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The epoxy insulation used in high frequency transformers encountered breakdown easily due to bipolar square wave voltage with steep rising/falling edge and high frequency. An insight into the frequency dependence of electrical tree development in epoxy resin under bipolar square wave voltage was elucidated in this paper. It was found that luminescence existed in all treeing channels, where the intensity of luminescence at the electrical tree tip under a high frequency (>4 kHz) was stronger than that at a low frequency (<4 kHz), indicating an electric field delivery from the needle tip to the channel tip at high frequency. Correspondingly, the fluorescent material deposited on the wall of the tree channel evolved from discontinuous at a low frequency to continuous at a high frequency with aggravated degradation. In addition, the frequency dependence of electrical tree breakdown related to field delivery was revealed. By combining the field delivery along treeing channels and the frequency dependence of the mechanical properties of epoxy resin, the growing model of an electrical tree under bipolar square wave voltage was illustrated elaborately. It was proposed that the dominant factors that drove electrical tree propagation were electric field force at a low frequency and partial discharge at a high frequency, respectively. This work can boost the advancement of polymers, electrical equipment, and power electronics at a high frequency. [ABSTRACT FROM AUTHOR]

Experimental studies of the shock wave properties of two epoxy resins with the same composition but different curing temperatures (160 and 200 °C) at up to 330 GPa pressure have been carried out. Laser interferometry was used to record particle velocity profiles at up to 73 GPa pressure while measuring the shock wave velocity. The release sound velocity was experimentally determined in the 3–73 GPa pressure range. Cumulative explosive shock wave generators were used to study the shock Hugoniot of epoxy resins at pressures above 100 GPa. It was shown that the shock compressibility data of both samples are approximated by a single shock Hugoniot within the experimental error. A kink on Hugoniot recorded close to 25 GPa pressure indicates a chemical decomposition in epoxy resin. Above this kink, a change in the shock wave front structure was recorded. Hugoniots of epoxy resin and unidirectional carbon/epoxy composite were compared at up to 370 GPa pressure. [ABSTRACT FROM AUTHOR]

Surface flashover that occurs on the surface of epoxy resin (EP) is one of the main causes of insulation failure in the power system. The newly emerging polar groups on the surface are highly desirable for enhancing the surface flashover performance of EP. Here, we present a facile ultraviolet (UV) irradiation method to enable the controlled introduction of C–OH and C = O groups on the EP surface. The resultant UV-irradiated EPs (UV-EPs) are highly uniform with little variation in surface roughness while exhibiting tunable polar content with the irradiation time. We also present the first systematic investigation into the effect of UV irradiation time on the surface flashover voltage of UV-EPs, with a maximum increase of 23.07% compared to the pristine EP. Mechanistic studies suggest that the enhancement of the surface flashover voltage is mainly dominated by the density of the deep trap, which is strongly dependent on the UV-induced C–OH and C = O groups on the surface. Besides that, the UV-EPs also display long-term stability due to the stable presence of polar groups, which further demonstrates the feasibility of this method for the development of EP with excellent properties. [ABSTRACT FROM AUTHOR]

Author(s): Neha Sharma [1]; Ramesh Kumar [1]; Devendra Yadav [1]; Asha Nyati [1]; Suresh Kumar Jain (corresponding author) [1]; Apoorva Panwar [1] Introduction India is a country with diverse socio-religious [...], Background: India is a country with diverse religious and cultural practices instigating skin diseases which may be missed due to lack of awareness. Contact dermatitis (CD) to lac is not uncommon yet an underreported entity. Objectives: To study clinical patterns of allergic CD due to lac bangles and to assess common contact allergens. Methodology: A retrospective study was conducted after approval by an ethical committee. Out of 850 patients attending the CD clinic from January 2021 to December 2022, the prevalence of CD lac bangles was 40 (4.7). After obtaining consent, the history of sites, duration, morphology, and DLQI were recorded from patients' medical records. Patch testing with Indian standard series (ISS) and raw lac powder mixed with control was done. Results: A total of 40 females were evaluated. The mean duration between contact and first symptom was 14.8 ± 10.43 months. Morphology was dry eczematous in 18 (45), lichenoid in 10 (25), oozy eczematous in 5 (12.5), urticarial in 5 (12.5) and vesiculobullous in 2 (5) patients. In 14 (35) females, lesions were disseminated. In 12 (30) females, CD to bindi (4), lipstick (1), Sindhoor (5), rings (1), and plastic slippers (1) were associated. The mean DLQI was 19.37 ± 3.4. Patch test results were positive with ISS allergen epoxy in 9 (22.5) patients, nickel in 6 (15), cobalt in 6 (15), paraphenylenediamine in 5 (12.5), and lac in only 2 (5) patients. Conclusion: Data observed in the present study suggests that CD to lac is a distinct clinical entity. Low positivity with lac in patch test proposes the need for standardized testing material. Keywords: Allergic contact dermatitis, cultural dermatology¸, lac, patch test, retrospective study

