Diglycidyl Ether Of Bisphenol A Research Articles

Exploring the Impact of Molecular Structure on Curing Kinetics: A Comparative Study of Diglycidyl Ether of Bisphenol A and F Epoxy Resins.

Epoxy resins are essential for various applications, and their properties depend on the curing reactions during which epoxy and amine compounds form the network structure. We here focus on how the presence or absence of two methyl groups in common epoxy bases, diglycidyl ether of bisphenol A and F (4,4'-DGEBA and 4,4'-DGEBF), affects the curing kinetics. The chemical reactions of both 4,4'-DGEBA and 4,4'-DGEBF, when cured with the same amine, were monitored by Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Despite no difference in the reactivity of epoxy groups between 4,4'-DGEBA and 4,4'-DGEBF, the initial curing reaction was slower for the latter. This delay for the 4,4'-DGEBF system was attributed to intermolecular stacking, which hindered the approach of unreacted epoxy groups to amino groups and vice versa. This conclusion was drawn from the results obtained through ultraviolet (UV) spectroscopy, wide-angle X-ray scattering (WAXS), density functional theory (DFT) calculation, and all-atom molecular dynamics (MD) simulation.

Accelerating effect of metal ionic liquids for epoxy-anhydride copolymerization

One of the main drawbacks of high-performance epoxy-anhydride thermosets is slow cross-link kinetics requiring high temperature and long curing cycle. Herein, the accelerating effect of imidazolium metal-based ionic liquids (MILs) bearing (FeCl4)-, (ZnCl4)2-, and (CoCl4)2- anions on epoxy-anhydride copolymerization was investigated. It was observed that MILs accelerated bisphenol diglycidyl ether (DGEBA) − methylhexahydrophthalic anhydride (MHHPA) cross-linking, better than the reference catalysts (1-methylimidazole and 1-butyl-3-methylimidazolium chloride), especially at low temperatures through their ability to activate a rapid anhydride ring opening and formation of carboxyl groups, which initiates polyesterification. A detailed investigation of the polymerization mechanism revealed the formation of alternating epoxy-anhydride copolymers although several MILs-induced initiation mechanisms were detected. Despite the multiple-initiation consisting of imidazole, counter anion, and polyesterification pathways, the cross-linking kinetics was successfully fitted up to vitrification by the Kamal-Sourour model. Finally, MILs-induced cross-linking leads to homogeneous network build-up enabling to produce thermosetting materials with an increased cross-link density, a glass transition temperature above 150 °C, and excellent thermal stability.

Effects of Chemical Composition and Cross-Linking Degree on the Thermo-Mechanical Properties of Bio-Based Thermosetting Resins: A Molecular Dynamics Simulation Study.

Bio-based epoxy resins have received significant attention in terms of concerns regarding carbon emission. Epoxidized soybean oil (ESO) derived from sustainable feedstock has been widely used to blend with traditional diglycidyl ether of bisphenol-A (DGEBA) to replace some of the petroleum-based components. In this work, molecular dynamics (MD) simulations were applied to track the network formation and predict the performance of methyl hexahydrophthalic anhydride (MHHPA)-cured ESO/DGEBA blend systems. The effects of ESO content and cross-linking degree on the mass density, volumetric shrinkage, glass transition temperature (Tg), coefficient of thermal expansion (CTE), Young's modulus, yield strength, and Poisson's ratio of the epoxy resin were systematically investigated. The results show that systems with high ESO content achieve gelation at low cross-linking degree. The Tg value, Young's modulus, and yield strength increase with the increase in cross-linking degree, but the CTE at the glassy state and Poisson's ratio decrease. The comparison results between the simulated and experimental data demonstrated that the MD simulations can accurately predict the thermal and mechanical properties of ESO-based thermosets. This study gains insight into the variation in thermo-mechanical properties of anhydride-cured ESO/DGEBA-based epoxy resins during the cross-linking process and provides a rational strategy for optimizing bio-based epoxy resins.

