Neat Coatings Research Articles

Performance of concrete superficially treated with nano-modified coatings under sulfuric acid exposures

Protection of concrete surface layer is crucial for preserving serviceability and durability of concrete structures during their service life. Chemical attack by sulfuric acid is an aggressive exposure, commonly causing significant damage to concrete elements such as buildings' foundations and basement walls, buildings and structures affected by acid rain, industrial facilities, and wastewater treatment facilities. Hence, this study endeavored to evaluate the performance of nano-modified composites as surface treatments for concrete under severe chemical exposures. Nano-calcium carbonate and nano-clay particles were dispersed at different dosages (0, 2.5, and 5% by mass) in the neat coatings: vinyl ester (membrane-forming polymer) and silane (hydrophobic agent). Moreover, an amorphous colloidal silica (SiO2>50%) was also used as a superficial treatment for concrete. These coatings were applied to concrete specimens with water-to-binder ratios (w/b) of 0.40 (representing good quality/low penetrability concrete treated for prohibition of deterioration) and 0.60 (representing deteriorated/high penetrability concrete in need for rehabilitation). the wettability and initial transport characteristics of the coated concrete specimens were determined. In addition, the durability of superficially treated concrete specimens was examined under two aggressive exposures: full submergence in a 5% (by volume) sulfuric acid solution, and 5% sulfuric acid solution combined with wetting-drying cycles. During both exposures, the deterioration of concrete specimens was observed by visual inspection and quantified in terms of mass change. Furthermore, the damage mechanisms and coatings’ performance were studied by microstructural, mineralogical, and thermal analyses. The overall results showed that vinyl ester and vinyl ester nanocomposites significantly improved the durability of concrete specimens by an average of around 64% relative to that of the silane and silane nanocomposites; hence, they are recommended for field applications.

Effect of Polymer/Nano-Clay Coatings on the Performance of Concrete with High-Content Supplementary Cementitious Materials under Harsh Exposures.

In recent concrete research, a novel category of coatings has emerged: polymers/nanoparticles blends. The efficacy of such coatings warrants extensive examination across various concrete mixtures, particularly those incorporating high-volume supplementary cementitious materials (SCMs) to mitigate carbon footprints, an industry imperative. This study used three vulnerable concrete mixtures to assess the effectiveness of ethyl silicate and high-molecular-weight methyl methacrylate blended with 2.5% and 5% halloysite and montmorillonite nano-clay. Findings from physical, thermal, and microstructural analyses confirmed vulnerabilities in concretes with a high water-to-binder ratio (0.6) under severe exposure conditions, notably with high SCM content (40% and 60% fly ash and slag, respectively). Neat ethyl silicate or high-molecular-weight methyl methacrylate coatings inadequately protected those concretes against physical salt attacks and salt-frost scaling exposures. However, the incorporation of halloysite nano-clay or montmorillonite nano-clay in these polymers yielded moderate-to-superior concrete protection compared to neat coatings. Ethyl silicate-based nanocomposites provided full protection, achieving up to 100% improvement (no or limited surface scaling) against both exposures, particularly when incorporating halloysite-based nano-clay at a 2.5% dosage by mass. In contrast, high-molecular-weight methyl methacrylate-based nano-clay composites effectively mitigated physical salt attacks but exhibited insufficient protection throughout the entire salt-frost scaling exposure, peeling off at 15 cycles.

Electrospray deposited plant-based polymer nanocomposite coatings with enhanced antibacterial activity for Ti-6Al-4V implants

The present study was designed to apply the Electrospray Deposition (ESD) coating on metallic biomaterials used in dentistry with plant-based polymer nanocomposite materials. Nano silvers (AgNPs) were produced with an average size of 34 nm and homogenous distribution. As the nanosilver modification rate in the coatings increased, the surface roughness decreased compared with that of the neat sample. The most mechanically and chemically stable coating samples were the 0.1 %, 0.3 %, and 0.5 % nanosilver-modified samples. In addition, plant extracts increased the mechanical strength of Polyvinyl Alcohol (PVA) coatings by at least two times compared to that of neat coatings. Atomic Force Microscopy (AFM) images revealed that the surface roughness of the nanosilver-modified coatings was lower than that of the plant extract-modified and neat samples. It was observed that bacterial growth could be reduced by up to 100 times with increasing nano‑silver ratio in all nano-silver-modified coatings. Toxicity tests confirmed that the green synthesized nano-silvers did not show toxic effects on HaCaT live cells and A549 lung cancer cells, with the use of concentrations of 62 μg/mL and below in coatings.

