Epoxy Prepolymer Research Articles

Novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties

As one of the most commonly used thermosetting resins, the flammability of epoxy resins (EPs) has become a key factor limiting the expansion of their application range. Herein, a novel phosphorous-containing epoxy monomer (EDPPO) was synthesized using diallyl amine and diphenyl phosphoryl chloride as the starting materials. Subsequently, EDPPO was thermally cured with two diamine hardeners, 4, 4′-diaminodiphenyl sulfone (DDS) and 4,4′-dithiodianiline (DTDA). Additionally, commercial diglycidyl ether of bisphenol A (DGEBA)-type epoxy pre-polymers were cured with DDS and DTDA as comparative samples. The cured EDPPO-based thermosets showed excellent flame-retardant properties coupled with smoke suppression. Specifically, the limiting oxygen index (LOI) for the EDPPO/DDS (P content 6.4 wt.%) reached 32.0 %, and the UL-94 vertical burning test reached a V-0 rating. In addition, the PHRR, THR, and TSP values of EDPPO/DDS were 61.6 %, 49.1 %, and 58.5 % lower than those of DGEBA/DDS, respectively. The flame retardant mechanism analysis indicated that the excellent flame retardancy for cured EDPPO-based thermosets was attributed to the combined modes of action in condensed (promoting the charring capacity) and gaseous phases (quenching the active radicals). More importantly, EDPPO/DDS and EDPPO/DTDA exhibited lower dielectric constant and dielectric loss than DGEBA/DDS and DGEBA/DTDA. This work provided novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties.

Toughing epoxy nanocomposites with Graphite-Nanocellulose layered framework

Epoxy nanocomposites hold immense promise for advanced high-performance applications in coatings, adhesives, and fiber-reinforced composite matrices. However, their widespread use is hindered by low fracture toughness, attributed to highly cross-linked network structure. Here, this study presents a synergistic manufacturing strategy combining ultrasonic graphite-nanocellulose assembly and bidirectional freeze casting to fabricate epoxy nanocomposites with remarkable layered architectures. Subsequent infiltration and curing with epoxy prepolymer produce nanocomposites exhibiting a fracture toughness 4.67 times higher than pure epoxy. Both experimental and theoretical analyses demonstrate the nanocomposite's superior crack propagation resistance, attributable to a range of synergistic toughening mechanisms. These include robust interfacial bonding and mechanical interlocking, which arise from fiber pull-out/flake fracture effects, effectively impeding crack growth. Additionally, the distinctive layered architecture promotes tortuous crack pathways, optimizing fracture energy dissipation. This work offers pivotal insights into structure–property relationships, paving the way for the design of next-generation nanocomposites with tailored, superior mechanical performance.

Investigation of the Reaction between a Homemade PEEK Oligomer and an Epoxy Prepolymer: Optimisation of Critical Parameters Using Physico-Chemical Methods.

Several researchers have examined the interest in using a thermoplastic to increase thermoset polymers' shock resistance. However, fewer studies have examined the nature of the mechanisms involved between both kinds of polymers. This was the objective of our work, which was carried out using a gradual approach. First, we describe the synthesis of a poly(ether ether ketone) oligomer (oPEEK) with hydroxyl terminations from the reaction of hydroquinone and 4,4'-difluorobenzophenone in N-methyl-2-pyrrolidone. Then, the main physicochemical properties of this oligomer were determined using different thermal analyses (i.e., differential scanning calorimetry (DSC), thermogravimetric (ATG), and thermomechanical analyses) to isolate its response alone. The chemical characterisation of this compound using conventional analytical chemistry techniques was more complex due to its insolubility. To this end, it was sulfonated, according to a well-known process, to make it soluble and enable nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) experiments. Additional information about the structural and chemical characteristics of the oligomer and its average molecular weight could thus be obtained. The synthesis of an oligoPEEK with α,ω-hydroxyl end-groups and a molecular weight of around 5070 g/mol was thus confirmed by NMR. This value was in accordance with that determined by SEC analysis. Next, the reaction of oPEEK with an epoxy prepolymer was demonstrated using DSC and dynamic rheometry. To this end, uncured mixtures of epoxy prepolymer (DGEBA) with different proportions of oPEEK (3, 5, 10 and 25%) were prepared and characterised by both techniques. Ultimately, the epoxy-oPEEK mixture was cured with isophorone diamine. Finally, topological analyses were performed by atomic force microscopy (AFM) in tapping mode to investigate the interface quality between the epoxy matrix and the oPEEK particles indirectly. No defects, such as decohesion areas, microvoids, or cracks, were observed between both systems.

