Search Results (31)

Epoxy-based composite materials, widely used in various industries such as coatings, adhesives, aerospace, electronics, and biomedical engineering, remain a topic of global interest due to their varying characteristics based on the base resin and curing agents used. This paper employs molecular dynamics simulation to examine the thermal and mechanical properties, as well as molecular behaviors, of epoxy systems cured with diglycidyl ether of bisphenol F as the base resin and aromatic amine curing agents, specifically the meta structure of 3,3′-diaminodiphenyl sulfone (3,3′-DDS) and the para structure of 4,4′-diaminodiphenyl sulfone (4,4′-DDS). The 3,3′-DDS system demonstrated a greater density and Young’s modulus than the 4,4′-DDS system. This tendency was analyzed based on differences in molecular fractional free volume and cohesive energy density (CED). The 4,4′-DDS system exhibits a higher glass transition temperature (T_g) compared to the 3,3′-DDS system, with values of 406.36 K and 431.22 K, respectively. To understand this behavior, we examined atomic-scale displacements at T_g through mean squared displacement analysis, which revealed that the onset of molecular motion occurs at a lower temperature in the 3,3′-DDS system. Molecular-level study reveals how the structural features of each curing agent appear in thermal and mechanical properties, offering important insights for epoxy system development. Full article

A durable and easy-to-operate treatment, modified epoxy composite coating (MECC), was proposed in this study as a potential alternative to traditional epoxy resin protectants to enhance the protection of concrete structures. This new material consists of epoxy resin as the base material, dimethyl carbonate as the solvent, and modified amines and polyaniline as a composite curing agent that reacts with epoxy resin to form a film over the surface of concrete, thus protecting concrete structures from surface cracking, peeling, and spalling when exposed to chloride. Salt frost resistance tests indicated that MECC specimens had lower water absorption and much higher salt frost resistance. Compared with non-coating (NS) specimens, after 200 freeze–thaw cycles, the relative dynamic elastic modulus (RDEM) was 21.62% higher, and the mass loss was merely 19.14% of that of the NS specimens. Better performance was achieved as compared with ordinary epoxy resin coating (EC) and silicate coating (SC) too. After 120 days of erosion in 10.0% NaCl, the coating could effectively prevent environmental liquids and chloride from intruding through the cracks. The reason behind the increased salt frost durability is that treatment with MECC improved the internal structure of concrete and made its surface dense enough to prevent the intrusion of environmental liquids and chloride. Under repeated freezing and thawing, the degree of chloride-induced damage and the icing pressure inside the concrete were greatly reduced. This relieved the frost damage inside the concrete and elongated the service life of the concrete. Full article

In this study, a series of amine-modified mesoporous silica (AMS)-based epoxy composites with superhydrophobic biomimetic structure surface of Xanthosoma sagittifolium leaves (XSLs) were prepared and applied as anti-corrosion and anti-biofilm coatings. Initially, the AMS was synthesized by the base-catalyzed sol–gel reaction of tetraethoxysilane (TEOS) and triethoxysilane (APTES) through a non-surfactant templating route. Subsequently, a series of AMS-based epoxy composites were prepared by performing the ring-opening polymerization of DGEBA with T-403 in the presence of AMS spheres, followed by characterization through FTIR, TEM, and CA. Furthermore, a nano-casting technique with polydimethylsiloxane (PDMS) as the soft template was utilized to transfer the surface pattern of natural XSLs to AMS-based epoxy composites, leading to the formation of AMS-based epoxy composites with biomimetic structure. From a hydrophilic CA of 69°, the surface of non-biomimetic epoxy significantly increased to 152° upon introducing XSL surface structure to the AMS-based epoxy composites. Based on the standard electrochemical anti-corrosion and anti-biofilm measurements, the superhydrophobic BEAMS3 composite was found to exhibit a remarkable anti-corrosion efficiency of ~99% and antimicrobial efficacy of 82% as compared to that of hydrophilic epoxy coatings. Full article

In this study, an array of environmentally friendly and heavy-duty anticorrosion composite coatings were prepared. The synthesis involved amine-capped aniline trimer (ACAT) produced by an oxidative coupling reaction and graphene oxide (GO) prepared based on Hummer’s method, and later, the waterborne epoxy thermoset composite (WETC) coatings were prepared by thermal ring-opening polymerization of EP 147w, a commercial waterborne epoxy resin, in the presence of ACAT and/or GO with zinc dust (ZD). A synergistic effect was observed by replacing a significant amount of the ZD loading in the WETC by simultaneously incorporating a small amount of ACAT and GO. The electrochemical corrosion measurements of the as-prepared WETC coatings indicated that incorporating 5% w/w ACAT or 0.5% w/w GO separately replaced approximately 30% w/w or 15% w/w of the ZD, respectively. Moreover, the WETC coatings containing 5% w/w ACAT and 0.5% w/w GO simultaneously were found to replace 45% w/w of the ZD. A salt spray test based on ASTM B-117 also showed a consistent trend with the electrochemical results. Incorporating small amounts of ACAT and GO in WETC coatings instead of ZD not only maintains the anticorrosion performance but also enhances adhesion and abrasion resistance, as demonstrated by the adhesion and abrasion tests. Full article

