Springer Science and Business Media LLC

Protective epoxy coatings, as a result of their inherent brittleness, show insufficient resistance towards initiation and propagation of cracks, which can occur as early as during the curing process. To improve premature crack initiation resistance, it is essential to understand the underlying mechanisms. In this work, a solvent-based novolac epoxy, cured with a cycloaliphatic amine, was reinforced with either an epoxypropoxypropyl-terminated polydimethylsiloxane (PDMS), nanoparticles of strontium titanate (SrTiO3), or core-shell rubber (CSR) nanoparticles. The effects on coating property transients, curing-induced internal stress, and premature crack initiation susceptibility of the modifier types and CSR (MX 217 and MX 267) concentrations were investigated. In addition, using a digital microscope, the defect and crack morphology in coatings applied to rigid, flat substrates and inner 90-degree angles were characterized. Finally, to evaluate the anticorrosive barrier performance of the reinforced coatings, an electrochemical impedance spectroscopy analysis was employed. Despite a slightly reduced crack initiation susceptibility, the flexible PDMS chains, due to phase separation, resulted in a deteriorated barrier performance. The inclusion of SrTiO3 nanoparticles also led to a reduced anticorrosion performance, relative to a neat epoxy coating, with a slightly lower crack initiation susceptibility and a minor increase (around 0.2 MPa) in the average internal stress. For 5 wt% MX 217 and MX 267 CSR toughened coatings, the maximum internal stress and crack initiation susceptibility in the series, as well as an associated reduced corrosion resistance, were seen. In spite of a reduction in the elastic modulus, an improved barrier performance and a reduced internal stress and crack initiation susceptibility were observed for 25 wt% MX 217 and 37 wt% MX 267 CSR toughened coatings. To improve barrier properties and avoid premature crack initiation of epoxy coatings, guidelines on modifier selection are provided.

Amine curing agents pose serious health hazards and controlling their release is crucially important. Extraction of unbounded amine from cured epoxy polymers can improve the ecological characteristics of such products. Even 1 min exposure of cured epoxy resins to hot water reduces three- to ten-fold the residual amount of amine present in the epoxy polymer. Different temperatures and extraction times were tested, enabling the selection of the most optimal extraction conditions, which correspond to 5 min of heating in 100°C. This additional cost-effective extraction step is very easy to perform and leads to a significant reduction of unbounded curing agent, making cured epoxy resins much more eco-friendly products. The documented positive and linear trends of logarithms of viscosity and the amount of released amine suggest the selection from such curing agents and such epoxy resins that are characterized by lowest possible viscosities, which guarantees that there is only a low amount of unbounded amine that needs to be released from the polymer.

Binder polymers functionalized with a small amount of polar groups satisfy both the dispersion quality of paints and the mechanical strength of coating films. For industrial-grade polydisperse dispersant polymers, functional groups are not evenly distributed among the polymer chains. The functional group distribution in polyurethane dispersant polymers was investigated by statistical estimation and an adsorption experiment. The polymeric dispersants had a broad functional group distribution and contained a significant amount of nonfunctionalized chains. By considering the existence of these ineffective chains, the dispersion behavior of the paint was more clearly explained. The described method can be a useful tool to analyze the structure and the properties of polydisperse functionalized polymers for various applications.

In this study, the quality and durability of powder-coated hot-dip galvanized products have been investigated. Standard steel coupons hot-dip galvanized in conventional and delta (i.e., high temperature) conditions were coated with powder paint systems or a high quality solvent-based system and then subjected to a wide range of test methods representing mild or highly aggressive exposure conditions. Additional variables in the project were the silicon content of the steel and the treatment prior to painting. The use of delta-galvanized steel as a base for painting offers a number of advantages such as much greater hardness and improved paint adhesion. Maximum corrosion protection is observed if the galvanized base is treated with chromate and sequentially powder coated with an epoxy primer followed by a polyester topcoat.