Alternating current (AC) loss measurement is crucial for the theoretical evaluation and optimization in the fabrication of superconducting AC devices. Lock-in amplifier based on the lock-in phase is commonly adopted and inevitably involves with phase error. In this work, a novel approach for measuring transport AC loss by determining the minimum compensated voltage (MCV) was developed, in which the lock-in amplifier was removed. Since it just uses the voltage signal from an AC voltmeter, it is phase-error immune. Experimental results demonstrated that when using the lock-in amplifier, there existed a system error as the initial phase difference between the sampled (reference) and real current phases, which required careful compensation. In contrast, the phase error no longer needed to be considered by the MCV method, and the AC loss results were obtained much more conveniently with the relative error between the theoretical and the experimental of less than 5%. Finally, the AC loss of a coated conductor spiral wound on an epoxy bar was obtained using the presented approach, demonstrating its low cost, ease of operation, and high accuracy. [ABSTRACT FROM AUTHOR]

Packaging insulation materials with high thermal conductivity and excellent dielectric properties are favorable to meet the high demand and rapid development of third generation power semiconductors. In this study, we propose to improve the thermal conductivity of epoxy resin (EP) by incorporating a three-dimensional boron nitride thermally conductive network. Detailedly, polyurethane foam (PU) was used as a supporter, and boron nitride nanosheets (BNNSs) were loaded onto the PU supporter through chemical bonding (BNNS@PU). After immersing BNNS@PU into the EP resin, EP-based thermally conductive composites were prepared by vacuum-assisted impregnation. Fourier transform infrared spectrometer and scanning electron microscope were used to characterize the chemical bonding and morphological structure of BNNS@PU, respectively. The content of BNNS in BNNS@PU/EP composites was quantitatively analyzed by TGA. The results show that the thermal conductivity of the BNNS@PU/EP composites reaches 0.521 W/m K with an enhancement rate η of 30.89 at an ultra-low BNNS filler content (5.93 wt. %). Additionally, the BNNS@PU/EP composites have excellent dielectric properties with the frequency range from 101 to 106 Hz. This paper provides an interesting idea for developing high thermal conductivity insulating materials used for power semiconductor packaging. [ABSTRACT FROM AUTHOR]

In order to prepare highly heat-resistant packaging insulation materials, in this paper, bismaleimide/epoxy resin (BMI/EP55) composites with different contents of BMI were prepared by melt blending BMI into amino tetrafunctional and phenolic epoxy resin (at a ratio of 5:5). The microstructures and thermal and electrical properties of the composites were tested. The electrostatic potential distribution, energy level distribution, and molecular orbitals of BMI were calculated using Gaussian. The results showed that the carbonyl group in BMI is highly electronegative, implying that the carbonyl group has a strong electron trapping ability. The thermal decomposition temperature of the composites gradually increased with the increase of BMI content, and the 20% BMI/EP55 composites had the highest heat-resistance index, along with a glass transition temperature (Tg) of >250 °C. At different test temperatures, with increase in the BMI content, the conductivity of epoxy resin composites showed a tendency to first decrease and then increase, the breakdown field strength showed a tendency to first increase and then decrease, and the dielectric constant was gradually decreased. Two trap centers were present simultaneously in the composites, where the shallow trap energy level is the deepest in 20% BMI/EP composites and the deep trap energy level is the deepest in 10% BMI/EP55 composites. Correspondingly, the 10% BMI/EP55 composite had a slower charge decay rate, while the 20% BMI/EP55 had a faster charge decay rate. In summary, the BMI/EP55 composites with high heat resistance and insulating properties were prepared in this study, which provided ideas for preparing high-temperature packaging insulating materials. [ABSTRACT FROM AUTHOR]

Frontal polymerization has great potential in complementing additive manufacturing processes such as direct ink writing as a continuous cure synchronized to the printing speed can overcome issues such as sagging. To study the incorporation of frontal polymerization into a potential printing process, a frontally polymerizable DGEBA epoxy resin has been developed for both UV and thermal initiation. Through frontal polymerization alone, full conversion is observed with a starting glass transition of 150[degrees]C for both initiation methods. Resulting thermal behavior is shown to have little dependence on either initiation irradiance or temperature utilized and much greater dependence on initiator concentration in the resin. Mechanical behavior is maximized by varying initiator concentration and cure conditions achieving tensile stress of 75 MPa and [K.sub.1C] of 1.2 MPa-[m.sup.1/2]. Shelf stability of the resin proves promising with no viscosity change after 12 weeks of room temperature storage. Future studies will concern adapting the resin for both direct ink writing and continuous fiber additive manufacturing applications. Highlights * Frontal polymerization of EPON 826 using RICFP * Utilized a tetrakis borate containing diaryliodonium cationic initiator * Stable and polymerizable after 12 weeks * Resin printed and frontally cured using UV initiation KEYWORDS direct ink writing, epoxy, frontal polymerization, 1 | INTRODUCTION Frontal polymerization has continued to be a promising rapid manufacturing solution in which polymerization propagates in a localized reaction zone. (1) More specifically, a single stimulus initiation [...]