Exploring Sustainable Coating Solutions for Applications in Highly Corrosive Environments

To protect carbon steel from degradation via corrosion, it is usually coated using a multilayer system of paints composed of petroleum-based polymers. The chemical industry is currently moving towards more sustainable chemistry, in which one of the main objectives is to reduce fossil fuel use and the derived raw materials. However, the replacement of petroleum-based raw materials with those that are bio-based is not straightforward since the properties of these new materials are often inferior to the traditional ones. One of the most used resins in primer paints is Diglycidyl ether bisphenol A (DGEBA). This is an epoxy resin synthesized from bisphenol A (BPA), a toxic and carcinogenic petroleum-based compound. This study investigates the substitution of the primer coating in a three-layer coating system with two different types of primer coating formulations, one which is partially bio-based and another that is BPA-free. The corrosion protection effectiveness of these sustainable coatings is assessed not only at the laboratory scale but also in real offshore conditions. Moreover, the adhesion of the different coating systems is evaluated before and after each ageing test. The results reveal that these novel coatings exhibit comparable performance to conventional paints while providing a more sustainable corrosion protection alternative.

Improving flame retardancy in BADGE epoxy via novel phosphorus‐functionalized epoxy integration

AbstractA novel epoxy resin, DPHP, was synthesized from diphenolic acid, which contains biobased levulinic acid, with triethylphosphite, to improve the flame retardancy of bisphenol‐A diglycidyl ether (BADGE) epoxy. Curing experiments were conducted using isophorone diamine as a curing agent for BADGE and DPHP mixtures. Variations in cure kinetics, mechanical properties, and flame retardancy were evaluated across different DPHP contents. The introduction of phosphorus functional groups into DPHP affected the polarization of epoxide CO bonds, resulting in reduced apparent activation energy for epoxy curing reactions. However, the higher epoxy equivalent weight of DPHP compared with that of BADGE led to a decrease in the tensile strength and the glass transition temperature of the cured material with increasing DPHP content. A significant increase in char yield for combustion of the epoxy blend was observed, ranging from 8.3% at 0 wt% DPHP to 20.1% at 50 wt% DPHP. Additionally, cone calorimeter measurements showed significant reductions in heat release rate and total heat release, leading to a decrease in fire spread from 1.07 MJm−2 s−1 at 0 wt% DPHP to 0.43 MJm−2 s−1 at 50 wt% DPHP. These results show that the flame retardancy of the cured material improved significantly as the DPHP content increased.

Electronic Interaction of Epoxy Resin with Copper at the Adhered Interface.

A better understanding of the aggregation states of adhesive molecules in the interfacial region with an adherend is crucial for controlling the adhesion strength and is of great inherent academic interest. The adhesion mechanism has been described through four theories: adsorption, mechanical, diffusion, and electronic. While interfacial characterization techniques have been developed to validate the aforementioned theories, that related to the electronic theory has not yet been thoroughly studied. We here directly detected the electronic interaction between a commonly used thermosetting adhesive, cured epoxy of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-diaminodiphenylmethane (DDM), and copper (Cu). This study used a combination of density functional theory (DFT) calculations and femtosecond transient absorption spectroscopic (TAS) measurements as this epoxy adhesive-Cu pairing is extensively used in electronic device packaging. The DFT calculations predicted that π electrons in a DDM molecule adsorbed onto the Cu surface flowed out onto the Cu surface, resulting in a positive charge on the DDM. TAS measurements for the Cu/epoxy multilayer film, a model sample containing many metal/adhesive interfaces, revealed that the electronic states of excited DDM moieties at the Cu interface were different from those in the bulk region. These results were in good accordance with the prediction by DFT calculations. Thus, it can be concluded that TAS is applicable to characterize the electronic interaction of adhesives with metal adherends in a nondestructive manner.

