In-situ AFM and EIS study of a solventborne alkyd coating with nanoclay for corrosion protection of carbon steel

A solventborne alkyd composite coating containing modified montmorillonite (MMT) nanoclay was made on carbon steel, and its corrosion protection was investigated by in-situ atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) measurements in 3 wt.% NaCl solution. X-ray diffraction (XRD) analysis indicated intercalation of the MMT sheets in the composite coating. Thermo-gravimetric analysis (TGA) demonstrated improved thermal stability of the composite coating due to the modified nanoclay. Scanning electron microscopy (SEM) and AFM examination revealed dispersion and also some aggregation of the nanoclay particles in the coating. In-situ AFM images show a stable coating surface at nano-scale during relative long time exposure in the NaCl solution, indicating an enhanced stability of the composite coating. The EIS results confirmed that the composite coating provides an enhanced barrier type corrosion protection for carbon steel in the corrosive solution, which could be attributed to the intercalated lamellar MMT sheets in the coating that block the defects and decrease the transport of water and corrosive species.     

Influence of coating system composition on moisture dynamic performance of coated wood

Model coatings with known composition were assessed for liquid water permeability both as single coat systems and combined as primers and topcoats to form regularly used coating systems—in total 38 different systems. The water permeability of the coatings, expressed as water absorption value, was measured by a method similar to the method that now is proposed as a European standard for the assessment of liquid water permeability. During artificial weathering, the samples were measured for a water absorption value, thus showing the change in water permeability as a function of weathering. The study has shown that an excess of surfactants in the alkyd emulsions has a negative effect on the coating’s ability to exclude water from the test samples. A waterborne acrylic paint based on a dispersion of larger particle size (0.4 μm) showed a poor ability to exclude water compared to a similar paint based on smaller dispersion particles (0.1 μm). The alkyd emulsion paints, as single coats, showed high water absorption values compared to solventborne paints and acrylic paints. P.O. Box 5609, SE 114 86 Stockholm, Sweden     

Electrochemical impedance spectroscopy (EIS) study of nano-alumina modified alkyd based waterborne coatings

A nano-composite coating was formed by dispersing nano-Al₂O₃ as pigments in different concentrations, to a specially developed alkyd based waterborne coating. The nano-Al₂O₃ based composite coatings were applied on mild steel substrate by dipping. The dispersion of particles in coating system was investigated by using SEM and AFM techniques. The effect of addition of these nano-pigments on the electrochemical behavior of the coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy (EIS). It was found that coating modified with higher concentration of nano-Al₂O₃ particles showed comparatively better performance as it was evident from pore resistance (R_p) and coating capacitance (C_c) values after 30 days of exposure. In general, the study showed an improvement in the corrosion resistance of the nano-particle modified coatings as compared to the neat coating, confirming the positive effect of nano-particle addition in coatings.     

Synthesis and properties of Ricinodendron heudelotii oil based hybrid alkyd–acrylate latexes via miniemulsion polymerization

Ricinodendron heudelotii (R. heudelotii) oil-based novel alkyd–acrylate hybrid latexes were synthesized as waterborne environmental friendly binder for coating systems. Long oil length alkyd resins were synthesized by two-stage alcoholysis–polyesterification reaction with variation of phthalic anhydride (PA) and maleic anhydride (MAH) proportion and further polymerized with methyl methacrylate (MMA) and butyl acrylate (BA) via miniemulsion polymerization. It is found that increasing the proportion of MAH in the alkyd resin enhances monomer conversion and total solid content of the hybrid latex. The latexes exhibited fast drying time at room temperature. The prepared latexes showed a bimodal particle size distribution motion. It is shown that the increase in MAH content in the alkyd moiety has a significant effect on the improved performance properties of hybrid latexes as well as latex films including, fast drying time at room temperature, highly crosslinked network, improved mechanical characteristics before and after UV exposure, better shore A hardness and hydrophobic water repellency contact angle. The results suggested that, the R. heudelotii oil-based alkyd–acrylate hybrid latexes have potential improved properties for manufacture of waterborne coatings and are usable as an alternative to petroleum-based coating systems.     