We outline a coarse-grained model of epoxy resins (bisphenol-F-diglycidyl-ether/3,5-diethyltoluene-2,4-diamine) to describe elastic and plastic deformation, cavitation, and fracture at the μm scale. For this, molecular scale simulation data collected from quantum and molecular mechanics studies are coarsened into an effective interaction potential featuring a single type of beads that mimic 100 nm scale building blocks of the material. Our model allows bridging the time–length scale problem toward experimental tensile testing, thus effectively reproducing the deformation and fracture characteristics observed for strain rates of 10−1 to 10−5 s−1. This paves the way to analyzing viscoelastic deformation, plastic behavior, and yielding characteristics by means of "post-atomistic" simulation models that retain the molecular mechanics of the underlying epoxy resin at length scales of 0.1–10 µm. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated and compared the bond strengths, microleakage, microgaps, and marginal adaptation of self-adhesive resin composites (SAC) to dentin with or without universal adhesives. Materials and Methods: Dentin surfaces of 75 molars were prepared for shear and microtensile bond strength testing (SBS and μTBS). Silicon molds were used to build up direct restorations using the following materials to form 5 groups: 1. Surefil One; 2. Prime&Bond active Universal Adhesive + Surefil One; 3. Vertise Flow; 4. OptiBond Universal + Vertise Flow; 5. Scotchbond Universal + Filtek Z500 (control group). Bonded specimens were thermocycled 10,000x before being tested either for SBS or μTBS using a universal testing machine at a crosshead speed of 0.5mm/min. Direct mesial and distal class-II cavities were created on 100 sound premolars, with the gingival margin of distal cavities placed below CEJ and restored according to the five groups. After thermocycling, microleakage scores were assessed following immersion of restored premolars in 2% methylene blue dye for 24h, while marginal gaps and adaptation percentages were investigated on epoxy resin replicas under SEM at magnifications of 2000X and 200X, respectively. Results were statistically analyzed with parametric and non-parametric tests as applicable, with a level of significance set at a = 0.05. Results: Bond strengths, microleakage scores, microgaps, and percent marginal adaptation of Surefil One and Vertise Flow were significantly (p<0.001) inferior to the control group. Dentin preconditioning with universal adhesives significantly increased the study parameter outcomes of Surefil One and Vertise Flow, yet they were still significantly below the performance of the control group. Conclusion: Conventional resin composite outperformed the SAC whether applied solely or in conjunction with their corresponding universal adhesives. [ABSTRACT FROM AUTHOR]

We report the synthesis of cyclic diglycerols, which are the smallest repeating units in polyglycerols. Linear diglycerol epoxy alcohols are treated with a catalytic amount of boron trifluoride–diethyl ether complex (BF 3 ·OEt 2) in highly dilute dichloromethane (CH 2 Cl 2) to give the corresponding 1,4-dioxepane- and 1,4-dioxane-type cyclic diglycerols in high yields as single structural isomers. The structures of the cyclic products are determined by 1D and 2D NMR spectral analysis. The observed results indicate that the cyclizations are consistent with Baldwin's rules. The synthesized cyclic diglycerols can serve as standards for further studies. [ABSTRACT FROM AUTHOR]

This study investigated the pin-loaded tensile behavior, bearing strength, and failure mechanisms of thermosetting and thermoplastic composite materials. Specifically, the investigation focuses on carbon-fiber-reinforced polyetherketoneketone (CF/PEKK) and carbon-fiber-reinforced epoxy (CF/EPOXY). Notably, CF/PEKK exhibited a shear-out failure mode, surpassing CF/EPOXY with a 56.4% higher peak load. The absence of crack propagation in CF/EPOXY, attributed to the presence of yarn at a 90∘ angle, leads to bearing failure. In contrast, CF/PEKK demonstrates a significantly higher bearing strength, approximately 150 MPa greater than CF/EPOXY. This discrepancy in performance suggests that CF/PEKK holds promise as a structural material for applications involving the fastening of thermoplastic composites, presenting a viable alternative to traditional thermosetting composites. The findings imply that the unique failure mechanisms and enhanced mechanical properties of CF/PEKK make it a compelling candidate for use in scenarios where thermosetting composites are conventionally applied. This study contributes valuable insights into the potential advancements and applications of thermoplastic composites in structural materials, paving the way for optimized and innovative engineering solutions. [ABSTRACT FROM AUTHOR]

In the field of electronic packaging, epoxy resins with good thermal and dielectric performances have attracted extensive attention. In this work, a novel epoxy resin was synthesized from resveratrol, and its structure was characterized by NMR and FTIR. The resveratrol‐based epoxy resin was cured with an active ester, and the properties of the cured system were further studied. The results showed that the resveratrol‐based epoxy cured with active ester had excellent comprehensive properties, its dielectric constant (Dk) was 2.63, dissipation factor (Df) was 4.91‰ at high frequency of 10 GHz; moreover, its glass transition temperature (Tg) was 188°C, coefficient of thermal expansion (CTE) was 70.7 ppm/°C, 5% mass loss temperature (Td5%) was 390°C. These results suggested that a biomass epoxy resin with excellent thermal and dielectric performances had been successfully synthesized, which had potential application in the field of high‐frequency communication. [ABSTRACT FROM AUTHOR]