Bio-based vitrimers present a promising solution to the issues associated with non-renewable and non-recyclable attributes of traditional thermosetting resins, showcasing extensive potential for diverse applications. However, their broader adoption has been hindered by the requirement for catalyst inclusion during the synthesis process. In this study, a cardanol-based curing agent with poly-hydroxy and tertiary amine structures was prepared by a clean synthetic method under the theory of click chemistry. The reaction of a cardanol-based curing agent with diglycidyl ether of bisphenol A formed catalyst-free, self-healing, and recyclable bio-based vitrimers. The poly-hydroxy and tertiary amine structures in the vitrimers promoted the curing of epoxy-carboxylic acid in the cross-linked network and served as internal catalysts of dynamic transesterification. In the absence of catalysts, the vitrimers network can achieve topological network rearrangement through dynamic transesterification, exhibiting excellent reprocessing performance. Moreover, the vitrimers exhibited faster stress relaxation (1500 s at 180 °C), lower activation energy (92.29 kJ·mol⁻¹) and the tensile strength of the recycled material reached almost 100% of the original sample. This work offers a new method for preparing cardanol-based epoxy vitrimers that be used to make coatings, hydrogels, biomaterials, adhesives, and commodity plastics in the future. Full article

Due to its long and continuous cellulose fibers, flax offers excellent specific tensile strength and stiffness relative to other natural fibers such sisal or jute, and it is widely used as fiber reinforcement in composites with relevance in industries such as automotive, sports and maritime environments. However, the use of natural fibers poses additional challenges relative to synthetic fibers in ensuring the functional lifetime of composites; in particular, water resistance and resistance against UV conditions should be improved for outdoor use. Therefore, a protective coating that offers high resistance against environmental conditions and mechanical damage can be applied to avoid direct surface exposure of natural fibers. The linseed oil or wax coatings increase the hydrophobic surface properties and limit water ingress, but they have drawbacks such as extended curing periods via oxidative crosslinking and weak mechanical performance. In seeking alternatives for natural fiber composites, the potential of bio-based crosslinked coatings to enhance mechanical robustness, surface protection and durability was explored by screening various coating grades, including bio-based epoxy resin, diluents and crosslinkers. The epoxy coatings with a bio-based phenalkamine crosslinker offer higher hardness and scratch resistance, and the water resistance was improved in the presence of an amine crosslinker with long alkyl chains. In parallel, the mechanical abrasion resistance of the crosslinked coatings significantly increased in relation to the intrinsic mechanical properties and crosslinking density of the coatings. The processing of the epoxy coatings was further enhanced by adding a bio-based trifunctional diluent with low viscosity while providing limited shrinkage and good compatibility with the composite substrate. Moreover, the UV resistance was better for epoxy coatings with a bio-based diluent, likely via migration effects and the formation of a protective layer at the outer surface. Full article

The properties of epoxy can be adapted depending on the selection of bio-based diluents and crosslinkers to balance the appropriate viscosity for processing and the resulting mechanical properties for coating applications. This work presents a comprehensive study on the structure–property relationships for epoxy coatings with various diluents of mono-, di-, and bio-based trifunctional glycidyl ethers or bio-based epoxidized soybean oil added in appropriate concentration ranges, in combination with a traditional fossil-based amine or bio-based phenalkamine crosslinker. The viscosity of epoxy resins was already reduced for diluents with simple linear molecular configurations at low concentrations, while higher concentrations of more complex multifunctional diluents were needed for a similar viscosity reduction. The curing kinetics were evaluated through the fitting of data from differential scanning calorimetry to an Arrhenius equation, yielding the lowest activation energies for difunctional diluents in parallel with a balance between viscosity and reactivity. While the variations in curing kinetics with a change in diluent were minor, the phenalkamine crosslinkers resulted in a stronger decrease in activation energy. For cured epoxy resins, the glass transition temperature was determined as an intrinsic parameter that was further related to the mechanical coating performance. Considerable effects of the diluents on coating properties were investigated, mostly showing a reduction in abrasive wear for trifunctional diluents in parallel with the variations in hardness and ductility. The high hydrophobicity for coatings with diluents remained after wear and provided good protection. In conclusion, the coating performance could be related to the intrinsic mechanical properties independently of the fossil- or bio-based origin of diluents and crosslinkers, while additional lubricating properties are presented for vegetable oil diluents. Full article

