Phenolic Coatings Research Articles

Flame-retardant aramid felt-reinforced phenolic coatings for carbon fiber-reinforced polymers (CFRPs)

For over fifty years since carbon fiber-reinforced polymers (CFRPs) were introduced to the automotive industry, enhancing their flame-retardant properties has been studied due to their vulnerability to fire. Coating is one method of flame-retardant enhancement, accomplished by modifying surface characteristic to achieve its goal. Phenolic resin-based coatings, as a candidate material, offer advantages such as good chemical compatibility and cost efficiency. However, to meet the necessary specifications for flame-retardant performance, a thick coating layer with higher brittleness is required. In this study, we developed an aramid felt-reinforced coating layer to address the limitations of phenolic coatings. The effectiveness of the flame-retardant coating was demonstrated through various tests, including limiting oxygen index (LOI), micro-combustion calorimetry, heat exposure test with cone shaped heater, and mechanical property tests including surface-burning test. Consequently, the aramid felt-reinforced phenolic coating exhibited superior flame-retardant enhancement using a cost-effective, easy-to-follow, and lightweight method, achieved with a relatively thin coating fabrication.

Phyto-fabrication and characterization of silver nanoparticles usingWithania somnifera: Investigating antioxidant potential

AbstractThis study aimed to develop a green and safe method for producing silver nanoparticles (AgNPs) using the root extract ofWithania somnifera(WS) and evaluate their antioxidant properties. UV-visible spectroscopy revealed a maximum absorption peak at 430 nm. Fourier-transformed infrared spectroscopy confirmed the presence of phenolic coatings on Ws-AgNPs, indicating their role in stabilizing and reducing Ag ions into Ws-AgNPs. Scanning electron microscopy analysis demonstrated that Ws-AgNPs had a spherical shape and a size range of 74–88 nm. Energy dispersive X-ray spectroscopy analysis confirmed silver as the primary element in Ws-AgNPs. X-ray powder diffraction analysis indicated a face-centered cubic crystalline structure for Ws-AgNPs. The potential antioxidant activities of Ws-AgNPs were evaluated using various scavenging assays. At the highest concentration tested (500 µg/mL), 95 ± 1.3%, 98 ± 1.6%, 76.9 ± 1.44%, and 89.6 ± 1.6% scavenging activities were observed with 2,2-diphenyl-1-picrylhydrazyl, 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid, phosphomolybdate, and H2O2, respectively. Moreover, the reducing power of Ws-AgNPs was higher than that of the methanolic WS root extract and showed a concentration-dependent trend. In conclusion, the green-synthesized Ws-AgNPs fromW. somniferashowed remarkable antioxidant activity, as evidenced by their low IC50values. Due to these findings, it is suggested that Ws-AgNPs have the potential to be used as potent antioxidant agents in the cosmetic, food, and pharmaceutical industries.

Phenolic-Compound-Based Functional Coatings: Versatile Surface Chemistry and Biomedical Applications.

Phenolic-compound-based functional coatings that allow for flexible modulation of chemical and surface properties have found widespread uses in a diverse range of biomedical applications from antibiofouling and antioxidation to bioimaging, therapeutics, and controlled drug delivery. It is imperative to understand the formation mechanism of phenolic coatings to fully meet the needs of their emerging applications in controlling the surface properties of biomaterials and medical devices. In this Perspective, we highlight the versatile chemical and self-assembly approaches to generate phenolic coatings with tailored surface properties and reactivities and also discuss how the surface properties and chemical reactivities impart functional materials for translational research.

Cell‐Mediated Biointerfacial Phenolic Assembly for Probiotic Nano Encapsulation

AbstractThe use of cell‐mediated chemistry is an emerging strategy that exploits the metabolic processes of living cells to develop biomimetic materials with advanced functionalities and enhanced biocompatibility. Here, a concept of a cell‐mediated catalytic process for forming protective nano‐shells on individual probiotic cells is demonstrated. This process is leveraged by the cell environment to induce oxidative polymerization of phenolic compounds, and simultaneously these phenolic polymers assemble to form nano‐coatings around individual cell surfaces. The detailed analysis reveals that the oxidation process is triggered by an essential nutrient (manganese) of the probiotic cells, which significantly increases the oxidation rate of phenolic compounds. The phenolic coatings, encapsulating each cell in nanometre scale, demonstrate excellent biocompatibility and biodegradability. Additionally, the in situ encapsulated probiotic cells display an improved gastric tolerance of up to ≈1.4 times higher than the native cells and enhanced adhesion as high as ≈1.6 times onto a model of intestinal epithelial cells. Finally, the coated probiotic cells exhibit a high antioxidant activity as an advanced feature. Overall, this method provides a unique approach to improve the probiotic delivery using the cell machinery to engineer encapsulating nanocoatings with protective benefits and new functionalities.

