Self-stratifying Coatings Research Articles

Anticorrosive self-stratified PDMS-epoxy coating for marine structures

Four self-stratified coatings were prepared by dispersion of titanium dioxide (TiO2) and hydrophobic fumed silica (SiO2) nanoparticles in polydimethylsiloxane (PDMS)-Epoxy mix separately and in combination. Incorporating a definite ratio of nanofillers in PDMS-Epoxy incompa ible polymer blend to form a single coat paint system with anticorrosive and improved hydrophobic properties by the self-stratifying process is the chief highlight of this research work. The appropriate characterization techniques like Fourier Transform Infrared (FTIR) spectroscopy in Attenuated Total Reflection (ATR) mode of the coatings top and bottom layers emphasized the intended stratification. The Field Emission Scanning Electron Microscopy (FESEM) displayed the morphology of the coated samples top and bottom layers and the existence of the intended stratification in the coatings cross-section. The PDMS-Epoxy coating inclusive of both the nanofillers exhibited improved hydrophobic nature, appreciable surface free energy, augmented adherence to the substrate and lesser shear force in pseudo barnacle strength test in terms of shear. This innovative formulation pertains to the application on underwater substrates with improved anti-biofouling properties.

Designing Multicomponent Polymer Colloids for Self-Stratifying Films.

Aqueous polymer colloids known as latexes are widely used in coating applications. Multicomponent latexes comprised of two incompatible polymeric species organized into a core-shell particle morphology are a promising system for self-stratifying coatings that spontaneously partition into multiple layers, thereby yielding complex structured coatings requiring only a single application step. Developing new materials for self-stratifying coatings requires a clear understanding of the thermodynamic and kinetic properties governing phase separation and polymeric species transport. In this work, we study phase separation and self-stratification in polymer films based on multicomponent acrylic (shell) and acrylic-silicone (core) latex particles. Our results show that the molecular weight of the shell polymer and heat aging conditions of the film critically determine the underlying transport phenomena, which ultimately controls phase separation in the film. Unentangled shell polymers result in efficient phase separation within hours with heat aging at reasonable temperatures, whereas entangled shell polymers effectively inhibit phase separation even under extensive heat aging conditions over a period of months due to kinetic limitations. Transmission electron microscopy is used to track morphological changes as a function of thermal aging. Interestingly, our results show that the rheological properties of the latex films are highly sensitive to morphology, and linear shear rheology is used to understand morphological changes. Overall, these results highlight the importance of bulk rheology as a simple and effective tool for understanding changes in morphology in multicomponent latex films.

Tailoring a variety of self-stratifying patterns in a light-curable coating on the substrates with different surface free energies

Self-stratification is an ecological method that leads to the stratified structures by one-layer application to reduce solvent emissions and energy consumption. Despite the great importance of the effect of surface properties on the self-stratification phenomena, the influence of the substrate type has not been examined in self-stratifying light-curing systems. This study aimed to design dissimilar self-stratifying patterns by using several substrates namely glass, steel, Al, polyethylene, polyethylene terephthalate, polyvinyl chloride, polypropylene, polystyrene, with different surface free energies (γ) (high γ: 59–63, medium: 41–43 and low: 31–34 mN.m−1) based on incompatible bio-renewable light-curable materials including methacrylated gelatin (GelMA) and acrylated epoxidized soybean oil diluted by the acrylated glycidyl neodecanoate (AESO-GN). To this, the impact of the essential substrate characteristics including γ and roughness on the self-stratifying behavior and other properties of the achieved coatings were studied by using SEM-EDX, contact angle (CA), FTIR-ATR, and the other conventional coating analyses. The results disclosed that the Funke theory had the potential to predict the self-stratifying behavior of the abovementioned light-curing coatings on a variety of substrates. Moreover, it was understood that self-stratification dealt with the γ of the substrate, so that the application and light-curing of coatings on the substrates with high and medium γ resulted in a bi-layered and a gradient concentration self-stratified structures, respectively. Furthermore, it was revealed that applying this coating on substrates with low γ led to an incoherent structure. Consequently, the know-how for tailoring several self-stratified coatings with different gloss values (54–88 at 60°), pendulum hardness (43–76), MEK double rub resistance (25–45)), glass transition temperature (44–72 °C), swelling degree (20–29 %), gel fraction (74–89 %), water CA (61–86°), and cross-cut adhesion (0B4B) was realized. Besides, the findings demonstrated that increasing the surface roughness of steel substrate intensified the self-stratification. Accordingly, the coating-substrate interface is of great importance for self-stratification as its characteristics will identify the stratification pattern.In addition, it was observed that appropriate bi-layered coatings could not be attained by the consecutive application and curing of GelMA and AESO-GN layers. Consequently, this attempt provided beneficial insight into the design of green coatings via an ecological fast-curing methodology.

