A perspective approach on the amine reactivity and the hydrogen bonds effect on epoxy-amine systems

Bio-based epoxy resin/carbon nanotube coatings applied on cotton fabrics for smart wearable systems

Electroactive coatings for smart wearable textiles based on a furan bio-epoxy monomer (BOMF) crosslinked with isophorone diamine (IPD) and additivated with carbon nanotubes (CNTs) are reported herein. The effect of BOMF/IPD molar ratio on the curing reaction, as well as on the properties of the crosslinked resins was first assessed, and it was found that 1.5:1 BOMF/IPD molar ratio provided higher heat of reaction, glass transition temperature, and mechanical performance. The resin was then modified with CNT to prepare electrically conductive nanocomposite films, which exhibited conductivity values increased by eight orders of magnitude upon addition of 5 phr of CNTs. The epoxy/CNT nanocomposites were finally applied as coatings onto a cotton fabric to develop electrically conductive, hydrophobic and breathable textiles. Notably, the integration of CNTs imparted efficient and reversible electrothermal behavior to the cotton fabric, showcasing its potential application in smart and comfortable wearable electronic devices.

Chemically and physically enhanced adhesion for robust interfaces in all-soft vertical organic photodetectors

We report all-soft vertical organic photodetectors composed of only soft components. Chemically and physically enhanced interfacial adhesion between layers enables robust operation under mechanical deformation. Their excellent light-sensing capability and deformable features, combined with powerless operation, promise significant advancements in optoelectronic applications.

Kraft (Nano)Lignin as Reactive Additive in Epoxy Polymer Bio-Composites

The demand for high-performance bio-based materials towards achieving more sustainable manufacturing and circular economy models is growing significantly. Kraft lignin (KL) is an abundant and highly functional aromatic/phenolic biopolymer, being the main side product of the pulp and paper industry, as well as of the more recent 2nd generation biorefineries. In this study, KL was incorporated into a glassy epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) and an amine curing agent (Jeffamine D-230), being utilized as partial replacement of the curing agent and the DGEBA prepolymer or as a reactive additive. A D-230 replacement by pristine (unmodified) KL of up to 14 wt.% was achieved while KL-epoxy composites with up to 30 wt.% KL exhibited similar thermo-mechanical properties and substantially enhanced antioxidant properties compared to the neat epoxy polymer. Additionally, the effect of the KL particle size was investigated. Ball-milled kraft lignin (BMKL, 10 μm) and nano-lignin (NLH, 220 nm) were, respectively, obtained after ball milling and ultrasonication and were studied as additives in the same epoxy system. Significantly improved dispersion and thermo-mechanical properties were obtained, mainly with nano-lignin, which exhibited fully transparent lignin-epoxy composites with higher tensile strength, storage modulus and glass transition temperature, even at 30 wt.% loadings. Lastly, KL lignin was glycidylized (GKL) and utilized as a bio-based epoxy prepolymer, achieving up to 38 wt.% replacement of fossil-based DGEBA. The GKL composites exhibited improved thermo-mechanical properties and transparency. All lignins were extensively characterized using NMR, TGA, GPC, and DLS techniques to correlate and justify the epoxy polymer characterization results.

Design of Amine-Containing Nanoporous Materials for Postcombustion CO2 Capture from Engineering Perspectives

