A Comparative Study on Graphene Oxide and Carbon Nanotube Reinforcement of PMMA-Siloxane-Silica Anticorrosive Coatings

Advanced Anticorrosive Graphene Oxide-Doped Organic-Inorganic Hybrid Nanocomposite Coating Derived from Leucaena leucocephala Oil

Metal corrosion poses a substantial economic challenge in a technologically advanced world. In this study, novel environmentally friendly anticorrosive graphene oxide (GO)-doped organic-inorganic hybrid polyurethane (LFAOIH@GO-PU) nanocomposite coatings were developed from Leucaena leucocephala oil (LLO). The formulation was produced by the amidation reaction of LLO to form diol fatty amide followed by the reaction of tetraethoxysilane (TEOS) and a dispersion of GOx (X = 0.25, 0.50, and 0.75 wt%) along with the reaction of isophorane diisocyanate (IPDI) (25-40 wt%) to form LFAOIH@GOx-PU35 nanocomposites. The synthesized materials were characterized by Fourier transform infrared spectroscopy (FTIR); 1H, 13C, and 29Si nuclear magnetic resonance; and X-ray photoelectron spectroscopy. A detailed examination of LFAOIH@GO0.5-PU35 morphology was conducted using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. These studies revealed distinctive surface roughness features along with a contact angle of around 88 G.U preserving their structural integrity at temperatures of up to 235 °C with minimal loading of GO. Additionally, improved mechanical properties, including scratch hardness (3 kg), pencil hardness (5H), impact resistance, bending, gloss value (79), crosshatch adhesion, and thickness were evaluated with the dispersion of GO. Electrochemical corrosion studies, involving Nyquist, Bode, and Tafel plots, provided clear evidence of the outstanding anticorrosion performance of the coatings.

Durable Polyacrylic/Siloxane-Silica Coating for the Protection of Cast AlSi7Mg0.3 Alloy against Corrosion in Chloride Solution

This study presented a novel corrosion protective coating based on polyacrylic/siloxane-silica (PEHA-SS) deposited on lightweight cast aluminium alloy AlSi7Mg0.3. The synthesis of PEHA-SS comprises organic monomer 2-ethylhexyl acrylate and organically modified silane 3-(trimethoxysilyl)propyl methacrylate as well as an inorganic silane, tetraethyl orthosilicate. The steps during the synthesis process were monitored using real-time infrared spectroscopy. The coating deposited onto the AlSi7Mg0.3 surface was characterised using various techniques, including infrared spectroscopy, 3D contact profilometry, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The corrosion resistance of the coated alloy in sodium chloride solutions was evaluated using electrochemical impedance spectroscopy. The accelerated testing of the uncoated and coated sample was performed using the Machu test. This novel, nine micrometres thick PEHA-SS coating achieved durable corrosion (barrier) protection for the AlSi7Mg0.3 alloy in 0.1 M NaCl during the first four months of immersion or under accelerated corrosion conditions in a Machu chamber containing NaCl, acetic acid, and hydrogen peroxide at 37 °C.

Development of Metallo (Calcium/Magnesium) Polyurethane Nanocomposites for Anti-Corrosive Applications

Long-term corrosion protection of metals might be provided by nanocomposite coatings having synergistic qualities. In this perspective, rapeseed oil-based polyurethane (ROPU) and nanocomposites with calcium and magnesium ions were designed. The structure of these nanocomposites was established through Fourier-transform infrared spectroscopy (FT-IR). The morphological studies were carried out using scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). Their thermal characteristics were studied using thermogravimetric analysis (TGA). Electrochemical experiments were applied for the assessment of the corrosion inhibition performance of these coatings in 3.5 wt. % NaCl solution for 7 days. After completion of the test, the results revealed a very low i_corr value of 7.73 × 10^-10 A cm^-2, a low corrosion rate of 8.342 × 10^-5 mpy, impedance 1.0 × 10⁷ Ω cm², and phase angle (approx 90°). These findings demonstrated that nanocomposite coatings outperformed ordinary ROPU and other published methods in terms of anticorrosive activity. The excellent anti-corrosive characteristic of the suggested nanocomposite coatings opens up new possibilities for the creation of advanced high-performance coatings for a variety of metal industries.