Eco friendly self-stratifying powder coatings

Eco friendly self-stratifying powder coatings

Self-stratifying powder coatings based on epoxy/silicone technology for corrosion and weather protection

Self-stratifying powder coatings based on epoxy/silicone technology for corrosion and weather protection

Self-stratified fouling release coatings based on polydimethylsiloxane incorporated with acrylate-MQ silicone copolymer

In this study, an acrylate-MQ silicone copolymer (A-MQ) was synthesized and characterized by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and differential scanning calorimetry. Next, fouling release coatings based on polydimethylsiloxane (PDMS) were prepared by incorporating A-MQ. Self-stratified coatings were prepared by controlling the additive amount of A-MQ. Surface property analysis results showed that the appropriate A-MQ additive amount ensured surface smoothness and hydrophobicity in the prepared coatings (P/A-MQ18). Incorporating A-MQ enhanced the mechanical properties of the coatings. Moreover, the shore hardness values of the surface and interface were different, indicating stratification. Observing the fracture microstructures further confirmed the formation of self-stratified structures owing to the enrichment of the surface layer by PDMS during the curing process. More importantly, a high additive amount of A-MQ led to further phase separation with the appearance of “sea–island structures” in the prepared coatings, and this deteriorated the mechanical properties of the coatings (P/A-MQ20). The pull-off test results indicated that the self-stratified coating broke from the upper layer enriched with PDMS, indicating high adhesion strength. The biofilm adhesion assay confirmed the excellent antifouling performance of the self-stratified coating, which also resulted from the enrichment of the upper layer by PDMS. These findings can be extremely useful for developing high-performance fouling release coatings.

Design of different self-stratifying patterns in a VOC-free light-curable coating containing bio-renewable materials: Study on formulation and processing conditions

The self-stratification is an ecologic approach providing the solvent emission reduction and formation of a laminated multi-functional structure by one-coat application. Although light-curing systems as a point of interest have been developed extensively, the self-stratifying phenomena and its governing parameters have not been investigated in such a fast-curable coating. This study aimed to design solvent-free and light-curable coatings with various self-stratifying behavior using methacrylated gelatin (GelMA) and acrylated epoxidized soybean oil (AESO). The influences of several essential factors including flash-off time, irradiation time, light intensity, photoinitiator concentration (PI%), coating thickness, and raw materials weight ratio on the stratification level were evaluated by SEM-EDX, AFM, ATR-FTIR spectroscopy, water contact angle (WCA), and conventional coating analyses. It was learned that about 10 min of flash-off time was required to start the phase separation and create gradient integrated layered structures. Also, the results demonstrated that the self-stratification was not impressed by prolonging the irradiation time after the formation of the lattice structure. Furthermore, increasing the coating thickness to 300 μm or decreasing it to 30 μm led to uncured or slightly gradient stratified coatings, respectively. Besides, the lower GelMA content resulted in the lower mixture viscosity and sharper gradient self-stratified structures. Moreover, the increasing of crosslinking rate by PI% or light intensity increment changed the bilayer stratified structure into the gradient ones; therefore, self-stratifying in this fast-curing system was both thermodynamically and kinetically controlled. Subsequently, the know-how for preparing different self-stratified coatings with various features, namely swelling degree (11–29%), gel fraction (74–92%), glass transition temperature (43–72 °C), WCA (67.1–81.6°), MEK double rub resistance (25–55), pendulum hardness (45–83), cross-cut adhesion (0B4B), gloss (53–87 at 60°), and surface roughness (72.8–235.7 nm) was achieved. Additionally, the relation of the surface GelMA content and the surface roughness, gloss, hardness, and WCA were derived. Accordingly, this attempt gave a helpful insight into the self-stratification phenomena to establish the optimum formulation and processing conditions as a promising prospect to prepare green coatings for advanced bio and food applications.