Sono‐Fenton Chemistry Converts Phenol and Phenyl Derivatives into Polyphenols for Engineering Surface Coatings

We report a sono-Fenton strategy to mediate the supramolecular assembly of metal-phenolic networks (MPNs) as substrate-independent coatings using phenol and phenyl derivatives as building blocks. The assembly process is initiated from the generation of hydroxyl radicals (. OH) using high-frequency ultrasound (412 kHz), while the metal ions synergistically participate in the production of additional . OH for hydroxylation/phenolation of phenol and phenyl derivatives via the Fenton reaction and also coordinate with the phenolic compounds for film formation. The coating strategy is applicable to various phenol and phenyl derivatives and different metal ions including FeII , FeIII , CuII , and CoII . In addition, the sono-Fenton strategy allows real-time control over the assembly process by turning the high-frequency ultrasound on or off. The properties of the building blocks are maintained in the formed films. This work provides an environmentally friendly and controllable method to expand the application of phenolic coatings for surface engineering.

Sono‐Fenton Chemistry Converts Phenol and Phenyl Derivatives into Polyphenols for Engineering Surface Coatings

AbstractWe report a sono‐Fenton strategy to mediate the supramolecular assembly of metal–phenolic networks (MPNs) as substrate‐independent coatings using phenol and phenyl derivatives as building blocks. The assembly process is initiated from the generation of hydroxyl radicals (.OH) using high‐frequency ultrasound (412 kHz), while the metal ions synergistically participate in the production of additional .OH for hydroxylation/phenolation of phenol and phenyl derivatives via the Fenton reaction and also coordinate with the phenolic compounds for film formation. The coating strategy is applicable to various phenol and phenyl derivatives and different metal ions including FeII, FeIII, CuII, and CoII. In addition, the sono‐Fenton strategy allows real‐time control over the assembly process by turning the high‐frequency ultrasound on or off. The properties of the building blocks are maintained in the formed films. This work provides an environmentally friendly and controllable method to expand the application of phenolic coatings for surface engineering.

Liquid Metal-Triggered Assembly of Phenolic Nanocoatings with Antioxidant and Antibacterial Properties

Liquid metal (LM) catalysts have been demonstrated to accelerate chemical reactions, providing an intriguing route to fine chemical synthesis with immense technological implications. Herein, we explore gallium-based LMs as catalysts to promote the oxidative self-polymerization of natural polyphenols, an emerging class of natural building blocks for surface functionalization with diverse biochemical properties. The oxidative polymerization of polyphenols, triggered by eutectic alloy of gallium and indium, results in nanocoatings with remarkably high reaction kinetics. The oxidative polymerization occurs in a wide pH range including an acidic environment—a condition previously unexplored for the deposition of phenolic coatings. The LM triggers the generation of highly active radical species from the oxidant causing the rapid oxidation of the polyphenols and their subsequent deposition on a range of different substrates. We further show that the LM-based catalytic system addresses several other limitations of existing coating methods including a narrow pH range, substrate specificity (precursor–dependent), and low coating uniformity. Finally, we demonstrate that the phenolic nanocoatings obtained from the acidic pH environment have excellent antioxidant and antibacterial properties without requiring any post-functionalization step. This process for creating phenolic nanocoatings may find applications in a wide range of industries, food science, and biomedicine.