The preparation of biomass flame retardants with efficient flame‐retardant properties is conducive to the realization of sustainable development and is of great practical significance. In this work, a green and sustainable biomass flame retardant PATAPEI was prepared by using phytic acid (PA), tannic acid (TA), and polyethyleneimine (PEI) as reactants via a one‐step method to develop biomass flame retardants that can synchronize enhanced flame retardation, smoke suppression, and mechanical performance of epoxy resin (EP). The EP with only a 3% PATAPEI (EP/3PTP) has a LOI value of 28.5% with a UL‐94 V‐0 classification. The peak heat release rate (PHRR), total heat release (THR), and total smoke release (TSR) of EP/3PTP were decreased by 29.72%, 25.80%, and 21.16%, respectively, in comparison with the ones of pure EP. Additionally, the tensile and impact strengths of EP/3PTP are higher than the ones of pure EP. PATAPEI on heating decomposes to produce phosphorus‐containing acids and biphenyltriol‐containing compounds, which promote to form a good char layer with the aromatic structures during the combustion of EP/3PTP. Therefore, PATAPEI has prospects of wide application in the development of sustainable biomass flame retardant EP. [ABSTRACT FROM AUTHOR]

The poor dielectric properties of epoxy resins limit their application in microelectronics, and active ester curing agent is an effective means to enhance the dielectric properties of epoxy resins. However, the phenyl active ester curing resins nowadays have the problem of low mechanical properties. In this work, a novel naphthalene‐based active ester‐cured resveratrol epoxy resin system (REP/NDA) was prepared for the first time. Compared with the phenyl‐active ester‐cured epoxy resin (REP/PDA), the naphthyl‐active ester prepared epoxy resin has obvious advantages in mechanical properties. The experimental results indicated a tensile strength measurement for REP/NDA at 91.9 MPa, the tensile strength of REP/PDA was 65.3 MPa, and the tensile strength of REP/NDA was 141% of that of REP/PDA. The prepared REP/NDA epoxy resin exhibits favorable dielectric properties, evidenced by a dielectric constant of 3.02 at 10 MHz and a dielectric loss of 0.0042, very good thermal stability (T5% of 379°C), excellent water absorption (only 0.49% for 7 days from 2 to 8°C) and good dimensional stability (coefficient of thermal expansion below Tg of 77 ppm). The first synthesis of naphthalene‐based active ester curing agent offers a reference for creating new low dielectric epoxy resin materials that work out exceptionally. [ABSTRACT FROM AUTHOR]

Single pack epoxy adhesives, known for their simple operation process, combined with good reactivity at moderate temperatures and excellent storage stability, have gained extensive attention. An appropriate accelerator is crucial for enhancing their performance. This study demonstrates that the zinc zeolitic imidazolate framework ZIF‐8 (Zn(2‐methylimidazole)2) can effectively serve as an effective accelerator for the epoxy‐anhydride system, as evidenced by the complete exothermic curing curve obtained via differential scanning calorimetry (DSC) tests of the epoxy (A‐128) and anhydride (THPA) adhesive sample with ZIF‐8. The optimal addition amount of ZIF‐8 (0.9%) was determined by assessing the glass transition temperature (Tg) of the cured resin with varying ZIF‐8 weight fractions. Furthermore, the ideal curing conditions—gel temperature of 388.4 K, curing temperature of 416.7 K, and post‐treatment temperature of 441.9 K—were established by analyzing heating curves at different circumstances. The epoxy (A‐128) and anhydride (THPA) system with accelerator ZIF‐8 exhibited superior stability compared to the commercial accelerators like PN‐23 or DMP‐30. This is attributed to the steric hindrance and coordination bonds of ZIF‐8, indicated by a large pre‐exponential factor (A1 = 5.58 × 108) and low‐value reaction rate constant (k1 = 0.3461 × 10−3 s−1). In addition, the kinetic parameters, and an autocatalytic equation model for the epoxy (A‐128) and anhydride (THPA) system with accelerator ZIF‐8 have been derived through isothermal curing kinetics analysis. [ABSTRACT FROM AUTHOR]

The development of an energy-saving method to recycle expensive carbon fibers (CFs) from end-of-life thermosetting resin-based CF-reinforced composites (CFRCs) is strongly desired because of the environmental and economic issues. The replacement of traditional thermosetting matrixes with controllably degradable epoxy resins provides a promising solution to this challenging task. In this work, a liquid acetal-containing semi-cycloaliphatic epoxy resin (H-ER) is designed and synthesized. After curing, H-ER shows simultaneously increased thermal stability, shearing strength, flexural strength, strain at break, and critical stress intensity factors by 126%, 26.5%, 17.0%, and 29.5%, respectively, in comparison with ERL-4221. Particularly, the cured H-ER is sufficiently resistant to organic solvents, bases, and weak acids but degrades rapidly in a modestly strong acidic aqueous solution, and the rate of degradation is controlled by modulating the acidity. GC-MS and FTIR spectra demonstrate that the degradation is indeed due to the cleavage of acetal linkages in the network, and the degradation-generated benzaldehyde may be reused as a raw material for the synthesis of the H-ER resin. More importantly, for the CFRCs using H-ER as a matrix, the CFs are readily recovered without detectable damage and are able to be recycled for CFRC fabrication. [ABSTRACT FROM AUTHOR]