Thermal, Mechanical, and Morphological Characterisations of Graphene Nanoplatelet/Graphene Oxide/High-Hard-Segment Polyurethane Nanocomposite: A Comparative Study

The current work investigates the effect of the addition of graphene nanoplatelets (GNPs) and graphene oxide (GO) to high hard-segment polyurethane (75% HS) on its thermal, morphological, and mechanical properties. Polyurethane (PU) and its nanocomposites were prepared with different ratios of GNP and GO (0.25, 0.5, and 0.75 wt.%). A thermal stability analysis demonstrated an enhancement in the thermal stability of PU with GNP and GO incorporated compared to pure PU. Differential Scanning Calorimetry (DSC) showed that both GNP and GO act as heterogeneous nucleation agents within a PU matrix, leading to an increase in the crystallinity of PU. The uniform dispersion and distribution of GNP and GO flakes in the PU matrix were confirmed by SEM and TEM. In terms of the mechanical properties of the PU nanocomposites, it was found that the interaction between PU and GO was better than that of GNP due to the functional groups on the GO's surface. This leads to a significant increase in tensile strength for 0.5 wt.% GNP and GO compared with pure PU. This can be attributed to interfacial interaction between the GO and PU chains, resulting in an improvement in stress transferring from the matrix to the filler and vice versa. This work sheds light on the understanding of the interactions between graphene-based fillers and their influence on the mechanical properties of PU nanocomposites.

Hydrophobicity and corrosion resistance of waterborne fluorinated acrylate/silica nanocomposite coatings

This study aims to improve the hydrophobic properties and corrosion resistance of fluorinated acrylate coatings. The surface of nano-SiO2 was modified by the silicone coupling reagent (KH-570), and the reactive functional groups were introduced to modify fluorinated acrylates. The functionalized SiO2-modified waterborne fluorinated acrylate emulsion was prepared by free polymerization with dual initiators. The structure of the polymer was analyzed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectro-meter (1H-NMR), X-ray photoelectron spectroscopy (XPS) and Waters gel chromatography (GPC). The properties of the films and coatings were analyzed by contact angle, atomic force microscopy, scanning electron microscopy, and electrochemical analysis. The results showed that the contact angle reached 120° when the SiO2 content was 3%, the electrochemical impedance value reached 1.49 × 107 Ω·cm2, and the pencil hardness was 3H.

Acrylate-Based Hybrid Sol-Gel Coating for Corrosion Protection of AA7075-T6 in Aircraft Applications: The Effect of Copolymerization Time

Pre-hydrolysed/condensed tetraethyl orthosilicate (TEOS) was added to a solution of methyl methacrylate (MMA) and 3-methacryloxypropyltrimethoxysilane (MAPTMS), and then copolymerised for various times to study the influence of the latter on the structure of hybrid sol-gel coatings as corrosion protection of aluminium alloy 7075-T6. The reactions taking place during preparation were characterised using real-time Fourier transform infrared spectroscopy, dynamic light scattering and gel permeation chromatography. The solution characteristics were evaluated, using viscosimetry, followed by measurements of thermal stability determined by thermogravimetric analysis. The optimal temperature for the condensation reaction was determined with the help of high-pressure differential scanning calorimetry. Once deposited on 7075-T6 substrates, the coatings were evaluated using a field emission scanning electron microscope coupled to an energy dispersive spectrometer to determine surface morphology, topography, composition and coating thickness. Corrosion properties were tested in dilute Harrison's solution (3.5 g/L (NH4)2SO4 and 0.5 g/L NaCl) using electrochemical impedance spectroscopy. The copolymerization of MMA and MAPTMS over 4 h was optimal for obtaining 1.4 µm thick coating with superior barrier protection against corrosion attack (Z10 mHz 1 GΩ cm2) during three months of exposure to the corrosive medium.

The Effect of the Methyl and Ethyl Group of the Acrylate Precursor in Hybrid Silane Coatings Used for Corrosion Protection of Aluminium Alloy 7075-T6

This study investigated polysiloxane hybrid sol-gel coatings synthesized from tetraethyl orthosilicate (TEOS), 3-(trimethoxysilyl)propyl methacrylate (MAPTMS) and two different precursors, i.e., methyl- or ethyl- methacrylate (MMA or EMA), as corrosion protection of aluminium alloy 7075-T6. The hypothesis was that the additional alkyl group might affect the chemical properties and, consequently, the corrosion properties. Synthesis of the sols proceeded in two steps, each involving either MMA or EMA in the same molar ratio. The resulting sols, siloxane-(poly(methyl methacrylate-co-MAPTMS)) or siloxane-(poly(ethyl methacrylate-co-MAPTMS)), were applied on aluminium alloy followed by characterization in terms of chemical structure and composition, topography, wettability, adhesion and corrosion resistance in 0.1 M sodium chloride solution. The chemical properties of sols, monoliths and coatings were investigated using Fourier transform infrared spectrometry, solid state nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Coatings were similar in terms of surface topography, while the wettability of the coating with EMA showed 6° greater water contact angle compared to the coating with MMA. Both coatings were shown, by electrochemical impedance spectroscopy in 0.1 M NaCl solution, to act as barriers to protect the underlying substrate in which coating with EMA exhibits better protection properties after 2 months of immersion. Adhesion tests confirmed the highest grade of adhesion to the substrate for both coatings. Testing in a salt-spray chamber demonstrated excellent corrosion protection, where coatings remaining intact after more than 600 h of exposure.