Novel resveratrol-based hyperbranched epoxy resin suitable for comprehensive modification of epoxy resins

Hyperbranched epoxy resins are efficient modifiers for epoxy resins but still require simultaneous improvements in terms of thermomechanical/mechanical properties and thermal stability. Herein, a novel resveratrol-based hyperbranched polyether epoxy resin (HBPEER) was designed for all-purpose epoxy resin modification. To this end, hyperbranched polyether with terminal phenolic hydroxyl groups was first synthesized from commercially available 1,6-dibromohexane (A2-type monomer) and resveratrol (B'B2-type monomer). Surface modification with epichlorohydrin was afterward implemented to produce hyperbranched polyether with terminal epoxy groups (HBPEER). Next, various HBPEER-modified epoxy thermosets were prepared and characterized. The results suggested that compared to the neat diglycidyl ether of bisphenol A (DGEBA) thermoset, the 6 wt% HBPEER-modified epoxy thermoset showed an increase in impact strength, elongation at break, critical stress intensity factor (KIC), critical crack propagation energy release rate (GIC), flexural strength, tensile strength, storage modulus, glass transition temperature (Tg), and initial thermal decomposition temperature (Td5%) by 69.6 %, 87.0 %, 32.0 %, 68.2 %, 29.3 %, 37.0 %, 8.1 %, 3.5 %, and 1.6 % respectively. Moreover, the dielectric constant and loss of 6 wt% HBPEER-modified epoxy thermoset decreased by 16.2 % and 16.5 %, respectively. Such comprehensive performance modifications were caused by the combined effects of crosslink density improvement, efficient intramolecular cavity, rigid stilbene units, and flexible aliphatic backbone of HBPEER.

A systematic investigation of the transfer of polyphosphate/inorganic silicate flame retardants from epoxy resins to layered glass fiber‐reinforced composites and their post‐furnace flexural properties

AbstractThe systematic transfer of solvent‐free, additive flame retardant (FR) formulations from epoxy resins to glass fiber‐reinforced epoxy composites (GFRECs) through prepregs is difficult. Additionally, obtaining data on their post‐fire mechanics is often challenging. Utilizing melamine polyphosphate (MPP), ammonium polyphosphate (APP), and silane‐coated ammonium polyphosphate (SiAPP) FRs with low‐melting inorganic silicates (InSi) in an 8:2 proportion and 10% loading by weight in a diglycidyl ether of bisphenol A (DGEBA) resin, a systematic investigation of the processing properties, room‐temperature mechanics, and temperature‐based mechanics of the systems was performed. The resin was cured with a dicyandiamide hardener (DICY) and a urone accelerator. The results revealed no substantial impact of these FRs at the current loading on the resin's glass transition temperature or processability. However, the fire residues from cone calorimetry tests of the composites containing FRs were found to be only 15‐20% of the thickness of the resins, implying a suppression of intumescence upon transfer. At room temperature, the decrease in the flexural modulus for the composites containing FRs was negligible. Exposure of the composites in a furnace at 400°C as a preliminary study before ignition tests was shown to cause significant flexural moduli reductions after 2.5 min of exposure and complete delamination after 3 min making further testing unviable. This study emphasizes the need for future research on recovering modes of action upon transfer of FR formulations from resins to composites. Based on the challenges outlined in this investigation, sample adaptation methods for post‐fire analysis will be developed in a future study.Highlights Processibility of resins for prepreg production unaffected by polyphosphate/inorganic silicate flame retardants (FRs). FR formulations had a negligible effect on the mechanics of the composites. 15%–25% increase in the fracture toughness of the DGEBA‐based resin matrix with FRs. Suppression of intumescent behavior in the composites verified quantitatively. Significant reduction in flexural moduli of the composites post‐400°C exposure in a furnace.

Photobleachable coumarin-thioester derivatives with low cytotoxicity as visible-light photoinitiators for free radical and cationic photopolymerization

The development of photoinitiators is suffering from deep color, low solubility, and biotoxicity caused by the introduction of large-conjugated structures, also the complex synthetic procedures constrain the application of photoinitiators. To overcome this issue, nine kinds of coumarin thioester photoinitiators (CTEs) have been delicately designed and synthesized through a simple, metal-free two-step reaction. CTEs with excellent light absorption properties in the visible light range can be used not only as a type I photoinitiator but also as a type II photoinitiator, and sensitizer in the cationic photoinitiating system. CTEs effectively initiate the photopolymerization of tripropylene glycol diacrylate (TPGDA) under the irradiation of 405 nm LED, and the double bond conversions are similar to or better than those of commercial photoinitiators. Also, the cationic photopolymerization of bisphenol A diglycidyl ether (BADGE) is successfully initiated by CTEs/IOD systems. Notably, the epoxy group conversion initiated by 6O-CTE/IOD reaches 72.1 %, surpassing that of the commercial photoinitiating system. The photoinitiating mechanism of CTEs is proposed and supported by theoretical calculations. Furthermore, the bond cleavage abilities of CS bonds endow CTEs with photobleaching properties. The colorless cured film initiated by 6O-CTE was obtained under only 15 s irradiation, indicating their application prospects of CTEs in colorless photopolymerization. More importantly, the cytotoxicity of CTEs is much lower than that of commercial photoinitiator TPO. This work provides new insight into the design of biocompatible photoinitiators with a photobleaching property for LED photopolymerization.