Corrosion Resistance of Clay Modified Resole and Novolac Phenolic Coatings

In this study corrosion resistance and adhesion properties of two types of phenolic coatings, novolac and resol, have been investigated. Phenolic coatings containing clay particles were prepared and the effect of clay content on the corrosion protection performance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS), DC polarization and salt fog tests. On the other hand, adhesion and toughness characterization of prepared phenolic coatings was measured using pull off and cupping tests, respectively. Results indicated that adding of clay particles, improves the corrosion protection performance both of both types of phenolic coatings. Novolac phenolic coating containing 3 wt % of clay showed higher corrosion resistance than the others. Also, test results showed that the flexibility and adhesion of resol coating was more than that of the novolac coating.

Effect of Recycled Polystyrene/Limonene Coating on the Mechanical Properties of Kraft Paper: A Comparative Study with Commercial Coatings

In this work, the mechanical properties of Kraft paper (KP) coated with a coating formulated with recycled polystyrene dissolved in the solvent lime limonene (rEPS/LL) are investigated. These mechanical properties are compared with those of KP coated with three different commercial coatings: oil-based alkyd coating (ALKY), oil-based phenolic coating (PHEN) and water-based acrylic coating (ACRY). The morphology characterization via scanning electron microscopy showed the KP coated with rEPS/LL resembles a layered structure, in which, part of the coating remained on the surface and part of the coating was absorbed by the KP. The KP coated with rEPS/LL exhibited the highest tensile stiffness and compression strength when compared to the uncoated KP and KP coated with commercial coatings. The remarkable compression properties of the KP coated with rEPS/LL coating may be explained by the bending and crushing mechanisms observed during the ring crush test. The excellent mechanical performance of rEPS/LL combined with an environmentally friendly process to obtain recycled EPS using a bio-based solvent presents several advantages for coating applications. These results warrant further research to fully understand the properties of KP coated with rEPS/LL.

In Vitro Performance of Bioinspired Phenolic Nanocoatings for Endosseous Implant Applications.

In the quest for finding new strategies to enhance tissue integration and to reduce the risk of bacterial colonization around endosseous implants, we report the application of auto-oxidative phenolic coatings made of tannic acid and pyrogallol to titanium surfaces. The functionalized surfaces were screened for their biological performance using cultures of primary human osteoblasts and biofilm-forming bioluminescent staphylococci S. epidermidis Xen43 and S. aureus Xen29. No toxic effect of the coatings on osteoblasts was detected. While tannic acid coatings seemed to induce a delay in osteoblast maturation, they revealed anti-inflammatory potential. Similar effects were observed for pyrogallol coatings deposited for 24 h. Thin pyrogallol coatings deposited for 2 h seemed to promote osteoblast maturation and revealed increased calcium deposition. The effects on osteoblast were found to be related to the release of phenolic compounds from the surfaces. While the phenolic coatings could not inhibit staphylococcal biofilm formation on the titanium surfaces, released phenolic compounds had an inhibitory effect the growth of planktonic bacteria. In conclusion, the assessed coating systems represent a versatile functionalization method which exhibit promising effects for endosseous implant applications.

Low temperature curing coating technology for corrosion under insulation mitigation

In the oil and gas industry, the application of epoxy phenolic coatings has been the main route to obtain high heat resistance from coatings and to mitigate corrosion under insulation (CUI) of both insulated carbon and stainless steel pipes operating up to 200°C. These coatings, however, are sensitive to over-application, are prone to cracking and costly to repair when damaged. Additionally, if they are applied below 10°C epoxy phenolic coatings do not cure properly and can fail prematurely, and when applied close to this temperature, can impact shop heating costs, maintenance schedules, and productivity.

One-step synthesis of g-C3N4 nanosheets to improve tribological properties of phenolic coating

Abstract In the present work, g-C3N4 nanosheets are prepared by calcination the mixture of urea and melamine. Resulting production is characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, indicating an effective synthesis of g-C3N4 nanosheets. Phenolic coatings with addition of different content of g-C3N4 nanosheets are used to evaluate the tribological performance of g-C3N4 nanosheets as a role of enhancement phase. Bulk g-C3N4 and graphite are also utilized as fillers to further insight different wear mechanism under dry sliding condition. Experimental results show 1 wt% g-C3N4 nanosheets/phenolic coating exhibit the optimal tribological properties. A higher surface area with more active sites and formation of a continuous transfer film are two important factors for the improvement.