ConspectusCarbon dioxide (CO2) capture and storage (CCS) is a means to enable the continued use of fossil fuels in the short term. In particular, postcombustion CO2 capture has attracted considerable attention because it can be retrofitted into existing power plants and industrial plants. Among various CO2 capture technologies, the absorption of CO2 using aqueous amines has been industrially employed for decades. However, such amine scrubbing technologies have inherent limitations of environmental and health concerns due to volatile amine loss, corrosion, and high energy demands for regeneration. To overcome these limitations, CO2 adsorption using solid adsorbents has emerged as a promising alternative due to its noncorrosiveness and low energy demand. Various amine-containing adsorbents have been synthesized and investigated for postcombustion CO2 capture. These materials are prepared by physically impregnating low-vapor-pressure amine polymers or by chemically grafting amines onto nanoporous materials. A wide variety of amine guests and nanoporous hosts (e.g., SiO2, Al2O3, zeolites, MOFs, and polymers) have been combined to develop advanced CO2 adsorbents.The design of CO2 adsorbents is a multifaceted puzzle that must ultimately consider integration with large-scale CO2 capture processes. Various engineering aspects need to be carefully considered. Unfortunately, a significant proportion of previous studies has primarily focused on the use of novel materials for improving the CO2 adsorption capacity. In this Account, we describe key challenges and solutions to develop energy-efficient and stable amine-containing adsorbents for postcombustion CO2 capture via temperature swing adsorption (TSA). We found that a high CO2 working capacity, often overemphasized in the literature, does not necessarily guarantee a low energy demand for CO2 capture. Suppressing coadsorption of H2O during the CO2 adsorption in humid flue gas is also a significant factor. Amine-containing adsorbents can be degraded through various pathways, including hydrothermal degradation of nanoporous hosts and chemical degradation of amine guests via urea formation and oxidation. To inhibit such degradation pathways, it is extremely important to properly design the nanoporous structures of the hosts and the molecular structures of the amine guests. By combining macroporous silica hosts, poly(ethylenimine) (PEI) functionalized with various alkyl epoxides, and phosphate-based oxidative stabilizers, we could synthesize adsorbents exhibiting low energy demands for CO2 capture and unprecedentedly high thermochemical stability under TSA conditions. The macroporous silica host synthesized by assembling fumed silica particles via spray-drying exhibited high hydrothermal stability and enabled uniform distribution of bulky amine polymers within its pores. The functionalization of PEI with alkyl epoxides converted its primary amines into hindered secondary amines, leading to a significant reduction in energy demand for TSA cycles and a remarkable improvement in long-term stabilities. The oxidative stability of amines could be drastically improved by adding phosphate metal-binding reagents, which can poison ppm-level metal impurities that catalyze amine oxidation. The present discussions will provide important insights into designing practical adsorbents for CO2 capture from engineering perspectives.

Anion Exchange Membranes Based on Chemical Modification of Recycled PET Bottles

This study presents an innovative and effective solution for recycling PET bottles as raw for producing anion exchange membranes (AEMs) for electrochemical applications. This approach reduces the demand for pristine materials, a key principle of the circular economy and sustainability. PET was subjected to chemical modification by introducing cationic functional groups followed by methylation and OH- exchange process. The amination synthesis was optimized based on reaction time. The results indicate that ion exchange capacity, water uptake, and swelling ratio properties mainly depend on the degree of cationic functionalization. The optimized AEM exhibits ionic conductivity of 5.3 × 10-2 S·cm-1 and alkaline stability of 432 h in 1 M KOH at 80 °C. The membrane properties before and after the alkaline treatment were investigated using Fourier-transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy analysis. Computational chemistry analysis was employed to gain further insights into the membrane degradation mechanisms and pathways under alkaline conditions. This research and its findings are a step toward using recycled materials in the field of AEM technology.

Bisphenol A Diglycidyl Ether-Primary Amine Cooligomer-poly(ε-caprolactone) Networks: Synthesis and Characterization

