flawless technology (F-Tech) that suppresses typical defects such as crystalline inclusions in the amorphous matrix of the tantalum oxide dielectric. The accelerated tests were performed; failure rates were calculated based on the cumulative percent of failed parts vs time and acceleration factor. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and thermo-gravimetric/deferential scanning calorimetry analysis (TGA/DSC) were included in the investigation to analyze chemical and structural transformations in the capacitors failed in the accelerated tests. Results show strong impact of technology on reliability and failure mode including the lowest failure rate and no wear-out failure mode in Polymer Tantalum capacitors manufactured with F-Tech. No ignition and burning tantalum were found in the Solid Electrolytic Tantalum capacitors that failed short. Limiting temperatures and protecting the encapsulating epoxy compound from ignition and burning at normal conditions of the accelerated testing take place via ablation process—heat consuming irreversible structural and chemical transformations in the material such as carbonization process.

Experimental investigation of cracking behaviors of ductile and brittle rock-like materials

The cracking characteristics of ductile rocks were studied by similar materials with sand, barite, epoxide resin, polyamide, silicone rubber and alcohol, while the cracking characteristics of brittle rocks were investigated by similar material with sand, barite, rosin and alcohol. In this paper, to enhance the application range of the rock-like materials in the field of geotechnical engineering model tests, the values of the elastic modulus and the compressive strength of the artificial rock-like materials are changed in a wide range by adjusting the amount of cementitious materials (epoxide resin, polyamide, rosin, etc). The elastic modulus, compressive strength and cracking characteristics were obtained from the complete axial stress–strain curves of the specimens made of similar materials, which were cast using the different mixture ratios. These experimental data can provide quantitative investigation on mixture ratios of similar materials of rocks to model the geotechnical engineering. Furthermore, the effect of mixture ratios on mechanical properties and crack propagation pattern of specimens were also investigated by the specimens with pre-existing flaws under uniaxial compressive tests

DFT Studies of Selected Epoxies with Mesogenic Units-Impact of Molecular Structure on Electro-Optical Response.

Theoretical studies of molecular structure and electric charge distribution were carried out for three epoxy compounds with different mesogenic cores. The compounds exhibit a nematic phase and form polymer networks that are potential bases for various composites. Results were compared to analogous materials with non-polar chains. A customized process involving geometry optimization of a series of conformations was employed to greatly increase likelihood of reaching global energy minimum for each molecule. All computations used Density Functional Theory (DFT) electron correlation model with the B3LYP hybrid functional. Molecular structure calculations yielded several parameters, including the magnitude and direction of the dipole moment, polarizability (α), first hyperpolarizability (β), and highest-occupied/lowest-unoccupied molecular orbital (HOMO-LUMO) energies. These parameters can help predict electronic properties of the nematic phase and the polymer network and assess their predisposition for application in electrooptical devices. In particular, the magnitude and direction of the dipole moment determine molecular alignment of liquid crystal phases in electric field, which enables controlling molecular order also in cured networks. Theoretical results were supplemented with observations of the nematics and their behavior in electric field. It was demonstrated for the studied compounds that a change in aliphatic chain polarity helps preserve and reinforce perpendicular alignment of molecules induced by electric field.