On the fatigue behaviour of epoxy-based nanostructured composite materials

Epoxy composites and nanocomposites enable the creation of high-performance structures and innovative designs. However, there is limited research focused on their fatigue characterization. The purpose of this study is to analyze the fatigue resistance results of nanostructured composite materials made with an epoxy matrix of Diglycidyl Ether of Bisphenol F and 9,9-bis(3-chloro-4-aminophenyl) fluorine (DGEBF-CAF) reinforced with 5%wt of elastomeric nanoparticles with an average diameter of 200 nm. The tests are conducted at variable load and frequency using Rotating Bending (R-B) and Tensile-Tensile (T-T) tests, and the results are compared to those obtained with pure resin. The occurrence of thermal fatigue phenomena during the tests is monitored using a thermal camera. The results confirm that pure epoxy resin exhibits poor crack propagation resistance due to its low ductility and toughness, and the introduction of a second phase leads to an improvement of approximately 3 times in T-T tests and 5 times in R-B tests.

Effect of catalysts on the mechanical, thermal, and adhesive properties of polyrotaxane-modified epoxy resin

Polyrotaxane (PR) is a supramolecular polymer, in which an axial polymer extends through multiple cyclic molecules. PR specifically comprises polyethylene glycol, α-cyclodextrin, and adamantane as the axial polymer, cyclic molecule, and terminal blocking group, respectively. It is a useful stress-relaxing material because the cyclic polymers can freely slide and rotate in cyclic motions on the axial polymer. In this study, diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured with phenolic resin (PN) was blended with PR, which has methacryl groups at the ends of side chains of the cyclic molecules, as a toughness modifier. The effect of the methacryl group polymerization catalyst (DCP) on the cured properties of epoxy resin was reported. PR was homogeneously dispersed in the DGEBA/PN resin matrix. Increasing the PR concentration significantly improved the toughness, impact resistance, and adhesive properties of the DGEBA/PN/PR alloy. Moreover, adding DCP resulted in an increase in the glass transition temperature due to the decreased molecular mobility of the network. This phenomenon was attributed to the synergistic effect of the formation of an interpenetrating polymer network, which is an entangled network of the curing reaction of the DGEBA/PN resin and polymerization of PR, and the intermolecular hydrogen bonds between carbonyl and hydroxyl groups of PR and hydroxyl groups of the DGEBA/PN resin. In contrast, the increased interfacial adhesion between PR and the DGEBA/PN did not result in significant improvement of flexural properties.

POSS/EHTPB synergistically toughened epoxy resin for cryogenic application

The high brittleness of epoxy resin at cryogenic temperature restricts their wide application in cryogenic engineering. In this study, polyhedral oligomeric silsesquioxane (POSS) with -Si-O-Si- molecular chains were synthesized, and the mechanical properties of diglycidyl ether of bisphenol A (E51 epoxy resin) were significantly enhanced at room temperature (RT) by incorporating a 4% POSS and curing agent 4,4′-diamino-diphenylmethane (DDM) as the E51/POSS/DDM resin system. Subsequently, by adding different contents of epoxidation hydroxyl-terminated polybutadiene (EHTPB) into the E51/POSS/DDM resin system, the EHTPB-E51/POSS/DDM resin system was prepared. The investigation into the impact of EHTPB content on the mechanical properties of EHTPB-E51/POSS/DDM resin system at room temperature (RT) revealed that EHTPB-E51/POSS/DDM resin system with 10% EHTPB exhibited the most favorable results. Specifically, the elongation at break, flexural strength, and critical stress intensity factor (KIC) were measured to be 6.82%, 143.75 MPa, and 1.83 MPa·m1/2, respectively. These values demonstrated a notable improvement of 53.3%, 26.9%, and 86.7% compared to those for the E51/DDM resin system. Concurrently, at 77 K, the elongation at break and critical stress intensity factor (KIC) increased by 37.8% and 73.5%, respectively. The toughening mechanism of the prepared EHTPB-E51/POSS/DDM resin system was further explored through resin-curing cross-linking simulation networks and SEM images of the fracture surface of resin samples. The study of EHTPB and POSS synergistically toughened epoxy resin provided a new efficient method to prepare epoxy resins with high toughness at low temperatures.