Microautoradiographic studies of the penetration of alkyd, alkyd emulsion and linseed oil coatings into wood

The penetration of wood coating primer products into pine and spruce softwood was evaluated with microautoradiography.¹⁴C-labeled binders of alkyd and linseed oil were synthesized and used in eight different products. The penetration front in wood is uneven due to a heterogeneous structure with different types of wood cells. It was demonstrated that conventional solventborne alkyd primers and waterborne alkyd emulsion primers have similar ability to penetrate into wood. Improved penetration was found for products with lower viscosity, such as an alkyd stain and a linseed oil coating. A priming oil had superior penetration. Generally better penetration was obtained for coatings applied onto sawn and rough surfaces as compared to planed and smooth surfaces. Box 5609, S-11486 Stockholm, Sweden. P.O. Box 160, 2001 Lillestr?m, Norway. Box 5607, S-11486 Stockholm, Sweden.     

Solventborne paint systems on carbon steel and hot-dip galvanized steel for a wide range of atmospheric exposures

The paper analyzes the performance of solventborne paint systems applied on carbon steel and hot-dip galvanized steel in a wide range of atmospheric exposures. The study has involved paint systems exposure for 3.5 years in eight natural atmospheres. The atmospheric conditions cover from temperate rural climates to tropical severe marine and Antarctic coastal regions. The paint systems included several alkyds formulated with a variety of pigments (anticorrosive and barrier), epoxies, chlorinated rubber, and zinc-rich (ethyl silicate and epoxy). It has been concluded that in rural and urban atmospheres alkyd systems afford equivalent anticorrosive protection of steel to the epoxy/polyurethane system. The toxic red lead pigment may be replaced in long linseed-oil alkyd primer paints by non-toxic pigments, such as a mixture of micaceous iron oxides (MIO) and black iron oxides or zinc phosphate, without affecting the anticorrosive properties of the paint system. In aggressive atmospheres (industrial, marine), paint systems including zinc-rich primers or applied on galvanized steel must be used, especially in surface regions with coating faults (scribes).     

Thermally modified Scots pine and Norway spruce wood as substrate for coating systems

Thermally modified wood (TMW) is increasingly used in exterior applications as an alternative to tropical hardwoods or wood impregnated with biocides. Despite its enhanced biological durability and dimensional stability, a surface treatment of TMW with coating systems can be required in certain applications. This study assessed material characteristics of Norway spruce and Scots pine wood that was thermally modified according to the ThermoWood^® process and their effect on the performance of commercially available coating systems: a solventborne oil, a waterborne alkyd-reinforced acrylate paint and a waterborne acrylate paint. Residual extractives and remaining degradation products found in TMW, carry the risk of causing discoloration or of interfering with the curing reactions of coating systems. The penetration of coating systems into TMW was not found to differ from unmodified wood, although an excessive penetration of solventborne oil was found occasionally for TMW. The adhesion strength of waterborne coatings depended on the system that was used. While one system performed sufficiently on TMW, the other coating systems showed a considerable reduction in adhesion strength already after a mild treatment (<200°C). This reduction could not be attributed to the increase in hydrophobicity of TMW that was evident from contact angle measurements, but was rather related to the mechanical interaction of the specific substrate/coating system.     

Electrochemical stability and surface analysis of a new alkyd paint with low content of volatile organic compounds

This paper presents the results regarding the electrochemical stability and surface analysis of a new alkyd paint with low content of volatile organic compounds in comparison with a conventional alkyd paint. The alkyd films were realized on carbon steel substrate. Dry films thickness in 30–35 μm range was obtained. The experimental tests were carried out in 3% NaCl solution at the 25 °C temperature. The electrochemical techniques (electrochemical impedance spectroscopy (EIS), potentiodynamic and Tafel polarization) and surface analysis techniques (AFM, SEM, EDX) were used to evaluate protective properties of the tested paint films. The correlation of all experimental results established that the new alkyd paint with low content of volatile organic compounds presents better protective performances and lower permeability than conventional alkyd paint. AFM, SEM and EDX indicated a compact, homogenous, non-porous and adherent coating.     