Comparative study on the corrosion and mechanical properties of nano-composite coatings incorporated with TiO 2 nano-particles, TiO 2 nano-tubes, and ZnO nano-flowers

Abstract TiO2 nano-particles (NP-TiO2), TiO2 nano-tubes (NT-TiO2) and novel nano-composite TiO2 nano-tubes and ZnO nano-flowers (NT-TiO2 + NF-ZnO) were prepared by sol-gel and modified hydrothermal methods, respectively. These pigments were characterized by XRD, HRTEM, FTIR and Raman spectroscopy. The effects of these pigments on the mechanical and anticorrosion performance of alkyd coating were evaluated using electrochemical impedance spectroscopy (EIS), water permeability, elastic modulus and hardness measurements. EIS measurements showed that the alkyd resin resistance and charge transfer resistance increased via the incorporation of nano-pigments into neat coatings. The order of anticorrosion performance of the three nano-pigments was as follows: NT-TiO2 + NF-ZnO ˃ NT-TiO2 ˃ NP-TiO2.

Formulation and evaluation of nano-structured polymeric coatings for corrosion protection

The effect of the addition of multi-walled carbon nano-tubes (MWCNT) to epoxy and vinyl chloride/vinyl acetate copolymer coatings on their ability to protect the substrates was studied. Coatings were formulated from these resins with and without MWCNT reinforcement. Steel substrates were prepared and coated with each formulated coating and submerged in 5% NaCl solution to study their corrosion resistance by means of Electrochemical Impedance Spectroscopy (EIS). In addition, thin films from these polymers, with and without nano-reinforcement, were cast. Dogbone specimens were cut in order to study their mechanical properties. Some of these specimens were immersed in the NaCl solution for two weeks in order to compare their mechanical properties with samples not exposed to salt water. Optical microscopy was used to capture the progress of sample corrosion. EIS measurements showed that the addition of MWCNTs to epoxy and vinyl chloride/vinyl acetate copolymer (VYHH) coatings increased their charge transfer resistance in comparison with the neat coatings. This is an indication of the enhanced corrosion protection of the nano-coatings. In addition, mechanical strength tests, both before and after immersion in 5% NaCl solution, showed that thin films from both epoxy and VYHH resins containing MWCNTs had improved strength, an indication of an improvement in the coatings' cohesive properties.

Bench‐scale evaluations and mechanistic studies of intumescent/fire‐protective coatings for polyvinyl chloride nitrile rubber

AbstractThe object of this study was to identify, for future large‐scale testing, and adequate fire‐protective coating for the substrate, polyvinyl chloride (PVC) nitrile rubber (MIL‐P‐15280 Rev H). Fifteen fire protective coatings which included ten intumescent, two ablatives, two fire retardants and one photon diffusive coatings were evaluated using bench‐scale thermal insults. To discern the possible mechanism(s) whereby the coatings offer fire protection, the effect of radiant heat versus the flame source employed was investigated and thermogravimetric analysis (TGA) of the neat coatings was performed. In selected cases, the effect of coating thickness and repeatability of the results were evaluated. The differences in coating effectiveness, and the varied repeatability in three of the four cases examined, focus on the inherent complexity of intumescence, as well as on the importance of scaled‐up testing of coatings that appeared promising. Thermogravimetric analyses of the coatings indicate that two selected TGA measurements/parameters, when used in conjunction, appear useful in characterizing mechanistic differences between the less effective and more effective coatings. Based on the rigorous criterion adopted, one candidate (a water‐based intumescent coating at 100 mil (2.54 mm) thickness) appears promising for the substrate, PVC nitrile rubber. Its effectiveness is attributable to it exhibiting good insulative and re‐radiative properties and an apparent low susceptibility to crack formation.

Electrochemical coating for prevention of carbon fibre release from polymer composites: Thermogravimetric analysis of organophosphorus coatings on carbon fibres

Fire retardant coatings of phosphorus compounds were formed on graphite fibres by a new electrochemical technique. Thus, tetrakis (hydroxymethyl)-phosphonium sulphate, ammonium polyphosphate, titanium di(dioctylpyrophosphate) oxyacetate, di(dioctylphosphato)ethylene titanate, and propargyltriphenyl-phosphonium bromide, were electrodeposited or electropolymerized on commercial graphite fibres used for polymer reinforcement. The effect of these coatings on the thermal oxidative behaviour of the coated carbon fibres, epoxy resin, and composites prepared from them was studied by thermogravimetric analysis, and compared with that of polyimide coatings. Generally, the coated fibres showed higher decomposition temperature than the untreated carbon fibres. The fire retardant phosphorus compounds promoted the formation of char from the matrix resin, and accelerated the decomposition of char. Organophosphorus titanate coatings left an incombustible, white residual layer of titanium dioxide. The polyphosphate coating caused the decomposition of the fibres in the epoxy composite to occur at a reduced temperature compared to that in the absence of the matrix resin. A synergistic interaction between the polyphosphate and the amine-cured, epoxy resin to catalyse the decomposition of carbon fibres is inferred from this. Polyimide precursor coatings lowered the oxidation temperature of the carbon fibres, both as neat coatings and in the presence of epoxy matrix resin, thus reducing the temperature of survival of the fibres under combustion conditions. The results confirm the potential of this novel approach of forming precursor coatings on carbon fibres to minimize the release of conductive fibre fragments from carbon fibre-reinforced polymer composites exposed to fire.