In English

Natural fibre reinforced polymer composites nowadays are considered to be attractive cheap, safe and eco-friendly materials. The main problem of such composites related to the hydrophilicity of plant fibres may be successfully solved by chemical modification of their surface. However, some characteristics of the materials may be suppressed after this procedure. Therefore, the aim of the research is to find out the impact of chemical modification of filler on thermooxidative stability, tensile and flexural strength, as well as on biodegradability of polymer composites. The novelty of this work is in the examining new materials on the basis of Si-containing epoxyurethanes and chemically treated hemp woody core (HWC). Woody core that is the side product of hemp industry requiring its apropriate utilization was exposed to mercerization with sodium hydroxide solution and to further functionalization with epoxidized soybean oil (ESO) or 3-aminopropyltriethoxysilane (APS). Raw and surface treated HWC was used as reinforcement for two types of organic-inorganic epoxyurethane matrices made from sodium silicate, polyurethane prepolymer based on polyisocyanate and castor oil, and either diglycidyl ether of bisphenol-A (DGEBA) or ESO as epoxy component. Functionalization of HWC led to better mechanical properties of composites. Compared to the corresponding materials including untreated filler, maximum increase in flexural strength (26 %) was observed for the samples with ESO-containing epoxyurethane and silanized HWC, while maximum increase in tensile strength (53 %) was revealed for the ones with DGEBA-containing epoxyurethane and oil treated HWC. Thermooxidative stability was also higher for composites reinforced with functionalized HWC. The specimens with APS-treated HWC performed the best at thermal decomposition. The values of their T50% were up to 68 °C more than those for composites with unmodified filler. At the same time, the samples based on APS- or ESO-treated HWC were the most resistant to biodegradation, which may be concluded from their smallest weight loss during soil burial test.

Functional cellulose-derived epoxy cross-linked with BADGE resin to construct high-performance epoxy composites

The development of equipped bio-based epoxy materials has been gaining much attention recently. Nevertheless, finding the balance between the structure and properties of materials remains a significant challenge. In this work, cellulose-based epoxy (PHPCEP) with “soft” and “hard” cooperative structures was designed and demonstrated to endow bisphenol A diglycidyl ether (BADGE) with excellent toughness, heat resistance, mechanical strength, glass transition temperature, thermal stability, and solvent resistance. When 5 wt% PHPCEP was incorporated into BADGE composites, the resulting materials exhibited the maximum flexural strength (121.9 MPa) and tensile strength (71.4 MPa), a high glass transition temperature (148.3 °C), and 10 wt% PHPCEP/BADGE demonstrated the highest impact strength (70.5 kJ/m2). These figures are 18.8 %, 16.1 %, 21.5 %, and 254.3 % higher than the corresponding values of neat BADGE. The results of dynamic mechanical properties and heat degradation of the cured specimens also suggest that PHPCEP/BADGE materials have superior stiffness and toughness than neat BADGE, which could be attributed to the strong interaction between PHPCEP and BADGE, delivering better thermal stability for the composites compared to the pristine resin. Considering the remarkable effect, this work provides an effective way of highly efficient utilization of abundant cellulose and a high-performance additive for composite materials.

