Epoxy Amine Research Articles

The effect of DOPO concentration and epoxy amine stoichiometry on the rheological, thermal, mechanical and fire‐retardant properties of crosslinked networks

AbstractPresented here is an investigation into the effect of a phosphorus‐based fire retardant on the thermal, rheological and mechanical properties and flammability of an epoxyamine network prepared using stoichiometric and off‐stoichiometric epoxyamine compositions. The flame retardant 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was reactively incorporated into a blend of a bisphenol‐F diglycidyl ether epoxy resin and a polyfunctional epoxidized phenol Novolac resin, then cured with diethyltoluenediamine and accelerated using imidazole. Increased DOPO concentration improved fire retardancy, but reduced reactivity and thermal and mechanical properties. An increasing amino excess stoichiometry, however, comparatively increased reactivity and improved thermal and mechanical properties. Despite evidence of an earlier onset of degradation and higher char yield, enhanced graphitisation and reduced volatile emissions for the off‐stoichiometric networks, no significant improvements in fire resistance as a function of stoichiometry were observed using UL‐94 and limiting oxygen index measurements. © 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Reactive Molecular Dynamics Study of Hygrothermal Degradation of Crosslinked Epoxy Polymers

Epoxy thermosets are often exposed to high humidity environments in various applications, undergoing reversible and irreversible degradation depending on the environment. This study presents a reactive molecular dynamics (MD) simulation framework to gain deeper insights into the hygrothermal aging process, which is essential to develop a targeted approach to combat water-assisted degradation in epoxy thermosets. By applying ReaxFF potential, an epoxy–amine network is created at low temperatures to avoid unwanted high-temperature side reactions, where the water molecules are added to achieve the desired degree of moisture contamination. The simulations show that in addition to the plasticization effect from the moisture ingress, the epoxy network shows recovery in mechanical properties and density due to the multi-site interaction of the water molecule with the electronegative sites within the network. Moreover, long-term exposure to humidity or direct exposure due to cracking can induce irreversible changes in the epoxy–amine network. The protonation of the water molecule and nucleophilic attack on the C–O bond of the ether linkages in the epoxy–amine networks are successfully simulated by applying reactive MD simulations. Remarkably, the simulations show that the selectivity of water molecules for the hydrolysis reaction in the epoxy network depends on the spatial arrangement and the steric hindrance of the network. This work provides molecular level insights into hygrothermal aging by elucidating the interplay between free volume and polarity of the network in the physical aging of the moist epoxy networks, paving a way for advanced design strategy toward better durability and performance of epoxy thermosets in humid environments.

Biobased diglycidyl ether diphenolates: Effect of the ester moiety on fragrance oil microencapsulation by interfacial polymerization

Health risks are associated with capsule-forming synthetic chemicals such as formaldehyde, isocyanates, and bisphenol A (BPA). This work is focused on using safe biobased molecules to build capsule walls for oil encapsulation. Cellulose-derived diphenolic acid was converted into a series of diglycidyl ether n-alkyl diphenolates (DGEDP-esters). Interfacial polymerization of oil-soluble DGEDP-esters and water-soluble amine hardeners, hexamethylenediamine (HMDA) and chitosan oligosaccharide (COS), were used to build capsule walls. DGEDP-esters with small methyl and polar monomethyl ethylene glycol (DGEDP-ME and DGEDP-MG, respectively) are most reactive forming compact crosslinked capsules with high microencapsulation efficiency (EE of 97% and 94.3%) and good stability (oil leaking was ≤ 15.7% after acidification, and ≤ 64.2% after sonication). With increased hydrophobicity of the DGEDP ester moiety, deformed capsules with low EE (63 – 87%) and poor stability (oil leaking was ≥ 18.4% after acidification, and ≥ 81.8% after sonication) were obtained. Oil encapsulated with DGEDP-esters exhibits oil release of 0.5 – 8% at day 30 (45 °C and 11 kPa). The use of COS as the hardener yields capsules with EE (88.3 – 94%) and higher oil release (9–15% at day 30) compared to HMDA, but the acid stability was remarkably improved (oil leaking ≤ 3.7%). Cytotoxicity tests suggest that capsules formed with DGEDP-ME and HMDA or COS show very low cytotoxicity against human breast cancer cells and human fibroblasts cells (cell viability of 87–102% after 24 h exposure at capsule concentration of 2 mg/mL). These observations demonstrate that the structures of DGEDP epoxy monomers and amine hardeners have significant effects. Preferred DGEDP ester groups were methyl and mono-methoxy, and effective capsule formation was achieved using either HMDA or COS, the latter providing the advantage of being a readily renewable biobased multifunctional amine.