Improvement of anticorrosive performance of phosphate-based alkyd paints with suitable additives

The purpose of this investigation was focused on reducing the content of zinc phosphate in anticorrosive paints by means of the incorporation of low quantities of selected soluble corrosion inhibitors. The article describes the anticorrosive behavior of alkyd paints containing reduced levels of zinc phosphate, zinc oxide, and some soluble compounds used as additives (e.g., sodium polyphosphate, sodium phosphate, and sodium benzoate). Anticorrosive solventborne alkyd paints were formulated with a zinc phosphate content of 10% by volume (v/v) with respect to the total pigment concentration. In all cases, the PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ratio was 0.8. Experimental paints, applied on sandblasted SAE 1010 panels, were evaluated by accelerated tests (salt spray cabinet) and electrochemical measurements (electrochemical impedance spectroscopy, EIS). The results show that the additions of small amounts of soluble corrosion inhibitors to low content zinc phosphate paint formulations enhance their performance in a very remarkable way. Perhaps, the most outstanding feature is that the employment of soluble additives allowed the reduction of the zinc phosphate content with concomitant savings.     

Plasma Treatment of Wood–Plastic Composites to Enhance Their Adhesion Properties

In this study, the adhesion properties of adhesives and paints on wood–plastic composites (WPCs) after plasma treatment at atmospheric pressure and ambient air were investigated. Surface energy determination by means of contact angle measurements according to the Owens–Wendt approach and atomic force microscopy to detect changes in surface topography were carried out. An increase in the polar component of surface energy and an increase in surface roughness after plasma treatment were detected, indicating enhanced bond strength. To confirm these results, bond strength tests were conducted. By tensile bond strength tests, increased adhesion of waterborne, solventborne and oil-based paints on plasma treated surfaces was found. Furthermore, by shear bond strength tests, an increase in bond strength of plasma treated WPCs bonded with poly(vinyl acetate) and polyurethane adhesives was ascertained.     

Smart corrosion sensing phenanthroline modified alkyd coatings

Alkyd resin was chemically modified with 1,10-phenanthroline-5-amine and characterized by Fourier transform infrared (FTIR) and ¹³C Nuclear magnetic resonance (¹³C NMR) spectroscopy. The complex forming ability of phenanthroline modified alkyd resin with Fe²⁺ ions was studied by UV–Visible spectroscopy. Mixture of Fe²⁺ solution and modified alkyd resin showed new absorption bands in UV–Visible spectroscopy confirmed the formation of modified alkyd resin-Fe(II) complex. Corrosion sensing property of modified alkyd coating was evaluated by immersing the coated mild steel specimens in 3.5% NaCl solution. Color change was observed in the coating due to onset of corrosion at metal-coating interface. Electrochemical impedance spectroscopy (EIS) was used for correlating the polarization resistance (R_p) of coating with color change. Scanning electron microscopic (SEM) analysis on the surface of metal specimens indicated that the point of color change was the corrosion site. Results revealed that phenanthroline modified alkyd resin can be used in corrosion sensing coating formulations.     

Novel coatings from soybean oil phosphate ester polyols

Novel coatings with excellent properties have been formulated from polyols derived from the renewable resource soybean oil. Partially and fully epoxidized soybean oils (ESBO) were converted to novel soybean oil phosphate ester polyols (SOPEP) which were successfully incorporated into solventborne and waterborne bake coatings. Thermally cured waterborne alkyd coatings were produced with improved coating adhesion, low volatile organic compounds (VOC), excellent impact resistance, good hardness, less severe curing conditions, and lower cost. Solventborne alkyd coatings gave similar results. Soybean oil phosphate ester polyols appear to offer the coatings industry a low cost route to tough, durable, environmentally compliant, high performance coatings. Presented at the 27th International Waterborne, High-Solids, and Powder Coatings Symposium, on March 1–3, 2000, in New Orleans, LA. 430 West Forest Avenue, Ypsilanti, MI 48197.     