Analysis and testing of bisphenol A, bisphenol A diglycidyl ether and their derivatives in canned dog foods

An analytical method was developed for the simultaneous determination of bisphenol A (BPA), bisphenol A diglycidyl ether (BADGE) and their derivatives, BADGE·2H2O, BADGE·H2O, BADGE·HCl·H2O, BADGE·2HCl and BADGE·HCl, in canned animal food commodities using reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection. The samples were cleaned up using solid-phase extraction (SPE) with hydrophobic polystyrene–divinylbenzene (PS/DVB) copolymer sorbent. The performance characteristics confirmed that the method used was in accordance with the EU validation criteria. The recovery values ranged from 62 to 97%. The repeatability (CVr) and within-laboratory reproducibility (CVW) values ranged from 2.3 to 9.7% and from 2.8 to 10.8%, respectively, while the limit of detection (LOD) and the limit of quantification (LOQ) values ranged from 5 to 10 µg/kg and from 5 to 15 µg/kg, respectively. The method was successfully used to evaluate the levels of 7 bisphenols in 24 of the canned dog foods retailed on the Slovenian market. BADGE·2H2O was found in all the samples tested, with values ranging from 16 to 540 µg/kg, while BPA was found in 96% of the samples tested and ranged from <5 to 208 µg/kg. The contribution of BADGE·H2O and BADGE·HCl·H2O was minor, while no traces of BADGE, BADGE·2HCl or BADGE·HCl were detected. Epoxy phenolic coatings were identified in the cans tested by the Fourier transform infrared spectroscopy (FTIR) analysis. Given the temporary human tolerable daily intake (TDI) value of 4 µg/kg b.w./day recently laid down by the European Food Safety Authority (EFSA), these results, especially those for the BPA in canned dog foods, merit further attention and investigation.

Evaluation of Short-Term and Long-Term Migration Testing from Can Coatings into Food Simulants: Epoxy and Acrylic-Phenolic Coatings.

Traditionally, migration testing during 10 days at 40 °C has been considered sufficient and appropriate for simulating the potential migration of substances from food-contact materials into foods. However, some packages, such as food cans, may be stored holding food for extended time periods (years). This study attempts to verify whether common testing conditions accurately estimate long-term migration. Two types of can coatings, epoxy and acrylic-phenolic, were subjected to short-term and long-term migration testing (1 day-1.5 years) using food simulants (water, 3% acetic acid, 50% ethanol, and isooctane) at 40 °C. Using HPLC-DAD/CAD, HPLC-MS, UHPLC-HRMS (where HRMS is accurate mass, mass spectrometry), and DART-HRMS, we identified potential migrants before starting the experiment: BPA, BADGE, BADGE derivatives, benzoguanamine, and other relevant marker compounds. During the experiment using a water-based food simulant, migrants remained stable. Most of the cans in contact with 3% acetic acid did not survive the experimental conditions. Tracked migrants were not detected in isooctane. In the presence of 50% ethanol, the traditional migration test during 10 days at 40 °C did not predict migration during long-term storage. These results suggest that migration protocols should be modified to account for long-term storage.

Deposition Kinetics of Bioinspired Phenolic Coatings on Titanium Surfaces.

Polyphenols can form functional coatings on a variety of different materials through auto-oxidative surface polymerization in a manner similar to polydopamine coatings. However, the mechanisms behind the coating deposition are poorly understood. We report the coating deposition kinetics of the polyphenol tannic acid (TA) and the simple phenolic compound pyrogallol (PG) on titanium surfaces. The coating deposition was followed in real time over a period of 24 h using a quartz crystal microbalance with dissipation monitoring (QCM-D). TA coatings revealed a multiphasic layer formation: the deposition of an initial rigid layer was followed by the buildup of an increasingly dissipative layer, before mass adsorption stopped after approximately 5 h of coating time. The PG deposition was biphasic, starting with the adsorption of a nonrigid viscoelastic layer which was followed by layer stiffening upon further mass adsorption. Coating evaluation by ellipsometry and AFM confirmed the deposition kinetics determined by QCM-D and revealed maximum coating thicknesses of approximately 50 and 75 nm for TA and PG, respectively. Chemical characterization of the coatings and polymerized polyphenol particles indicated the involvement of both physical and chemical interactions in the auto-oxidation reactions.