In this work, the preparation and systematic investigation of cross-linked polyurethane-epoxy (PU-EP) polymer systems are reported. The PU-EP polymers were prepared using a reaction of isocyanate (NCO)-terminated PU-prepolymer with diglycidyl ether of bisphenol A (DGEBA)-amine cooligomer. The oligomerization of DGEBA was carried out by adding furfurylamine (FA) or ethanolamine (EA), resulting in DGEBA-amine cooligomers. For the synthesis of NCO-terminated PU-prepolymer, poly(ε-caprolactone)diol (PCD) (M_n = 2 kg/mol) and 1,6-hexamethylene diisocyanate (HDI) were used. The cross-linking was achieved by adding DGEBA-amine cooligomer to PU-prepolymer, in which the obtained urethane bonds, due to the presence of free hydroxil groups in the activated DGEBA, served as netpoints. During cross-linking, ethanolamine provides an additional free hydroxyl group for the formation of a new urethane bond, while furfurylamine can serve as a thermoreversible coupling element (e.g., Diels-Alder adduct). The PU-EP networks were characterized using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA) and scanning electron microscopy (SEM). The DMA curves of some PU-EPs (depending on the compositions and the synthetic method) revealed a plateau-like region above the melting temperature (T_m) of PCD, confirming the presence of a cross-linked structure. This property resulted in a shape memory (SM) behavior for these samples, which can be fine-tuned in the presence of furfurylamine through the formation of additional thermoreversible bonds (e.g., Diels-Alder adduct).

Biobased epoxy reactive diluents prepared from monophenol derivatives: effect on viscosity and glass transition temperature of epoxy resins

The use of reactive diluents is undeniably of paramount importance to develop epoxy resins which would meet more demanding and restrictive processes and applications in terms of viscosity and glass transition temperature. In the context of developing resins with low carbon impacts, 3 natural phenols namely carvacrol, guaiacol and thymol were selected and converted into monofunctional epoxies using a general glycidylation procedure. Without advanced purification, the developed liquid-state epoxies showed very low viscosities of 16 cPs to 55 cPs at 20 °C, which could be further reduced to 12 cPs at 20 °C when purification by distillation is applied. The dilution effect of each reactive diluent on DGEBA's viscosity was also assessed for concentrations ranging from 5 to 20 wt% and compared to commercial and formulated DGEBA-based resin analogues. Interestingly, the use of these diluents reduced the initial viscosity of DGEBA by a factor of ten while maintaining glass transition temperatures above 90 °C. This article provides compelling evidence of the possibility of developing new sustainable epoxy resins with characteristics and properties that can be fine-tuned by only adjusting the reactive diluent concentration.

Mechanism-based and computational modeling of hydrogen sulfide biogenesis inhibition: interfacial inhibition

Hydrogen sulfide (H₂S) is a gaseous signaling molecule that participates in various signaling functions in health and diseases. The tetrameric cystathionine γ-lyase (CSE) contributes to H₂S biogenesis and several investigations provide evidence on the pharmacological modulation of CSE as a potential target for the treatment of a multitude of conditions. D-penicillamine (D-pen) has recently been reported to selectively impede CSE-catalyzed H₂S production but the molecular bases for such inhibitory effect have not been investigated. In this study, we report that D-pen follows a mixed-inhibition mechanism to inhibit both cystathionine (CST) cleavage and H₂S biogenesis by human CSE. To decipher the molecular mechanisms underlying such a mixed inhibition, we performed docking and molecular dynamics (MD) simulations. Interestingly, MD analysis of CST binding reveals a likely active site configuration prior to gem-diamine intermediate formation, particularly H-bond formation between the amino group of the substrate and the O3' of PLP. Similar analyses realized with both CST and D-pen identified three potent interfacial ligand-binding sites for D-pen and offered a rational for D-pen effect. Thus, inhibitor binding not only induces the creation of an entirely new interacting network at the vicinity of the interface between enzyme subunits, but it also exerts long range effects by propagating to the active site. Overall, our study paves the way for the design of new allosteric interfacial inhibitory compounds that will specifically modulate H₂S biogenesis by cystathionine γ-lyase.