Waterborne epoxy protective coatings for metal

Recent enhancements in waterborne resin system polymers as well as the way they are formulated have produced paints with a set of barrier properties that are superior to their standard solventborne analogs. New generation waterborne epoxy and curing agent dispersions, and the paints formulated from them, have been introduced with changes from older generation waterbornes. These changes include (1) totally nonionically dispersed paints in place of the older ionically dispersed types, (2) quicker coalescing, mutually soluble epoxy/amine vehicle resins rather than the former slow coalescing, highly branched epoxy/amine systems, and (3) utilization of stable, water compatible additives and fillers that complement the nonionic epoxy/amine resin vehicles. In this paper, the success of these implemented technology changes is demonstrated by comparing the performance properties of the new generation with an industry standard epoxy/polyamide solventborne paint. This paper presents novel two-component waterborne epoxy resin and amine curing agent technology for ambient cure metal coatings. Presented at the 79th Annual Meeting of the Federation of Societies for Coatings Technology, on November 4–7, 2001, in Atlanta, GA. P. O. Box 1380, Houston, TX 77251.     

Study of degradation of organic coatings in seawater by using EIS and AFM methods

In this article, electrochemical behaviors and their topography observation for four organic coatings used in seawater, by using both electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) methods to study environment behaviors of different coatings as well as the effects of their film formation, pigments, and fillers on anticorrosion behaviors, were measured. The results show that polyurethane, epoxy, and chlorinated rubber coatings all present one capacitive loop in their tested EIS which contains phenomenally only one time constant, whereas alkyd coating presents two capacitive semicircle arcs. With two capacitive loops, the capacitive semicircle in the high frequency range represents barrier layer property, but the semicircle in the low frequency range represents corrosion reaction of metals under the film. Polyurethane coating used in seawater has well anticorrosion property in seawater immersion test. The appearance features of different layers are visible different between different layers of tested coatings at their surface topography. The property of polyurethane paint film coated on metal is better than other layers, and film of alkyd coating has many pits at its surface by observing the layer's images. AFM photos imaged have also been used to further detail surface topography for four organic coatings, and to approve effects of topography of these coatings on its electrochemical behaviors, from two views of both height and phase modes. It is beneficial to explain deeply the environment behaviors and degradation mechanism of organic coatings. To further study failure of these organic coatings and dynamic processes of corrosion of metal under the film, two equivalent circuit models, according to these tested EIS, have been suggested to explain the corrosive kinetics of these four coatings. To polyurethane, epoxy, and chlorinated rubber coatings used in seawater which have good protection effects for substrate metal, the diffusion process for water, from their layer's surface to interface of film/metal, is mainly controlled factor for degradation. However, the electrochemical reaction process has may become a control procedure for corrosion of alkyd coated metal. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Adhesion of waterborne paints to wood

Using a modified torque technique, statistically significant differences in adhesion values were detected for waterborne model paints on wood as a function of moisture content, waterborne preservative, and after fungal inoculation. Change in a paint constituent sometimes resulted in a significant change in the adhesion value. The adhesion values of the alkyd emulsion paints tested decreased after inoculation with a blue stain fungus. On the contrary, the adhesion values of the acrylic dispersion paints tested became significantly higher after inoculation. Wood Biology Section, Department of Forest Products, P.O. Box 7008, S-750 07 Uppsala, Sweden.     

Determination of the adhesion properties of an alkyd pigmented coating by electrochemical impedance spectroscopy

One of the most modern methods of characterizing the electrical properties of coatings is by electrochemical impedance spectroscopy (EIS). EIS can provide useful information about the transport of water and corrosive species through a coating. In this study, impedance measurements were performed in different frequency ranges at open circuit potential for an alkyd coating with TiO₂ as a mineral pigment in 3% NaCl. The most probable impedance equivalent circuit method (MPI) was considered for data analysis. The interpretation of the impedance spectra permitted the determination of water permeation, the formation of blisters, swelling of the coating, and the loss of adhesion.     

