A review on fundamentals and strategy of epoxy-resin-based anticorrosive coating materials

Surface-Modification Strategy to Produce Highly Anticorrosive Ti3C2Tx MXene-Based Polymer Composite Coatings: A Mini-Review

MXenes are a group of novel two-dimensional (2D) materials with merits such as large specific surface area, abundant surface-functional groups, high chemical activity, excellent mechanical properties, high hydrophilicity, and good compatibility with various polymers. In recent years, many novel high-performance organic anticorrosion coatings using MXenes as nanofillers have been reported and have attracted widespread attention. As the first successfully prepared MXene material, Ti3C2Tx is the most extensively studied and typical member of the MXene family. Therefore, it is taken as the representative of its family, and the status of Ti3C2Tx MXene/epoxy resin (EP) and MXene/waterborne polyurethane (WPU) polymer anticorrosive composite coatings is reviewed. Firstly, the structure, characteristics, and main synthesis methods of MXenes are briefly introduced. Then, the latest progress of four surface-modification strategies to improve the dispersion, compatibility, stability, and anti-aggregation properties of MXenes, namely functionalization grafting, orientation regulation, heterostructure nanocomposite design, and stabilization and greening treatment, are analyzed and summarized. Finally, the current challenges and future opportunities regarding MXene-based corrosion-resistant organic composite coatings are discussed prospectively.

Halloysite nanotubes-enhanced epoxy acrylate latex emulsion as a novel anticorrosive protective coating for metal surface in 3.5% NaCl solution

Corrosion is a major problem that can lead to the degradation of metal structures. In this study, we developed a novel corrosion-protective coating for metal substrates based on a modified epoxy acrylate formulation reinforced with halloysite nanotubes (HNTs). Epoxy acrylate oligomers were first synthesized through the acrylation of epoxy using acrylic acid, followed by copolymerization with butyl methacrylate/vinyl acetate monomers to produce grafted epoxy acrylates (GEA). HNTs were then incorporated into the polymeric dispersion at weight loadings of 1%, 1.5%, and 2%. The corrosion resistance and waterproofing properties of the coatings were evaluated. The results showed that steel samples coated with HNTs-modified GEA showed no signs of rusting even after 16 days of immersion in a corrosive solution, whereas those coated with GEA alone showed rusting after only 9 days. These results demonstrate the effectiveness of HNTs-modified GEA coatings in protecting steel surfaces against corrosion. The coatings are also water-resistant and can be easily applied. This work provides a new approach to developing corrosion-protective coatings for metal substrates.

Water Uptake in Epoxy Ionic Liquid Free Film Polymer by Gravimetric Analysis and Comparison with Nondestructive Dielectric Analysis

Due to their high surface coverage, good adhesion to metal surfaces, and their excellent corrosion resistance, epoxy thermosets are widely used as protective coatings. However, anticorrosion protection of these coatings can be improved against water uptake and can be tuned by changing the chemical nature of the curing agents. In this work, a comparative study has been performed on the water uptake of an epoxy-amine based on bisphenol A diglycidyl ether (DGEBA) cured with an aliphatic amine and the same epoxy initiated with a phosphonium ionic liquid (IL). Thus, the epoxy networks were immersed in saline water solution in a controlled temperature environment. Gravimetric and electric impedance measurements were carried out for a maximum of 3 months. Results were analyzed in order to assess the water diffusion coefficients and water saturation limits. Two models, the Brasher-Kingsbury and a novel mixing rule, were applied on permittivity values. Results highlighted that epoxy-ionic liquid systems are less sensitive to water uptake than conventional epoxy-amine networks. Due to their higher hydrophobic properties the water diffusion coefficient of epoxy-ionic liquid systems are two times less compared to epoxy-amine samples and the water saturation limit is more than four times less. The analysis also shows that the novel mixing rule model proposed here is prone to better estimate the water uptake with accuracy from electrical impedance measurements.

Resistive Response of Carbon Nanotube-Based Composites Subjected to Water Aging

This work aimed to monitor, through the changes in electrical resistance, the evolution of the mechanical properties due to aging caused by water sorption in carbon nanotube-based epoxy composites. The epoxy/CNT nanocomposites were prepared by dispersing the filler in the precursor through the ultra-sonication process and mixing the hardener by mechanical stirring. After an evaluation of the electrical properties, detected through a two-probe electrical measurement method, of nanocomposites at different percentages by weight of the filler (0.025, 0.05, 0.1, 0.3, 0.5, and 1.0), a concentration (0.1% by weight), close to that of the electrical percolation threshold, was chosen to evaluate the resistive response. This specific concentration was selected in order to obtain maximized values of the variation detected for the changes in the electrical resistance resulting from phenomena of structural relaxations/rearrangements due to water absorption. In particular, the electrical conductivity value switched from 8.2 × 10^-14 S/m for the unfilled epoxy resin to 6.3 × 10^-2 S/m for carbon nanotube-based epoxy composite at 0.1% by weight of the nanofiller. The water sorption caused a reduction in the mechanical properties (storage modulus and tan δ) due to swelling and plasticization phenomena, which caused the structural reorganization of the conductive interparticle contacts in the matrix with a consequent variation in the electrical resistance of the material. The found 'non-Fickian' water diffusion behavior was very similar to the variation in the electrical resistance with time. This last correlation allows the association of the measurement of the electrical resistance with the quantity of absorbed water and, therefore, with the aging of the material to water absorption, through the sensitivity factor (β). The resistive nature of the composite can be used to monitor the amount of water absorption and the changes in the structure of the material subject to water aging.