Organic Coatings Research Articles

Corrosion-Resistant Sacrificial Metallic Coatings Produced By Cold-Spray for Al Alloys

Corrosion is a massive disaster in many sectors that caused the loss of billions of dollars. For example, it was reported that the total direct estimated cost of corrosion was about $ 276 billion in 1998 in the US, which is 3.1% of the nation’s GDP. Therefore, a necessity to develop methods to overcome this challenge arose in the last few decades. Thus, the development of corrosion resistive coatings is significantly attracted researchers' attention. In combination with the corrosion inhibitors, organic and conversion coatings are used to improve the corrosion resistance of high-strength Al alloys. However, many corrosion inhibitors are carcinogenic: Chromate conversion coating performed very well, but alternative options need to be explored due to restrictions on its applications due to the health and environmental regulations. Moreover, organic coatings provide good corrosion resistance, but poor wear resistance and mechanical damage lead to corrosion issues. Metallic coatings are an alternative, and galvanized steel is one of the prominent examples. However, metallic coatings produced by elements such as Cr, Ni, Ti, or Ta are noble for Al or Mg-based alloys. Therefore, in any event of coating breakdown, the substrate would be more active and act as an anode and, corrode rapidly by galvanic interaction. Thus, such metallic coatings produced by the above-mentioned corrosion resistance elements are not very attractive for Al alloys.We present a sacrificial metallic coating with outstanding corrosion resistance. Al was alloyed with V using high-energy ball milling (HEBM) which enabled the formation of a superstrated solid solution of V in Al. Al-V alloy powder produced by HEBM was used for coating the high-strength substrate using cold spray. The corrosion behavior and corrosion mechanisms of cold sprayed specimens were investigated using advanced electrochemical and analytical techniques. The cold sprayed specimens exhibit high pitting potential, low corrosion current density, and a less noble corrosion potential than the substrate. This indicates that in any event of coating breakdown, the coating would corrode (i.e., act as a sacrificial anode) and prevent the substrate from corrosion. Alloy composition is chosen such that corrosion of coating releases chemical species that could inhibit corrosion by decreasing the cathodic efficiency of the substrate.

Sustainable and Repulpable Barrier Coatings for Fiber-Based Materials for Food Packaging: A Review

Due to the inherent hydrophilic nature and porosity of the paper fibers, hydrophobic polymeric materials, waxes, and inorganic fillers have been widely utilized as coatings and fillers, respectively, on a fiber-based substrate. Coatings also impart oxygen, aroma, and oil barrier properties desirable for food packaging applications. In addition, coatings improve the functional properties and characteristics of paper, including reduced water absorbance, enhanced surface finish, gloss finish, printability, readability, dimensional stability of the substrate, and antimicrobial performance. Such functional properties are highly desirable for consumer packaging applications. However, such coatings may limit the repulpability, recyclability, biodegradability, and compostability of paper and paperboard. In addition, the contamination of the substrate by-product also limits the recyclability of the fiber-based substrates, and the paper, paperboard, or corrugated material ends up in landfill sites. This review focuses on bioderived, biodegradable, compostable, and functional organic, inorganic, and hybrid hydrophobic coatings, which promote the circular economy by improving the repulpability or reduces carbon footprints.

New Corrosion Inhibitors Based on Perylene Units in Epoxy Ester Resin Coatings

Four new compounds from perylene dianhydride were prepared and tested for their anti-corrosion properties. Dizinc salt of perylene-3,4,9,10-tetracarboxylic acid and dimagnesium salts of perylene-3,4,9,10-tetracarboxylic acid, 5,5′-(1,3,8,10-tetraoxo-1,3,8,10-tetrahydroanthra[2,1,9-def:6,5,10-d′e′f′] diisoquinoline-2,9-diyl) bis(2-hydroxybenzoic acid) and N,N′-bis[3,3′-(dimethylamino)propylamine]-3,4,9,10-perylenediimide were characterized by analytical methods (SEM, EDX, X-ray) and parameters used in the field of paints (density, oil number and critical volume concentrations of pigment). The pigments (in a pigment volume concentration series) were used to prepare paints also containing a perylene C26H14N2O4 (Compound I) derivative pigment plus inert titanium dioxide to maintain a constant concentration of solids in the paint film. A mixture containing zinc nitroisophthalate and both the perylene derivative and titanium dioxide served as the reference material. The paints were applied to steel panels in two layers with a ruler. The organic coatings were subjected to electrochemical measurements and accelerated cyclic corrosion tests. The highest corrosion resistance was found for the coating containing C24H8O8Mg2. Superior to the coating containing either C26H14N2O4 or the conventional corrosion inhibitor C8H5N06-Zn, this pigment type acted mainly by a mechanism based on the compound’s complexation capacity at the metallic surface/organic coating/corrosion medium interface. The organic coatings containing perylene acid salts also attained high mechanical resistance.