Self-stratifying powder coatings based on eco-friendly, solvent-free epoxy/silicone technology for simultaneous corrosion and weather protection

A melt-based self-stratifying coating based on silicone/epoxy blend systems is reported as an easy-to-use, eco-friendly, and industrial favorable procedure.The powder forms of the silicone and epoxy resins were mixed either by dry-blending or co-melt-mixing processing method, and blends were electrostatically applied onto steel sheets and cured. Self-stratification of cured coatings with a thickness of 100 ± 30 μm occurred and was investigated by an adopted ATR-FTIR method and consolidated SEM-EDX and X-ray photoelectron spectroscopy.Fundamental studies on influencing parameters on phase separation and stratification in coatings such as surface tension, the mass ratio of silicone/epoxy resins, crosslinking reaction, and manufacturing processes were performed and discussed in detail. It is corroborated that the dry-blending of methyl substituent silicone resin with the high and medium molecular weight epoxy resins at a 1/3 mass ratio (silicone/epoxy) leads to a complete stratification structure (Type I), having the silicone phase located on the top of the coating and the epoxy phase towards the steel surface, resulting in good adhesion.3/1 mass ratio of the silicone/epoxy blends led to the dispersion of epoxy droplets into the silicone matrix (Type IV) and 1/1 mass ratio, showed lateral phase separation morphology.The co-melt-mixing process was yielded the formation of a thin homogenous layer of silicone phase on the top surface of the coating and a mixture of large and small drops of silicone dispersed into the epoxy matrix (Type I–Type III).Finally, the protective properties of the silicone/epoxy self-stratifying coatings with different stratification structures were evaluated.

Exploring the mechanism of self-stratifying coatings with aggregation-induced emission

Self-stratifying coatings are excellent replacements for traditional coatings, which need primers and sealers during their application on substrates. In this work, we introduced aggregation-induced emission (AIE) luminogens (AIEgens) during the synthesis of self-stratifying coating to study and trace the mechanism and reactions between the individual components of the coating resin, its film-forming properties, and response to the environment in real time. The AIEgens introduced into the coating materials were a backbone to these studies. They can emit light (under excitation) with different properties depending on how their molecular rotors are restricted or free to move. More still, the reported fluorescent AIE-based self-stratifying coatings demonstrated reliable hydrophobicity and self-cleaning properties (contact angle above 130°), good thermal tolerance (above 350°), excellent toughness, chemical, and corrosion resistance. Such coatings can find use in various home and industrial applications.

A new approach to design of anti-corrosive three layers self-stratifying coatings

ABSTRACT A self-stratifying coating contains at least two resins of different nature, which spontaneously stratify after applying on a substrate. Various self-stratifying systems are reported in the literature, however self-starting coatings, with three layers containing anti-corrosive pigments, and their properties are rarely discussed. In this paper, self-stratifying coatings from epoxy resin and fluorinated ethylene-vinyl ether containing three pigments i.e. zinc dust, micaceous iron oxide, and titanium dioxide have cooperated in formulations. The viscosity of the total mixture has a great effect on stratification and pigment locations. Xylene as a solvent has been used for these formulations. The results show the ratio of binders and different pigment percentages in formulations has not a great effect on the stratification and location of pigments. In addition, the type of solvents with different evaporation rates does not have an effect on stratification and location of pigments in this system.

Self-stratified bio-based coatings: Formulation and elucidation of critical parameters governing stratification

Self-stratification is an innovative one-step process used to design multi-functional coatings gathering simultaneously in a one-pot formulation the primer, the intermediate layer and the top coat properties. Many self-stratifying coatings contain oil-based epoxy resins but the literature is scarce in the development of “greener” solutions. In this work, silicone resins and bio-based epoxy resins were dissolved in various solvent blends, applied on a composite substrate and cured under different conditions to obtain stratified coatings. To reach a perfect stratification, the influence of various parameters including (i) the surface tension and the polarity of the resins, (ii) the solvents volatility, (iii) the curing temperature and (iv) the reactivity of the epoxy/amine reaction was studied by a systematic approach. In accordance with the literature, it was demonstrated that a large difference in surface energy and polarity favors resins separation. The volatility of the solvent blend was also shown to be a key factor in the stratification process. However, the predominant parameter, rarely taken into account, is the curing temperature, which impacts the cross-linking reaction of the epoxy resin. The increase in molecular weight (MW) of epoxy resins due to the cross-linking reaction favors the incompatibility between resins by increasing the difference in MW between epoxy and silicone resins. Thus, optimization of process conditions allowed the design of perfectly stratified bio-based epoxy/silicone coatings. The mechanism of film stratification was also elucidated thanks to in-situ analyses.