This research focuses on the mechanical characterization of FG material graded with Graphene nano-platelets (GPLs) in the transverse direction. Different weight percentages of GPL (0–2 wt. %) were incorporated into epoxy resin for manufacturing the FGM using a simple casting method and the effects were analyzed. This paper aims to enhance the material's performance, especially focusing on its potential use in biomedical tools. Mechanical tests including assessment on tensile, flexural, impact strength, and microhardness demonstrated substantial improvement in strength and stiffness as compared to other nanocomposite structures. Microstructural analysis using scanning electron microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) analysis which hint at the strong chemical interaction and physical association of GPL nanofiller with the epoxy resin. Thermal analysis was conducted using the Dynamic Mechanical Analysis (DMA) test, which revealed enhanced thermal stability of the FG specimen with a higher glass transition temperature than other carbon nanofillers mixed in epoxy resin. This is advantageous for the FG material to maintain its glassy state, maintaining safety and reliability during high-temperature medical applications. All these findings indicate that the proposed FG-GPL material possesses the necessary mechanical properties, suggesting that customized nanofiller integration could lead to significant advancements in medical procedures, such as in vivo stomach biopsy treatments, drug delivery systems, etc. The material also meets specific anatomical requirements and reduces the risk of malfunction, thereby ensuring patient safety as justified by current experimental investigations. [ABSTRACT FROM AUTHOR]

In order to help establish a new theory of deep rock mechanics and better guide the development of deep engineering, it is crucial to develop a deep in-situ conditionpreserved coring device capable of obtaining cores while maintaining their original in-situ temperature and pressure conditions. To achieve insulation functionality within a compact design, a passive insulation system must be developed for such coring devices. Considering the size constraints and thermal insulation requirements, a passive thermal insulation system combining a vacuum layer and an insulating material layer has been designed in this work. Epoxy resin was selected as the insulation material due to its high compressive strength and low thermal conductivity. The type and dosage of curing agents, as well as the curing process with epoxy resin, were optimized. The ideal resin achieved a compressive strength of 241.03 MPa and a thermal conductivity as low as 0.25 W/m·K. Additionally, it exhibited excellent thermal stability and a high decomposition temperature. Under hightemperature and high-pressure water conditions simulating deep-earth environments, the epoxy resin's maximum water absorption was below 0.7%. The insulation layer could effectively minimize heat exchange between the core and the external environment by up to 19.01%. These findings provide a significant contribution to the advancement of passive insulation systems for deep in-situ core drilling operations. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to characterize a new structural bi-material (scaffold and filler). Design/methodology/approach: The bi-material has been obtained by means of an additive manufacturing system consisting of a fused filament fabrication extruder head and an epoxy resin depositor head. The new bi-material will consist of a thermoplastic material that will serve as the main structure and an epoxy resin that will serve as a filler and adhesion between layers. The creation of this new bi-material will improve the physical–chemical and mechanical properties with respect to the thermoplastic material. This paper will focus on the impact behavior of IZOD and the impact behavior of punctures. Findings: The new polylactic acid (PLA) and epoxy bi-material allow improvements in toughness and puncture impact resistance compared to the PLA thermoplastic. This increase in toughness is between 20% and 30% depending on the orientation of the print. In the same way, the energy absorbed in the puncture impact test has been increased by 42%–48%. Practical implications: The improvement in the impact absorption capacity of this new bi-material makes it ideal for the manufacture of medical parts in which customization, lightness and impact resistance are their main characteristics such as sports protection systems. Originality/value: The originality of creating parts through additive manufacturing that combines a material generated with cold extrusion, such as epoxy resin and a material generated with hot extrusion, such as thermoplastics, lies in the unique synergy that this mixed and simultaneous technique offers. By uniting these two manufacturing methods, it allows the exploration of new physical and chemical properties in the resulting parts, taking advantage of the individual advantages of each material. This combination opens the door to the creation of components with a wider range of characteristics, from strength and durability to flexibility and temperature resistance, thus offering innovative and versatile solutions for various applications in fields such as engineering, medicine and design. [ABSTRACT FROM AUTHOR]

This study evaluated Zn–Al–NO2− layered double hydroxide as a corrosion inhibitor in a high-thickness epoxy resin coating (200 µm). The layered double hydroxide was tested in a NaCl solution, using electrochemical impedance spectroscopy. The formed oxides were analysed by X-ray diffraction and energy dispersive X-ray spectroscopy. The corrosion resistance of the epoxy coating (with and without layered double hydroxide) was analysed by electrochemical impedance spectroscopy after exposure to a NaCl solution, salt spray, or a weather-O-meter chamber in a simulated atmospheric environment. The electrochemical impedance spectroscopy measurements for the free layered double hydroxide in a NaCl solution revealed that layered double hydroxide prompted the formation of a compact, protective, and insoluble oxide layer on the carbon steel surface. The Cl− permeability through the epoxy resin film was 5.88 times lower for the film containing layered double hydroxide than for the control. The layered double hydroxide was added to the epoxy coating at a 5 wt-% to evaluate the behaviour of the coating in aggressive environments. The entry of aggressive ions was controlled by the ability of the layered double hydroxide to capture them and release the corrosion inhibitors. Thus, the layered double hydroxide worked as a trap for these aggressive ions and enhanced the performance of the coating. Therefore, a layered double hydroxide addition could benefit a high-thickness coating exposed to an aggressive environment and UV radiation. [ABSTRACT FROM AUTHOR]