The effect of pulse current cathodic protection on cathodic disbondment of epoxy coatings

For coated pipelines with cathodic protection, cathodic delamination has been judged as the main reason of coating delamination. This work aims to use the pulse current cathodic protection (PCCP) to mitigate the coating cathodic delamination. Cathodic delamination tests, electrochemical impedance spectroscopy and wire beam electrode method (WBE) were used to study the effect of PCCP on the mitigation of coating disbondment. The results show that PCCP could successfully retard the cathodic delamination rates of organic coatings. Under different cathodic protection potential, the delamination area of the coating protected using PCCP is much smaller than that using direct current cathodic protection. With the increasing pulse frequency and duty ratio, the mitigation effect decreases. Within the range of pulse frequency from 5 Hz to 500 Hz and duty ratio from 0.1 to 0.9, the results of cathodic delamination tests and WBE tests indicate that when the cathodic potential is −1.5 V, the mitigation effect reaches the maximum with the pulse frequency of 5 Hz and the duty ratio of 0.1. PCCP alleviates cathodic delamination of coating mainly by intermittently shifting the surface polarization potential to positive direction and reducing the consumption of cathodic reaction charge.

Thermal treatment of ion‐exchanged glass

AbstractThermal treatments of ion‐exchanged glasses are often needed for postprocessing steps, including deposition or curing of inorganic or organic coatings deposited on the glass surface. In this study, we investigate the effects of post–ion exchange thermal treatment on the concentration profile, residual stress, and final strength of the ion‐exchanged glass. A new general solution of the diffusion problem with variable boundary conditions is presented together with its integration in a recent residual stress model, including fast and slow relaxation terms. Strength is evaluated as a function of the surface flaw depth in both solely ion‐exchanged glass and ion‐exchanged glass subjected to subsequent thermal treatments. Results indicate that the thermal treatment may have significant detrimental consequences in terms of strength, which should be carefully considered in the design of glass components to avoid unexpected immediate or time‐delayed breakages.

Synthesis of Smart Nanofiber Coatings with Autonomous Self-Warning and Self-Healing Functions.

Organic protective coatings are widely used to protect metal structures from corrosion but they are vulnerable to undetectable damage. Without timely detection and repair, it could lead to severe consequences. How to warn and heal damaged areas simultaneously and automatically has become a challenging problem. Herein, we report an intelligent protective coating with self-warning and self-healing functions. This strategy was achieved by embedding bifunctional nanofibers containing 1,10-phenanthroline (Phen) in organic coatings. The nanofibers with Phen as a core and a poly(vinyl alcohol) (PVA)─chitosan (CS) blend solution as a shell were synthesized by coaxial electrospinning. The PVA/CS@Phen nanofiber-embedded coating displayed self-healing and high contrast indication function of the damaged area on coatings. Prominent red could warn microdamage and macrosurface damage, which occurred rapidly and healed permanently. The intelligent coating exhibited high healing performance under artificial injury with self-warning characteristics, and the cure rate was about 98.4% without external intervention. In the healing process, free amino groups of CS in the shell of nanofibers enhanced the sustained release of Phen. This convenient, economical, and efficient strategy with cooperative functions of self-warning and self-healing delivers an effective solution for prolonging the service life of protective coatings. This multifunctional coating exhibits excellent potential in the field of marine engineering applications.