Preparation and Performance Test of Modified Aromatic Amine Epoxy Resin Curing Agent

Preparation and Performance Test of Modified Aromatic Amine Epoxy Resin Curing Agent

Investigation of the processability, thermal, mechanical and flame retardant properties of bisoxazoline composites

Presented here is an investigation into the cure kinetics, thermal and mechanical properties, and fire resistance of a carbon fibre composite using a polymer matrix blend composed of 1,3 phenylene bisoxazoline, a phenolic resin and dodecylbenzene sulfonic acid . This polymer matrix is further modified with a benzoxazine, a tetra-functional epoxy amine resin and the engineering thermoplastic , polyether sulfone (PES) to explore their effect on the reaction mechanism and final properties of the composite after cure and post-cure. The modifiers reduce the reactivity of polymerisation and the final glass transition temperature of the network as shown by the rate constants, determined from the Kissinger and Sestak–Berggren models. Subsequent post-curing of the composite increases the glass transition temperature, thermal stability, interlaminar shear strength , and fire performance as determined by UL-94 vertical burn test. Ensuring the network is fully cured is clearly critical to optimum performance of the composite. The high char yields of the bisoxazoline polymer networks , particularly after post-cure illustrate great potential for applications where high temperature resistance is required.

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.

One-step preparation of epoxy resin-based ionic gel electrolyte for quasi-solid-state lithium metal batteries

Quasi-solid-state lithium metal batteries have attracted wide attentions in recent years due to their high energy density, flexibility, and high safety. In this work, a novel epoxy resin-based ionic gel electrolyte (IGE) is synthesized via one-step curing polymerization of epoxy monomer and amine hardener with soft segments in the presence of ionic liquid electrolytes. The morphology and molecular structure of IGE are characterized by scanning electron microscopy, atomic force microscope and attenuated total reflection Fourier transform infrared. The amorphous microstructure and high thermal stability (≥270 °C) are identified by X-ray diffraction and thermogravimetric analysis. The obtained IGEs show high room temperature ionic conductivity from 0.05 mS cm−1 to 1.69 mS cm−1 due to the formation of dual continuous ionic conduction. In addition, the evolution of solid electrolyte interface (SEI) between IGE and lithium metal is investigated by electrochemical impedance spectroscopy, galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy. Finally, the Li/IGE/LiFePO4 cells can maintain a discharge capacity of 157 mAh g−1 at 0.1 C after 50 cycles at 60 °C and 132 mAh g−1 at 0.2 C after 150 cycles at room temperature.

REMOVED: Catalysis of reduced tin oxide in various epoxy resins

Epoxy resins are the most widely used thermoset materials for various applications, including electronic devices such as semiconductor packaging. In this study, tin (Sn) catalysis in diverse epoxy binary systems containing amine, acid or anhydride was explored by using various differential scanning calorimetry (DSC) techniques and rheological properties. Catalytic effects of Sn were observed in epoxy–anhydride and epoxy–diacid systems but not in epoxy–amine systems. For instance, the incorporation of 1 vol% Sn into the epoxy–succinic anhydride and epoxy–pimelic acid systems reduced the DSC exothermic peak temperature from 295 °C to 202 °C and 243–196 °C, respectively. By contrast, Sn presented no catalytic effect in epoxy–amine systems. Sn catalysis was investigated using isothermal curing temperatures and time. The onset temperature during viscosity measurements for the epoxy–anhydride and epoxy–diacid systems substantially decreased as a function of Sn concentration. These catalytic effects of Sn metal particles (oxidized in air) in the epoxy–anhydride and epoxy–diacid systems can be utilized to accelerate the reactions of epoxy resins and to anticipate the reaction conditions in various applications such as electronic devices involving Sn and epoxy resins. • Sn catalysis was observed in epoxy-anhydride and epoxy-diacid curing systems. • Epoxy-amine curing system did not show the Sn catalytic effect. • Various DSC and rheometry measurement techniques were used. • Latent catalytic effects were also examined.