Evaluation of the curing reaction of epoxy resins by electrochemical measurement and molecular orbital method

Epoxy resin is a thermosetting resin with excellent mechanical properties. It has been pointed out that there are problems on its mechanical properties due to poor polymerization of the epoxy ring caused by water and chlorine impurities during resin production. In this study, we focused on the electrochemical behavior during curing reaction of epoxy resin. To investigate the electrochemical reaction, galvanostat meter was used to measure the voltage behavior during chemical reaction. Molecular Orbital (MO) method was used to understand the mechanisms of voltage behavior during curing reaction. Furthermore, the effect of water existence during curing reaction was investigated by experimentally and analytically. As a result of experimental electrochemical reaction, we successfully measured the voltage behavior associated with the curing reaction. In the case of MO analysis, the epoxy and curing agent models were prepared. Before the reaction, each molecule had zero charge, but after the reaction, it was confirmed that the epoxy had a positive charged and the amine had a negative charged. It is thought that the voltage could be observed due to the movement of this charge during curing reaction. It has been also demonstrated through experimentation and analysis that water accelerates the curing reaction. It was observed that the accelerating effect amplifies as the quantity of water increases. Building upon these results, it was confirmed that the factor leading to the increase in voltage is due to the amount of water. To examine the presence of chlorine impurities during the production of epoxy resin, MO analysis was conducted on the production reaction of epoxy prepolymers. The findings indicated that as the water content increases, the reaction that results in the production of by-products is amplified. This outcome suggested that by-products were already incorporated during the formation of the epoxy. In conclusion, this study provides significant insights into the electrochemical behavior during the curing reaction of epoxy resin, the role of water in accelerating the reaction, and the impact of chlorine impurities during resin production. The findings pave the way for further research to optimize the production process and enhance the mechanical properties of epoxy resin.

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.

Synthesis, structural characterization and anticorrosion properties of a new hexafunctional epoxy prepolymer based on urea and phosphorus trichloride for E24 carbon steel in 1.0 M HCl

Our goal is to set up a synthetic method to produce the hexaglycidyl amine tri-urea phosphoric acid (HGATUP), a novel hexafunctional prepolymer. We created this prepolymer by phosphorylating urea in two processes. Next, to generate the new prepolymer, we added epichlorohydrin. In addition, we focused on its microscopic characterization using FTIR and NMR. The novel HGATUP prepolymer was utilized as a corrosion inhibitor for E24 carbon steel in a 1.0M hydrochloric acid (HCl) solution. PDP, EIS, EFM, DFT, Monte Carlo (MC), and molecular dynamic (MD) simulations were used in this study. SEM/EDS and XPS studies were also used to investigate the surface morphology. These methods allowed us to examine the sample's surface characteristics and chemical composition, which added to our understanding of the adsorption along with corrosion prevention processes. The electrochemical tests' outcomes also showed that the concentration of HGATUP enhanced inhibitory performance. PDP results indicated that HGATUP at a concentration of 10-3M had a corrosion inhibition efficiency of 97.6% at 298K ambient temperature. The polarization curve confirmed that the HGATUP was a mixed type of inhibitor that could inhibit steel anodic and cathodic reactions. The Langmuir model predicted that an epoxy prepolymer protected the surface of E24 carbon steel. Calculated thermodynamic kinetic parameters were used to analyze the inhibitor adsorption processes.