Resistance of metallic substrates protected by an organic coating containing glass flakes

The resistance against corrosion of an epoxy-polyamine-based coating immersed in a 3 wt.% sodium chloride solution was investigated by electrochemical impedance spectroscopy (EIS). The organic coating contained glass flakes as pigment in order to enhance its barrier characteristics. The data show that this coating is more strongly adhered and exhibits higher protection characteristics when applied onto carbon steel substrates than on galvanized steel. Though the capacitance of the coating (C_C) does not show any appreciable variation with immersion time, the resistance (R_PO) of the film is observed to increase with time upon immersion. The analysis of the data sustains that the organic film behaves as a porous, non-barrier coating. Two time constants are observed even at earlier exposures, and the improved corrosion resistance developed after the coating system was exposed to the test electrolyte is considered to originate from the precipitation of corrosion products within the pores in the film.     

Corrosion protection performance of nanocomposite coatings under static,UV, and dynamic conditions

Silicone-modified epoxy polymeric matrix was successfully fabricated and reinforced with 1–2 wt% SiO₂, TiO₂, and TiSiO₄ nanoparticles. Fourier-transform infrared spectroscopy, contact angle measurements, differential scanning calorimetry, and field-emission scanning electron microscopy together with energy-dispersive X-ray spectroscopy were employed to investigate different characteristics of the prepared coatings. To simulate operating conditions, all samples were characterized via electrochemical impedance spectroscopy (EIS) after being subjected to different conditions. Corrosion under static conditions, in which the samples were exposed to a static electrolyte without further change in other parameters, was investigated. Furthermore, to study the effects of ultraviolet (UV) radiation in accelerating the degradation of the coatings, samples were characterized after being subjected to UV while immersed statically in the electrolyte. Additionally, the corrosion protection performance was investigated after subjecting the coated substrates to dynamic conditions involving continuous movement of the sample in the electrolyte, simulating continuous wear of the coated surfaces. Compared with the static condition, the EIS results revealed the vital role of the silicone resin and nanoparticles in improving the stability of the coating film against corrosion degradation in the presence of UV radiation, while poor performance in dynamic condition was recorded for all the coating systems.     

Calcium tripolyphosphate: An anticorrosive pigment for paint

The objective of this work was to evaluate the performance of calcium tripolyphosphate in anticorrosive paints. Its anticorrosive properties were studied in pigment suspensions and in solventborne paints with 10% and 30% of the pigment by volume and a pigment volume concentration/critical pigment volume concentration (PVC/CPVC) equal to 0.8. The behavior of paints formulated with epoxy and alkyd resins was assessed by accelerated (salt spray cabinet and humidity chamber) and electrochemical tests (corrosion potential, ionic resistance, and polarization resistance). Calcium tripolyphosphate was proven to inhibit steel corrosion when incorporated in a paint film. Good protection was achieved employing only 10% by volume of the pigment, instead of 30%, as was suggested in the case of phosphates. The anticorrosion protection afforded by alkyd paints was impaired when the pigment content was increased. Epoxy paints seemed to be less sensitive to the pigment content. Centro de Investigación y Desarrollo en Tecnología de Pinturas (CIC-CONICET), Calle 52 e/121 y 122. (1900) La Plata. Argentina. Fax: 54.221.427. 1537. email: cidepint@ba.net     

Control of film defects in solventborne high-solids coatings: The non-additives vs. a new additives approach

Acetylenic based surfactants have long found utility in compliant coatings such as waterborne systems and are demonstrated here to enhance performance of solventborne high solids systems. Three new additives are shown to reduce surface defects such as craters and orange peel in conventionally spray applied polyester and epoxy paints. Important to this new additive technology is the lack of adverse effect on physical properties, recoatability, and durability of the applied coating. Also discussed are the theory and background of the origins of surface defects with emphasis on the influence of additives on paint rheology, compatibility, and surface tension. Presented at the Latin American Coatings Show, August 27–28, 1997, Mexico City, Mexico by Joel Schwartz and the 5th International Exhibition of Paint Industry Suppliers, September 15–17, 1997, Sao Paulo, Brazil, by Frank Lee. 7201 Hamilton Blvd., Allentown, PA 18195. 109 Lukens Dr., New Castle, DE 19720.