High-performance coating could be used to protect steels in engineering. The GPTMS-TEOS hybrid coatings were successfully prepared using (3-glycidoxypropyl) trimethoxysilane (GPTMS) and tetraethylorthosilicate (TEOS) as reaction raw materials and diethylenetriamine (DETA) as both a curing agent and catalyst at room temperature. The hybrid coating contained amorphous SiO₂ and was characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The DETA content of the hybrid coating has a significant impact on the performance of the coating. As the DETA content increases, the thermal stability of the hybrid coating increases at 400–600 °C due to the production of more SiO₂ in the amine-rich state. However, the gelation time decreases dramatically, preventing the hybrid coating from better infiltrating the surface of the steel substrate. In addition, there are not enough silicon hydroxyl groups to bond with the hydroxyl groups on the surface of carbon steel and adhesion is significantly reduced. Therefore, hybrid coatings with a moderate DETA content (NH:epoxy ratio equivalent to 1:1) show the best corrosion resistance, with a third-order magnitude increase in corrosion resistance compared to that of carbon steel. Full article

Intrinsic self-healing polymers via dynamic covalent bonds have been attracting extensive attention because of their repeatable self-healing property. Herein, a novel self-healing epoxy resin was synthesized with disulfide-containing curing agent via the condensation of dimethyl 3,3′-dithiodipropionate (DTPA) and polyether amine (PEA). Therefore, in the structure of cured resin, flexible molecular chains and disulfide bonds were imported into the cross-linked polymer networks for triggering self-healing performance. The self-healing reaction of cracked samples was realized under a mild condition (60 °C for 6 h). The distribution of flexible polymer segments, disulfide bonds and hydrogen bonds in cross-linked networks plays a great role in the self-healing process of prepared resins. The molar ratio of PEA and DTPA strongly affects the mechanical performance and self-healing property. Especially when that molar ratio of PEA to DTPA is 2, the cured self-healing resin sample showed great ultimate elongation (795%) and excellent healing efficiency (98%). The products can be used as an organic coating, in which the crack could self-repair during a limited time. The corrosion resistance of a typical cure coating sample has been testified by an immersion experiment and electrochemistry impedance spectrum (EIS). This work provided a simple and low-cost route to prepare a self-healing coating for prolonging the service life of conventional epoxy coatings. Full article

The phenalkamines (PK) derived from cardanol oil can be used as a bio-based crosslinker for epoxy coatings as an alternative for traditional fossil amines (FA). First, the reaction kinetics of an epoxy resin with four PK and FA crosslinkers are compared by differential scanning calorimetry, illustrating a fast reaction rate and higher conversion of PK at room temperature in parallel with a moderate exothermal reaction. Second, the performance of coatings with various concentrations of PK and PK/FA ratios indicates good mixing compatibility between crosslinkers resulting in higher hardness, scratch resistance, hydrophobicity, and abrasive wear resistance of coatings with PK. The superior performance is confirmed over a broad range of resin/crosslinker ratios, facilitating the processing with viscosity profiles depending on the PK type. Although fossil- and bio-based crosslinkers have different chemical structures, the unique linear relationships between intrinsic mechanical properties (i.e., ductility and impact resistance) and coating performance indicate that the degree of crosslinking is a primary parameter controlling coating performance, where PK simultaneously provides high hardness and ductility. In conclusion, the optimization of the processing range for bio-based PK as a crosslinker for epoxy coatings delivers suitable processing conditions and superior mechanical performance compared to traditional amine crosslinkers. Full article

The dependence of the apparent activation energy for the epoxy-amine reaction on the degree of conversion can be obtained by applying iso-conversional methods to the non-isothermal cure data obtained by using differential scanning calorimetry (DSC). The application of three iso-conversional methods has been utilized for the analysis of non-isothermal DSC cure data for three commercial high solids epoxy-amine coatings. The average apparent activation energy for cure of the fully formulated commercial product(s) is very similar to that previously reported for the epoxy-amine clear coats, indicating that the presence of additives does not influence the epoxy-amine apparent activation energy. Among the methods tested, Friedman’s method performed the best in fitting the experimental DSC data. In addition, all three methods underpredict the experimental isothermal cure data for three commercial products at two different cure conditions (i.e., 23 °C/50% RH and 40 °C/70% RH), showing that the non-isothermal DSC experiments cannot capture the catalytic effect of water on the curing reaction of epoxy-amine coatings. Furthermore, for high-solids epoxy-amine products, at least 60% conversion is required to achieve the time when the applied coating will not show any tackiness (i.e., the T2 time measured using the Beck Koller method). Full article