Novel rich aromatic and phosphorus-containing compound cured epoxy resins toward outstanding comprehensive performances

Epoxy resin (EP) is quite flammable, which limits its application in areas such as coatings and electronic and electrical materials. In this study, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) (or diphenylphosphine oxide (DPO)) 3-cyclohexene-1-formaldehyde (CC) and 4,4’diaminodiphenylmethane (DDM) were selected for the synthesis of two rich aromatic and phosphorus-containing compounds (DOPO-CC and DPO-CC). DOPO-CC and DPO-CC were introduced into epoxy pre-polymers to prepare epoxy thermosets with flame retardancy. When 5 wt% DOPO-CC (P content of 0.50 wt%) or DPO-CC (P content of 0.52 wt%) was added, the LOI values of the epoxy thermosets increased from 25.5% (pure EP) to 33.5% (EP added DOPO-CC) and 31.0% (EP added DPO-CC), respectively, and these epoxy thermosets also achieved the UL-94 V-0 rating. Additionally, cone calorimeter tests showed that the peak heat release rate (PHRR) and total heat release (THR) of epoxy thermoset containing 5 wt% DPO-CC reduced by 42.0% and 39.7% compared to those of pure EP, respectively. By reducing the thermal degradation rate (condensed phase) and combining and quenching free radicals (gaseous phase), the introduction of DOPO-CC or DPO-CC can efficiently improve the flame retardancy of epoxy thermosets. More importantly, the epoxy thermosets containing DOPO-CC or DPO-CC exhibited better mechanical properties than pure EP, which could be proven by the storage modulus and tensile strength. This study provided a new class of rich aromatic and phosphorus-containing compounds that can serve as co-curing agents for epoxy thermosets with outstanding comprehensive performances.

Gallic acid ester-based flexible UV-shielding epoxy thermosets with tunable properties

Epoxy thermosets are usually limited by their inherent brittleness and low-impact resistance. Henceforth, a series of bio-based epoxy resins were synthesized from gallic acid (GA) esters. Varying the chain length of flexible poly(ethylene glycol) (PEG) enabled tailoring the thermomechanical properties of the thermosets. Decreasing the chain length of the epoxy prepolymer, resulted in the increase of tensile strength from 2.89 to 15.18 MPa with a decrease in elongation from 121.7 to 16.91% and an increase in viscosity of the epoxy resins from 5.25 to 228.46 Pa.s. The low viscosity of epoxy resins with longer chain lengths offers good processability and broadens their relevance as reactive diluents for resins of high viscosity. Additionally, the thermosets exhibited decent transparency and UV shielding ability with satisfactory biodegradable attributes. The study revealed a direct correlation between chain length and thermomechanical properties of the epoxy thermosets.

Improved structural efficiency in composite manufacturing via hammered printing for large-curvature fiber paths

Maximizing the structural efficiency of composite materials is often limited by the minimum turning radius of fibers in composite manufacturing. Neglected defects, such as local fiber buckling, become more pronounced in regions with a large curvature, leading to reduced load-carrying capabilities and a deviation from the target design specifications. This study introduces “hammered printing” as a novel approach for achieving a large curvature of the fiber path in composite manufacturing. By utilizing the transition of the modulus with temperature of a thermoset epoxy pre-polymer, the proposed hammered printing technique generates a unique pressure effect that improves adhesion between the fiber tow and the substrate. This enables the production of accurate and uniform composite structures with a minimum curvature radius of 2 mm, while reducing the occurrence of wrinkling and bending deformations. A continuous fiber path with a small radius (2 mm) for open-hole plates was accurately printed using this printing pattern. Compared with conventional laminates and drilled composites, the obtained printed samples exhibit 75.3% and 28.8% increments in the tensile and bearing strengths, respectively, indicating that this continuous small-radius fiber path can effectively retain the strength and safety of fastened composite parts. Finally, comparisons indicate the great potential of the proposed technique as a large-curvature-path and high-performance manufacturing alternative for the cutout of composite assemblies in the aerospace and related engineering industries.

