Search

Epoxies derived from natural sources as an alternative to conventional petroleum-based epoxy resins have been used in sustainable coating applications. This study aims to create corrosion-resistant bio-based epoxy nanocoatings in the context of sustainable development. For this purpose, vegetable oil-based epoxy resins from cardanol and soybean oil were prepared. The structure of bio-based epoxies was confirmed by FTIR and 1H-NMR spectroscopy techniques. The epoxy functional silane precursor is synthesized from tetraethyl orthosilicate and (3-Glycidyloxypropyltrimethoxysilane by means of the sol–gel method. Amine curing agent and inorganic silica skeletons as polyhedral oligomeric silsesquioxanes and sol–gel precursor were added to the epoxy adduct and then cured. The curing kinetics of the formulations was followed by a differential scanning calorimeter. The chemical, mechanical, thermal, and anti-corrosive properties of the prepared coatings were investigated using various tests. The sustainable epoxy-based nanocoatings exhibited higher mechanical and thermal stability. In addition, the nanocoatings showed excellent corrosion resistance without the use of any anti-corrosive agent. The prepared green sustainable coatings will provide a more sustainable way to prepare bio-based coatings. [ABSTRACT FROM AUTHOR]

The poly(methyl methacrylate) (PMMA)-based organic coating suffers from a poor adhesion of PMMA molecules with Mg alloy surface, necessitates the incorporation of an inorganic phase and a coupling agent, improving the adhesion and rendering a robust inorganic-organic hybrid coating to combat corrosion in Mg alloy. Therefore, the present work explores approx. ∼25 μm thick hybrid coating comprising PMMA and ceria mitigating saltwater corrosion of Mg-4.0 wt% Y-4.0 wt% Zn-0.5 wt% Zr-0.2 wt% Ca (WZ44) alloy. The specimens undergoing Ce(NO 3) 3 + phosphate bath treatment before PMMA (CePT→PMMA), or Ce(NO 3) 3 and PMMA treatment together (Ce+PMMA) displayed micro-pores and hairline cracks on coating with higher surface roughness owing to dehydration-induced tensile stress during drying. On the contrary, the specimen subjected to Ce(NO 3) 3 followed by PMMA (CeCC→PMMA) demonstrates a uniform, nonporous, and crack-free coating with the lowest surface roughness due to the effective closure of micro-pores/hairline cracks by PMMA molecules. Tafel polarization and electrochemical impedance spectroscopy demonstrate lowest corrosion current density (I corr ∼0.36 µA/cm2) and highest coating (R 1), polarization resistance (R 2) of ∼41015 Ω.cm2 and ∼8541 Ω.cm2, respectively, for CeCC→PMMA specimen indicating superior corrosion resistance. Overall, optimization of the experimental parameter(s) of PMMA-ceria based hybrid coating minimizes corrosion of WZ44 alloy in saline water by developing ∼25 μm thick nonporous coating behaving as a shield between the reactive Mg/chlorinated solution interface. [Display omitted] • Ceria and PMMA-based ∼25 μm thick inorganic-organic hybrid coating developed to mitigate corrosion of WZ44 alloy. • Ambient and high temperature drying of coating have pronounced effect on morphology and associated corrosion in saline water. • The Ce+PMMA and CePT→PMMA coated specimens show micro-pores and hairline cracks originate from dehydration induced tensile stress. • CeCC→PMMA specimen shows nonporous, crack-free coating with lowest surface roughness (R a = 1.52 µm) and corrosion current density (∼0.36 μA/cm2). [ABSTRACT FROM AUTHOR]

Reinforcement steel extensively applied in civil construction is susceptible to corrosion due to the carbonation process in reinforced concrete and chloride ions diffusion. Epoxy-silica-based coatings are a promising option to guarantee the long-term stability of reinforced concrete structures. In this study, the influence of the proportion between the poly (bisphenol-A-co-epichlorhydrin) resin (DGEBA) and the curing agent diethylenetriamine (DETA) on the structural, morphological, and barrier properties of epoxy–silica nanocomposites were evaluated. To simulate different stages of concrete aging, electrochemical impedance spectroscopy (EIS) assays were performed for coated samples in a 3.5 wt.% NaCl solution (pH 7) and in simulated concrete pore solutions (SCPS), which represent the hydration environment in fresh concrete (SCPS2, pH 14) and after carbonation (SCPS1, pH 8). The results showed that coatings with an intermediate DETA to DGEBA ratio of 0.4, presented the best long-term corrosion protection with a low-frequency impedance modulus of up to 3.8 GΩ cm2 in NaCl and SCPS1 solutions. Small-angle X-ray scattering and atomic force microscopy analysis revealed that the best performance observed for the intermediate DETA proportion is associated with the presence of larger silica nanodomains, which act as a filler in the cross-linked epoxy matrix, thus favoring the formation of an efficient diffusion barrier. [ABSTRACT FROM AUTHOR]