Reaction kinetics of bioinspired (poly)phenolic coatings on titanium implant surfaces

Reaction kinetics of bioinspired (poly)phenolic coatings on titanium implant surfaces

Furan resins as replacement of phenolic protective coatings: Structural, mechanical and functional characterization

Phenolic coatings are usually a convenient and economical way to protect metallic materials against wear and corrosion. Furan resins are analogous to phenolics, as they are obtained by replacing formaldehyde by furfural in their formulation. In this work, a furan resin based on furfural and phenol was synthesized and used as an aluminum coating. Thus, toxic emissions of formaldehyde were avoided, while a biobased derivative was used instead. The performance of the proposed resin was compared with the one of a traditional phenolic resin. Physicochemical characteristics including chemical structure, surface polarity and glass transition temperature were evaluated by means of Fourier transform infrared spectroscopy, contact angle measurements and dynamic–mechanical analysis, respectively. Nanomechanical and nanotribological properties were assessed by depth sensing indentation techniques. As well, the corrosion resistance of the furan coating was determined by potentiodynamic polarization tests. The obtained results validate the furan resin as a feasible alternative to phenolics to protect aluminum.

Development of a novel method to measure the film thickness of cured can coatings

A new technique was developed for measuring the thickness of can coatings applied to a metal substrate. A metal disc with a known radius creates a small indent in the coating, stopping exactly when the coating thickness is cut through. The indent length is employed to calculate the coating thickness. Accurate measurement of thin films is achieved as the indent is much larger than the respective film thickness. The thickness of epoxy phenolic coatings on tinplate were measured and the results were validated by micrographic cross section analysis and by confocal laser scanning microscopy (CLSM). The coating thicknesses measured using the indentation method coincide with the film thicknesses measured by CLSM, whereas discrepancies were observed using the micrographic cross section analysis. The new technique, presented in this paper, uses simple equipment, is inexpensive, fast and easy to use, and is suitable for film thickness measurements in laboratories and production plants.

Electrochemical characterisation of protective organic coatings for food packaging

A very common material for food packaging is steel, in the form of metallic containers (cans), in particular for beverage packaging. The corrosion degradation of the packaging must be carefully controlled, not only because the packaging integrity must be preserved, but also in order to avoid any significant contamination of the food or drink, compromising the flavour. In order to increase the coating performance and the food compatibility, new organic coatings are under development with very high protective properties, with the final aim to increase the shelf life of the product. An electrochemical characterisation is often used to study the protective performance of organic coatings on metal substrate for various applications. Some different coatings for food packaging were considered in the present study, including materials with different chemical composition and different pigments content. The protective properties were quantified using electrochemical impedance spectroscopy (EIS) measurements, comparing the electrochemical substrate activity with electrochemical noise (EN) and scanning Kelvin probe (SKP) measurements. The influence of mechanical deformations on the protective properties was also investigated. The results obtained on the studied coatings confirmed the validity of the electrochemical approach and showed that, in general, the coatings containing pigments (TiO2) have better performance than clearcoats, while comparing the different polymers, epoxy–phenolic coatings have a better corrosion protection than epoxy–melamine coatings.

Study on the tribological behaviors of the phenolic composite coating filled with modified nano-TiO 2

In order to overcome the disadvantages generated by the loosened nanoparticle agglomerates dispersed in polymer composite coatings, nano-TiO 2 particles are modified using trifluoracetic acid. The friction and wear properties of the phenolic coatings filled with different surface treated nano-TiO 2, sliding against AISI-C-52100 steel ring under dry sliding, were investigated on a MHK-500 wear tester. Owing to the effective improvement of their dispersibility in the phenolic coating, compared with the cases of untreated nano-TiO 2, the employment of modified nano-TiO 2 provided the phenolic coating with much better tribological performance. Worn surfaces of the untreated nano-TiO 2 or modified nano-TiO 2 filled phenolic coating and transfer films formed on the surface of the counterpart ring sliding against the composite coating were respectively investigated by SEM and optical microscope (OM), from which it is assumed that the optimal content of TiO 2 or TF-TiO 2 is able to enhance the adhesion of the transfer films to the surface of counterpart ring. As a result, the wear resistance of the phenolic composite coating filled with modified nano-TiO 2 was significantly enhanced, especially at extreme wear conditions, i.e. high contact pressures.