Effect of peroxide concentration on the epoxidation of vegetable seed oil

The present study focuses on the development of a novel epoxidized vegetable oil (EKO) prepared by the insitu epoxidation of Karingotta oil (KO), a non-edible feedstock with high iodine value (119 g/100 g oil). The key parameters that affect the epoxidation reaction are temperature, time, molar ratio of DB (No. of double bonds in oil): H2O2, molar ratio of DB: CH3COOH and the amount of catalyst. The effect of molar ratio of DB:H2O2 on the epoxidation of Karingotta oil is presented here. Epoxidation was carried out at three different ratios of DB: H2O2 viz, 1:1.1 (P1.1), 1:1.5 (P 1.5) and 1:2.0 (P2.0). The determination of iodine value indicated that the double bond conversion was higher for P1.5 in comparison to P1.1 and P2.0. The increase in the concentration of peroxide from 1.5 to 2.0 did not affect the double bond conversion. Further, the oxirane value increased for P1.5 compared to P1.1 However, for P2.0, the oxirane value reduced indicating the possibility of ring opening side reaction of epoxy group at higher concentration of H2O2. FTIR spectra of all the epoxidized samples exhibited characteristic peak at 827 cm−1 confirming the formation of epoxy functionality in the oil. Quantitative estimation of epoxidation was carried out using 1H NMR which indicated 43 % epoxidation for P1.1, 54 % epoxidation for P1.5 and 43 % epoxidation for P2.0. The iodine value, oxirane value and 1H NMR spectral analysis revealed that a DB:H2O2 ratio of 1:1.5 can promote significant epoxidation of Karingotta oil which can be a potential source for epoxy prepolymers.

Preparation of a novel intrinsic flame retardant epoxy resin based on L-arginine functionalized magnesium hydroxide

In this study, bio-based L-arginine (Arg) and phosphite were selected as raw materials and used to modify magnesium hydroxide, generating an intermediate (APM) that was reacted with melamine (MEL) to produce a curing agent (APM-MEL) with flame retardant properties. A flame retardant epoxy resin (EP) was prepared in a curing reaction by adding APM-MEL and ammonium polyphosphate (APP) to the epoxy prepolymer in varying amounts (wt%). The chemical structure and surface morphology of APM-MEL have been characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The thermal stability, flame retardancy and mechanical properties were evaluated by thermogravimetric analysis (TG), the UL-94 vertical combustion test, use of the limiting oxygen index (LOI), cone calorimetry and bending tests. The results have revealed that the epoxy resin prepared from the addition of 5% APM-MEL and 15% APP achieved a UL-94 V-0 level with a LOI of 30.8%. Compared with pure EP, the peak heat release rate, total heat release, smoke production rate and total smoke production of the samples were reduced by 85.68%, 53.15%, 85.86% and 62.05%, respectively. The flexural strength and flexural modulus were improved by 117.3% and 130.5%, respectively. The bio-based functionalized magnesium hydroxide curing agent prepared in this study exhibits excellent flame retardant and mechanical properties, effectively reducing fire risk and can serve as the basis for the development of multifunctional curing agents.

Design and synthesis of epoxy prepolymer containing aromatic imide structures for thermoset with excellent thermal, mechanical and dielectric properties

Recently, the development of epoxy thermosets with imide rings has received extensive attention due to their superior integrated properties, especially for thermal, mechanical and dielectric properties, compared to those of commercialized bisphenol A epoxy thermosets, yet remains substantial challenges, such as the high epoxy equivalent weight (EEW) of the epoxy prepolymers and the poor processibility of the epoxy systems. In this work, an imide-containing epoxy prepolymer (BAPT-EP) was facilely synthesized. It had a relatively low EEW of 340 g/equiv. and could be dissolved in hardener methylhexahydrophthalic anhydride (MHHPA) to give a homogeneous BAPT-EP/MHHPA system with good processibility. Thanks to the aromatic imide structures, the cured BAPT-EP/MHHPA showed improved overall properties. In particular, it had a 47.9 °C, 24.7 °C, 29.4%, 77.3% and 10.0% increase in the glass transition temperature, temperature at 5% mass loss, tensile strength, Young’s modulus and tensile toughness, respectively, compared to those of bisphenol A epoxy prepolymer (DGEBA)/MHHPA thermoset. Meanwhile, BAPT-EP/MHHPA thermoset featured good charring ability with a high char yield of 26.4% (800 °C/N2), remarkable dimensional stability with a low coefficient of thermal expansion of 52.5 ppm/°C and good dielectric properties with a low dielectric constant of 3.24 at 100 MHz. This work provides an elegant strategy to prepare high-performance epoxy thermosets with imide structures, which have promising applications in electronics.