Amine-catalyzed site- and stereo-selective coupling of epoxy amines and carbon dioxide to construct oxazolidinones

NEt3catalyzed the cycloaddition of epoxy amine and CO2, which generated oxazolidinones. Reactions of chiral epoxy amine achieved 100% configuration inversion, enabling the synthesis of linezolid. DFT studies show that NEt3acted as a nucleophile.

Cationic porphyrin-based nanoparticles for photodynamic inactivation and identification of bacteria strains.

The emergence of antibiotic drug resistance has undermined the efficacy of antibiotics, and is becoming a severe threat to public health. To combat antibiotic drug resistance and to replace traditional antibiotic treatment, an alternative strategy based on antibacterial photodynamic therapy (APDT), which has broad applicability, high efficiency and less potential of developing antibiotic drug resistance, has been developed. In this work, the cationic porphyrin-based nanoparticles (NPs) were prepared by epoxy-amine chain extension polymerization of diepoxy-terminated poly(ethylene glycol) (PEG) and tetraamino-containing porphyrin, followed by quaternization with methyl iodine and butyl bromide. The as-obtained cationic porphyrin NPs preserved the photophysical properties of porphyrin derivatives, and can efficiently generate singlet oxygen (1O2) under 635 nm laser irradiation. The cationic porphyrin-based NPs displayed intrinsic antibacterial properties, and exhibited strong APDT effect on Gram-positive bacteria by destroying the bacterial cell membranes. Upon incubation with different bacterial strains, it was found that they could be utilized to identify Gram-positive bacteria by observing the sedimentation behavior of their mixtures, and visualizing their co-cultured and centrifugal bacteria cakes. In addition, the cationic porphyrin-based NPs had good hemocompatibility and low dark cytotoxicity.

Effect of stoichiometry on crosslinked epoxy resin characteristics: structural heterogeneities, topological defects, properties, free volume and segmental mobility.

Experimental studies have shown that changes in stoichiometry (R, ratio of amine groups to epoxy groups) cause considerable variations in the properties of epoxy-amine systems. Rationales based on free volume concepts have been routinely used to address these variations in properties but have hardly been satisfactorily substantiated. Many of these rationales remain as unverified conjectures to date. Substantiating these rationales will certainly bolster our understanding of the structure-stoichiometry-property relationship, but is difficult, due to inherent challenges involved in unambiguously characterizing the structural heterogeneities induced by changes in stoichiometry (structural heterogeneities include compositional distribution in the functionality of monomers, non-uniform dispersion of elastic chains and topological defects). The aim of the present work is to gain molecular-level insights into this relationship and to verify the rationales that rely on free volume concepts used for addressing the variations in properties with stoichiometry, with the help of all-atom molecular dynamics (MD) simulations. Five epoxy-amine systems with varying R ranging from 0.4 to 3, including the stoichiometric system (R = 1), were considered for these purposes. The properties of interest namely density, glass transition temperature (Tg) and thermal expansion coefficient in the rubbery state (αrl) of these systems were predicted. The local structure, fractional free volume and segmental mobility of these systems were then subsequently characterized as a function of stoichiometry and the results were analysed in detail. The role played by defects in properties and fractional free volume was then investigated. The results revealed significant insights into the compositional distribution of monomers with different functionalities as well as offered insights into the dispersion state and mobility of dangling chains, sols and elastic chains in the systems. Further, strong correlations were found between defect composition, fractional free volume at an elevated temperature (600 K) and thermomechanical properties (Tg and αrl) and it was established that the key mechanism underlying these correlations was the plasticization caused by defects. Analysis based on the rule of mixture models showed that these correlations were found to be in good agreement with the interpretations based on free volume concepts. The results also revealed a strong negative correlation between fractional free volume at room temperature and defect composition, a phenomenon typically associated with the antiplasticization effect.

Kinetics of the interfacial curing reaction for an epoxy-amine mixture.

A better understanding of the chemical reaction between epoxy and amine compounds at a solid interface is crucial for the design and fabrication of materials with appropriate adhesive strength. Here, we examined the curing reaction kinetics of epoxy phenol novolac and 4,4'-diaminodiphenyl sulfone at the outermost interface using sum-frequency generation spectroscopy, and X-ray and neutron reflectivity in conjunction with a full atomistic molecular dynamics simulation. The reaction rate constant was much larger at the quartz interface than in the bulk. While the apparent activation energy at the quartz interface obtained from an Arrhenius plot was almost identical to the bulk value, the frequency factor at the quartz interface was greater than that in the bulk. These results could be explained in terms of the densification and orientation of reactants at the interface, facilitating the encounter of the reactants present.