Detection of in Situ Early Corrosion on Polymer-Coated Metal Substrates

Protective coating systems (PCS) are a common and facile method to protect metal substrates from corrosion. The corrosion control performance of polymer-coated metal substrates is still predominantly evaluated by visual assessment. Unfortunately, for many decades, PCS material development and performance testing has basically been a complicated process of waiting to determine which coating, in relative terms, allows corrosion to occur first from an intentionally created breach through the coating. This type of testing provides only relative ratings between PCS performance. Electrochemical methods, such as electrochemical impedance spectroscopy, each have caveats and pitfalls for qualifying or quantifying polymer-coated metal substrates. When these data are studied carefully, these measurements result in many false positive and false negative results compared with real environmental testing and the paths to failure vary dramatically. The critical issue is that these methods do not result in a scientific basis for understanding either the pathway(s) or progressive milestones toward diminished PCS performance, failure, and the loss of substrate structural integrity for coated substrates. Data supports that ultimately all PCS fail to provide the necessary substrate protection. However, to make substantive gains, scientists and engineers require a rational basis to design, engineer, test, quantify, and/or estimate service life and remaining service life and repair future generations of PCS. Our research goal was to establish a quantifiable characterization protocol (CP) that directly detected, monitored, and ideally quantified the pathway(s) and important milestones of PCS corrosion spatially and temporally, with or without defects which related with testing and assessment variables regardless of environmental severity (real, laboratory, or accelerated). We report herein the CP and the results from an embedded pH-sensitive "turn-on" fluorescent probe blended with a simplified thermoplastic model PCS. The results support that the average-localized macroscopic pH is detected and tracked, and these "molecular titrations" result in values consistent with literature pH citations for premacroscopic corrosion processes, that is, before delamination and a detectable breach. The CP results are an improvement over visual corrosion detection and yet proportional to the steel substrate corrosion. The CP results deliver extreme early detection (within minutes), spatial and temporal tracking, and potentially quantifiable performance differences for the pathways and milestones toward failure of coated substrates with validated sensitivity to variables such as defect versus defect-free films, blending solvent type(s) influence, differences from varied degrees of annealing relative to T_g (thermoplastic films), substrate topography, and preparation differences. The CP utilizes small sample areas (25 mm spheres) and gathers data in a manner designed to improve statistical relevancy, provide results within short timeframes using real-time testing, diminish materials-testing timelines, and connect results with laboratory, accelerated, and real environmental severity differences. The results support that the CP directly measured the earliest possible in situ corrosion processes using defect and defect-free simplified model PCS.

Carbon nanotube incorporation in PMMA to prevent microbial adhesion

Although PMMA-based biomaterials are widely used in clinics, a major hurdle, namely, their poor antimicrobial (i.e., adhesion) properties, remains and can accelerate infections. In this study, carboxylated multiwalled carbon nanotubes (CNTs) were incorporated into poly(methyl methacrylate) (PMMA) to achieve drug-free antimicrobial adhesion properties. After characterizing the mechanical/surface properties, the anti-adhesive effects against 3 different oral microbial species (Staphylococcus aureus, Streptococcus mutans, and Candida albicans) were determined for roughened and highly polished surfaces using metabolic activity assays and staining for recognizing adherent cells. Carboxylated multiwalled CNTs were fabricated and incorporated into PMMA. Total fracture work was enhanced for composites containing 1 and 2% CNTs, while other mechanical properties were gradually compromised with the increase in the amount of CNTs incorporated. However, the surface roughness and water contact angle increased with increasing CNT incorporation. Significant anti-adhesive effects (35~95%) against 3 different oral microbial species without cytotoxicity to oral keratinocytes were observed for the 1% CNT group compared to the PMMA control group, which was confirmed by microorganism staining. The anti-adhesive mechanism was revealed as a disconnection of sequential microbe chains. The drug-free antimicrobial adhesion properties observed in the CNT-PMMA composite suggest the potential utility of CNT composites as future antimicrobial biomaterials for preventing microbial-induced complications in clinical settings (i.e., Candidiasis).