In this study, a rubber-composite-nanoparticle-modified epoxy powder composite coating with low curing temperature and high toughness was successfully fabricated. The effects of N,N-dimethylhexadecylamine (DMA) carboxy-terminated nitrile rubber (CNBR) composite nanoparticles on the microstructure, curing behavior, and mechanical properties of epoxy-powder coating were systematically investigated. SEM and TEM analysis revealed a uniform dispersion of DMA-CNBR in the epoxy-powder coating, with average diameter of 100 nm. The curing temperature of the epoxy-composite coatings had reduced almost 19.1% with the addition of 1phr DMA-4CNBR into the coating. Impact strength tests confirmed that DMA-CNBR-modified epoxy-composite coatings showed significant improvements compared with the neat EP coating, which was potentially attributed to the nanoscale dispersion of DMA-CNBR particles in epoxy coatings and their role in triggering microcracks. Other mechanical properties, including adhesion and cupping values, were improved in the same manner. In addition, thermal and surface properties were also studied. The prepared epoxy composite powder coating with the combination of low curing temperature and high toughness broadened the application range of the epoxy coatings. Full article

Biofouling has destructive effects on shipping and leisure vessels, thus producing severe problems for marine and naval sectors due to corrosion with consequent elevated fuel consumption and higher maintenance costs. The development of anti-fouling or fouling release coatings creates deterrent surfaces that prevent the initial settlement of microorganisms. In this regard, new silica-based materials were prepared using two alkoxysilane cross-linkers containing epoxy and amine groups (i.e., 3-Glycidyloxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane, respectively), in combination with two functional fluoro-silane (i.e., 3,3,3-trifluoropropyl-trimethoxysilane and glycidyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorononylether) featuring well-known hydro repellent and anti-corrosion properties. As a matter of fact, the co-condensation of alkoxysilane featuring epoxide and amine ends, also mixed with two opportune long chain and short chain perfluorosilane precursors, allows getting stable amphiphilic, non-toxic, fouling release coatings. The sol–gel mixtures on coated glass slides were fully characterized by FT-IR spectroscopy, while the morphology was studied by scanning electron microscopy (SEM), and atomic force microscopy (AFM). The fouling release properties were evaluated through tests on treated glass slides in different microbial suspensions in seawater-based mediums and in seawater natural microcosms. The developed fluorinated coatings show suitable antimicrobial activities and low adhesive properties; no biocidal effects were observed for the microorganisms (bacteria). Full article

A coating system integrating three distinct chemistries was developed to protect materials used in monuments and construction. Initial curing is achieved using a UV-initiated thiol-ene reaction to form a non-impressionable/non-sticky surface. Second, amine/epoxy reactions form a firm surface adhesion and give mechanical strength through consolidation. Third, alkoxysilane sol-gel curing integrates the siloxane network while adding thermal stability, hydrophobicity, and a hardened surface. The final design utilizes a photoacid generator to increase the reaction speed of the second and third curing steps. The coating can be applied by spray, dip, or wipe on methods and exhibits a rapid non-impressionable surface (as fast as 10 min) that resists graffiti and environmental conditions, and is used and stored as a single-component system with a pot life exceeding six months. A series of experiments were used to determine the coating properties and durability, including field testing and accelerated weathering. Full article

For delayed crosslinking of waterborne epoxy varnishes, dicyandiamide (DICY) is often used as a latent curing agent. While, for amine-based curing agents such as diaminoethane (DAE), chemical interactions with metal oxides are well described, so far, no studies have been performed for DICY and waterborne epoxy varnishes. Hence, in this work X-ray photoelectron spectroscopy (XPS) was used to investigate reactions of DICY and varnishes with technical surfaces of Al, Zn, and Sn. To directly study the reaction of DICY with metal oxides, immersion tests in a boiling solution of DICY in pure water were performed. A clear indication of the formation of metal–organic complexes was deduced from the change in the N1s peak of DICY. To understand the interfacial interaction and consequently the interphase formation during coating of waterborne epoxy varnishes, advanced cryo ultra-low-angle microtomy (cryo-ULAM) was implemented. Interestingly, a comparable reaction mechanism and the formation of metal complexes were confirmed for varnishes. The coatings exhibited a pronounced enrichment of the DICY hardener at the metal oxide–polymer interface. Full article