Life cycle assessment of multi-step versus one-step coating processes using oil or bio-based resins

Abstract Nowadays, before setting up an industrial process, special attention has to be paid to its environmental footprint. This new way of thinking allows evaluating the hotspots so as to propose solutions to conceive more eco-friendly processes. Thus, the coating industry is increasingly preoccupied by the environmental impacts of newly designed paints. That is why innovation tries to take into consideration both the formulation composition and the application and drying methods. Following a Life Cycle Assessment (LCA) approach, the present study aims to compare the environmental impacts of self-stratifying coatings (with three process steps), either oil-based or bio-based, to those of an oil-based multilayered coating (with six process steps). The concept of the self-stratifying coating is to bring the primer, the intermediate and the top coat properties together in a one-pot formulation to produce a multi-functional coating through a less laborious process. The total environmental impact of each process can be characterized by four main categories of impacts: Climate Change Human Health (CCHH), Human Toxicity (HT), Climate Change Ecosystem (CCE) and Fossil Depletion (FD), which together represent approximately 86% of the global impact for each system. The results obtained show that the self-stratifying oil-based coating process is more energy efficient compared to the currently used multilayered oil-based coating process, with a 15% decrease of CCHH, HT and CCE indicators and a 14% decrease of FD indicator, corresponding to a 13.6% decrease of the total environmental impact. However, as this decrease was lower than expected, particular attention was then paid to the chemicals used (resins, solvents) and to the process conditions. The substitution of the oil-based epoxy resin by a bio-based one and the use of less harmful solvents allow reducing the total environmental impact by 32.4% compared to the multilayered oil-based system (with 30% decrease of CCHH indicator, 50% of HT indicator, 31% of CCE indicator and 34% of FD indicator). In a global way, electricity consumption control and the nature of chemicals used were reported to contribute in a significant way to the improvement of the process environmental impact.

Migration of fluorinated alkyd and fluorinated tung oil additives for partially self-stratifying coatings

A high solids alkyd coating was developed with surface active polymers to improve performance at the surface, while maintaining adhesion at the substrate. A fluorinated long oil alkyd (FLOA) was prepared through a partial polyol substitution of 2,2,3,3,4,4,5,5-octafluoro-1,6- hexanediol for glycerol with phthalic anhydride and linseed oil in a long oil alkyd (LOA). A previously synthesized fluorinated tung oil (FTO) reactive diluent was also synthesized via a Diels- Alder reaction with 2,2,2-trifluoroethyl methacrylate. The alkyd and reactive diluent were characterized with 1H-NMR and MALDI-TOF mass spectroscopy. The FLOA was used as an additive up to 40 wt.% of the total alkyd, in increments of 10 wt.%. The FTO was used as an additive up to 10 wt.% of the total alkyd, in increments of 2.5 wt.%. The film formation was examined using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX) to show phase separation and domains of the low surface energy additive. Analysis of a cross-section of the coating showed an increase in fluorine concentration of 40% at the surface, compared to substrate, which preserves adhesion. A variety of coatings tests were performed to evaluate hardness, adhesion, mechanical strength and flexibility of the coating. The contact angle of FLOA/FTO coatings shifted from hydrophilic to hydrophobic surface energy. An increase in corrosion protection for FLOA/FTO coatings was evaluated using electrochemical impedance spectroscopy (EIS).

Corrosion resistance of self-stratifying coatings using fluorovinyl ether/BPA epoxide

Fluoroethylene vinyl ether and an alkoxysilane modified bisphenol A epoxides (BPA) were mixed together and applied onto polar substrates. The molecular weight of each phase, curing agents, and curing conditions were varied to control the self-stratification. Miscibility of the two phases was investigated by using DSC, and one combination showed two Tg with higher molecular weight for both phases. Cured coatings were each analyzed with contact angle and surface tension. Based on surface tension, interfacial tensions of two phases were calculated. During film formation, curing albeit crosslinking of the fluorine phase was faster than the alkoxylsilane of the BPA epoxide phase. Evaporation typically lagged beyond the initial crosslinking was as a consequence, viewed as more of a secondary force in the stratification process. Using a salt spray test, stratified coating showed better initial corrosion resistance.