Liquid-liquid phase separation reduces radiative absorption by aged black carbon aerosols

Black carbon aerosols absorb radiation and their absorptive strength is influenced by particle mixing structures and coating compositions. Liquid-liquid phase separation can move black carbon to organic particle coatings which affects absorptive capacity, but it is unclear which conditions favour this redistribution. Here we combine field observations, laboratory experiments, and transmission electron microscopy to demonstrate that liquid-liquid phase separation redistributes black carbon from inorganic particle cores to organic coatings under a wide range of relative humidity. We find that the ratio of organic coating thickness to black carbon size influences the redistribution. When the ratio is lower than 0.12, over 90% of black carbon is inside inorganic salt cores. However, when the ratio exceeds 0.24, most black carbon is redistributed to organic coatings, due to a change in its affinity for inorganic and organic phases. Using an optical calculation model, we estimate that black carbon redistribution reduces the absorption enhancement effect by 28–34%. We suggest that climate models assuming a core-shell particle structure probably overestimate radiative absorption of black carbon aerosols by approximately 18%.

A review of a novel enzyme system for the management of thatch and soil water repellency in turfgrass

AbstractManaging soil organic matter is a crucial component of greenkeeping and turfgrass maintenance. Organic matter accumulation as thatch is a major problem in modern turfgrass management. Additionally, soil water repellency (SWR) caused by hydrophobic organic coatings on sand particles can create serious soil water infiltration and potential runoff problems and contribute to a reduction in turf quality and playability. Lignin is a major component of thatch and acts as protective matrix limiting microbial degradation of cellulose and hemi‐celluloses. This article reviews lignin structure and its unique oxidation mechanism that makes it suitable for use in turfgrass systems and the research progress to develop laccase as a tool to manage thatch layer and SWR. A series of experiments explored the potential for direct application of fungal produced enzymes to degrade lignin, speed thatch degradation, and thereby reduce thatch accumulation. Greenhouse studies provided proof of concept and confirmed laccase impact on physical and chemical properties of thatch. Field studies verified the effectiveness of laccase application on different turfgrass species and optimized application rates and frequency. The reduction in thatch layer thickness by laccase treatments was similar to reductions achieved by cultural management and greater reductions occurred when applied in combination with cultural management. The use of laccase and other enzymes to ameliorate SWR was verified by a series of laboratory and field studies. Single applications of laccase were effective in reducing SWR but not as effective as wetting agents. Enzyme applications combined with a wetting agent to provide maximum relief of SWR. Application of laccase in combination with core‐aeration and sand topdressing could reduce the number of mechanical cultivations necessary to keep thatch layers at desired levels and reduce the potential for SWR. Laccase could provide a nondisruptive organic approach to manage thatch and SWR on highly managed turfgrass.

Surface modification of acrylic coating with anti‐corrosion and anti‐UV materials

AbstractThe use of organic coatings is the most common method of corrosion protection of metal structures in aggressive environments which act as a barrier between the corrosive environment and the metal structure. In this work, to increase the corrosion resistance and UV resistance of steel structures, an acrylic coating containing titanium oxide (TiO2), zinc phosphate (ZP), and benzophenone was used and the coating was characterized by open circuit potential (OCP) techniques, electrochemical impedance spectroscopy (EIS), dynamic polarization, Adhesive strength, salt spray, and UV weathering. The results showed that in the case of the acrylic sample, it has poor corrosion resistance and requires the presence of nanofillers. With the presence of TiO2 nanofillers, microporous and other defects were effectively blocked and the penetration of corrosive components into the interface of the metal coating and substrate was prevented. In the presence of ZP along with TiO2, all anodic and cathodic sites were coated with a film consisting of inhibitors released from zinc phosphate nanoparticles and thus acted as a barrier against electrolyte penetration into active metal sites. With the presence of an anti‐UV agent, benzophenone partially blocked surface defects and along with corrosion products prevented a sharp drop in resistance over longer periods.

Correlations between standard accelerated tests for protective organic coatings and field performance

Accelerated testing is widely used in development and pre-qualification of protective organic coatings. In this work 26 coating systems have been investigated in a 2-year C5 atmospheric exposure field test, ISO 9227 salt spray test, ISO 12944-9 cyclic ageing and ISO 16773 electrochemical impedance spectroscopy measurement of coating resistance. Of the 26 coating systems, 16 have epoxy mastic primers and 10 have zinc rich epoxy primers. In the field test, the zinc rich primer improved corrosion creep resistance from scribe by a factor of about 10. However, this is not reflected in any of the accelerated lab tests. The lab tests all show rather poor correlation to the field test with respect to corrosion creep. All the coatings had little corrosion creep from scribe in the field test, even the coating systems with epoxy mastic primers. The large focus on this parameter in coating pre-qualification testing, e.g. in ISO 12944-6 and 12944-9, may therefore not be justified.