From Epoxy Prepolymers to Tunable Epoxy–Ionic Liquid Networks: Mechanistic Investigation and Thermo-Mechanical Properties

From Epoxy Prepolymers to Tunable Epoxy–Ionic Liquid Networks: Mechanistic Investigation and Thermo-Mechanical Properties

Cover Image, Volume 140, Issue 9

The cover designed by Shinji Kanehashi presents the development of novel bio-based polymers derived from the shell liquid of cashew nuts, which is a phenolic compound in non-edible plant oil obtained from cashew nut shells. The epoxy polymer was prepared from cardanol derivatives, epoxy prepolymer and phenalkamine at room temperature without solvent. This epoxy polymer possessed anti-microbial activity against E.coli and S. aureus. The mechanical and thermal properties of this epoxy polymer were improved effectively by a post-curing process. DOI: 10.1002/app.53450

Synthesis and characterization of novel bio‐based epoxy polymers derived from natural phenolic compound

AbstractBio‐based epoxy polymer was prepared from cardanol derivatives, epoxy prepolymer and phenalkamine at room temperature without solvent. Chemical structures of cured epoxy polymers were analyzed by FT‐IR and 1H NMR spectroscopy. The drying, physical, thermal, optical, and mechanical properties of the epoxy polymers were investigated in terms of the composition of epoxy and amine compounds, molecular weight of the epoxy prepolymer, and the effect of post‐curing process. The resultant epoxy polymers showed flexible nature, thermal stability (e.g., thermal decomposition temperature of 300°C). Furthermore, the epoxy polymers possessed the anti‐microbial activity against Escherichia coli and Staphylococcus aureus The molecular weight of the epoxy prepolymer also strongly affected the drying property, suggesting that the drying time can be controlled by the molecular weight of the prepolymer. Thermal treatment of the polymers as post‐curing was effective approach to improve the hardness, thermal stability, and mechanical strength. Hence, this cardanol derivatives‐based novel epoxy polymer can be expected as highly green functional epoxy polymers for coating, film and resin applications.

Functional Epoxy Elastomer Integrating Self-Healing Capability and Degradability for a Flexible Stretchable Strain Sensor.

With the rapid development of flexible electronics and the increasing deterioration of the natural environment, functional and environmentally friendly flexible strain sensors have become one of the frontier research hotspots. Here, we propose a novel strategy to synthesize a functional epoxy elastomer integrating self-healing capability and degradability for flexible stretchable strain sensors. A carboxyl-terminated epoxy prepolymer was first synthesized using carboxyl-terminated PEG (PEG-COOH), 2,2'-dithiodibenzoic acid (DTSA), and 1,4-butanediol diglycidyl ether (BDDE), and then crosslinked by epoxidized soybean oil (ESO) to yield an epoxy elastomer. The obtained elastomer exhibited not only high tensile stress (5.07 MPa), large stretchability (477%), and high healing efficiency (92.5%) but also superior degradability in alkaline aqueous solution. The elastomer-based stretchable strain sensor with microstructure showed high sensitivity (GF = 176.71) and was successfully applied for detecting human motions and recognizing objects with various shapes. Moreover, the healed sensor could restore stable sensing ability. The prepared functional epoxy elastomer is of great significance for the preparation of environmentally friendly and high-performance sensors and is promising for applications in the fields of healthcare monitoring, intelligent robots, and wearable electronics.