A study on the flame retardant modification of bisphenol A benzoxazine

AbstractIn this article, a P‐N synergistic flame retardant AG601‐DOPO (abbreviated as A‐D) was prepared by the reaction of tetrafunctional glycidyl amine epoxy resin (AG601) with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO). The chemical structure of the product was confirmed by Fourier transform infrared (FT‐IR) spectroscopy and mass spectrometry (MS). Then, A‐D and bisphenol A benzoxazine (BA‐a) were mixed in different proportions to form a binary mixed system BA‐a‐A‐D (abbreviated as BAD) to improve the flame retardant properties of BA‐a. The results showed that the addition of A‐D can greatly improve the flame retardancy of BA‐a. When the content of A‐D was greater than or equal to 10%, the UL‐94 of BAD cured resin can reach the V‐0 rating. With the increasing of A‐D content, the LOI of BAD cured resin was increased from 23.8% to 37.1%. The results of cone calorimetry (CONE) test indicated that the total heat release (THR) was decreased from 120.7 to 78.2 MJ/m2, and the decrease was 35.2%. In addition, the effect of the introduction of A‐D on the thermal stability and heat resistance of BA‐a resin was analyzed. It was found that the temperature of the BAD‐cured resin at 5% thermal weight loss (Td5%) was above 300°C and the glass transition temperature (Tg) was above 186°C, still maintaining good thermal properties. Finally, the mechanical properties of BAD cured resin decreased slightly without affecting the use of materials.

Aromatic tetra-glycidyl ether versus tetra-glycidyl amine epoxy networks: Influence of monomer structure and epoxide conversion

In this work, two epoxy resins, bis(2,7 glycidyl ether naphthalenediol) methane (NNE), tetraglycidyl diaminodiphenylmethane (TGDDM) and a miscible blend of the two are cured with 4,4′-diaminodiphenylsulfone (DDS) to investigate the differences between glycidyl ether and glycidyl amine crosslinked networks. This work explores in depth, and directly compares for the first time, the structure/property relationships of a highly aromatic and thermally stable glycidyl ether epoxy network with a well-known highly aromatic and thermally stable glycidyl amine epoxy network. The highly aromatic naphthalene motif of NNE imparts improved thermal stability and a significantly higher glass transition temperature, above 340 °C depending on the measurement technique. However, it also produces comparatively lower epoxide conversion, higher moisture ingress and lower flexural properties. These properties are attributed to the NNE having higher free volume and glassy state mobility as suggested by the sub-ambient β relaxations. The glycidyl ether groups react primarily via epoxide amino addition displaying only very minor evidence of homopolymerisation or other side reactions even at 240 °C. This contrasts with the glycidyl amine groups of TGDDM which exhibit a much higher degree of non-epoxy amine addition. Increasing cure conversion also increases the glass transition temperature, fracture toughness and reduced coefficient of thermal expansion. Overall, the results show that despite some reduced mechanical and thermal properties the NNE epoxy resin system is a very thermally stable high temperature epoxy resin based upon glycidyl ether functional groups suitable for a wide range of new applications.

Formulation based predictive cure kinetics modelling of epoxy resins

Matrix formulation for aero-grade high-performance carbon fibre reinforced thermoset composites is a challenging task relying on extensive knowledge of chemistry, legacy information and trial-and-error iterations to identify a suitable pre-polymer resin/curative combination. This work proposes the development and application of a cure kinetics methodology to tailor preliminary matrix formulations focusing on matrix constituents reactivity. The kinetics of a ternary system containing either one epoxy pre-polymer and two amine curatives or two epoxy pre-polymers and one amine curative is approximated as a linear combination of the kinetics of its elementary binary systems containing the corresponding epoxy pre-polymer and amine curative. The method has been evaluated on a wide range of epoxy/amine formulations and shown to be valid with a reaction rate error lower than 0.003 min−1. The application of this predictive method allows the design of matrix systems with tailored reactivity and cure time without extensive experimentation.