In this study, we investigated the effect of organosilane monomer on the adhesion strength and corrosion protection of the water-reducible alkyd coatings. For this purpose, firstly, alkyd resin was synthesized and modified with acrylic monomers by changing organosilane monomer content in the range of 4–16 wt% in all acrylic monomer compositions. Then, the carboxyl groups on the hybrid resins were neutralized with a base and the coating recipes were formulated using these water-reducible resins. The chemical structure and composition of the synthesized polymers were confirmed using 1H-NMR and FTIR spectroscopies. Mechanical properties of coatings applied on the cold-rolled steel surfaces were investigated via crosshatch adhesion, pendulum hardness, gloss, impact, and conical mandrel bend tester. According to the results, it can be said that water-reducible acrylic-modified alkyd coatings offer a good balance of hardness and flexibility. Then, the line was scratched parallel to the coating system and the surface coating properties of the coated panels, such as the adhesion strength after being exposed to humidity and corrosion resistance, were comparatively investigated. The best results for corrosion resistance and adhesion strength were obtained with the coating which was formulated with the resin having organosilane monomer of 8 wt% in all acrylic monomer mixtures. As the organosilane monomer amount increased to 16 wt%, the coatings’ corrosion resistance and adhesion strength decreased. As a result, it was observed that organosilane modification is significantly effective in improving the adhesion strength and corrosion resistance of water-reducible alkyd coatings. However, increasing the amount of silane monomer may reverse the positive results obtained. This study also reveals significant results about the correlation between the adhesion strength and corrosion resistance of coatings by presenting visual results.

Changes in film composition and characteristics that occur during and/or immediately after the application of latex paints on porous inorganic substrates were investigated. Gas chromatography (GC) and thermal analysis were among the techniques used for this purpose. The changes in coalescing agent and binder content were determined by GC and thermogravimetric-analysis, respectively, and the changes in glass transition temperature by differential scanning calo rimetry. It was found that the type of porous substrate could significantly affect the paint composition (pigment volume concentration, coalescent level) during the film formation process.

Novel aluminum ammonium phosphates (AAP) were tested as anticorrosion fillers in two-component solventborne polyurethane paints. Their properties were compared with microsized aluminum zinc phosphate (AZP) as well as with nanosized (nAP) and microsized (AP) aluminum phosphates. Generally, coating compositions containing AAP exhibited similar or slightly higher viscosity than the systems with AZP and AP. Moreover, cured polyurethane coats with AAP reached higher gloss and better adhesion to a steel substrate. The results of salt spray tests (2500 h) showed that anticorrosive properties of coats containing 10 wt% of AAP were similar or better than those noted for coats with 15.6 wt% of AZP or 13.7 wt% of AP. Electrochemical impedance spectroscopic tests revealed markedly higher barrier properties of coats with AAP in comparison to an AP-based sample.

The optical properties of pigments used for paper coating are linked to their morphology. The light scattering through coated layers depends upon the size and the size distribution of the pigments and their packing behavior. In this report the effect of particle packing of various calcium carbonate pigments on the whiteness of the final coated paper is studied. Different grades of calcium carbonate pigments of different particle size distribution and optics were used for coating applications on base papers. Base papers of different optics were also selected. The entire study was carried out at different coat weights. It was observed that the overall scattering from the coated sheet depends upon the light scattering from the base paper as well as through the coated layer. Higher light scattering through the coated layer will lower the effect of the base paper, whether it is dark or bright. So high bright and white pigments are not only the criteria for an enhancement in the optical properties of coated paper; the particle size and size distribution should also be considered before introducing any pigment into a coating formulation. The base optics should also be chosen on the bases of the pigments’ optics and their morphology.

Cottonseed oil (CSO) was converted into a polymerizable polyol by in-situ epoxidation and hydroxylation in the presence of water as nucleophile and sulfuric acid as catalyst. This hydroxylated CSO (HCSO) was polymerized with isophorone diisocyanate at different NCO-to-OH ratios to furnish polyurethane coatings of different composition. The mechanical properties of the resulting moisture-cured films were studied. The adhesion, abrasion resistance, impact strength, flexibility, water vapor permeability, and chemical and/or solvent and corrosion resistance of the coatings were investigated.