Assessment of commercial polymers with and without reactive groups using amino acid derivative reactivity assay based on both molar concentration approach and gravimetric approach

The amino acid derivative reactivity assay (ADRA), an alternative method for testing skin sensitization, has been established based on the molar concentration approach. However, the additional development of gravimetric concentration and fluorescence detection methods has expanded its range of application to mixtures, which cannot be evaluated using the conventional testing method, the direct peptide reactivity assay (DPRA). Although polymers are generally treated as mixtures, there have been no reports of actual polymer evaluations using alternative methods owing to their insolubility. Therefore, in this study, we evaluated skin sensitization potential of polymers, which is difficult to predict, using ADRA. As polymers have molecular weights ranging from several thousand to more than several tens of thousand Daltons, they are unlikely to cause skin sensitization due to their extremely low penetration into the skin, according to the 500-Da rule. However, if highly reactive functional groups remain at the ends or side chains of polymers, relatively low-molecular-weight polymer components may penetrate the skin to cause sensitization. Polymers can be roughly classified into three major types based on the features of their constituent monomers; we investigated the sensitization capacity of each type of polymer. Polymers with alert sensitization structures at their ends were classified as skin sensitizers, whereas those with no residual reactive groups were classified as nonsensitizers. Although polymers with a glycidyl group need to be evaluated carefully, we concluded that ADRA (0.5 mg/ml) is generally sufficient for polymer hazard assessment.

Investigating the Synthesis and Characteristics of UV-Cured Bio-Based Epoxy Vegetable Oil-Lignin Composites Mediated by Structure-Directing Agents

Bio-based composites were developed from the epoxy derivatives of Lallemantia iberica oil and kraft lignin (ELALO and EpLnK), using UV radiation as a low energy consumption tool for the oxiranes reaction. To avoid the filler sedimentation or its inhomogeneous distribution in the oil matrix, different structure-directing agents (SDA) were employed: 1,3:2,4-dibenzylidene-D-sorbitol (DBS), 12-hydroxystearic acid (HSA) and sorbitan monostearate (Span 60). The SDA and EpLnK effect upon the ELALO-based formulations, their curing reaction and the performance of the resulting materials were investigated. Fourier-transform Infrared Spectrometry (FTIR) indicates different modes of molecular arrangement through H bonds for the initial ELALO-SDA or ELALO-SDA-EpLnK systems, also confirming the epoxy group's reaction through the cationic mechanism for the final composites. Gel fraction measurements validate the significant conversion of the epoxides for those materials containing SDAs or 1% EpLnK; an increased EpLnK amount (5%), with or without SDA addition, conduced to an inefficient polymerization process, with the UV radiation being partially absorbed by the filler. Thermo-gravimetric and dynamic-mechanical analyses (TGA and DMA) revealed good properties for the ELALO-based materials. By loading 1% EpLnK, the thermal stability was improved to with 10 °C (for Td3%) and the addition of each SDA differently influenced the Tg values but also gave differences in the glassy and rubbery states when the storage moduli were interrogated, depending on their chemical structures. Water affinity and morphological studies were also carried out.

Influence of Phosphorus Structures and Their Oxidation States on Flame-Retardant Properties of Polyhydroxyurethanes

This article focuses on the synthesis of polyhydroxyurethane (PHU) materials containing novel phosphorus flame retardants (FR). Four different phosphorus compounds were grafted onto cyclic carbonate: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diethyl phosphite (DEP), diphenyl phosphite (DPP) and dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO). Thus, three novel phosphorus reactive cyclic carbonates which have never been reported so far were synthetized. Phosphorus FR containing PHU materials were characterized by FTIR to evidence the total conversion of the cyclic carbonate. Moreover, the gel contents up to 80% confirmed the formation of the polymer network. Then, the thermal stability and the flame-retardant properties were investigated by thermogravimetric analyses, cone calorimeter and pyrolysis combustion flow calorimeter. The mode of action of phosphorus compounds, depending on the oxidation state, was especially highlighted. Phosphonate (+III) provided better action in a condensed phase than phosphinate thanks to a more efficient char formation. Among phosphonates, differences were observed in terms of char-formation rate and expansion. DEP provided the best flame-retardant properties, with a reduction of 76% of pHRR with 2 wt% of phosphorus in cone calorimeter analysis. Therefore, this article highlighted the different modes of action of phosphorus flame retardants, depending on the oxidation state of phosphorus, in PHU materials.