New out-performing structured pigments for anticorrosive practical applications

PurposeLong time ago, multistructured materials showed great interest being considered as the bridge between bulk and atomic materials. Core-shell particles are kind of composite materials that refer to multilayered structures with a core totally surrounded by shell(s) (onion-like structure). These new structures can offer an advantage of applying new adjustable parameters like shape, stoichiometry and chemical ordering, in addition to the opportunity of tailoring more complexed structures for different applications. Recently it was found that these structures can be tuned and taken for more advanced path with novel structures formed of core surrounded by multishells. The purpose of this study is to study the effect of the new anticorrosive pigments with its mutual shells and how each shell affects the performance of the pigment in protecting the metal and which shell will be more relevant in its effect.Design/methodology/approachThe prepared pigments were characterized using X-ray fluorescence, X-ray diffraction, TEM and SEM/EDX to prove their core-shell structure, and then they were integrated in coating formulations to evaluate their anticorrosive activity using immersion test and electrochemical impedance spectroscopy (EIS).FindingsThe results showed that the prepared core-shell pigments possess a lot of unique characteristics and can offer improved anticorrosive performance in the generated coatings.Originality/valueCore-mutual shells structured pigments were prepared for improving the corrosion resistivity of the organic coatings as a new trend in anticorrosive pigments.

Characterization of coir fiber powder (cocos nucifera L.) as an environmentally friendly inhibitor pigment for organic coatings

The reuse of an agricultural by-product in consense with the development of green coatings, motivated the characterization of coconut fiber powder, as a renewable inhibitor pigment. Coconut microfibers are a new, efficient, eco-friendly inhibitor pigment. The aim of this work to homogenize the particle size - MESH 250 -, the fiber was milled and sieved. The coconut fiber powder underwent an alkaline treatment, with immersion in sodium hydroxide solution - NaOH 5% (w/w) - for 24 h. The morphological characterization of untreated microfiber (UM) and treated microfiber (TM) were performed using laser diffraction and scanning electron microscopy (SEM). The compositions of the UM and TM samples were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and their thermal decomposition by the thermogravimetric analysis (TG/DG). The samples were characterized as a coating pigment in terms of density, oil absorption, and CPVC. Weight loss and potentiodynamic polarization curves tests were performed for understanding the inhibitory effect of fiber powder samples. Despite the high oil absorption of the samples (UM-95.73, TM-99.46) it has a low density, therefore presenting CPVC values that allow the formulation of coatings with ideal PVC. The FTIR showed that the untreated microfiber samples had lignocellulosic matrix and tannins in their composition, the treated sample showed removal of some materials from the structure, increasing the lignin concentration. The mass loss and potentiodynamic assays showed an inhibition efficiency of approximately 70% for UM and 90% for TM.

Novel approach to measure water vapor permeability in pre-painted metals using adapted cup method: Correlation between permeation rate and tendency to blistering

Corrosion protection ability of paint systems is influenced by the amount of water transported to the metal/paint interface through defects in organic coatings. It can be precisely determined using the blind hole cup method with a free-standing paint film. In this paper, a procedure for preparation of free-standing paint films from as-received prepainted metal sheets is described. The blind hole cup method was able to provide accurate information about water actually permeating to the metal/paint interface excluding the water present in blind defects. The paint system with a lower water permeability was less blistered after both accelerated test and field exposure.