Interlaminar fracture of structural fibre/epoxy composites integrating damage sensing and healing

Technologies to control and reduce delamination damage in fibre reinforced polymer composites involve the use of fibre optic sensors and self-healing polymers, respectively. While the former technology can monitor the evolution of damage by measuring microscopic variations in the material's strain field, the latter can repair delamination damage by recreating broken interfaces. To evaluate the combination of these technologies, a high-performance epoxy vitrimer was used as the matrix phase of a fibre-glass composites incorporating Fibre Bragg Grating (FBG) sensors. Different laminates, manufactured with varying ratios a dynamic crosslinker and epoxy prepolymer, were compared. The analysis involved thermal characterization, mechanical tests to measure interlaminar fracture toughness, and microscope imaging of the cracked and repaired surfaces. Furthermore, FBG sensors to monitor in-situ damage and healing processes of the composites were employed. It was demonstrated that laminates with a larger proportion of dynamic crosslinker exhibit better repair abilities but lower thermal properties. The average and maximum recorded healing efficiency at the first healing cycle, calculated based on the critical fracture toughness, were at 89% and 95% respectively, while it averaged a steady 50% efficiency after several repairing cycles.

Synthesis Characterization and Highly Protective Efficiency of Tetraglycidyloxy Pentanal Epoxy Prepolymer as a Potential Corrosion Inhibitor for Mild Steel in 1 M HCl Medium.

Anticorrosive protection efficiency of novel tetrafunctional epoxy prepolymer, namely 2,3,4,5-tetraglycidyloxy pentanal (TGP), for mild steel in 1 M HCl medium was assessed through potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), contact angle (CA), adsorption isotherm model, temperature effect and thermodynamic parameters. The synthesized TGP was characterized and confirmed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR). The inhibitory efficiencies found at lower concentration of the prepolymer TGP were85% (PDP) and 87.17% (EIS). PDP measurement illustrated that the TGP behaved as a mixed-type inhibitor in the realized solution. SEM and EDS analysis showeda significant decrease in the corrosion of the MS surface in the presence of the inhibitory prepolymer compared with the blank (1 M HCl). Langmuir adsorption isotherm is the most acceptable modelto describe the TGP epoxy prepolymer on the MS area.

Tack of epoxy resin films for aerospace-grade prepregs: Influence of resin formulation, B-staging and toughening

Aerospace-grade prepreg resin films based on multifunctional tetraglycidyl-4,4′-methylenedianiline (TGMDA), triglycidyl p-aminophenol (TGAP), Bisphenol A diglycidyl ether (DGEBA) and curing agent 4,4'diaminodiphenyl sulfone (DDS) are investigated in terms of tackiness by probe testing. The model epoxy systems are modified regarding the thermoplastic toughener content (polyethersulfone, PES) and the B-stage level, which is adjusted by cure prediction based on a model-free isoconversional method (Flynn-Wall-Ozawa). Additional DSC and rheological analysis are performed to study the thermal and viscoelastic material behavior in conjunction to its impact on temperature-dependent tack. Maximum achievable tack is found to decrease as a function of both degree of conversion and toughener content. Meanwhile, both influencing factors shift the tack maximum towards higher temperatures corresponding to increased flow characteristics attributed to evolving network formation and the incorporation of high molecular weight PES. In terms of absolute tack level and corresponding temperature, probe tack values similar to commercial prepreg systems (∼100 μJ mm−2) are recorded for TGMDA-based formulations containing 10 wt% PES at 20% pre-cure. Model formulations, which have neither been exposed to B-staging nor toughened, show exceptionally high tack below room temperature for all investigated epoxy prepolymers and are therefore not considered processable by automated fiber placement.

Molecular interactions at the metal-liquid interfaces.

We reported molecular simulations of the interactions among water, an epoxy prepolymer diglycidic ether of bisphenol A (DGEBA), and a hardener isophorone diamine (IPDA) on an aluminum surface. This work proposes a comprehensive thermodynamic characterization of the adhesion process from the calculation of different interfacial tensions. The cross-interactions between the atoms of the metal surface and different molecules are adjusted so as to reproduce the experimental work of adhesion. Water nanodroplets on the metal surface are then simulated to predict their contact angle. Liquid-vapor surface tensions of the epoxy prepolymer (DGEBA) and hardener (IPDA) and the solid-vapor surface tension of the aluminum surface are also calculated to provide the solid-liquid interfacial tension that remains very difficult to obtain from the mechanical definition.