Effects of curing conditions on adhesive and fatigue properties of hydrogenated epoxy resins in bulk state and single-lap-joint configuration

The adhesive and fatigue properties of single-lap-joint (SLJ) epoxy resins are strongly affected by not only the network structures of an epoxy resin adhesive, but also the adhesive strength between an adhesive and adherend. These properties are closely related to curing conditions, such as curing temperature, and curing time, and their combination. In this study, the effects of curing conditions on an adhesive and fatigue properties of an epoxy resin [hydrogenated diglycidyl ether of bisphenol A and cyclohexanebis(methylamine)] were investigated via a single lap-shear test, a fatigue test, and wide-angle X-ray scattering (WAXS). The tensile and fatigue properties of a bulk epoxy resin were also investigated for comparison. The SLJ and bulk samples were prepared with three different curing conditions to obtain high (H), middle (M), and low (L) cross-linking (CL) density of the network structure. They are denoted as “CL-H″, “CL-M″, and “CL-L″, respectively. SLJ-CL-L and Bulk-CL-L exhibited the lowest degree of cure, adhesive and tensile strengths of the three. Both Bulk-CL-H and Bulk-CL-M yielded in tensile testing and Bulk-CL-M was tougher than Bulk-CL-H. In contrast, neither SLJ-CL-H and SLJ-CL-M yielded, and SLJ-CL-H was tougher than SLJ-CL-M. This can be ascribed that the SLJ sample broke before yielding of epoxy resin adhesive and SLJ-CL-H exhibited a higher adhesive strength between the epoxy resin and adherend than SLJ-CL-M. This was confirmed by X-ray photoelectron spectroscopy. Concerning the fatigue properties, SLJ-CL-H exhibited enhanced properties than SLJ-CL-M, although Bulk-CL-M were better than Bulk-CL-H. This trend corresponds well with difference between single lap-shear and tensile tests. The WAXS measurements revealed that the strain values calculated using distance between molecular chains were almost identical for the bulk and SLJ samples immediately before yielding and breaking, respectively. This is because an increase in stress stopped at yielding of bulk and break of SLJ.

Reversible adhesives from epoxy-based transesterification-induced vitrimers

Vitrimers are a class of materials that combine the excellent mechanical performance of thermosetting polymers with the malleability of thermoplastic polymers. One of the applications that most benefits from these features is structural adhesives. In this work, epoxy-based vitrimers from diglycidyl ether of bisphenol A, succinic anhydride, and trimethylolpropane are used as reversible adhesives. These materials show glass transition temperatures up to 80 °C as well as a homogeneous network structure. They also show high lap-shear stress values of up to 26 MPa. These adhesives are suitable for reversible adhesion thanks to their excellent vitrimeric behavior, with characteristic relaxation times that are under 10 min at 180 °C. This allows for the re-utilization of the same joint through re-adhesion after failure, the dismantling of adhesive joints with posterior re-bonding, and the application of the adhesive as a coating to make the joint in a different stage. The re-adhesion reaches values up to 96% with respect to the values of the first adhesion. Finally, chemical recycling is achieved through alcoholysis in ethyleneglycol, and this methodology is used to remove adhesive remains from adherend plates, so that they can be used for any other purpose. In summary, these vitrimer adhesives not only show high adhesion shear stress, suitable for structural applications, but also allow re-joining the bond in case of failure, the dismantling of the joint at the end of the bond lifetime, thermally activate the adhesive joint, and recover the adherends to be used for another purpose.

A new platform for designing high‐performance epoxy film adhesive with poly (butyl acrylate‐block‐styrene) block copolymer and alumina nano particles in aluminum–aluminum bonded joints: Preparation and analysis of the mechanical, adhesion, and thermal properties