Abstract: Organic–inorganic hybrid materials can be defined as materials combining organic and inorganic domains in a nanometric scale. The development of these organic–inorganic hybrids has achieved properties from both organic and inorganic materials. In this research we have studied the scratch behaviour of coatings of organic–inorganic hybrid materials prepared by sol–gel processing, using as precursors, trialkoxysilanes with organic functionalities that react via free radical polymerization. We have also evaluated the influence of pure inorganic precursor as tetralkoxysilanes or pure organic precursors on the scratch behaviour. The main goal of this research was to evaluate how the chemical structure of the organic–inorganic hybrid influences the scratch behaviour of the coatings. [Copyright &y& Elsevier]

Organic-inorganic hybrids are considered an effective and environmentally compliant alternative to chromate-based anticorrosive coatings, currently banned due to the high toxicity of hexavalent chromium. In this work, hybrid nanocomposites based on poly(methyl methacrylate) (PMMA), covalently bonded to cerium oxide nanoparticles through the 2-hydroxyethyl methacrylate (HEMA) coupling agent, were tailored by carefully tuning the inorganic colloidal precursor to provide films with active corrosion protection for metallic substrates. Lithium hydroxide was exploited as oxidizing agent of cerium nitrate to form ceria nanoparticles. Precursor solutions and solid nanocomposites with different LiOH to Ce(NO 3) 3 .6H 2 O molar ratios were analyzed using spectroscopic and electron microscopy techniques and theoretical simulations. Electrochemical impedance spectroscopy (EIS) was used to study the anticorrosive performance of the coatings on carbon steel and 7075 aluminum alloy. The results showed that increasing amounts of LiOH lead to the formation of higher ceria content and larger primary nanoparticles, ranging from 1.7 to 2.8 nm. The homogenous ~20 μm-thick coatings present excellent anticorrosive performance on carbon steel and AA7075 substrates. Coatings on carbon steel with low LiOH loading (1Li:1Ce) showed long-term durability and high impedance modulus of up to 29 GΩ cm2 after 1 day in saline solution. On the AA7075 alloy, the presence of larger cerium oxide particles at higher LiOH content (3Li:1Ce) acted as effective reservoirs of cerium ions, providing high barrier coatings (395 GΩ cm2) with active corrosion protection. [Display omitted] • LiOH was used as oxidizing agent of cerium nitrate to form ceria nanoparticles. • Homogenous distribution of CeO x nanoparticles in the PMMA matrix for Li:Ce = 1. • PMMA-cerium oxide coatings exhibited excellent anticorrosive performance. • Coatings containing higher CeO 2 content showed self-healing ability. • Active protection was achieved by Ce4+ depletion forming insoluble cerium species. [ABSTRACT FROM AUTHOR]

Ti6Al4V is the mostly applied metallic alloy for orthopedic and dental implants, however, its lack of osseointegration and poor long-term corrosion resistance often leads to a secondary surgical intervention, recovery delay and toxicity to the surrounding tissue. As a potential solution of these issues poly(methyl methacrylate)-silicon dioxide (PMMA-silica) coatings have been applied on a Ti6Al4V alloy to act simultaneously as an anticorrosive barrier and bioactive film. The nanocomposite, composed of PMMA covalently bonded to the silica phase through 3-(trimethoxysilyl)propyl methacrylate (MPTS), has been synthesized combining the sol-gel process with radical polymerization of methyl methacrylate. The 5 μm thick coatings deposited on Ti6Al4V have a smooth surface, are homogeneous, transparent, free of pores and cracks, and show a strong adhesion to the metallic substrate (11.6 MPa). Electrochemical impedance spectroscopy results proved an excellent anticorrosive performance of the coating, with an impedance modulus of 26 GΩ cm2 and long-term durability in simulated body fluid (SBF) solution. Moreover, after 21 days of immersion in SBF, the PMMA-silica coating presented apatite crystal deposits, which suggests in vivo bone bioactivity. This was confirmed by biological characterization showing enhanced osteoblast proliferation, explained by the increased surface free energy and protein adsorption. The obtained results suggest that PMMA-silica hybrids can act in a dual role as efficient anticorrosive and bioactive coating for Ti6Al4V alloys. Unlabelled Image • Conjugation of silica and PMMA yielded homogeneous and adherent hybrid coatings. • PMMA-silica coatings provide efficient corrosion protection for a Ti6Al4V alloy. • Apatite formation in SBF solution predicts bone-bonding ability. • The coatings promote osteoblastic proliferation. • Effective protection metallic implants by bioactive anticorrosion coatings [ABSTRACT FROM AUTHOR]