The blending behavior of thermosetting epoxy asphalt in recycled mixtures is significantly different from that of thermoplastic asphalt. Investigations into the degree of blending (DOB) between epoxy asphalt and aged asphalt is of great practical significance for improving the performance and design of recycled asphalt mixtures. In this study, epoxy component–modified recycled asphalt (EA) and mixture (EAM) with two DOBs were designed, including EA-A and EAM-A with full blending, and EA-B and EAM-B with partial blending. A series of performances of EA and EAM were evaluated using rheological, low-temperature and fatigue tests. The DOB mechanism on the performance of EAM was revealed from the microscopic scale. The results show that the addition of the epoxy component enhanced the stiffness and fatigue performance of the EA. The EAM had good cracking resistance and fatigue performance. At 10%–30% epoxy component content, the lower DOB contributed to the fatigue performance of EA-B better than that of EA-A. Meanwhile, the cracking resistance and fatigue performance of EAM-B were better than that of EAM-A. However, the opposite pattern was observed at 40% epoxy component content. The morphology of the interface showed that the epoxy component of EAM-B was concentrated in a certain area of the interface due to the lower DOB, especially with 30% epoxy component content. When 40% epoxy component content, the denser crosslinked network was formed in the EAM-A with higher DOB. Overall, full blending was not required, and 30% epoxy component content was recommended in EAM. [ABSTRACT FROM AUTHOR]

In our study, in order to prepare PLA microcellular foam at high temperature, linear polylactic acid (L-lactone) (PLLA) was mixed with epoxy resin chain extender, and then blended with polylactic acid (D-lactone) (PDLA) to prepare bPLLA/PDLA mixture. The bPLLA/PDLA mixture produces stereocomplex (SC) crystals. The addition of SC crystal as a melt enhancer resulted in a significant enhancement of the melt strength of bPLLA, with an increase of 104. Furthermore, the nucleation effect increased the overall crystallinity (XC) of the bPLLA/PDLA blends from 5.29 to 23.21%, thereby enhancing the heat resistance of the bPLLA/PDLA blends. The hot deformation temperature was increased from 55.5 °C to 62.4 °C. During the foaming process, SC crystals acted as nucleating agents for bubbles, reducing the cell diameter from 30.59 μm to 3.09 μm, increasing the cell density by 102, and improving cell uniformity. In addition, an increase in PDLA content resulted in a notable enhancement in the compressive strength of bPLLA foam, from 0.44 MPa to 0.72 MPa. After heat treatment at 150 °C, the dimensional deformation was found to decrease from 42.59 to 13.13%, accompanied by an improvement in heat resistance. This study presents a simple method for the preparation of PLA microporous foam at high temperatures, resulting in the production of high-performance PLA foam, which is of great significance for the development of batch foaming towards industrial continuous foaming production. [ABSTRACT FROM AUTHOR]

Context: Following chemomechanical preparation, the application of intracanal medicaments is recommended to further decrease the microbial count. To combat endodontic infections, the application of antibiotics as intracanal medicaments has been an option for years in endodontics. Aim: The aim of this study was to compare and evaluate the effect of antibiotic pastes on the push-out bond strength (POBS) of resin-based root canal sealer. Materials and Methods: Forty-eight extracted single-rooted teeth were used after decoronation to a standardized root length of 15 mm. Canals were enlarged up to size F3 using Protaper rotary instruments. Samples were randomly divided into three groups according to the intracanal medicament used. Group A: Nitrofurantoin (NIT) Paste, Group B: Triple antibiotic paste (TAP), and Group C: Control group (without intracanal dressing). After removal of the medicament (endoactivator), obturation was done with AH Plus sealer. Push-out bond strength was calculated using universal testing machine. Statistical Analysis: Data were analyzed using one-way ANOVA followed by post hoc Tukey and Kruskal–Wallis test (with a significance level of P < 0.05). Results: Compared to the control group, the POBS significantly increased after using intracanal medicaments with P < 0.05 (The results showed that the mean bond strength of TAP was highest, closely followed by NIT and least with the control group). Conclusion: Under the limitations of this study, it can be concluded that the use of TAP and NIT increases the POBS of the Epoxy Resin Sealer. [ABSTRACT FROM AUTHOR]