Volatile Organic Compound Monitoring during Extreme Wildfires: Assessing the Potential of Sensors Based on LbL and Sputtering Films

A new theory suggests that flammable gases generated by heated vegetation, in particular the volatile organic compounds (VOC) common to Mediterranean plants, may, under certain topographic and wind conditions, accumulate in locations where, after the arrival of the ignition source, they rapidly burst into flames as explosions. Hence, there is a need for the development of a system that can monitor the development of these compounds. In this work, a sensor's array is proposed as a method for monitoring the amount of eucalyptol and α-pinene, the major VOC compounds of the Eucalyptus and Pine trees. The detection of the target compounds was assessed using the impedance spectroscopy response of thin films. Combinations of layers of polyelectrolytes, such as poly(allylamine hydrochloride) (PAH), polyethyleneimine (PEI), poly(sodium 4-sytrenesulfonate) (PSS) graphene oxide (GO), and non/functionalized multiwall nanotubes (MWCNT-COOH or MWCNT), namely, PAH/GO, PEI/PSS, PEI/GO, PAH/MWCNT, PAH/MWCNT-COOH, films, and TiO₂ and ZnO sputtered films, were deposited onto ceramic supports coated with gold interdigitated electrodes. The results showed that concentrations of the target VOCs, within the range of 68 to 999 ppm_v, can be easily distinguished by analyzing the impedance spectra, particularly in the case of the ZnO- and PAH/GO-film-based sensors, which showed the best results in the detection of the target compounds. Through principal component analysis (PCA), the best set of features attained for the ZnO and PAH/GO based sensor devices revealed a linear trend of the PCA's first principal component with the concentration within the range 109 and 807 ppm_v. Thus, the values of sensitivity to eucalyptol and α-pinene concentrations, which were (2.2 ± 0.3) × 10^-4 and (5.0 ± 0.7) × 10^-5 per decade, respectively, as well as resolutions of 118 and 136 ppb_v, respectively, were identified.

Network Formation and Physical Properties of Epoxy Resins for Future Practical Applications

Epoxy resins are used in various fields in a wide range of applications such as coatings, adhesives, modeling compounds, impregnation materials, high-performance composites, insulating materials, and encapsulating and packaging materials for electronic devices. To achieve the desired properties, it is necessary to obtain a better understanding of how the network formation and physical state change involved in the curing reaction affect the resultant network architecture and physical properties. However, this is not necessarily easy because of their infusibility at higher temperatures and insolubility in organic solvents. In this paper, we summarize the knowledge related to these issues which has been gathered using various experimental techniques in conjunction with molecular dynamics simulations. This should provide useful ideas for researchers who aim to design and construct various thermosetting polymer systems including currently popular materials such as vitrimers over epoxy resins.

Development and chromatographic exploration of stable-bonded crosslinked amino silica against classical amino phases

The present work reports on a novel stable-bonded amino silica stationary phase obtained by crosslinking of surface aminopropyl moieties using triglycidyl isocyanurate. The obtained crosslinked amido-amino network silica material exhibited superior hydrolytic stability compared to classical 3-aminopropyl phases and showed, inter alia, excellent separation of nine therapeutically effective sulfonamides in hydrophilic interaction / weak anion exchange chromatography elution mode. Additionally, the separation of carbohydrates was investigated under classical hydrophilic interaction chromatography conditions as well proving the suitability of the novel phase for such applications. For the evaluation of the hydrolytic stability the prepared material, as well as two commercially available benchmark columns and a set of in-house synthesized amino modified materials, were exposed to harsh aqueous mobile phase conditions for in total 50 hours at elevated temperature. In this context, the materials were examined by elemental analysis, (¹³ C and ²⁹ Si cross-polarization/magic angle spinning) solid-state NMR and a chromatographic test before and subsequent to the exposure to these stress conditions. Lastly, the new stationary phase was classified in comparison to a set of commercially available stationary phases by principal component analysis of resultant retention factors gained from chromatographic standard tests. This article is protected by copyright. All rights reserved.