Efficient capture and release of carboxylated benzisothiazolinone from UiO-66-NH2 for antibacterial and antifouling applications

Marine biofouling is a generic term for animas plants and micro-organisms that grow on the surface of all installations on the hull and in the sea. Currently, the incorporation of antifouling agents into organic coatings is the most economical and effective means to combat marine biofouling. UiO-66-NH2 based metal–organic frameworks are a new type of nanocontainers for encapsulation and release of molecules due to their porous structure, large specific surface area, high crystallinity, and tunable chemical functionality. In this study, carboxylated benzisothiazolinones (BIT-COOH) encapsulated metal–organic frame-work (UiO-66-NH2) was prepared as release vehicle for stable release of antifoulants. The antibacterial activities of the prepared BIT-COOH, UIO-66-NH2 without and with BIT-COOH, against Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria were determined by the zone of inhibition test (ZOI), minimum inhibitory concentration (MIC) and plate colony count. The results show that UiO-66-NH2-loaded BIT-COOH (UiO-66-NH2@BIT-COOH) containing 0.1 mg/mL has a bactericidal effect close to 100 % after 6 h. The antifouling coating prepared with UiO-66-NH2@BIT-COOH mixed with acrylic resin had excellent anti-bacterial, bacterial seaweed adhesion at lower levels (4 wt%). The study is a guide to the development of novel long-lasting antifouling coatings.

Influencing Parameters for the Failure Mechanism of Carbon-FRCM (Fibre Reinforced Cementitious Matrix Systems)

Nowadays, FRCM (Fibre Reinforced Cementitious Matrix) systems are highly attractive for the building materials market; thus, their optimization and development cover an essential role. This work points out the chemical and physical parameters influencing the carbon-FRCM mechanical behaviour. Three different FRCMs composed of commercially available carbon fabric and different inorganic matrices are involved. Matrices are specifically developed to enhance the adhesion with the fabric and differ in organic additive used. Moreover, different fabric geometry (twisted and untwisted) and fibre coatings are considered: micro-silica, fine silica aggregate and medium-size silica aggregate. A new shear test setup is designed to obtain an inexpensive characterization method and employs traditional mechanical tests. Morphological and compositional analyses were performed on the surface fractures. On equal reinforcement typology, significant improvements in shear strength are promoted by organic additives and fabric coatings. Also, pull-out test displays that the twisted bundle promoted the fibre-to-matrix adhesion and remarkably modified the sample failure mechanism compared to the untwisted one. Finally, the FRCM mechanical performance is primarily influenced by mechanical adhesion contribution that might be increased by adopting simple geometrical choices or fabric surface treatments.

Uses of Scanning Electrochemical Microscopy (SECM) for the Characterization with Spatial and Chemical Resolution of Thin Surface Layers and Coating Systems Applied on Metals: A Review

Scanning Electrochemical Microscopy (SECM) is increasingly used in the study and characterization of thin surface films as well as organic and inorganic coatings applied on metals for the collection of spatially- and chemically-resolved information on the localized reactions related to material degradation processes. The movement of a microelectrode (ME) in close proximity to the interface under study allows the application of various experimental procedures that can be classified into amperometric and potentiometric operations depending on either sensing faradaic currents or concentration distributions resulting from the corrosion process. Quantitative analysis can be performed using the ME signal, thus revealing different sample properties and/or the influence of the environment and experimental variables that can be observed on different length scales. In this way, identification of the earlier stages for localized corrosion initiation, the adsorption and formation of inhibitor layers, monitoring of water and specific ions uptake by intact polymeric coatings applied on metals for corrosion protection as well as lixiviation, and detection of coating swelling—which constitutes the earlier stages of blistering—have been successfully achieved. Unfortunately, despite these successful applications of SECM for the characterization of surface layers and coating systems applied on metallic materials, we often find in the scientific literature insufficient or even inadequate description of experimental conditions related to the reliability and reproducibility of SECM data for validation. This review focuses specifically on these features as a continuation of a previous review describing the applications of SECM in this field.

Anti-corrosion and self-healing behaviors of waterborne polyurethane composite coatings enhanced via chitosan-modified graphene oxide and phosphate intercalated hydrotalcite

Surface coating technology has been widely used in anti-corrosion field. A well-stacked layered material offers a strong barrier and labyrinth effect to improve the corrosion resistance of organic coatings. However, as a typical layered material, the hydrotalcite dispersion is unstable and prone to delamination. Herein, a strategy for grafting chitosan on graphene oxide and then electrostatic self-assembling with hydrotalcite was proposed. The graphene oxide was modified with chitosan to enhance its barrier performance and corrosion resistance, and then hydrotalcite was coated on the surface of graphene oxide through electrostatic self-assembly to improve the dispersion of hydrotalcite and the interfacial compatibility with resin. At the same time, PO43− between the hydrotalcite layers provides the coating with self-healing ability. Chitosan, graphene oxide and hydrotalcite nano-hybrid materials were introduced into waterborne polyurethane, and a corrosion-resistant coating with a thickness of about 40 μm was prepared. Excellent anti-corrosion behaviors were obtained through the synergistic effect of graphene oxide and hydrotalcite stacking due to the formation of a dense protective layer and the self-healing characteristics of chitosan and phosphate ions. This new type of waterborne polyurethane composite coatings offers broad application prospects in the research and development of high-performance self-healing anti-corrosive coatings.