This work concerns the study of the effect of adding microgranules containing a phase change material (PCM) on the thermal diffusivity value of the resulting composite structure. Two commercially available epoxy resins were applied as the composite matrix material: pure epoxy resin and epoxy resin with a filler in the form of metal powder. The dispersed phase was the BASF Micronal DS5038 X microgranulate, i.e. a bed of polymer spherical shells containing PCM filling. The tests were carried out using the modified Ångström method in a symmetrical bilateral harmonic excitation of the temperature of outer sides of assembled two tested disc-shaped samples. The temperature range of measurements covered the interval from 273.15 K to 308.15 K, i.e. most of the typical working range of microgranules. In selected measurement cases, the tests were extended to temperatures from 263.15 K to 348.15 K. The results obtained for the four structures studied were compared and analyzed to illustrate the quantitative effects of structure modification and to document the qualitative effects of the observed phase changes that occurred both on heating and cooling. [ABSTRACT FROM AUTHOR]

In the study, acoustic emission (AE) technique was applied to monitor polymer failures. Specimens produced of two aluminum flat bars bonded together with a thick layer of cured epoxy resin were subjected to double cantilever beam (DCB) test. Epidian 5 epoxy resin cured with PAC curing agent as well as Epidian 53 epoxy resin cured with Z1 curing agent were used as adhesives. However, a special procedure of specimens preparation was needed which was elaborated by authors after preliminary research including aditional analysis of surface roughness parameters and surface free energy of aluminum flat bars. Acoustic emission system was then used to register AE signal parameters during fracture test: frequency of elastic waves emitted inside the material, number of hits (event), number of counts, energy and amplitude. Next, the obtained AE parameters were deeply analyzed and compared to the results of mechanical test and authors' previously conducted examinations. Moreover, a special emphasis was put on applicability of wawelet transform (WT) as well as numerical simulation for fracture analysis was conducted. [ABSTRACT FROM AUTHOR]

This article aims to assess the suitability of natural neem gum in various composite material applications in place of epoxy resin. The assessment was done by thermal characterisation, experimental study and comparative analysis of thermal behaviour, Fourier transform IR spectroscopy (FTIR) characterisation and comparison of functional groups and mechanical properties of neat epoxy and neat neem resins. To study and compare thermal behaviour differential scanning calorimetry (DSC), thermogravimetric (TG) and relative derivative TG (DTG) analysis were conducted. The glass transition temperatures, exothermic and endothermic peaks, curing of thermosetting epoxy and crystallisation of polymeric neem, value of % cure and mass change or mass loss concerning temperature of both the resins were experimentally determined and comparative analysis was conducted to find the suitability of neem resin in composite material applications in place of epoxy resin. Functional groups of neem gum were identified and mechanical properties such as bond strength, toughness, rigidity and ductility were characterised and compared with that of epoxy resin by conducting FTIR. [ABSTRACT FROM AUTHOR]

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Summary: This research proposes a novel low‐cost aperture coupled elliptic patch nanoantenna which works best when it has a stable radiation pattern and good gain. On the upper portion of the substratum, a cross‐shaped hole was additionally engraved from a metallic strip with a silver composition. Elliptical‐shaped silicon material is employed as a patch in this antenna design which is made on a substrate made of inexpensive glass epoxy. The silver substance makes up the nanometallic strip line at the substrate's base. A cross‐shaped hole has also been etched from a metallic strip with a silver composition on the upper section of the substrate. As the foam substrate to be used in between the feed and antenna substrates, Rohacell was adopted. A proposed simple cross‐shaped aperture enhanced the bandwidth of the planned antenna without degrading its radiation performance and is loaded on a proximity‐linked elliptical microstrip antenna. To achieve the highest coupling, the lowest back radiation, the least amount of spurious radiation, and good efficiency, the patch and feed line are positioned in the middle, at a right angle over the slot. The proposed antenna was simulated in HFSS, and optimum results were observed from the output. The results were evaluated based on radiation pattern, return loss, smith chart, radiation efficiency, and 3D polar plot for 300, 500, and 800 THz frequencies. Also, the impedance bandwidth, gain, and a number of bands were compared with other conventional methods and our proposed method proved to outperform the existing method in all aspects. [ABSTRACT FROM AUTHOR]

Conventional pressure-type anchoring systems face challenges such as difficulty in recovery, low recovery efficiency, and insufficient durability over long-term use. Although the single-use cost of Carbon Fibre Reinforced Polymer (CFRP) strand anchors is higher than that of conventional steel strands, recovery and reuse can significantly reduce costs. Therefore, this study aims to investigate the bonded anchoring method of CFRP and proposes an innovative thermoplastic CFRP prestressed strand design that combines both anchoring strength and recoverability to address the shortcomings of existing anchoring systems. Two bonding materials, thermosetting resin and thermoplastic resin, were selected for bond strength tests under different conditions. The results indicated that epoxy resin had a bonding force of 280 kN and an anchoring efficiency of approximately 70%, making it the most suitable material. However, the anchoring efficiency still needs improvement. Based on this, an improved design scheme was proposed, which can increase anchoring efficiency to over 95%. Additionally, based on the dispersed bonding anchor system, this study explored a solution that involves adding a positioning plate at the end of the anchor strand and using epoxy resin for anchoring. The anchoring performance tests showed that the tensile strength of the CFRP strand ranged from 2.7–2.8 GPa, with an average anchoring efficiency of 100.5%, demonstrating excellent anchoring performance. Further thermoplastic recovery tests showed that when the temperature increased to 90°C, the maximum recovery force of the strand was 17.2 kN, about 4.4% of the ultimate load. When the temperature increased to 150°C, the maximum recovery force was 7.5 kN. The recovered CFRP strands were clean, with no resin residue, and had no damage, maintaining an intact structure. The proposed thermoplastic CFRP prestressed strand design demonstrates significant advantages in anchoring strength and recoverability. With the improved design, anchoring efficiency can be increased to over 95%, and the high-temperature recovery process shows good feasibility. Compared with traditional anchoring systems, CFRP strands offer higher anchoring efficiency, lower recovery force requirements, better economics, and sustainability, making them a promising solution for engineering applications. [ABSTRACT FROM AUTHOR]