Resin migration tracking via real-time monitoring FTIR- ATR in a self-stratifying system

The importance of self-stratifying coatings in attaining two layers by one coat application makes it a point of interest to understand the mechanism of self-separating of resins into two distinct layers.Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (FTIR-ATR) is a good analysis method with the facility of real-time monitoring for tracking the position of components during the film formation. The migration of main components of silicon /epoxy as a self-stratifying coating system during film formation is followed on ZnSe and Ge cells as substrates. By following up the spectra of real-time monitoring during the film formation it was found that the mechanism of epoxy chains movement toward surface in a self-stratifying coating can not be diffusion.

Self-stratifying coatings: a review

A self-stratifying coating is an economical coating containing multiresinous components with different functional groups, which spontaneously stratify after application to the substrate. These coating systems could be composed of two or more different layers to protect substrates against corrosion, by first layer, and simultaneously to create a desirable appearance, by second layer, with decorative properties. Conventional multilayer coating systems encounter some problems such as poor interfacial adhesion, application, and labor costs and also lengthy processing time. The concentration gradient of two layers would eliminate the inter-coating boundary which can be the point of failure in conventional coatings. In this paper, the surface tension and solubility theory regarding these coatings are discussed. In addition, the effects of different factors on the pigment location into the coating systems are studied. The main factors, including curing mechanisms, substrate effects, thickness, viscosity, kinetics of reaction, evaporation rate of solvents, dispersing agents, and surface properties of pigments have been reviewed. The models for prediction of self-stratifying coatings such as UNIFAC and computer simulation have also been addressed and taken into consideration. The prospect of these coatings and their application in different industries is presented.

Self-stratifying coatings: A review

Abstract Self-stratifying coatings are promising coating systems based on incompatible polymer blends which can produce polymer/polymer laminate. A complex multi-layer or gradient coating structure is formed from one single coat, providing an undercoat and finishing coating. The preferential distribution of concentration through the film thickness greatly eliminates the interfacial adhesion failure without compromising the advantages of a multi-layer system, and thus favors an industrial eco-efficient process. Powder, waterborne and solventborne coating systems are able to stratify: the most well-known and effective systems are described in this review. Finally, this concept constitutes a great possible versatile process for a broad range of applications and could thus favor the development of new products, taking into account the reduction of solvent and labor cost

One pot flame retardant and weathering resistant coatings for plastics: a novel approach

The first epoxy/fluoropolymer/iron oxide self-stratified coatings (thickness < 100 μm) with outstanding fireproofing performances were designed for polycarbonate substrates.

Self-stratifying coatings based on Schiff base epoxy resins

Schiff base epoxy resin was used as a component of self-stratifying compositions, in which different acrylic resins were used. The degree of stratification was determined using the ATR FTIR spectroscopy and microscopy technique. Results were compared with those for commercial epoxy resins with a comparable epoxy number. A determination was made of the mechanical properties of the coatings obtained. Based on the previous studies, it was concluded that Schiff base epoxy resin in a film-forming composition behaves in a similar manner to BPA-based epoxy resins. The best mechanical properties and a high degree of stratification were achieved using a Schiff base epoxy resin/poly(isobutyl methacrylate) composition. Use of a self-stratifying composition not only reduces the time and cost of preparing a multilayer coating system, thanks to the formation of two layers in one application, but also causes the Schiff based epoxy coatings to become more flexible.

Design and development of self-stratifying systems as sustainable coatings

Thermosetting polyurethane coating formulations which stratify into two distinct layers after application have been prepared. In a thermosetting system the polymer phase separation among other factors is seen to be kinetically controlled and have less dependence on parameters such as surface tension gradient and polymer solubility. Certain coating applications including those used in architectural, automotive, industrial maintenance and aerospace require a combination of primer/topcoat or basecoat/clearcoat layers. These multilayered systems necessitate complex application and curing procedures. Multiple product formulation, application and processing steps not only require significant amounts of processing time, and contributing to environmental waste generation and pollution they also consume excessive amount of energy and manpower until a solid film has been produced. It would be desirable to reduce the number of layers to a minimum while providing the equal or better overall performance. In this paper we report the design and development of thermosetting polyurethane coatings that self-stratify to two distinct phases upon application and cure. It was demonstrated that kinetically controlled reactions aided by incompatible polymers possessing gradient surface free energies can afford self-stratifying coatings. This investigation also revealed that solvent type, evaporation rate, and gravity did not contribute to stratification of thermosetting coatings. Prototype pigmented systems were applied and cured and characterized by FTIR, SEM/EDX and were evaluated using standard coating test methods. The results of this investigation provide a new understanding of stratification phenomenon and establish that preferentially reactive polymers can be a basis for formulating cross-linkable self-stratifying coatings.