Uncovering the Mechanism of Size Effect on the Thermomechanical Properties of Highly Cross-Linked Epoxy Resins

Epoxy resins are widely used as matrix resins, especially for carbon-fiber-reinforced plastic, due to their outstanding physical and mechanical properties. To date, most research into cross-linking processes using simulation has considered only a distance-based criterion to judge the probability of reaction. In this work, a new algorithm was developed for use with the large-scale atomic/molecular massively parallel simulator (LAMMPS) simulation package to study the cross-linking process; this new approach combines both a distance-based criterion and several kinetic criteria to identify whether the reaction has occurred. Using this simulation framework, we investigated the effect of model size on predicted thermomechanical properties of three different structural systems: diglycidyl ether of bisphenol A (DGEBA)/4,4'-diaminodiphenyl sulfone (4,4'-DDS), DGEBA/diethylenetriamine (DETA), and tetraglycidyl diaminodiphenylmethane (TGDDM)/4,4'-DDS. Derived values of gel point, volume shrinkage, and cross-linked resin density were found to be insensitive to model size in these three systems. Other thermomechanical properties, i.e., glass-transition temperature, Young's modulus, and yield stress, were found to reach stable values for systems larger than ∼40 000 atoms for both DGEBA/4,4'-DDS and DGEBA/DETA. However, these same properties modeled for TGDDM/4,4'-DDS did not stabilize until the system size reached 50 000 atoms. Our results provide general guidelines for simulation system size and procedures to more accurately predict the thermomechanical properties of epoxy resins.

Taking advantage of β-hydroxy amine enhanced reactivity and functionality for the synthesis of dual covalent adaptable networks

This study highlights the potential of β-hydroxy amines as building blocks for aza-Michael CANs.

Cut-off Scale and Complex Formation in Density Functional Theory Computations of Epoxy-Amine Reactivity

Most of the properties of epoxy resins are tied to their degree of cross-linking, making understanding the reactivity of different epoxy systems a crucial aspect of their utilization. Here, epoxy-amine reactivity is studied with density functional theory (DFT) at various cut-off levels to explore the suitability of the method for estimating the reactivity of specific epoxy systems. Although it is common to use minimal structures in DFT to reduce computational cost, the results of this study highlight the important role of hydrogen bonding and other noncovalent interactions in the reactivity. This is a promising result for differentiating the most probable reactive paths for different resin systems. The significance of amine groups as a potential source of catalyzing H-bonds was also explored and, while not quite as effective as a catalyst as a hydroxyl group, a clear catalyzing effect was observed in the transition state energies. Unfortunately, the added complexity of a more representative reactive system also results in increased computational cost, highlighting the need for proper selection of structural cutoffs.

Chelating Fabrics Prepared by an Organic Solvent-Free Process for Boron Removal from Water

A chelating fabric was prepared by graft polymerization of glycidyl methacrylate (GMA) onto a nonwoven fabric, followed by attachment reaction of N-methyl-D-glucamine (NMDG) using an organic solvent-free process. The graft polymerization was performed by immersing the gamma-ray pre-irradiated fabric into the GMA emulsion, while the attachment reaction was carried out by immersing the grafted fabric in the NMDG aqueous solution. The chelating capacity of the chelating fabric prepared by reaction in the NMDG aqueous solution without any additives reached 1.74 mmol/g, which further increased to above 2.0 mmol/g when surfactant and acid catalyst were added in the solution. The boron chelation of the chelating fabric was evaluated in a batch mode. Fourier transform infrared spectrophotometer (FTIR) was used to characterize the fabrics. The chelating fabric can quickly chelate boron from water to form a boron ester, and a high boron chelating ability close to 18.3 mg/g was achieved in the concentrated boron solution. The chelated boron can be eluted completely by HCl solution. The regeneration and stability of the chelating fabric were tested by 10 cycles of the chelation-elution operations. Considering the organic solvent-free preparation process and the high boron chelating performance, the chelating fabric is promising for the boron removal from water.