Braided composites are gaining attention in the most industrial applications. To design rods with optimal tensile properties against combined loads, experimental studies were conducted to investigate the effect of using axial yarn and core in different categories on the tensile properties of braided reinforced composite rods. In this study, six types of braided composite rods with different arrangements of braid components (axial yarn or core type) were produced using glass and polyester fibers with epoxy resin as the matrix. The elastic modulus, ultimate tensile strength, and work of fracture of these rods were tested, and the experimental elastic modulus of samples were compared with previously developed models. Moreover, comparing the stress-strain results of the samples revealed that the produced hybrid samples demonstrate pseudo-ductile tensile behavior, showing varying trends as the type of reinforcement is altered. The results indicate that using a double-layer triaxial braid as reinforcement for the composite can increase the elastic modulus up to 13% compared to the similar single-layer sample. Additionally, employing a double-layer triaxial braid as reinforcement for the composite leads to a greater work of fracture. However, in terms of ultimate tensile strength, biaxial braid reinforcement demonstrates better performance in reinforcing the composite rods. [ABSTRACT FROM AUTHOR]

[Display omitted] Thermoset epoxy resin-based materials are widely used, but their permanent cross-linked network limits their processability and reusability, which can lead to environmental burdens. In this work, by exploiting the weak reactivity of aniline to design appropriate reaction ratios, we achieved a linear link between the epoxy resin and the curing agent. This linear link, along with the crosslinking points provided by the flexibly branched polyurethanes, avoids the inherent brittleness associated with the highly crosslinked network of conventional epoxy resins. As a result, the adhesive exhibits extraordinary improvements in extensibility and toughness. The lap shear strength, tensile strength and elongation at break reach 11.9 MPa, 14.4 MPa and 607 %, respectively. The fracture toughness is as high as 109.6 kJ/m2, far beyond the existing epoxy adhesives. The synergistic effect of disulfide bonds and hydrogen bonds confers the adhesive with self-healing and repeatable bonding characteristics. The multi-level hydrogen bonding and appropriate phase separation structure are key to optimizing toughness, resulting in excellent comprehensive performance. The introduction of polyurethane not only improves toughness but also enhances the interfacial bonding force between the adhesive and the substrate, broadening the scope of applications. The prepared high-performance polymers provide new insights into reusable epoxy adhesives. [ABSTRACT FROM AUTHOR]

Establishment of high‐performance epoxy resin with satisfactory fire safety, mechanical properties, and excellent transparency is urgently desirable, but still remains significant challenges. Herein, a super‐tough yet high flame retardant epoxy resin (EP/BTD) was designed and prepared by incorporating bi‐DOPO structure and hydrogen‐bonding networks. Although the phosphorus content was only 0.69 wt% (10 wt% of bi‐DOPO flame retardant [BTD]), EP/BTD‐10 showed a high limiting oxygen index value (33.4%), satisfactory UL‐94 rating (V‐0), and good heat suppression ability (total heat release [THR] and peak heat release rate [PHRR] reduced to 29.0% and 42.2%, respectively). Furthermore, the flame retardant mechanism of EP/BTD was illustrated and attributed to dual‐phase fire‐retardant effect. Additionally, EP/BTD‐7.5 featured notably mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 44.6%, 40.0%, and 232.6%, respectively, due to hydrogen‐bonding network and π–π interaction. More importantly, EP/BTD maintained high visible light transmittance and excellent UV‐blocking properties. In summary, this work provided a guidance for the development of high‐performance epoxy resin and was expected to expand the practical applications. [ABSTRACT FROM AUTHOR]

In the research on amino acids as bio‐based curing agents for epoxy resins, L‐tryptophan and L‐tyrosine have emerged as promising alternatives. Understanding the curing reactions and reaction kinetics is crucial for designing an appropriate curing regime to tailor the mechanical properties of thermosets. This study provides a comprehensive analysis of the curing reactions, curing kinetics, and latency of epoxy resin cured with L‐tryptophan or L‐tyrosine in the presence of urea‐based accelerators. L‐tryptophan involves three distinct curing reactions, corresponding to its three functional groups, while data on L‐tyrosine as a curing agent is less definitive. The degree of cure can be reliably predicted using model‐free kinetics for all resin systems studied. Overall, the inclusion of accelerators facilitates rapid curing at elevated temperatures while maintaining adequate processability for up to four weeks of storage at room temperature. [ABSTRACT FROM AUTHOR]