Cure Kinetics and Network Development of a Very High Tg Naphthalene-Based Epoxy Amine Network

Cure Kinetics and Network Development of a Very High Tg Naphthalene-Based Epoxy Amine Network

Adding Two Antimicrobial Glasses to an Endodontic Sealer to Prevent Bacterial Root Canal Reinfection: An In Vivo Pilot Study in Dogs.

Current endodontic procedures continue to be unsuccessful for completely removing pathogens present inside the root canal system, which can lead to recurrent infections. In this study, we aimed to assess the antimicrobial capacity and tissue response of two inorganic bactericidal additives incorporated into a paste root canal sealer on contaminated root dentin in vivo. An experimental study was performed in 30 teeth of five Beagle dogs. After inducing microbiological contamination, root canal systems were treated by randomly incorporating one of two antimicrobial additives into a commercial epoxy-amine resin sealer (AH Plus), i.e., G3T glass-ceramic (n = 10) and ZnO-enriched glass (n = 10); 10 samples were randomized as a control group. After having sacrificed the animals, microbiological, radiological, and histological analyses were performed, which were complemented with an in vitro bactericidal test and characterization by field emission scanning electron microscopy. The tested groups demonstrated a non-significant microbiological reduction in the postmortem periapical index values between the control group and the bactericidal glass-ceramic group (p = 0.885), and between the control group and the ZnO-enriched glass group (p = 0.169). The histological results showed low values of inflammatory infiltrate, and a healing pattern characterized by fibrosis in 44.4% of the G3T glass-ceramic and 60.0% of ZnO-enriched glass. Bactericidal glassy additives incorporated in this root canal sealer are safe and effective in bacterial reduction.

Local oxidation of the buried epoxy-amine/iron oxide interphase

Epoxy-amine resins continue to find widespread use as the binders of corrosion protective organic coatings. In service, exposure to the environment ultimately results in oxidative deterioration of epoxy coatings, limiting the performance lifetime. Whilst the mechanisms underpinning surface oxidation have been characterized, few studies have examined polymeric degradation in the polymer/metal interphase, the integrity of which is central to performance. This is in part due to the inaccessibility of the buried interphase, which lies beyond the resolution limits of most organic analysis techniques. In this study, two innovative approaches are used to examine early stages of oxidative degradation of the buried polymer/iron oxide interphase for diglycidyl ether of bisphenol-A (DGEBA) coatings cross-linked with an aliphatic amine hardener, triethylenetetraamine (TETA). First, high fractions of iron oxide interfaces are introduced into the resin systems using synthetic hematite, Fe2O3, magnetite, Fe3O4 and goethite, Fe(O)OH powders, and the oxidation process is monitored using conventional infrared spectroscopy. Next, the buried interphase of coatings applied to iron is examined directly using nanoscale cross-sectional infrared analysis (via the photothermal infrared, PTIR, atomic force microscopy technique, known as AFM-IR). Diffusion limited oxidation is shown to initiate at the buried polymer-metal interface and progress slowly into the polymer, in accordance with pre-established mechanisms, resulting in chemical gradients of <400 nm after 28 days exposure to mild thermal aging conditions (70 °C, 14% RH).

Multiscale Characterization of Creep and Fatigue Crack Propagation Resistance of Fully Bio-Based Epoxy-Amine Resins

Multiscale Characterization of Creep and Fatigue Crack Propagation Resistance of Fully Bio-Based Epoxy-Amine Resins

Enhanced mechanical and thermal properties of ionic liquid core/silica shell microcapsules-filled epoxy microcomposites

A new type of phosphonium ionic liquid (trihexyl (tetradecyl) phosphonium bis(2,4,4-trimethylpentyl) phosphinate core/silica shell microcapsules (IL@SiO2) was successfully synthesized by one pot sol-gel process in IL/H2O emulsion and combined to epoxy amine networks as reinforcing fillers. Different amounts of IL@SiO2microcapsules and epoxy-to- amine stoichiometric ratios were considered in order to investigate the mechanical and thermal properties of IL@SiO2 filled epoxy composites. It has been found that IL@SiO2could be easily well dispersed in the epoxy matrix and low amounts of microcapsules can improve modulus and fracture toughness of epoxy-IL@SiO2 composites without damaging thermal properties. This reinforcement effect could be also observed when the epoxy-to-aminohydrogen ratio is over 1.0. This study is a preliminary work combining these new microcapsules with thermosetting polymers and give inspirations for the design of functional new epoxy-based materials.