AbstractEpoxy film adhesives are typically used in different industries. However, these adhesives suffer from brittleness, low flexibility, and thermal stability problems. In this research, phenolic resin (Novolac) and poly (butyl acrylate‐block‐styrene) were used in the formulation of epoxy film adhesive (Diglycidyl ether bisphenol A) to increase thermal stability and adhesion strength and as the toughening agent, respectively. Alumina nanoparticles were also employed to enhance the mechanical properties. The influence of block copolymer and alumina nano particles was also assessed on the mechanical and thermal properties of epoxy‐based film adhesives. The investigation of the mechanical properties of dumbbell‐shaped samples and adhesion strength of the Al‐Al bonded joints were evaluated by tensile, lap shear, and T‐peel tests. The thermal stability of the optimal samples was assessed by thermogravimetry analysis (TGA). SEM analysis was also utilized to study the toughening mechanism. Tensile test of the dumbbell‐shaped samples indicated that the incorporation of 2.5 phr block copolymer and 2 phr alumina nanoparticles enhanced the toughness to 250%. The shear and peel strengths of this sample also exhibited 51% and 76% increase, respectively, showing a remarkable synergistic effect. On the other hand, TGA results revealed that the incorporation of block copolymer improved the thermal stability of the adhesive matrix. The copresence of these two materials also showed a considerable synergistic effect on the thermal stability. The SEM results were also in line with the results of mechanical tests as the crack deviation, crack pinning, and debonding were the most important mechanisms of toughening.Highlights A new platform was developed for designing epoxy films adhesives with high mechanical, adhesion, and thermal properties. The hybrid of butyl acrylate block styrene copolymer, phenolic resin, and alumina nanoparticles showed synergistic effects on the lap shear and T‐peel strength. The greatest improvement in toughness was related to the epoxy adhesive containing 2.5 phr block copolymer and 2 phr alumina nanoparticles. Analysis of the fracture surface showed that by using hybrid of nanoparticles and block copolymers in the epoxy film adhesive formulation, the cohesive failure occurred. The use of hybrid additives in film adhesive formulations enlightened manufacture of adhesives for future studies on adhesive formulations.

Comparing Surface and Bulk Curing Processes of an Epoxy Vitrimer.

We used atomic force microscopy-based infrared spectroscopy (AFM-IR) and nanomechanical mapping (AFM-NM) to image the surface of a vitrimer, specifically dicarboxylic acid-cured diglycidyl ether of bisphenol A (DGEBA), to assess the curing process of a surface layer and compared this to the process in the bulk. We identified the β-hydroxy esters with various functionalities that are the key to form the cross-links for a system, including difunctional DGEBA and carboxylic acids. The IR peaks of the carbonyl group in generated ester groups are distinguished clearly from those in acids, allowing us to quantitatively assess the curing process at the surface and in the bulk. The initial curing at the surface exhibits a gradual cross-linking and is found to be lower than a rapid cross-linking in the bulk due to a relatively lower concentration of the β-hydroxy esters with high functionalities. This curing process leads to a smaller chemically and mechanically heterogeneous nanostructure at the surface relative to the bulk. After multiple reprocessings, a substantial number of esters lacking dynamic exchange capability form in the bulk, which decrease the flowability and reprocessability of the vitrimers and therefore the mechanical properties.

Non-isocyanate epoxy vinyl ester urethane prepolymer based on diglycidyl ether of bisphenol-A

Non-isocyanate epoxy vinyl ester urethane prepolymer based on diglycidyl ether of bisphenol-A

Length effect of short base resin on thermomechanical properties of crosslinked epoxy resin via molecular dynamics simulation

Epoxy resin is commonly used as the matrix in carbon fiber-reinforced polymer (CFRP), fabricated through the curing reaction of the base resin and curing agent, whose properties have a deep relationship with the crosslinking degree of the polymer. However, under certain circumstances, the desired conversion rate cannot be achieved in the experiments. To shed light on this phenomenon and the underlying mechanisms, the curing process of diglycidyl ether of bisphenol A (DGEBA) with different chain lengths and 4,4′-diamino diphenyl sulfone (4,4′-DDS) was simulated as per our previously developed crosslinking algorithm. The longer chain length postpones but does not change the reaction progress (like the gel point), leading to a lower conversion rate, and ultimately a decrease in the diffusion coefficient. In addition, the influence on the glass transition temperature is the result of the competing effects of the conversion rate and monomer diffusivity. Moreover, the negligible effect on thermal conductivity is closely linked with a slight change in the monomeric degree index (MDI), reflecting the whole internal intrinsic structure. Furthermore, the effect on Young's modulus and yield stress has a deep relationship with the ring degree index (RDI), i.e., higher RDI demands more non-bonded energy for the collective movement of monomer chains. Our systematic investigation unifies the mechanism of the impact of chain length on various thermomechanical properties, which is instructive for the improved performance of epoxy resins.