Vanadium Pentoxide-Enwrapped Polydiphenylamine/Polyurethane Nanocomposite: High-Performance Anticorrosive Coating

Nanocomposite coatings with synergistic properties hold a potential in long-term corrosion protection for carbon steel. Polydiphenylamine (PDPA) and vanadium pentoxide (V₂O₅) have rarely been used as a corrosion inhibitor. Moreover, oleo polyurethanes are always demanded in the field of anticorrosive coatings. In view of this, we have synthesized safflower oil polyurethane (SFPU) and their nanocomposites using V₂O₅-enwrapped PDPA (V₂O₅-PDPA) as nanofiller. Fourier-transform infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis were used to characterize the structural, morphological, and thermal properties of these coatings. Corrosion resistance performance of these coatings in 5 wt % NaCl solution was determined by electrochemical measurements and salt spray tests. These studies exhibited very low I_corr (7.45 × 10^-11 A cm^-2), high E_corr (-0.04 V), impedance (1.69 × 10¹¹ Ω cm²), and phase angle (84°) after the exposure of 30 days. An immersion test, in 1 M H₂SO₄ solution for 24 h, was also performed to investigate the effect of oxidizing acid on the surface of coatings. These results revealed the superior anticorrosive activity of nanocomposite coatings compared to those of plain SFPU and other such reported systems. The superior anticorrosive property of the proposed nanocomposite coatings provides a new horizon in the development of high-performance anticorrosive coatings for various industries.

MWCNT/TiO2 hybrid nano filler toward high-performance epoxy composite

In this work, multi-walled carbon nanotubes (MWCNTs) are decorated by TiO₂ nanoparticles and formed a new hybrid structure of filler (MWCNT/TiO₂ hybrid filler). The MWCNT/TiO₂ hybrid filler is reinforced in epoxy matrix and studied the mechanical and anti-corrosion properties of epoxy. The morphology of newly formed MWCNT/TiO₂ hybrid nano filler has been studied using transmission electron microscopy (TEM). Field Emission Scanning Electron Microscope (FESEM) images of tensile fracture surface confirmed the superior dispersion of MWCNT/TiO₂ in the epoxy matrix. The resultant MWCNT/TiO₂ hybrid-epoxy nanocomposite exhibits superior anti-corrosion and mechanical performance than the nanocomposite produced by loading of only MWCNTs or TiO₂ nanoparticles as well as neat epoxy. For example, tensile strength and storage modulus of epoxy increased by 61% and 43% respectively on loading of MWCNT/TiO₂ hybrid nano filler. Furthermore, the coating of MWCNT/TiO₂ hybrid-epoxy nanocomposite on mild steel reduces the corrosion rate upto 0.87×10^-3MPY from 16.81MPY.

Precipitated silica agglomerates reinforced with cellulose nanofibrils as adsorbents for heavy metals

Silicon-containing compounds such as silica are effective heavy metal sorbents which can be employed in many applications. This is attributed to the porous nature of hydrothermally-stable silica, endowing such materials with high surface area and rich surface chemistry, all responsible for improving adsorption and desorption performance. However, to this day, the wide application of silica is limited by its skeletal brittleness and high production cost coupled with a risky traditional supercritical drying method. To solve the named problems, herein, precipitated silica agglomerates (referred to as PSA) was crosslinked with TEMPO-oxidized cellulose nanofibrils (TO-CNF) as a reinforcement in the presence of 3-aminopropyltriethoxysilane (APTES), via a facile dual metal synthesis approach, is reported. The resultant new silica-based sponges (TO-CNF PSA) showed desirable properties of flexibility, porosity and multifaceted sorption of various heavy metals with re-usability. The experimental results showed maximum adsorption capacities of 157.7, 33.22, 140.3 and 130.5 mg g⁻¹ for Pb(ii), Hg(ii), Cr(iii) and Cd(ii) ions, respectively. Such a facile approach to modify silica materials by attaching active groups together with reinforcement can provide improved and reliable silica-based materials which can be applied in water treatment, gas purification, thermal insulation etc.

PSA was inexpensively ameliorated by cellulose nanofibrils reinforcement. The resultant sponge with mechanically strong skeleton was evaluated as an excellent adsorbent for heavy metals.

Grafting heteroelement-rich groups on graphene oxide: Tuning polarity and molecular interaction with bio-ionic liquid for enhanced lubrication

Two different heteroelement-rich molecules have been successfully grafted on graphene oxide (GO) sheets which were then used as lubricant additives in bio-ionic liquid. The grafting was processed with reactions between GO sheets and synthesized heteroelement-rich molecules (Imidazol-1-yl phosphonic dichloride and 1H-1,2,4-triazol-1-yl phosphonic dichloride, respectively). The modified GO (m-GO) was added into [Choline][Proline] ([CH][P]) bio-ionic liquid, and has been demonstrated effective additive in promoting lubrication. Different characterization techniques have been utilized to study the reaction between GO and the two modifiers. The effect of molecular structure of the modifiers on the rheological and tribological properties of m-GO/[CH][P] lubricants was systematically investigated. Both theoretical calculation and experimental results demonstrated that the introduced heteroelement-rich groups are beneficial to increase the robustness of lubrication film by intensified hydrogen bonding and enhance the lubricant/friction surface adhesion by increased polarity of the m-GO. As a result, the interfacial lubrication could be significantly improved by these newly developed m-GO/[CH][P] lubricants.