The use of nanostructured fluids for the removal of polymer coatings from a Nuxalk monumental carving – exploring the cleaning mechanism

• Nuxalk painted carving conserved at AMNH was darkened by aged organic coatings • The stubborn coating was identified via FTIR and NMR as aged poly(vinyl acetal) • Poly(vinyl acetal) could not be removed using conventional methodologies • Nanofluids-loaded PVA-based hydrogels were used to successfully clean the carving • Lab experiments were performed to unveil the physico-chemical cleaning mechanism While undertaking treatment of a monumental Northwest Coast wooden carving at the American Museum of Natural History, conservators encountered a difficult cleaning challenge. The 19 th century painted red cedar carving served as a house entry pole in the Nuxalk village of Bella Coola in the province of British Columbia, Canada. The painted surface was weathered by years out of doors in front of the house of Chief Pootlass and obscured by darkened museum-applied coatings and grime acquired during more than 100 years of open display at the museum. The methods used to reduce the grime and cellulose nitrate coating found on the surface overall were not successful when applied to the green painted areas on the bottom of the pole, as it was covered with an additional coating of poly(vinyl acetal) resin. The present work reports on the testing and use of aqueous nanostructured fluids (NSFs) and hydrogels for succesfully cleaning these areas, where other methods could not be used safely. There have only been a few published examples of these recently developed cleaning fluids and gels being used on art objects and this is the first known use on this type of material. Further analyses were performed following the cleaning. Micro-reflectance FTIR, optical microscopy, SEM-EDX, and NMR were used to characterize paint and coating samples taken from the carving. In addition, laboratory tests were performed to evaluate the response of poly(vinyl acetal) to a selection of NSFs, providing an understanding of the mechanisms underlying the successful cleaning performed on the pole by the conservators.

Metal Oxide Chemiresistors: A Structural and Functional Comparison between Nanowires and Nanoparticles.

Metal oxide nanowires have become popular materials in gas sensing, and more generally in the field of electronic and optoelectronic devices. This is thanks to their unique structural and morphological features, namely their single-crystalline structure, their nano-sized diameter and their highly anisotropic shape, i.e., a large length-to-diameter aspect ratio. About twenty years have passed since the first publication proposing their suitability for gas sensors, and a rapidly increasing number of papers addressing the understanding and the exploitation of these materials in chemosensing have been published. Considering the remarkable progress achieved so far, the present paper aims at reviewing these results, emphasizing the comparison with state-of-the-art nanoparticle-based materials. The goal is to highlight, wherever possible, how results may be related to the particular features of one or the other morphology, what is effectively unique to nanowires and what can be obtained by both. Transduction, receptor and utility-factor functions, doping, and the addition of inorganic and organic coatings will be discussed on the basis of the structural and morphological features that have stimulated this field of research since its early stage.

Design of a Chipless RFID Tag to Monitor the Performance of Organic Coatings on Architectural Cladding.

Coating degradation is a critical issue when steel surfaces are subject to weathering. This paper presents a chipless, passive antenna tag, which can be applied onto organically coated steel. Simulations indicated that changes associated with organic coating degradation, such as the formation of defects and electrolyte uptake, produced changes in the backscattered radar cross section tag response. This may be used to determine the condition of the organic coating. Simulating multiple aging effects simultaneously produced a linear reduction in tag resonant frequency, suggesting coating monitoring and lifetime estimation may be possible via this method. For coatings thinner than calculations would suggest to be optimum, it was found that the simulated response could be improved by the use of a thin substrate between the coated sample and the antenna without vastly affecting results. Experimental results showed that changes to the dielectric properties of the coating through both the uptake of water and chemical degradation were detected through changes in the resonant frequency.